Sample records for abundant impact craters

  1. Shock metamorphism and impact melting in small impact craters on Earth: Evidence from Kamil crater, Egypt

    NASA Astrophysics Data System (ADS)

    Fazio, Agnese; Folco, Luigi; D'Orazio, Massimo; Frezzotti, Maria Luce; Cordier, Carole

    2014-12-01

    Kamil is a 45 m diameter impact crater identified in 2008 in southern Egypt. It was generated by the hypervelocity impact of the Gebel Kamil iron meteorite on a sedimentary target, namely layered sandstones with subhorizontal bedding. We have carried out a petrographic study of samples from the crater wall and ejecta deposits collected during our first geophysical campaign (February 2010) in order to investigate shock effects recorded in these rocks. Ejecta samples reveal a wide range of shock features common in quartz-rich target rocks. They have been divided into two categories, as a function of their abundance at thin section scale: (1) pervasive shock features (the most abundant), including fracturing, planar deformation features, and impact melt lapilli and bombs, and (2) localized shock features (the least abundant) including high-pressure phases and localized impact melting in the form of intergranular melt, melt veins, and melt films in shatter cones. In particular, Kamil crater is the smallest impact crater where shatter cones, coesite, stishovite, diamond, and melt veins have been reported. Based on experimental calibrations reported in the literature, pervasive shock features suggest that the maximum shock pressure was between 30 and 60 GPa. Using the planar impact approximation, we calculate a vertical component of the impact velocity of at least 3.5 km s-1. The wide range of shock features and their freshness make Kamil a natural laboratory for studying impact cratering and shock deformation processes in small impact structures.

  2. Venus - Multiple-Floored, Irregular Impact Crater

    NASA Image and Video Library

    1996-09-26

    NASA' sMagellan imaged this multiple-floored, irregular impact crater at latitude 16.4 degrees north, longitude 352.1 degrees east, during orbits 481 and 482 on 27 September 1990. This crater, about 9.2 kilometers in maximum diameter, was formed on what appears to be a slightly fractured, radar-dark (smooth) plain. The abundant, low viscosity flows associated with this cratering event have, however, filled local, fault-controlled troughs (called graben). These shallow graben are well portrayed on this Magellan image but would be unrecognizable but for their coincidental infilling by the radar-bright crater flows. This fortuitous enhancement by the crater flows of fault structures that are below the resolution of the Magellan synthetic aperture radar is providing the Magellan Science Team with valuable geologic information. The flow deposits from the craters are thought to consist primarily of shock melted rock and fragmented debris resulting from the nearly simultaneous impacts of two projectile fragments into the hot (800 degrees Fahrenheit) surface rocks of Venus. The presence of the various floors of this irregular crater is interpreted to be the result of crushing, fragmentation, and eventual aerodynamic dispersion of a single entry projectile during passage through the dense Venusian atmosphere. http://photojournal.jpl.nasa.gov/catalog/PIA00462

  3. Meteor Crater (Barringer Meteorite Crater), Arizona: Summary of Impact Conditions

    NASA Astrophysics Data System (ADS)

    Roddy, D. J.; Shoemaker, E. M.

    1995-09-01

    Meteor Crater in northern Arizona represents the most abundant type of impact feature in our Solar System, i.e., the simple bowl-shaped crater. Excellent exposures and preservation of this large crater and its ejecta blanket have made it a critical data set in both terrestrial and planetary cratering research. Recognition of the value of the crater was initiated in the early 1900's by Daniel Moreau Barringer, whose 27 years of exploration championed its impact origin [1]. In 1960, Shoemaker presented information that conclusively demonstrated that Meteor Crater was formed by hypervelocity impact [2]. This led the U.S. Geological Survey to use the crater extensively in the 1960-70's as a prime training site for the Apollo astronauts. Today, Meteor Crater continues to serve as an important research site for the international science community, as well as an educational site for over 300,000 visitors per year. Since the late 1950's, studies of this crater have presented an increasingly clearer view of this impact and its effects and have provided an improved view of impact cratering in general. To expand on this data set, we are preparing an upgraded summary on the Meteor Crater event following the format in [3], including information and interpretations on: 1) Inferred origin and age of the impacting body, 2) Inferred ablation and deceleration history in Earth's atmosphere, 3) Estimated speed, trajectory, angle of impact, and bow shock conditions, 4) Estimated coherence, density, size, and mass of impacting body, 5) Composition of impacting body (Canyon Diablo meteorite), 6) Estimated kinetic energy coupled to target rocks and atmosphere, 7) Terrain conditions at time of impact and age of impact, 8) Estimated impact dynamics, such as pressures in air, meteorite, and rocks, 9) Inferred and estimated material partitioning into vapor, melt, and fragments, 10) Crater and near-field ejecta parameters, 11) Rock unit distributions in ejecta blanket, 12) Estimated far

  4. Raman spectroscopy of shocked gypsum from a meteorite impact crater

    NASA Astrophysics Data System (ADS)

    Brolly, Connor; Parnell, John; Bowden, Stephen

    2017-07-01

    Impact craters and associated hydrothermal systems are regarded as sites within which life could originate on Earth, and on Mars. The Haughton impact crater, one of the most well preserved craters on Earth, is abundant in Ca-sulphates. Selenite, a transparent form of gypsum, has been colonized by viable cyanobacteria. Basement rocks, which have been shocked, are more abundant in endolithic organisms, when compared with un-shocked basement. We infer that selenitic and shocked gypsum are more suitable for microbial colonization and have enhanced habitability. This is analogous to many Martian craters, such as Gale Crater, which has sulphate deposits in a central layered mound, thought to be formed by post-impact hydrothermal springs. In preparation for the 2020 ExoMars mission, experiments were conducted to determine whether Raman spectroscopy can distinguish between gypsum with different degrees of habitability. Ca-sulphates were analysed using Raman spectroscopy and results show no significant statistical difference between gypsum that has experienced shock by meteorite impact and gypsum, which has been dissolved and re-precipitated as an evaporitic crust. Raman spectroscopy is able to distinguish between selenite and unaltered gypsum. This shows that Raman spectroscopy can identify more habitable forms of gypsum, and demonstrates the current capabilities of Raman spectroscopy for the interpretation of gypsum habitability.

  5. Impact Crater

    NASA Technical Reports Server (NTRS)

    2002-01-01

    [figure removed for brevity, see original site]

    Today marks the 45th anniversary of the dawn of the Space Age (October 4, 1957). On this date the former Soviet Union launched the world's first satellite, Sputnik 1. Sputnik means fellow traveler. For comparison Sputnik 1 weighed only 83.6 kg (184 pounds) while Mars Odyssey weighs in at 758 kg (1,671 pounds).

    This scene shows several interesting geologic features associated with impact craters on Mars. The continuous lobes of material that make up the ejecta blanket of the large impact crater are evidence that the crater ejecta were fluidized upon impact of the meteor that formed the crater. Volatiles within the surface mixed with the ejecta upon impact thus creating the fluidized form. Several smaller impact craters are also observed within the ejecta blanket of the larger impact crater giving a relative timing of events. Layering of geologic units is also observed within the large impact crater walls and floor and may represent different compositional units that erode at variable rates. Cliff faces, dissected gullies, and heavily eroded impact craters are observed in the bottom half of the image at the terminus of a flat-topped plateau.

    Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.

    NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS

  6. Noachian and more recent phyllosilicates in impact craters on Mars.

    PubMed

    Fairén, Alberto G; Chevrier, Vincent; Abramov, Oleg; Marzo, Giuseppe A; Gavin, Patricia; Davila, Alfonso F; Tornabene, Livio L; Bishop, Janice L; Roush, Ted L; Gross, Christoph; Kneissl, Thomas; Uceda, Esther R; Dohm, James M; Schulze-Makuch, Dirk; Rodríguez, J Alexis P; Amils, Ricardo; McKay, Christopher P

    2010-07-06

    Hundreds of impact craters on Mars contain diverse phyllosilicates, interpreted as excavation products of preexisting subsurface deposits following impact and crater formation. This has been used to argue that the conditions conducive to phyllosilicate synthesis, which require the presence of abundant and long-lasting liquid water, were only met early in the history of the planet, during the Noachian period (> 3.6 Gy ago), and that aqueous environments were widespread then. Here we test this hypothesis by examining the excavation process of hydrated minerals by impact events on Mars and analyzing the stability of phyllosilicates against the impact-induced thermal shock. To do so, we first compare the infrared spectra of thermally altered phyllosilicates with those of hydrated minerals known to occur in craters on Mars and then analyze the postshock temperatures reached during impact crater excavation. Our results show that phyllosilicates can resist the postshock temperatures almost everywhere in the crater, except under particular conditions in a central area in and near the point of impact. We conclude that most phyllosilicates detected inside impact craters on Mars are consistent with excavated preexisting sediments, supporting the hypothesis of a primeval and long-lasting global aqueous environment. When our analyses are applied to specific impact craters on Mars, we are able to identify both pre- and postimpact phyllosilicates, therefore extending the time of local phyllosilicate synthesis to post-Noachian times.

  7. Simultaneous impact and lunar craters

    NASA Technical Reports Server (NTRS)

    Oberbeck, V. R.

    1972-01-01

    The existence of large terrestrial impact crater doublets and crater doublets that have been inferred to be impact craters on Mars suggests that simultaneous impact of two or more bodies can occur at nearly the same point on planetary surfaces. An experimental study of simultaneous impact of two projectiles near one another shows that doublet craters with ridges perpendicular to the bilateral axis of symmetry result when separation between impact points relative to individual crater diameter is large. When separation is progressively less, elliptical craters with central ridges and peaks, and circular craters with deep round bottoms are produced. These craters are similar in structure to many of the large lunar craters. Results suggest that the simultaneous impact of meteoroids near one another may be an important mechanism for the production of central peaks in large lunar craters.

  8. Experimental impact crater morphology

    NASA Astrophysics Data System (ADS)

    Dufresne, A.; Poelchau, M. H.; Hoerth, T.; Schaefer, F.; Thoma, K.; Deutsch, A.; Kenkmann, T.

    2012-04-01

    The research group MEMIN (Multidisciplinary Experimental and Impact Modelling Research Network) is conducting impact experiments into porous sandstones, examining, among other parameters, the influence of target pore-space saturation with water, and projectile velocity, density and mass, on the cratering process. The high-velocity (2.5-7.8 km/s) impact experiments were carried out at the two-stage light-gas gun facilities of the Fraunhofer Institute EMI (Germany) using steel, iron meteorite (Campo del Cielo IAB), and aluminium projectiles with Seeberg Sandstone as targets. The primary objectives of this study within MEMIN are to provide detailed morphometric data of the experimental craters, and to identify trends and characteristics specific to a given impact parameter. Generally, all craters, regardless of impact conditions, have an inner depression within a highly fragile, white-coloured centre, an outer spallation (i.e. tensile failure) zone, and areas of arrested spallation (i.e. spall fragments that were not completely dislodged from the target) at the crater rim. Within this general morphological framework, distinct trends and differences in crater dimensions and morphological characteristics are identified. With increasing impact velocity, the volume of craters in dry targets increases by a factor of ~4 when doubling velocity. At identical impact conditions (steel projectiles, ~5km/s), craters in dry and wet sandstone targets differ significantly in that "wet" craters are up to 76% larger in volume, have depth-diameter ratios generally below 0.19 (whereas dry craters are almost consistently above this value) at significantly larger diameters, and their spallation zone morphologies show very different characteristics. In dry craters, the spall zone surfaces dip evenly at 10-20° towards the crater centre. In wet craters, on the other hand, they consist of slightly convex slopes of 10-35° adjacent to the inner depression, and of sub-horizontal tensile

  9. Hailar crater - A possible impact structure in Inner Mongolia, China

    NASA Astrophysics Data System (ADS)

    Xiao, Zhiyong; Chen, Zhaoxu; Pu, Jiang; Xiao, Xiao; Wang, Yichen; Huang, Jun

    2018-04-01

    Hailar crater, a probable impact structure, is a circular depression about 300 m diameter in Inner Mongolia, northeast China. With broad elevated rims, the present rim-to-floor depth is 8-20 m. Regional geological background and geomorphological comparison suggest that this feature is likely not formed by surface processes such as salt diapir, karst, aeolian, glacial, or volcanic activity. Its unique occurrence in this region and well-preserved morphology are most consistent with it being a Cenozoic impact crater. Two field expeditions in 2016 and 2017 investigated the origin of this structure, recognizing that (1) no additional craters were identified around Hailar crater in the centimeter-scale digital topography models that were constructed using a drone imaging system and stereo photogrammetry; (2) no bedrock exposures are visible within or adjacent to the crater because of thick regolith coverage, and only small pieces of angular unconsolidated rocks are present on the crater wall and the gently-sloped crater rim, suggesting recent energetic formation of the crater; (3) most samples collected from the crater have identical lithology and petrographic characteristics with the background terrain, but some crater samples contain more abundant clasts and silicate hydrothermal veins, indicating that rocks from depths have been exposed by the crater; (4) no shock metamorphic features were found in the samples after thin section examinations; and (5) a systematic sample survey and iron detector scan within and outside of the crater found no iron-rich meteorites larger than 2 cm in size in a depth of 30 cm. Although no conclusive evidence for an impact origin is found yet, Hailar crater was most likely formed by an impact based on its unique occurrence and comparative geomorphologic study. We suggest that drilling in the crater center is required to verify the impact origin, where hypothesized melt-bearing impactites may be encountered.

  10. Noachian and more recent phyllosilicates in impact craters on Mars

    PubMed Central

    Fairén, Alberto G.; Chevrier, Vincent; Abramov, Oleg; Marzo, Giuseppe A.; Gavin, Patricia; Davila, Alfonso F.; Tornabene, Livio L.; Bishop, Janice L.; Roush, Ted L.; Gross, Christoph; Kneissl, Thomas; Uceda, Esther R.; Dohm, James M.; Schulze-Makuch, Dirk; Rodríguez, J. Alexis P.; Amils, Ricardo; McKay, Christopher P.

    2010-01-01

    Hundreds of impact craters on Mars contain diverse phyllosilicates, interpreted as excavation products of preexisting subsurface deposits following impact and crater formation. This has been used to argue that the conditions conducive to phyllosilicate synthesis, which require the presence of abundant and long-lasting liquid water, were only met early in the history of the planet, during the Noachian period (> 3.6 Gy ago), and that aqueous environments were widespread then. Here we test this hypothesis by examining the excavation process of hydrated minerals by impact events on Mars and analyzing the stability of phyllosilicates against the impact-induced thermal shock. To do so, we first compare the infrared spectra of thermally altered phyllosilicates with those of hydrated minerals known to occur in craters on Mars and then analyze the postshock temperatures reached during impact crater excavation. Our results show that phyllosilicates can resist the postshock temperatures almost everywhere in the crater, except under particular conditions in a central area in and near the point of impact. We conclude that most phyllosilicates detected inside impact craters on Mars are consistent with excavated preexisting sediments, supporting the hypothesis of a primeval and long-lasting global aqueous environment. When our analyses are applied to specific impact craters on Mars, we are able to identify both pre- and postimpact phyllosilicates, therefore extending the time of local phyllosilicate synthesis to post-Noachian times. PMID:20616087

  11. Tabular comparisons of the Flynn Creek impact crater, United States, Steinheim impact crater, Germany and Snowball explosion crater, Canada

    NASA Technical Reports Server (NTRS)

    Roddy, D. J.

    1977-01-01

    A tabular outline of comparative data is presented for 340 basic dimensional, morphological, and structural parameters and related aspects for three craters of the flat-floored, central uplift type, two of which are natural terrestrial impact craters and one is a large-scale experimental explosion crater. The three craters are part of a general class, in terms of their morphology and structural deformation that is represented on each of the terrestrial planets including the moon. One of the considered craters, the Flynn Creek Crater, was formed by a hypervelocity impact event approximately 360 m.y. ago in what is now north central Tennessee. The impacting body appears to have been a carbonaceous chondrite or a cometary mass. The second crater, the Steinheim Crater, was formed by an impact event approximately 14.7 m.y. ago in what is now southwestern Germany. The Snowball Crater was formed by the detonation of a 500-ton TNT hemisphere on flat-lying, unconsolidated alluvium in Alberta, Canada.

  12. Centrifuge impact cratering experiment 5

    NASA Technical Reports Server (NTRS)

    1984-01-01

    Transient crates motions, cratering flow fields, crates dynamics, determining impact conditions from total crater welt, centrifuge quarter-space cratering, and impact cratering mechanics research is documented.

  13. Centrifuge Impact Cratering Experiments

    NASA Technical Reports Server (NTRS)

    Schmidt, R. M.; Housen, K. R.; Bjorkman, M. D.

    1985-01-01

    The kinematics of crater growth, impact induced target flow fields and the generation of impact melt were determined. The feasibility of using scaling relationships for impact melt and crater dimensions to determine impactor size and velocity was studied. It is concluded that a coupling parameter determines both the quantity of melt and the crater dimensions for impact velocities greater than 10km/s. As a result impactor radius, a, or velocity, U cannot be determined individually, but only as a product in the form of a coupling parameter, delta U micron. The melt volume and crater volume scaling relations were applied to Brent crater. The transport of melt and the validity of the melt volume scaling relations are examined.

  14. Impact craters on Titan

    USGS Publications Warehouse

    Wood, Charles A.; Lorenz, Ralph; Kirk, Randy; Lopes, Rosaly; Mitchell, Karl; Stofan, Ellen; ,

    2010-01-01

    Five certain impact craters and 44 additional nearly certain and probable ones have been identified on the 22% of Titan's surface imaged by Cassini's high-resolution radar through December 2007. The certain craters have morphologies similar to impact craters on rocky planets, as well as two with radar bright, jagged rims. The less certain craters often appear to be eroded versions of the certain ones. Titan's craters are modified by a variety of processes including fluvial erosion, mass wasting, burial by dunes and submergence in seas, but there is no compelling evidence of isostatic adjustments as on other icy moons, nor draping by thick atmospheric deposits. The paucity of craters implies that Titan's surface is quite young, but the modeled age depends on which published crater production rate is assumed. Using the model of Artemieva and Lunine (2005) suggests that craters with diameters smaller than about 35 km are younger than 200 million years old, and larger craters are older. Craters are not distributed uniformly; Xanadu has a crater density 2-9 times greater than the rest of Titan, and the density on equatorial dune areas is much lower than average. There is a small excess of craters on the leading hemisphere, and craters are deficient in the north polar region compared to the rest of the world. The youthful age of Titan overall, and the various erosional states of its likely impact craters, demonstrate that dynamic processes have destroyed most of the early history of the moon, and that multiple processes continue to strongly modify its surface. The existence of 24 possible impact craters with diameters less than 20 km appears consistent with the Ivanov, Basilevsky and Neukum (1997) model of the effectiveness of Titan's atmosphere in destroying most but not all small projectiles.

  15. Impact craters on Titan

    USGS Publications Warehouse

    Wood, C.A.; Lorenz, R.; Kirk, R.; Lopes, R.; Mitchell, Ken; Stofan, E.

    2010-01-01

    Five certain impact craters and 44 additional nearly certain and probable ones have been identified on the 22% of Titan's surface imaged by Cassini's high-resolution radar through December 2007. The certain craters have morphologies similar to impact craters on rocky planets, as well as two with radar bright, jagged rims. The less certain craters often appear to be eroded versions of the certain ones. Titan's craters are modified by a variety of processes including fluvial erosion, mass wasting, burial by dunes and submergence in seas, but there is no compelling evidence of isostatic adjustments as on other icy moons, nor draping by thick atmospheric deposits. The paucity of craters implies that Titan's surface is quite young, but the modeled age depends on which published crater production rate is assumed. Using the model of Artemieva and Lunine (2005) suggests that craters with diameters smaller than about 35 km are younger than 200 million years old, and larger craters are older. Craters are not distributed uniformly; Xanadu has a crater density 2-9 times greater than the rest of Titan, and the density on equatorial dune areas is much lower than average. There is a small excess of craters on the leading hemisphere, and craters are deficient in the north polar region compared to the rest of the world. The youthful age of Titan overall, and the various erosional states of its likely impact craters, demonstrate that dynamic processes have destroyed most of the early history of the moon, and that multiple processes continue to strongly modify its surface. The existence of 24 possible impact craters with diameters less than 20 km appears consistent with the Ivanov, Basilevsky and Neukum (1997) model of the effectiveness of Titan's atmosphere in destroying most but not all small projectiles. ?? 2009 Elsevier Inc.

  16. Zhamanshin and Aouelloul - Craters produced by impact of tektite-like glasses?

    NASA Technical Reports Server (NTRS)

    O'Keefe, John A.

    1987-01-01

    It is shown that the enhanced abundance of siderophile elements and chromium in tektite-like glasses from the two impact craters of Zhamanshin and Aouelloul cannot be explained as a result of contamination of the country rock by meteorites nor, probably, comets. The pattern is, however, like that found in certain Australasian tektites, and in Ivory Coast tektites. It is concluded, in agreement with earlier suggestions by Campbell-Smith and Hey, that these craters were formed by the impact of large masses of tektite-like glass, of which the glasses which were studied are fragments. It follows that it is necessary, in considering an impact crater, to bear in mind that the projectile may have been a glass.

  17. Zhamanshin and Aouelloul - Craters produced by impact of tektite-like glasses?

    NASA Astrophysics Data System (ADS)

    O'Keefe, John A.

    1987-09-01

    It is shown that the enhanced abundance of siderophile elements and chromium in tektite-like glasses from the two impact craters of Zhamanshin and Aouelloul cannot be explained as a result of contamination of the country rock by meteorites nor, probably, comets. The pattern is, however, like that found in certain Australasian tektites, and in Ivory Coast tektites. It is concluded, in agreement with earlier suggestions by Campbell-Smith and Hey, that these craters were formed by the impact of large masses of tektite-like glass, of which the glasses which were studied are fragments. It follows that it is necessary, in considering an impact crater, to bear in mind that the projectile may have been a glass.

  18. Occurrence and mechanisms of impact melt emplacement at small lunar craters

    NASA Astrophysics Data System (ADS)

    Stopar, Julie D.; Hawke, B. Ray; Robinson, Mark S.; Denevi, Brett W.; Giguere, Thomas A.; Koeber, Steven D.

    2014-11-01

    Using observations from the Lunar Reconnaissance Orbiter Camera (LROC), we assess the frequency and occurrence of impact melt at simple craters less than 5 km in diameter. Nine-hundred-and-fifty fresh, randomly distributed impact craters were identified for study based on their maturity, albedo, and preservation state. The occurrence, frequency, and distribution of impact melt deposits associated with these craters, particularly ponded melt and lobate flows, are diagnostic of melt emplacement mechanisms. Like larger craters, those smaller than a few kilometers in diameter often exhibit ponded melt on the crater floor as well as lobate flows near the crater rim crest. The morphologies of these deposits suggest gravity-driven flow while the melt was molten. Impact melt deposits emplaced as veneers and ;sprays;, thin layers of ejecta that drape other crater materials, indicate deposition late in the cratering process; the deposits of fine sprays are particularly sensitive to degradation. Exterior melt deposits found near the rims of a few dozen craters are distributed asymmetrically around the crater and are rare at craters less than 2 km in diameter. Pre-existing topography plays a role in the occurrence and distribution of these melt deposits, particularly for craters smaller than 1 km in diameter, but does not account for all observed asymmetries in impact melt distribution. The observed relative abundance and frequency of ponded melt and flows in and around simple lunar craters increases with crater diameter, as was previously predicted from models. However, impact melt deposits are found more commonly at simple lunar craters (i.e., those less than a few kilometers in diameter) than previously expected. Ponded melt deposits are observed in roughly 15% of fresh craters smaller than 300 m in diameter and 80% of fresh craters between 600 m and 5 km in diameter. Furthermore, melt deposits are observed at roughly twice as many non-mare craters than at mare craters. We

  19. The Explorer's Guide to Impact Craters

    NASA Technical Reports Server (NTRS)

    Chuang, F.; Pierazzo, E.; Osinski, G.

    2005-01-01

    Impact cratering is a fundamental geologic process of our solar system. It competes with other processes, such as plate tectonics, volcanism, fluvial, glacial and eolian activity, in shaping the surfaces of planetary bodies. In some cases, like the Moon and Mercury, impact craters are the dominant landform. On other planetary bodies impact craters are being continuously erased by the action of other geological processes, like volcanism on Io, erosion and plate tectonics on the Earth, tectonic and volcanic resurfacing on Venus, or ancient erosion periods on Mars. The study of crater populations is one of the principal tools for understanding the geologic history of a planetary surface. Among the general public, impact cratering has drawn wide attention through its portrayal in several Hollywood movies. Questions that are raised after watching these movies include: How do scientists learn about impact cratering? , and What information do impact craters provide in understanding the evolution of a planetary surface? Fundamental approaches used by scientists to learn about impact cratering include field work at known terrestrial craters, remote sensing studies of craters on various solid surfaces of solar system bodies, and theoretical and laboratory studies using the known physics of impact cratering.

  20. Venus - Impact Crater 'Jeanne

    NASA Technical Reports Server (NTRS)

    1991-01-01

    This Magellan full-resolution image shows Jeanne crater, a 19.5 kilometer (12 mile) diameter impact crater. Jeanne crater is located at 40.0 degrees north latitude and 331.4 degrees longitude. The distinctive triangular shape of the ejecta indicates that the impacting body probably hit obliquely, traveling from southwest to northeast. The crater is surrounded by dark material of two types. The dark area on the southwest side of the crater is covered by smooth (radar-dark) lava flows which have a strongly digitate contact with surrounding brighter flows. The very dark area on the northeast side of the crater is probably covered by smooth material such as fine-grained sediment. This dark halo is asymmetric, mimicking the asymmetric shape of the ejecta blanket. The dark halo may have been caused by an atmospheric shock or pressure wave produced by the incoming body. Jeanne crater also displays several outflow lobes on the northwest side. These flow-like features may have formed by fine-grained ejecta transported by a hot, turbulent flow created by the arrival of the impacting object. Alternatively, they may have formed by flow of impact melt.

  1. Degradation studies of Martian impact craters

    NASA Technical Reports Server (NTRS)

    Barlow, N. G.

    1991-01-01

    The amount of obliteration suffered by Martian impact craters is quantified by comparing measurable attributes of the current crater shape to those values expected for a fresh crater of identical size. Crater diameters are measured from profiles obtained using photoclinometry across the structure. The relationship between the diameter of a fresh crater and a crater depth, floor width, rim height, central peak height, etc. was determined by empirical studies performed on fresh Martian impact craters. We utilized the changes in crater depth and rim height to judge the degree of obliteration suffered by Martian impact craters.

  2. Impact Crater with Peak

    NASA Technical Reports Server (NTRS)

    2002-01-01

    (Released 14 June 2002) The Science This THEMIS visible image shows a classic example of a martian impact crater with a central peak. Central peaks are common in large, fresh craters on both Mars and the Moon. This peak formed during the extremely high-energy impact cratering event. In many martian craters the central peak has been either eroded or buried by later sedimentary processes, so the presence of a peak in this crater indicates that the crater is relatively young and has experienced little degradation. Observations of large craters on the Earth and the Moon, as well as computer modeling of the impact process, show that the central peak contains material brought from deep beneath the surface. The material exposed in these peaks will provide an excellent opportunity to study the composition of the martian interior using THEMIS multi-spectral infrared observations. The ejecta material around the crater can is well preserved, again indicating relatively little modification of this landform since its initial creation. The inner walls of this approximately 18 km diameter crater show complex slumping that likely occurred during the impact event. Since that time there has been some downslope movement of material to form the small chutes and gullies that can be seen on the inner crater wall. Small (50-100 m) mega-ripples composed of mobile material can be seen on the floor of the crater. Much of this material may have come from the walls of the crater itself, or may have been blown into the crater by the wind. The Story When a meteor smacked into the surface of Mars with extremely high energy, pow! Not only did it punch an 11-mile-wide crater in the smoother terrain, it created a central peak in the middle of the crater. This peak forms kind of on the 'rebound.' You can see this same effect if you drop a single drop of milk into a glass of milk. With craters, in the heat and fury of the impact, some of the land material can even liquefy. Central peaks like the one

  3. Venus - Impact Crater Jeanne

    NASA Image and Video Library

    1996-11-20

    This full-resolution image from NASA Magellan spacecraft shows Jeanne crater, a 19.5 kilometer (12 mile) diameter impact crater. Jeanne crater is located at 40.0 degrees north latitude and 331.4 degrees longitude. The distinctive triangular shape of the ejecta indicates that the impacting body probably hit obliquely, traveling from southwest to northeast. The crater is surrounded by dark material of two types. The dark area on the southwest side of the crater is covered by smooth (radar-dark) lava flows which have a strongly digitate contact with surrounding brighter flows. The very dark area on the northeast side of the crater is probably covered by smooth material such as fine-grained sediment. This dark halo is asymmetric, mimicking the asymmetric shape of the ejecta blanket. The dark halo may have been caused by an atmospheric shock or pressure wave produced by the incoming body. Jeanne crater also displays several outflow lobes on the northwest side. These flow-like features may have formed by fine-grained ejecta transported by a hot, turbulent flow created by the arrival of the impacting object. Alternatively, they may have formed by flow of impact melt. http://photojournal.jpl.nasa.gov/catalog/PIA00472

  4. Estimated Rock Abundance and Thermophysical Parameters in Oppenheimer Crater on the Moon

    NASA Astrophysics Data System (ADS)

    Bauch, Karin E.; Hiesinger, Harald; Ivanov, Mikhail; van der Bogert, Carolyn H.; Pasckert, Jan-Hendrik; Weinauer, Julia

    2016-04-01

    Oppenheimer crater is located in the north-east of the South Pole-Aitken basin (SPA), the largest impact structure on the Moon [e.g., 1]. The crater is ˜215km in diameter and has an estimated age of ˜4.1 Ga [2]. The floor of Oppenheimer shows evidence of dark mantling deposits and a concentric system of graben structures close to the rim of the crater [3]. Image and topography data show that the floor is flat apart from the graben structures and subsequent impacts on the floor. Oppenheimer-U (˜40km) and -H (˜35km) are floor-fractured craters within the north-west and south-east portions of Oppenheimer crater [3]. Dark mantling deposits on the floor are associated with the graben system. [3] estimated an age between ˜3.98Ga and ˜3.66Ga for the pyroclastic activity, based on crater size-frequency distribution (CSFD) measurements on Lunar Reconnaissance Orbiter (LRO) WAC and NAC images. In this study we compare the mapping results of [3] with temperature data of the LRO Diviner experiment [4] using a numerical model [5, 6]. Nighttime temperature variations are directly influenced by the surface and subsurface thermophysical properties, namely bulk density, heat capacity, and thermal conductivity [7, 8]. These properties can be summarized to a thermal inertia, which represents the ability to conduct and store heat [8]. Low thermal inertia units, such as dust and other fine grained material, quickly respond to temperature changes, which results in large temperature amplitudes between the lunar day and night. On the other hand, high thermal inertia material, e.g. rocks or bedrock, take more time to heat up during the day and reradiate the heat during the night [8]. Relative rock abundances are derived from temperature measurements of the same location at different wavelengths. Brightness temperatures are a function of wavelength and increase with decreasing wavelength [9, 10]. This nonlinearity of the Planck radiance can be used to determine the amount of

  5. The Explorer's Guide to Impact Craters

    NASA Astrophysics Data System (ADS)

    Pierazzo, E.; Osinski, G.; Chuang, F.

    2004-12-01

    Impact cratering is a fundamental geologic process of our solar system. It competes with other processes, such as plate tectonics, volcanism, or fluvial, glacial and eolian activity, in shaping the surfaces of planetary bodies. In some cases, like the Moon and Mercury, impact craters are the dominant landform. On other planetary bodies impact craters are being continuously erased by the action of other geological processes, like volcanism on Io, erosion and plate tectonics on the Earth, tectonic and volcanic resurfacing on Venus, or ancient erosion periods on Mars. The study of crater populations is one of the principal tools for understanding the geologic history of a planetary surface. Among the general public, impact cratering has drawn wide attention through its portrayal in several Hollywood movies. Questions that are raised after watching these movies include: ``How do scientists learn about impact cratering?'', and ``What information do impact craters provide in understanding the evolution of a planetary surface?'' Fundamental approaches used by scientists to learn about impact cratering include field work at known terrestrial craters, remote sensing studies of craters on various solid surfaces of solar system bodies, and theoretical and laboratory studies using the known physics of impact cratering. We will provide students, science teachers, and the general public an opportunity to experience the scientific endeavor of understanding and exploring impact craters through a multi-level approach including images, videos, and rock samples. This type of interactive learning can also be made available to the general public in the form of a website, which can be addressed worldwide at any time.

  6. Impact Cratering Calculations

    NASA Technical Reports Server (NTRS)

    Ahrens, Thomas J.

    1997-01-01

    Understanding the physical processes of impact cratering on planetary surfaces and atmospheres as well as collisions of finite-size self-gravitating objects is vitally important to planetary science. The observation has often been made that craters are the most ubiquitous landform on the solid planets and the satellites. The density of craters is used to date surfaces on planets and satellites. For large ringed basin craters (e.g. Chicxulub), the issue of identification of exactly what 'diameter' transient crater is associated with this structure is exemplified by the arguments of Sharpton et al. (1993) versus those of Hildebrand et al. (1995). The size of a transient crater, such as the K/T extinction crater at Yucatan, Mexico, which is thought to be the source of SO,-induced sulfuric acid aerosol that globally acidified surface waters as the result of massive vaporization of CASO, in the target rock, is addressed by our present project. The impact process excavates samples of planetary interiors. The degree to which this occurs (e.g. how deeply does excavation occur for a given crater diameter) has been of interest, both with regard to exposing mantle rocks in crater floors, as well as launching samples into space which become part of the terrestrial meteorite collection (e.g. lunar meteorites, SNC's from Mars). Only in the case of the Earth can we test calculations in the laboratory and field. Previous calculations predict, independent of diameter, that the depth of excavation, normalized by crater diameter, is d(sub ex)/D = 0.085 (O'Keefe and Ahrens, 1993). For Comet Shoemaker-Levy 9 (SL9) fragments impacting Jupiter, predicted excavation depths of different gas-rich layers in the atmosphere, were much larger. The trajectory and fate of highly shocked material from a large impact on the Earth, such as the K/T bolide is of interest. Melosh et al. (1990) proposed that the condensed material from the impact upon reentering the Earth's atmosphere induced. radiative

  7. Reconciling LCROSS and Orbital Neutron Water Abundance Estimates in Cabeus Crater

    NASA Technical Reports Server (NTRS)

    Elphic, Richard; Teodoro, Luis F.; Eke, Vincent R.; Paige, David A.; Siegler, Matthew A.; Colaprete, Anthony

    2011-01-01

    The Lunar Prospector Neutron Spectrometer (LPNS) first revealed Cabeus crater (84.9 deg S, 35.5degW) as having the highest inferred hydrogen on the Moon. Because of the broad LPNS footprint (approximately 40 km FWHM), the apparent peak water-equivalent hydrogen (WEH) concentration is only approximately 0.25 wt%, but could be much higher in smaller areas than the spectrometer footprint. Earlier image reconstruction work suggested that areas within permanent shadow have abundances approximately 1 wt% WEH. However, the LCROSS impact yielded total water estimates, ice plus vapor, of between 3 and 10 wt%. The large disagreement between LCROSS and apparent orbital values imply that either the ice is buried, by perhaps as much as 50 to 100 cm; or the ice distribution within Cabeus is spatially inhomogeneous, or both. Modeling reveals that the areal extent of a "shallow permafrost zone" is far greater than the area of permanent shadow. Ice can be virtually stable for billions of years within a few tens of centimeters of the surface in these areas. However, the LCROSS impact took place in an area of permanent shadow. If stably-trapped volatiles can be found in locales that receive occasional, oblique sunlight, landed missions may target these sites and eventual resource exploitation may be done more easily. Are orbital neutron data consistent with areally-extensive, volatile-rich cold traps? Orbital epithermal neutron data over the northern half of Cabeus (near the LCROSS impact site) are consistent with 0.2 wt% WEH or less in the "permafrost zone" near the crater. On the other hand, pixon reconstructions that confine the hydrogen enhancements to permanent shadow result in higher abundance estimates -- around 1 wt% if homogeneously mixed. But if the PSR abundance is increased to 10 wt%, consistent with the sum of all H-bearing compounds seen by LCROSS, a much larger-than-observed reduction in neutron count rate would be seen from orbit. It is likely that volatiles are

  8. Successive Formation of Impact Craters

    NASA Image and Video Library

    2012-02-16

    This image from NASA Dawn spacecraft shows two overlapping impact craters on asteroid Vesta. The rims of the craters are both reasonably fresh but the larger crater must be older because the smaller crater cuts across the larger crater rim.

  9. Asteroid (21) Lutetia: Semi-Automatic Impact Craters Detection and Classification

    NASA Astrophysics Data System (ADS)

    Jenerowicz, M.; Banaszkiewicz, M.

    2018-05-01

    The need to develop an automated method, independent of lighting and surface conditions, for the identification and measurement of impact craters, as well as the creation of a reliable and efficient tool, has become a justification of our studies. This paper presents a methodology for the detection of impact craters based on their spectral and spatial features. The analysis aims at evaluation of the algorithm capabilities to determinate the spatial parameters of impact craters presented in a time series. In this way, time-consuming visual interpretation of images would be reduced to the special cases. The developed algorithm is tested on a set of OSIRIS high resolution images of asteroid Lutetia surface which is characterized by varied landforms and the abundance of craters created by collisions with smaller bodies of the solar system.The proposed methodology consists of three main steps: characterisation of objects of interest on limited set of data, semi-automatic extraction of impact craters performed for total set of data by applying the Mathematical Morphology image processing (Serra, 1988, Soille, 2003), and finally, creating libraries of spatial and spectral parameters for extracted impact craters, i.e. the coordinates of the crater center, semi-major and semi-minor axis, shadow length and cross-section. The overall accuracy of the proposed method is 98 %, the Kappa coefficient is 0.84, the correlation coefficient is ∼ 0.80, the omission error 24.11 %, the commission error 3.45 %. The obtained results show that methods based on Mathematical Morphology operators are effective also with a limited number of data and low-contrast images.

  10. The Martian impact cratering record

    NASA Technical Reports Server (NTRS)

    Strom, Robert G.; Croft, Steven K.; Barlow, Nadine G.

    1992-01-01

    A detailed analysis of the Martian impact cratering record is presented. The major differences in impact crater morphology and morphometry between Mars and the moon and Mercury are argued to be largely the result of subsurface volatiles on Mars. In general, the depth to these volatiles may decrease with increasing latitude in the southern hemisphere, but the base of this layer may be at a more or less constant depth. The Martial crustal dichotomy could have been the result of a very large impact near the end of the accretion of Mars. Monte Carlo computer simulations suggest that such an impact was not only possible, but likely. The Martian highland cratering record shows a marked paucity of craters less than about 30 km in diameter relative to the lunar highlands. This paucity of craters was probably the result of the obliteration of craters by an early period of intense erosion and deposition by aeolian, fluvial, and glacial processes.

  11. Space Radar Image of the Yucatan Impact Crater Site

    NASA Image and Video Library

    1999-01-27

    This is a radar image of the southwest portion of the buried Chicxulub impact crater in the Yucatan Peninsula, Mexico. The radar image was acquired on orbit 81 of space shuttle Endeavour on April 14, 1994 by the Spaceborne Imaging Radar C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR). The image is centered at 20 degrees north latitude and 90 degrees west longitude. Scientists believe the crater was formed by an asteroid or comet which slammed into the Earth more than 65 million years ago. It is this impact crater that has been linked to a major biological catastrophe where more than 50 percent of the Earth's species, including the dinosaurs, became extinct. The 180-to 300-kilometer-diameter (110- to 180-mile) crater is buried by 300 to 1,000 meters (1,000 to 3,000 feet) of limestone. The exact size of the crater is currently being debated by scientists. This is a total power radar image with L-band in red, C-band in green, and the difference between C-band L-band in blue. The 10-kilometer-wide (6-mile) band of yellow and pink with blue patches along the top left (northwestern side) of the image is a mangrove swamp. The blue patches are islands of tropical forests created by freshwater springs that emerge through fractures in the limestone bedrock and are most abundant in the vicinity of the buried crater rim. The fracture patterns and wetland hydrology in this region are controlled by the structure of the buried crater. Scientists are using the SIR-C/X-SAR imagery to study wetland ecology and help determine the exact size of the impact crater. http://photojournal.jpl.nasa.gov/catalog/PIA01723

  12. Small Impact Crater

    NASA Technical Reports Server (NTRS)

    2005-01-01

    22 June 2005 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a small impact crater with a 'butterfly' ejecta pattern. The butterfly pattern results from an oblique impact. Not all oblique impacts result in an elliptical crater, but they can result in a non-radial pattern of ejecta distribution. The two-toned nature of the ejecta -- with dark material near the crater and brighter material further away -- might indicate the nature of subsurface materials. Below the surface, there may be a layer of lighter-toned material, underlain by a layer of darker material. The impact throws these materials out in a pattern that reflects the nature of the underlying layers.

    Location near: 3.7oN, 348.2oW Image width: 3 km (1.9 mi) Illumination from: lower left Season: Northern Autumn

  13. Impact cratering calculations

    NASA Technical Reports Server (NTRS)

    Ahrens, Thomas J.; Okeefe, J. D.; Smither, C.; Takata, T.

    1991-01-01

    In the course of carrying out finite difference calculations, it was discovered that for large craters, a previously unrecognized type of crater (diameter) growth occurred which was called lip wave propagation. This type of growth is illustrated for an impact of a 1000 km (2a) silicate bolide at 12 km/sec (U) onto a silicate half-space at earth gravity (1 g). The von Misses crustal strength is 2.4 kbar. The motion at the crater lip associated with this wave type phenomena is up, outward, and then down, similar to the particle motion of a surface wave. It is shown that the crater diameter has grown d/a of approximately 25 to d/a of approximately 4 via lip propagation from Ut/a = 5.56 to 17.0 during the time when rebound occurs. A new code is being used to study partitioning of energy and momentum and cratering efficiency with self gravity for finite-sized objects rather than the previously discussed planetary half-space problems. These are important and fundamental subjects which can be addressed with smoothed particle hydrodynamic (SPH) codes. The SPH method was used to model various problems in astrophysics and planetary physics. The initial work demonstrates that the energy budget for normal and oblique impacts are distinctly different than earlier calculations for silicate projectile impact on a silicate half space. Motivated by the first striking radar images of Venus obtained by Magellan, the effect of the atmosphere on impact cratering was studied. In order the further quantify the processes of meteor break-up and trajectory scattering upon break-up, the reentry physics of meteors striking Venus' atmosphere versus that of the Earth were studied.

  14. The role of volatiles and lithology in the impact cratering process

    NASA Technical Reports Server (NTRS)

    Kieffer, S. W.; Simonds, C. H.

    1980-01-01

    A survey of published descriptions of 32 of the largest, least eroded terrestrial impact structures shows that the amount of melt at craters in crystalline rocks is approximately two orders of magnitude greater than that at craters in sedimentary rocks. A model is proposed for the impact process, and it is examined whether the difference in melt abundance is due to differences in the amount of melt generated in various target materials or due to differences in the fate of the melt during late stages of the impact. The model accounts semiquantitatively for the effects of porosity and water and volatile content on the cratering process. Important features of the model are noted. Even if the recondensation of released volatiles is very efficient, the cumulative effect of repeated impacts on accreting planets would be to continually transfer volatiles toward the outer surface. By this process, volatiles might be enriched toward the outer layer of a growing planet.

  15. Why do complex impact craters have elevated crater rims?

    NASA Astrophysics Data System (ADS)

    Kenkmann, Thomas; Sturm, Sebastian; Krueger, Tim

    2014-05-01

    Most of the complex impact craters on the Moon and on Mars have elevated crater rims like their simple counterparts. The raised rim of simple craters is the result of (i) the deposition of a coherent proximal ejecta blanket at the edge of the transient cavity (overturned flap) and (ii) a structural uplift of the pre-impact surface near the transient cavity rim during the excavation stage of cratering [1]. The latter occurs either by plastic thickening or localized buckling of target rocks, as well as by the emplacement of interthrust wedges [2] or by the injection of dike material. Ejecta and the structural uplift contribute equally to the total elevation of simple crater rims. The cause of elevated crater rims of large complex craters [3] is less obvious, but still, the rim height scales with the final crater diameter. Depending on crater size, gravity, and target rheology, the final crater rim of complex craters can be situated up to 1.5-2.0 transient crater radii distance from the crater center. Here the thickness of the ejecta blanket is only a fraction of that occurring at the rim of simple craters, e.g. [4], and thus cannot account for a strong elevation. Likewise, plastic thickening including dike injection of the underlying target may not play a significant role at this distance any more. We started to systematically investigate the structural uplift and ejecta thickness along the rim of complex impact craters to understand the cause of their elevation. Our studies of two lunar craters (Bessel, 16 km diameter and Euler, 28 km diameter) [5] and one unnamed complex martian crater (16 km diameter) [6] showed that the structural uplift at the final crater rim makes 56-67% of the total rim elevation while the ejecta thickness contributes 33-44%. Thus with increasing distance from the transient cavity rim, the structural uplift seems to dominate. As dike injection and plastic thickening are unlikely at such a distance from the transient cavity, we propose that

  16. A New Impact Crater

    NASA Image and Video Library

    2018-05-29

    NASA's Mars Reconnaissance Orbiter (MRO) keeps finding new impact sites on Mars. This one occurred within the dense secondary crater field of Corinto Crater, to the north-northeast. The new crater and its ejecta have distinctive color patterns. Once the colors have faded in a few decades, this new crater will still be distinctive compared to the secondaries by having a deeper cavity compared to its diameter. https://photojournal.jpl.nasa.gov/catalog/PIA22462

  17. Spatial distribution of impact craters on Deimos

    NASA Astrophysics Data System (ADS)

    Hirata, Naoyuki

    2017-05-01

    Deimos, one of the Martian moons, has numerous impact craters. However, it is unclear whether crater saturation has been reached on this satellite. To address this issue, we apply a statistical test known as nearest-neighbor analysis to analyze the crater distribution of Deimos. When a planetary surface such as the Moon is saturated with impact craters, the spatial distribution of craters is generally changed from random to more ordered. We measured impact craters on Deimos from Viking and HiRISE images and found (1) that the power law of the size-frequency distribution of the craters is approximately -1.7, which is significantly shallower than those of potential impactors, and (2) that the spatial distribution of craters over 30 m in diameter cannot be statistically distinguished from completely random distribution, which indicates that the surface of Deimos is inconsistent with a surface saturated with impact craters. Although a crater size-frequency distribution curve with a slope of -2 is generally interpreted as indicating saturation equilibrium, it is here proposed that two competing mechanisms, seismic shaking and ejecta emplacement, have played a major role in erasing craters on Deimos and are therefore responsible for the shallow slope of this curve. The observed crater density may have reached steady state owing to the obliterations induced by the two competing mechanisms. Such an occurrence indicates that the surface is saturated with impact craters despite the random distribution of craters on Deimos. Therefore, this work proposes that the age determined by the current craters on Deimos reflects neither the age of Deimos itself nor that of the formation of the large concavity centered at its south pole because craters should be removed by later impacts. However, a few of the largest craters on Deimos may be indicative of the age of the south pole event.

  18. Measuring impact crater depth throughout the solar system

    USGS Publications Warehouse

    Robbins, Stuart J.; Watters, Wesley A.; Chappelow, John E.; Bray, Veronica J.; Daubar, Ingrid J.; Craddock, Robert A.; Beyer, Ross A.; Landis, Margaret E.; Ostrach, Lillian; Tornabene, Livio L.; Riggs, Jamie D.; Weaver, Brian P.

    2018-01-01

    One important, almost ubiquitous, tool for understanding the surfaces of solid bodies throughout the solar system is the study of impact craters. While measuring a distribution of crater diameters and locations is an important tool for a wide variety of studies, so too is measuring a crater's “depth.” Depth can inform numerous studies including the strength of a surface and modification rates in the local environment. There is, however, no standard data set, definition, or technique to perform this data‐gathering task, and the abundance of different definitions of “depth” and methods for estimating that quantity can lead to misunderstandings in and of the literature. In this review, we describe a wide variety of data sets and methods to analyze those data sets that have been, are currently, or could be used to derive different types of crater depth measurements. We also recommend certain nomenclature in doing so to help standardize practice in the field. We present a review section of all crater depths that have been published on different solar system bodies which shows how the field has evolved through time and how some common assumptions might not be wholly accurate. We conclude with several recommendations for researchers which could help different data sets to be more easily understood and compared.

  19. Small Rayed Crater Ejecta Retention Age Calculated from Current Crater Production Rates on Mars

    NASA Technical Reports Server (NTRS)

    Calef, F. J. III; Herrick, R. R.; Sharpton, V. L.

    2011-01-01

    Ejecta from impact craters, while extant, records erosive and depositional processes on their surfaces. Estimating ejecta retention age (Eret), the time span when ejecta remains recognizable around a crater, can be applied to estimate the timescale that surface processes operate on, thereby obtaining a history of geologic activity. However, the abundance of sub-kilometer diameter (D) craters identifiable in high resolution Mars imagery has led to questions of accuracy in absolute crater dating and hence ejecta retention ages (Eret). This research calculates the maximum Eret for small rayed impact craters (SRC) on Mars using estimates of the Martian impactor flux adjusted for meteorite ablation losses in the atmosphere. In addition, we utilize the diameter-distance relationship of secondary cratering to adjust crater counts in the vicinity of the large primary crater Zunil.

  20. Low-emissivity impact craters on Venus

    NASA Technical Reports Server (NTRS)

    Weitz, C. M.; Elachi, C.; Moore, H. J.; Basilevsky, A. T.; Ivanov, B. A.; Schaber, G. G.

    1992-01-01

    An analysis of 144 impact craters on Venus has shown that 11 of these have floors with average emissivities lower than 0.8. The remaining craters have emissivities between 0.8 and 0.9, independent of the specific backscatter cross section of the crater floors. These 144 impact craters were chosen from a possible 164 craters with diameters greater than 30 km as identified by researchers for 89 percent of the surface of Venus. We have only looked at craters below 6053.5 km altitude because a mineralogical change causes high reflectivity/low emissivity above the altitude. We have also excluded all craters with diameters smaller than 30 km because the emissivity footprint at periapsis is 16 x 24 km and becomes larger at the poles.

  1. Geology of five small Australian impact craters

    USGS Publications Warehouse

    Shoemaker, E.M.; Macdonald, F.A.; Shoemaker, C.S.

    2005-01-01

    Here we present detailed geological maps and cross-sections of Liverpool, Wolfe Creek, Boxhole, Veevers and Dalgaranga craters. Liverpool crater and Wolfe Creek Meteorite Crater are classic bowlshaped, Barringer-type craters, Liverpool was likely formed during the Neoproterozoic and was filled and covered with sediments soon thereafter. In the Cenozoic, this cover was exhumed exposing the crater's brecciated wall rocks. Wolfe Creek Meteorite Crater displays many striking features, including well-bedded ejecta units, crater-floor faults and sinkholes, a ringed aeromagnetic anomaly, rim-skirting dunes, and numerous iron-rich shale balls. Boxhole Meteorite Crater, Veevers Meteorite Crater and Dalgaranga crater are smaller, Odessa-type craters without fully developed, steep, overturned rims. Boxhole and Dalgaranga craters are developed in highly follated Precambrian basement rocks with a veneer of Holocene colluvium. The pre-existing structure at these two sites complicates structural analyses of the craters, and may have influenced target deformation during impact. Veevers Meteorite Crater is formed in Cenozoic laterites, and is one of the best-preserved impact craters on Earth. The craters discussed herein were formed in different target materials, ranging from crystalline rocks to loosely consolidated sediments, containing evidence that the impactors struck at an array of angles and velocities. This facilitates a comparative study of the influence of these factors on the structural and topographic form of small impact craters. ?? Geological Society of Australia.

  2. Impact craters - Are they useful?

    NASA Astrophysics Data System (ADS)

    Masaitis, V. L.

    1992-03-01

    Terrestrial impact craters are important geological and geomorphological objects that are significant not only for scientific research but for industrial and commercial purposes. The structures may contain commercial minerals produced directly by thermodynamic transformation of target rocks (including primary forming ores) controlled by some morphological, structural or lithological factors and exposed in the crater. Iron and uranium ores, nonferrous metals, diamonds, coals, oil shales, hydrocarbons, mineral waters and other raw materials occur in impact craters. Impact morphostructures may be used for underground storage of gases or liquid waste material. Surface craters may serve as reservoirs for hydropower. These ring structures may be of value to society in other ways. Scientific investigation of them is especially important in comparative planetology, terrestrial geology and in other divisions of the natural sciences.

  3. Experimental simulation of impact cratering on icy satellites

    NASA Technical Reports Server (NTRS)

    Greeley, R.; Fink, J. H.; Gault, D. E.; Guest, J. E.

    1982-01-01

    Cratering processes on icy satellites were simulated in a series of 102 laboratory impact experiments involving a wide range of target materials. For impacts into homogeneous clay slurries with impact energies ranging from five million to ten billion ergs, target yield strengths ranged from 100 to 38 Pa, and apparent viscosities ranged from 8 to 200 Pa s. Bowl-shaped craters, flat-floored craters, central peak craters with high or little relief, and craters with no relief were observed. Crater diameters increased steadily as energies were raised. A similar sequence was seen for experiment in which impact energy was held constant but target viscosity and strength progressively decreases. The experiments suggest that the physical properties of the target media relative to the gravitationally induced stresses determined the final crater morphology. Crater palimpsests could form by prompt collapse of large central peak craters formed in low target strength materials. Ages estimated from crater size-frequency distributions that include these large craters may give values that are too high.

  4. Hydrothermal Alteration at Lonar Crater, India and Elemental Variations in Impact Crater Clays

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.; Nelson, M. J.; Shearer, C. K.; Misra, S.; Narasimham, V.

    2005-01-01

    The role of hydrothermal alteration and chemical transport involving impact craters could have occurred on Mars, the poles of Mercury and the Moon, and other small bodies. We are studying terrestrial craters of various sizes in different environments to better understand aqueous alteration and chemical transport processes. The Lonar crater in India (1.8 km diameter) is particularly interesting being the only impact crater in basalt. In January of 2004, during fieldwork in the ejecta blanket around the rim of the Lonar crater we discovered alteration zones not previously described at this crater. The alteration of the ejecta blanket could represent evidence of localized hydrothermal activity. Such activity is consistent with the presence of large amounts of impact melt in the ejecta blanket. Map of one area on the north rim of the crater containing highly altered zones at least 3 m deep is shown.

  5. Scaling Impact-Melt and Crater Dimensions: Implications for the Lunar Cratering Record

    NASA Technical Reports Server (NTRS)

    Cintala , Mark J.; Grieve, Richard A. F.

    1997-01-01

    The consequences of impact on the solid bodies of the solar system are manifest and legion. Although the visible effects on planetary surfaces, such as the Moon's, are the most obvious testimony to the spatial and temporal importance of impacts, less dramatic chemical and petrographic characteristics of materials affected by shock abound. Both the morphologic and petrologic aspects of impact cratering are important in deciphering lunar history, and, ideally, each should complement the other. In practice, however, a gap has persisted in relating large-scale cratering processes to petrologic and geochemical data obtained from lunar samples. While this is due in no small part to the fact that no Apollo mission unambiguously sampled deposits of a large crater, it can also be attributed to the general state of our knowledge of cratering phenomena, particularly those accompanying large events. The most common shock-metamorphosed lunar samples are breccias, but a substantial number are impact-melt rocks. Indeed, numerous workers have called attention to the importance of impact-melt rocks spanning a wide range of ages in the lunar sample collection. Photogeologic studies also have demonstrated the widespread occurrence of impact-melt lithologies in and around lunar craters. Thus, it is clear that impact melting has been a fundamental process operating throughout lunar history, at scales ranging from pits formed on individual regolith grains to the largest impact basins. This contribution examines the potential relationship between impact melting on the Moon and the interior morphologies of large craters and peaking basins. It then examines some of the implications of impact melting at such large scales for lunar-sample provenance and evolution of the lunar crust.

  6. Modeling Low Velocity Impacts: Predicting Crater Depth on Pluto

    NASA Astrophysics Data System (ADS)

    Bray, V. J.; Schenk, P.

    2014-12-01

    The New Horizons mission is due to fly-by the Pluto system in Summer 2015 and provides the first opportunity to image the Pluto surface in detail, allowing both the appearance and number of its crater population to be studied for the first time. Bray and Schenk (2014) combined previous cratering studies and numerical modeling of the impact process to predict crater morphology on Pluto based on current understanding of Pluto's composition, structure and surrounding impactor population. Predictions of how the low mean impact velocity (~2km/s) of the Pluto system will influence crater formation is a complex issue. Observations of secondary cratering (low velocity, high angle) and laboratory experiments of impact at low velocity are at odds regarding how velocity controls depth-diameter ratios: Observations of secondary craters show that these low velocity craters are shallower than would be expected for a hyper-velocity primary. Conversely, gas gun work has shown that relative crater depth increases as impact velocity decreases. We have investigated the influence of impact velocity further with iSALE hydrocode modeling of comet impact into Pluto. With increasing impact velocity, a projectile will produce wider and deeper craters. The depth-diameter ratio (d/D) however has a more complex progression with increasing impact velocity: impacts faster than 2km/s lead to smaller d/D ratios as impact velocity increases, in agreement with gas-gun studies. However, decreasing impact velocity from 2km/s to 300 m/s produced smaller d/D as impact velocity was decreased. This suggests that on Pluto the deepest craters would be produced by ~ 2km/s impacts, with shallower craters produced by velocities either side of this critical point. Further simulations to investigate whether this effect is connected to the sound speed of the target material are ongoing. The complex relationship between impact velocity and crater depth for impacts occurring between 300m/s and 10 km/s suggests

  7. The Cretaceous-Tertiary (K/T) impact: One or more source craters?

    NASA Technical Reports Server (NTRS)

    Koeberl, Christian

    1992-01-01

    The Cretaceous-Tertiary (K/T) boundary is marked by signs of a worldwide catastrophe, marking the demise of more than 50 percent of all living species. Ever since Alvarez et al. found an enrichment of IR and other siderophile elements in rocks marking the K/T boundary and interpreted it as the mark of a giant asteroid (or comet) impact, scientists have tried to understand the complexities of the K/T boundary event. The impact theory received a critical boost by the discovery of shocked minerals that have so far been found only in association with impact craters. One of the problems of the K/T impact theory was, and still is, the lack of an adequate large crater that is close to the maximum abundance of shocked grains in K/T boundary sections, which was found to occur in sections in Northern America. The recent discovery of impact glasses from a K/T section in Haiti has been crucial in establishing a connection with documented impact processes. The location of the impact-glass findings and the continental nature of detritus found in all K/T sections supports at least one impact site near the North American continent. The Manson Impact Structure is the largest recognized in the United States, 35 km in diameter, and has a radiometric age indistinguishable from that of the Cretaceous-Tertiary (K/T) boundary. Although the Manson structure may be too small, it may be considered at least one element of the events that led to the catastrophic loss of life and extinction of many species at that time. A second candidate for the K/T boundary crater is the Chicxulub structure, which was first suggested to be an impact crater more than a decade ago. Only recently, geophysical studies and petrological (as well as limited chemical) analyses have indicated that this buried structure may in fact be of impact origin. At present we can conclude that the Manson crater is the only confirmed crater of K/T age, but Chicxulub is becoming a strong contender; however, detailed geochemical

  8. The Cretaceous-Tertiary (K/T) impact: One or more source craters?

    NASA Astrophysics Data System (ADS)

    Koeberl, Christian

    The Cretaceous-Tertiary (K/T) boundary is marked by signs of a worldwide catastrophe, marking the demise of more than 50 percent of all living species. Ever since Alvarez et al. found an enrichment of IR and other siderophile elements in rocks marking the K/T boundary and interpreted it as the mark of a giant asteroid (or comet) impact, scientists have tried to understand the complexities of the K/T boundary event. The impact theory received a critical boost by the discovery of shocked minerals that have so far been found only in association with impact craters. One of the problems of the K/T impact theory was, and still is, the lack of an adequate large crater that is close to the maximum abundance of shocked grains in K/T boundary sections, which was found to occur in sections in Northern America. The recent discovery of impact glasses from a K/T section in Haiti has been crucial in establishing a connection with documented impact processes. The location of the impact-glass findings and the continental nature of detritus found in all K/T sections supports at least one impact site near the North American continent. The Manson Impact Structure is the largest recognized in the United States, 35 km in diameter, and has a radiometric age indistinguishable from that of the Cretaceous-Tertiary (K/T) boundary. Although the Manson structure may be too small, it may be considered at least one element of the events that led to the catastrophic loss of life and extinction of many species at that time. A second candidate for the K/T boundary crater is the Chicxulub structure, which was first suggested to be an impact crater more than a decade ago. Only recently, geophysical studies and petrological (as well as limited chemical) analyses have indicated that this buried structure may in fact be of impact origin. At present we can conclude that the Manson crater is the only confirmed crater of K/T age, but Chicxulub is becoming a strong contender; however, detailed geochemical

  9. El'gygytgyn impact crater, Chukotka, Arctic Russia: Impact cratering aspects of the 2009 ICDP drilling project

    NASA Astrophysics Data System (ADS)

    Koeberl, Christian; Pittarello, Lidia; Reimold, Wolf Uwe; Raschke, Ulli; Brigham-Grette, Julie; Melles, Martin; Minyuk, Pavel

    2013-07-01

    The El'gygytgyn impact structure in Chukutka, Arctic Russia, is the only impact crater currently known on Earth that was formed in mostly acid volcanic rocks (mainly of rhyolitic, with some andesitic and dacitic, compositions). In addition, because of its depth, it has provided an excellent sediment trap that records paleoclimatic information for the 3.6 Myr since its formation. For these two main reasons, because of the importance for impact and paleoclimate research, El'gygytgyn was the subject of an International Continental Scientific Drilling Program (ICDP) drilling project in 2009. During this project, which, due to its logistical and financial challenges, took almost a decade to come to fruition, a total of 642.3 m of drill core was recovered at two sites, from four holes. The obtained material included sedimentary and impactite rocks. In terms of impactites, which were recovered from 316.08 to 517.30 m depth below lake bottom (mblb), three main parts of that core segment were identified: from 316 to 390 mblb polymict lithic impact breccia, mostly suevite, with volcanic and impact melt clasts that locally contain shocked minerals, in a fine-grained clastic matrix; from 385 to 423 mblb, a brecciated sequence of volcanic rocks including both felsic and mafic (basalt) members; and from 423 to 517 mblb, a greenish rhyodacitic ignimbrite (mostly monomict breccia). The uppermost impactite (316-328 mblb) contains lacustrine sediment mixed with impact-affected components. Over the whole length of the impactite core, the abundance of shock features decreases rapidly from the top to the bottom of the studied core section. The distinction between original volcanic melt fragments and those that formed later as the result of the impact event posed major problems in the study of these rocks. The sequence that contains fairly unambiguous evidence of impact melt (which is not very abundant anyway, usually less than a few volume%) is only about 75 m thick. The reason for

  10. El'gygytgyn impact crater, Chukotka, Arctic Russia: Impact cratering aspects of the 2009 ICDP drilling project.

    PubMed

    Koeberl, Christian; Pittarello, Lidia; Reimold, Wolf Uwe; Raschke, Ulli; Brigham-Grette, Julie; Melles, Martin; Minyuk, Pavel; Spray, John

    2013-07-01

    The El'gygytgyn impact structure in Chukutka, Arctic Russia, is the only impact crater currently known on Earth that was formed in mostly acid volcanic rocks (mainly of rhyolitic, with some andesitic and dacitic, compositions). In addition, because of its depth, it has provided an excellent sediment trap that records paleoclimatic information for the 3.6 Myr since its formation. For these two main reasons, because of the importance for impact and paleoclimate research, El'gygytgyn was the subject of an International Continental Scientific Drilling Program (ICDP) drilling project in 2009. During this project, which, due to its logistical and financial challenges, took almost a decade to come to fruition, a total of 642.3 m of drill core was recovered at two sites, from four holes. The obtained material included sedimentary and impactite rocks. In terms of impactites, which were recovered from 316.08 to 517.30 m depth below lake bottom (mblb), three main parts of that core segment were identified: from 316 to 390 mblb polymict lithic impact breccia, mostly suevite, with volcanic and impact melt clasts that locally contain shocked minerals, in a fine-grained clastic matrix; from 385 to 423 mblb, a brecciated sequence of volcanic rocks including both felsic and mafic (basalt) members; and from 423 to 517 mblb, a greenish rhyodacitic ignimbrite (mostly monomict breccia). The uppermost impactite (316-328 mblb) contains lacustrine sediment mixed with impact-affected components. Over the whole length of the impactite core, the abundance of shock features decreases rapidly from the top to the bottom of the studied core section. The distinction between original volcanic melt fragments and those that formed later as the result of the impact event posed major problems in the study of these rocks. The sequence that contains fairly unambiguous evidence of impact melt (which is not very abundant anyway, usually less than a few volume%) is only about 75 m thick. The reason for

  11. El'gygytgyn impact crater, Chukotka, Arctic Russia: Impact cratering aspects of the 2009 ICDP drilling project

    PubMed Central

    Koeberl, Christian; Pittarello, Lidia; Reimold, Wolf Uwe; Raschke, Ulli; Brigham-Grette, Julie; Melles, Martin; Minyuk, Pavel; Spray, John

    2013-01-01

    The El'gygytgyn impact structure in Chukutka, Arctic Russia, is the only impact crater currently known on Earth that was formed in mostly acid volcanic rocks (mainly of rhyolitic, with some andesitic and dacitic, compositions). In addition, because of its depth, it has provided an excellent sediment trap that records paleoclimatic information for the 3.6 Myr since its formation. For these two main reasons, because of the importance for impact and paleoclimate research, El'gygytgyn was the subject of an International Continental Scientific Drilling Program (ICDP) drilling project in 2009. During this project, which, due to its logistical and financial challenges, took almost a decade to come to fruition, a total of 642.3 m of drill core was recovered at two sites, from four holes. The obtained material included sedimentary and impactite rocks. In terms of impactites, which were recovered from 316.08 to 517.30 m depth below lake bottom (mblb), three main parts of that core segment were identified: from 316 to 390 mblb polymict lithic impact breccia, mostly suevite, with volcanic and impact melt clasts that locally contain shocked minerals, in a fine-grained clastic matrix; from 385 to 423 mblb, a brecciated sequence of volcanic rocks including both felsic and mafic (basalt) members; and from 423 to 517 mblb, a greenish rhyodacitic ignimbrite (mostly monomict breccia). The uppermost impactite (316–328 mblb) contains lacustrine sediment mixed with impact-affected components. Over the whole length of the impactite core, the abundance of shock features decreases rapidly from the top to the bottom of the studied core section. The distinction between original volcanic melt fragments and those that formed later as the result of the impact event posed major problems in the study of these rocks. The sequence that contains fairly unambiguous evidence of impact melt (which is not very abundant anyway, usually less than a few volume%) is only about 75 m thick. The reason for

  12. Impact cratering experiments in brittle targets with variable thickness: Implications for deep pit craters on Mars

    NASA Astrophysics Data System (ADS)

    Michikami, T.; Hagermann, A.; Miyamoto, H.; Miura, S.; Haruyama, J.; Lykawka, P. S.

    2014-06-01

    High-resolution images reveal that numerous pit craters exist on the surface of Mars. For some pit craters, the depth-to-diameter ratios are much greater than for ordinary craters. Such deep pit craters are generally considered to be the results of material drainage into a subsurface void space, which might be formed by a lava tube, dike injection, extensional fracturing, and dilational normal faulting. Morphological studies indicate that the formation of a pit crater might be triggered by the impact event, and followed by collapse of the ceiling. To test this hypothesis, we carried out laboratory experiments of impact cratering into brittle targets with variable roof thickness. In particular, the effect of the target thickness on the crater formation is studied to understand the penetration process by an impact. For this purpose, we produced mortar targets with roof thickness of 1-6 cm, and a bulk density of 1550 kg/m3 by using a mixture of cement, water and sand (0.2 mm) in the ratio of 1:1:10, by weight. The compressive strength of the resulting targets is 3.2±0.9 MPa. A spherical nylon projectile (diameter 7 mm) is shot perpendicularly into the target surface at the nominal velocity of 1.2 km/s, using a two-stage light-gas gun. Craters are formed on the opposite side of the impact even when no target penetration occurs. Penetration of the target is achieved when craters on the opposite sides of the target connect with each other. In this case, the cross section of crater somehow attains a flat hourglass-like shape. We also find that the crater diameter on the opposite side is larger than that on the impact side, and more fragments are ejected from the crater on the opposite side than from the crater on the impact side. This result gives a qualitative explanation for the observation that the Martian deep pit craters lack a raised rim and have the ejecta deposit on their floor instead. Craters are formed on the opposite impact side even when no penetration

  13. Impact Crater in Coastal Patagonia

    NASA Technical Reports Server (NTRS)

    D'Antoni, Hector L; Lasta, Carlos A.; Condon, Estelle (Technical Monitor)

    2000-01-01

    Impact craters are geological structures attributed to the impact of a meteoroid on the Earth's (or other planet's) surface (Koeberl and Sharpton. 1999). The inner planets of the solar system as well as other bodies such as our moon show extensive meteoroid impacts (Gallant 1964, French 1998). Because of its size and gravity, we may assume that the Earth has been heavily bombarded but weathering and erosion have erased or masked most of these features. In the 1920's, a meteor crater (Mark 1987) was identified in Arizona and to this first finding the identification of a large number of impact structures on Earth followed (Hodge 1994). Shock metamorphic effects are associated with meteorite impact craters. Due to extremely high pressures, shatter cones are produced as well as planar features in quartz and feldspar grains, diaplectic glass and high-pressure mineral phases such as stishovite (French 1998).

  14. Interplanetary meteoroid debris in LDEF metal craters

    NASA Technical Reports Server (NTRS)

    Brownlee, D. E.; Joswiak, D.; Bradley, J.; Hoerz, Friedrich

    1993-01-01

    We have examined craters in Al and Au LDEF surfaces to determine the nature of meteoroid residue in the rare cases where projectile material is abundantly preserved in the crater floor. Typical craters contain only small amounts of residue and we find that less than 10 percent of the craters in Al have retained abundant residue consistent with survival of a significant fraction (greater than 20 percent) of the projectile mass. The residue-rich craters can usually be distinguished optically because their interiors are darker than ones with little or no apparent projectile debris. The character of the meteoroid debris in these craters ranges from thin glass liners, to thick vesicular glass containing unmelted mineral fragments, to debris dominated by unmelted mineral fragments. In the best cases of meteoroid survival, unmelted mineral fragments preserve both information on projectile mineralogy as well as other properties such as nuclear tracks caused by solar flare irradiation. The wide range of the observed abundance and alteration state of projectile residue is most probably due to differences in impact velocity. The crater liners are being studied to determine the composition of meteoroids reaching the Earth. The compositional types most commonly seen in the craters are: (1) chondritic (Mg, Si, S, Fe in approximately solar proportions), (2) Mg silicate. amd (3) iron sulfide. These are also the most common compositional types of extraterrestrial particle types collected in the stratosphere. The correlation between these compositions indicates that vapor fractionation was not a major process influencing residue composition in these craters. Although the biases involved with finding analyzable meteoroid debris in metal craters differ from those for extraterrestrial particles collected in and below the atmosphere, there is a common bias favoring particles with low entry velocity. For craters this is very strong and probably all of the metal craters with abundant

  15. Calculational investigation of impact cratering dynamics - Material motions during the crater growth period

    NASA Technical Reports Server (NTRS)

    Austin, M. G.; Thomsen, J. M.; Ruhl, S. F.; Orphal, D. L.; Schultz, P. H.

    1980-01-01

    The considered investigation was conducted in connection with studies which are to provide a better understanding of the detailed dynamics of impact cratering processes. Such an understanding is vital for a comprehension of planetary surfaces. The investigation is the continuation of a study of impact dynamics in a uniform, nongeologic material at impact velocities achievable in laboratory-scale experiments conducted by Thomsen et al. (1979). A calculation of a 6 km/sec impact of a 0.3 g spherical 2024 aluminum projectile into low strength (50 kPa) homogeneous plasticene clay has been continued from 18 microseconds to past 600 microseconds. The cratering flow field, defined as the material flow field in the target beyond the transient cavity but well behind the outgoing shock wave, has been analyzed in detail to see how applicable the Maxwell Z-Model, developed from analysis of near-surface explosion cratering calculations, is to impact cratering

  16. Lonar Lake, India: An impact Crater in basalt

    USGS Publications Warehouse

    Fredriksson, K.; Dube, A.; Milton, D.J.; Balasundaram, M.S.

    1973-01-01

    Discovery of shock-metamorphosed material establishes the impact origin of Lonar Crater. Coarse breccia with shatter coning and microbreccia with moderately shocked fragments containing maskelynite were found in drill holes through the crater floor. Trenches on the rim yield strongly shocked fragments in which plagioclase has melted and vesiculated, and bombs and spherules of homogeneous rock melt. As the only known terrestrial impact crater in basalt, Lonar Crater provides unique opportunities for comparison with lunar craters. In particular, microbreccias and glass spherules from Lonar Crater have close analogs among the Apollo specimens.

  17. Artificial lunar impact craters: Four new identifications, part I

    NASA Technical Reports Server (NTRS)

    Whitaker, E. A.

    1972-01-01

    The Apollo 16 panoramic camera photographed the impact locations of the Ranger 7 and 9 spacecraft and the S-4B stage of the Apollo 14 Saturn launch vehicle. Identification of the Ranger craters was very simple because each photographed its target point before impact. Identification of the S-4B impact crater proved to be a simple matter because the impact location, as derived from earth-based tracking, displayed a prominent and unique system of mixed light and dark rays. By using the criterion of a dark ray pattern, a reexamination of the Apollo 14 500 mm Hasselblad sequence taken of the Apollo 13 S-4B impact area was made. This examination quickly led to the discovery of the ray system and the impact crater. The study of artificial lunar impact craters, ejecta blankets, and ray systems provides the long-needed link between the various experimental terrestrial impact and explosion craters, and the naturally occurring impact craters on the moon. This elementary study shows that lunar impact crater diameters are closely predictable from a knowledge of the energies involved, at least in the size range considered, and suggests that parameters, such as velocity, may have a profound effect on crater morphology and ejecta blanket albedo.

  18. Colorful Impact Ejecta from Hargraves Crater

    NASA Image and Video Library

    2017-05-08

    The collision that created Hargraves Crater impacted into diverse bedrock lithologies of ancient Mars; the impact ejecta is a rich mix of rock types with different colors and textures, as seen by NASA Mars Reconnaissance Orbiter. The crater is named after Robert Hargraves who discovered and studied meteorite impacts on the Earth. https://photojournal.jpl.nasa.gov/catalog/PIA21609

  19. Snow-avalanche impact craters in southern Norway: Their morphology and dynamics compared with small terrestrial meteorite craters

    NASA Astrophysics Data System (ADS)

    Matthews, John A.; Owen, Geraint; McEwen, Lindsey J.; Shakesby, Richard A.; Hill, Jennifer L.; Vater, Amber E.; Ratcliffe, Anna C.

    2017-11-01

    This regional inventory and study of a globally uncommon landform type reveals similarities in form and process between craters produced by snow-avalanche and meteorite impacts. Fifty-two snow-avalanche impact craters (mean diameter 85 m, range 10-185 m) were investigated through field research, aerial photographic interpretation and analysis of topographic maps. The craters are sited on valley bottoms or lake margins at the foot of steep avalanche paths (α = 28-59°), generally with an easterly aspect, where the slope of the final 200 m of the avalanche path (β) typically exceeds 15°. Crater diameter correlates with the area of the avalanche start zone, which points to snow-avalanche volume as the main control on crater size. Proximal erosional scars ('blast zones') up to 40 m high indicate up-range ejection of material from the crater, assisted by air-launch of the avalanches and impulse waves generated by their impact into water-filled craters. Formation of distal mounds up to 12 m high of variable shape is favoured by more dispersed down-range deposition of ejecta. Key to the development of snow-avalanche impact craters is the repeated occurrence of topographically-focused snow avalanches that impact with a steep angle on unconsolidated sediment. Secondary craters or pits, a few metres in diameter, are attributed to the impact of individual boulders or smaller bodies of snow ejected from the main avalanche. The process of crater formation by low-density, low-velocity, large-volume snow flows occurring as multiple events is broadly comparable with cratering by single-event, high-density, high-velocity, small-volume projectiles such as small meteorites. Simple comparative modelling of snow-avalanche events associated with a crater of average size (diameter 85 m) indicates that the kinetic energy of a single snow-avalanche impact event is two orders of magnitude less than that of a single meteorite-impact event capable of producing a crater of similar size

  20. Constraining the Origin of Impact Craters on Al Foils from the Stardust Interstellar Dust Collector

    NASA Technical Reports Server (NTRS)

    Stroud, Rhonda M.; Achilles, Cheri; Allen, Carlton; Ansari, Asna; Bajt, Sasa; Bassim, Nabil; Bastien, Ron S.; Bechtel, H. A.; Borg, Janet; Brenker, Frank E.; hide

    2012-01-01

    Preliminary examination (PE) of the aerogel tiles and Al foils from the Stardust Interstellar Dust Collector has revealed multiple impact features. Some are most likely due to primary impacts of interstellar dust (ISD) grains, and others are associated with secondary impacts of spacecraft debris, and possibly primary impacts of interplanetary dust particles (IDPs) [1, 2]. The current focus of the PE effort is on constraining the origin of the individual impact features so that definitive results from the first direct laboratory analysis of contemporary ISD can be reported. Because crater morphology depends on impacting particle shape and composition, in addition to the angle and direction of impact, unique particle trajectories are not easily determined. However, elemental analysis of the crater residues can distinguish real cosmic dust from the spacecraft debris, due to the low cosmic abundance of many of the elements in the spacecraft materials. We present here results from the elemental analysis of 24 craters and discuss the possible origins of 4 that are identified as candidate ISD impacts

  1. Aboriginal oral traditions of Australian impact craters

    NASA Astrophysics Data System (ADS)

    Hamacher, Duane W.; Goldsmith, John

    2013-11-01

    In this paper we explore Aboriginal oral traditions that relate to Australian meteorite craters. Using the literature, first-hand ethnographic records and field trip data, we identify oral traditions and artworks associated with four impact sites: Gosses Bluff, Henbury, Liverpool and Wolfe Creek. Oral traditions describe impact origins for Gosses Bluff, Henbury and Wolfe Creek Craters, and non-impact origins for Liverpool Crater, with Henbury and Wolfe Creek stories having both impact and non-impact origins. Three impact sites that are believed to have been formed during human habitation of Australia -- Dalgaranga, Veevers, and Boxhole -- do not have associated oral traditions that are reported in the literature.

  2. Titan's Impact Cratering Record: Erosion of Ganymedean (and other) Craters on a Wet Icy Landscape

    NASA Astrophysics Data System (ADS)

    Schenk, P.; Moore, J.; Howard, A.

    2012-04-01

    We examine the cratering record of Titan from the perspective of icy satellites undergoing persistent landscape erosion. First we evaluate whether Ganymede (and Callisto) or the smaller low-gravity neighboring icy satellites of Saturn are the proper reference standard for evaluating Titan’s impact crater morphologies, using topographic and morphometric measurements (Schenk, 2002; Schenk et al. (2004) and unpublished data). The special case of Titan’s largest crater, Minrva, is addressed through analysis of large impact basins such as Gilgamesh, Lofn, Odysseus and Turgis. Second, we employ a sophisticated landscape evolution and modification model developed for study of martian and other planetary landforms (e.g., Howard, 2007). This technique applies mass redistribution principles due to erosion by impact, fluvial and hydrological processes to a planetary landscape. The primary advantage of our technique is the possession of a limited but crucial body of areal digital elevation models (DEMs) of Ganymede (and Callisto) impact craters as well as global DEM mapping of Saturn’s midsize icy satellites, in combination with the ability to simulate rainfall and redeposition of granular material to determine whether Ganymede craters can be eroded to resemble Titan craters and the degree of erosion required. References: Howard, A. D., “Simulating the development of martian highland landscapes through the interaction of impact cratering, fluvial erosion, and variable hydrologic forcing”, Geomorphology, 91, 332-363, 2007. Schenk, P. "Thickness constraints on the icy shells of the galilean satellites from impact crater shapes". Nature, 417, 419-421, 2002. Schenk, P.M., et al. "Ages and interiors: the cratering record of the Galilean satellites". In: Jupiter: The Planet, Satellites, and Magnetosphere, Cambridge University Press, Cambridge, UK, pp. 427-456, 2004.

  3. Impact Cratering Calculations

    NASA Technical Reports Server (NTRS)

    Ahrens, Thomas J.

    2002-01-01

    Many Martian craters are surrounded by ejecta blankets which appear to have been fluidized forming lobate and layered deposits terminated by one or more continuous distal scarps, or ramparts. One of the first hypotheses for the formation of so-called rampart ejecta features was shock-melting of subsurface ice, entrainment of liquid water into the ejecta blanket, and subsequent fluidized flow. Our work quantifies this concept. Rampart ejecta found on all but the youngest volcanic and polar regions, and the different rampart ejecta morphologies are correlated with crater size and terrain. In addition, the minimum diameter of craters with rampart features decreases with increasing latitude indicating that ice laden crust resides closer to the surface as one goes poleward on Mars. Our second goal in was to determine what strength model(s) reproduce the faults and complex features found in large scale gravity driven craters. Collapse features found in large scale craters require that the rock strength weaken as a result of the shock processing of rock and the later cratering shear flows. In addition to the presence of molten silicate in the intensely shocked region, the presence of water, either ambient, or the result of shock melting of ice weakens rock. There are several other mechanisms for the reduction of strength in geologic materials including dynamic tensile and shear induced fracturing. Fracturing is a mechanism for large reductions in strength. We found that by incorporating damage into the models that we could in a single integrated impact calculation, starting in the atmosphere produce final crater profiles having the major features found in the field measurements (central uplifts, inner ring, terracing and faulting). This was accomplished with undamaged surface strengths (0.1 GPa) and in depth strengths (1.0 GPa).

  4. Impact Craters on Titan? Cassini RADAR View

    NASA Technical Reports Server (NTRS)

    Wood, Charles A.; Lopes, Rosaly; Stofan, Ellen R.; Paganelli, Flora; Elachi, Charles

    2005-01-01

    Titan is a planet-size (diameter of 5,150 km) satellite of Saturn that is currently being investigated by the Cassini spacecraft. Thus far only one flyby (Oct. 26, 2004; Ta) has occurred when radar images were obtained. In February, 2005, and approximately 20 more times in the next four years, additional radar swaths will be acquired. Each full swath images about 1% of Titan s surface at 13.78 GHz (Ku-band) with a maximum resolution of 400 m. The Ta radar pass [1] demonstrated that Titan has a solid surface with multiple types of landforms. However, there is no compelling detection of impact craters in this first radar swath. Dione, Tethys and other satellites of Saturn are intensely cratered, there is no way that Titan could have escaped a similar impact cratering past; thus there must be ongoing dynamic surface processes that erase impact craters (and other landforms) on Titan. The surface of Titan must be very young and the resurfacing rate must be significantly higher than the impact cratering rate.

  5. Impact cratering through geologic time

    USGS Publications Warehouse

    Shoemaker, E.M.; Shoemaker, C.S.

    1998-01-01

    New data on lunar craters and recent discoveries about craters on Earth permit a reassessment of the bombardment history of Earth over the last 3.2 billion years. The combined lunar and terrestrial crater records suggest that the long-term average rate of production of craters larger than 20 km in diameter has increased, perhaps by as much as 60%, in the last 100 to 200 million years. Production of craters larger than 70 km in diameter may have increased, in the same time interval, by a factor of five or more over the average for the preceding three billion years. A large increase in the flux of long-period comets appears to be the most likely explanation for such a long-term increase in the cratering rate. Two large craters, in particular, appear to be associated with a comet shower that occurred about 35.5 million years ago. The infall of cosmic dust, as traced by 3He in deep sea sediments, and the ages of large craters, impact glass horizons, and other stratigraphic markers of large impacts seem to be approximately correlated with the estimated times of passage of the Sun through the galactic plane, at least for the last 65 million years. Those are predicted times for an increased near-Earth flux of comets from the Oort Cloud induced by the combined effects of galactic tidal perturbations and encounters of the Sun with passing stars. Long-term changes in the average comet flux may be related to changes in the amplitude of the z-motion of the Sun perpendicular to the galactic plane or to stripping of the outer Oort cloud by encounters with large passing stars, followed by restoration from the inner Oort cloud reservoir.

  6. Hypervelocity impact cratering calculations

    NASA Technical Reports Server (NTRS)

    Maxwell, D. E.; Moises, H.

    1971-01-01

    A summary is presented of prediction calculations on the mechanisms involved in hypervelocity impact cratering and response of earth media. Considered are: (1) a one-gram lithium-magnesium alloys impacting basalt normally at 6.4 km/sec, and (2) a large terrestrial impact corresponding to that of Sierra Madera.

  7. 100 New Impact Crater Sites Found on Mars

    NASA Astrophysics Data System (ADS)

    Kennedy, M. R.; Malin, M. C.

    2009-12-01

    Recent observations constrain the formation of 100 new impact sites on Mars over the past decade; 19 of these were found using the Mars Global Surveyor Mars Orbiter Camera (MOC), and the other 81 have been identified since 2006 using the Mars Reconnaissance Orbiter Context Camera (CTX). Every 6 meter/pixel CTX image is examined upon receipt and, where they overlap images of 0.3-240 m/pixel scale acquired by the same or other Mars-orbiting spacecraft, we look for features that may have changed. New impact sites are initially identified by the presence of a new dark spot or cluster of dark spots in a CTX image. Such spots may be new impact craters, or result from the effect of impact blasts on the dusty surface. In some (generally rare) cases, the crater is sufficiently large to be resolved in the CTX image. In most cases, however, the crater(s) cannot be seen. These are tentatively designated as “candidate” new impact sites, and the CTX team then creates an opportunity for the MRO spacecraft to point its cameras off-nadir and requests that the High Resolution Imaging Science Experiment (HiRISE) team obtain an image of ~0.3 m/pixel to confirm whether a crater or crater cluster is present. It is clear even from cursory examination that the CTX observations are areographically biased to dusty, higher albedo areas on Mars. All but 3 of the 100 new impact sites occur on surfaces with Lambert albedo values in excess of 23.5%. Our initial study of MOC images greatly benefited from the initial global observations made in one month in 1999, creating a baseline date from which we could start counting new craters. The global coverage by MRO Mars Color Imager is more than a factor of 4 poorer in resolution than the MOC Wide Angle camera and does not offer the opportunity for global analysis. Instead, we must rely on partial global coverage and global coverage that has taken years to accumulate; thus we can only treat impact rates statistically. We subdivide the total data

  8. Stratigraphy Exposed by an Impact Crater

    NASA Image and Video Library

    2017-05-10

    Geologists love roadcuts because they reveal the bedrock stratigraphy (layering). Until we have highways on Mars, we can get the same information from fresh impact craters as shown in this image from NASA's Mars Reconnaissance Orbiter. This image reveals these layers filling a larger crater, perhaps a combination of lava, impact ejecta, and sediments. https://photojournal.jpl.nasa.gov/catalog/PIA21631

  9. Analysis of impact craters of Mercury

    NASA Astrophysics Data System (ADS)

    Cremonese, G.; Martellato, E.; Marzari, F.; Massironi, M.; Capria, M. T.

    The size of an impact crater depends on many parameters. As a consequence, it is a demanding task to derive the physical and dynamical properties of the projectile from the knowledge of the crater diameter and making few assumptions. In this work we have assumed the same impact velocity of 34 km/s. We report the analysis of some impact crater on Mercury, based on the Mariner 10 images. We have used the classical scaling law (Schmidt and Housen, 1987) to obtain the impactor diameter and the experimental law proposed by OKeefe and Ahrens (1982) to calculate the melt volume produced. The calculations have been performed for different meteoroid compositions (iron, basalt, chondrite, and ice), assuming the surface composition of Mercury based on anorthosite.

  10. IS THE LARGE CRATER ON THE ASTEROID (2867) STEINS REALLY AN IMPACT CRATER?

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Morris, A. J. W.; Price, M. C.; Burchell, M. J., E-mail: m.j.burchell@kent.ac.uk

    The large crater on the asteroid (2867) Steins attracted much attention when it was first observed by the Rosetta spacecraft in 2008. Initially, it was widely thought to be unusually large compared to the size of the asteroid. It was quickly realized that this was not the case and there are other examples of similar (or larger) craters on small bodies in the same size range; however, it is still widely accepted that it is a crater arising from an impact onto the body which occurred after its formation. The asteroid (2867) Steins also has an equatorial bulge, usually consideredmore » to have arisen from redistribution of mass due to spin-up of the body caused by the YORP effect. Conversely, it is shown here that, based on catastrophic disruption experiments in laboratory impact studies, a similarly shaped body to the asteroid Steins can arise from the break-up of a parent in a catastrophic disruption event; this includes the presence of a large crater-like feature and equatorial bulge. This suggests that the large crater-like feature on Steins may not be a crater from a subsequent impact, but may have arisen directly from the fragmentation process of a larger, catastrophically disrupted parent.« less

  11. Impact Cratering Calculations

    NASA Technical Reports Server (NTRS)

    Ahrens, Thomas J.

    2001-01-01

    We examined the von Mises and Mohr-Coulomb strength models with and without damage effects and developed a model for dilatancy. The models and results are given in O'Keefe et al. We found that by incorporating damage into the models that we could in a single integrated impact calculation, starting with the bolide in the atmosphere produce final crater profiles having the major features found in the field measurements. These features included a central uplift, an inner ring, circular terracing and faulting. This was accomplished with undamaged surface strengths of approximately 0.1 GPa and at depth strengths of approximately 1.0 GPa. We modeled the damage in geologic materials using a phenomenological approach, which coupled the Johnson-Cook damage model with the CTH code geologic strength model. The objective here was not to determine the distribution of fragment sizes, but rather to determine the effect of brecciated and comminuted material on the crater evolution, fault production, ejecta distribution, and final crater morphology.

  12. Recognition of Terrestrial Impact Craters with COSMO-SkyMed

    NASA Astrophysics Data System (ADS)

    Virelli, M.; Staffieri, S.; Battagliere, M. L.; Komatsu, G.; Di Martino, M.; Flamini, E.; Coletta, A.

    2016-08-01

    All bodies having a solid surface, without distinction, show, with greater or lesser evidence, the marks left by the geological processes they undergone during their evolution. There is a geomorphological feature that is evident in all the images obtained by the probes sent to explore our planetary system: impact craters.Craters formed by the impact of small cosmic bodies have dimensions ranging from some meters to hundreds of kilometers. However, for example on the Lunar regolith particles, have been observed also sub- millimeter craters caused by dust impacts. The kinetic energy of the impactor, which velocity is in general of the order of tens km/s, is released in fractions of a second, generally in a explosive way, generating complex phenomena that transform not only the morphology of the surface involved by the impact, but also the mineralogy and crystallography of the impacted material. Even our planet is not immune to these impacts. At present, more than 180 geological structures recognized as of impact origin are known on Earth.In this article, we aim to show how these impact structures on Earth's surface are observed from space. To do this, we used the images obtained by the COSMO-SkyMed satellite constellation.Starting from 2013, ASI proposed, in collaboration with the Astrophysical Observatory of Turin and University D'Annunzio of Chieti, the realization of an Encyclopedic Atlas of Terrestrial Impact Craters using COSMO-SkyMed data that will become the first atlas of all recognized terrestrial impact craters based on images acquired by a X band radar. To observe these impact craters all radar sensor modes have been used, according to the size of the analyzed crater.The project includes research of any new features that could be classified as impact craters and, for the sites whereby it is considered necessary, the implementation of a geological survey on site to validate the observations.In this paper an overview of the Atlas of Terrestrial Impact

  13. Ganymede Impact Crater Morphology as Revealed by Galileo

    NASA Astrophysics Data System (ADS)

    Weitz, C. M.; Head, J. W.; Pappalardo, R.; Chapman, C.; Greeley, R.; Helfenstein, P.; Neukum, G.; Galileo SSI Team

    1997-07-01

    We have used the Galileo G1, G2, G7, and G8 images to study the morpholo- gy and degradation of impact craters on Ganymede. Results from the G1 and G2 data showed three types of degradation states: pristine, partially degraded, and heavily degraded. With the more recent G7 and G8 images, there are now several other distinct crater morphologies that we have identified. Enki Catena is about 120 km in length and consists of 13 attached impact craters. The six craters in the chain that impacted onto the bright terrain have visible bright ejecta while those that impacted onto the dark terrain have barely visible ejecta. Kittu crater is about 15 km in diameter and it has a bright central peak surrounded by a bright floor and hummocky wall material. The crater rim in the north is linear in appearance at the location that corresponds to the boundary between the groove terrain and the adjacent dark terrain, indicating structural control by the underlying topography. The dark rays that are easily seen in the Voyager images are barely visible in the Galileo image. Neith crater has a central fractured dome surrounded by a jagged central ring, smoother outer ejecta facies, and less prominent outer rings. Achelous crater and its neighbor, which were imaged at low sun angle to show topography, have smooth floors and subdued pedestal ejecta. Nicholson Regio has tectonically disrupted craters on the groove and fractured terrains while the surrounding smoother dark terrain has numerous degrad- ed craters that may indicate burial by resurfacing or by regolith development.

  14. Authentication controversies and impactite petrography of the New Quebec Crater

    NASA Technical Reports Server (NTRS)

    Marvin, Ursula B.; Kring, David A.

    1992-01-01

    The literature reports that led to the current acceptance of New Quebec Crater (Chubb Crater) as an authentic impact crater are reviewed, and it is noted that, for reasons that are not entirely clear, a meteoritic origin for the New Quebec Crater achieved wider acceptance at an earlier data than for the Lake Bosumtwi Crater, for which petrographic and chemical evidence is more abundant and compelling. The petrography of two impact melt samples from the New Quebec Crater was investigated, and new evidence is obtained on the degrees of shock metamorphism affecting the accessory minerals such as apatite, sphene, magnetite, and zircon.

  15. Martian cratering. II - Asteroid impact history.

    NASA Technical Reports Server (NTRS)

    Hartmann, W. K.

    1971-01-01

    This paper considers the extent to which Martian craters can be explained by considering asteroidal impact. Sections I, II, and III of this paper derive the diameter distribution of hypothetical asteroidal craters on Mars from recent Palomar-Leiden asteroid statistics and show that the observed Martian craters correspond to a bombardment by roughly 100 times the present number of Mars-crossing asteroids. Section IV discusses the early bombardment history of Mars, based on the capture theory of Opik and probable orbital parameters of early planetesimals. These results show that the visible craters and surface of Mars should not be identified with the initial, accreted surface. A backward extrapolation of the impact rates based on surviving Mars-crossing asteroids can account for the majority of Mars craters over an interval of several aeons, indicating that we see back in time no further than part-way into a period of intense bombardment. An early period of erosion and deposition is thus suggested. Section V presents a comparison with results and terminology of other authors.

  16. Fresh Impact Craters on Asteroid Vesta

    NASA Image and Video Library

    2011-12-06

    This image combines two separate views of the giant asteroid Vesta obtained by NASA Dawn spacecraft. The fresh impact craters in this view are located in the south polar region, which has been partly covered by landslides from the adjacent crater.

  17. Impact cratering experiments in Bingham materials and the morphology of craters on Mars and Ganymede

    NASA Technical Reports Server (NTRS)

    Fink, J. H.; Greeley, R.; Gault, D. E.

    1982-01-01

    Results from a series of laboratory impacts into clay slurry targets are compared with photographs of impact craters on Mars and Ganymede. The interior and ejecta lobe morphology of rampart-type craters, as well as the progression of crater forms seen with increasing diameter on both Mars and Ganymede, are equalitatively explained by a model for impact into Bingham materials. For increasing impact energies and constant target rheology, laboratory craters exhibit a morphologic progression from bowl-shaped forms that are typical of dry planetary surfaces to craters with ejecta flow lobes and decreasing interior relief, characteristic of more volatile-rich planets. A similar sequence is seen for uniform impact energy in slurries of decreasing yield strength. The planetary progressions are explained by assuming that volatile-rich or icy planetary surfaces behave locally in the same way as Bingham materials and produce ejecta slurries with yield strenghs and viscosities comparable to terrestrial debris flows. Hypothetical impact into Mars and Ganymede are compared, and it is concluded that less ejecta would be produced on Ganymede owing to its lower gravitational acceleration, surface temperature, and density of surface materials.

  18. Analysis of impact craters on Mercury's surface.

    NASA Astrophysics Data System (ADS)

    Martellato, E.; Cremonese, G.; Marzari, F.; Massironi, M.; Capria, M. T.

    The formation of a crater is a complex process, which can be analyzed with numerical simulations and/or observational methods. This work reports a preliminary analysis of some craters on Mercury, based on the Mariner 10 images. The physical and dynamical properties of the projectile may not derive from the knowledge of the crater alone, since the size of an impact crater depends on many parameters. We have calculated the diameter of the projectile using the scaling law of Schmidt and Housen (\\citep{SandM87}). It is performed for different projectile compositions and impact velocities, assuming an anorthositic composition of the surface. The melt volume production at the initial phases of the crater formation is also calculated by the experimental law proposed by O'Keefe and Ahrens (\\citep{OA82}), giving the ratio between melt and projectile mass.

  19. Machine cataloging of impact craters on Mars

    NASA Astrophysics Data System (ADS)

    Stepinski, Tomasz F.; Mendenhall, Michael P.; Bue, Brian D.

    2009-09-01

    This study presents an automated system for cataloging impact craters using the MOLA 128 pixels/degree digital elevation model of Mars. Craters are detected by a two-step algorithm that first identifies round and symmetric topographic depressions as crater candidates and then selects craters using a machine-learning technique. The system is robust with respect to surface types; craters are identified with similar accuracy from all different types of martian surfaces without adjusting input parameters. By using a large training set in its final selection step, the system produces virtually no false detections. Finally, the system provides a seamless integration of crater detection with its characterization. Of particular interest is the ability of our algorithm to calculate crater depths. The system is described and its application is demonstrated on eight large sites representing all major types of martian surfaces. An evaluation of its performance and prospects for its utilization for global surveys are given by means of detailed comparison of obtained results to the manually-derived Catalog of Large Martian Impact Craters. We use the results from the test sites to construct local depth-diameter relationships based on a large number of craters. In general, obtained relationships are in agreement with what was inferred on the basis of manual measurements. However, we have found that, in Terra Cimmeria, the depth/diameter ratio has an abrupt decrease at ˜38°S regardless of crater size. If shallowing of craters is attributed to presence of sub-surface ice, a sudden change in its spatial distribution is suggested by our findings.

  20. Roter Kamm Impact Crater in Namibia

    NASA Image and Video Library

    1996-11-13

    This space radar image shows the Roter Kamm impact crater in southwest Namibia. The crater rim is seen in the lower center of the image as a radar-bright, circular feature. Geologists believe the crater was formed by a meteorite that collided with Earth approximately 5 million years ago. The data were acquired by the Spaceborne Imaging Radar-C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR) instrument onboard space shuttle Endeavour on April 14, 1994. The area is located at 27.8 degrees south latitude and 16.2 degrees east longitude in southern Africa. The colors in this image were obtained using the following radar channels: red represents the L-band (horizontally transmitted and received); green represents the L-band (horizontally transmitted and vertically received); and blue represents the C-band (horizontally transmitted and vertically received). The area shown is approximately 25.5 kilometers (15.8 miles) by 36.4 kilometers (22.5 miles), with north toward the lower right. The bright white irregular feature in the lower left corner is a small hill of exposed rock outcrop. Roter Kamm is a moderate sized impact crater, 2.5 kilometers (1.5 miles) in diameter rim to rim, and is 130 meters (400 feet) deep. However, its original floor is covered by sand deposits at least 100 meters (300 feet) thick. In a conventional aerial photograph, the brightly colored surfaces immediately surrounding the crater cannot be seen because they are covered by sand. The faint blue surfaces adjacent to the rim may indicate the presence of a layer of rocks ejected from the crater during the impact. The darkest areas are thick windblown sand deposits which form dunes and sand sheets. The sand surface is smooth relative to the surrounding granite and limestone rock outcrops and appears dark in radar image. The green tones are related primarily to larger vegetation growing on sand soil, and the reddish tones are associated with thinly mantled limestone outcrops. Studies of impact craters on

  1. Low-velocity impact craters in ice and ice-saturated sand with implications for Martian crater count ages.

    USGS Publications Warehouse

    Croft, S.K.; Kieffer, S.W.; Ahrens, T.J.

    1979-01-01

    We produced a series of decimeter-sized impact craters in blocks of ice near 0oC and -70oC and in ice-saturated sand near -70oC as a preliminary investigation of cratering in materials analogous to those found on Mars and the outer solar satellites. Crater diameters in the ice-saturated sand were 2 times larger than craters in the same energy and velocity range in competent blocks of granite, basalt and cement. Craters in ice were c.3 times larger. Martian impact crater energy versus diameter scaling may thus be a function of latitude. -from Authors

  2. Interior and Ejecta Morphologies of Impact Craters on Ganymede

    NASA Astrophysics Data System (ADS)

    Barlow, Nadine G.; Klaybor, K.; Katz-Wigmore, J.

    2006-09-01

    We are utilizing Galileo SSI imagery of Ganymede to classify impact crater interior and ejecta morphologies. Although we are in the early stages of compiling our Catalog of Impact Craters on Ganymede, some interesting trends are beginning to emerge. Few craters display obvious ejecta morphologies, but 68 craters are classified as single layer ejecta and 3 as double layer ejecta. We see no obvious correlation of layered ejecta morphologies with terrain or latitude. All layered ejecta craters have diameters between 10 and 40 km. Sinuosity ("lobateness") and ejecta extent ("ejecta mobility ratio") of Ganymede layered ejecta craters are lower than for martian layered ejecta craters. This suggests less mobility of ejecta materials on Ganymede, perhaps due to the colder temperatures. Interior structures being investigated include central domes, peaks, and pits. 57 dome craters, 212 central peak craters, and 313 central pit craters have been identified. Central domes occur in 50-100 km diameter craters while peaks are found in craters between 20 and 50 km and central pit craters range between 29 and 74 km in diameter. The Galileo Regio region displays higher concentrations of central dome and central pit craters than other regions we have investigated. 67% of central pit craters studied to date are small pits, where the ratio of pit diameter to crater diameter is <0.2. Craters containing the three interior structures preferentially occur on darker terrain units, suggesting that an ice-silicate composition is more conducive to interior feature formation than pure ice alone. Results of this study have important implications not only for the formation of specific interior and ejecta morphologies on Ganymede but also for analogous features associated with Martian impact craters. This research is funded through NASA Outer Planets Research Program Award #NNG05G116G to N. G. Barlow.

  3. Space Radar Image of the Yucatan Impact Crater Site

    NASA Technical Reports Server (NTRS)

    1999-01-01

    This is a radar image of the southwest portion of the buried Chicxulub impact crater in the Yucatan Peninsula, Mexico. The radar image was acquired on orbit 81 of space shuttle Endeavour on April 14, 1994 by the Spaceborne Imaging Radar C/X-Band Synthetic Aperture Radar (SIR-C/X-SAR). The image is centered at 20 degrees north latitude and 90 degrees west longitude. Scientists believe the crater was formed by an asteroid or comet which slammed into the Earth more than 65 million years ago. It is this impact crater that has been linked to a major biological catastrophe where more than 50 percent of the Earth's species, including the dinosaurs, became extinct. The 180-to 300-kilometer-diameter (110- to 180-mile)crater is buried by 300 to 1,000 meters (1,000 to 3,000 feet) of limestone. The exact size of the crater is currently being debated by scientists. This is a total power radar image with L-band in red, C-band in green, and the difference between C-band L-band in blue. The 10-kilometer-wide (6-mile) band of yellow and pink with blue patches along the top left (northwestern side) of the image is a mangrove swamp. The blue patches are islands of tropical forests created by freshwater springs that emerge through fractures in the limestone bedrock and are most abundant in the vicinity of the buried crater rim. The fracture patterns and wetland hydrology in this region are controlled by the structure of the buried crater. Scientists are using the SIR-C/X-SAR imagery to study wetland ecology and help determine the exact size of the impact crater. Spaceborne Imaging Radar-C and X-band Synthetic Aperture Radar (SIR-C/X-SAR) is part of NASA's Mission to Planet Earth. The radars illuminate Earth with microwaves allowing detailed observations at any time, regardless of weather or sunlight conditions. SIR-C/X-SAR uses three microwave wavelengths: L-band (24 cm), C-band (6 cm) and X-band (3 cm). The multi-frequency data will be used by the international scientific community

  4. Fresh Impact Crater and Rays in Tharsis

    NASA Technical Reports Server (NTRS)

    2002-01-01

    The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) Extended Mission has included dozens of opportunities to point the spacecraft directly at features of interest so that pictures of things not seen during the earlier Mapping Mission can be obtained. The example shown here is a small meteorite impact crater in northern Tharsis near 17.2oN, 113.8oW. Viking Orbiter images from the late 1970's showed at this location what appeared to be a dark patch with dark rays emanating from a brighter center. The MOC team surmised that the dark rays may be indicating the location of afresh crater formed by impact sometime in the past few centuries (since dark ray are quickly covered by dust falling out of the martian atmosphere). All through MOC's Mapping Mission in 1999 and 2000, attempts were made to image the crater as predictions indicated that the spacecraft would pass over the site, but the crater was never seen. Finally, in June 2001, Extended Mission operations allowed the MOC team to point the spacecraft (and hence the camera, which is fixed to the spacecraft)directly at the center of the dark rays, where we expected to find the crater.

    The picture on the left (above, A) is a mosaic of three MOC high resolution images and one much lower-resolution Viking image. From left to right, the images used in the mosaic are: Viking 1 516A55, MOC E05-01904, MOCM21-00272, and MOC M08-03697. Image E05-01904 is the one taken in June 2001 by pointing the spacecraft. It captured the impact crater responsible for the rays. A close-up of the crater, which is only 130 meters (427 ft)across, is shown on the right (above, B). This crater is only one-tenth the size of the famous Meteor Crater in northern Arizona.

    The June 2001 MOC image reveals many surprises about this feature. For one, the crater is not located at the center of the bright area from which the dark rays radiate. The rays point to the center of this bright area, not the crater. Further, the dark material ejected

  5. Impact craters and Venus resurfacing history

    NASA Technical Reports Server (NTRS)

    Phillips, Roger J.; Raubertas, Richard F.; Arvidson, Raymond E.; Sarkar, Ila C.; Herrick, Robert R.; Izenberg, Noam; Grimm, Robert E.

    1992-01-01

    The history of resurfacing by tectonism and volcanism on Venus is reconstructed by means of an analysis of Venusian impact crater size-frequency distributions, locations, and preservation states. An atmospheric transit model for meteoroids demonstrates that for craters larger than about 30 km, the size-frequency distribution is close to the atmosphere-free case. An age of cessation of rapid resurfacing of about 500 Ma is obtained. It is inferred that a range of surface ages are recorded by the impact crater population; e.g., the Aphrodite zone is relatively young. An end-member model is developed to quantify resurfacing scenarios. It is argued that Venus has been resurfacing at an average rate of about 1 sq km/yr. Numerical simulations of resurfacing showed that there are two solution branches that satisfy the completely spatially random location restraint for Venusian craters: a is less than 0.0003 (4 deg diameter circle) and a is greater than 0.1 (74 deg diameter circle).

  6. HiRISE observations of new impact craters exposing Martian ground ice

    USGS Publications Warehouse

    Dundas, Colin M.; Byrne, Shane; McEwen, Alfred S.; Mellon, Michael T.; Kennedy, Megan R.; Daubar, Ingrid J.; Saper, Lee

    2014-01-01

    Twenty small new impact craters or clusters have been observed to excavate bright material inferred to be ice at mid and high latitudes on Mars. In the northern hemisphere, the craters are widely distributed geographically and occur at latitudes as low as 39°N. Stability modeling suggests that this ice distribution requires a long-term average atmospheric water vapor content around 25 precipitable microns, more than double the present value, which is consistent with the expected effect of recent orbital variations. Alternatively, near-surface humidity could be higher than expected for current column abundances if water vapor is not well-mixed with atmospheric CO2, or the vapor pressure at the ice table could be lower due to salts. Ice in and around the craters remains visibly bright for months to years, indicating that it is clean ice rather than ice-cemented regolith. Although some clean ice may be produced by the impact process, it is likely that the original ground ice was excess ice (exceeding dry soil pore space) in many cases. Observations of the craters suggest small-scale heterogeneities in this excess ice. The origin of such ice is uncertain. Ice lens formation by migration of thin films of liquid is most consistent with local heterogeneity in ice content and common surface boulders, but in some cases nearby thermokarst landforms suggest large amounts of excess ice that may be best explained by a degraded ice sheet.

  7. A first-order model for impact crater degradation on Venus

    NASA Technical Reports Server (NTRS)

    Izenberg, Noam R.; Arvidson, Raymond E.; Phillips, Roger J.

    1993-01-01

    A first-order impact crater aging model is presented based on observations of the global crater population of Venus. The total population consists of 879 craters found over the approximately 98 percent of the planet that has been mapped by the Magellan spacecraft during the first three cycles of its mission. The model is based upon three primary aspects of venusian impact craters: (1) extended ejecta deposits (EED's); (2) crater rims and continuous ejecta deposits; and (3) crater interiors and floors.

  8. Impact cratering in viscous targets - Laboratory experiments

    NASA Technical Reports Server (NTRS)

    Greeley, R.; Fink, J.; Snyder, D. B.; Gault, D. E.; Guest, J. E.; Schultz, P. H.

    1980-01-01

    To determine the effects of target yield strength and viscosity on the formation and morphology of Martian multilobed, slosh and rampart-type impact craters, 75 experiments in which target properties and impact energies were varied were carried out for high-speed motion picture observation in keeping with the following sequence: (1) projectile initial impact; (2) crater excavation and rise of ejecta plume; (3) formation of a transient central mound which generates a surge of material upon collapse that can partly override the plume deposit; and (4) oscillation of the central mound with progressively smaller surges of material leaving the crater. A dimensional analysis of the experimental results indicates that the dimensions of the central mound are proportional to (1) the energy of the impacting projectile and (2) to the inverse of both the yield strength and viscosity of the target material, and it is determined that extrapolation of these results to large Martian craters requires an effective surface layer viscosity of less than 10 to the 10th poise. These results may also be applicable to impacts on outer planet satellites composed of ice-silicate mixtures.

  9. Dimensional scaling for impact cratering and perforation

    NASA Technical Reports Server (NTRS)

    Watts, Alan; Atkinson, Dale; Rieco, Steve

    1993-01-01

    This report summarizes the development of two physics-based scaling laws for describing crater depths and diameters caused by normal incidence impacts into aluminum and TFE Teflon. The report then describes equations for perforations in aluminum and TFE Teflon for normal impacts. Lastly, this report also studies the effects of non-normal incidence on cratering and perforation.

  10. The Carancas meteorite impact crater, Peru: Geologic surveying and modeling of crater formation and atmospheric passage

    NASA Astrophysics Data System (ADS)

    Kenkmann, T.; Artemieva, N. A.; Wünnemann, K.; Poelchau, M. H.; Elbeshausen, D.; Núñez Del Prado, H.

    2009-08-01

    The recent Carancas meteorite impact event caused a worldwide sensation. An H4-5 chondrite struck the Earth south of Lake Titicaca in Peru on September 15, 2007, and formed a crater 14.2 m across. It is the smallest, youngest, and one of two eye-witnessed impact crater events on Earth. The impact violated the hitherto existing view that stony meteorites below a size of 100 m undergo major disruption and deceleration during their passage through the atmosphere and are not capable of producing craters. Fragmentation occurs if the strength of the meteoroid is less than the aerodynamic stresses that occur in flight. The small fragments that result from a breakup rain down at terminal velocity and are not capable of producing impact craters. The Carancas cratering event, however, demonstrates that meter-sized stony meteoroids indeed can survive the atmospheric passage under specific circumstances. We present results of a detailed geologic survey of the crater and its ejecta. To constrain the possible range of impact parameters we carried out numerical models of crater formation with the iSALE hydrocode in two and three dimensions. Depending on the strength properties of the target, the impact energies range between approximately 100-1000 MJ (0.024- 0.24 t TNT). By modeling the atmospheric traverse we demonstrate that low cosmic velocities (12- 14 kms-1) and shallow entry angles (<20°) are prerequisites to keep aerodynamic stresses low (<10 MPa) and thus to prevent fragmentation of stony meteoroids with standard strength properties. This scenario results in a strong meteoroid deceleration, a deflection of the trajectory to a steeper impact angle (40-60°), and an impact velocity of 350-600 ms-1, which is insufficient to produce a shock wave and significant shock effects in target minerals. Aerodynamic and crater modeling are consistent with field data and our microscopic inspection. However, these data are in conflict with trajectories inferred from the analysis of

  11. Impact crater outflows on Venus: Morphology and emplacement mechanisms

    USGS Publications Warehouse

    Chadwick, D. John; Schaber, Gerald G.

    1993-01-01

    Many of the 932 impact craters discovered by the Magellan spacecraft at Venus are associated with lobate flows that originate at or near the crater rim. They extend for several to several hundred kilometers from the crater, and they commonly have a strong radar backscatter. A morphologic study of all identifiable crater outflows on Venus has revealed that many individual flows each consist of two areas, defined by distinct morphologic features. These two areas appear to represent two stages of deposition for each flow. The part of the flow that is generally deposited closest to the crater tends to be on the downrange side of the crater, flows in the downrange direction, and it is interpreted to be a late-stage ejecta. In many cases, this proximal part of the flow is too thin to completely bury the large blocks in subjacent ejecta deposits. Dendritic channels, present in many proximal flows, appear to have drained liquid from the proximal part in the downhill direction, and they debouch to feed the outer part of the flows. This distal part flows downhill, fills small grabens, and is ponded by ridges, behavior that mimics that of volcanic lava flows. The meandering and dendritic channels and the relation of the distal flows to topography strongly suggest that the distal portion is the result of coalescence and slow drainage of impact melt from the proximal portion. Impact melt forms a lining to the transient crater and mixes turbulently with solid clasts, and part of this mixture may be ejected to form the proximal part of the flow during the excavation stage of crater development. A statistical study of the Venusian craters has revealed that, in general, large craters produced by impacts with relatively low incidence angles to the surface are more likely to produce flows than small craters produced by higher-angle impacts. The greater flow production and downrange focusing of the proximal flows with decreasing incidence angle indicate a strong control of the flows

  12. The missing impact craters on Venus

    NASA Technical Reports Server (NTRS)

    Speidel, D. H.

    1993-01-01

    The size-frequency pattern of the 842 impact craters on Venus measured to date can be well described (across four standard deviation units) as a single log normal distribution with a mean crater diameter of 14.5 km. This result was predicted in 1991 on examination of the initial Magellan analysis. If this observed distribution is close to the real distribution, the 'missing' 90 percent of the small craters and the 'anomalous' lack of surface splotches may thus be neither missing nor anomalous. I think that the missing craters and missing splotches can be satisfactorily explained by accepting that the observed distribution approximates the real one, that it is not craters that are missing but the impactors. What you see is what you got. The implication that Venus crossing impactors would have the same type of log normal distribution is consistent with recently described distribution for terrestrial craters and Earth crossing asteroids.

  13. Rampart craters on Ganymede: Their implications for fluidized ejecta emplacement

    NASA Astrophysics Data System (ADS)

    Boyce, Joseph; Barlow, Nadine; Mouginis-Mark, Peter; Stewart, Sarah

    2010-04-01

    Some fresh impact craters on Ganymede have the overall ejecta morphology similar to Martian double-layer ejecta (DLE), with the exception of the crater Nergal that is most like Martian single layer ejecta (SLE) craters (as is the terrestrial crater Lonar). Similar craters also have been identified on Europa, but no outer ejecta layer has been found on these craters. The morphometry of these craters suggests that the types of layered ejecta craters identified by Barlow et al. (2000) are fundamental. In addition, the mere existence of these craters on Ganymede and Europa suggests that an atmosphere is not required for ejecta fluidization, nor can ejecta fluidization be explained by the flow of dry ejecta. Moreover, the absence of fluidized ejecta on other icy bodies suggests that abundant volatiles in the target also may not be the sole cause of ejecta fluidization. The restriction of these craters to the grooved terrain of Ganymede and the concentration of Martian DLE craters on the northern lowlands suggests that these terrains may share key characteristics that control the development of the ejecta of these craters. In addition, average ejecta mobility (EM) ratios indicate that the ejecta of these bodies are self-similar with crater size, but are systematically smaller on Ganymede and Europa. This may be due to the effects of the abundant ice in the crusts of these satellites that results in increased ejection angle causing ejecta to impact closer to the crater and with lower horizontal velocity.

  14. Evolution of Lunar Crater Ejecta Through Time: Influence of Crater Size on the Record of Dynamic Processes

    NASA Astrophysics Data System (ADS)

    Ghent, R. R.; Tai Udovicic, C.; Mazrouei, S.; Bottke, W. F., Jr.

    2017-12-01

    The bombardment history of the Moon holds the key to understanding important aspects of the evolution of the Solar System at 1AU. It informs our thinking about the rates and chronology of events on other planetary bodies and the evolution of the asteroid belt. In previous work, we established a quantitative relationship between the ages of lunar craters and the rockiness of their ejecta. That result was based on the idea that crater-forming impacts eject rocks from beneath the regolith, instantaneously emplacing a deposit with characteristic initial physical properties, such as rock abundance. The ejecta rocks are then gradually removed and / or covered by a combination of mechanical breakdown via micrometeorite bombardment, emplacement of regolith fines due to nearby impacts, and possibly rupture due to thermal stresses. We found that ejecta rocks, as detected by the Lunar Reconnaissance Orbiter Diviner thermal radiometer disappear on a timescale of 1 Gyr, eventually becoming undetectable by the Diviner instrument against the ambient background rock abundance of the regolith.The "index" craters we used to establish the rock abundance—age relationship are all larger than 15 km (our smallest index crater is Byrgius A, at 18.7 km), and therefore above the transition diameter between simple and complex craters (15-20 km). Here, we extend our analysis to include craters smaller than the transition diameter. It is not obvious a priori that the initial ejecta properties of simple and complex craters should be identical, and therefore, that the same metrics of crater age can be applied to both populations. We explore this issue using LRO Diviner rock abundance and a high-resolution optical maturity dataset derived from Kaguya multiband imager VIS/NIR data to identify young craters to 5 km diameter. We examine the statistical properties of this population relative to that of the NEO population, and interpret the results in the context of our recently documented evidence

  15. Impact mechanics at Meteor Crater, Arizona

    USGS Publications Warehouse

    Shoemaker, Eugene Merle

    1959-01-01

    Meteor Crator is a bowl-shaped depression encompassed by a rim composed chiefly of debris stacked in layers of different composition. Original bedrock stratigraphy is preserved, inverted, in the debris. The debris rests on older disturbed strata, which are turned up at moderate to steep angles in the wall of the crater and are locally overturned near the contact with the debris. These features of Meteor Crater correspond closely to those of a crater produced by nuclear explosion where depth of burial of the device was about 1/5 the diameter of the resultant crater. Studies of craters formed by detonation of nuclear devices show that structures of the crater rims are sensitive to the depth of explosion scaled to the yield of the device. The structure of Meteor Crater is such as would be produced by a very strong shock originating about at the level of the present crater floor, 400 feet below the original surface. At supersonic to hypersonic velocity an impacting meteorite penetrates the ground by a complex mechanism that includes compression of the target rocks and the meteorite by shock as well as hydrodynamic flow of the compressed material under high pressure and temperature. The depth of penetration of the meteorite, before it loses its integrity as a single body, is a function primarily of the velocity and shape of the meteorite and the densities and equations of state of the meteorite and target. The intensely compressed material then becomes dispersed in a large volume of breccia formed in the expanding shock wave. An impact velocity of about 15 km/sec is consonant with the geology of Meteor Crater in light of the experimental equation of state of iron and inferred compressibility of the target rocks. The kinetic energy of the meteorite is estimated by scaling to have been from 1.4 to 1.7 megatons TNT equivalent.

  16. Small Impact Craters with Dark Ejecta Deposits

    NASA Technical Reports Server (NTRS)

    1999-01-01

    When a meteor impacts a planetary surface, it creates a blast very much like a bomb explosion. Shown here are two excellent examples of small impact craters on the martian surface. Each has a dark-toned deposit of material that was blown out of the crater (that is, ejected) during the impact. Materials comprising these deposits are called ejecta. The ejecta here is darker than the surrounding substrate because each crater-forming blast broke through the upper, brighter surface material and penetrated to a layer of darker material beneath. This darker material was then blown out onto the surface in the radial pattern seen here.

    The fact that impact craters can penetrate and expose material from beneath the upper surface of a planet is very useful for geologists trying to determine the nature and composition of the martian subsurface. The scene shown here is illuminated from the upper left and covers an area 1.1 km (0.7 mi) wide by 1.4 km (0.9 mi). The larger crater has a diameter of about 89 meters (97 yards), the smaller crater is about 36 meters (39 yards) across. The picture is located in Terra Meridiani and was taken by the Mars Global Surveyor Mars Orbiter Camera.

    Malin Space Science Systems and the California Institute of Technology built the MOC using spare hardware from the Mars Observer mission. MSSS operates the camera from its facilities in San Diego, CA. The Jet Propulsion Laboratory's Mars Surveyor Operations Project operates the Mars Global Surveyor spacecraft with its industrial partner, Lockheed Martin Astronautics, from facilities in Pasadena, CA and Denver, CO.

  17. Secondary Craters

    NASA Image and Video Library

    2016-12-21

    This image of a southern mid-latitude crater was intended to investigate the lineated material on the crater floor. At the higher resolution of HiRISE, the image reveals a landscape peppered by small impact craters. These craters range from about 30 meters in diameter down to the resolution limit (about 2 meter diameter in this image acquired by averaging 2x2 picture elements). Such dense clusters of small craters are frequently formed by secondary craters, caused by the impact of material that was excavated and ejected from the surface of Mars during the creation of a larger nearby crater by the impact of a comet or an asteroid. Secondary impact craters are both interesting and vexing. They are interesting because they show the trajectories of the material that was ejected from the primary impact with the greatest speeds, typically material from near the surface of the blast zone. Secondary craters are often found along the traces of crater rays, linear features that extend radially from fresh impact craters and can reach many crater diameters in length. Secondary craters can be useful when crater rays are visible and the small craters can be associated with a particular primary impact crater. They can be used to constrain the age of the surface where they fell, since the surface must be older than the impact event. The age of the crater can be approximately estimated from the probability of an impact that produced a crater of such a size within a given area of Mars over a given time period. But these secondary craters can also be perplexing when no crater rays are preserved and a source crater is not easily identifiable, as is the case here. The impact that formed these secondary craters took place long enough ago that their association with a particular crater has been erased. They do not appear along the trace of a crater ray that is still apparent in visible or thermal infrared observations. These secondary craters complicate the task of estimating the age of

  18. Impact craters on Venus: Initial analysis from Magellan

    USGS Publications Warehouse

    Phillips, R.J.; Arvidson, R. E.; Boyce, J.M.; Campbell, D.B.; Guest, J.E.; Schaber, G.G.; Soderblom, L.A.

    1991-01-01

    Magellan radar images of 15 percent of the planet show 135 craters of probable impact origin. Craters more than 15 km across tend to contain central peaks, multiple central peaks, and peak rings. Many craters smaller than 15 km exhibit multiple floors or appear in clusters; these phenomena are attributed to atmospheric breakup of incoming meteoroids. Additionally, the atmosphere appears to have prevented the formation of primary impact craters smaller than about 3 km and produced a deficiency in the number of craters smaller than about 25 km across. Ejecta is found at greater distances than that predicted by simple ballistic emplacement, and the distal ends of some ejecta deposits are lobate. These characteristics may represent surface flows of material initially entrained in the atmosphere. Many craters are surrounded by zones of low radar albedo whose origin may have been deformation of the surface by the shock or pressure wave associated with the incoming meteoroid. Craters are absent from several large areas such as a 5 million square kilometer region around Sappho Patera, where the most likely explanation for the dearth of craters is volcanic resurfacing, There is apparently a spectrum of surface ages on Venus ranging approximately from 0 to 800 million years, and therefore Venus must be a geologically active planet.

  19. Analysis of Cometary Dust Impact Residues in the Aluminum Foil Craters of Stardust

    NASA Technical Reports Server (NTRS)

    Graham, G. A.; Kearsley, A. T.; Vicenzi, E. P.; Teslich, N.; Dai, Z. R.; Rost, D.; Horz, F.; Bradley, J. P.

    2007-01-01

    In January 2006, the sample return capsule from NASA s Stardust spacecraft successfully returned to Earth after its seven year mission to comet Wild-2. While the principal capture medium for comet dust was low-density graded silica aerogel, the 1100 series aluminum foil (approximately 100 m thick) which wrapped around the T6064 aluminum frame of the sample tray assembly (STA) contains micro-craters that constitute an additional repository for Wild-2 dust. Previous studies of similar craters on spacecraft surfaces, e.g. the Long Duration Exposure Facility (LDEF), have shown that impactor material can be preserved for elemental and mineralogical characterization, although the quantity of impact residue in Stardust craters far exceeds previous missions. The degree of shock-induced alteration experienced by the Wild-2 particles impacting on foil will generally be greater than for those captured in the low-density aerogel. However, even some of the residues found in LDEF craters showed not only survival of crystalline silicates but even their solar flare tracks, which are extremely fragile structures and anneal at around 600 C. Laboratory hypervelocity experiments, using analogues of Wild-2 particles accelerated into flight-grade foils under conditions close to those of the actual encounter, showed retention of abundant projectile residues at the Stardust encounter velocity of 6.1 km/s. During the preliminary examination (PE) of the returned foils, using optical and electron microscopy studies, a diverse range in size and morphologies of micro-craters was identified. In this abstract we consider the state of residue preservation in a diverse range of craters with respect to their elemental composition and inferred mineralogy of the original projectiles.

  20. Evidence of the impacting body of the Ries crater - the discovery of Fe-Cr-Ni veinlets below the crater bottom

    USGS Publications Warehouse

    El, Goresy A.; Chao, E.C.T.

    1976-01-01

    Fe-Cr-Ni particles and veinlets have been discovered in the top 15 m of the compressed zone with abundant shatter cones below the bottom of the Ries crater. The metallic particles are less than a few microns across. They occur in various minerals along healed intergranular and locally in intragranular microfractures in quartz diorite, amphibolite and chloritized granite of the basement crystalline rocks. The particles consist of major Fe, Cr, and Ni with minor Si and Ca. Origin due to contamination is absolutely ruled out. We believe that these Fe-Cr-Ni particles are probably condensed from the vaporized impacting body which produced the Ries crater. These particles were injected with high velocity into microfractures near the top of the compressed zone, implanted in and across various minerals before these microfractures were resealed. The presence of Si and Ca as well as the fact that the Cr content is nearly twice that of Ni, led us to conclude that the Ries impacting body is very likely not an iron meteorite but a stony meteorite. ?? 1976.

  1. Martian subsurface properties and crater formation processes inferred from fresh impact crater geometries

    NASA Astrophysics Data System (ADS)

    Stewart, Sarah T.; Valiant, Gregory J.

    2006-10-01

    The geometry of simple impact craters reflects the properties of the target materials, and the diverse range of fluidized morphologies observed in Martian ejecta blankets are controlled by the near-surface composition and the climate at the time of impact. Using the Mars Orbiter Laser Altimeter (MOLA) data set, quantitative information about the strength of the upper crust and the dynamics of Martian ejecta blankets may be derived from crater geometry measurements. Here, we present the results from geometrical measurements of fresh craters 3-50 km in rim diameter in selected highland (Lunae and Solis Plana) and lowland (Acidalia, Isidis, and Utopia Planitiae) terrains. We find large, resolved differences between the geometrical properties of the freshest highland and lowland craters. Simple lowland craters are 1.5-2.0 times deeper (≥5σo difference) with >50% larger cavities (≥2σo) compared to highland craters of the same diameter. Rim heights and the volume of material above the preimpact surface are slightly greater in the lowlands over most of the size range studied. The different shapes of simple highland and lowland craters indicate that the upper ˜6.5 km of the lowland study regions are significantly stronger than the upper crust of the highland plateaus. Lowland craters collapse to final volumes of 45-70% of their transient cavity volumes, while highland craters preserve only 25-50%. The effective yield strength of the upper crust in the lowland regions falls in the range of competent rock, approximately 9-12 MPa, and the highland plateaus may be weaker by a factor of 2 or more, consistent with heavily fractured Noachian layered deposits. The measured volumes of continuous ejecta blankets and uplifted surface materials exceed the predictions from standard crater scaling relationships and Maxwell's Z model of crater excavation by a factor of 3. The excess volume of fluidized ejecta blankets on Mars cannot be explained by concentration of ejecta through

  2. Crater size estimates for large-body terrestrial impact

    NASA Technical Reports Server (NTRS)

    Schmidt, Robert M.; Housen, Kevin R.

    1988-01-01

    Calculating the effects of impacts leading to global catastrophes requires knowledge of the impact process at very large size scales. This information cannot be obtained directly but must be inferred from subscale physical simulations, numerical simulations, and scaling laws. Schmidt and Holsapple presented scaling laws based upon laboratory-scale impact experiments performed on a centrifuge (Schmidt, 1980 and Schmidt and Holsapple, 1980). These experiments were used to develop scaling laws which were among the first to include gravity dependence associated with increasing event size. At that time using the results of experiments in dry sand and in water to provide bounds on crater size, they recognized that more precise bounds on large-body impact crater formation could be obtained with additional centrifuge experiments conducted in other geological media. In that previous work, simple power-law formulae were developed to relate final crater diameter to impactor size and velocity. In addition, Schmidt (1980) and Holsapple and Schmidt (1982) recognized that the energy scaling exponent is not a universal constant but depends upon the target media. Recently, Holsapple and Schmidt (1987) includes results for non-porous materials and provides a basis for estimating crater formation kinematics and final crater size. A revised set of scaling relationships for all crater parameters of interest are presented. These include results for various target media and include the kinematics of formation. Particular attention is given to possible limits brought about by very large impactors.

  3. Morphometry of impact craters on Mercury from MESSENGER altimetry and imaging

    NASA Astrophysics Data System (ADS)

    Susorney, Hannah C. M.; Barnouin, Olivier S.; Ernst, Carolyn M.; Johnson, Catherine L.

    2016-06-01

    Data acquired by the Mercury Laser Altimeter and the Mercury Dual Imaging System on the MESSENGER spacecraft in orbit about Mercury provide a means to measure the geometry of many of the impact craters in Mercury's northern hemisphere in detail for the first time. The combination of topographic and imaging data permit a systematic evaluation of impact crater morphometry on Mercury, a new calculation of the diameter Dt at which craters transition with increasing diameter from simple to complex forms, and an exploration of the role of target properties and impact velocity on final crater size and shape. Measurements of impact crater depth on Mercury confirm results from previous studies, with the exception that the depths of large complex craters are typically shallower at a given diameter than reported from Mariner 10 data. Secondary craters on Mercury are generally shallower than primary craters of the same diameter. No significant differences are observed between the depths of craters within heavily cratered terrain and those of craters within smooth plains. The morphological attributes of craters that reflect the transition from simple to complex craters do not appear at the same diameter; instead flat floors first appear with increasing diameter in craters at the smallest diameters, followed with increasing diameter by reduced crater depth and rim height, and then collapse and terracing of crater walls. Differences reported by others in Dt between Mercury and Mars (despite the similar surface gravitational acceleration on the two bodies) are confirmed in this study. The variations in Dt between Mercury and Mars cannot be adequately attributed to differences in either surface properties or mean projectile velocity.

  4. An Assessment of Regional Variations in Martian Modified Impact Crater Morphology

    NASA Astrophysics Data System (ADS)

    Craddock, Robert A.; Bandeira, Lourenço.; Howard, Alan D.

    2018-03-01

    Impact craters on Mars have been extensively modified by ancient geologic processes that may have included rainfall and surface runoff, snow and ice, denudation by lava flows, burial by eolian material, or others. Many of these processes can leave distinct signatures on the morphometry of the modified impact crater as well as the surrounding landscape. To look for signs of potential regional differences in crater modification processes, we conducted an analysis of different morphometric parameters related to modified impact craters located in the Margaritifer Sinus, Sinus Sabaeus, Iapygia, Mare Tyrrhenum, Aeolis, and Eridania quadrangles, including depth, crater wall slope, crater floor slope, the curvature between the interior wall and the crater floor slope, and the curvature between the interior wall and surrounding landscape. A Welch's t test analysis comparing these parameters shows that fresh impact craters (Type 4) have consistent morphologies regardless of their geographic location examined in this study, which is not unexpected. Modified impact craters both in the initial (Type 3) and terminal stages (Type 1) of modification also have statistically consistent morphologies. This would suggest that the processes that operated in the late Noachian were globally ubiquitous, and that modified craters eventually reached a stable crater morphology. However, craters preserved in advanced (but not terminal) stages of modification (Type 2) have morphologies that vary across the quadrangles. It is possible that these variations reflect spatial differences in the types and intensity of geologic processes that operated during the Noachian, implying that the ancient climate also varied across regions.

  5. Surficial Geology of the Chicxulub Impact Crater, Yucatan, Mexico

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.; Ocampo, Adriana C.; Duller, Charles E.

    1993-01-01

    The Chicxulub impact crater in northwestern Yucatan, Mexico is the primary candidate for the proposed impact that caused mass extinctions at the end of the Cretaceous Period. The crater is buried by up to a kilometer of Tertiary sediment and the most prominent surface expression is a ring of sink holes, known locally as cenotes, mapped with Landsat imagery. This 165 +/- 5 km diameter Cenote Ring demarcates a boundary between unfractured limestones inside the ring, and fractured limestones outside. The boundary forms a barrier to lateral ground water migration, resulting in increased flows, dissolution, and collapse thus forming the cenotes. The subsurface geology indicates that the fracturing that created the Cenote Ring is related to slumping in the rim of the buried crater, differential thicknesses in the rocks overlying the crater, or solution collapse within porous impact deposits. The Cenote Ring provides the most accurate position of the Chicxulub crater's center, and the associated faults, fractures, and stratigraphy indicate that the crater may be approx. 240 km in diameter.

  6. Surficial geology of the Chicxulub impact crater, Yucatan, Mexico

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.; Ocampo, Adriana C.; Duller, Charles E.

    1993-01-01

    The Chicxulub impact crater in northwestern Yucatan, Mexico is the primary candidate for the proposed impact that caused mass extinctions at the end of the Cretaceous Period. The crater is buried by up to a kilometer of Tertiary sediment and the most prominent surface expression is a ring of sink holes, known locally as cenotes, mapped with Landsat imagery. This 165 +/- 5 km diameter Cenote Ring demarcates a boundary between unfractured limestones inside the ring, and fractured limestones outside. The boundary forms a barrier to lateral ground water migration, resulting in increased flows, dissolution, and collapse thus forming the cenotes. The subsurface geology indicates that the fracturing that created the Cenote Ring is related to slumping in the rim of the buried crater, differential thicknesses in the rocks overlying the crater, or solution collapse within porous impact deposits. The Cenote Ring provides the most accurate position of the Chicxulub crater's center, and the associated faults, fractures, and stratigraphy indicate that the crater may be approximately 240 km in diameter.

  7. Impact Crater Identified on the Navajo Nation Near Chinle, Arizona

    NASA Astrophysics Data System (ADS)

    Shoemaker, E. M.; Roddy, D. J.; Moore, C. B.; Pfeilsticker, R.; Curley, C. L.; Dunkelman, T.; Kuerzel, K.; Taylor, M.; Shoemaker, C.; Donnelly, P.

    1995-09-01

    A small impact crater has been identified about 8 km north of Chinle, Arizona on the Navajo Nation. Preliminary studies show that the crater is elongate in a N-S direction, measuring about 23 by 34 m in diameter, with a depth of about 1.3 m. The impact origin of the crater is identified by its shape, subsurface deformation, and an iron-nickel oxide fragment. We estimate the age to be about 150 to 250 years. The impact site is on the east side of the Chinle Valley at an altitude of 1685 m and is about 2 km east of Chinle Wash. The crater formed on an alluvial surface that slopes gently west toward the Wash. About 2 m of reddish brown alluvial sand and silt of the Jeddito Formation of late Pleistocene age rests on the Petrified Forest Member of the Chinle Formation of late Triassic age. A moderately developed late Pleistocene pedocal soil has developed on the Jeddito. Several thin discontinuous caliche horizons occur at a depth of about 1 m. The caliche horizons provided easily traced markers by which we could delimit the original walls of the crater and recognize deformation along the crater walls. Three trenches were excavated down to the top of the Chinle bedrock: 1) an east- west trench 31 m long across the center of the crater, 2) a north-south trench 13 m long in the north crater rim, and 3) a north-south trench 12 m long in the south crater rim. Excavation width was about 1 m and provided excellent exposures of the subsurface stratigraphy and deformation. The trenches revealed that the original crater was about 23 m wide and 27 m long. The original rim crests have entirely eroded away so that no perceptible raised rim remains. At the center of the crater, the original depth was about 3 m; material washed from the rims now fills the crater floor to a depth of 1.5 m. The crater is symmetrical; however, the deepest part of the original crater lies south of the center and was not reached in the south trench. The east-west trench showed that the initial floor of

  8. Abundance and Speciation of Water and Sulfate at Gusev Crater and Meridiani Planum

    NASA Technical Reports Server (NTRS)

    Ming, D. W.; Clark, B. C.; Klingelhoefer, G.; Gellert, R.; Rodionov, D.; Schroeder, C.; deSouza, P.; Yen, A.

    2005-01-01

    A major science goal of the Mars Exploration Rover (MER) mission is to search for evidence of water activity, and direct mineralogical evidence for aqueous activity has been reported for Meridiani Planum in the form of the iron sulfate hydroxide mineral jarosite and at Gusev crater in the form of goethite. The Spirit and Opportunity rovers have each collected 110+ Moessbauer (MB) and 75+ Alpha Particle X-Ray Spectrometer (APXS) spectra from Gusev crater and Meridiani Planum [1 - 4]. In this abstract, we use mineralogical and elemental data, primarily from the Moessbauer and APXS instruments, to infer the speciation and estimate the abundance of sulfate and water (as either the H2O molecule or the hydroxyl anion) at Gusev crater and Meridiani Planum. Throughout the abstract, we adopt a format for mineral formulas that shows water explicitly rather than the usual practice of structure-based formulas (e.g., for goethite we write Fe2O3xH2O instead of FeOOH).

  9. Population characteristics of submicrometer-sized craters on regolith particles from asteroid Itokawa

    NASA Astrophysics Data System (ADS)

    Matsumoto, Toru; Hasegawa, S.; Nakao, S.; Sakai, M.; Yurimoto, H.

    2018-03-01

    We investigated impact crater structures on regolith particles from asteroid Itokawa using scanning electron microscopy. We observed the surfaces of 51 Itokawa particles, ranging from 15 μm to 240 μm in size. Craters with average diameters ranging from 10 nm to 2.8 μm were identified on 13 Itokawa particles larger than 80 μm. We examined the abundance, spatial distribution, and morphology of approximately 900 craters on six Itokawa particles. Craters with sizes in excess of 200 nm are widely dispersed, with spatial densities from 2.6 μm2 to 4.5 μm2; a fraction of the craters was locally concentrated with a density of 0.1 μm2. The fractal dimension of the cumulative crater diameters ranges from 1.3 to 2.3. Craters of several tens of nanometers in diameter exhibit pit and surrounding rim structures. Craters of more than 100 nm in diameter commonly have melted residue at their bottom. These morphologies are similar to those of submicrometer-sized craters on lunar regolith. We estimated the impactor flux on Itokawa regolith-forming craters, assuming that the craters were accumulated during direct exposure to the space environment for 102 to 104 yr. The range of impactor flux onto Itokawa particles is estimated to be at least one order of magnitude higher than the interplanetary dust flux and comparable to the secondary impact flux on the Moon. This indicates that secondary ejecta impacts are probably the dominant cratering process in the submicrometer range on Itokawa regolith particles, as well as on the lunar surface. We demonstrate that secondary submicrometer craters can be produced anywhere in centimeter- to meter-sized depressions on Itokawa's surface through primary interplanetary dust impacts. If the surface unevenness on centimeter to meter scales is a significant factor determining the abundance of submicrometer secondary cratering, the secondary impact flux could be independent of the overall shapes or sizes of celestial bodies, and the secondary

  10. Isotope analysis of crystalline impact melt rocks from Apollo 16 stations 11 and 13, North Ray Crater

    NASA Technical Reports Server (NTRS)

    Reimold, W. U.; Nyquist, L. E.; Bansal, B. M.; Shih, C.-Y.; Weismann, H.; Wooden, J. L.; Mackinnon, I. D. R.

    1985-01-01

    The North Ray Crater Target Rock Consortium was formed to study a large number of rake samples collected at Apollo 16 stations 11 and 13 with comparative chemical, mineralogical, and chronological techniques in order to provide a larger data base for the discussion of lunar highland evolution in the vicinity of the Apollo 16 landing region. The present investigation is concerned with Rb-Sr and Sm-Nd isotopic analyses of a number of whole-rock samples of feldspathic microporhyritic (FM) impact melt, a sample type especially abundant among the North Ray crater (station 11) sample collection. Aspects of sample mineralogy and analytical procedures are discussed, taking into account FM impact melt rocks 6715 and 63538, intergranular impact melt rock 67775, subophitic impact melt rock 67747, subophitic impact melt rock 67559, and studies based on the utilization of electron microscopy and mass spectroscopy.

  11. Ceres and the terrestrial planets impact cratering record

    NASA Astrophysics Data System (ADS)

    Strom, R. G.; Marchi, S.; Malhotra, R.

    2018-03-01

    Dwarf planet Ceres, the largest object in the Main Asteroid Belt, has a surface that exhibits a range of crater densities for a crater diameter range of 5-300 km. In all areas the shape of the craters' size-frequency distribution is very similar to those of the most ancient heavily cratered surfaces on the terrestrial planets. The most heavily cratered terrain on Ceres covers ∼15% of its surface and has a crater density similar to the highest crater density on <1% of the lunar highlands. This region of higher crater density on Ceres probably records the high impact rate at early times and indicates that the other 85% of Ceres was partly resurfaced after the Late Heavy Bombardment (LHB) at ∼4 Ga. The Ceres cratering record strongly indicates that the period of Late Heavy Bombardment originated from an impactor population whose size-frequency distribution resembles that of the Main Belt Asteroids.

  12. Martian impact crater degradation studies: Implications for localized obliteration episodes

    NASA Technical Reports Server (NTRS)

    Barlow, N. G.

    1992-01-01

    Early spacecraft missions to Mars revealed that impact craters display a range of degradational states, but full appreciation of the range of preservational characteristics was not revealed until the Mariner 9 and Viking missions in the 1970's. Many studies have described the spatial and temporal distribution of obliteration episodes based on qualitative descriptions of crater degradation. Recent advances in photoclinometric techniques have led to improved estimates of crater morphometric characteristics. The present study is using photoclinometry to determine crater profiles and is comparing these results with the crater geometry expected for pristine craters of identical size. The result is an estimate of the degree of degradation suffered by Martian impact craters in selected regions of the planet. Size-frequency distribution analyses of craters displaying similar degrees of degradation within localized regions of the planet may provide information about the timing of obliteration episodes in these regions.

  13. A Numerical Investigation into Low-Speed Impact Cratering Events

    NASA Astrophysics Data System (ADS)

    Schwartz, Stephen; Richardson, D. C.; Michel, P.

    2012-10-01

    Impact craters are the geological features most commonly observed on the surface of solid Solar System bodies. Crater shapes and features are crucial sources of information regarding past and present surface environments, and can provide indirect information about the internal structures of these bodies. In this study, we consider the effects of low-speed impacts into granular material. Studies of low-speed impact events are suitable for understanding the cratering process leading, for instance, to secondary craters. In addition, upcoming asteroid sample return missions will employ surface sampling strategies that use impacts into the surface by a projectile. An understanding of the process can lead to better sampling strategies. We use our implementation of the Soft-Sphere Discrete Element Method (SSDEM) (Schwartz et al. 2012, Granular Matter 14, 363-380) into the parallel N-body code PKDGRAV (cf. Richardson et al. 2011, Icarus 212, 427-437) to model the impact cratering process into granular material. We consider the effects of boundary conditions on the ejecta velocity profile and discuss how results relate to the Maxwell Z-Model during the crater growth phase. Cratering simulations are compared to those of Wada et al. 2006 (Icarus 180, 528-545) and to impact experiments performed in conjunction with Hayabusa 2. This work is supported in part by grants from the National Science Foundation under grant number AST1009579 and from the Office of Space Science of NASA under grant number NNX08AM39G. Part of this study resulted from discussions with the International Team (#202) sponsored by ISSI in Bern (Switzerland). Some simulations were performed on the YORP cluster administered by the Center for Theory and Computation of the Department of Astronomy at the University of Maryland in College Park and on the SIGGAM computer cluster hosted by the Côte d'Azur Observatory in Nice (France).

  14. Coring the Chesapeake Bay impact crater

    USGS Publications Warehouse

    Poag, C.W.

    2004-01-01

    In July 1983, the shipboard scientists of Deep Sea Drilling Project Leg 95 found an unexpected bonus in a core taken 150 kilometers east of Atlantic City, N.J. At Site 612, the scientists recovered a 10-centimeter-thick layer of late Eocene debris ejected from an impact about 36 million years ago. Microfossils and argon isotope ratios from the same layer reveal that the ejecta were part of a broad North American impact debris field, previously known primarily from the Gulf of Mexico and Caribbean Sea. Since that serendipitous beginning, years of seismic reflection profiling, gravity measurements and core drilling have confirmed the source of that strewn field - the Chesapeake Bay impact crater, the largest structure of its kind in the United States, and the sixth-largest impact crater on Earth.

  15. Impact cratering on porous targets in the strength regime

    NASA Astrophysics Data System (ADS)

    Nakamura, Akiko M.

    2017-12-01

    Cratering on small bodies is crucial for the collision cascade and also contributes to the ejection of dust particles into interplanetary space. A crater cavity forms against the mechanical strength of the surface, gravitational acceleration, or both. The formation of moderately sized craters that are sufficiently larger than the thickness of the regolith on small bodies, in which mechanical strength plays the dominant role rather than gravitational acceleration, is in the strength regime. The formation of microcraters on blocks on the surface is also within the strength regime. On the other hand, the formation of a crater of a size comparable to the thickness of the regolith is affected by both gravitational acceleration and cohesion between regolith particles. In this short review, we compile data from the literature pertaining to impact cratering experiments on porous targets, and summarize the ratio of spall diameter to pit diameter, the depth, diameter, and volume of the crater cavity, and the ratio of depth to diameter. Among targets with various porosities studied in the laboratory to date, based on conventional scaling laws (Holsapple and Schmidt, J. Geophys. Res., 87, 1849-1870, 1982) the cratering efficiency obtained for porous sedimentary rocks (Suzuki et al., J. Geophys. Res. 117, E08012, 2012) is intermediate. A comparison with microcraters formed on a glass target with impact velocities up to 14 km s-1 indicates a different dependence of cratering efficiency and depth-to-diameter ratio on impact velocity.

  16. Ancient impact and aqueous processes at Endeavour Crater, Mars

    USGS Publications Warehouse

    Squyres, S. W.; Arvidson, R. E.; Bell, J.F.; Calef, F.J.; Clark, B. C.; Cohen, B. A.; Crumpler, L.A.; de Souza, P. A.; Farrand, W. H.; Gellert, Ralf; Grant, J.; Herkenhoff, K. E.; Hurowitz, J.A.; Johnson, J. R.; Jolliff, B.L.; Knoll, A.H.; Li, R.; McLennan, S.M.; Ming, D. W.; Mittlefehldt, D. W.; Parker, T.J.; Paulsen, G.; Rice, M.S.; Ruff, S.W.; Schröder, C.; Yen, A. S.; Zacny, K.

    2012-01-01

    The rover Opportunity has investigated the rim of Endeavour Crater, a large ancient impact crater on Mars. Basaltic breccias produced by the impact form the rim deposits, with stratigraphy similar to that observed at similar-sized craters on Earth. Highly localized zinc enrichments in some breccia materials suggest hydrothermal alteration of rim deposits. Gypsum-rich veins cut sedimentary rocks adjacent to the crater rim. The gypsum was precipitated from low-temperature aqueous fluids flowing upward from the ancient materials of the rim, leading temporarily to potentially habitable conditions and providing some of the waters involved in formation of the ubiquitous sulfate-rich sandstones of the Meridiani region.

  17. Long-Term Recovery of Life in the Chicxulub Crater

    NASA Astrophysics Data System (ADS)

    Lowery, C.; Jones, H.; Bralower, T. J.; Smit, J.; Rodriguez-Tovar, F. J.; Whalen, M. T.; Owens, J. D.; Expedition 364 Science Party, I. I.

    2017-12-01

    The Chicxulub Crater on the Yucatán Peninsula of Mexico was formed by the impact of an asteroid 66 Ma that caused the extinction of 75% of genera on Earth. Immediately following the impact, the decimated ecosystem began the long process of recovery, both in terms of primary productivity and species diversity. This well-documented process was heterogeneous across the world ocean, but until the present time it has been inaccessible at ground zero of the impact. IODP/ICDP Exp. 364 recovered 9.5 m of pelagic limestone spanning the entire Paleocene, including a continuous section spanning the first 5 myr following the impact. The Chicxulub Crater is the largest known marine impact crater on Earth, and the recovery of the ecosystem presented here is the first such record of long-term primary succession in the sterile zone of a large impact crater. Planktic and benthic foraminifera, calcareous nannoplankton, calcispheres, bioturbation, and geochemical proxies all indicate that export productivity in the Chicxulub Crater recovered rapidly (within 30 kyr) following the impact. Recovery in terms of diversity and species abundance took much longer, and varied between groups. Planktic foraminifera quickly diversified, with all common Paleocene tropical/subtropical species appearing roughly when expected. Trace fossils appear rapidly after the event, with a progressive recovery through the lowermost Paleocene. Calcareous nannoplankton took much longer to recover, and disaster taxa like Braarudosphaera dominated the assemblage well into the late Paleocene. Paleoecology and geochemistry relate these trends to oceanographic conditions within the Chicxulub Crater. Planktic foraminifera from known depth habitats, including Morozovellids, Acarininids, Chiloguembelinids, and Subbotinids, track changes in the water column structure and paleoredox conditions within the crater. Diverse and abundant macro- and microbenthic organisms indicate food availability and good oxygen conditions

  18. Subsurface volatile content of martian double-layer ejecta (DLE) craters

    USGS Publications Warehouse

    Viola, Donna; McEwen, Alfred S.; Dundas, Colin M.; Byrne, Shane

    2017-01-01

    Excess ice is widespread throughout the martian mid-latitudes, particularly in Arcadia Planitia, where double-layer ejecta (DLE) craters also tend to be abundant. In this region, we observe the presence of thermokarstically-expanded secondary craters that likely form from impacts that destabilize a subsurface layer of excess ice, which subsequently sublimates. The presence of these expanded craters shows that excess ice is still preserved within the adjacent terrain. Here, we focus on a 15-km DLE crater that contains abundant superposed expanded craters in order to study the distribution of subsurface volatiles both at the time when the secondary craters formed and, by extension, remaining today. To do this, we measure the size distribution of the superposed expanded craters and use topographic data to calculate crater volumes as a proxy for the volumes of ice lost to sublimation during the expansion process. The inner ejecta layer contains craters that appear to have undergone more expansion, suggesting that excess ice was most abundant in that region. However, both of the ejecta layers had more expanded craters than the surrounding terrain. We extrapolate that the total volume of ice remaining within the entire ejecta deposit is as much as 74 km3 or more. The variation in ice content between the ejecta layers could be the result of (1) volatile preservation from the formation of the DLE crater, (2) post-impact deposition in the form of ice lenses; or (3) preferential accumulation or preservation of subsequent snowfall. We have ruled out (2) as the primary mode for ice deposition in this location based on inconsistencies with our observations, though it may operate in concert with other processes. Although none of the existing DLE formation hypotheses are completely consistent with our observations, which may merit a new or modified mechanism, we can conclude that DLE craters contain a significant quantity of excess ice today.

  19. Surface Composition Near the Trailing Hemisphere Apex on Europa: The Manannán Impact Crater and Neighboring Terrain

    NASA Astrophysics Data System (ADS)

    Dalton, J. B.; Prockter, L. M.; Shirley, J. H.; Kamp, L.; Phillips, C. B.; Valenti, M.

    2012-12-01

    The Manannán impact crater and surrounding areas were imaged by Galileo's Near Infrared Mapping Spectrometer (NIMS) during the C3 orbital encounter. We have applied a linear mixture model based on cryogenic infrared reflectance spectroscopy to a "despiked" version of this NIMS observation (C3ENLINEA01A) to estimate abundances of sulfuric acid hydrate, hydrated sulfate salts, water ice and brines in surface exposures. Here we supplement our previously reported abundance estimates (Dalton et al., 2011) with additional results from our ongoing investigation. New geologic mapping precisely registered to the NIMS observation allows the extraction of high-quality near-infrared spectra specific to individual geologic units and morphological features. Detailed high resolution geologic mapping indicates the likely presence of extensive deposits of impact melt materials largely filling the crater floor (Moore et al. 2001), together with surrounding continuous ejecta deposits that may have been excavated from Europa's interior. We find that the crater floor and nearby ejecta exhibit low sulfuric acid abundance relative to the surroundings, with the abundance increasing with radial distance. Where the ejecta begins to thin and break up, the spectral mixture resembles a combination of pre-existing, high-acid-content materials and cleaner, excavated water ice. Several geologic units exhibit significantly lower sulfuric acid hydrate than expected for this region near the trailing hemisphere apex, varying from 53-64 wt% over the observation. This suggests that these surface units have received a reduced cumulative radiation dose (electrons and ions) compared to nearby terrain; this in turn implies geologic youth. We will present model compositions for several of Manannán's key stratigraphic units, including the crater floor deposits and the adjacent chaos and linea. We will interpret these results in the context of ongoing investigations of the interplay of exogenic and

  20. Chesapeake Bay impact structure: Morphology, crater fill, and relevance for impact structures on Mars

    USGS Publications Warehouse

    Horton, J. Wright; Ormo, J.; Powars, D.S.; Gohn, G.S.

    2006-01-01

    The late Eocene Chesapeake Bay impact structure (CBIS) on the Atlantic margin of Virginia is one of the largest and best-preserved "wet-target" craters on Earth. It provides an accessible analog for studying impact processes in layered and wet targets on volatile-rich planets. The CBIS formed in a layered target of water, weak clastic sediments, and hard crystalline rock. The buried structure consists of a deep, filled central crater, 38 km in width, surrounded by a shallower brim known as the annular trough. The annular trough formed partly by collapse of weak sediments, which expanded the structure to ???85 km in diameter. Such extensive collapse, in addition to excavation processes, can explain the "inverted sombrero" morphology observed at some craters in layered targets. The distribution of crater-fill materials i n the CBIS is related to the morphology. Suevitic breccia, including pre-resurge fallback deposits, is found in the central crater. Impact-modified sediments, formed by fluidization and collapse of water-saturated sand and silt-clay, occur in the annular trough. Allogenic sediment-clast breccia, interpreted as ocean-resurge deposits, overlies the other impactites and covers the entire crater beneath a blanket of postimpact sediments. The formation of chaotic terrains on Mars is attributed to collapse due to the release of volatiles from thick layered deposits. Some flat-floored rimless depressions with chaotic infill in these terrains are impact craters that expanded by collapse farther than expected for similar-sized complex craters in solid targets. Studies of crater materials in the CBIS provide insights into processes of crater expansion on Mars and their links to volatiles. ?? The Meteoritical Society, 2006.

  1. Block oscillation model for impact crater collapse

    NASA Astrophysics Data System (ADS)

    Ivanov, B. A.; Kostuchenko, V. N.

    1997-03-01

    Previous investigations of the impact crater formation mechanics have shown that the late stage, a transient cavity collapse in a gravity field, may be modeled with a traditional rock mechanics if one ascribes very specific mechanical properties of rock in the vicinity of a crater: an effective strength of rock needed is around 30 bar, and effective angle of internal friction below 5 deg. The rock media with such properties may be supposed 'temporary fluidized'. The nature of this fluidization is now poorly understood; an acoustic (vibration) nature of this fluidization has been suggested. This model now seems to be the best approach to the problem. The open question is how to implement the model (or other possible models) in a hydrocode for numerical simulation of a dynamic crater collapse. We study more relevant models of mechanical behavior of rocks during cratering. The specific of rock deformation is that the rock media deforms not as a plastic metal-like continuum, but as a system of discrete rock blocks. The deep drilling of impact craters revealed the system of rock blocks of 50 m to 200 m in size. We used the model of these block oscillations to formulate the appropriate rheological law for the subcrater flow during the modification stage.

  2. Dynamics of yield-stress droplets: Morphology of impact craters

    NASA Astrophysics Data System (ADS)

    Neufeld, Jerome; Sohr, David; Ferrari, Leo; Dalziel, Stuart

    2017-11-01

    Yield strength can play an important role for the dynamics of droplets impacting on surfaces, whether at the industrial or planetary scale, and can capture a zoo of impact crater morphologies, from simple parabolic craters, to more complex forms with forms with, for example, multiple rings, central peaks. Here we show that the morphology of planetary impact craters can be reproduced in the laboratory using carbopol, a transparent yield-stress fluid, as both impactor and bulk fluid. Using high-speed video photography, we characterise the universal, transient initial excavation stage of impact and show the dependence of the subsequent relaxation to final crater morphology on impactor size, impact speed and yield stress. To further interrogate our laboratory impacts, we dye our impactor to map its final distribution and use particle tracking to determine the flow fields during impact and the maximal extent of the yield surface. We characterise the flow-fields induced during impact, and the maximal extent of the yield surface, by tracking particles within the bulk fluid and map the distribution of impactor and bulk by tracing the final distribution of dyed impactor. The results of laboratory impact droplets are used to infer the properties of planetary impactors, and aid in inter.

  3. Standardizing the nomenclature of Martian impact crater ejecta morphologies

    USGS Publications Warehouse

    Barlow, Nadine G.; Boyce, Joseph M.; Costard, Francois M.; Craddock, Robert A.; Garvin, James B.; Sakimoto, Susan E.H.; Kuzmin, Ruslan O.; Roddy, David J.; Soderblom, Laurence A.

    2000-01-01

    The Mars Crater Morphology Consortium recommends the use of a standardized nomenclature system when discussing Martian impact crater ejecta morphologies. The system utilizes nongenetic descriptors to identify the various ejecta morphologies seen on Mars. This system is designed to facilitate communication and collaboration between researchers. Crater morphology databases will be archived through the U.S. Geological Survey in Flagstaff, where a comprehensive catalog of Martian crater morphologic information will be maintained.

  4. Lunar prospector epithermal neutrons from impact craters and landing sites: Implications for surface maturity and hydrogen distribution

    USGS Publications Warehouse

    Johnson, J. R.; Feldman, W.C.; Lawrence, D.J.; Maurice, S.; Swindle, T.D.; Lucey, P.G.

    2002-01-01

    Initial studies of neutron spectrometer data returned by Lunar Prospector concentrated on the discovery of enhanced hydrogen abundances near both lunar poles. However, the nonpolar data exhibit intriguing patterns that appear spatially correlated with surface features such as young impact craters (e.g., Tycho). Such immature crater materials may have low hydrogen contents because of their relative lack of exposure to solar wind-implanted volatiles. We tested this hypothesis by comparing epithermal* neutron counts (i.e., epithermal -0.057 ?? thermal neutrons) for Copernican-age craters classified as relatively young, intermediate, and old (as determined by previous studies of Clementine optical maturity variations). The epithermal* counts of the crater and continuous ejecta regions suggest that the youngest impact materials are relatively devoid of hydrogen in the upper 1 m of regolith. We also show that the mean hydrogen contents measured in Apollo and Luna landing site samples are only moderately well correlated to the epithermal* neutron counts at the landing sites, likely owing to the effects of rare earth elements. These results suggest that further work is required to define better how hydrogen distribution can be revealed by epithermal neutrons in order to understand more fully the nature and sources (e.g., solar wind, meteorite impacts) of volatiles in the lunar regolith.

  5. The effect of impact angle on craters formed by hypervelocity particles

    NASA Technical Reports Server (NTRS)

    Hill, David C.; Rose, M. Frank; Best, Steve R.; Crumpler, Michael S.; Crawford, Gary D.; Zee, Ralph H.-C.; Bozack, Michael J.

    1995-01-01

    The Space Power Institute (SPI) at Auburn University has conducted experiments on the effects of impact angle on crater morphology and impactor residue retention for hypervelocity impacts. Copper target plates were set at angles of 30 deg, 45 deg, 60 deg, and 75 deg from the particle flight path. For the 30 deg and 45 deg impacts, in the velocity regime greater than 8 km s(exp -1) the resultant craters are almost identical to normal incidence impacts. The only difference found was in the apparent distribution of particle residue within the crater, and further research is needed to verify this. The 60 deg and 75 deg impacts showed marked differences in crater symmetry, crater lip shape, and particle residue distribution in the same velocity regime. Impactor residue shock fractionation effects have been quantified in first-order. It is concluded that a combination of analysis techniques can yield further information on impact velocity, direction, and angle of incidence.

  6. Microbial abundance in the deep subsurface of the Chesapeake Bay impact crater: Relationship to lithology and impact processes

    USGS Publications Warehouse

    Cockell, Charles S.; Gronstal, Aaron L.; Voytek, Mary A.; Kirshtein, Julie D.; Finster, Kai; Sanford, Ward E.; Glamoclija, Mihaela; Gohn, Gregroy S.; Powars, David S.; Horton, J. Wright

    2009-01-01

    Asteroid and comet impact events are known to cause profound disruption to surface ecosystems. The aseptic collection of samples throughout a 1.76-km-deep set of cores recovered from the deep subsurface of the Chesapeake Bay impact structure has allowed the study of the subsurface biosphere in a region disrupted by an impactor. Microbiological enumerations suggest the presence of three major microbiological zones. The upper zone (127–867 m) is characterized by a logarithmic decline in microbial abundance from the surface through the postimpact section of Miocene to Upper Eocene marine sediments and across the transition into the upper layers of the impact tsunami resurge sediments and sediment megablocks. In the middle zone (867–1397 m) microbial abundances are below detection. This zone is predominantly quartz sand, primarily composed of boulders and blocks, and it may have been mostly sterilized by the thermal pulse delivered during impact. No samples were collected from the large granite block (1096–1371 m). The lowest zone (below 1397 m) of increasing microbial abundance coincides with a region of heavily impact-fractured, hydraulically conductive suevite and fractured schist. These zones correspond to lithologies influenced by impact processes. Our results yield insights into the influence of impacts on the deep subsurface biosphere.

  7. Mosaic of Large Impact Craters

    NASA Image and Video Library

    1996-09-13

    This mosaic from NASA Magellan data is in the Lavinia region of Venus. Three large impact craters can be seen located in a region of fractured plains. http://photojournal.jpl.nasa.gov/catalog/PIA00086

  8. Shallow and deep fresh impact craters in Hesperia Planum, Mars

    NASA Technical Reports Server (NTRS)

    Mouginis-Mark, Peter J.; Hayashi, Joan N.

    1993-01-01

    The depths of 109 impact craters about 2-16 km in diameter, located on the ridged plains materials of Hesperia Planum, Mars, have been measured from their shadow lengths using digital Viking Orbiter images (orbit numbers 417S-419S) and the PICS computer software. On the basis of their pristine morphology (very fresh lobate ejecta blankets, well preserved rim crests, and lack of superposed impact craters), 57 of these craters have been selected for detailed analysis of their spatial distribution and geometry. We find that south of 30 deg S, craters less than 6.0 km in diameter are markedly shallower than similar-sized craters equatorward of this latitude. No comparable relationship is observed for morphologically fresh craters greater than 6.0 km diameter. We also find that two populations exist for older craters less than 6.0 km diameter. When craters that lack ejecta blankets are grouped on the basis of depth/diameter ratio, the deeper craters also typically lie equatorward of 30 S. We interpret the spatial variation in crater depth/diameter ratios as most likely due to a poleward increase in volatiles within the top 400 m of the surface at the times these craters were formed.

  9. Impact craters on Venus - Initial analysis from Magellan

    NASA Technical Reports Server (NTRS)

    Phillips, Roger J.; Arvidson, Raymond E.; Boyce, Joseph M.; Campbell, Donald B.; Guest, John E.

    1991-01-01

    The general features of impact craters are described emphasizing two aspects: the effect of the atmosphere on crater and ejecta morphology and the implications of the distribution and appearance of the craters for the volcanic and tectonic resurfacing history of Venus. Magellan radar images reveal 135 craters about 15 km in diameter containing central peaks, multiple central peaks, and peak rings. Craters smaller than 15 km exhibit multiple floors or appear in clusters. Surface flows of material initially entrained in the atmosphere are characterized. Zones of low radar albedo originated from deformation of the surface by the shock or pressure wave associated with the incoming meteoroid surround many craters. A spectrum of surface ages on Venus ranging from 0 to 800 million years indicates that Venus must be a geologically active planet.

  10. Migration of the Cratering Flow-Field Center with Implications for Scaling Oblique Impacts

    NASA Technical Reports Server (NTRS)

    Anderson, J. L. B.; Schultz, P. H.; Heineck, J. T.

    2004-01-01

    Crater-scaling relationships are used to predict many cratering phenomena such as final crater diameter and ejection speeds. Such nondimensional relationships are commonly determined from experimental impact and explosion data. Almost without exception, these crater-scaling relationships have used data from vertical impacts (90 deg. to the horizontal). The majority of impact craters, however, form by impacts at angles near 45 deg. to the horizontal. While even low impact angles result in relatively circular craters in sand targets, the effects of impact angle have been shown to extend well into the excavation stage of crater growth. Thus, the scaling of oblique impacts needs to be investigated more thoroughly in order to quantify fully how impact angle affects ejection speed and angle. In this study, ejection parameters from vertical (90 deg.) and 30 deg. oblique impacts are measured using three-dimensional particle image velocimetry (3D PIV) at the NASA Ames Vertical Gun Range (AVGR). The primary goal is to determine the horizontal migration of the cratering flow-field center (FFC). The location of the FFC at the time of ejection controls the scaling of oblique impacts. For vertical impacts the FFC coincides with the impact point (IP) and the crater center (CC). Oblique impacts reflect a more complex, horizontally migrating flow-field. A single, stationary point-source model cannot be used accurately to describe the evolution of the ejection angles from oblique impacts. The ejection speeds for oblique impacts also do not follow standard scaling relationships. The migration of the FFC needs to be understood and incorporated into any revised scaling relationships.

  11. (abstract) Radiophysical Properties of Venusian Impact Craters

    NASA Technical Reports Server (NTRS)

    Weitz, C. M.; Saunders, R. S.; Plaut, J. J.; Elachi, C.; Moore, H. J.

    1993-01-01

    An analysis of 222 large (greater than 20-km-diameter) impact craters on Venus using both cycle 1 and cycle 2 Magellan data is being conducted to determine the radiophysical properties (i.e., backscatter cross section, emissivity, reflectivity, rms slope) of the craters and to search for correlations with target region properties and subsequent geological history.

  12. Icy Satellites of Saturn: Impact Cratering and Age Determination

    NASA Technical Reports Server (NTRS)

    Dones, L.; Chapman, C. R.; McKinnon, William B.; Melosh, H. J.; Kirchoff, M. R.; Neukum, G.; Zahnle, K. J.

    2009-01-01

    Saturn is the first giant planet to be visited by an orbiting spacecraft that can transmit large amounts of data to Earth. Crater counts on satellites from Phoebe inward to the regular satellites and ring moons are providing unprecedented insights into the origin and time histories of the impacting populations. Many Voyager-era scientists concluded that the satellites had been struck by at least two populations of impactors. In this view, the Population I impactors, which were generally judged to be comets orbiting the Sun, formed most of the larger and older craters, while Population II impactors, interpreted as Saturn-orbiting ejecta from impacts on satellites, produced most of the smaller and younger craters. Voyager data also implied that all of the ring moons, and probably some of the midsized classical moons, had been catastrophically disrupted and reaccreted since they formed. We examine models of the primary impactor populations in the Saturn system. At the present time, ecliptic comets, which likely originate in the Kuiper belt/scattered disk, are predicted to dominate impacts on the regular satellites and ring moons, but the models require extrapolations in size (from the observed Kuiper belt objects to the much smaller bodies that produce the craters) or in distance (from the known active Jupiter family comets to 9.5 AU). Phoebe, Iapetus, and perhaps even moons closer to Saturn have been struck by irregular satellites as well. We describe the Nice model, which provides a plausible mechanism by which the entire Solar System might have experienced an era of heavy bombardment long after the planets formed. We then discuss the three cratering chronologies, including one based upon the Nice model, that have been used to infer surface ages from crater densities on the saturnian satellites. After reviewing scaling relations between the properties of impactors and the craters they produce, we provide model estimates of the present-day rate at which comets impact

  13. Galileo SSI lunar observations: Copernican craters and soils

    NASA Technical Reports Server (NTRS)

    Mcewen, A. S.; Greeley, R.; Head, James W.; Pieters, C. M.; Fischer, E. M.; Johnson, T. V.; Neukum, G.

    1993-01-01

    The Galileo spacecraft completed its first Earth-Moon flyby (EMI) in December 1990 and its second flyby (EM2) in December 1992. Copernican-age craters are among the most prominent features seen in the SSI (Solid-State Imaging) multispectral images of the Moon. The interiors, rays, and continuous ejecta deposits of these youngest craters stand out as the brightest features in images of albedo and visible/1-micron color ratios (except where impact melts are abundant). Crater colors and albedos (away from impact melts) are correlated with their geologic emplacement ages as determined from counts of superposed craters; these age-color relations can be used to estimate the emplacement age (time since impact event) for many Copernican-age craters on the near and far sides of the Moon. The spectral reflectivities of lunar soils are controlled primarily by (1) soil maturity, resulting from the soil's cumulative age of exposure to the space environment; (2) steady-state horizontal and vertical mixing of fresh crystalline materials ; and (3) the mineralogy of the underlying bedrock or megaregolith. Improved understanding of items (1) and (2) above will improve our ability to interpret item (3), especially for the use of crater compositions as probes of crustal stratigraphy. We have examined the multispectral and superposed crater frequencies of large isolated craters, mostly of Eratosthenian and Copernican ages, to avoid complications due to (1) secondaries (as they affect superposed crater counts) and (2) spatially and temporally nonuniform regolith mixing from younger, large, and nearby impacts. Crater counts are available for 11 mare craters and 9 highlands craters within the region of the Moon imaged during EM1. The EM2 coverage provides multispectral data for 10 additional craters with superposed crater counts. Also, the EM2 data provide improved spatial resolution and signal-to-noise ratios over the western nearside.

  14. Melting and its relationship to impact crater morphology

    NASA Technical Reports Server (NTRS)

    Okeefe, John D.; Ahrens, Thomas J.

    1992-01-01

    Shock-melting features occur on planets at scales that range from micrometers to megameters. It is the objective of this study to determine the extent of thickness, volume geometry of the melt, and relationship with crater morphology. The variation in impact crater morphology on planets is influenced by a broad range of parameters: e.g., planetary density, thermal state, strength, impact velocity, gravitational acceleration. We modeled the normal impact of spherical projectiles on a semi-infinite planet over a broad range of conditions using numerical techniques.

  15. Martian Cratering 7: The Role of Impact Gardening

    NASA Astrophysics Data System (ADS)

    Hartmann, William K.; Anguita, Jorge; de la Casa, Miguel A.; Berman, Daniel C.; Ryan, Eileen V.

    2001-01-01

    Viking-era researchers concluded that impact craters of diameter D<50 m were absent on Mars, and thus impact gardening was considered negligible in establishing decameter-scale surface properties. This paper documents martian crater populations down to diameter D˜11 m and probably less on Mars, requiring a certain degree of impact gardening. Applying lunar data, we calculate cumulative gardening depth as a function of total cratering. Stratigraphic units exposed since Noachian times would have experienced tens to hundreds of meters of gardening. Early Amazonian/late Hesperian sites, such as the first three landing sites, experienced cumulative gardening on the order of 3-14 m, a conclusion that may conflict with some landing site interpretations. Martian surfaces with less than a percent or so of lunar mare crater densities have negligible impact gardening because of a probable cutoff of hypervelocity impact cratering below D˜1 m, due to Mars' atmosphere. Unlike lunar regolith, martian regolith has been affected, and fines removed, by many processes. Deflation may have been a factor in leaving widespread boulder fields and associated dune fields, observed by the first three landers. Ancient regolith provided a porous medium for water storage, subsurface transport, and massive permafrost formation. Older regolith was probably cemented by evaporites and permafrost, may contain interbedded sediments and lavas, and may have been brecciated by later impacts. Growing evidence suggests recent water mobility, and the existence of duricrust at Viking and Pathfinder sites demonstrates the cementing process. These results affect lander/rover searches for intact ancient deposits. The upper tens of meters of exposed Noachian units cannot survive today in a pristine state. Intact Noachian deposits might best be found in cliffside strata, or in recently exhumed regions. The hematite-rich areas found in Terra Meridiani by the Mars Global Surveyor are probably examples of the

  16. The impact crater as a habitat: effects of impact processing of target materials.

    PubMed

    Cockell, Charles S; Osinski, Gordon R; Lee, Pascal

    2003-01-01

    Impact structures are a rare habitat on Earth. However, where they do occur they can potentially have an important influence on the local ecology. Some of the types of habitat created in the immediate post-impact environment are not specific to the impact phenomenon, such as hydrothermal systems and crater lakes that can be found, for instance, in post-volcanic environments, albeit with different thermal characteristics than those associated with impact. However, some of the habitats created are specifically linked to processes of impact processing. Two examples of how impact processing of target materials has created novel habitats that improve the opportunities for colonization are found in the Haughton impact structure in the Canadian High Arctic. Impact-shocked rocks have become a habitat for endolithic microorganisms, and large, impact-shattered blocks of rock are used as resting sites by avifauna. However, some materials produced by an impact, such as melt sheet rocks, can make craters more biologically depauperate than the area surrounding them. Although there are no recent craters with which to study immediate post-impact colonization, these data yield insights into generalized mechanisms of how impact processing can influence post-impact succession. Because impact events are one of a number of processes that can bring localized destruction to ecosystems, understanding the manner in which impact structures are recolonized is of ecological interest. Impact craters are a universal phenomenon on solid planetary surfaces, and so they are of potential biological relevance on other planetary surfaces, particularly Mars.

  17. The impact crater as a habitat: effects of impact processing of target materials

    NASA Technical Reports Server (NTRS)

    Cockell, Charles S.; Osinski, Gordon R.; Lee, Pascal

    2003-01-01

    Impact structures are a rare habitat on Earth. However, where they do occur they can potentially have an important influence on the local ecology. Some of the types of habitat created in the immediate post-impact environment are not specific to the impact phenomenon, such as hydrothermal systems and crater lakes that can be found, for instance, in post-volcanic environments, albeit with different thermal characteristics than those associated with impact. However, some of the habitats created are specifically linked to processes of impact processing. Two examples of how impact processing of target materials has created novel habitats that improve the opportunities for colonization are found in the Haughton impact structure in the Canadian High Arctic. Impact-shocked rocks have become a habitat for endolithic microorganisms, and large, impact-shattered blocks of rock are used as resting sites by avifauna. However, some materials produced by an impact, such as melt sheet rocks, can make craters more biologically depauperate than the area surrounding them. Although there are no recent craters with which to study immediate post-impact colonization, these data yield insights into generalized mechanisms of how impact processing can influence post-impact succession. Because impact events are one of a number of processes that can bring localized destruction to ecosystems, understanding the manner in which impact structures are recolonized is of ecological interest. Impact craters are a universal phenomenon on solid planetary surfaces, and so they are of potential biological relevance on other planetary surfaces, particularly Mars.

  18. The role of impact cratering for Mars sample return

    NASA Technical Reports Server (NTRS)

    Schultz, P. H.

    1988-01-01

    The preserved cratering record of Mars indicates that impacts play an important role in deciphering Martian geologic history, whether as a mechanism to modify the lithosphere and atmosphere or as a tool to sample the planet. The various roles of impact cratering in adding a broader understanding of Mars through returned samples are examined. Five broad roles include impact craters as: (1) a process in response to a different planetary localizer environment; (2) a probe for excavating crustal/mantle materials; (3) a possible localizer of magmatic and hydrothermal processes; (4) a chronicle of changes in the volcanic, sedimentary, atmospheric, and cosmic flux history; and (5) a chronometer for extending the geologic time scale to unsampled regions. The evidence for Earth-like processes and very nonlunar styles of volcanism and tectonism may shift the emphasis of a sampling strategy away from equally fundamental issues including crustal composition, unit ages, and climate history. Impact cratering not only played an important active role in the early Martian geologic history, it also provides an important tool for addressing such issues.

  19. Centrifuge impact cratering experiments: Scaling laws for non-porous targets

    NASA Technical Reports Server (NTRS)

    Schmidt, Robert M.

    1987-01-01

    A geotechnical centrifuge was used to investigate large body impacts onto planetary surfaces. At elevated gravity, it is possible to match various dimensionless similarity parameters which were shown to govern large scale impacts. Observations of crater growth and target flow fields have provided detailed and critical tests of a complete and unified scaling theory for impact cratering. Scaling estimates were determined for nonporous targets. Scaling estimates for large scale cratering in rock proposed previously by others have assumed that the crater radius is proportional to powers of the impactor energy and gravity, with no additional dependence on impact velocity. The size scaling laws determined from ongoing centrifuge experiments differ from earlier ones in three respects. First, a distinct dependence of impact velocity is recognized, even for constant impactor energy. Second, the present energy exponent for low porosity targets, like competent rock, is lower than earlier estimates. Third, the gravity exponent is recognized here as being related to both the energy and the velocity exponents.

  20. Cometary Dust Characteristics: Comparison of Stardust Craters with Laboratory Impacts

    NASA Technical Reports Server (NTRS)

    Kearsley, A. T.; Burchell, M. J.; Graham, G. A.; Horz, F.; Wozniakiewicz, P. A.; Cole, M. J.

    2007-01-01

    Aluminium foils exposed to impact during the passage of the Stardust spacecraft through the coma of comet Wild 2 have preserved a record of a wide range of dust particle sizes. The encounter velocity and dust incidence direction are well constrained and can be simulated by laboratory shots. A crater size calibration programme based upon buckshot firings of tightly constrained sizes (monodispersive) of glass, polymer and metal beads has yielded a suite of scaling factors for interpretation of the original impacting grain dimensions. We have now extended our study to include recognition of particle density for better matching of crater to impactor diameter. A novel application of stereometric crater shape measurement, using paired scanning electron microscope (SEM) images has shown that impactors of differing density yield different crater depth/diameter ratios. Comparison of the three-dimensional gross morphology of our experimental craters with those from Stardust reveals that most of the larger Stardust impacts were produced by grains of low internal porosity.

  1. Enhancing Magnetic Interpretation Towards Meteorite Impact Crater at Bukit Bunuh, Perak, Malaysia

    NASA Astrophysics Data System (ADS)

    Nur Amalina, M. K. A.; Nordiana, M. M.; Saad, Rosli; Saidin, Mokhtar

    2017-04-01

    Bukit Bunuh is the most popular area of suspected meteorite impact crater. In the history of meteorite impact hitting the earth, Bukit Bunuh has complex crater of a rebound zone of positive magnetic anomaly value. This study area was located at Lenggong, Perak of peninsular Malaysia. The crater rim extended 5 km outwards with a clear subdued zone and immediately surround by a positive magnetic residual crater rim zone. A recent study was done to enhance the magnetic interpretation towards meteorite impact crater on this study area. The result obtained is being correlated with boreholes data to determine the range of local magnetic value. For the magnetic survey, the equipment used is Geometric G-856 Proton Precision magnetometers with the aids of other tools such as compass and GPS. In advance, the using of proton precision magnetometer causes it able in measures the magnetic fields separately within interval of second. Also, 18 boreholes are accumulated at study area to enhance the interpretation. The additional boreholes data had successfully described the structure of the impact crater at Bukit Bunuh in detailed where it is an eroded impact crater. Correlations with borehole records enlighten the results acquired from magnetic methods to be more reliable. A better insight of magnetic interpretation of Bukit Bunuh impact crater was done with the aid of geotechnical methods.

  2. The missing large impact craters on Ceres

    PubMed Central

    Marchi, S.; Ermakov, A. I.; Raymond, C. A.; Fu, R. R.; O'Brien, D. P.; Bland, M. T.; Ammannito, E.; De Sanctis, M. C.; Bowling, T.; Schenk, P.; Scully, J. E. C.; Buczkowski, D. L.; Williams, D. A.; Hiesinger, H.; Russell, C. T.

    2016-01-01

    Asteroids provide fundamental clues to the formation and evolution of planetesimals. Collisional models based on the depletion of the primordial main belt of asteroids predict 10–15 craters >400 km should have formed on Ceres, the largest object between Mars and Jupiter, over the last 4.55 Gyr. Likewise, an extrapolation from the asteroid Vesta would require at least 6–7 such basins. However, Ceres' surface appears devoid of impact craters >∼280 km. Here, we show a significant depletion of cerean craters down to 100–150 km in diameter. The overall scarcity of recognizable large craters is incompatible with collisional models, even in the case of a late implantation of Ceres in the main belt, a possibility raised by the presence of ammoniated phyllosilicates. Our results indicate that a significant population of large craters has been obliterated, implying that long-wavelength topography viscously relaxed or that Ceres experienced protracted widespread resurfacing. PMID:27459197

  3. The missing large impact craters on Ceres.

    PubMed

    Marchi, S; Ermakov, A I; Raymond, C A; Fu, R R; O'Brien, D P; Bland, M T; Ammannito, E; De Sanctis, M C; Bowling, T; Schenk, P; Scully, J E C; Buczkowski, D L; Williams, D A; Hiesinger, H; Russell, C T

    2016-07-26

    Asteroids provide fundamental clues to the formation and evolution of planetesimals. Collisional models based on the depletion of the primordial main belt of asteroids predict 10-15 craters >400 km should have formed on Ceres, the largest object between Mars and Jupiter, over the last 4.55 Gyr. Likewise, an extrapolation from the asteroid Vesta would require at least 6-7 such basins. However, Ceres' surface appears devoid of impact craters >∼280 km. Here, we show a significant depletion of cerean craters down to 100-150 km in diameter. The overall scarcity of recognizable large craters is incompatible with collisional models, even in the case of a late implantation of Ceres in the main belt, a possibility raised by the presence of ammoniated phyllosilicates. Our results indicate that a significant population of large craters has been obliterated, implying that long-wavelength topography viscously relaxed or that Ceres experienced protracted widespread resurfacing.

  4. The missing large impact craters on Ceres

    USGS Publications Warehouse

    Marchi, S.; Ermakov, A.; Raymond, C.A.; Fu, R.R.; O'Brien, D.P.; Bland, Michael T.; Ammannito, E.; De Sanctis, M.C.; Bowling, Tim; Schenk, P.; Scully, J.E.C.; Buczkowski, D.L.; Williams, D.A.; Hiesinger, H.; Russell, C.T.

    2016-01-01

    Asteroids provide fundamental clues to the formation and evolution of planetesimals. Collisional models based on the depletion of the primordial main belt of asteroids predict 10–15 craters >400 km should have formed on Ceres, the largest object between Mars and Jupiter, over the last 4.55 Gyr. Likewise, an extrapolation from the asteroid Vesta would require at least 6–7 such basins. However, Ceres’ surface appears devoid of impact craters >~280 km. Here, we show a significant depletion of cerean craters down to 100–150 km in diameter. The overall scarcity of recognizable large craters is incompatible with collisional models, even in the case of a late implantation of Ceres in the main belt, a possibility raised by the presence of ammoniated phyllosilicates. Our results indicate that a significant population of large craters has been obliterated, implying that long-wavelength topography viscously relaxed or that Ceres experienced protracted widespread resurfacing.

  5. Martian Impact Craters as Revealed by MGS and Odyssey

    NASA Technical Reports Server (NTRS)

    Barlow, N. G.

    2005-01-01

    A variety of ejecta and interior morphologies were revealed for martian impact craters by Viking imagery. Numerous studies have classified these ejecta and interior morphologies and looked at how these morphologies correlate with crater diameter, latitude, terrain, and elevation [1, 2, 3, 4]. Many of these features, particularly the layered (fluidized) ejecta morphologies and central pits, have been proposed to result when the crater formed in target material containing high concentrations of volatiles. The Catalog of Large Martian Impact Craters was originally derived from the Viking 1:2,000,000 photomosaics and contains information on 42,283 impact craters 5-km diameter distributed across the entire martian surface. The information in this Catalog has been used to study the distributions of craters displaying specific ejecta and interior morphologies in an attempt to understand the environmental conditions which give rise to these features and to estimate the areal and vertical extents of subsurface volatile reservoirs [4, 5]. The Catalog is currently undergoing revision utilizing Mars Global Surveyor (MGS) and Mars Odyssey data [6]. The higher resolution multispectral imagery is resulting in numerous revisions to the original classifications and the addition of new elemental, thermophysical, and topographic data is allowing new insights into the environmental conditions under which these features form. A few of the new results from analysis of data in the revised Catalog are discussed below.

  6. A Nine Kilometer Impact Crater and Its Central Peak

    NASA Image and Video Library

    2017-02-08

    found across the Martian surface. Each impact crater on Mars possesses a unique origin and composition, which makes the HiRISE team very interested in sampling as many of them as possible! Like the impact of a droplet into fluid, once an impact has occurred on the surface of Mars, an ejecta curtain forms immediately after, contributing to the raised rim visible at the top of the crater's walls. After the formation of the initial crater, if it is large enough, then a central peak appears as the surface rebounds. These central peaks can expose rocks that were previously deeply buried beneath the Martian surface. The blue and red colors in this enhanced-contrast image reflect the effects of post-impact sedimentation and weathering over time. http://photojournal.jpl.nasa.gov/catalog/PIA08395

  7. Geological Mapping of Impact Melt Deposits at Lunar Complex Craters: New Insights into Morphological Diversity, Distribution and the Cratering Process

    NASA Astrophysics Data System (ADS)

    Dhingra, D.; Head, J. W., III; Pieters, C. M.

    2014-12-01

    We have completed high resolution geological mapping of impact melt deposits at the young lunar complex craters (<1 billion years) Copernicus, Jackson and Tycho using data from recent missions. Crater floors being the largest repository of impact melt, we have mapped their morphological diversity expressed in terms of varied surface texture, albedo, character and occurrence of boulder units as well as relative differences in floor elevation. Examples of wall and rim impact melt units and their relation to floor units have also been mapped. Among the distinctive features of these impact melt deposits are: 1) Impact Melt Wave Fronts: These are extensive (sometimes several kilometers in length) and we have documented their occurrence and distribution in different parts of the crater floor at Jackson and Tycho. These features emphasize melt mobility and style of emplacement during the modification stage of the craters. 2) Variations in Floor Elevations: Spatially extensive and coherent sections of crater floors have different elevations at all the three craters. The observed elevation differences could be caused by subsidence due to cooling of melt and/or structural failure, together with a contribution from regional slope. 3) Melt-Covered Megablocks: We also observe large blocks/rock-fragments (megablocks) covered in impact melt, which could be sections of collapsed wall or in some cases, subdued sections of central peaks. 4) Melt-Covered Central Peaks: Impact melt has also been mapped on the central peaks but varies in spatial extent among the craters. The presence of melt on peaks must be taken into account when interpreting peak mineralogy as exposures of deeper crust. 5) Boulder Distribution: Interesting trends are observed in the distribution of boulder units of various sizes; some impact melt units have spatially extensive boulders, while boulder distribution is very scarce in other units on the floor. We interpret these distributions to be influenced by a) the

  8. Geomechanical models of impact cratering: Puchezh-Katunki structure

    NASA Technical Reports Server (NTRS)

    Ivanov, B. A.

    1992-01-01

    Impact cratering is a complex natural phenomenon that involves various physical and mechanical processes. Simulating these processes may be improved using the data obtained during the deep drilling at the central mound of the Puchezh-Katunki impact structure. A research deep drillhole (named Vorotilovskaya) has been drilled in the Puchezh-Katunki impact structure (European Russia, 57 deg 06 min N, 43 deg 35 min E). The age of the structure is estimated at about 180 to 200 m.y. The initial rim crater diameter is estimated at about 40 km. The central uplift is composed of large blocks of crystalline basement rocks. Preliminary study of the core shows that crystalline rocks are shock metamorphosed by shock pressure from 45 GPa near the surface to 15-20 GPa at a depth of about 5 km. The drill core allows the possibility of investigating many previously poorly studied cratering processes in the central part of the impact structure. As a first step one can use the estimates of energy for the homogeneous rock target. The diameter of the crater rim may be estimated as 40 km. The models elaborated earlier show that such a crater may be formed after collapse of a transient cavity with a radius of 10 km. The most probable range of impact velocities from 11.2 to 30 km/s may be inferred for the asteroidal impactor. For the density of a projectile of 2 g/cu cm the energy of the impact is estimated as 1E28 to 3E28 erg. In the case of vertical impact, the diameter of an asteroidal projectile is from 1.5 to 3 km for the velocity range from 11 to 30 km/s. For the most probable impact angle of 45 deg, the estimated diameter of an asteroid is slightly larger: from 2 to 4 km. Numerical simulation of the transient crater collapse has been done using several models of rock rheology during collapse. Results show that the column at the final position beneath the central mound is about 5 km in length. This value is close to the shock-pressure decay observed along the drill core. Further

  9. GT-57633 catalogue of Martian impact craters developed for evaluation of crater detection algorithms

    NASA Astrophysics Data System (ADS)

    Salamunićcar, Goran; Lončarić, Sven

    2008-12-01

    Crater detection algorithms (CDAs) are an important subject of the recent scientific research. A ground truth (GT) catalogue, which contains the locations and sizes of known craters, is important for the evaluation of CDAs in a wide range of CDA applications. Unfortunately, previous catalogues of craters by other authors cannot be easily used as GT. In this paper, we propose a method for integration of several existing catalogues to obtain a new craters catalogue. The methods developed and used during this work on the GT catalogue are: (1) initial screening of used catalogues; (2) evaluation of self-consistency of used catalogues; (3) initial registration from three different catalogues; (4) cross-evaluation of used catalogues; (5) additional registrations and registrations from additional catalogues; and (6) fine-tuning and registration with additional data-sets. During this process, all craters from all major currently available manually assembled catalogues were processed, including catalogues by Barlow, Rodionova, Boyce, Kuzmin, and our previous work. Each crater from the GT catalogue contains references to crater(s) that are used for its registration. This provides direct access to all properties assigned to craters from the used catalogues, which can be of interest even to those scientists that are not directly interested in CDAs. Having all these craters in a single catalogue also provides a good starting point for searching for craters still not catalogued manually, which is also expected to be one of the challenges of CDAs. The resulting new GT catalogue contains 57,633 craters, significantly more than any previous catalogue. From this point of view, GT-57633 catalogue is currently the most complete catalogue of large Martian impact craters. Additionally, each crater from the resulting GT-57633 catalogue is aligned with MOLA topography and, during the final review phase, additionally registered/aligned with 1/256° THEMIS-DIR, 1/256° MDIM and 1/256° MOC

  10. The Interaction of Impact Melt, Impact-Derived Sediment, and Volatiles at Crater Tooting, Mars

    NASA Technical Reports Server (NTRS)

    Mouginis-Mark, P.; Boyce, J.

    2010-01-01

    We are producing a 1:200K geologic map of Tooting crater, Mars. This work has shown that an incredible amount of information can be gleaned from mapping at even larger scales (1:10K 1:25K) using CTX and HiRISE data. We have produced two new science papers (Morris et al., 2010; Mouginis-Mark and Boyce, 2010) from this mapping, and additional science questions continue to arise from our on-going analysis of Tooting crater: 1) What was the interplay of impact melt and volatile-rich sediments that, presumably, were created during the impact? Kieffer and Simonds [1980] predicted that melt would have been destroyed during impacts on Mars because of the volatiles present within the target we seek to understand if this is indeed the case at Tooting crater. We have identified pitted and fractured terrain that formed during crater modification, but the timing of the formation of these materials in different parts of the crater remains to be resolved. Stratigraphic relationships between these units and the central peak may reveal deformation features as well as overlapping relationships. 2) Morris et al. [2010] identified several lobate flows on the inner and outer walls of Tooting crater. It is not yet clear what the physical characteristics of the source areas of these flows really are; e.g., what are the sizes of the source areas, what elevations are they located at relative to the floor of the crater, are they interconnected, and are they on horizontal or tilted surfaces? 3) What were the details of dewatering of the inner wall of Tooting crater (Fig. 1)? We find evidence within Tooting crater of channels carved by water release, and the remobilization of sediment (which is inferred to have formed during the impact event). Sapping can be identified along the crest of unit 8 near the floor of the crater (Fig. 2a, 2b). This unit displays amphitheater-headed canyons that elsewhere on Mars are typically attributed to water leaking from the substrate [Laity and Malin, 1985

  11. Vesta Surface at High Resolution: Dominated by Impact Craters

    NASA Image and Video Library

    2012-02-13

    This image from NASA Dawn spacecraft shows a large number of craters, formed by collisions into the surface of asteroid Vesta. The relatively large circular depressions in this image are older, heavily degraded impact craters.

  12. Carbonate-silicate liquid immiscibility upon impact melting, Ries Crater, Germany

    NASA Astrophysics Data System (ADS)

    Graup, Guenther

    1999-05-01

    The 24-km-diameter Ries impact crater in southern Germany is one of the most studied impact structures on Earth. The Ries impactor struck a Triassic to Upper Jurassic sedimentary sequence overlying Hercynian crystalline basement. At the time of impact (14.87 +/- 0.36 Ma; Storzer et al., 1995), the 350 m thick Malm limestone was present only to the S and E of the impact site. To the N and W, the Malm had been eroded away, exposing the underlying Dogger and Lias. The largest proportion of shocked target material is in the impact melt-bearing breccia suevite. The suevite had been believed to be derived entirely from the crystalline basement. Calcite in the suevite has been interpreted as a post-impact hydrothermal deposit. From optical inspection of 540 thin sections of suevite from 32 sites, I find that calcite in the suevite shows textural evidence of liquid immiscibility with the silicate impact melt. Textural evidence of liquid immiscibility between silicate and carbonate melt in the Ries suevite includes: carbonate globules within silicate glass, silicate globules embedded in carbonate, deformable and coalescing carbonate spheres within silicate glass, sharp menisci or cusps and budding between silicate and carbonate melt, fluidal textures and gas vesicles in carbonate schlieren, a quench crystallization sequence of the carbonate, spinifex textured quenched carbonate, separate carbonate spherules in the suevite mineral-fragment-matrix, and inclusions of mineral fragments suspended in carbonate blebs. Given this evidence of liquid immiscibility, the carbonate in the suevite has, therefore, like the silicate melt a primary origin by impact shock melting. Evidence of carbonate-silicate liquid immiscibility is abundant in the suevites to the SW to E of the Ries crater. The rarer suevites to the W to NE of the crater are nearly devoid of carbonate melts. This correspondence between the occurrence of outcropping limestones at the target surface and the formation of

  13. Some implications of large impact craters and basins on Venus for terrestrial ringed craters and planetary evolution

    NASA Technical Reports Server (NTRS)

    Mckinnon, W. B.; Alexopoulos, J. S.

    1994-01-01

    Approximately 950 impact craters have been identified on the surface of Venus, mainly in Magellan radar images. From a combination of Earth-based Arecibo, Venera 15/1, and Magellan radar images, we have interpreted 72 as unequivocal peak-ring craters and four as multiringed basins. The morphological and structural preservation of these craters is high owing to the low level of geologic activity on the venusian surface (which is in some ways similar to the terrestrial benthic environment). Thus these craters should prove crucial to understanding the mechanics of ringed crater formation. They are also the most direct analogs for craters formed on the Earth in Phanerozoic time, such as Chicxulub. We summarize our findings to date concerning these structures.

  14. Thickness of a Europan ice shell from impact crater simulations.

    PubMed

    Turtle, E P; Pierazzo, E

    2001-11-09

    Several impact craters on Jupiter's satellite Europa exhibit central peaks. On the terrestrial planets, central peaks consist of fractured but competent rock uplifted during cratering. Therefore, the observation of central peaks on Europa indicates that an ice layer must be sufficiently thick that the impact events did not completely penetrate it. We conducted numerical simulations of vapor and melt production during cratering of water ice layers overlying liquid water to estimate the thickness of Europa's icy crust. Because impacts disrupt material well beyond the zone of partial melting, our simulations put a lower limit on ice thickness at the locations and times of impact. We conclude that the ice must be more than 3 to 4 kilometers thick.

  15. Block Distribution Analysis of Impact Craters in the Tharsis and Elysium Planitia Regions on Mars

    NASA Astrophysics Data System (ADS)

    Button, N.; Karunatillake, S.; Diaz, C.; Zadei, S.; Rajora, V.; Barbato, A.; Piorkowski, M.

    2017-12-01

    The block distribution pattern of ejecta surrounding impact craters reveals clues about their formation. Using images from High Resolution Imaging Science Experiment (HiRISE) image onboard the Mars Reconnaissance Orbiter (MRO), we indentified two rayed impact craters on Mars with measurable ejecta fields to quantitatively investigate in this study. Impact Crater 1 (HiRISE image PSP_008011_1975) is located in the Tharsis region at 17.41°N, 248.75°E and is 175 m in diameter. Impact Crater 2 (HiRISE image ESP_018352_1805) is located in Elysium Planitia at 0.51°N, 163.14°E and is 320 m in diameter. Our block measurements, used to determine the area, were conducted using HiView. Employing methods similar to Krishna and Kumar (2016), we compared block size and axis ratio to block distance from the center of the crater, impact angle, and direction. Preliminary analysis of sixteen radial sectors around Impact Crater 1 revealed that in sectors containing mostly small blocks (less than 10 m2), the small blocks were ejected up to three times the diameter of the crater from the center of the crater. These small block-dominated sectors lacked blocks larger than 10 m2. Contrastingly, in large block-dominated sectors (larger than 30 m2) blocks rarely traveled farther than 200 m from the center of the crater. We also seek to determine the impact angle and direction. Krishna and Kumar (2016) calculate the b-value (N(a) = Ca-b; "N(a) equals the number of fragments or craters with a size greater than a, C is a constant, and -b is a power index") as a method to determine the impact direction. Our preliminary results for Impact Crater 1 did not clearly indicate the impact angle. With improved measurements and the assessment of Impact Crater 2, we will compare Impact Crater 1 to Impact Crater 2 as well as assess the impact angle and direction in order to determine if the craters are secondary craters. Hood, D. and Karunatillake, S. (2017), LPSC, Abstract #2640 Krishna, N., and P. S

  16. Survival of refractory presolar grain analogs during Stardust-like impact into Al foils: Implications for Wild 2 presolar grain abundances and study of the cometary fine fraction

    NASA Astrophysics Data System (ADS)

    Croat, T. K.; Floss, C.; Haas, B. A.; Burchell, M. J.; Kearsley, A. T.

    2015-08-01

    We present results of FIB-TEM studies of 12 Stardust analog Al foil craters which were created by firing refractory Si and Ti carbide and nitride grains into Al foils at 6.05 km s-1 with a light-gas gun to simulate capture of cometary grains by the Stardust mission. These foils were prepared primarily to understand the low presolar grain abundances (both SiC and silicates) measured by SIMS in Stardust Al foil samples. Our results demonstrate the intact survival of submicron SiC, TiC, TiN, and less-refractory Si3N4 grains. In small (<2 μm) craters that are formed by single grain impacts, the entire impacting crystalline grain is often preserved intact with minimal modification. While they also survive in crystalline form, grains at the bottom of larger craters (>5 μm) are typically fragmented and are somewhat flattened in the direction of impact due to partial melting and/or plastic deformation. The low presolar grain abundance estimates derived from SIMS measurements of large craters (mostly >50 μm) likely result from greater modification of these impactors (i.e., melting and isotopic dilution), due to higher peak temperatures/pressures in these crater impacts. The better survivability of grains in smaller craters suggests that more accurate presolar grain estimates may be achievable through measurement of such craters. It also suggests small craters can provide a complementary method of study of the Wild 2 fine fraction, especially for refractory CAI-like minerals.

  17. Large craters on the meteoroid and space debris impact experiment

    NASA Technical Reports Server (NTRS)

    Humes, Donald H.

    1991-01-01

    The distribution around the Long Duration Exposure Facility (LDEF) of 532 large craters in the Al plates from the Meteoroid and Space Debris Impact Experiment (S0001) is discussed along with 74 additional large craters in Al plates donated to the Meteoroid and Debris Special Investigation Group by other LDEF experimenters. The craters are 0.5 mm in diameter and larger. Crater shape is discussed. The number of craters and their distribution around the spacecraft are compared with values predicted with models of the meteoroid environment and the manmade orbital debris environment.

  18. Scientific Drilling of Impact Craters - Well Logging and Core Analyses Using Magnetic Methods (Invited)

    NASA Astrophysics Data System (ADS)

    Fucugauchi, J. U.; Perez-Cruz, L. L.; Velasco-Villarreal, M.

    2013-12-01

    Drilling projects of impact structures provide data on the structure and stratigraphy of target, impact and post-impact lithologies, providing insight on the impact dynamics and cratering. Studies have successfully included magnetic well logging and analyses in core and cuttings, directed to characterize the subsurface stratigraphy and structure at depth. There are 170-180 impact craters documented in the terrestrial record, which is a small proportion compared to expectations derived from what is observed on the Moon, Mars and other bodies of the solar system. Knowledge of the internal 3-D deep structure of craters, critical for understanding impacts and crater formation, can best be studied by geophysics and drilling. On Earth, few craters have yet been investigated by drilling. Craters have been drilled as part of industry surveys and/or academic projects, including notably Chicxulub, Sudbury, Ries, Vredefort, Manson and many other craters. As part of the Continental ICDP program, drilling projects have been conducted on the Chicxulub, Bosumtwi, Chesapeake, Ries and El gygytgyn craters. Inclusion of continuous core recovery expanded the range of paleomagnetic and rock magnetic applications, with direct core laboratory measurements, which are part of the tools available in the ocean and continental drilling programs. Drilling studies are here briefly reviewed, with emphasis on the Chicxulub crater formed by an asteroid impact 66 Ma ago at the Cretaceous/Paleogene boundary. Chicxulub crater has no surface expression, covered by a kilometer of Cenozoic sediments, thus making drilling an essential tool. As part of our studies we have drilled eleven wells with continuous core recovery. Magnetic susceptibility logging, magnetostratigraphic, rock magnetic and fabric studies have been carried out and results used for lateral correlation, dating, formation evaluation, azimuthal core orientation and physical property contrasts. Contributions of magnetic studies on impact

  19. Impact and cratering rates onto Pluto

    NASA Astrophysics Data System (ADS)

    Greenstreet, Sarah; Gladman, Brett; McKinnon, William B.

    2015-09-01

    The New Horizons spacecraft fly-through of the Pluto system in July 2015 will provide humanity's first data for the crater populations on Pluto and its binary companion, Charon. In principle, these surfaces could be dated in an absolute sense, using the observed surface crater density (# craters/km2 larger than some threshold crater diameter D). Success, however, requires an understanding of both the cratering physics and absolute impactor flux. The Canada-France Ecliptic Plane Survey (CFEPS) L7 synthetic model of classical and resonant Kuiper belt populations (Petit, J.M. et al. [2011]. Astron. J. 142, 131-155; Gladman, B. et al. [2012]. Astron. J. 144, 23-47) and the scattering object model of Kaib et al. (Kaib, N., Roškar, R., Quinn, T. [2011]. Icarus 215, 491-507) calibrated by Shankman et al. (Shankman, C. et al. [2013]. Astrophys. J. 764, L2-L5) provide such impact fluxes and thus current primary cratering rates for each dynamical sub-population. We find that four sub-populations (the q < 42AU hot and stirred main classicals, the classical outers, and the plutinos) dominate Pluto's impact flux, each providing ≈ 15- 25 % of the total rate. Due to the uncertainty in how the well-characterized size distribution for Kuiper belt objects (with impactor diameter d > 100km) connects to smaller projectiles, we compute cratering rates using five model impactor size distributions: a single power-law, a power-law with a knee, a power-law with a divot, as well as the "wavy" size distributions described in Minton et al. (Minton, D.A. et al. [2012]. Asteroids Comets Meteors Conf. 1667, 6348) and Schlichting et al. (Schlichting, H.E., Fuentes, C.I., Trilling, D.E. [2013]. Astron. J. 146, 36-42). We find that there is only a small chance that Pluto has been hit in the past 4 Gyr by even one impactor with a diameter larger than the known break in the projectile size distribution (d ≈ 100km) which would create a basin on Pluto (D ⩾ 400km in diameter). We show that due to

  20. Tektite-like bodies at Lonar Crater, India - Implications for the origin of tektites

    NASA Technical Reports Server (NTRS)

    Murali, A. V.; Zolensky, M. E.; Blanchard, D. P.

    1987-01-01

    Homogeneous dense glass bodies (both irregular and splash form) with high silica contents (about 67 pct SiO2) occur in the vicinity of Lonar Crater, India. Their lack of microlites and mineral remnants and their uniform chemical composition virtually preclude a volcanic origin. They are similar to tektites reported in the literature. While such a close association of tektite-like bodies with impact craters is already known (Aouelloul Crater, Mauritania; Zhamanshin Crater, U.S.S.R.), the tektite-like bodies at Lonar Crater are unique in that they occur in an essentially basaltic terrain. Present geochemical data are consistent with these high silica glass bodies being impact melt products of two-thirds basalt and one-third local intertrappean sediment (chert). The tektite-like bodies of the impact craters Lonar, Zhamanshin, and Aouelloul are generally similar. Strong terrestrial geochemical signatures reflect the target rock REE patterns and abundance ratios and demonstrate their terrestrial origin resulting from meteorite impact, as has been suggested by earlier workers.

  1. Coupled effects of impact and orogeny: Is the marine Lockne crater, Sweden, pristine?

    NASA Astrophysics Data System (ADS)

    Kenkmann, T.; Kiebach, F.; Rosenau, M.; Raschke, U.; Pigowske, A.; Mittelhaus, K.; Eue, D.

    Our current understanding of marine-impact cratering processes is partly inferred from the geological structure of the Lockne crater. We present results of a mapping campaign and structural data indicating that this crater is not pristine. In the western part of the crater, pre-impact, impact, and post-impact rocks are incorporated in Caledonian thrust slices and are subjected to folding and faulting. A nappe outlier in the central crater depression is a relic of the Caledonian nappe cover that reached a thickness of more than 5 km. The overthrusted crater is gently deformed. Strike of strata and trend of fold axes deviate from standard Caledonian directions (northeast-southwest). Radially oriented crater depressions, which were previously regarded as marine resurge gullies formed when resurging seawater erosively cut through the crater brim, are interpreted to be open synclines in which resurge deposits were better preserved.The presence of the impact structure influenced orogenesis due to morphological and lithological anomalies of the crater: i) a raised crater brim zone acted as an obstacle during nappe propagation, (ii) the occurrence of a central crater depression caused downward sagging of nappes, and (iii) the lack of an appropriate detachment horizon (alum shale) within the crater led to an enhanced mechanical coupling and internal deformation of the nappe and the overthrusted foreland. Preliminary results of 3-D-analogue experiments suggest that a circular high-friction zone representing the crater locally hinders nappe propagation and initiates a circumferentially striking ramp fault that delineates the crater. Crustal shortening is also partitioned into the crater basement and decreases laterally outward. Deformation of the foreland affected the geometry of the detachment and could be associated with the activation of a deeper detachment horizon beneath the crater. Strain gradients both vertically and horizontally result in non-plane strain deformation

  2. Impact craters on Venus: An overview from Magellan observations

    NASA Technical Reports Server (NTRS)

    Schaber, G. G.; Strom, R. G.; Moore, H. J.; Soderblom, L. A.; Kirk, R. L.; Chadwick, D. J.; Dawson, D. D.; Gaddis, L. R.; Boyce, J. M.; Russell, J.

    1992-01-01

    Magellan has revealed an ensemble of impact craters on Venus that is unique in many important ways. We have compiled a database describing 842 craters on 89 percent of the planet's surface mapped through orbit 2578 (the craters range in diameter from 1.5 to 280 km). We have studied the distribution, size-frequency, morphology, and geology of these craters both in aggregate and, for some craters, in more detail. We have found the following: (1) the spatial distribution of craters is highly uniform; (2) the size-density distribution of craters with diameters greater than or equal to 35 km is consistent with a 'production' population having a surprisingly young age of about 0.5 Ga (based on the estimated population of Venus-crossing asteroids); (3) the spectrum of crater modification differs greatly from that on other planets--62 percent of all craters are pristine, only 4 percent volcanically embayed, and the remainder affected by tectonism, but none are severely and progressively depleted based on size-density distribution extrapolated from larger craters; (4) large craters have a progression of morphologies generally similar to those on other planets, but small craters are typically irregular or multiple rather than bowl shaped; (5) diffuse radar-bright or -dark features surround some craters, and about 370 similar diffuse 'splotches' with no central crater are observed whose size-density distribution is similar to that of small craters; and (6) other features unique to Venus include radar-bright or -dark parabolic arcs opening westward and extensive outflows originating in crater ejecta.

  3. Polygonal Impact Craters on selected Minor Bodies: Rhea, Dione, Tethys, Ceres, and Vesta

    NASA Astrophysics Data System (ADS)

    Neidhart, Tanja; Leitner, Johannes; Firneis, Maria

    2017-04-01

    A polygonal impact crater (PIC) is a crater that does not have a full circular shape in plane view but consists of straight crater rim segments. PICs are common on all objects in our solar system that show a cratered surface. Previous studies showed that PICs make up about 10-25% of craters on Mercury, Venus, Mars, and the Moon [1, 2, 3, 4]. Although there have been several studies on PICs on the terrestrial planets, and the Moon there are only very few investigations on PICs on minor bodies, even though there exist surface maps of Rhea, Tethys, Dione, Ceres, and Vesta that have an appropriate resolution. The aim of this study is to get more information about the abundance and characteristics of PICs on these objects. We analysed all approved craters on Rhea, Dione, Tethys, Ceres, and Vesta using images provided by the IAU/NASA/USGS Planetary Database [5]. For the classification of PICs the definition by [2] was used which states that a crater is polygonal if it consists of at least two straight crater rim segments having a discernable angle. In total 417 impact craters were examined and 227 of them were classified as polygonal. On Rhea about 48% of the approved craters are PICs, on Dione 59%, on Tethys 34%, on Ceres 74%, and on Vesta 56%. The comparison with studies on PICs on terrestrial planets, and the Moon conducted by [1, 2, 3, 4] showed that the percentage of PICs found in this study is much higher. Most of the PICs have two or three straight rim segments and only few PICs are hexagonal or pentagonal. The mean angle between the straight rims yields 121° for Rhea, 124° for Dione, 123° for Tethys, 133° for Ceres, and 134° for Vesta. These angles are well in accordance to an average angle of 112° on Mercury [1]. Also the size distribution of PICs is in accordance to results by [4] who proved that PICs seem to favor small to middle size diameters. The largest diameters of non-polygonal craters on Vesta range from 0.6 km to 450 km while the diameters of

  4. Geologic Mapping of the Martian Impact Crater Tooting

    NASA Technical Reports Server (NTRS)

    Mouginis-Mark, Peter; Boyce, Joseph M.

    2008-01-01

    Tooting crater is approximately 29 km in diameters, is located at 23.4 deg N, 207.5 deg E and is classified as a multi-layered ejecta crater. Tooting crater is a very young crater, with an estimated age of 700,000 to 2M years. The crater formed on virtually flat lava flows within Amazonis Planitia where there appears to have been no major topographic features prior to the impact, so that we can measure ejecta thickness and cavity volume. In the past 12 months, the authors have: published their first detailed analysis of the geometry of the crater cavity and the distribution of the ejecta layers; refined the geologic map of the interior of Tooting crater through mapping of the cavity at a scale of 1:1100K; and continued the analysis of an increasing number of high resolution images obtained by the CTX and HiRISE instruments. Currently the authors seek to resolve several science issues that have been identified during this mapping, including: what is the origin of the lobate flows on the NW and SW rims of the crater?; how did the ejecta curtain break apart during the formation of the crater, and how uniform was the emplacement process for the ejecta layers; and, can we infer physical characteristics about the ejecta? Future study plans include the completion of a draft geologic map of Tooting crater and submission of it to the U.S. Geological survey for a preliminary review, publishing a second research paper on the detailed geology of the crater cavity and the distribution of the flows on the crater rim, and completing the map text for the 1:100K geologic map description of units at Tooting crater.

  5. Impact Craters on Mars: Natural 3D Exploration Probes of Geological Evolution

    NASA Technical Reports Server (NTRS)

    Garvin, James B.

    2005-01-01

    Introduction: The population of impact craters preserved on the surface of Mars offers fundamental constraints on the three- dimensional mechanical characteristics of the martian crust, its volatile abundance, and on the styles of erosion that have operated during essentially all epochs of martian geological history. On the basis of the present- day wealth of morphologic and geometric observations of impact landforms on Mars [ 1-31, an emerging understanding of the three-dimensional physical properties of the martian uppermost crust in space and time is at hand. In this summary, the current basis of understanding of the relatively non- degraded population of impact landforms on Mars is reviewed, and new Mars Global Surveyor (MGS)-based (MOLA) measurements of global geometric properties are summarized in the context of upcoming observations by Mars Reconnaissance Orbiter (MRO).

  6. Reading the Magnetic Patterns in Earth complex impact craters to detect similarities and cues from some Nectarian craters of the Moon

    NASA Astrophysics Data System (ADS)

    Isac, Anca; Mandea, Mioara; Purucker, Michael

    2013-04-01

    Most of the terrestrial impact craters have been obliterated by other terrestrial geological processes. Some examples however remain. Among them, complex craters such as Chicxculub, Vredefort, or the outsider Bangui structure (proposed but still unconfirmed as a result of an early Precambrian large impact) exert in the total magnetic field anomaly global map (WDMAM-B) circular shapes with positive anomalies which may suggest the circularity of a multiring structure. A similar pattern is observed from the newest available data (global spherical model of the internal magnetic field by Purucker and Nicolas, 2010) for some Nectarian basins as Moscovienese, Mendel-Rydberg or Crissium. As in the case of Earth's impacts, the positive anomalies appear near the basin center and inside the first ring, this distribution being strongly connected with crater-forming event. Detailed analysis of largest impact craters from Earth and Moon --using a forward modeling approach by means of the Equivalent Source Dipole method--evaluates the shock impact demagnetization effects--a magnetic low--by reducing the thickness of the pre-magnetized lithosphere due to the excavation process (the impact crater being shaped as a paraboloid of revolution). The magnetic signature of representative early Nectarian craters, Crissium, as well as Earth's complex craters, defined by stronger magnetic fields near the basin center and/or inside the first ring, might be a consequence of the shock remanent magnetization of the central uplift plus a thermoremanent magnetization of the impact melt in a steady magnetizing field generated by a former active dynamo. In this case, ESD method is not able to obtain a close fit of the forward model to the observation altitude map or model.

  7. Numerical modeling of seismic anomalies at impact craters on a laboratory scale

    NASA Astrophysics Data System (ADS)

    Wuennemann, K.; Grosse, C. U.; Hiermaier, S.; Gueldemeister, N.; Moser, D.; Durr, N.

    2011-12-01

    Almost all terrestrial impact craters exhibit a typical geophysical signature. The usually observed circular negative gravity anomaly and reduced seismic velocities in the vicinity of crater structures are presumably related to an approximately hemispherical zone underneath craters where rocks have experienced intense brittle plastic deformation and fracturing during formation (see Fig.1). In the framework of the "MEMIN" (multidisciplinary experimental and modeling impact crater research network) project we carried out hypervelocity cratering experiments at the Fraunhofer Institute for High-Speed Dynamics on a decimeter scale to study the spatiotemporal evolution of the damage zone using ultrasound, acoustic emission techniques, and numerical modeling of crater formation. 2.5-10 mm iron projectiles were shot at 2-5.5 km/s on dry and water-saturated sandstone targets. The target material was characterized before, during and after the impact with high spatial resolution acoustic techniques to detect the extent of the damage zone, the state of rocks therein and to record the growth of cracks. The ultrasound measurements are applied analog to seismic surveys at natural craters but used on a different - i.e. much smaller - scale. We compare the measured data with dynamic models of crater formation, shock, plastic and elastic wave propagation, and tensile/shear failure of rocks in the impacted sandstone blocks. The presence of porosity and pore water significantly affects the propagation of waves. In particular the crushing of pores due to shock compression has to be taken into account. We present preliminary results showing good agreement between experiments and numerical model. In a next step we plan to use the numerical models to upscale the results from laboratory dimensions to the scale of natural impact craters.

  8. The Calvin impact crater and its associated oil production, Cass County, Michigan

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Milstein, R.L.

    1996-01-01

    The Calvin impact crater is an isolated, nearly circular subsurface structure of Late Ordovician age in southwestern Michigan. The crater is defined by 110 oil and gas test wells, has a diameter of 6.2 km, and consists of a central dome exhibiting 415 m of structural uplift, an annular depression, and an encircling anticlinal rim. Exploration and development of three Devonian oil fields associated wit this structure provide all available subsurface data. All oil production is from the Middle Devonian Traverse Limestone, with the exception of one well producing from the Middle Devonian Sylvania Sandstone. This study models the grossmore » morphology of the Calvin structure using multiple tools and compares the results to known impact craters. Combined results of reflection seismic, gravity, magnetic, and resistivity data, as well as organized relationships between stratigraphic displacement and structural diameters observed in complex impact craters, suggest the Calvin structure is morphologically similar to recognized complex impact craters in sedimentary targets. In addition, individual quartz grains recovered from the Calvin structure exhibit decorated shock lamellae, Boehm lamellae, rhombohederal cleavage, and radiating concussion fractures. Based on the available data, I conclude the Calvin structure is a buried complex impact crater and that the trapping and reservoir characteristics of the associated Calvin 20, Juno Lake, and Calvin 28 oil fields are resultant of the craters morphology.« less

  9. The Calvin impact crater and its associated oil production, Cass County, Michigan

    DOE Office of Scientific and Technical Information (OSTI.GOV)

    Milstein, R.L.

    1996-12-31

    The Calvin impact crater is an isolated, nearly circular subsurface structure of Late Ordovician age in southwestern Michigan. The crater is defined by 110 oil and gas test wells, has a diameter of 6.2 km, and consists of a central dome exhibiting 415 m of structural uplift, an annular depression, and an encircling anticlinal rim. Exploration and development of three Devonian oil fields associated wit this structure provide all available subsurface data. All oil production is from the Middle Devonian Traverse Limestone, with the exception of one well producing from the Middle Devonian Sylvania Sandstone. This study models the grossmore » morphology of the Calvin structure using multiple tools and compares the results to known impact craters. Combined results of reflection seismic, gravity, magnetic, and resistivity data, as well as organized relationships between stratigraphic displacement and structural diameters observed in complex impact craters, suggest the Calvin structure is morphologically similar to recognized complex impact craters in sedimentary targets. In addition, individual quartz grains recovered from the Calvin structure exhibit decorated shock lamellae, Boehm lamellae, rhombohederal cleavage, and radiating concussion fractures. Based on the available data, I conclude the Calvin structure is a buried complex impact crater and that the trapping and reservoir characteristics of the associated Calvin 20, Juno Lake, and Calvin 28 oil fields are resultant of the craters morphology.« less

  10. Mars Exploration Rover Field Observations of Impact Craters at Gusev Crater and Meridiani Planum and Implications for Climate Change

    NASA Technical Reports Server (NTRS)

    Golombek, M.; Grant, J. A.; Crumpler, L. S.

    2005-01-01

    The Mars Exploration Rovers have provided a field geologist's perspective of impact craters in various states of degradation along their traverses at Gusev crater and Meridiani Planum. This abstract will describe the craters observed and changes to the craters that constrain the erosion rates and the climate [l]. Changes to craters on the plains of Gusev argue for a dry and desiccating environment since the Late Hesperian in contrast to the wet and likely warm environment in the Late Noachian at Meridiani in which the sulfate evaporites were deposited in salt-water playas or sabkhas.

  11. Mapping Ejecta Thickness Around Small Lunar Craters

    NASA Astrophysics Data System (ADS)

    Brunner, A.; Robinson, M. S.

    2016-12-01

    Detailed knowledge of the distribution of ejecta around small ( 1 km) craters is still a key missing piece in our understanding of crater formation. McGetchin et al. [1] compiled data from lunar, terrestrial, and synthetic craters to generate a semi-empirical model of radial ejecta distribution. Despite the abundance of models, experiments, and previous field and remote sensing studies of this problem, images from the 0.5 m/pixel Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC) [2] provides the first chance to quantify the extent and thickness of ejecta around kilometer scale lunar craters. Impacts excavate fresh (brighter) material from below the more weathered (darker) surface, forming a relatively bright ejecta blanket. Over time space weathering tends to lower the reflectance of the ejected fresh material [3] resulting in the fading of albedo signatures around craters. Relatively small impacts that excavate through the high reflectance immature ejecta of larger fresh craters provide the means of estimating ejecta thickness. These subsequent impacts may excavate material from within the high reflectance ejecta layer or from beneath that layer to the lower-reflectance mature pre-impact surface. The reflectance of the ejecta around a subsequent impact allows us to categorize it as either an upper or lower limit on the ejecta thickness at that location. The excavation depth of each crater found in the ejecta blanket is approximated by assuming a depth-to-diameter relationship relevant for lunar simple craters [4, e.g.]. Preliminary results [Figure] show that this technique is valuable for finding the radially averaged profile of the ejecta thickness and that the data are roughly consistent with the McGetchin equation. However, data from craters with asymmetric ejecta blankets are harder to interpret. [1] McGetchin et al. (1973) Earth Planet. Sci. Lett., 20, 226-236. [2] Robinson et al. (2010) Space Sci. Rev., 150, 1-4, 81-124. [3] Denevi et al

  12. Impacts into Coarse-Grained Spheres at Moderate Impact Velocities: Implications for Cratering on Asteroids and Planets

    NASA Technical Reports Server (NTRS)

    Barnouin, Olivier S.; Daly, R. Terik; Cintala, Mark J.; Crawford, David A.

    2018-01-01

    The surfaces of many planets and asteroids contain coarsely fragmental material generated by impacts or other geologic processes. The presence of such pre-existing structures may affect subsequent impacts, particularly when the width of the shock is comparable to or smaller than the size of pre-existing structures. Reasonable theoretical predictions and low speed (<300m/s) impact experiments suggest that in such targets the cratering process should be highly dissipative, which would reduce cratering efficiencies and cause a rapid decay in ejection velocity as a function of distance from the impact point. In this study, we assess whether these results apply at higher impact speeds between 0.5 and 2.5 km s-1. This study shows little change in cratering efficiency when 3.18 mm diameter glass beads are launched into targets composed of these same beads. These impacts are very efficient, and ejection velocity decays slowly as function of distance from the impact point. This slow decay in ejection velocity probably indicates a correspondingly slow decay of the shock stresses. However, these experiments reveal that initial interactions between projectile and target strongly influence the cratering process and lead to asymmetries in crater shape and ejection angles, as well as significant variations in ejection velocity at a given launch position. Such effects of asymmetric coupling could be further enhanced by heterogeneity in the initial distribution of grains in the target and by mechanical collisions between grains. These experiments help to explain why so few craters are seen on the rubble-pile asteroid Itokawa: impacts into its coarsely fragmental surface by projectiles comparable to or smaller than the size of these fragments likely yield craters that are not easily recognizable.

  13. Locating the LCROSS Impact Craters

    NASA Technical Reports Server (NTRS)

    Marshall, William; Shirley, Mark; Moratto, Zachary; Colaprete, Anthony; Neumann, Gregory A.; Smith, David E.; Hensley, Scott; Wilson, Barbara; Slade, Martin; Kennedy, Brian; hide

    2012-01-01

    The Lunar CRater Observations and Sensing Satellite (LCROSS) mission impacted a spent Centaur rocket stage into a permanently shadowed region near the lunar south pole. The Sheperding Spacecraft (SSC) separated approx. 9 hours before impact and performed a small braking maneuver in order to observe the Centaur impact plume, looking for evidence of water and other volatiles, before impacting itself. This paper describes the registration of imagery of the LCROSS impact region from the mid- and near-infrared cameras onboard the SSC, as well as from the Goldstone radar. We compare the Centaur impact features, positively identified in the first two, and with a consistent feature in the third, which are interpreted as a 20 m diameter crater surrounded by a 160 m diameter ejecta region. The images are registered to Lunar Reconnaisance Orbiter (LRO) topographical data which allows determination of the impact location. This location is compared with the impact location derived from ground-based tracking and propagation of the spacecraft's trajectory and with locations derived from two hybrid imagery/trajectory methods. The four methods give a weighted average Centaur impact location of -84.6796 deg, -48.7093 deg, with a 1s uncertainty of 115 m along latitude, and 44 m along longitude, just 146 m from the target impact site. Meanwhile, the trajectory-derived SSC impact location is -84.719 deg, -49.61 deg, with a 1 alpha uncertainty of 3 m along the Earth vector and 75 m orthogonal to that, 766 m from the target location and 2.803 km south-west of the Centaur impact. We also detail the Centaur impact angle and SSC instrument pointing errors. Six high-level LCROSS mission requirements are shown to be met by wide margins. We hope that these results facilitate further analyses of the LCROSS experiment data and follow-up observations of the impact region

  14. Fluid mechanical scaling of impact craters in unconsolidated granular materials

    NASA Astrophysics Data System (ADS)

    Miranda, Colin S.; Dowling, David R.

    2015-11-01

    A single scaling law is proposed for the diameter of simple low- and high-speed impact craters in unconsolidated granular materials where spall is not apparent. The scaling law is based on the assumption that gravity- and shock-wave effects set crater size, and is formulated in terms of a dimensionless crater diameter, and an empirical combination of Froude and Mach numbers. The scaling law involves the kinetic energy and speed of the impactor, the acceleration of gravity, and the density and speed of sound in the target material. The size of the impactor enters the formulation but divides out of the final empirical result. The scaling law achieves a 98% correlation with available measurements from drop tests, ballistic tests, missile impacts, and centrifugally-enhanced gravity impacts for a variety of target materials (sand, alluvium, granulated sugar, and expanded perlite). The available measurements cover more than 10 orders of magnitude in impact energy. For subsonic and supersonic impacts, the crater diameter is found to scale with the 1/4- and 1/6-power, respectively, of the impactor kinetic energy with the exponent crossover occurring near a Mach number of unity. The final empirical formula provides insight into how impact energy partitioning depends on Mach number.

  15. Crater Impacts on Vesta

    NASA Image and Video Library

    2012-05-10

    This graphic shows the global distribution of craters that hit the giant asteroid Vesta, based on data from NASA Dawn mission. The yellow circles indicate craters of 2 miles or wider, with the size of the circles indicating the size of the crater.

  16. Experimental impact cratering provides ground truth data for understanding planetary-scale collision processes

    NASA Astrophysics Data System (ADS)

    Poelchau, Michael H.; Deutsch, Alex; Kenkmann, Thomas

    2013-04-01

    Impact cratering is generally accepted as one of the primary processes that shape planetary surfaces in the solar system. While post-impact analysis of craters by remote sensing or field work gives many insights into this process, impact cratering experiments have several advantages for impact research: 1) excavation and ejection processes can be directly observed, 2) physical parameters of the experiment are defined and can be varied, and 3) cratered target material can be analyzed post-impact in an unaltered, uneroded state. The main goal of the MEMIN project is to comprehensively quantify impact processes by conducting a stringently controlled experimental impact cratering campaign on the meso-scale with a multidisciplinary analytical approach. As a unique feature we use two-stage light gas guns capable of producing impact craters in the decimeter size-range in solid rocks that, in turn, allow detailed spatial analysis of petrophysical, structural, and geochemical changes in target rocks and ejecta. In total, we have carried out 24 experiments at the facilities of the Fraunhofer EMI, Freiburg - Germany. Steel, aluminum, and iron meteorite projectiles ranging in diameter from 2.5 to 12 mm were accelerated to velocities ranging from 2.5 to 7.8 km/s. Targets were solid rocks, namely sandstone, quartzite and tuff that were either dry or saturated with water. In the experimental setup, high speed framing cameras monitored the impact process, ultrasound sensors were attached to the target to record the passage of the shock wave, and special particle catchers were positioned opposite of the target surface to capture the ejected target and projectile material. In addition to the cratering experiments, planar shock recovery experiments were performed on the target material, and numerical models of the cratering process were developed. The experiments resulted in craters with diameters up to 40 cm, which is unique in laboratory cratering research. Target porosity

  17. Geology of the Gusec cratered plains from the Spirit rover transverse

    NASA Technical Reports Server (NTRS)

    Golombek, M. P.; Crumpler, L. S.; Grant, J. A.; Greely, R.; Cabrol, N. A.; Parker, T. J.; Rice, J. W., Jr.; Ward, J. G.; Arvidson, R. E.; Moersch, J. E.; hide

    2006-01-01

    The cratered plains of Gusev traversed by Spirit are generally low-relief rocky plains dominated by impact and eolian processes. Ubiquitous shallow, soil-filled, circular depressions, called hollows, are modified impact craters. Rocks are dark, fine-grained basalts, and the upper 10 m of the cratered plains appears to be an impact-generated regolith developed over intact basalt flows. Systematic field observations across the cratered plains identified vesicular clasts and rare scoria similar to original lava flow tops, consistent with an upper inflated surface of lava flows with adjacent collapse depressions. Crater and hollow morphometry are consistent with most being secondaries. The size frequency distribution of rocks >0.1 m diameter generally follows exponential functions similar to other landing sites for total rock abundances of 5-35%. Systematic clast counts show that areas with higher rock abundance and more large rocks have higher thermal inertia. Plains with lower thermal inertia have fewer rocks and substantially more pebbles that are well sorted and evenly spaced, similar to a desert pavement or lag. Eolian bed forms (ripples and wind tails) have coarse surface lags, and many are dust covered and thus likely inactive. Deflation of the surface _5-25 cm likely exposed two-toned rocks and elevated ventifacts and transported fines into craters creating the hollows. This observed redistribution yields extremely slow average erosion rates of _0.03 nm/yr and argues for very little long-term net change of the surface and a dry and desiccating environment similar to today's since the Hesperian (or _3 Ga).

  18. Impact Craters on Earth: Lessons for Understanding Martian Geological Materials and Processes

    NASA Astrophysics Data System (ADS)

    Osinski, G. R.

    2015-12-01

    Impact cratering is one of the most ubiquitous geological processes in the Solar System and has had a significant influence on the geological evolution of Mars. Unlike the Moon and Mercury, the Martian impact cratering record is notably diverse, which is interpreted to reflect interactions during the impact process with target volatiles and/or the atmosphere. The Earth also possesses a volatile-rich crust and an atmosphere and so is one of the best analogues for understanding the effects of impact cratering on Mars. Furthermore, fieldwork at terrestrial craters and analysis of samples is critical to ground-truth observations made based on remote sensing data from Martian orbiters, landers, and rovers. In recent years, the effect of target lithology on various aspects of the impact cratering process has emerged as a major research topic. On Mars, volatiles have been invoked to be the primary factor influencing the morphology of ejecta deposits - e.g., the formation of single-, double- and multiple-layered ejecta deposits - and central uplifts - e.g., the formation of so-called "central pit" craters. Studies of craters on Earth have also shown that volatiles complicate the identification of impactites - i.e., rocks produced and/or affected by impact cratering. Identifying impactites on Earth is challenging, often requiring intensive and multi-technique laboratory analysis of hand specimens. As such, it is even more challenging to recognize such materials in remote datasets. Here, observations from the Haughton (d = 23 km; Canada), Ries (d = 24 km; Germany), Mistastin (d = 28 km; Canada), Tunnunik, (d = 28 km; Canada), and West Clearwater Lake (d = 36 km; Canada) impact structures are presented. First, it is shown that some impactites mimic intrusive, volcanic, volcanoclastic and in some cases sedimentary clastic rocks. Care should, therefore, be taken in the identification of seemingly unusual igneous rocks at rover landing sites as they may represent impact melt

  19. Ringed impact craters on Venus: An analysis from Magellan images

    NASA Technical Reports Server (NTRS)

    Alexopoulos, Jim S.; Mckinnon, William B.

    1992-01-01

    We have analyzed cycle 1 Magellan images covering approximately 90 percent of the venusian surface and have identified 55 unequivocal peak-ring craters and multiringed impact basins. This comprehensive study (52 peak-ring craters and at least 3 multiringed impact basins) complements our earlier independent analysis of Arecibo and Venera images and initial Magellan data and that of the Magellan team.

  20. The self-secondary crater population of the Hokusai crater on Mercury

    NASA Astrophysics Data System (ADS)

    Xiao, Zhiyong; Prieur, Nils C.; Werner, Stephanie C.

    2016-07-01

    Whether or not self-secondaries dominate small crater populations on continuous ejecta deposits and floors of fresh impact craters has long been a controversy. This issue potentially affects the age determination technique using crater statistics. Here the self-secondary crater population on the continuous ejecta deposits of the Hokusai crater on Mercury is unambiguously recognized. Superposition relationships show that this population was emplaced after both the ballistic sedimentation of excavation flows and the subsequent veneering of impact melt, but it predated the settlement and solidification of melt pools on the crater floor. Fragments that formed self-secondaries were launched via impact spallation with large angles. Complex craters on the Moon, Mercury, and Mars probably all have formed self-secondaries populations. Dating young craters using crater statistics on their continuous ejecta deposits can be misleading. Impact melt pools are less affected by self-secondaries. Overprint by subsequent crater populations with time reduces the predominance of self-secondaries.

  1. Shallow drilling in the 'Bunte Breccia' impact deposits, Ries Crater, Germany

    NASA Technical Reports Server (NTRS)

    Hoerz, F.; Gall, H.; Huettner, R.; Oberbeck, V. R.

    1977-01-01

    The paper is a field report concerning a shallow core drilling program in the multicolored breccia deposits which constitute 90% of all the impact breccias beyond the outer rim of the Ries, a 26-km-diam impact crater. About 480 m of core was recovered from 11 locations with radial ranges between 16.5 and 35 km from the crater center. The cores consist of breccias, whose components are derived from the crater itself and the terrain outside the crater. The local components dominate the breccias at the larger ranges, and possibly constitute more than 90% of the breccia volume at the greatest distances investigated. The great depth of the Bunte Breccia (84 m at 27 km range), together with the preponderance of local components, necessitates an emplacement mechanism that ploughed up and mixed the crater surroundings to depths greater than 50 m.

  2. Periodic Impact Cratering and Extinction Events Over the Last 260 Million Years

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Caldeira, Ken

    2015-01-01

    The claims of periodicity in impact cratering and biological extinction events are controversial. Anewly revised record of dated impact craters has been analyzed for periodicity, and compared with the record of extinctions over the past 260 Myr. A digital circular spectral analysis of 37 crater ages (ranging in age from 15 to 254 Myr ago) yielded evidence for a significant 25.8 +/- 0.6 Myr cycle. Using the same method, we found a significant 27.0 +/- 0.7 Myr cycle in the dates of the eight recognized marine extinction events over the same period. The cycles detected in impacts and extinctions have a similar phase. The impact crater dataset shows 11 apparent peaks in the last 260 Myr, at least 5 of which correlate closely with significant extinction peaks. These results suggest that the hypothesis of periodic impacts and extinction events is still viable.

  3. Geomorphologic mapping of the lunar crater Tycho and its impact melt deposits

    NASA Astrophysics Data System (ADS)

    Krüger, T.; van der Bogert, C. H.; Hiesinger, H.

    2016-07-01

    Using SELENE/Kaguya Terrain Camera and Lunar Reconnaissance Orbiter Camera (LROC) data, we produced a new, high-resolution (10 m/pixel), geomorphological and impact melt distribution map for the lunar crater Tycho. The distal ejecta blanket and crater rays were investigated using LROC wide-angle camera (WAC) data (100 m/pixel), while the fine-scale morphologies of individual units were documented using high resolution (∼0.5 m/pixel) LROC narrow-angle camera (NAC) frames. In particular, Tycho shows a large coherent melt sheet on the crater floor, melt pools and flows along the terraced walls, and melt pools on the continuous ejecta blanket. The crater floor of Tycho exhibits three distinct units, distinguishable by their elevation and hummocky surface morphology. The distribution of impact melt pools and ejecta, as well as topographic asymmetries, support the formation of Tycho as an oblique impact from the W-SW. The asymmetric ejecta blanket, significantly reduced melt emplacement uprange, and the depressed uprange crater rim at Tycho suggest an impact angle of ∼25-45°.

  4. An Impact Cratering Interactive Website Used for Outreach and in Professional Development Workshops for Middle School Science Teachers

    NASA Astrophysics Data System (ADS)

    Croft, S. K.; Pierazzo, E.; Canizo, T.; Lebofsky, L. A.

    2009-12-01

    Impact cratering is one of the fundamental geologic processes affecting all planetary and asteroidal bodies in the Solar System. With few exceptions, all bodies with solid surfaces explored so far show the presence of impact craters - from the less than 200 known craters on Earth to the many thousands seen on the Moon, Mercury, and other bodies. Indeed, the study of crater populations is one of the principal tools for understanding the geologic history of planetary surfaces. In recent years, impact cratering has gained public notoriety through its portrayal in several Hollywood movies. Questions that are raised after watching these movies include: “How often do impacts occur?” “How do scientists learn about impact cratering?” and “What information do impact craters provide in understanding the evolution planetary surfaces?” On our website: “Explorer’s Guide to Impact Craters,” we answer those questions in a fun, informative and interactive way. The website provides the interested public with an opportunity to: 1) experience how scientists explore known terrestrial craters through a virtual fieldtrips; 2) learn more about the dynamics of impact cratering using numerical simulations of various impacts; and 3) investigate how impact cratering affects rocks via images and descriptions of field samples of impact rocks. This learning tool has been a popular outreach endeavor (recently reaching 100,000 hits), and it has recently been incorporated in the Impact Cratering Workshop developed by scientists and EPO specialists at the Planetary Science Institute. The workshop provides middle school science teachers with an inquiry-based understanding of the process of impact cratering and how it affects the solar system. Participants are instructed via standards-based multimedia presentations, analysis of planetary images, hands-on experience with geologic samples from terrestrial impact craters, and first-hand experience forming impact craters. Through the

  5. New geological and geophysical antecedents at the Monturaqui Impact Crater, Chile

    NASA Astrophysics Data System (ADS)

    Ugalde, H.; Valenzuela, M.; Casas, E.; Milkereit, B.; Grandon, M.; Contreras, S.

    2004-05-01

    Impact structures are a common and important landform on planetary surfaces. Currently there are 168 confirmed impact structures in the Earth [1]. Out of those, the Monturaqui crater (<400 m diameter, 0.1 Ma [2]), located in the north of Chile, represents a grand opportunity for a detailed study of simple impact craters: it is accessible, well preserved and exposed. In December 2003 a field expedition accomplished detailed geological and geophysical mapping on it. The geology of the Monturaqui area is characterized by a basement of Paleozoic granites overlain by Pliocene ignimbrite units [3]. The granite outcrops mostly at the higher terrain in the crater rim, while the ignimbrites outcrop at lower levels filling the crater. Gravity, magnetic, differential GPS surveying and geological mapping built a detailed dataset of the crater. From the DGPS survey, its dimensions are 370 m EW, 350 m NS, and ~34 m deep. In the centre it has an uplift of 3 m approx, coincident with lime sediments. The northern edge of the crater exhibits magnetic anomalies with inverted polarization, presumably due to magnetic remanence. This could have been caused by post-impact alteration [4]. The Bouguer gravity anomaly shows a negative anomaly of ~1mGal at the centre, associated with fracturing and brecciation of the target rocks. Due to its lower competence than the granite, the shock wave fractured the ignimbrite instead of deforming it, building the regolith that presently fills the crater. Then the shock wave melted the basement locally. Breccia and melt were ejected hundreds of metres around the crater, and excavation raised the edges of the ignimbrite strata and granite. Late erosion was controlled mainly by mechanical weathering due to the extreme arid conditions of the area since the mid-Miocene [5]. References: [1] Earth Impact Database, www.unb.ca/passc/ImpactDatabase/, 2003; [2] Buchwald V. F. Handbook of Iron meteorites. University of California Press, v3, 1975; [3] Ramírez, C

  6. An object-based classification method for automatic detection of lunar impact craters from topographic data

    NASA Astrophysics Data System (ADS)

    Vamshi, Gasiganti T.; Martha, Tapas R.; Vinod Kumar, K.

    2016-05-01

    Identification of impact craters is a primary requirement to study past geological processes such as impact history. They are also used as proxies for measuring relative ages of various planetary or satellite bodies and help to understand the evolution of planetary surfaces. In this paper, we present a new method using object-based image analysis (OBIA) technique to detect impact craters of wide range of sizes from topographic data. Multiresolution image segmentation of digital terrain models (DTMs) available from the NASA's LRO mission was carried out to create objects. Subsequently, objects were classified into impact craters using shape and morphometric criteria resulting in 95% detection accuracy. The methodology developed in a training area in parts of Mare Imbrium in the form of a knowledge-based ruleset when applied in another area, detected impact craters with 90% accuracy. The minimum and maximum sizes (diameters) of impact craters detected in parts of Mare Imbrium by our method are 29 m and 1.5 km, respectively. Diameters of automatically detected impact craters show good correlation (R2 > 0.85) with the diameters of manually detected impact craters.

  7. Granular impact cratering by liquid drops: Understanding raindrop imprints through an analogy to asteroid strikes

    PubMed Central

    Zhao, Runchen; Zhang, Qianyun; Tjugito, Hendro; Cheng, Xiang

    2015-01-01

    When a granular material is impacted by a sphere, its surface deforms like a liquid yet it preserves a circular crater like a solid. Although the mechanism of granular impact cratering by solid spheres is well explored, our knowledge on granular impact cratering by liquid drops is still very limited. Here, by combining high-speed photography with high-precision laser profilometry, we investigate liquid-drop impact dynamics on granular surface and monitor the morphology of resulting impact craters. Surprisingly, we find that despite the enormous energy and length difference, granular impact cratering by liquid drops follows the same energy scaling and reproduces the same crater morphology as that of asteroid impact craters. Inspired by this similarity, we integrate the physical insight from planetary sciences, the liquid marble model from fluid mechanics, and the concept of jamming transition from granular physics into a simple theoretical framework that quantitatively describes all of the main features of liquid-drop imprints in granular media. Our study sheds light on the mechanisms governing raindrop impacts on granular surfaces and reveals a remarkable analogy between familiar phenomena of raining and catastrophic asteroid strikes. PMID:25548187

  8. Crater gradation in Gusev crater and Meridiani Planum, Mars

    USGS Publications Warehouse

    Grant, J. A.; Arvidson, R. E.; Crumpler, L.S.; Golombek, M.P.; Hahn, B.; Haldemann, A.F.C.; Li, R.; Soderblom, L.A.; Squyres, S. W.; Wright, S.P.; Watters, W.A.

    2006-01-01

    The Mars Exploration Rovers investigated numerous craters in Gusev crater and Meridiani Planum during the first ???400 sols of their missions. Craters vary in size and preservation state but are mostly due to secondary impacts at Gusev and primary impacts at Meridiani. Craters at both locations are modified primarily by eolian erosion and infilling and lack evidence for modification by aqueous processes. Effects of gradation on crater form are dependent on size, local lithology, slopes, and availability of mobile sediments. At Gusev, impacts into basaltic rubble create shallow craters and ejecta composed of resistant rocks. Ejecta initially experience eolian stripping, which becomes weathering-limited as lags develop on ejecta surfaces and sediments are trapped within craters. Subsequent eolian gradation depends on the slow production of fines by weathering and impacts and is accompanied by minor mass wasting. At Meridiani the sulfate-rich bedrock is more susceptible to eolian erosion, and exposed crater rims, walls, and ejecta are eroded, while lower interiors and low-relief surfaces are increasingly infilled and buried by mostly basaltic sediments. Eolian processes outpace early mass wasting, often produce meters of erosion, and mantle some surfaces. Some small craters were likely completely eroded/buried. Craters >100 m in diameter on the Hesperian-aged floor of Gusev are generally more pristine than on the Amazonian-aged Meridiani plains. This conclusion contradicts interpretations from orbital views, which do not readily distinguish crater gradation state at Meridiani and reveal apparently subdued crater forms at Gusev that may suggest more gradation than has occurred. Copyright 2006 by the American Geophysical Union.

  9. Crater gradation in Gusev crater and Meridiani Planum, Mars

    NASA Astrophysics Data System (ADS)

    Grant, J. A.; Arvidson, R. E.; Crumpler, L. S.; Golombek, M. P.; Hahn, B.; Haldemann, A. F. C.; Li, R.; Soderblom, L. A.; Squyres, S. W.; Wright, S. P.; Watters, W. A.

    2006-01-01

    The Mars Exploration Rovers investigated numerous craters in Gusev crater and Meridiani Planum during the first ~400 sols of their missions. Craters vary in size and preservation state but are mostly due to secondary impacts at Gusev and primary impacts at Meridiani. Craters at both locations are modified primarily by eolian erosion and infilling and lack evidence for modification by aqueous processes. Effects of gradation on crater form are dependent on size, local lithology, slopes, and availability of mobile sediments. At Gusev, impacts into basaltic rubble create shallow craters and ejecta composed of resistant rocks. Ejecta initially experience eolian stripping, which becomes weathering-limited as lags develop on ejecta surfaces and sediments are trapped within craters. Subsequent eolian gradation depends on the slow production of fines by weathering and impacts and is accompanied by minor mass wasting. At Meridiani the sulfate-rich bedrock is more susceptible to eolian erosion, and exposed crater rims, walls, and ejecta are eroded, while lower interiors and low-relief surfaces are increasingly infilled and buried by mostly basaltic sediments. Eolian processes outpace early mass wasting, often produce meters of erosion, and mantle some surfaces. Some small craters were likely completely eroded/buried. Craters >100 m in diameter on the Hesperian-aged floor of Gusev are generally more pristine than on the Amazonian-aged Meridiani plains. This conclusion contradicts interpretations from orbital views, which do not readily distinguish crater gradation state at Meridiani and reveal apparently subdued crater forms at Gusev that may suggest more gradation than has occurred.

  10. An in-depth study of Marcia Crater, Vesta

    NASA Astrophysics Data System (ADS)

    Hiesinger, Harald; Ruesch, Ottaviano; Williams, David A.; Nathues, Andreas; Prettyman, Thomas H.; Tosi, Frederico; De Sanctis, M. Christina; Scully, Jennifer E. C.; Schenk, Paul M.; Aileen Yingst, R.; Denevi, Bret W.; Jaumann, Ralf; Raymond, Carol A.; Russell, Chris T.

    2014-05-01

    After visiting the second most massive asteroid Vesta from July 2011 to September 2012, the Dawn spacecraft is now on its way to asteroid Ceres. Dawn observed Vesta with three instruments: the German Framing Camera (FC), the Italian Visible and InfraRed mapping spectrometer (VIR), and the American Gamma Ray and Neutron Detector (GRaND) [1]. Marcia crater (190°E, 10°N; 68 x 58 km) is the largest of three adjacent impact structures: Marcia (youngest), Calpurnia, and Minucia (oldest). It is the largest well-preserved post-Rheasilvia impact crater, shows a complex geology [2], is young [2], exhibits evidence for gully-like mass wasting [3], contains the largest location of pitted terrain [4], has smooth impact melt ponds [5], shows enhanced spectral pyroxene signatures on its inner walls [2], and has low abundances of OH and H in comparison to the surrounding low-albedo terrain [6, 7]. Geophysically, the broad region of Marcia and Calpurnia craters is characterized by a higher Bouguer gravity, indicating denser material [9]. Williams et al. [2] have produced a detailed geologic map of Marcia crater and the surrounding terrain. They identified several units within Marcia crater, including bright crater material, pitted terrain, and smooth material. Units outside Marcia, include undivided crater ejecta material, bright lobate material, dark lobate material, and dark crater ray material [2]. Because of its extensive ejecta and fresh appearance, the Marcia impact defines a major stratigraphic event, postdating the Rheasilvia impact [2]. However, the exact age of Marcia crater is still under debate. Compositionally, Marcia crater is characterized by higher iron abundances, which were interpreted as more basaltic-eucrite-rich materials suggesting that this region has not been blanketed by diogenitic materials from large impact events [10, 11]. Using FC data, [13] identified "gray material" associated with the ejecta blanket of Marcia crater. This material is characterized

  11. Exploring Martian Impact Craters: Why They are Important for the Search for Life

    NASA Technical Reports Server (NTRS)

    Schwenzer, S. P.; Abramov, O.; Allen, C. C.; Clifford, S.; Filiberto, J.; Kring, D. A.; Lasue, J.; McGovern, P. J.; Newsom, H. E.; Treiman, A. H.; hide

    2010-01-01

    Fluvial features and evidence for aqueous alteration indicate that Mars was wet, at least partially and/or periodically, in the Noachian. Also, impact cratering appears to have been the dominant geological process [1] during that epoch. Thus, investigation of Noachian craters will further our understanding of this geologic process, its effects on the water-bearing Martian crust, and any life that may have been present at the time. Impact events disturbed and heated the water- and/or ice-bearing crust, likely initiated long-lived hydrothermal systems [2-4], and formed crater lakes [5], creating environments suitable for life [6]. Thus, Noachian impact craters are particularly important exploration targets because they provide a window into warm, water-rich environments of the past which were possibly conducive to life. In addition to the presence of lake deposits, assessment of the presence of hydrothermal deposits in the walls, floors and uplifts of craters is important in the search for life on Mars. Impact craters are also important for astrobiological exploration in other ways. For example, smaller craters can be used as natural excavation pits, and so can provide information and samples that would otherwise be inaccessible (e.g., [7]). In addition, larger (> 75 km) craters can excavate material from a potentially habitable region, even on present-day Mars, located beneath a >5-km deep cryosphere.

  12. Geological mapping of lunar highland crater Lalande: Topographic configuration, morphology and cratering process

    NASA Astrophysics Data System (ADS)

    Li, Bo; Ling, Zongcheng; Zhang, Jiang; Chen, Jian; Liu, ChangQing; Bi, Xiangyu

    2018-02-01

    Highland crater Lalande (4.45°S, 8.63°W; D = 23.4 km) is located on the PKT area of the lunar near side, southeast of the Mare Insularum. It is a complex crater in Copernican era and has three distinguishing features: high silicic anomaly, the highest Th abundance and special landforms on its floor. There are some low-relief bulges on the left of Lalande's floor with regular circle or ellipse shapes. They are ∼250-680 m wide and ∼30-91 m high with maximum flank slopes >20°. There are two possible scenarios for the formation of these low-relief bulges which are impact melt products or young silicic volcanic eruptions. We estimated the absolute model ages of the ejecta deposits, several melt ponds and the hummocky floor and determined the ratio of diameter and depth of the crater Lalande. In addition, we found some similar bugle features within other Copernican-aged craters and there were no volcanic source vents on Lalande's floor. Thus, we hypothesized that these low-relief bulges were most consistent with an origin of impact melts during the crater formation instead of small and young volcanic activities occurring on the floor. Based on Kaguya Terrain Camera (TC) ortho-mosaic and Digital Terrain Model (DTM) data produced by TC imagery in stereo, geological units and some linear features on the floor and wall of Lalande have been mapped. Eight geological units are organized by crater floor units: hummocky floor, central peak and low-relief bulges; and crater wall units: terraced walls, channeled and veneered walls, interior walls, mass wasting areas, blocky areas, and melt ponds. These geological units and linear features provided us a chance to understand some details of the cratering process and elevation differences on the floor. We proposed that subsidence due to melt cooling, late-stage wall collapse and rocks uplifted from beneath the surface could be the possible causes of the observed elevation differences on Lalande's floor.

  13. Secondary craters on Europa and implications for cratered surfaces.

    PubMed

    Bierhaus, Edward B; Chapman, Clark R; Merline, William J

    2005-10-20

    For several decades, most planetary researchers have regarded the impact crater populations on solid-surfaced planets and smaller bodies as predominantly reflecting the direct ('primary') impacts of asteroids and comets. Estimates of the relative and absolute ages of geological units on these objects have been based on this assumption. Here we present an analysis of the comparatively sparse crater population on Jupiter's icy moon Europa and suggest that this assumption is incorrect for small craters. We find that 'secondaries' (craters formed by material ejected from large primary impact craters) comprise about 95 per cent of the small craters (diameters less than 1 km) on Europa. We therefore conclude that large primary impacts into a solid surface (for example, ice or rock) produce far more secondaries than previously believed, implying that the small crater populations on the Moon, Mars and other large bodies must be dominated by secondaries. Moreover, our results indicate that there have been few small comets (less than 100 m diameter) passing through the jovian system in recent times, consistent with dynamical simulations.

  14. Gale Crater: An Amazonian Impact Crater Lake at the Plateau/Plain Boundary

    NASA Technical Reports Server (NTRS)

    Cabrol, N. A.; Grin, E. A.

    1998-01-01

    Gale is a 140-km diameter impact crater located at the plateau/plain boundary in the Aeolis Northeast subquadrangle of Mars (5S/223W). The crater is bordered in the northward direction by the Elysium Basin, and in eastward direction by Hesperian channels and the Aeolis Mensae 2. The crater displays a rim with two distinct erosion stages: (a) though eroded, the south rim of Gale has an apparent crest line visible from the north to the southwest (b) the west and northwest rims are characterized by a strong erosion that, in some places, partially destroyed the rampart, leaving remnant pits embayed in smooth-like deposits. The same type of deposits is observed north, outside Gale, it also borders the Aeolis Mensae, covers the bottom of the plateau scarp, and the crater floor. The central part of Gale shows a 6400 km2 subround and asymmetrical deposit: (a) the south part is composed of smooth material, (b) the north part shows spectacular terraces, streamlines, and channels. The transition between the two parts of the deposit is characterized by a scarp ranging from 200 to 2000 in high. The highest point of the scarp is at the center of the crater, and probably corresponds to a central peak. Gale crater does not show a major channel directly inflowing. However, several large fluvi systems are bordering the crater, and could be at the origin of the flooding of the crater, or have contributed to. One fluvial system is entering the crater by the southwest rim but cannot be accounted alone for the volume of sediment deposited in the crater. This channel erodes the crater floor deposit, and ends in a irregular-shaped and dark albedo feature. Gale crater shows the morphology of a crater filled during sedimentation episodes, and then eroded Part of the lower sediment deposition contained in Gale might be ancient and not only aqueous in origin. According to the regional geologic history, the sedimentary deposit could be a mixture of aeolian and pyroclastic material, and aqueous

  15. What Really Happened to Earth's Older Craters?

    NASA Astrophysics Data System (ADS)

    Bottke, William; Mazrouei, Sara; Ghent, Rebecca; Parker, Alex

    2017-10-01

    Most assume the Earth’s crater record is heavily biased, with erosion/tectonics destroying older craters. This matches expectations, but is it actually true? To test this idea, we compared Earth’s crater record, where nearly all D ≥ 20 km craters are < 650 Myr old, to the Moon’s. Here lunar crater ages were computed using a new method employing LRO-Diviner temperature data. Large lunar rocks have high thermal inertia and remain warm through the night relative to the regolith. Analysis shows young craters with numerous meter-sized fragments are easy to pick out from older craters with eroded fragments. Moreover, an inverse relationship between rock abundance (RA) and crater age exists. Using measured RA values, we computed ages for 111 rocky craters with D ≥ 10 km that formed between 80°N and 80°S over the last 1 Gyr.We found several surprising results. First, the production rate of D ≥ 10 km lunar craters increased by a factor of 2.2 [-0.9, +4.4; 95% confidence limits] over the past 250 Myr compared to the previous 750 Myr. Thus, the NEO population is higher now than it has been for the last billion years. Second, the size and age distributions of lunar and terrestrial craters for D ≥ 20 km over the last 650 Myr have similar shapes. This implies that crater erasure must be limited on stable terrestrial terrains; in an average sense, for a given region, the Earth either keeps all or loses all of its D ≥ 20 craters at the same rate, independent of size. It also implies the observed deficit of large terrestrial craters between 250-650 Myr is not preservation bias but rather reflects a distinctly lower impact flux. We predict 355 ± 86 D ≥ 20 km craters formed on Earth over the last 650 Myr. Only 38 ± 6 are known, so the ratio, 10.7 ± 3.1%, is a measure of the Earth’s surface that is reasonably stable to large crater formation over 650 Myr. If erosion had dominated, the age distribution of terrestrial craters would be strongly skewed toward

  16. The Zhamanshin impact feature: A new class of complex crater?

    NASA Technical Reports Server (NTRS)

    Garvin, J. B.; Schnetzler, C. C.

    1992-01-01

    The record of 10-km-scale impact events of Quaternary age includes only two 'proven' impact structures: the Zhamanshin Impact Feature (ZIF) and the Bosumtwi Impact Crater (BIC). What makes these impact landforms interesting from the standpoint of recent Earth history is their almost total lack of morphologic similarity, in spite of similar absolute ages and dimensions. The BIC resembles pristine complex craters on the Moon to first order (i.e., 'U'-shaped topographic cross section with preserved rim), while the ZIF displays virtually none of the typical morphologic elements of a 13- to 14-km-diameter complex crater. Indeed, this apparent lack of a craterlike surficial topographic expression initially led Soviet geologists to conclude that the structure was only 5.5 to 6 km in diameter and at least 4.5 Ma in age. However, more recent drilling and geophysical observations at the ZIF have indicated that its pre-erosional diameter is at least 13.5 km, and that its age is most probably 0.87 Ma. Why the present topographic expression of a 13.5-km complex impact crater less than 1 m.y. old most closely resembles heavily degraded Mesozoic shield craters such as Lappajarvi is a question of considerable debate. Hypotheses for the lack of a clearly defined craterlike form at the ZIF include a highly oblique impact, a low-strength 'cometary' projectile, weak or water-saturated target materials, and anomalous erosion patterns. The problem remains unresolved because typical erosion rates within the arid sedimentary platform environment of central Kazakhstan in which the ZIF is located are typically low; it would require at least a factor of 10 greater erosion at the ZIF in order to degrade the near-rim ejecta typical of a 13.5-km complex crater by hundreds of meters in only 0.87 Ma, and to partially infill an inner cavity with 27 cu km (an equivalent uniform thickness of infill of 166 m). Our analysis of the degree of erosion and infill at the ZIF calls for rates in the 0.19 to

  17. Impact Cratering Processes as Understood Through Martian and Terrestrial Analog Studies

    NASA Astrophysics Data System (ADS)

    Caudill, C. M.; Osinski, G. R.; Tornabene, L. L.

    2016-12-01

    Impact ejecta deposits allow an understanding of subsurface lithologies, volatile content, and other compositional and physical properties of a planetary crust, yet development and emplacement of these deposits on terrestrial bodies throughout the solar system is still widely debated. Relating relatively well-preserved Martian ejecta to terrestrial impact deposits is an area of active research. In this study, we report on the mapping and geologic interpretation of 150-km diameter Bakhuysen Crater, Mars, which is likely large enough to have produced a significant volume of melt, and has uniquely preserved ejecta deposits. Our mapping supports the current formation hypothesis for Martian crater-related pitted material, where pits are likened to collapsed degassing features identified at the Ries and Haughton terrestrial impact structures. As hot impact melt-bearing ejecta deposits are emplaced over volatile-saturated material during crater formation, a rapid degassing of the underlying layer results in lapilli-like fluid and gas flow pipes which may eventually lead to collapse features on the surface. At the Haughton impact structure, degassing pipes are related to crater fracture and fault systems; this is analogous to structure and collapse pits mapped in Bakhuysen Crater. Based on stratigraphic superposition, surface and flow texture, and morphological and thermophysical mapping of Bakhuysen, we interpret the top-most ejecta unit to be likely melt-bearing and analogous to terrestrial impact deposits (e.g., Ries suevites). Furthermore, we suggest that Chicxulub is an apt terrestrial comparison based on its final diameter and the evidence of a ballistically-emplaced and volatile-entrained initial ejecta. This is significant as Bakhuysen ejecta deposits may provide insight into larger impact structures where limited exposures make studies difficult. This supports previous work which suggests that given similarities in volatile content and subsurface stratigraphy

  18. Dione's resurfacing history as determined from a global impact crater database

    NASA Astrophysics Data System (ADS)

    Kirchoff, Michelle R.; Schenk, Paul

    2015-08-01

    Saturn's moon Dione has an interesting and unique resurfacing history recorded by the impact craters on its surface. In order to further resolve this history, we compile a crater database that is nearly global for diameters (D) equal to and larger than 4 km using standard techniques and Cassini Imaging Science Subsystem images. From this database, spatial crater density maps for different diameter ranges are generated. These maps, along with the observed surface morphology, have been used to define seven terrain units for Dione, including refinement of the smooth and "wispy" (or faulted) units from Voyager observations. Analysis of the terrains' crater size-frequency distributions (SFDs) indicates that: (1) removal of D ≈ 4-50 km craters in the "wispy" terrain was most likely by the formation of D ≳ 50 km craters, not faulting, and likely occurred over a couple billion of years; (2) resurfacing of the smooth plains was most likely by cryovolcanism at ∼2 Ga; (3) most of Dione's largest craters (D ⩾ 100 km), including Evander (D = 350 km), may have formed quite recently (<2 Ga), but are still relaxed, indicating Dione has been thermally active for at least half its history; and (4) the variation in crater SFDs at D ≈ 4-15 km is plausibly due to different levels of minor resurfacing (mostly subsequent large impacts) within each terrain.

  19. Microstructural Study of Micron-Sized Craters Simulating Stardust Impacts in Aluminum 1100 Targets

    NASA Technical Reports Server (NTRS)

    Leroux, Hugues; Borg, Janet; Troadec, David; Djouadi, Zahia; Horz, Friedrich

    2006-01-01

    Various microscopic techniques were used to characterize experimental micro- craters in aluminium foils to prepare for the comprehensive analysis of the cometary and interstellar particle impacts in aluminium foils to be returned by the Stardust mission. First, SEM (Scanning Electron Microscopy) and EDS (Energy Dispersive X-ray Spectroscopy) were used to study the morphology of the impact craters and the bulk composition of the residues left by soda-lime glass impactors. A more detailed structural and compositional study of impactor remnants was then performed using TEM (Transmission Electron Microscopy), EDS, and electron diffraction methods. The TEM samples were prepared by Focused Ion Beam (FIB) methods. This technique proved to be especially valuable in studying impact crater residues and impact crater morphology. Finally, we also showed that InfraRed microscopy (IR) can be a quick and reliable tool for such investigations. The combination of all of these tools enables a complete microscopic characterization of the craters.

  20. Morphology correlation of craters formed by hypervelocity impacts

    NASA Technical Reports Server (NTRS)

    Crawford, Gary D.; Rose, M. Frank; Zee, Ralph H.

    1993-01-01

    Dust-sized olivine particles were fired at a copper plate using the Space Power Institute hypervelocity facility, simulating micrometeoroid damage from natural debris to spacecraft in low-Earth orbit (LEO). Techniques were developed for measuring crater volume, particle volume, and particle velocity, with the particle velocities ranging from 5.6 to 8.7 km/s. A roughly linear correlation was found between crater volume and particle energy which suggested that micrometeoroids follow standard hypervelocity relationships. The residual debris analysis showed that for olivine impacts of up to 8.7 km/s, particle residue is found in the crater. By using the Space Power Institute hypervelocity facility, micrometeoroid damage to satellites can be accurately modeled.

  1. The Mechanics of Peak-Ring Impact Crater Formation from the IODP-ICDP Expedition 364

    NASA Astrophysics Data System (ADS)

    Melosh, H.; Collins, G. S.; Morgan, J. V.; Gulick, S. P. S.

    2017-12-01

    The Chicxulub impact crater is one of very few peak-ring impact craters on Earth. While small (less than 3 km on Earth) impact craters are typically bowl-shaped, larger craters exhibit central peaks, which in still larger (more than about 100 km on Earth) craters expand into mountainous rings with diameters close to half that of the crater rim. The origin of these peak rings has been contentious: Such craters are far too large to create in laboratory experiments and remote sensing of extraterrestrial examples has not clarified the mechanics of their formation. Two principal models of peak ring formation are currently in vogue, the "nested crater" model, in which the peak ring originates at shallow depths in the target, and the "dynamic collapse" model in which the peak ring is uplifted at the base of a collapsing, over-steepened central peak and its rocks originate at mid-crustal depths. IODP-ICDP Expedition 364 sought to elucidate, among other important goals, the mechanics of peak ring formation in the young (66 Myr), fresh, but completely buried Chicxulub impact crater. The cores from this borehole now show unambiguously that the rocks in the Chicxulub peak ring originated at mid-crustal depths, apparently ruling out the nested crater model. These rocks were shocked to pressures on the order of 10-35 GPa and were so shattered that their densities and seismic velocities now resemble those of sedimentary rocks. The morphology of the final crater, its structure as revealed in previous seismic imaging, and the results from the cores are completely consistent with modern numerical models of impact crater excavation and collapse that incorporate a model for post-impact weakening. Subsequent to the opening of a ca. 100 km diameter and 30 km deep transient crater, this enormous hole in the crust collapsed over a period of about 10 minutes. Collapse was enabled by movement of the underlying rocks, which briefly behaved in the manner of a high-viscosity fluid, a brittle

  2. Compositional Variations of Titan's Impact Craters Indicates Active Surface Erosion

    NASA Astrophysics Data System (ADS)

    Werynski, Alyssa; Neish, Catherine; Le Gall, Alice; Janssen, Michael A.

    2017-10-01

    Titan’s crust is assumed to be mostly water-ice. However, the surface composition is not well constrained due to its thick atmosphere. Based on infrared and radiometry data, the surface appears enriched in organics, with only few areas showing evidence of exposed water-ice. Regions of water-ice enrichment include the rims and ejecta blankets of impact craters. This study utilizes these geologic features to examine compositional variations across Titan’s surface, and their subsequent modification due to erosional processes.Sixteen craters and their ejecta blankets were mapped on a Cassini RADAR mosaic. These features were selected because they are some of the best preserved craters on Titan. Composition was inferred from Cassini’s Visual and Infrared Mapping Spectrometer (VIMS) and 2-cm emissivity data from the Cassini radiometer. With VIMS, different compositional units were inferred from their reflectivity at specific wavelengths. With the emissivity data, high values suggest more organic-rich material, while lower values indicate strong volume scattering. Areas with low emissivity have been interpreted to be water-ice rich, as water-ice is a favorable medium for volume scattering.Results show fresher, well-preserved craters in the dunes regions have a low emissivity indicative of water-ice, and a VIMS spectrum consistent with an unknown material, possibly a mixture of water-ice and organics. As these craters erode over time, the VIMS spectra remain the same but the emissivity increases. Well-preserved craters in the mid-latitude plains show VIMS spectra and emissivity values consistent with water-ice. As these plain craters degrade, the VIMS spectra remain the same, but the emissivity increases. The differing VIMS signatures suggest more mixing with organics during the cratering event in the organic-rich dunes than the plains. The changes in emissivity over time are consistent with organic infilling of subsurface fractures in both regions, with limited

  3. Distribution and abundance of zooplankton populations in Crater Lake, Oregon

    USGS Publications Warehouse

    Larson, G.L.; McIntire, C.D.; Buktenica, M.W.; Girdner, S.F.; Truitt, R.E.

    2007-01-01

    The zooplankton assemblages in Crater Lake exhibited consistency in species richness and general taxonomic composition, but varied in density and biomass during the period between 1988 and 2000. Collectively, the assemblages included 2 cladoceran taxa and 10 rotifer taxa (excluding rare taxa). Vertical habitat partitioning of the water column to a depth of 200 m was observed for most species with similar food habits and/or feeding mechanisms. No congeneric replacement was observed. The dominant species in the assemblages were variable, switching primarily between periods of dominance of Polyarthra-Keratella cochlearis and Daphnia. The unexpected occurrence and dominance of Asplanchna in 1991 and 1992 resulted in a major change in this typical temporal shift between Polyarthra-K. cochlearis and Daphnia. Following a collapse of the zooplankton biomass in 1993 that was probably caused by predation from Asplanchna, Kellicottia dominated the zooplankton assemblage biomass between 1994 and 1997. The decline in biomass of Kellicottia by 1998 coincided with a dramatic increase in Daphnia biomass. When Daphnia biomass declined by 2000, Keratella biomass increased again. Thus, by 1998 the assemblage returned to the typical shift between Keratella-Polyarthra and Daphnia. Although these observations provided considerable insight about the interannual variability of the zooplankton assemblages in Crater Lake, little was discovered about mechanisms behind the variability. When abundant, kokanee salmon may have played an important role in the disappearance of Daphnia in 1990 and 2000 either through predation, inducing diapause, or both. ?? 2007 Springer Science+Business Media B.V.

  4. Large Crater Clustering tool

    NASA Astrophysics Data System (ADS)

    Laura, Jason; Skinner, James A.; Hunter, Marc A.

    2017-08-01

    In this paper we present the Large Crater Clustering (LCC) tool set, an ArcGIS plugin that supports the quantitative approximation of a primary impact location from user-identified locations of possible secondary impact craters or the long-axes of clustered secondary craters. The identification of primary impact craters directly supports planetary geologic mapping and topical science studies where the chronostratigraphic age of some geologic units may be known, but more distant features have questionable geologic ages. Previous works (e.g., McEwen et al., 2005; Dundas and McEwen, 2007) have shown that the source of secondary impact craters can be estimated from secondary impact craters. This work adapts those methods into a statistically robust tool set. We describe the four individual tools within the LCC tool set to support: (1) processing individually digitized point observations (craters), (2) estimating the directional distribution of a clustered set of craters, back projecting the potential flight paths (crater clusters or linearly approximated catenae or lineaments), (3) intersecting projected paths, and (4) intersecting back-projected trajectories to approximate the local of potential source primary craters. We present two case studies using secondary impact features mapped in two regions of Mars. We demonstrate that the tool is able to quantitatively identify primary impacts and supports the improved qualitative interpretation of potential secondary crater flight trajectories.

  5. Well-preserved low thermal inertia ejecta deposits surrounding young secondary impact craters on Mars

    NASA Astrophysics Data System (ADS)

    Hill, J. R.; Christensen, P. R.

    2017-06-01

    Following the most recent updates to the Mars Odyssey Thermal Emission Imaging System daytime and nighttime infrared global mosaics, a colorized global map was produced that combines the thermophysical information from the nighttime infrared global mosaic with the morphologic context of the daytime infrared global mosaic. During the validation of this map, large numbers of low thermal inertia ejecta deposits surrounding small young impact craters were observed. A near-global survey (60°N-60°S) identified 4024 of these low thermal inertia ejecta deposits, which were then categorized based on their apparent state of degradation. Mapping their locations revealed that they occur almost exclusively in regions with intermediate-to-high thermal inertias, with distinct clusters in northern Terra Sirenum, Solis Planum, and southwestern Daedalia Planum. High-Resolution Imaging Science Experiment images show that the thermophysically distinct facies of the deposits are well correlated with the estimated average ejecta grain sizes, which decrease with radial distance from the crater. Comparisons with recent primary impact craters and secondary impact craters surrounding Zunil Crater show that the low thermal inertia ejecta deposits very closely resemble the secondary craters, but not the primary craters. We conclude that the low thermal inertia ejecta deposits are secondary impact crater ejecta deposits, many of which originated from the rayed crater primary impact events, and are both well preserved and easily identifiable due to the absence of dust cover and aeolian modification that would otherwise reduce the thermal contrast between the ejecta facies and the surrounding terrain.

  6. Melt production in large-scale impact events: Implications and observations at terrestrial craters

    NASA Technical Reports Server (NTRS)

    Grieve, Richard A. F.; Cintala, Mark J.

    1992-01-01

    The volume of impact melt relative to the volume of the transient cavity increases with the size of the impact event. Here, we use the impact of chondrite into granite at 15, 25, and 50 km s(sup -1) to model impact-melt volumes at terrestrial craters in crystalline targets and explore the implications for terrestrial craters. Figures are presented that illustrate the relationships between melt volume and final crater diameter D(sub R) for observed terrestrial craters in crystalline targets; also included are model curves for the three different impact velocities. One implication of the increase in melt volumes with increasing crater size is that the depth of melting will also increase. This requires that shock effects occurring at the base of the cavity in simple craters and in the uplifted peaks of central structures at complex craters record progressively higher pressures with increasing crater size, up to a maximum of partial melting (approx. 45 GPa). Higher pressures cannot be recorded in the parautochthonous rocks of the cavity floor as they will be represented by impact melt, which will not remain in place. We have estimated maximum recorded pressures from a review of the literature, using such observations as planar features in quartz and feldspar, diaplectic glasses of feldspar and quartz, and partial fusion and vesiculation, as calibrated with estimates of the pressures required for their formation. Erosion complicates the picture by removing the surficial (most highly shocked) rocks in uplifted structures, thereby reducing the maximum shock pressures observed. In addition, the range of pressures that can be recorded is limited. Nevertheless, the data define a trend to higher recorded pressures with crater diameter, which is consistent with the implications of the model. A second implication is that, as the limit of melting intersects the base of the cavity, central topographic peaks will be modified in appearance and ultimately will not occur. That is

  7. Formation (and dating) of small impact craters on Earth as an analogue for Mars (Ilumetsa Craters Estonia)

    NASA Astrophysics Data System (ADS)

    Losiak, Anna; Jõeleht, Argo; Plado, Juri; Szyszka, Mateusz; Wild, Eva Maria; Bronikowska, Malgorzata; Belcher, Claire; Kirsimäe, Kalle; Steier, Peter

    2017-04-01

    Crater-strewn-fields are present on planetary bodies with an atmosphere such as Earth and Mars, but the process of their formation is still not fully understood. For example, a recent discovery of small pieces of impact-produced-charcoal within the ejecta blanket of 100 m in diameter Kaali crater (Losiak et al. 2016) may suggest existence of very local ( 10 cm thick layer in the distance of 10 m from the rim), short lived ( hours) thermal anomalies ( 300°C) in the ejecta blanket of even small craters. Ilumetsa in SE Estonia is an atypical example of crater-strewn-field consisting of only two relatively large, rimmed structures with diameters of 75-80 m (Ilumetsa Large: IL) and 50 m (Ilumetsa Small: IS) with true depths of about 8 and 3.5 m, respectively (Plado 2012 MAPS). Structures were previously dated by the 14C analysis of gyttja from the bottom of IL (Liiva et al. 1979 Eesti Loodus) to be 7170-6660 cal. BP. About 600 years older age (7570-7320 cal. BC: Raukas et al. 2001, MAPS) was proposed based on dated layer of peat in which glassy spherules, interpreted as dissipated melt or condensed vapor (however their chemical composition was not reported). Ilumetsa is listed as a proven meteorite impact in the Earth Impact Database, but neither remnants of the projectile nor other identification criteria (e.g., PDFs) have been found up to this point. The aim of this study was to search for possible impact related charcoals in order to determine the size and extend of thermal anomalies around small impact craters, as well as to determine how this atypical strew field was formed. Additionally, we hoped to determine/confirm the age of those structures. We have found charcoal in a similar geological setting as in Kaali Main crater in both Ilumetsa structures. The calibrated (95,4% probability) time ranges of four dated samples from IL and one sample of IS span the time interval from 7670-6950 cal. BP (consistent with previous dating). One sample from IS is younger (4830

  8. Excavation of buried hydrated minerals on Mars by impact cratering? (Invited)

    NASA Astrophysics Data System (ADS)

    Carter, J.; Poulet, F.; Loizeau, D.; Bibring, J.

    2010-12-01

    Impact cratering is a key process when studying Mars’s past aqueous environments. It is a widespread and dynamic process which has been active throughout Mars’s history, especially during the Noachian era. Noachian-aged hydrated minerals have been reported on Mars (e.g. [1, 2]) and provide strong constrains on the alleged early wet Martian environment [3]. Our knowledge of this early wet environment will be greatly improved if we understand how hydrated minerals are formed, modified or destroyed by impact processes. One main consequence of impact cratering is the excavation of buried material. Excavated material is found in walls, ejecta and central uplifts in the case of large complex craters. It may originate from the deeply buried crust or subsurface, depending on crater size [4]. In this case craters act as natural boreholes that allow orbital spectroscopic inquiry of otherwise hidden material and is of great importance when investigating the aqueous alteration of Mars. This process has proven particularly useful when studying the northern crust of Mars which is covered by a thick mantling unit [5]. Large craters have penetrated the cover and exhumed buried hydrated crustal material, including the low-grade metamorphic mineral prehnite and there is evidence that the ancient crust has been altered by water down to kilometer depths, both in the northern plains and southern highlands [6]. Using the OMEGA and CRISM [7, 8] near-infrared hyperspectral instruments currently in orbit around Mars we have mapped surface exposures of hydrated minerals and found that many are associated with impact structures [9]. Here we report how detailed analysis of these sites reveal exposures of various hydrated minerals including phyllosilicates, zeolites and sulfates, associated with crater central uplifts, floors, walls, rims and ejecta. We focus on the heavily cratered Tyrrhena Terra region of Mars as well as the large northern plain craters. In both cases, excavation of

  9. Ganymede - Ancient Impact Craters in Galileo Regio

    NASA Image and Video Library

    1997-09-07

    Ancient impact craters shown in this image of Jupiter moon Ganymede taken by NASA Galileo spacecraft testify to the great age of the terrain, dating back several billion years. http://photojournal.jpl.nasa.gov/catalog/PIA00279

  10. Acoustic fluidization and the scale dependence of impact crater morphology

    NASA Technical Reports Server (NTRS)

    Melosh, H. J.; Gaffney, E. S.

    1983-01-01

    A phenomenological Bingham plastic model has previously been shown to provide an adequate description of the collapse of impact craters. This paper demonstrates that the Bingham parameters may be derived from a model in which acoustic energy generated during excavation fluidizes the rock debris surrounding the crater. Experimental support for the theoretical flow law is presented. Although the Bingham yield stress cannot be computed without detailed knowledge of the initial acoustic field, the Bingham viscosity is derived from a simple argument which shows that it increases as the 3/2 power of crater diameter, consistent with observation. Crater collapse may occur in material with internal dissipation Q as low as 100, comparable to laboratory observations of dissipation in granular materials. Crater collapse thus does not require that the acoustic field be regenerated during flow.

  11. Effects of the Venusian atmosphere on incoming meteoroids and the impact crater population

    NASA Technical Reports Server (NTRS)

    Herrick, Robert R.; Phillips, Roger J.

    1994-01-01

    The dense atmosphere on Venus prevents craters smaller than about 2 km in daimater from forming and also causes formation of several crater fields and multiple-floored craters (collectively referred to as multiple impacts). A model has been constructed that simulates the behavior of a meteoroid in a dense planetary atmosphere. This model was then combined with an assumed flux of incoming meteoroids in an effort to reproduce the size-frequency distribution of impact craters and several aspects of the population of the crater fields and multiple-floored craters on Venus. The modeling indicates that it is plausible that the observed rollover in the size-frequency curve for Venus is due entirely to atmospheric effects on incoming meteoroids. However, there must be substantial variation in the density and behavior of incoming meteoroids in the atmosphere. Lower-density meteoroids must be less likely to survive atmospheric passage than simple density differences can account for. Consequently, it is likely that the percentage of craters formed by high-density meteoroids is very high at small crater diameters, and this percentage decreases substantially with increasing crater diameter. Overall, high-density meteoroids created a disproportionately large percentage of the impact craters on Venus. Also, our results indicate that a process such as meteoroid flattening or atmospheric explosion of meteoroids must be invoked to prevent craters smaller than the observed minimum diameter (2 km) from forming. In terms of using the size-frequency distribution to age-date the surface, the model indicates that the observed population has at least 75% of the craters over 32 km in diameter that would be expected on an atmosphereless Venus; thus, this part of the curve is most suitable for comparison with calibrated curves for the Moon.

  12. Global Geometric Properties of Martian Impact Craters: A Preliminary Assessment Using Mars Orbiter Laser Altimeter (MOLA)

    NASA Technical Reports Server (NTRS)

    Garvin, J. B.; Sakimoto, S. E. H.; Schnetzler, C.; Frawley, J. J.

    1999-01-01

    Impact craters on Mars have been used to provide fundamental insights into the properties of the martian crust, the role of volatiles, the relative age of the surface, and on the physics of impact cratering in the Solar System. Before the three-dimensional information provided by the Mars Orbiter Laser Altimeter (MOLA) instrument which is currently operating in Mars orbit aboard the Mars Global Surveyor (MGS), impact features were characterized morphologically using orbital images from Mariner 9 and Viking. Fresh-appearing craters were identified and measurements of their geometric properties were derived from various image-based methods. MOLA measurements can now provide a global sample of topographic cross-sections of martian impact features as small as approx. 2 km in diameter, to basin-scale features. We have previously examined MOLA cross-sections of Northern Hemisphere and North Polar Region impact features, but were unable to consider the global characteristics of these ubiquitous landforms. Here we present our preliminary assessment of the geometric properties of a globally-distributed sample of martian impact craters, most of which were sampled during the initial stages of the MGS mapping mission (i.e., the first 600 orbits). Our aim is to develop a framework for reconsidering theories concerning impact cratering in the martian environment. This first global analysis is focused upon topographically-fresh impact craters, defined here on the basis of MOLA topographic profiles that cross the central cavities of craters that can be observed in Viking-based MDIM global image mosaics. We have considered crater depths, rim heights, ejecta topologies, cross-sectional "shapes", and simple physical models for ejecta emplacement. To date (May, 1999), we have measured the geometric properties of over 1300 impact craters in the 2 to 350 km diameter size interval. A large fraction of these measured craters were sampled with cavity-center cross-sections during the first

  13. Scaling law deduced from impact-cratering experiments on basalt targets

    NASA Astrophysics Data System (ADS)

    Takagi, Y.; Hasegawa, S.; Suzuki, A.

    2014-07-01

    Since impact-cratering phenomena on planetary bodies were the key process which modified the surface topography and formed regolith layers, many experiments on non-cohesive materials (sand, glass beads) were performed. On the other hand, experiments on natural rocks were limited. Especially, experiments on basalt targets are rare, although basalt is the most common rocky material on planetary surfaces. The reason may be the difficulties of obtaining basalt samples suitable for cratering experiments. Recently, we obtained homogenous and crackless large basalt blocks. We performed systematic cratering experiments using the basalt targets. Experimental Procedure: Impact experiments were performed using a double stage light-gas (hydrogen) gun on the JAXA Sagamihara campus. Spherical projectiles of nylon, aluminum, stainless steel, and tungsten carbide were launched at velocities between 2400 and 6100 m/sec. The projectiles were 1.0 to 7.1 mm in diameter and 0.004 to 0.22 g in mass. The incidence angle was fixed at 90 degrees. The targets were rectangular blocks of Ukrainian basalt. The impact plane was a square with 20-cm sides. The thickness was 9 cm. Samples were cut out from a columnar block so that the impact plane might become perpendicular to the axis of the columnar joint. The mass was about 10.5 kg. The density was 2920 ± 10 kg/m^3 . Twenty eight shots were performed. Three-dimensional shapes of craters were measured by an X-Y stage with a laser displacement sensor (Keyence LK-H150). The interval between the measurement points was 200 micrometer. The volume, depth, and aperture area of the crater were calculated from the 3-D data using analytical software. Since the shapes of the formed craters are markedly asymmetrical, the diameter of the circle whose area is equal to the aperture area was taken as the crater diameter. Results: The diameter, depth, and the volume of the formed craters are normalized by the π parameters. Experimental conditions are also

  14. Robust System for Automated Identification of Martian Impact Craters

    NASA Astrophysics Data System (ADS)

    Stepinski, T. F.; Mendenhall, M. P.

    2006-12-01

    Detailed analysis of the number and morphology of impact craters on Mars provides the worth of information about the geologic history of its surface. Global catalogs of Martian craters have been compiled (for example, the Barlow catalog) but they are not comprehensive, especially for small craters. Existing methods for machine detection of craters from images suffer from low efficiency and are not practical for global surveys. We have developed a robust two-stage system for an automated cataloging of craters from digital topography data (DEM). In the first stage an innovative crater-finding transform is performed on a DEM to identify centers of potential craters, their extents, and their basic characteristics. This stage produces a preliminary catalog. In the second stage a machine learning methods are employed to eliminate false positives. Using the MOLA derived DEMs with resolution of 1/128 degrees/pixel, we have applied our system to six ~ 106 km2 sites. The system has identified 3217 craters, 43% more than are present in the Barlow catalog. The extra finds are predominantly small craters that are most difficult to account for in manual surveys. Because our automated survey is DEM-based, the resulting catalog lists craters' depths in addition to their positions, sizes, and measures of shape. This feature significantly increases the scientific utility of any catalog generated using our system. Our initial calculations yield a training set that will be used to identify craters over the entire Martian surface with estimated accuracy of 95%. Moreover, because our method is pixel-based and scale- independent, the present training set may be used to identify craters in higher resolution DEMs derived from Mars Express HRSC images. It also can be applied to future topography data from Mars and other planets. For example, it may be utilized to catalog craters on Mercury and the Moon using altimetry data to be gathered by Messenger and Lunar Reconnaissance Orbiter

  15. A crater and its ejecta: An interpretation of Deep Impact

    NASA Astrophysics Data System (ADS)

    Holsapple, Keith A.; Housen, Kevin R.

    2007-03-01

    We apply recently updated scaling laws for impact cratering and ejecta to interpret observations of the Deep Impact event. An important question is whether the cratering event was gravity or strength-dominated; the answer gives important clues about the properties of the surface material of Tempel 1. Gravity scaling was assumed in pre-event calculations and has been asserted in initial studies of the mission results. Because the gravity field of Tempel 1 is extremely weak, a gravity-dominated event necessarily implies a surface with essentially zero strength. The conclusion of gravity scaling was based mainly on the interpretation that the impact ejecta plume remained attached to the comet during its evolution. We address that feature here, and conclude that even strength-dominated craters would result in a plume that appeared to remain attached to the surface. We then calculate the plume characteristics from scaling laws for a variety of material types, and for gravity and strength-dominated cases. We find that no model of cratering alone can match the reported observation of plume mass and brightness history. Instead, comet-like acceleration mechanisms such as expanding vapor clouds are required to move the ejected mass to the far field in a few-hour time frame. With such mechanisms, and to within the large uncertainties, either gravity or strength craters can provide the levels of estimated observed mass. Thus, the observations are unlikely to answer the questions about the mechanical nature of the Tempel 1 surface.

  16. A crater and its ejecta: An interpretation of Deep Impact

    NASA Astrophysics Data System (ADS)

    Holsapple, Keith A.; Housen, Kevin R.

    We apply recently updated scaling laws for impact cratering and ejecta to interpret observations of the Deep Impact event. An important question is whether the cratering event was gravity or strength-dominated; the answer gives important clues about the properties of the surface material of Tempel 1. Gravity scaling was assumed in pre-event calculations and has been asserted in initial studies of the mission results. Because the gravity field of Tempel 1 is extremely weak, a gravity-dominated event necessarily implies a surface with essentially zero strength. The conclusion of gravity scaling was based mainly on the interpretation that the impact ejecta plume remained attached to the comet during its evolution. We address that feature here, and conclude that even strength-dominated craters would result in a plume that appeared to remain attached to the surface. We then calculate the plume characteristics from scaling laws for a variety of material types, and for gravity and strength-dominated cases. We find that no model of cratering alone can match the reported observation of plume mass and brightness history. Instead, comet-like acceleration mechanisms such as expanding vapor clouds are required to move the ejected mass to the far field in a few-hour time frame. With such mechanisms, and to within the large uncertainties, either gravity or strength craters can provide the levels of estimated observed mass. Thus, the observations are unlikely to answer the questions about the mechanical nature of the Tempel 1 surface.

  17. Geological remote sensing signatures of terrestrial impact craters

    NASA Technical Reports Server (NTRS)

    Garvin, J. B.; Schnetzler, C.; Grieve, R. A. F.

    1988-01-01

    Geological remote sensing techniques can be used to investigate structural, depositional, and shock metamorphic effects associated with hypervelocity impact structures, some of which may be linked to global Earth system catastrophies. Although detailed laboratory and field investigations are necessary to establish conclusive evidence of an impact origin for suspected crater landforms, the synoptic perspective provided by various remote sensing systems can often serve as a pathfinder to key deposits which can then be targetted for intensive field study. In addition, remote sensing imagery can be used as a tool in the search for impact and other catastrophic explosion landforms on the basis of localized disruption and anomaly patterns. In order to reconstruct original dimensions of large, complex impact features in isolated, inaccessible regions, remote sensing imagery can be used to make preliminary estimates in the absence of field geophysical surveys. The experienced gained from two decades of planetary remote sensing of impact craters on the terrestrial planets, as well as the techniques developed for recognizing stages of degradation and initial crater morphology, can now be applied to the problem of discovering and studying eroded impact landforms on Earth. Preliminary results of remote sensing analyses of a set of terrestrial impact features in various states of degradation, geologic settings, and for a broad range of diameters and hence energies of formation are summarized. The intention is to develop a database of remote sensing signatures for catastrophic impact landforms which can then be used in EOS-era global surveys as the basis for locating the possibly hundreds of missing impact structures. In addition, refinement of initial dimensions of extremely recent structures such as Zhamanshin and Bosumtwi is an important objective in order to permit re-evaluation of global Earth system responses associated with these types of events.

  18. Phobos - Surface density of impact craters

    NASA Technical Reports Server (NTRS)

    Thomas, P.; Veverka, J.

    1977-01-01

    Revised crater counts for Phobos are presented which are based on uniform Mariner 9 imagery and Duxbury's (1974) map of the satellite. The contiguous portion of the satellite's surface on which all craters down to the limiting resolution of 0.2 to 0.3 km in diameter would be expected to be identified is delineated and found to contain 87 identifiable craters larger than 0.2 km in diameter. Analysis of the crater size distribution shows that the surface appears to be saturated for craters exceeding 1 km in diameter but the crater counts definitely fall below the saturation curve for smaller craters. Reasons for this fall-off are considered, and it is noted that too few craters are visible in Mariner 9 images of Deimos to permit meaningful crater counts on that satellite's surface. It is concluded that, contrary to a previous assertion, the surfaces of Phobos and Deimos are not known to be saturated with craters larger than 0.2 km in diameter.

  19. Impact craters at falling of large asteroids in Ukraine

    NASA Astrophysics Data System (ADS)

    Vidmachenko, A. P.

    2016-05-01

    Catastrophes of different scale that are associated with the fall of celestial bodies to the Earth - occurred repeatedly in its history. But direct evidence of such catastrophes has been discovered recently. Thus, in the late 1970s studies of terrestrial rocks showed that in layers of the earth's crust that corresponded to the period of 65 million years before the present, marked by the mass extinction of some species of living creatures, and the beginning of the rapid development of others. It was then - a large body crashed to Earth in the Gulf of Mexico in Central America. The consequence of this is the Chicxulub crater with a diameter of ~170 km on Yucatan Peninsula. Modern Earth's surface retains many traces of collisions with large cosmic bodies. To indicate the craters with a diameter of more than 2 km using the name "astrobleme". Today, it found more than 230. The largest astroblems sizes exceeding 200 km. Ukraine also has some own astroblems. In Ukraine, been found nine large impact craters. Ukrainian crystalline shield, because of its stability for a long time (more than 1.5 billion years), has the highest density of large astroblems on the Earth's surface. The largest of the Ukrainian astroblems is Manevytska. It has a diameter of 45 km. There are also Ilyinetskyi (7 km), Boltysh (25 km), Obolon' (20 km), Ternivka (12-15 km), Bilylivskyi (6 km), Rotmystrivka (3 km) craters. Zelenohayska astrobleme founded near the village Zelenyi Gay in Kirovograd region and consists of two craters: larger with diameter 2.5-3.5 km and smaller - with diameter of 800 m. The presence of graphite, which was the basis for the research of the impact diamond in astroblems of this region. As a result, the diamonds have been found in rocks of Ilyinetskyi crater; later it have been found in rocks in the Bilylivska, Obolon' and other impact structures. The most detailed was studied the geological structure and the presence of diamonds in Bilylivska astrobleme

  20. Terrestrial Analogs for Surface Properties Associated with Impact Cratering on the Moon - Self-secondary Impact Features at Kings Bowl, Idaho

    NASA Astrophysics Data System (ADS)

    Matiella Novak, M. A.; Zanetti, M.; Neish, C.; Kukko, A.; Fan, K.; Heldmann, J.; Hughes, S. S.

    2017-12-01

    The Kings Bowl (KB) eruptive fissure and lava field, located in the southern end of Craters of the Moon National Monument, Idaho, is an ideal location for planetary analogue field studies of surface properties related to volcanic and impact processes. Here we look at possible impact features present in the KB lava field near the main vent that resulted in squeeze-ups of molten lava from beneath a semi-solid lava lake crust. These may have been caused by the ejection of blocks during the phreatic eruption that formed the Kings Bowl pit, and their subsequent impact into a partially solidified lava pond. We compare and contrast these features with analogous self-secondary impact features, such as irregular, rimless secondary craters ("splash craters") observed in lunar impact melt deposits, to better understand how self-secondary impacts determine the surface properties of volcanic and impact crater terrains. We do this by analyzing field measurements of these features, as well as high-resolution DEM data collected through the Kinematic LiDAR System (KLS), both of which give us feature dimensions and distributions. We then compare these data with self-secondary impact features on the Moon and related surface roughness constrained through Lunar Reconnaissance Orbiter observations (Mini-RF and LROC NACs). Possible self-secondary impact features can be found in association with many lunar impact craters. These are formed when ballistic ejecta from the crater falls onto the ejecta blanket and melt surrounding the newly formed crater. Self-secondary impact features involving impact melt deposits are particularly useful to study because the visibly smooth melt texture serves to highlight the impact points in spacecraft imagery. The unusual morphology of some of these features imply that they formed when the melt had not yet completely solidified, strongly suggesting a source of impactors from the primary crater itself. We will also discuss ongoing efforts to integrate field

  1. Stickney-forming impact on PHOBOS - Crater shape and induced stress distribution

    NASA Astrophysics Data System (ADS)

    Fujiwara, A.

    1991-02-01

    The results of the present simplified modeling of the size and rim shape of the Phobos crater Stickney, together with the impact-generated stress patterns on the surface of the crater, account for the general features observed and suggest, on the basis of some of the P-waves' surface stress pattern, that a region of higher tensile stress may have occurred in the vicinity of 0 deg latitude and 270 deg W. The correlation of this pattern with the focusing of groove patterns that occurs on the trailing side of Phobos is suggested to demonstrate a connection between these grooves and the Stickney crater-forming impact.

  2. Impact Craters: Size-Dependent Degration Rates

    NASA Astrophysics Data System (ADS)

    Ravi, S.; Mahanti, P.; Meyer, H. M.; Robinson, M. S.

    2017-12-01

    From superposition relations, Shoemaker and Hackman (1) devised the lunar geologic timescale with Copernican and Eratosthenian as the most recent periods. Classifying craters into the two periods is key to understanding impactor flux and regolith maturation rates over the last 3 Ga. Both Copernican and Eratosthenian craters exhibit crisp morphologies (sharp rims, steep slopes), however, only the former exhibit high reflectance rays and ejecta (1). Based on the Optical Maturity Parameter (OMAT; 2), Grier et al. (3) classified 50 fresh craters (D >20 km) into 3 categories - young (OMAT >0.22), intermediate, and old (OMAT <0.16). In our previous work, Copernican craters (D > 10) were identified (4) from a catalogue of 11,875 craters (5). In this work; we compare two size ranges (D: 5 km - 10 km and 10 km to 15 km) of 177 Copernican craters based on the average OMAT, measured near the crater rim (3). OMAT is measured at the crater rim (as opposed to further away from the crater) to minimize the influence of spatial variation of OMAT (6) in our investigation. We found that OMAT values are typically lower for smaller craters (5km < D < 10km) in comparison to larger craters (10km < D < 15km). However, when compared against morphological freshness (as determined by d/D for simpler craters), the smaller craters were fresher (higher d/D value). Since the OMAT value decreases with age, craters with higher d/D value (morphologically fresher) should have higher OMAT, but this is not the case. We propose that quicker loss of OMAT (over time) for smaller craters compared to decrease in d/D with crater ageing, is responsible for the observed decreased OMAT for smaller craters. (1) Shoemaker and Hackman, 1962 (2) Lucey et al., 2000 (3) Grier et al., 2001 (4) Ravi et al., 2016 (5) Reinhold et al., 2015 (6) Mahanti et al., 2016

  3. Paleomagnetic and Magnetostratigraphic Studies in Drilling Projects of Impact Craters - Recent Studies, Challenges and Perspectives

    NASA Astrophysics Data System (ADS)

    Fucugauchi, J. U.; Velasco-Villarreal, M.; Perez-Cruz, L. L.

    2013-05-01

    Paleomagnetic studies have long been successfully carried out in drilling projects, to characterize the borehole columns and to investigate the subsurface structure and stratigraphy. Magnetic susceptibility logging and magnetostratigraphic studies provide data for lateral correlation, formation evaluation, azimuthal core orientation, physical properties, etc., and are part of the tools available in the ocean and continental drilling programs. The inclusion of continuous core recovery in scientific drilling projects have greatly expanded the range of potential applications of paleomagnetic and rock magnetic studies, by allowing laboratory measurements on core samples. For this presentation, we concentrate on drilling studies of impact structures and their usefulness for documenting the structure, stratigraphy and physical properties at depth. There are about 170-180 impact craters documented in the terrestrial record, which is a small number compared to what is observed in the Moon, Mars, Venus and other bodies of the solar system. Of the terrestrial impact craters, only a few have been studied by drilling. Some craters have been drilled as part of industry exploration surveys and/or academic projects, including notably the Sudbury, Ries, Vredefort, Manson and many other craters. As part of the Continental ICDP program, drilling projects have been conducted on the Chicxulub, Bosumtwi, Chesapeake and El gygytgyn craters. Drilling of terrestrial craters has proved important in documenting the shallow stratigraphy and structure, providing insight on the cratering and impact dynamics. Questions include several that can only be addressed by retrieving core samples and laboratory analyses. Paleomagnetic, rock magnetic and fabric studies have been conducted in the various craters, which are here summarized with emphasis on the Chicxulub crater and Yucatan carbonate platform. Chicxulub is buried under a kilometer of younger sediments, making drilling an essential tool. Oil

  4. The Chesapeake Bay Impact Crater: An Educational Investigation for Students into the Planetary Impact Process and its Environmental Consequences

    NASA Technical Reports Server (NTRS)

    Levine, Arlene S.

    2008-01-01

    Planetary impact craters are a common surface feature of many planetary bodies, including the Earth, the Moon, Mars, Mercury, Venus, and Jupiter s moons, Ganymede and Callisto. The NASA Langley Research Center in Hampton, VA, is located about 5 km inside the outer rim of the Chesapeake Bay Impact Crater. The Chesapeake Bay Impact Crater, with a diameter of 85 km is the sixth largest impact crater on our planet. The U.S. Geological Survey (USGS), in collaboration with the NASA Langley Research Center, the Virginia Department of Environmental Quality (VDEQ), the Hampton Roads Planning District Commission (HRPDC), and the Department of Geology of the College of William and Mary (WM) drilled into and through the crater at the NASA Langley Research Center and obtained a continuous core to a depth of 2075.9 ft (632.73 meters) from the Chesapeake Bay Impact Crater. At the NASA Langley location, the granite basement depth was at 2046 ft (623.87 meters). This collaborative drilling activity provided a unique educational opportunity and ongoing educational partnership between USGS, NASA Langley and the other collaborators. NASA Langley has a decade-long, ongoing educational partnership with the Colonial Coast Council of the Girl Scouts. The core drilling and on site analysis and cataloguing of the core segments provided a unique opportunity for the Girl Scouts to learn how geologists work in the field, their tools for scientific investigation and evaluation, how they perform geological analyses of the cores in an on-site tent and learn about the formation of impact craters and the impact of impacting bodies on the sub-surface, the surface, the oceans and atmosphere of the target body. This was accomplished with a two-part activity. Girl Scout day camps and local Girl Scout troops were invited to Langley Research Center Conference Center, where more than 300 Girl Scouts, their leaders and adult personnel were given briefings by scientists and educators from the USGS, NASA

  5. Impact and explosion crater ejecta, fragment size, and velocity

    NASA Technical Reports Server (NTRS)

    Okeefe, J. D.; Ahrens, T. J.

    1985-01-01

    The present investigation had the objective to develop models for the distribution of fragments which are ejected at a given velocity for both impact and explosion cratering. It is pointed out that the results have application to the physics of planetary accretion and the origin of meteorites. The impact ejection of fine dust into the earth's atmosphere has been proposed as a mechanism for extinctions which occurred at the end of the Cretaceous. A technique is developed for determining the distribution of fragments which are ejected at a given velocity. The experimental data base for the distribution fragments in the ejecta blankets of impact, explosion, and nuclear craters, are discussed. Attention is also given to impact flow field calculations, fragmentation theory, and the applications of the derived relations.

  6. Impact and Cratering History of the Pluto System

    NASA Astrophysics Data System (ADS)

    Greenstreet, Sarah; Gladman, Brett; McKinnon, William B.

    2014-11-01

    The observational opportunity of the New Horizons spacecraft fly-through of the Pluto system in July 2015 requires a current understanding of the Kuiper belt dynamical sub-populations to accurately interpret the cratering history of the surfaces of Pluto and its satellites. We use an Opik-style collision probability code to compute impact rates and impact velocity distributions onto Pluto and its binary companion Charon from the Canada-France Ecliptic Plane Survey (CFEPS) model of classical and resonant Kuiper belt populations (Petit et al., 2011; Gladman et al., 2012) and the scattering model of Kaib et al. (2011) calibrated to Shankman et al. (2013). Due to the uncertainty in how the well-characterized size distribution for Kuiper belt objects (with diameter d>100 km) connects to smaller objects, we compute cratering rates using three simple impactor size distribution extrapolations (a single power-law, a power-law with a knee, and a power-law with a divot) as well as the "curvy" impactor size distributions from Minton et al. (2012) and Schlichting et al. (2013). Current size distribution uncertainties cause absolute ages computed for Pluto surfaces to be entirely dependent on the extrapolation to small sizes and thus uncertain to a factor of approximately 6. We illustrate the relative importance of each Kuiper belt sub-population to Pluto's cratering rate, both now and integrated into the past, and provide crater retention ages for several cases. We find there is only a small chance a crater with diameter D>200 km has been created on Pluto in the past 4 Gyr. The 2015 New Horizons fly-through coupled with telescope surveys that cover objects with diameters d=10-100 km should eventually drop current crater retention age uncertainties on Pluto to <30%. In addition, we compute the "disruption timescale" (to a factor of three accuracy) for Pluto's smaller satellites: Styx, Nix, Kerberos, and Hydra.

  7. The early Martian environment: Clues from the cratered highlands and the Precambrian Earth

    NASA Technical Reports Server (NTRS)

    Craddock, R. A.; Maxwell, T. A.

    1993-01-01

    There is abundant geomorphic evidence to suggest that Mars once had a much denser and warmer atmosphere than present today. Outflow channel, ancient valley networks, and degraded impact craters in the highlands all suggest that ancient Martian atmospheric conditions supported liquid water on the surface. The pressure, composition, and duration of this atmosphere is largely unknown. However, we have attempted to place some constraints on the nature of the early Martian atmosphere by analyzing morphologic variations of highland impact crater populations, synthesizing results of other investigators, and incorporating what is know about the geologic history of the early Earth. This is important for understanding the climatic evolution of Mars, the relative abundance of martian volatiles, and the nature of highland surface materials.

  8. Shock-induced damage in rocks: Application to impact cratering

    NASA Astrophysics Data System (ADS)

    Ai, Huirong

    Shock-induced damage beneath impact craters is studied in this work. Two representative terrestrial rocks, San Marcos granite and Bedford limestone, are chosen as test target. Impacts into the rock targets with different combinations of projectile material, size, impact angle, and impact velocity are carried out at cm scale in the laboratory. Shock-induced damage and fracturing would cause large-scale compressional wave velocity reduction in the recovered target beneath the impact crater. The shock-induced damage is measured by mapping the compressional wave velocity reduction in the recovered target. A cm scale nondestructive tomography technique is developed for this purpose. This technique is proved to be effective in mapping the damage in San Marcos granite, and the inverted velocity profile is in very good agreement with the result from dicing method and cut open directly. Both compressional velocity and attenuation are measured in three orthogonal directions on cubes prepared from one granite target impacted by a lead bullet at 1200 m/s. Anisotropy is observed from both results, but the attenuation seems to be a more useful parameter than acoustic velocity in studying orientation of cracks. Our experiments indicate that the shock-induced damage is a function of impact conditions including projectile type and size, impact velocity, and target properties. Combined with other crater phenomena such as crater diameter, depth, ejecta, etc., shock-induced damage would be used as an important yet not well recognized constraint for impact history. The shock-induced damage is also calculated numerically to be compared with the experiments for a few representative shots. The Johnson-Holmquist strength and failure model, initially developed for ceramics, is applied to geological materials. Strength is a complicated function of pressure, strain, strain rate, and damage. The JH model, coupled with a crack softening model, is used to describe both the inelastic response of

  9. Shock-wave-induced fracturing of calcareous nannofossils from the Chesapeake Bay impact crater

    USGS Publications Warehouse

    ,

    2003-01-01

    Fractured calcareous nannofossils of the genus Discoaster from synimpact sediments within the Chesapeake Bay impact crater demonstrate that other petrographic shock indicators exist for the cratering process in addition to quartz minerals. Evidence for shock-induced taphonomy includes marginal fracturing of rosette-shaped Discoaster species into pentagonal shapes and pressure- and temperature-induced dissolution of ray tips and edges of discoasters. Rotational deformation of individual crystallites may be the mechanism that produces the fracture pattern. Shock-wave-fractured calcareous nannofossils were recovered from synimpact matrix material representing tsunami or resurge sedimentation that followed impact. Samples taken from cohesive clasts within the crater rubble show no evidence of shock-induced fracturing. The data presented here support growing evidence that microfossils can be used to determine the intensity and timing of wet-impact cratering.

  10. The structural inventory of a small complex impact crater: Jebel Waqf as Suwwan, Jordan

    NASA Astrophysics Data System (ADS)

    Kenkmann, Thomas; Sturm, Sebastian; Krüger, Tim; Salameh, Elias; Al-Raggad, Marwan; Konsul, Khalil

    2017-07-01

    The investigation of terrestrial impact structures is crucial to gain an in-depth understanding of impact cratering processes in the solar system. Here, we use the impact structure Jebel Waqf as Suwwan, Jordan, as a representative for crater formation into a layered sedimentary target with contrasting rheology. The complex crater is moderately eroded (300-420 m) with an apparent diameter of 6.1 km and an original rim fault diameter of 7 km. Based on extensive field work, IKONOS imagery, and geophysical surveying we present a novel geological map of the entire crater structure that provides the basis for structural analysis. Parametric scaling indicates that the structural uplift (250-350 m) and the depth of the ring syncline (<200 m) are anomalously low. The very shallow relief of the crater along with a NE vergence of the asymmetric central uplift and the enhanced deformations in the up-range and down-range sectors of the annular moat and crater rim suggest that the impact was most likely a very oblique one ( 20°). One of the major consequences of the presence of the rheologically anisotropic target was that extensive strata buckling occurred during impact cratering both on the decameter as well as on the hundred-meter scale. The crater rim is defined by a circumferential normal fault dipping mostly toward the crater. Footwall strata beneath the rim fault are bent-up in the down-range sector but appear unaffected in the up-range sector. The hanging wall displays various synthetic and antithetic rotations in the down-range sector but always shows antithetic block rotation in the up-range sector. At greater depth reverse faulting or folding is indicated at the rim indicating that the rim fault was already formed during the excavation stage.

  11. Multivariate analyses of crater parameters and the classification of craters

    NASA Technical Reports Server (NTRS)

    Siegal, B. S.; Griffiths, J. C.

    1974-01-01

    Multivariate analyses were performed on certain linear dimensions of six genetic types of craters. A total of 320 craters, consisting of laboratory fluidization craters, craters formed by chemical and nuclear explosives, terrestrial maars and other volcanic craters, and terrestrial meteorite impact craters, authenticated and probable, were analyzed in the first data set in terms of their mean rim crest diameter, mean interior relief, rim height, and mean exterior rim width. The second data set contained an additional 91 terrestrial craters of which 19 were of experimental percussive impact and 28 of volcanic collapse origin, and which was analyzed in terms of mean rim crest diameter, mean interior relief, and rim height. Principal component analyses were performed on the six genetic types of craters. Ninety per cent of the variation in the variables can be accounted for by two components. Ninety-nine per cent of the variation in the craters formed by chemical and nuclear explosives is explained by the first component alone.

  12. Impact and explosion crater ejecta, fragment size, and velocity

    NASA Technical Reports Server (NTRS)

    Okeefe, J. D.; Ahrens, T. J.

    1983-01-01

    A model was developed for the mass distribution of fragments that are ejected at a given velocity for impact and explosion craters. The model is semi-empirical in nature and is derived from (1) numerical calculations of cratering and the resultant mass versus ejection velocity, (2) observed ejecta blanket particle size distributions, (3) an empirical relationship between maximum ejecta fragment size and crater diameter and an assumption on the functional form for the distribution of fragements ejected at a given velocity. This model implies that for planetary impacts into competent rock, the distribution of fragments ejected at a given velocity are nearly monodisperse, e.g., 20% of the mass of the ejecta at a given velocity contain fragments having a mass less than 0.1 times a mass of the largest fragment moving at that velocity. Using this model, the largest fragment that can be ejected from asteroids, the moon, Mars, and Earth is calculated as a function of crater diameter. In addition, the internal energy of ejecta versus ejecta velocity is found. The internal energy of fragments having velocities exceeding the escape velocity of the moon will exceed the energy required for incipient melting for solid silicates and thus, constrains the maximum ejected solid fragment size.

  13. Experimental investigation of the relationship between impact crater morphology and impacting particle velocity and direction

    NASA Technical Reports Server (NTRS)

    Mackay, N. G.; Green, S. F.; Gardner, D. J.; Mcdonnell, J. A. M.

    1995-01-01

    Interpretation of the wealth of impact data available from the Long Duration Exposure Facility, in terms of the absolute and relative populations of space debris and natural micrometeoroids, requires three dimensional models of the distribution of impact directions, velocities and masses of such particles, as well as understanding of the impact processes. Although the stabilized orbit of LDEF provides limited directional information, it is possible to determine more accurate impact directions from detailed crater morphology. The applicability of this technique has already been demonstrated but the relationship between crater shape and impactor direction and velocity has not been derived in detail. We present the results of impact experiments and simulations: (1) impacts at micron dimensions using the Unit's 2MV Van de Graaff accelerator; (2) impacts at mm dimensions using a Light Gas Gun; and (3) computer simulations using AUTODYN-3D from which an empirical relationship between crater shape and impactor velocity, direction and particle properties we aim to derive. Such a relationship can be applied to any surface exposed to space debris or micrometeoroid particles for which a detailed pointing history is available.

  14. Impact-generated Hydrothermal Activity at the Chicxulub Crater

    NASA Astrophysics Data System (ADS)

    Kring, D. A.; Zurcher, L.; Abramov, O.

    2007-05-01

    Borehole samples recovered from PEMEX exploration boreholes and an ICDP scientific borehole indicate the Chicxulub impact event generated hydrothermal alteration throughout a large volume of the Maya Block beneath the crater floor and extending across the bulk of the ~180 km diameter crater. The first indications of hydrothermal alteration were observed in the crater discovery samples from the Yucatan-6 borehole and manifest itself in the form of anhydrite and quartz veins. Continuous core from the Yaxcopoil-1 borehole reveal a more complex and temporally extensive alteration sequence: following a brief period at high temperatures, impact- melt-bearing polymict breccias and a thin, underlying unit of impact melt were subjected to metasomatism, producing alkali feldspar, sphene, apatite, and magnetite. As the system continued to cool, smectite-series phyllosilicates appeared. A saline solution was involved. Stable isotopes suggest the fluid was dominated by a basinal brine created mostly from existing groundwater of the Yucatan Peninsula, although contributions from down-welling water also occurred in some parts of the system. Numerical modeling of the hydrothermal system suggests circulation occurred for 1.5 to 2.3 Myr, depending on the permeability of the system. Our understanding of the hydrothermal system, however, is still crude. Additional core recovery projects, particularly into the central melt sheet, are needed to better evaluate the extent and duration of hydrothermal alteration.

  15. Chicxulub's Cretaceous-Tertiary Boundary Twin Crater. Was There a Double Impact in the Yucatan Peninsula?

    NASA Astrophysics Data System (ADS)

    Camargo, A. Z.; Juarez, J. S.

    2004-05-01

    In 1980, Alvarez and co-authors proposed that the K/T extinctions were caused by the effects of a celestial body falling on Earth. After a long search for the impact site, the 1981 work by Penfield and Camargo on a 170 km structure in the Yucatan Peninsula got the attention of the specialists, and it was later proved that it was the crater created by the impact of that celestial body. New data suggests the existence of a second impact crater close to Chicxulub, both being of the same age and created by two fragments of the same celestial boby. A new magnetic map plotted as a color-coded shaded relief surface, reveals a feature not evident before: two interlaced ringed anomalies of about 100 and 50 km diameters, the larger one related to the magnetic signature of the Chicxulub Crater, and the second located at its E-SE edge. The 50 km anomaly, with morphology similar to Chicxulub's, is interpreted as also corresponding to an impact crater, centered at about 89 Deg. Long. W and 21 Deg. Lat. N, close to the city of Izamal. The anomaly size indicates that the diameter of the IZAMAL CRATER is about 85 km. The Chicxulub Crater, being buried under several hundred meters of Tertiary carbonate rocks, is not visible from the surface or from space; although some surface expression of its morphology has been reported. The best known is the ring of cenotes (sink holes) at the crater's rim, visible on satellite images and photographs. The JPL/NASA image PIA03379, is a color-coded shaded relief image of terrain elevation in which the topography was exagerated to highlight the Chicxulub Crater rim. On this image, a semi circular arc of dark spots is also visible immediately to the E-SE of the Chicxulub Crater rim. These spots are interpreted as large irregular karstic depressions, similar to the ones along the cenote ring of Chicxulub. On the evidence of the spatial relationship of the magnetic anomalies and the satellite image features, we tested how well the proposed Izamal

  16. Biospheric effects of a large extraterrestrial impact: Case study of the cretaceous/tertiary boundary crater

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.

    1995-01-01

    The Chicxulub impact crater, buried in the Yucatan carbonate platform in Mexico, is the site of the impact purported to have caused mass extinctions at the Cretaceous/Tertiary (K/T) boundary. A recently discovered Chicxulub ejecta deposit in Belize contains evidence of carbonate vaporization and precipitation from the vapor plume. Sulfate clasts are almost absent in the Belize ejecta, but are abundant in the coarse ejecta near the crater rim, hwich may reflect the greater abundance of sulfates deep in the target section. The absence of sulfate precipitates in Belize may indicate that most of the vaporized sulfur was deposited in the upper atmosphere. Hydrocode modeling of the impact indicates that between 0.4 to 7.0 x 10(exp 17) g of sulfur were vaporized by the impact in sulfates. Laser experiments indicate that SO2, SO3, and SO4 are produced, and that complex chemical reactions between plume constituents occur during condensation. The sulfur released as SO3 or SO4 converted rapidly into H2HO4 aerosol. A radiative transfer model coupled with a model of coagulation predicts that the aerosol prolonged the initial blackout period caused by impact dust only if it contained impurities. The sulfur released as SO2 converted to aerosol slowly due to the rate limiting oxidation of SO2. Radiative transfer calculations combined with rates of acid production, coagulation, and diffusion indicate that solar transmission was reduced to 10-20 percent of normal for a period of 8-13 years. This reduction produced a climate forcing (cooling) of -300 Wm(exp -2), which far exceeded the +8 Wm(exp -2) greenhouse warming caused by the CO2 released through the vaporization of carbonates, and therefore produced a decade of freezing and near-freezing temperatures. Several decades of moderate warming followed the decade of severe cooling due to the long residence time of CO2. The prolonged impact winter may have been a major cause of the K/T extinctions.

  17. Geologic signatures of atmospheric effects on impact cratering on Venus

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Highlights of the research include geologic signatures of impact energy and atmospheric response to crater formation. Laboratory experiments were performed at the NASA Ames Vertical Gun Range (AVGR) to assess the interaction between disrupted impactor and atmosphere during entry, and to assess the energy coupling between impacts and the surrounding atmosphere. The Schlieren imaging at the AVGR was used in combination with Magellan imaging and theoretical studies to study the evolution of the impactor following impact. The Schlieren imaging documented the downrange blast front created by vaporization during oblique impacts. Laboratory experiments allowed assessing the effect of impact angle on coupling efficiency with an atmosphere. And the impact angle's effect on surface blasts and run-out flows allowed the distinction of crater clusters created by simultaneous impacts from those created by isolated regions of older age.

  18. Craters on comets

    NASA Astrophysics Data System (ADS)

    Vincent, J.; Oklay, N.; Marchi, S.; Höfner, S.; Sierks, H.

    2014-07-01

    This paper reviews the observations of crater-like features on cometary nuclei. ''Pits'' have been observed on almost all cometary nuclei but their origin is not fully understood [1,2,3,4]. It is currently assumed that they are created mainly by the cometary activity with a pocket of volatiles erupting under a dust crust, leaving a hole behind. There are, however, other features which cannot be explained in this way and are interpreted alternatively as remnants of impact craters. This work focusses on the second type of pit features: impact craters. We present an in-depth review of what has been observed previously and conclude that two main types of crater morphologies can be observed: ''pit-halo'' and ''sharp pit''. We extend this review by a series of analysis of impact craters on cometary nuclei through different approaches [5]: (1) Probability of impact: We discuss the chances that a Jupiter Family Comet like 9P/Tempel 1 or the target of Rosetta 67P/Churyumov-Gerasimenko can experience an impact, taking into account the most recent work on the size distribution of small objects in the asteroid Main Belt [6]. (2) Crater morphology from scaling laws: We present the status of scaling laws for impact craters on cometary nuclei [7] and discuss their strengths and limitations when modeling what happens when a rocky projectile hits a very porous material. (3) Numerical experiments: We extend the work on scaling laws by a series of hydrocode impact simulations, using the iSALE shock physics code [8,9,10] for varying surface porosity and impactor velocity (see Figure). (4) Surface processes and evolution: We discuss finally the fate of the projectile and the effects of the impact-induced surface compaction on the activity of the nucleus. To summarize, we find that comets do undergo impacts although the rapid evolution of the surface erases most of the features and make craters difficult to detect. In the case of a collision between a rocky body and a highly porous

  19. Search for Impact Craters in the Volcanic and Volcano-Sedimentary Terrains of Mexico

    NASA Astrophysics Data System (ADS)

    Bartali, R.; Fucugauchi, J. U.

    2011-12-01

    It has long been recognized that the numbers of impact craters documented in the terrestrial record are small compared to those of the Moon and other planets and satellites. Processes acting on the Earth surface including tectonics, volcanism and erosion contribute to erase, modify and cover evidence of crater-forming impacts that have occurred through Earth's history. Even evidence on large impact structures is limited to few examples, with only three complex multi-ring structures so far recognized. Chicxulub is a ~200 km diameter multi-ring crater formed by an impact in the southern Gulf of Mexico about 65.5 Ma ago at the Cretaceous/Paleogene boundary. Chicxulub is the only impact structure documented in Mexico, Central and northern South America (http:www.unb.ca/passc/ImpactDatabase). Chicxulub, located in the Yucatan platform buried under a kilometer of carbonate rocks, was initially identified from its concentric semi-circular gravity and magnetic anomaly patterns. Yucatan peninsula has a low-relief topography and high contrasts in physical properties between carbonate rocks, impact lithologies and deformed target rocks. In contrast, most of the country has an abrupt topography with limited outcrops of Paleozoic and Precambrian terrains. The extensive igneous cover of the Sierra Madre Occidental, Trans-Mexican volcanic belt and Sierra Madre del Sur makes search for impact craters a difficult task. Early attempts were limited by the numerous volcanic craters and lack of high-resolution geophysical data. As part of a new country-wide search program, we have been conducting studies in northern Mexico using remote sensing and geophysical data to document circular and semi-circular crater-like features. The search has identified several structures, some well exposed and characterized by simple crater morphologies and topographic rims. These landforms have been mapped, estimating their dimensions, distribution and characterizing the surrounding terrains

  20. Synimpact-postimpact transition inside Chesapeake Bay crater

    USGS Publications Warehouse

    Poag, Claude (Wylie)

    2002-01-01

    The transition from synimpact to postimpact sedimentation inside Chesapeake Bay impact crater began with accumulation of fallout debris, the final synimpact deposit. Evi dence of a synimpact fallout layer at this site comes from the presence of unusual, millimeter- scale, pyrite microstructures at the top of the Exmore crater-fill breccia. The porous geometry of the pyrite microstructures indicates that they originally were part of a more extensive pyrite lattice that encompassed a layer of millimeter-scale glass microspherules—fallout melt particles produced by the bolide impact. Above this microspherule layer is the initial postimpact deposit, a laminated clay-silt-sand unit, 19 cm thick. This laminated unit is a dead zone, which contains abundant stratigraphically mixed and diagenetically altered or impact-altered microfossils (foraminifera, calcareous nannofossils, dinoflagellates, ostracodes), but no evidence of indigenous biota. By extrapolation of sediment- accumulation rates, I estimate that conditions unfavorable to microbiota persisted for as little as <1 k.y. to 10 k.y. after the bolide impact. Subsequently, an abrupt improvement of the late Eocene paleoenvironment allowed species-rich assemblages of foraminifera, ostracodes, dinoflagellates, radiolarians, and calcareous nannoplankton to quickly reoccupy the crater basin, as documented in the first sample of the Chickahominy Formation above the dead zone.

  1. Synimpact-postimpact transition inside Chesapeake Bay crater

    USGS Publications Warehouse

    Poag, C.W.

    2002-01-01

    The transition from synimpact to postimpact sedimentation inside Chesapeake Bay impact crater began with accumulation of fallout debris, the final synimpact deposit. Evidence of a synimpact fallout layer at this site comes from the presence of unusual, millimeter-scale, pyrite microstructures at the top of the Exmore crater-fill breccia. The porous geometry of the pyrite microstructures indicates that they originally were part of a more extensive pyrite lattice that encompassed a layer of millimeter-scale glass microspherules-fallout melt particles produced by the bolide impact. Above this microspherule layer is the initial postimpact deposit, a laminated clay-silt-sand unit, 19 cm thick. This laminated unit is a dead zone, which contains abundant stratigraphically mixed and diagenetically altered or impact-altered microfossils (foraminifera, calcareous nannofossils, dinoflagellates, ostracodes), but no evidence of indigenous biota. By extrapolation of sediment-accumulation rates, I estimate that conditions unfavorable to microbiota persisted for as little as <1 k.y. to 10 k.y. after the bolide impact. Subsequently, an abrupt improvement of the late Eocene paleoenvironment allowed species-rich assemblages of foraminifera, ostracodes, dinoflagellates, radiolarians, and calcareous nannoplankton to quickly reoccupy the crater basin, as documented in the first sample of the Chickahominy Formation above the dead zone.

  2. Preliminary Examination of Impact Craters on Al Foil from the Stardust Interstellar Dust Collector

    NASA Astrophysics Data System (ADS)

    Stroud, R.; Stardust Interstellar Preliminary Examination Team; 29,000 Stardust@home Dusters

    2011-12-01

    The Interstellar Dust Collector from the NASA Stardust mission provides an unprecedented opportunity for direct laboratory study of particles from the contemporary interstellar dust (ISD) stream in order to obtain such information as grain composition and microstructure. The collector is comprised of two collection media: silica aerogel tiles and Al foil strips. Preliminary examination (PE) of particles captured in each medium is on-going. To-date, four grains analyzed in situ in aerogel with synchrotron X-ray techniques show track trajectories and elemental composition that indicate a probable interstellar origin. In addition, we report here the discovery of one crater on an Al foil for which the residue elemental composition and crater shape are consistent with the impact of a grain of interstellar origin, although an interplanetary origin has not been ruled out. Automated mapping by SEM is the primary tool for identifi-cation of craters on the Al foils. A complete map of each foil requires collection of several thousand images at a resolution of ~ 50 nm/px. Automated software has been developed to identify crater candidates, but so far it has not replaced manual efforts. Identified candidates are then re-imaged at ~ 15 nm/px, for confirmation as impact craters. Fifteen foils have been imaged; crater identification is complete for eight, yielding 32 craters. The average areal density of craters is 9.7 cm-2, which extrapolates to ~1500 craters on the total foil collection area. Initial elemental analysis of residues in six craters has been performed with a combination of Auger spectroscopy, conventional, off-axis energy dispersive X-ray spectroscopy (EDX), on-axis, silicon drift-detector EDX. Additional analysis by TEM of the residue composition and crater morphology was obtained on FIB cross-sections of four of the craters. All craters contained detectable levels of Si and O. One crater was found to contain Mg, Si, O, Fe, Ni, S, Ca and Cr, indicative of an

  3. Cydonia Craters

    NASA Image and Video Library

    2003-03-22

    In this image from NASA Mars Odyssey, eroded mesas and secondary craters dot the landscape in an area of Cydonia Mensae. The single oval-shaped crater displays a butterfly ejecta pattern, indicating that the crater formed from a low-angle impact.

  4. Impact Crater Morphology and the Structure of Europa's Ice Shell

    NASA Astrophysics Data System (ADS)

    Silber, Elizabeth A.; Johnson, Brandon C.

    2017-12-01

    We performed numerical simulations of impact crater formation on Europa to infer the thickness and structure of its ice shell. The simulations were performed using iSALE to test both the conductive ice shell over ocean and the conductive lid over warm convective ice scenarios for a variety of conditions. The modeled crater depth-diameter is strongly dependent on the thermal gradient and temperature of the warm convective ice. Our results indicate that both a fully conductive (thin) shell and a conductive-convective (thick) shell can reproduce the observed crater depth-diameter and morphologies. For the conductive ice shell over ocean, the best fit is an approximately 8 km thick conductive ice shell. Depending on the temperature (255-265 K) and therefore strength of warm convective ice, the thickness of the conductive ice lid is estimated at 5-7 km. If central features within the crater, such as pits and domes, form during crater collapse, our simulations are in better agreement with the fully conductive shell (thin shell). If central features form well after the impact, however, our simulations suggest that a conductive-convective shell (thick shell) is more likely. Although our study does not provide a firm conclusion regarding the thickness of Europa's ice shell, our work indicates that Valhalla class multiring basins on Europa may provide robust constraints on the thickness of Europa's ice shell.

  5. Image and compositional characteristics of the LDEF Big Guy impact crater

    NASA Technical Reports Server (NTRS)

    Bunch, T. E.; Paque, Julie M.; Zolensky, Michael

    1995-01-01

    A 5.2 mm crater in Al-metal represents the largest found on LDEF. We have examined this crater by field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and time-of-flight/secondary ion mass spectroscopy (TOF-SIMS) in order to determine if there is any evidence of impactor residue. Droplet and dome-shaped columns, along with flow features, are evidence of melting. EDS from the crater cavity and rim show Mg, C, O and variable amounts of Si, in addition to Al. No evidence for a chondritic impactor was found, and it hypothesized that the crater may be the result of impact with space debris.

  6. Martian impact craters: Continuing analysis of lobate ejecta sinuosity

    NASA Technical Reports Server (NTRS)

    Barlow, Nadine G.

    1990-01-01

    The lobate ejecta morphology surrounding most fresh Martian impact craters can be quantitatively analyzed to determine variations in ejecta sinuosity with diameter, latitude, longitude, and terrain. The results of such studies provide another clue to the question of how these morphologies formed: are they the results of vaporization of subsurface volatiles or caused by ejecta entrainment in atmospheric gases. Kargel provided a simple expression to determine the degree of non-circularity of an ejecta blanket. This measure of sinuosity, called 'lobateness', is given by the ratio of the ejecta perimeter to the perimeter of a circle with the same area as that of the ejecta. The Kargel study of 538 rampart craters in selected areas of Mars led to the suggestion that lobateness increased with increasing diameter, decreased at higher latitude, and showed no dependence on elevation or geologic unit. Major problems with the Kargel analysis are the limited size and distribution of the data set and the lack of discrimination among the different types of lobate ejecta morphologies. Bridges and Barlow undertook a new lobateness study of 1582 single lobe (SL) and 251 double lobe (DL) craters. The results are summarized. These results agree with the finding of Kargel that lobateness increases with increasing diameter, but found no indication of a latitude dependence for SL craters. The Bridges and Barlow study has now been extended to multiple lobe (ML) craters. Three hundred and eighty ML craters located across the entire Martian surface were studied. ML craters provide more complications to lobateness studies than do SL and DL craters - in particular, the ejecta lobes surrounding the crater are often incomplete. Since the lobateness formula compares the perimeter of the ejecta lobe to that of a circle, the analysis was restricted only to complete lobes. The lobes are defined sequentially starting with the outermost lobe and moving inward.

  7. Martian Central Pit Craters

    NASA Technical Reports Server (NTRS)

    Hillman, E.; Barlow, N. G.

    2005-01-01

    Impact craters containing central pits are rare on the terrestrial planets but common on icy bodies. Mars is the exception among the terrestrial planets, where central pits are seen on crater floors ( floor pits ) as well as on top of central peaks ( summit pits ). Wood et al. [1] proposed that degassing of subsurface volatiles during crater formation produced central pits. Croft [2] argued instead that central pits might form during the impact of volatile-rich comets. Although central pits are seen in impact craters on icy moons such as Ganymede, they do show some significant differences from their martian counterparts: (a) only floor pits are seen on Ganymede, and (b) central pits begin to occur at crater diameters where the peak ring interior morphology begins to appear in terrestrial planet craters [3]. A study of craters containing central pits was conducted by Barlow and Bradley [4] using Viking imagery. They found that 28% of craters displaying an interior morphology on Mars contain central pits. Diameters of craters containing central pits ranged from 16 to 64 km. Barlow and Bradley noted that summit pit craters tended to be smaller than craters containing floor pits. They also noted a correlation of central pit craters with the proposed rings of large impact basins. They argued that basin ring formation fractured the martian crust and allowed subsurface volatiles to concentrate in these locations. They favored the model that degassing of the substrate during crater formation was responsible for central pit formation due to the preferential location of central pit craters along these basin rings.

  8. DARWIN Glass and DARWIN Crater Revisited. Multiple Impacts in the Australasian Strewn Field?

    NASA Astrophysics Data System (ADS)

    Meisel, T.; Biino, G. G.; Villa, I. M.; Chambers, J. E.; McHone, J. F.

    1995-09-01

    Darwin glass, an impact glass occurring in South West Tasmania, has been found at least since human beings reached Tasmania ca. 40 k.y. ago. Darwin glass, although in the proximity of the Australasian tektites strewn field, has never been counted as part of it. Darwin Crater was recognized about 30 years ago. Still, the existence of an impact structure in Tasmania has been neglected and does not show up in most compilations of known impact craters. Age determinations on Darwin Glass from the early 70's revealed a combined K-Ar and fission track age of 0.73 +/- 0.04 m.y. [1]. The most recent and most precise estimate for Australites and Indochinites yields 0.784 +/- 0.012 m.y. [2]. The two ages are indistinguishable from each other. This contemporaneity lead to the hypothesis that impact on Earth producing australites also formed Darwin Crater as a primary and/or secondary crater (Gentner et al., 1973). If one believes that all tektites of the Australian strewn field were produced by one impact in or near Indochina, then a special case is required to also form Darwin Crater, which is at least 5000 km away. Atmospheric breakup of a planetary body is a very unlikely possibility, because the distance travelled after breakup is too small to account for the dispersion. Double craters on Earth are always close to each other (e.g., Kara and Kara Ust). A more likely scenario could be an impact of an asteroidal body with an accompanying small moon (e.g., Ida and Gaspra). If one believes in multiple impacts for the formation of Muong Nong-type or layered tektites in the Australasian strewn field, then a collision of an asteroidal body with another body shortly before impact on Earth is required. In this case, an impact on Earth a large distance away (i.e., Tasmania) is realistic. To address the problem of crater recognition and possible simultaneous impact events, a new multidisciplinary investigation is currently underway. We intend to determine the age of three Darwin

  9. Foraminiferal repopulation of the late Eocene Chesapeake Bay impact crater

    USGS Publications Warehouse

    Poag, C. Wylie

    2012-01-01

    The Chickahominy Formation is the initial postimpact deposit in the 85km-diameter Chesapeake Bay impact crater, which is centered under the town of Cape Charles, Virginia, USA. The formation comprises dominantly microfossil-rich, silty, marine clay, which accumulated during the final ~1.6myr of late Eocene time. At cored sites, the Chickahominy Formation is 16.8-93.7m thick, and fills a series of small troughs and subbasins, which subdivide the larger Chickahominy basin. Nine coreholes drilled through the Chickahominy Formation (five inside the crater, two near the crater margin, and two ~3km outside the crater) record the stratigraphic and paleoecologic succession of 301 indigenous species of benthic foraminifera, as well as associated planktonic foraminifera and bolboformids. Two hundred twenty of these benthic species are described herein, and illustrated with scanning electron photomicrographs. Absence of key planktonic foraminiferal and Bolboforma species in early Chickahominy sediments indicates that detrimental effects of the impact also disturbed the upper oceanic water column for at least 80-100kyr postimpact. After an average of ~73kyr of stressed, rapidly fluctuating paleoenvironments, which were destabilized by after-effects of the impact, most of the cored Chickahominy subbasins maintained stable, nutrient-rich, low-oxygen bottom waters and interstitial microhabitats for the remaining ~1.3myr of late Eocene time.

  10. Impact Craters and Impactites as Important Targets for Mars Sample Return Missions

    NASA Astrophysics Data System (ADS)

    Osinski, G. R.; Cockell, C. S.; Pontefract, A.; Sapers, H. M.; Tornabene, L. L.

    2018-04-01

    Research conducted over the past few years reveals that meteorite impact craters provide substrates and habitats for life. We propose that craters and their products should be reconsidered as high priority targets for Mars Sample Return missions.

  11. Impact Crater Deposits in the Martian Highlands

    NASA Technical Reports Server (NTRS)

    Mest, S. C.; Crown, D. a.

    2005-01-01

    The martian highlands of Noachis Terra (20-30 deg S, 20-50 deg E), Tyrrhena Terra (0-30 deg S, 50- 100 deg E) and Terra Cimmeria (0-60 deg S, 120-170 deg E) preserve long and complex histories of degradation, but the relative effects of such factors as fluvial, eolian, and mass wasting processes have not been well constrained. The effects of this degradation are best observed on large (D greater than 10 km) impact craters that characterize the ancient highlands. Some craters exhibit distinct interior deposits, but precise origins of these deposits are enigmatic; infilling may occur by sedimentary (e.g., fluvial, lacustrine, eolian), mass wasting and (or) volcanic processes.

  12. Debris and meteoroid proportions deduced from impact crater residue analysis

    NASA Technical Reports Server (NTRS)

    Berthoud, Lucinda; Mandeville, Jean-Claude; Durin, Christian; Borg, Janet

    1995-01-01

    This study is a further investigation of space-exposed samples recovered from the LDEF satellite and the Franco-Russian 'Aragatz' dust collection experiment on the Mir Space Station. Impact craters with diameters ranging from 1 to 900 micron were found on the retrieved samples. Elemental analysis of residues found in the impact craters was carried out using Energy Dispersive X-ray spectrometry (EDX). The analyses show evidence of micrometeoroid and orbital debris origins for the impacts. The proportions of these two components vary according to particle size and experimental position with respect to the leading edge of the spacecraft. On the LDEF leading edge 17 percent of the impacts were apparently caused by micrometeoroids and 11 percent by debris; on the LDEF trailing edge 23 percent of the impacts are apparently caused by micrometeoroids and 4 percent consist of debris particles - mostly larger than 3 micron in diameter - in elliptical orbits around the Earth. For Mir, the analyses indicate that micrometeoroids form 23 percent of impacts and debris 9 percent. However, we note that 60-70 percent of the craters are unidentifiable, so the definitive proportions of natural v. man-made particles are yet to be determined. Experiments carried out using a light gas gun to accelerate glass spheres and fragments demonstrate the influence of particle shape on crater morphology. The experiments also show that it is more difficult to analyze the residues produced by an irregular fragment than those produced by a spherical projectile. If the particle is travelling above a certain velocity, it vaporizes upon impact and no residues are left. Simulation experiments carried out with an electrostatic accelerator indicate that this limit is about 14 km/s for Fe particles impacting Al targets. This chemical analysis cut-off may bias interpretations of the relative populations of meteoroid and orbital debris. Oblique impacts and multiple foil detectors provide a higher likelihood

  13. Ganymede - A relationship between thermal history and crater statistics

    NASA Technical Reports Server (NTRS)

    Phillips, R. J.; Malin, M. C.

    1980-01-01

    An approach for factoring the effects of a planetary thermal history into a predicted set of crater statistics for an icy satellite is developed and forms the basis for subsequent data inversion studies. The key parameter is a thermal evolution-dependent critical time for which craters of a particular size forming earlier do not contribute to present-day statistics. An example is given for the satellite Ganymede and the effect of the thermal history is easily seen in the resulting predicted crater statistics. A preliminary comparison with the data, subject to the uncertainties in ice rheology and impact flux history, suggests a surface age of 3.8 x 10 to the 9th years and a radionuclide abundance of 0.3 times the chondritic value.

  14. Filled Craters

    NASA Image and Video Library

    2006-05-11

    This MOC image shows adjacent impact craters located north-northwest of the Acheron Fossae region of Mars. The two craters are of similar size and formed by meteor impacts. However, one is much more filled than the other, indicating that it is older

  15. Gully formation in terrestrial simple craters: Meteor Crater, USA and Lonar Crater, India

    NASA Astrophysics Data System (ADS)

    Kumar, P.; Head, J. W.; Kring, D. A.

    2007-12-01

    Geomorphic features such as gullies, valley networks, and channels on Mars have been used as a proxy to understand the climate and landscape evolution of Mars. Terrestrial analogues provide significant insight as to how the various exogenic and endogenic processes might contribute to the evolution of these martian landscapes. We describe here a terrestrial example from Meteor Crater, which shows a spectacular development of gullies throughout the inner wall in response to rainwater precipitation, snow melting and groundwater discharge. As liquid water has been envisaged as one of the important agents of landscape sculpturing, Meteor Crater remains a useful landmark, where planetary geologists can learn some lessons. We also show here how the lithology and structural framework of this crater controls the gully distribution. Like many martian impact craters, it was emplaced in layered sedimentary rocks with an exceptionally well-developed centripetal drainage pattern consisting of individual alcoves, channels and fans. Some of the gullies originate from the rim crest and others from the middle crater wall, where a lithologic transition occurs. Deeply incised alcoves are well-developed on the soft sandstones of the Coconino Formation exposed on the middle crater wall, beneath overlying dolomite. In general, the gully locations are along crater wall radial fractures and faults, which are favorable locales of groundwater flow and discharge; these structural discontinuities are also the locales where the surface runoff from rain precipitation and snow melting can preferentially flow, causing degradation. Like martian craters, channels are well developed on the talus deposits and alluvial fans on the periphery of the crater floor. In addition, lake sediments on the crater floor provide significant evidence of a past pluvial climate, when groundwater seeped from springs on the crater wall. Caves exposed on the lower crater level may point to percolation of surface runoff

  16. Usability of small impact craters on small surface areas in crater count dating: Analysing examples from the Harmakhis Vallis outflow channel, Mars

    NASA Astrophysics Data System (ADS)

    Kukkonen, S.; Kostama, V.-P.

    2018-05-01

    The availability of very high-resolution images has made it possible to extend crater size-frequency distribution studies to small, deca/hectometer-scale craters. This has enabled the dating of small and young surface units, as well as recent, short-time and small-scale geologic processes that have occurred on the units. Usually, however, the higher the spatial resolution of space images is, the smaller area is covered by the images. Thus the use of single, very high-resolution images in crater count age determination may be debatable if the images do not cover the studied region entirely. Here we compare the crater count results for the floor of the Harmakhis Vallis outflow channel obtained from the images of the ConTeXt camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (MRO). The CTX images enable crater counts for entire units on the Harmakhis Vallis main valley, whereas the coverage of the higher-resolution HiRISE images is limited and thus the images can only be used to date small parts of the units. Our case study shows that the crater count data based on small impact craters and small surface areas mainly correspond with the crater count data based on larger craters and more extensive counting areas on the same unit. If differences between the results were founded, they could usually be explained by the regional geology. Usually, these differences appeared when at least one cratering model age is missing from either of the crater datasets. On the other hand, we found only a few cases in which the cratering model ages were completely different. We conclude that the crater counts using small impact craters on small counting areas provide useful information about the geological processes which have modified the surface. However, it is important to remember that all the crater counts results obtained from a specific counting area always primarily represent the results from the counting area-not the whole

  17. Calculational investigation of impact cratering dynamics - Early time material motions

    NASA Technical Reports Server (NTRS)

    Thomsen, J. M.; Austin, M. G.; Ruhl, S. F.; Schultz, P. H.; Orphal, D. L.

    1979-01-01

    Early time two-dimensional finite difference calculations of laboratory-scale hypervelocity (6 km/sec) impact of 0.3 g spherical 2024 aluminum projectiles into homogeneous plasticene clay targets were performed and the resulting material motions analyzed. Results show that the initial jetting of vaporized target material is qualitatively similar to experimental observation. The velocity flow field developed within the target is shown to have features quite similar to those found in calculations of near-surface explosion cratering. Specific application of Maxwell's analytic Z-Model (developed to interpret the flow fields of near-surface explosion cratering calculations), shows that this model can be used to describe the flow fields resulting from the impact cratering calculations, provided that the flow field center is located beneath the target surface, and that application of the model is made late enough in time that most of the projectile momentum has been dissipated.

  18. Target rocks, impact glasses, and melt rocks from the Lonar crater, India: Highly siderophile element systematics and Sr-Nd-Os isotopic signatures

    NASA Astrophysics Data System (ADS)

    Schulz, Toni; Luguet, Ambre; Wegner, Wencke; Acken, David; Koeberl, Christian

    2016-07-01

    The Lonar crater is a ~0.57-Myr-old impact structure located in the Deccan Traps of the Indian peninsula. It probably represents the best-preserved impact structure hosted in continental flood basalts, providing unique opportunities to study processes of impact cratering in basaltic targets. Here we present highly siderophile element (HSE) abundances and Sr-Nd and Os isotope data for target basalts and impactites (impact glasses and impact melt rocks) from the Lonar area. These tools may enable us to better constrain the interplay of a variety of impact-related processes such as mixing, volatilization, and contamination. Strontium and Nd isotopic compositions of impactites confirm and extend earlier suggestions about the incorporation of ancient basement rocks in Lonar impactites. In the Re-Os isochron plot, target basalts exhibit considerable scatter around a 65.6 Myr Re-Os reference isochron, most likely reflecting weathering and/or magma replenishment processes. Most impactites plot at distinctly lower 187Re/188Os and 187Os/188Os ratios compared to the target rocks and exhibit up to two orders of magnitude higher abundances of Ir, Os, and Ru. Moreover, the impactites show near-chondritic interelement ratios of HSE. We interpret our results in terms of an addition of up to 0.03% of a chondritc component to most impact glasses and impact melt rocks. The magnitude of the admixture is significantly lower than the earlier reported 12-20 wt% of extraterrestrial component for Lonar impact spherules, reflecting the typical difference in the distribution of projectile component between impact glass spherules and bulk impactites.

  19. Crater with Exposed Layers

    NASA Image and Video Library

    2017-01-17

    On Earth, geologists can dig holes and pull up core samples to find out what lies beneath the surface. On Mars, geologists cannot dig holes very easily themselves, but a process has been occurring for billions of years that has been digging holes for them: impact cratering. Impact craters form when an asteroid, meteoroid, or comet crashes into a planet's surface, causing an explosion. The energy of the explosion, and the resulting size of the impact crater, depends on the size and density of the impactor, as well as the properties of the surface it hits. In general, the larger and denser the impactor, the larger the crater it will form. The impact crater in this image is a little less than 3 kilometers in diameter. The impact revealed layers when it excavated the Martian surface. Layers can form in a variety of different ways. Multiple lava flows in one area can form stacked sequences, as can deposits from rivers or lakes. Understanding the geology around impact craters and searching for mineralogical data within their layers can help scientists on Earth better understand what the walls of impact craters on Mars expose. http://photojournal.jpl.nasa.gov/catalog/PIA12328

  20. A Triple Crater

    NASA Image and Video Library

    2017-06-01

    This image from NASA's Mars Reconnaissance Orbiter shows an elongated depression from three merged craters. The raised rims and ejecta indicate that these are impact craters rather than collapse or volcanic landforms. The pattern made by the ejecta and the craters suggest this was a highly oblique (low angle to the surface) impact, probably coming from the west. There may have been three major pieces flying in close formation to make this triple crater. https://photojournal.jpl.nasa.gov/catalog/PIA21652

  1. Monturaqui meteorite impact crater, Chile: A field test of the utility of satellite-based mapping of ejecta at small craters

    NASA Astrophysics Data System (ADS)

    Rathbun, K.; Ukstins, I.; Drop, S.

    2017-12-01

    Monturaqui Crater is a small ( 350 m diameter), simple meteorite impact crater located in the Atacama Desert of northern Chile that was emplaced in Ordovician granite overlain by discontinuous Pliocene ignimbrite. Ejecta deposits are granite and ignimbrite, with lesser amounts of dark impact melt and rare tektites and iron shale. The impact restructured existing drainage systems in the area that have subsequently eroded through the ejecta. Satellite-based mapping and modeling, including a synthesis of photographic satellite imagery and ASTER thermal infrared imagery in ArcGIS, were used to construct a basic geological interpretation of the site with special emphasis on understanding ejecta distribution patterns. This was combined with field-based mapping to construct a high-resolution geologic map of the crater and its ejecta blanket and field check the satellite-based geologic interpretation. The satellite- and modeling-based interpretation suggests a well-preserved crater with an intact, heterogeneous ejecta blanket that has been subjected to moderate erosion. In contrast, field mapping shows that the crater has a heavily-eroded rim and ejecta blanket, and the ejecta is more heterogeneous than previously thought. In addition, the erosion rate at Monturaqui is much higher than erosion rates reported elsewhere in the Atacama Desert. The bulk compositions of the target rocks at Monturaqui are similar and the ejecta deposits are highly heterogeneous, so distinguishing between them with remote sensing is less effective than with direct field observations. In particular, the resolution of available imagery for the site is too low to resolve critical details that are readily apparent in the field on the scale of 10s of cm, and which significantly alter the geologic interpretation. The limiting factors for effective remote interpretation at Monturaqui are its target composition and crater size relative to the resolution of the remote sensing methods employed. This

  2. Large, Fresh Crater Surrounded by Smaller Craters

    NASA Image and Video Library

    2014-05-22

    The largest crater associated with a March 2012 impact on Mars has many smaller craters around it, revealed in this image from the High Resolution Imaging Science Experiment HiRISE camera on NASA Mars Reconnaissance Orbiter.

  3. Crumpled Crater

    NASA Image and Video Library

    2015-03-30

    It is no secret that Mercury's surface is scarred by abundant tectonic deformation, the vast majority of which is due to the planet's history of cooling and contraction through time. Yet Mercury is also heavily cratered, and hosts widespread volcanic plains. So it's perhaps unsurprising that these three types of landform often intersect-literally-as shown in this scene. Here, an unnamed crater, about 7.5 km (4.7 mi.) in diameter was covered, and almost fully buried, by lava. At some point after, compression of the surface formed scarps and ridges in the area that, when they reached the buried crater, came to describe its curved outline. Many arcuate ridges on Mercury formed this way. In this high-resolution view, we can also see the younger, later population of smaller craters that pock-mark the surface. http://photojournal.jpl.nasa.gov/catalog/PIA19263

  4. A global catalogue of Ceres impact craters ≥ 1 km and preliminary analysis

    NASA Astrophysics Data System (ADS)

    Gou, Sheng; Yue, Zongyu; Di, Kaichang; Liu, Zhaoqin

    2018-03-01

    The orbital data products of Ceres, including global LAMO image mosaic and global HAMO DTM with a resolution of 35 m/pixel and 135 m/pixel respectively, are utilized in this research to create a global catalogue of impact craters with diameter ≥ 1 km, and their morphometric parameters are calculated. Statistics shows: (1) There are 29,219 craters in the catalogue, and the craters have a various morphologies, e.g., polygonal crater, floor fractured crater, complex crater with central peak, etc.; (2) The identifiable smallest crater size is extended to 1 km and the crater numbers have been updated when compared with the crater catalogue (D ≥ 20 km) released by the Dawn Science Team; (3) The d/D ratios for fresh simple craters, obviously degraded simple crater and polygonal simple crater are 0.11 ± 0.04, 0.05 ± 0.04 and 0.14 ± 0.02 respectively. (4) The d/D ratios for non-polygonal complex crater and polygonal complex crater are 0.08 ± 0.04 and 0.09 ± 0.03. The global crater catalogue created in this work can be further applied to many other scientific researches, such as comparing d/D with other bodies, inferring subsurface properties, determining surface age, and estimating average erosion rate.

  5. The Vichada Impact Crater in Northwestern South America and its Potential for Economic Deposits

    NASA Astrophysics Data System (ADS)

    Hernandez, O.; von Frese, R. R.

    2008-05-01

    A prominent positive free-air gravity anomaly mapped over a roughly 50-km diameter basin is consistent with a mascon centered on (4o30`N, -69o15`W) in the Vichada Department, Colombia, South America. The inferred large impact crater is nearly one third the size of the Chicxulub crater. It must have formed recently, in the last 30 m.a. because it controls the partially eroded and jungle-covered path of the Vichada River. No antipodal relationship has been detected. Thick sedimentary cover, erosional processes and dense vegetation greatly limit direct geological testing of the inferred impact basin. However, EGM-96 gravity data together with ground gravity and magnetic profiles support the interpretation of the impact crater structure. The impact extensively thinned and disrupted the Precambrian cratonic crust and may be associated with mineral and hydrocarbon deposits. A combined EM and magnetic airborne program is being developed to resolve additional crustal properties of the inferred Vichada impact basin Keywords: Impact crater, economic deposits, free-air gravity anomalies

  6. The formation of peak rings in large impact craters.

    PubMed

    Morgan, Joanna V; Gulick, Sean P S; Bralower, Timothy; Chenot, Elise; Christeson, Gail; Claeys, Philippe; Cockell, Charles; Collins, Gareth S; Coolen, Marco J L; Ferrière, Ludovic; Gebhardt, Catalina; Goto, Kazuhisa; Jones, Heather; Kring, David A; Le Ber, Erwan; Lofi, Johanna; Long, Xiao; Lowery, Christopher; Mellett, Claire; Ocampo-Torres, Rubén; Osinski, Gordon R; Perez-Cruz, Ligia; Pickersgill, Annemarie; Poelchau, Michael; Rae, Auriol; Rasmussen, Cornelia; Rebolledo-Vieyra, Mario; Riller, Ulrich; Sato, Honami; Schmitt, Douglas R; Smit, Jan; Tikoo, Sonia; Tomioka, Naotaka; Urrutia-Fucugauchi, Jaime; Whalen, Michael; Wittmann, Axel; Yamaguchi, Kosei E; Zylberman, William

    2016-11-18

    Large impacts provide a mechanism for resurfacing planets through mixing near-surface rocks with deeper material. Central peaks are formed from the dynamic uplift of rocks during crater formation. As crater size increases, central peaks transition to peak rings. Without samples, debate surrounds the mechanics of peak-ring formation and their depth of origin. Chicxulub is the only known impact structure on Earth with an unequivocal peak ring, but it is buried and only accessible through drilling. Expedition 364 sampled the Chicxulub peak ring, which we found was formed from uplifted, fractured, shocked, felsic basement rocks. The peak-ring rocks are cross-cut by dikes and shear zones and have an unusually low density and seismic velocity. Large impacts therefore generate vertical fluxes and increase porosity in planetary crust. Copyright © 2016, American Association for the Advancement of Science.

  7. Viscous relaxation of Ganymede's impact craters: Constraints on heat flux

    USGS Publications Warehouse

    Bland, Michael T.; Singer, Kelsi N.; McKinnon, William B.; Schenk, Paul M.

    2017-01-01

    Measurement of crater depths in Ganymede’s dark terrain have revealed substantial numbers of unusually shallow craters indicative of viscous relaxation [see companion paper: Singer, K.N., Schenk, P. M., Bland, M.T., McKinnon, W.B., (2017). Relaxed impact craters on Ganymede: Regional variations and high heat flow. Icarus, submitted]. These viscously relaxed craters provide insight into the thermal history of the dark terrain: the rate of relaxation depends on the size of the crater and the thermal structure of the lithosphere. Here we use finite element simulations of crater relaxation to constrain the heat flux within the dark terrain when relaxation occurred. We show that the degree of viscous relaxation observed cannot be achieved through radiogenic heating alone, even if all of the relaxed craters are ancient and experienced the high radiogenic fluxes present early in the satellite’s history. For craters with diameter ≥ 10 km, heat fluxes of 40–50 mW m-2−2"> can reproduce the observed crater depths, but only if the fluxes are sustained for ∼1 Gyr. These craters can also be explained by shorter-lived “heat pulses” with magnitudes of ∼100 mW m-2−2"> and timescales of 10–100 Myr. At small crater diameters (4 km) the observed shallow depths are difficult to achieve even when heat fluxes as high as 150 mW m-2−2"> are sustained for 1 Gyr. The extreme thermal conditions required to viscously relax small craters may indicate that mechanisms other than viscous relaxation, such as topographic degradation, are also in play at small crater diameters. The timing of the relaxation event(s) is poorly constrained due to the sparsity of adequate topographic information, though it likely occurred in Ganymede’s middle history (neither recently, nor shortly after satellite formation). The consistency between the timing and magnitude of the heat fluxes derived here and those inferred from other tectonic features suggests that a single event

  8. Viscous relaxation of Ganymede's impact craters: Constraints on heat flux

    NASA Astrophysics Data System (ADS)

    Bland, Michael T.; Singer, Kelsi N.; McKinnon, William B.; Schenk, Paul M.

    2017-11-01

    Measurement of crater depths in Ganymede's dark terrain have revealed substantial numbers of unusually shallow craters indicative of viscous relaxation [see companion paper: Singer, K.N., Schenk, P. M., Bland, M.T., McKinnon, W.B., (2017). Relaxed impact craters on Ganymede: Regional variations and high heat flow. Icarus, submitted]. These viscously relaxed craters provide insight into the thermal history of the dark terrain: the rate of relaxation depends on the size of the crater and the thermal structure of the lithosphere. Here we use finite element simulations of crater relaxation to constrain the heat flux within the dark terrain when relaxation occurred. We show that the degree of viscous relaxation observed cannot be achieved through radiogenic heating alone, even if all of the relaxed craters are ancient and experienced the high radiogenic fluxes present early in the satellite's history. For craters with diameter ≥ 10 km, heat fluxes of 40-50 mW m-2 can reproduce the observed crater depths, but only if the fluxes are sustained for ∼1 Gyr. These craters can also be explained by shorter-lived "heat pulses" with magnitudes of ∼100 mW m-2 and timescales of 10-100 Myr. At small crater diameters (4 km) the observed shallow depths are difficult to achieve even when heat fluxes as high as 150 mW m-2 are sustained for 1 Gyr. The extreme thermal conditions required to viscously relax small craters may indicate that mechanisms other than viscous relaxation, such as topographic degradation, are also in play at small crater diameters. The timing of the relaxation event(s) is poorly constrained due to the sparsity of adequate topographic information, though it likely occurred in Ganymede's middle history (neither recently, nor shortly after satellite formation). The consistency between the timing and magnitude of the heat fluxes derived here and those inferred from other tectonic features suggests that a single event caused both Ganymede's tectonic deformation and

  9. The role of strength defects in shaping impact crater planforms

    NASA Astrophysics Data System (ADS)

    Watters, W. A.; Geiger, L. M.; Fendrock, M.; Gibson, R.; Hundal, C. B.

    2017-04-01

    High-resolution imagery and digital elevation models (DEMs) were used to measure the planimetric shapes of well-preserved impact craters. These measurements were used to characterize the size-dependent scaling of the departure from circular symmetry, which provides useful insights into the processes of crater growth and modification. For example, we characterized the dependence of the standard deviation of radius (σR) on crater diameter (D) as σR ∼ Dm. For complex craters on the Moon and Mars, m ranges from 0.9 to 1.2 among strong and weak target materials. For the martian simple craters in our data set, m varies from 0.5 to 0.8. The value of m tends toward larger values in weak materials and modified craters, and toward smaller values in relatively unmodified craters as well as craters in high-strength targets, such as young lava plains. We hypothesize that m ≈ 1 for planforms shaped by modification processes (slumping and collapse), whereas m tends toward ∼ 1/2 for planforms shaped by an excavation flow that was influenced by strength anisotropies. Additional morphometric parameters were computed to characterize the following planform properties: the planform aspect ratio or ellipticity, the deviation from a fitted ellipse, and the deviation from a convex shape. We also measured the distribution of crater shapes using Fourier decomposition of the planform, finding a similar distribution for simple and complex craters. By comparing the strength of small and large circular harmonics, we confirmed that lunar and martian complex craters are more polygonal at small sizes. Finally, we have used physical and geometrical principles to motivate scaling arguments and simple Monte Carlo models for generating synthetic planforms, which depend on a characteristic length scale of target strength defects. One of these models can be used to generate populations of synthetic planforms which are very similar to the measured population of well-preserved simple craters on

  10. Lobate impact melt flows within the extended ejecta blanket of Pierazzo crater

    NASA Astrophysics Data System (ADS)

    Bray, Veronica J.; Atwood-Stone, Corwin; Neish, Catherine D.; Artemieva, Natalia A.; McEwen, Alfred S.; McElwaine, Jim N.

    2018-02-01

    Impact melt flows are observed within the continuous and discontinuous ejecta blanket of the 9 km lunar crater Pierazzo, from the crater rim to more than 40 km away from the center of the crater. Our mapping, fractal analysis, and thermal modeling suggest that melt can be emplaced ballistically and, upon landing, can become separated from solid ejecta to form the observed flow features. Our analysis is based on the identification of established melt morphology for these in-ejecta flows and supported by fractal analysis and thermal modeling. We computed the fractal dimension for the flow boundaries and found values of D = 1.05-1.17. These are consistent with terrestrial basaltic lava flows (D = 1.06-1.2) and established lunar impact melt flows (D = 1.06-1.18), but inconsistent with lunar dry granular flows (D = 1.31-1.34). Melt flows within discontinuous ejecta deposits are noted within just 1.5% of the mapping area, suggesting that the surface expression of impact melt in the extended ejecta around craters of this size is rare, most likely due to the efficient mixing of melts with solid ejecta and local target rocks. However, if the ejected fragments (both, molten and solid) are large enough, segregation of melt and its consequent flow is possible. As most of the flows mapped in this work occur on crater-facing slopes, the development of defined melt flows within ejecta deposits might be facilitated by high crater-facing topography restricting the flow of ejecta soon after it makes ground contact, limiting the quenching of molten ejecta through turbulent mixing with solid debris. Our study confirms the idea that impact melt can travel far beyond the continuous ejecta blanket, adding to the lunar regolith over an extensive area.

  11. Impact craters as biospheric microenvironments, Lawn Hill Structure, Northern Australia.

    PubMed

    Lindsay, John; Brasier, Martin

    2006-04-01

    Impact craters on Mars act as traps for eolian sediment and in the past may have provided suitable microenvironments that could have supported and preserved a stressed biosphere. If this is so, terrestrial impact structures such as the 18-km-diameter Lawn Hill Structure, in northern Australia, may prove useful as martian analogs. We sampled outcrop and drill core from the carbonate fill of the Lawn Hill Structure and recorded its gamma-log signature. Facies data along with whole rock geochemistry and stable isotope signatures show that the crater fill is an outlier of the Georgina Basin and was formed by impact at, or shortly before, approximately 509-506 million years ago. Subsequently, it was rapidly engulfed by the Middle Cambrian marine transgression, which filled it with shallow marine carbonates and evaporites. The crater formed a protected but restricted microenvironment in which sediments four times the thickness of the nearby basinal succession accumulated. Similar structures, common on the martian surface, may well have acted as biospheric refuges as the planet's water resources declined. Low-pH aqueous environments on Earth similar to those on Mars, while extreme, support diverse ecologies. The architecture of the eolian crater fill would have been defined by long-term ground water cycles resulting from intermittent precipitation in an extremely arid climate. Nutrient recycling, critical to a closed lacustrine sub-ice biosphere, could be provided by eolian transport onto the frozen water surface.

  12. Impact crater densities on volcanoes and coronae on venus: implications for volcanic resurfacing.

    PubMed

    Namiki, N; Solomon, S C

    1994-08-12

    The density of impact craters on large volcanoes on Venus is half the average crater density for the planet. The crater density on some classes of coronae is not significantly different from the global average density, but coronae with extensive associated volcanic deposits have lower crater densities. These results are inconsistent with both single-age and steady-state models for global resurfacing and suggest that volcanoes and coronae with associated volcanism have been active on Venus over the last 500 million years.

  13. Stardust Interstellar Foils I1061N,1 and I1031N,1: First Results from Automated Crater Searches and Future Analytical Possibilities

    NASA Astrophysics Data System (ADS)

    Floss, C.; Allen, C.; Bajt, S.; Bechtel, H. A.; Borg, J.; Brenker, F.; Bridges, J.; Brownlee, D. E.; Burchell, M.; Burghammer, M.; Butterworth, A. L.; Cloetens, P.; Davis, A. M.; Doll, R.; Flynn, G. J.; Frank, D.; Gainsforth, Z.; Grün, E.; Heck, P. R.; Hillier, J. K.; Hoppe, P.; Howard, L.; Huss, G. R.; Huth, J.; Kearsley, A.; King, A. J.; Lai, B.; Leitner, J.; Lemelle, L.; Leonard, A.; Leroux, H.; Nittler, L. R.; Ogliore, R. C.; Ong, W. J.; Postberg, F.; Price, M. C.; Sandford, S. A.; Sans Tresseras, J. A.; Schmitz, S.; Schoonjans, T.; Schreiber, K.; Silversmit, G.; Siminonovici, A.; Srama, R.; Stadermann, F. J.; Stephan, T.; Stodolna, J.; Stroud, R. M.; Sutton, S. R.; Toucoulou, R.; Trieloff, M.; Tsou, P.; Tsuchiyama, A.; Tyliczszak, T.; Vekemans, B.; Vincze, L.; Westphal, A. J.; Zolensky, M. E.; 29,000 Stardust@Home Dusters

    2011-03-01

    Ten submicrometer (235-700-nm) craters were identified on Stardust interstellar foils 1061N and 1031N. The craters are distributed randomly over the foil areas, indicating that the high abundance observed is not due to clusters of secondary impacts.

  14. Cratering and Grooved Terrain on Ganymede

    NASA Technical Reports Server (NTRS)

    1979-01-01

    This color picture as acquired by Voyager 1 during its approach to Ganymede on Monday afternoon (the 5th of March). At ranges between about 230 to 250 thousand km. The image shows detail on the surface with a resolution of four and a half km. This picture is just south of PIA001515 (P21161) and shows more craters. It also shows the two distinctive types of terrain found by Voyager, the darker ungrooved regions and the lighter areas which show the grooves or fractures in abundance. The most striking features are the bright ray craters which havE a distinctly 'bluer' color appearing white against the redder background. Ganymede's surface is known to contain large amounts of surface ice and it appears that these relatively young craters have spread bright fresh ice materials over the surface. Likewise, the lighter color and reflectivity of the grooved areas suggests that here too, there is cleaner ice. We see ray craters with all sizes of ray patterns, ranging from extensive systems of the crater in the northern part of this picture, which has rays at least 300-500 kilometers long, down to craters which have only faint remnants of bright ejecta patterns. This variation suggests that, as on the Moon, there are processes which act to darken ray material, probably 'gardening' by micrometeoroid impact. JPL manages and controls the Voyager project for NASA's Office of Space Science.

  15. Results of Prospecting of Impact Craters in Morocco

    NASA Astrophysics Data System (ADS)

    Chaabout, S.; Chennaoui Aoudjehane, H.; Reimold, W. U.; Baratoux, D.

    2014-09-01

    This work is based to use satellite images of Google Earth and Yahoo-Maps scenes; we examined the surface of our country to be able to locate the structures that have a circular morphology such as impact craters, which potentially could be.

  16. Impact cratering calculations. Part 1: Early time results

    NASA Technical Reports Server (NTRS)

    Thomsen, J. M.; Sauer, F. N.; Austin, M. G.; Ruhl, S. F.; Shultz, P. H.; Orphal, D. L.

    1979-01-01

    Early time two dimensional finite difference calculations of laboratory scale hypervelocity impact of 0.3 g spherical 2024 aluminum projectiles into homogeneous plasticene clay targets were performed. Analysis of resulting material motions showed that energy and momentum were coupled quickly from the aluminum projectile to the target material. In the process of coupling, some of the plasticene clay target was vaporized while the projectile become severely deformed. The velocity flow field developed within the target was shown to have features similar to those found in calculations of near surface explosion cratering. Specific application of Maxwell's analytic Z-Model showed that this model can be used to describe the early time flow fields resulting from the impact cratering calculations as well, provided the flow field centers are located beneath the target surface and most of the projectile momentum is dissipated before the model is applied.

  17. Delimitation of terrestrial impact craters by way of pseudotachylytic rock distribution

    NASA Technical Reports Server (NTRS)

    Spray, John G.

    1993-01-01

    The determination of the shape and size of terrestrial impact craters is problematic, yet is critical to understanding cratering mechanics and for scaling bolide mass, volume, and impact velocity with crater size and target response. The problem is particularly difficult in older geological terrains (e.g. Precambrian) which are more likely to have suffered post-impact deformation and hence distortion of the original structure and/or where weathering may have partly removed or obscured its original shape. Traditionally, a number of features are used to assist us in determining the shape and size of an impact structure. These include the following: (1) the occurrence of faults, especially those disposed concentrically relative to the crater--the outermost ring faults being interpreted as indicating a viable minimum diameter; and (2) the development of so-called breccias, some of which are also associated with faults (e.g. the Sudbury Breccia developed within the target rocks of the Sudbury Structure of Onta rio, Canada). 'Breccia' is not a satisfactory term because a number of breccia-types exist at impact sites (e.g. fall-back breccias and in-situ brecciated target material). Of relevance to crater diameter determination is the recognition of discrete zones and fault- and shock-related pseudotachylyte. Pseudotachylyte is a rock type comprising a fine-grained, usually dark matrix containing clasts of minerals and/or rock derived from the country rock target material. It origin is normally attributed to high-speed slip (including vibration) along a slip surface (i.e. fault) or to the passage of a shock wave through the host material. The clasts can occur as angular fragments (i.e. like a breccia), but are more commonly developed as rounded to sub-rounded fragments. Significantly, the scale of these pseudotachylytes can range from sub-millimeter thick veinlets to dyke-like bodies up to 1 km or more thick. It is the latter, larger occurrence which has been referred to

  18. What can we learn about impact mechanics from large craters on Venus?

    NASA Technical Reports Server (NTRS)

    Mckinnon, William B.; Alexopoulos, J. S.

    1992-01-01

    More than 50 unequivocal peak-ring craters and multiringed impact basins have been identified on Venus from Earth-based Arecibo, Venera 15/16, and Magellan radar images. These ringed craters are relatively pristine, and so serve as an important new dataset that will further understanding of the structural and rheological properties of the venusian surface and of impact mechanics in general. They are also the most direct analogues for craters formed on the Earth in Phanerozoic time. Finite-element simulations of basin collapse and ring formation were undertaken in collaboration with V. J. Hillgren (University of Arizona). These calculations used an axisymmetric version of the viscoelastic finite element code TECTON, modeled structures on the scale of Klenova or Meitner, and demonstrated two major points. First, viscous flow and ring formation are possible on the timescale of crater collapse for the sizes of multiringed basins seen on Venus and heat flows appropriate to the plant. Second, an elastic lithosphere overlying a Newtonian viscous asthenosphere results mainly in uplift beneath the crater. Inward asthenospheric flow mainly occurs at deeper levels. Lithospheric response is dominantly vertical and flexural. Tensional stress maxima occur and ring formation by normal faulting is predicted in some cases, but these predicted rings occur too far out to explain observed ring spacings on Venus (or on the Moon). Overall, these estimates and models suggest that multiringed basin formation is indeed possible at the scales observed on Venus. Furthermore, due to the strong inverse dependence of solid-state viscosity on stress, the absence of Cordilleran-style ring faulting in craters smaller than Meitner or Klenova makes sense. The apparent increase in viscosity of shock-fluidized rock with crater diameter, greater interior temperatures accessed by larger, deeper craters, and decreased non-Newtonian viscosity associated with larger craters may conspire to make the

  19. Amorphous and Crystalline H20 Ice at Rhea's Inktomi Crater

    NASA Technical Reports Server (NTRS)

    Lewis, Emma M.; Dalle Ore, Cristina M.; Cruikshank, Dale P.; White, Oliver L.

    2014-01-01

    We present the analysis of Cassini spectral data from spectral mapping of Saturnian icy moons Dione and Rhea, to investigate possible effects of impact crater formation on the relative abundances of crystalline and amorphous water ice in the moons' ice crusts. Both moons display morphologically young ray craters as well as older craters. Possible changes in ice properties due to crater formation are conjectured to be more visible in younger craters, and as such Rhea's well imaged ray crater Inktomi is analysed, as are older craters for comparison. We used data from Cassini's Visual and Infrared Mapping Spectrometer (VIMS). For each pixel in the VIMS maps, spectral data were extracted in the near-infrared range (1.75 micrometers less than lambda less than 2.45 micrometers). Analysis was begun by fitting a single Gaussian to the peak in absorption at 2.0 micrometers, which was then subtracted from the data, leaving residuals with a minimum on either side of the original 2.0-micrometers band. The spectra of the individual spatial pixels were then clustered by the differences between these minima, which are sensitive to changes in both ice grain size and crystallinity. This yielded preliminary maps which approximated the physical characteristics of the landscape and were used to identify candidates for further analysis. Spectra were then clustered by the properties of the 1.5-micrometers band, to divide the map into regions based on inferred grain size. For each region, the predicted differences in minima from the Gaussian residuals, over a range of crystallinities, were calculated based on the found grain sizes. This model was used to find the crystallinity of each pixel via grain size and characteristics of the residual function. Preliminary results show a greater degree of crystallization of young crater interiors, particularly in Rhea's ray crater Inktomi, where ice showed crystalline ice abundances between 33 percent and 61 percent. These patterns in ice

  20. Impact Cratering Physics al Large Planetary Scales

    NASA Astrophysics Data System (ADS)

    Ahrens, Thomas J.

    2007-06-01

    Present understanding of the physics controlling formation of ˜10^3 km diameter, multi-ringed impact structures on planets were derived from the ideas of Scripps oceanographer, W. Van Dorn, University of London's, W, Murray, and, Caltech's, D. O'Keefe who modeled the vertical oscillations (gravity and elasticity restoring forces) of shock-induced melt and damaged rock within the transient crater immediately after the downward propagating hemispheric shock has processed rock (both lining, and substantially below, the transient cavity crater). The resulting very large surface wave displacements produce the characteristic concentric, multi-ringed basins, as stored energy is radiated away and also dissipated upon inducing further cracking. Initial calculational description, of the above oscillation scenario, has focused upon on properly predicting the resulting density of cracks, and, their orientations. A new numerical version of the Ashby--Sammis crack damage model is coupled to an existing shock hydrodynamics code to predict impact induced damage distributions in a series of 15--70 cm rock targets from high speed impact experiments for a range of impactor type and velocity. These are compared to results of crack damage distributions induced in crustal rocks with small arms impactors and mapped ultrasonically in recent Caltech experiments (Ai and Ahrens, 2006).

  1. Secrets of the Wabar craters

    USGS Publications Warehouse

    Wynn, Jeffrey C.; Shoemaker, Eugene M.

    1997-01-01

    Focuses on the existence of craters in the Empty Quarter of Saudi Arabia created by the impact of meteors in early times. Mars Pathfinder and Mars Global Surveyor's encounter with impact craters; Elimination of craters in the Earth's surface by the action of natural elements; Impact sites' demand for careful scientific inspections; Location of the impact sites.

  2. Homogeneous impact melts produced by a heterogeneous target?. Sr-Nd isotopic evidence from the Popigai crater, Russia

    NASA Astrophysics Data System (ADS)

    Kettrup, B.; Deutsch, A.; Masaitis, V. L.

    The 35.7 ± 0.2 Ma old Popigai crater, Siberia, with a diameter of about 100 km is one of the best preserved large terrestrial impact structures. The heterogeneous target at the impact site consists of Archean to Lower Proterozoic metamorphic rocks of the crystalline basement, Upper Proterozoic quartzites and other clastic deposits, as well as Cambrian to Cretaceous clastic sediments and sedimentary rocks, including carbonate rocks. Moreover, Proterozoic and Permo-Triassic dolerite dykes are found in the target area. We report major element, Sr and Nd isotope data for 13 of these target rocks and for various types of impactites. The 15 analysed impactite samples include tagamites (impact melt rocks), suevites and impact glass from small veins. Furthermore, two impact breccias and two impact glass-coated gneiss bombs were analysed. We discuss the relation of these impactites to the target lithologies, and evaluate on the basis of literature data the relation of microkrystites (and associated microtektites) in Upper Eocene sediments to the Popigai event. The impactites have SiO 2 abundances ranging from 59 to 66 wt.% and show significant variations in the content of Fe, Ca, and Ti. They have present day 87Sr/ 86Sr ratios between 0.7191 and 0.7369. Their Sr model ages T SrUR range from 1.9 to 2.3 Ga. The 143Nd/ 144Nd ratios for the impactite samples cluster between 0.5113 and 0.5115. The Nd model ages T NdCHUR range from 1.9 to 2.1 Ga. In an ɛ CHUR(Nd)-ɛ UR(Sr) diagram, the impactites and Upper Eocene microkrystites (and associated microtektites) plot in a field delimited by Popigai target lithologies. The impactites are restricted to the field of crystalline basement rocks and Upper Proterozoic quartzites, but they show different isotopic signatures in different crater sectors. Impactites and Upper Eocene microkrystites plot in different, only partly overlapping clusters. The leucocratic microkrystites and microtektites have a higher affinity to the post

  3. A chemostratigraphic method to determine the end of impact-related sedimentation at marine-target impact craters (Chesapeake Bay, Lockne, Tvären)

    USGS Publications Warehouse

    Ormö, Jens; Hill, Andrew C.; Self-Trail, Jean M.

    2010-01-01

    To better understand the impact cratering process and its environmental consequences at the local to global scale, it is important to know when in the geological record of an impact crater the impact-related processes cease. In many instances, this occurs with the end of early crater modification, leaving an obvious sedimentological boundary between impactites and secular sediments. However, in marine-target craters the transition from early crater collapse (i.e., water resurge) to postimpact sedimentation can appear gradual. With the a priori assumption that the reworked target materials of the resurge deposits have a different chemical composition to the secular sediments we use chemostratigraphy (δ13Ccarb, %Corg, major elements) of sediments from the Chesapeake Bay, Lockne, and Tvären craters, to define this boundary. We show that the end of impact-related sedimentation in these cases is fairly rapid, and does not necessarily coincide with a visual boundary (e.g., grain size shift). Therefore, in some cases, the boundary is more precisely determined by chemostratigraphy, especially carbonate carbon isotope variations, rather than by visual inspection. It is also shown how chemostratigraphy can confirm the age of marine-target craters that were previously determined by biostratigraphy; by comparing postimpact carbon isotope trends with established regional trends.

  4. Bunte Breccia of the Ries - Continuous deposits of large impact craters

    NASA Technical Reports Server (NTRS)

    Horz, F.; Ostertag, R.; Rainey, D. A.

    1983-01-01

    The 26-km-diameter Ries impact crater in south Germany and the mechanism of ejection and emplacement associated with its formation about 15 Myr ago are discussed in detail, and the implications of the findings for models of crater formation on earth, moon, and planets are considered. Field observations and laboratory tests on 560-m core materials from nine locations are reported. The continuous deposits (Bunte Breccia) are found to be a chaotic mixture resulting from deposition at ambient temperatures in a highly turbulent environment, probably in the ballistic scenario proposed by Oberbeck et al. (1975), with an emplacement time of only about 5 min. Further impact parameters are estimated using the 'Z model' of Maxwell (1977): initial radius = 6.5 km, excavation depth = 1650 m, excavation volume = 136 cu km, and transient cavity volume = 230 cu km. The interpretation of lunar and planetary remote-sensing and in situ evidence from impact craters is reviewed in the light of the Ries findings. Numerous photographs, maps, diagrams, and tables illustrate the investigation.

  5. Cratering on Titan: A Pre-Cassini Perspective

    NASA Technical Reports Server (NTRS)

    Lorenz, R. D.

    1997-01-01

    (compared with 4 km on Venus, or 0.5 km on Earth). Crater chains are unlikely on Titan, since impactors must pass close enough to Saturn to be tidally disrupted; as a result, they would suffer aerodynamic disruption. Crater counting on adjacent satellites gives densities of about 200 per 10 (exp 6) square km for 20-km-diameter craters. However, the presence of a thick atmosphere leads to atmospheric shielding, depleting the relative abundance of small craters. This has been evaluated by models, and the relative abundance of small craters may be due to a diagnostic atmospheric collapse. A number of radar-dark "splotches" have been detected on Venus; these have been attributed to the interaction of the surface with the atmospheric shockwave produced by the Tunguska-like explosion of a bolide in the atmosphere. Simple analogy suggests that similar features might occur on Titan, but the shocked mass density (which controls the momentum coupling between the surface and the shockwave) of Titan's cold N2 atmosphere is about 20x smaller than that of Venus's hot CO2 atmosphere. Unless ice is much more easily turned to rubble than is rock, such features seem less probable on Titan. When the energy deposited by an impact forms a fireball with an equilibrate greater than one scale height, the fireball expands upward and can distribute ejecta. on ballistic exoatmospheric trajectories. On Venus this process is believed to be responsible for the parabolic features; the interaction of various-sized particles falling through the atmosphere with the zonal wind field winnows the particles to form a parabolic deposit. Although such a process is possible on Titan, the large scale height at higher altitudes would make it more difficult. Comparison with craters on other icy satellites suggests that craters on Titan will be fairly shallow (depth/diameter about 0.1) and craters greater than 10 km in diameter will have central peaks or domed bases, perhaps with central pits. The formation of ejecta

  6. Cratering on Titan: A Pre-Cassini Perspective

    NASA Astrophysics Data System (ADS)

    Lorenz, R. D.

    1997-01-01

    (compared with 4 km on Venus, or 0.5 km on Earth). Crater chains are unlikely on Titan, since impactors must pass close enough to Saturn to be tidally disrupted; as a result, they would suffer aerodynamic disruption. Crater counting on adjacent satellites gives densities of about 200 per 10 6 square km for 20-km-diameter craters. However, the presence of a thick atmosphere leads to atmospheric shielding, depleting the relative abundance of small craters. This has been evaluated by models, and the relative abundance of small craters may be due to a diagnostic atmospheric collapse. A number of radar-dark "splotches" have been detected on Venus; these have been attributed to the interaction of the surface with the atmospheric shockwave produced by the Tunguska-like explosion of a bolide in the atmosphere. Simple analogy suggests that similar features might occur on Titan, but the shocked mass density (which controls the momentum coupling between the surface and the shockwave) of Titan's cold N2 atmosphere is about 20x smaller than that of Venus's hot CO2 atmosphere. Unless ice is much more easily turned to rubble than is rock, such features seem less probable on Titan. When the energy deposited by an impact forms a fireball with an equilibrate greater than one scale height, the fireball expands upward and can distribute ejecta. on ballistic exoatmospheric trajectories. On Venus this process is believed to be responsible for the parabolic features; the interaction of various-sized particles falling through the atmosphere with the zonal wind field winnows the particles to form a parabolic deposit. Although such a process is possible on Titan, the large scale height at higher altitudes would make it more difficult. Comparison with craters on other icy satellites suggests that craters on Titan will be fairly shallow (depth/diameter about 0.1) and craters greater than 10 km in diameter will have central peaks or domed bases, perhaps with central pits. The formation of ejecta

  7. A Comparison of Crater-Size Scaling and Ejection-Speed Scaling During Experimental Impacts in Sand

    NASA Technical Reports Server (NTRS)

    Anderson, J. L. B.; Cintala, M. J.; Johnson, M. K.

    2014-01-01

    Non-dimensional scaling relationships are used to understand various cratering processes including final crater sizes and the excavation of material from a growing crater. The principal assumption behind these scaling relationships is that these processes depend on a combination of the projectile's characteristics, namely its diameter, density, and impact speed. This simplifies the impact event into a single point-source. So long as the process of interest is beyond a few projectile radii from the impact point, the point-source assumption holds. These assumptions can be tested through laboratory experiments in which the initial conditions of the impact are controlled and resulting processes measured directly. In this contribution, we continue our exploration of the congruence between crater-size scaling and ejection-speed scaling relationships. In particular, we examine a series of experimental suites in which the projectile diameter and average grain size of the target are varied.

  8. Ejecta velocity distribution of impact craters formed on quartz sand: Effect of projectile density on crater scaling law

    NASA Astrophysics Data System (ADS)

    Tsujido, Sayaka; Arakawa, Masahiko; Suzuki, Ayako I.; Yasui, Minami

    2015-12-01

    In order to clarify the effects of projectile density on ejecta velocity distributions for a granular target, impact cratering experiments on a quartz sand target were conducted by using eight types of projectiles with different densities ranging from 11 g cm-3 to 1.1 g cm-3, which were launched at about 200 m s-1 from a vertical gas gun at Kobe University. The scaling law of crater size, the ejection angle of ejecta grains, and the angle of the ejecta curtain were also investigated. The ejecta velocity distribution obtained from each projectile was well described by the π-scaling theory of v0/√{gR} =k2(x0/R)-1/μ , where v0, g, R and x0 are the ejection velocity, gravitational acceleration, crater radius and ejection position, respectively, and k2 and μ are constants mostly depending on target material properties (Housen, K.R., Holsapple, K.A. [2011]. Icarus 211, 856-875). The value of k2 was found to be almost constant at 0.7 for all projectiles except for the nylon projectile, while μ increased with the projectile density, from 0.43 for the low-density projectile to 0.6-0.7 for the high-density projectile. On the other hand, the π-scaling theory for crater size gave a μ value of 0.57, which was close to the average of the μ values obtained from ejecta velocity distributions. The ejection angle, θ, of each grain decreased slightly with distance, from higher than 45° near the impact point to 30-40° at 0.6 R. The ejecta curtain angle is controlled by the two elementary processes of ejecta velocity distribution and ejection angle; it gradually increased from 52° to 63° with the increase of the projectile density. The comparison of our experimental results with the theoretical model of the crater excavation flow known as the Z-model revealed that the relationship between μ and θ obtained by our experiments could not be described by the Z-model (Maxwell, D.E. [1977]. In: Roddy, D.J., Pepin, R.O., Merrill, R.B. (Eds.), Impact and Explosion Cratering

  9. Lunar impact basins: Stratigraphy, sequence and ages from superposed impact crater populations measured from Lunar Orbiter Laser Altimeter (LOLA) data

    NASA Astrophysics Data System (ADS)

    Fassett, C. I.; Head, J. W.; Kadish, S. J.; Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2012-02-01

    Impact basin formation is a fundamental process in the evolution of the Moon and records the history of impactors in the early solar system. In order to assess the stratigraphy, sequence, and ages of impact basins and the impactor population as a function of time, we have used topography from the Lunar Orbiter Laser Altimeter (LOLA) on the Lunar Reconnaissance Orbiter (LRO) to measure the superposed impact crater size-frequency distributions for 30 lunar basins (D ≥ 300 km). These data generally support the widely used Wilhelms sequence of lunar basins, although we find significantly higher densities of superposed craters on many lunar basins than derived by Wilhelms (50% higher densities). Our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains. The transition from a lunar impact flux dominated by Population 1 to Population 2 occurred before the mid-Nectarian. This is before the end of the period of rapid cratering, and potentially before the end of the hypothesized Late Heavy Bombardment. LOLA-derived crater densities also suggest that many Pre-Nectarian basins, such as South Pole-Aitken, have been cratered to saturation equilibrium. Finally, both crater counts and stratigraphic observations based on LOLA data are applicable to specific basin stratigraphic problems of interest; for example, using these data, we suggest that Serenitatis is older than Nectaris, and Humboldtianum is younger than Crisium. Sample return missions to specific basins can anchor these measurements to a Pre-Imbrian absolute chronology.

  10. Lunar Impact Basins: Stratigraphy, Sequence and Ages from Superposed Impact Crater Populations Measured from Lunar Orbiter Laser Altimeter (LOLA) Data

    NASA Technical Reports Server (NTRS)

    Fassett, C. I.; Head, J. W.; Kadish, S. J.; Mazarico, E.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.

    2012-01-01

    Impact basin formation is a fundamental process in the evolution of the Moon and records the history of impactors in the early solar system. In order to assess the stratigraphy, sequence, and ages of impact basins and the impactor population as a function of time, we have used topography from the Lunar Orbiter Laser Altimeter (LOLA) on the Lunar Reconnaissance Orbiter (LRO) to measure the superposed impact crater size-frequency distributions for 30 lunar basins (D = 300 km). These data generally support the widely used Wilhelms sequence of lunar basins, although we find significantly higher densities of superposed craters on many lunar basins than derived by Wilhelms (50% higher densities). Our data also provide new insight into the timing of the transition between distinct crater populations characteristic of ancient and young lunar terrains. The transition from a lunar impact flux dominated by Population 1 to Population 2 occurred before the mid-Nectarian. This is before the end of the period of rapid cratering, and potentially before the end of the hypothesized Late Heavy Bombardment. LOLA-derived crater densities also suggest that many Pre-Nectarian basins, such as South Pole-Aitken, have been cratered to saturation equilibrium. Finally, both crater counts and stratigraphic observations based on LOLA data are applicable to specific basin stratigraphic problems of interest; for example, using these data, we suggest that Serenitatis is older than Nectaris, and Humboldtianum is younger than Crisium. Sample return missions to specific basins can anchor these measurements to a Pre-Imbrian absolute chronology.

  11. Potential for Hydrothermal Deposits in Large Martian Impact Craters

    NASA Astrophysics Data System (ADS)

    Thorsos, I. E.; Newsom, H. E.; Davies, A.

    2000-12-01

    Investigation of environments on Mars favorable for pre-biotic chemistry or primitive life is a goal of current strategy. Deposits left by hydrothermal systems on Mars are high priority targets. Impact craters larger than 50 km in diameter should have breached local aquifers and provided sufficient heat to power hydrothermal systems. The amount of heat in craters depends on the size of the melt sheet and uplifted basement forming the central peak. The volume of melt is estimated using scaling relationships (Cintala & Grieve, 1998). The central uplift originates below the transient crater cavity and has a stratigraphic uplift of 1/10 the final crater diameter (Melosh & Ivanov, 1999). The central uplift's temperature with depth profile is estimated using a cylindrical "plug" model and adding the enthalpy profile at the time of maximum impactor penetration (O'Keefe & Ahrens, 1994) to the ambient thermal gradient. The heat from the two sources is estimated over a range of crater diameters. The next phase of this work is to model the longevity and extent of the hydrothermal systems. Cintala, H. J. & R. A. F. Grieve, Meteor. and Plan. Sci. 33, 889-912, 1998. Melosh, H. J. & B. A. Ivanov, Annual Rev. Earth Planet. Sci., 385-415, 1999. O'Keefe, J. D. & T. J. Ahrens, Geol. Soc. Amer. Spec. Paper 293, 103-109, 1994.

  12. Cratering mechanics

    NASA Technical Reports Server (NTRS)

    Ivanov, B. A.

    1986-01-01

    Main concepts and theoretical models which are used for studying the mechanics of cratering are discussed. Numerical two-dimensional calculations are made of explosions near a surface and high-speed impact. Models are given for the motion of a medium during cratering. Data from laboratory modeling are given. The effect of gravitational force and scales of cratering phenomena is analyzed.

  13. A meteorite crater on Earth formed on September 15, 2007: The Carancas hypervelocity impact

    NASA Astrophysics Data System (ADS)

    Tancredi, G.; Ishitsuka, J.; Schultz, P. H.; Harris, R. S.; Brown, P.; Revelle, D. O.; Antier, K.; Le Pichon, A.; Rosales, D.; Vidal, E.; Varela, M. E.; Sánchez, L.; Benavente, S.; Bojorquez, J.; Cabezas, D.; Dalmau, A.

    2009-01-01

    On September 15, 2007, a bright fireball was observed and a big explosion was heard by many inhabitants near the southern shore of Lake Titicaca. In the community of Carancas (Peru), a 13.5 m crater and several fragments of a stony meteorite were found close to the site of the impact. The Carancas event is the first impact crater whose formation was directly observed by several witnesses as well as the first unambiguous seismic recording of a crater-forming meteorite impact on Earth. We present several lines of evidence that suggest that the Carancas crater was a hypervelocity impact. An event like this should have not occurred according to the accepted picture of stony meteoroids ablating in the Earth’s atmosphere, therefore it challenges our present models of entry dynamics. We discuss alternatives to explain this particular event. This emphasizes the weakness in the pervasive use of “average” parameters (such as tensile strength, fragmentation behavior and ablation behavior) in current modeling efforts. This underscores the need to examine a full range of possible values for these parameters when drawing general conclusions from models about impact processes.

  14. Spectral properties of Titan's impact craters imply chemical weathering of its surface

    PubMed Central

    Barnes, J. W.; Sotin, C.; MacKenzie, S.; Soderblom, J. M.; Le Mouélic, S.; Kirk, R. L.; Stiles, B. W.; Malaska, M. J.; Le Gall, A.; Brown, R. H.; Baines, K. H.; Buratti, B.; Clark, R. N.; Nicholson, P. D.

    2015-01-01

    Abstract We examined the spectral properties of a selection of Titan's impact craters that represent a range of degradation states. The most degraded craters have rims and ejecta blankets with spectral characteristics that suggest that they are more enriched in water ice than the rims and ejecta blankets of the freshest craters on Titan. The progression is consistent with the chemical weathering of Titan's surface. We propose an evolutionary sequence such that Titan's craters expose an intimate mixture of water ice and organic materials, and chemical weathering by methane rainfall removes the soluble organic materials, leaving the insoluble organics and water ice behind. These observations support the idea that fluvial processes are active in Titan's equatorial regions. PMID:27656006

  15. False-Color Image of an Impact Crater on Vesta

    NASA Image and Video Library

    2011-08-24

    NASA Dawn spacecraft obtained this false-color image right of an impact crater in asteroid Vesta equatorial region with its framing camera on July 25, 2011. The view on the left is from the camera clear filter.

  16. A Lower Limit on the Thickness of Europa's Ice Shell from Numerical Simulations of Impact Cratering

    NASA Astrophysics Data System (ADS)

    Turtle, E. P.; Ivanov, B. A.

    2001-12-01

    If Europa has an ice-covered, liquid water ocean, the thickness of the ice shell can be tested by analyzing the impact crater morphologies revealed by Galileo images. Several of Europa's 28 primary impact structures have morphologies typical of complex impact craters on other planetary bodies: terraced rims, flat floors, and central peaks [1]. To constrain the minimum ice thickness necessary to reproduce the observed complex crater morphologies, we have performed numerical simulations, using the modified SALE-2D code [2], of the formation of impact craters in ice layers with thicknesses ranging from 5 to 11 km overlying liquid water. The target ice has ice strength properties from published laboratory data [3] with a gradual decrease towards the base of the ice as the temperature approaches the melting point. The projectile parameters were chosen to produce a 10 km diameter crater in thick ice. We find that ice layers less than 7 km thick are not sufficient to prevent an outburst of liquid water during collapse of the transient cavity. At thicknesses of 8 and 9 km we observe a boundary regime: crater collapse produces a flat or upward-domed floor, however the water under the crater center does not reach the surface. In ice greater than 10 km thick a normal transient cavity forms. These results indicate that the ice thickness, at the times and locations of complex crater formation, must have been comparable to the diameters of the transient craters, the largest of which was between 11.9 and 18.5 km [1]. Implementation of additional mechanisms such as acoustic fluidization and creep may affect the shape of the final crater produced in our simulations: acoustic fluidization can produce central peak and peak-ring craters [4], and creep may result in a flattened crater. We are currently investigating the influence of these processes on the final crater morphology. References: [1] Moore et al., Icarus 151, 2001. [2] Ivanov et al., GSA Spec. Pap., in press. [3] Beeman et

  17. Lunar Cratering Chronology: Calibrating Degree of Freshness of Craters to Absolute Ages

    NASA Astrophysics Data System (ADS)

    Trang, D.; Gillis-Davis, J.; Boyce, J. M.

    2013-12-01

    The use of impact craters to age-date surfaces of and/or geomorphological features on planetary bodies is a decades old practice. Various dating techniques use different aspects of impact craters in order to determine ages. One approach is based on the degree of freshness of primary-impact craters. This method examines the degradation state of craters through visual inspection of seven criteria: polygonality, crater ray, continuous ejecta, rim crest sharpness, satellite craters, radial channels, and terraces. These criteria are used to rank craters in order of age from 0.0 (oldest) to 7.0 (youngest). However, the relative decimal scale used in this technique has not been tied to a classification of absolute ages. In this work, we calibrate the degree of freshness to absolute ages through crater counting. We link the degree of freshness to absolute ages through crater counting of fifteen craters with diameters ranging from 5-22 km and degree of freshness from 6.3 to 2.5. We use the Terrain Camera data set on Kaguya to count craters on the continuous ejecta of each crater in our sample suite. Specifically, we divide the crater's ejecta blanket into quarters and count craters between the rim of the main crater out to one crater radii from the rim for two of the four sections. From these crater counts, we are able to estimate the absolute model age of each main crater using the Craterstats2 tool in ArcGIS. Next, we compare the degree of freshness for the crater count-derived age of our main craters to obtain a linear inverse relation that links these two metrics. So far, for craters with degree of freshness from 6.3 to 5.0, the linear regression has an R2 value of 0.7, which corresponds to a relative uncertainty of ×230 million years. At this point, this tool that links degree of freshness to absolute ages cannot be used with craters <8km because this class of crater degrades quicker than larger craters. A graphical solution exists for correcting the degree of

  18. MA130301GT catalogue of Martian impact craters and advanced evaluation of crater detection algorithms using diverse topography and image datasets

    NASA Astrophysics Data System (ADS)

    Salamunićcar, Goran; Lončarić, Sven; Pina, Pedro; Bandeira, Lourenço; Saraiva, José

    2011-01-01

    Recently, all the craters from the major currently available manually assembled catalogues have been merged into the catalogue with 57 633 known Martian impact craters (MA57633GT). In addition, the work on crater detection algorithm (CDA), developed to search for still uncatalogued impact craters using 1/128° MOLA data, resulted in MA115225GT. In parallel with this work another CDA has been developed which resulted in the Stepinski catalogue containing 75 919 craters (MA75919T). The new MA130301GT catalogue presented in this paper is the result of: (1) overall merger of MA115225GT and MA75919T; (2) 2042 additional craters found using Shen-Castan based CDA from the previous work and 1/128° MOLA data; and (3) 3129 additional craters found using CDA for optical images from the previous work and selected regions of 1/256° MDIM, 1/256° THEMIS-DIR, and 1/256° MOC datasets. All craters from MA130301GT are manually aligned with all used datasets. For all the craters that originate from the used catalogues (Barlow, Rodionova, Boyce, Kuzmin, Stepinski) we integrated all the attributes available in these catalogues. With such an approach MA130301GT provides everything that was included in these catalogues, plus: (1) the correlation between various morphological descriptors from used catalogues; (2) the correlation between manually assigned attributes and automated depth/diameter measurements from MA75919T and our CDA; (3) surface dating which has been improved in resolution globally; (4) average errors and their standard deviations for manually and automatically assigned attributes such as position coordinates, diameter, depth/diameter ratio, etc.; and (5) positional accuracy of features in the used datasets according to the defined coordinate system referred to as MDIM 2.1, which incorporates 1232 globally distributed ground control points, while our catalogue contains 130 301 cross-references between each of the used datasets. Global completeness of MA130301GT is up to

  19. Correlation of the Largest Craters, Stratigraphic Impact Signatures, and Extinction Events Over the Past 250 Myr

    NASA Technical Reports Server (NTRS)

    Rampino, Michael R.; Caldeira, Ken

    2017-01-01

    The six largest known impact craters of the last 250 Myr (greater than or equal to 70 km in diameter), which are capable of causing significant environmental damage, coincide with four times of recognized extinction events at 36 (with 2 craters), 66, and 145 Myr ago, and possibly with two provisional extinction events at 168 and 215 Myr ago. These impact cratering events are accompanied by layers in the geologic record interpreted as impact ejecta. Chance occurrences of impacts and extinctions can be rejected at confidence levels of 99.96 percent (for 4 impact/extinctions) to 99.99 percent (for 6 impact/extinctions). These results argue that several extinction events over the last 250 Myr may be related to the effects of large-body impacts.

  20. Ancient impact structures on modern continental shelves: The Chesapeake Bay, Montagnais, and Toms Canyon craters, Atlantic margin of North America

    USGS Publications Warehouse

    Poag, C. Wylie; Plescia, J.B.; Molzer, P.C.

    2002-01-01

    Three ancient impact craters (Chesapeake Bay - 35.7 Ma; Toms Canyon - 35.7 Ma; Montagnais - 51 Ma) and one multiring impact basin (Chicxulub - 65 Ma) are currently known to be buried beneath modern continental shelves. All occur on the passive Atlantic margin of North America in regions extensively explored by seismic reflection surveys in the search for oil and gas reserves. We limit our discussion herein to the three youngest structures. These craters were created by submarine impacts, which produced many structural and morphological features similar in construction, composition, and variability to those documented in well-preserved subaerial and planetary impact craters. The subcircular Chesapeake Bay (diameter 85 km) and ovate Montagnais (diameter 45-50 km) structures display outer-rim scarps, annular troughs, peak rings, inner basins, and central peaks similar to those incorporated in the widely cited conceptual model of complex impact craters. These craters differ in several respects from the model, however. For example, the Montagnais crater lacks a raised lip on the outer rim, the Chesapeake Bay crater displays only small remnants of a raised lip, and both craters contain an unusually thick body of impact breccia. The subtriangular Toms Canyon crater (diameter 20-22 km), on the other hand, contains none of the internal features of a complex crater, nor is it typical of a simple crater. It displays a prominent raised lip on the outer rim, but the lip is present only on the western side of the crater. In addition, each of these craters contains some distinct features, which are not present in one or both of the others. For example, the central peak at Montagnais rises well above the elevation of the outer rim, whereas at Chesapeake Bay, the outer rim is higher than the central peak. The floor of the Toms Canyon crater is marked by parallel deep troughs and linear ridges formed of sedimentary rocks, whereas at Chesapeake Bay, the crater floor contains

  1. Depth-diameter ratios for Martian impact craters: Implications for target properties and episodes of degradation

    NASA Technical Reports Server (NTRS)

    Barlow, N. G.

    1993-01-01

    This study determines crater depth through use of photoclinometric profiles. Random checks of the photoclinometric results are performed using shadow estimation techniques. The images are Viking Orbiter digital format frames; in cases where the digital image is unusable for photoclinometric analysis, shadow estimation is used to determine crater depths. The two techniques provide depth results within 2 percent of each other. Crater diameters are obtained from the photoclinometric profiles and checked against the diameters measured from the hard-copy images using a digitizer. All images used in this analysis are of approximately 40 m/pixel resolution. The sites that have been analyzed to date include areas within Arabia, Maja Valles, Memnonia, Acidalia, and Elysium. Only results for simple craters (craters less than 5 km in diameter) are discussed here because of the low numbers of complex craters presently measured in the analysis. General results indicate that impact craters are deeper than average. A single d/D relationship for fresh impact craters on Mars does not exist due to changes in target properties across the planet's surface. Within regions where target properties are approximately constant, however, d/D ratios for fresh craters can be determined. In these regions, the d/D ratios of nonpristine craters can be compared with the fresh crater d/D relationship to obtain information on relative degrees of crater degradation. This technique reveals that regional episodes of enhanced degradation have occurred. However, the lack of statistically reliable size-frequency distribution data prevents comparison of the relative ages of these events between different regions, and thus determination of a large-scale episode (or perhaps several episodes) cannot be made at this time.

  2. A newly discovered impact crater in Titan's Senkyo: Cassini VIMS observations and comparison with other impact features

    USGS Publications Warehouse

    Buratti, B.J.; Sotin, Christophe; Lawrence, K.; Brown, R.H.; Le, Mouelic S.; Soderblom, J.M.; Barnes, J.; Clark, R.N.; Baines, K.H.; Nicholson, P.D.

    2012-01-01

    Senkyo is an equatorial plain on Titan filled with dunes and surrounded by hummocky plateaus. During the Titan targeted flyby T61 on August 25, 2009, the Cassini Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft observed a circular feature, centered at 5.4?? N and 341??W, that superimposes the dune fields and a bright plateau. This circular feature, which has been named Paxsi by the International Astronomical Union, is 120??10 km in diameter (measured from the outer edge of the crater rim) and exhibits a central bright area that can be interpreted as the central peak or pit of an impact crater. Although there are only a handful of certain impact craters on Titan, there are two other craters that are of similar size to this newly discovered feature and that have been studied by VIMS: Sinlap (Le Mou??lic et al, 2008) and Selk (Soderblom et al, 2010). Sinlap is associated with a large downwind, fan-like feature that may have been formed from an impact plume that rapidly expanded and deposited icy particles onto the surface. Although much of the surrounding region is covered with dunes, the plume region is devoid of dunes. The formation process of Selk also appears to have removed (or covered up) dunes from parts of the adjacent dune-filled terrain. The circular feature on Senkyo is quite different: there is no evidence of an ejecta blanket and the crater itself appears to be infilled with dune material. The rim of the crater appears to be eroded by fluvial processes; at one point the rim is breached. The rim is unusually narrow, which may be due to mass wasting on its inside and subsequent infill by dunes. Based on these observations, we interpret this newly discovered feature to be a more eroded crater than both Sinlap and Selk. Paxsi may have formed during a period when Titan was warmer and more ductile than it is currently. ?? 2011 Elsevier Ltd. All rights reserved.

  3. Mitigation of EMU Glove Cut Hazard by MMOD Impact Craters on Exposed ISS Handrails

    NASA Technical Reports Server (NTRS)

    Christiansen, Eric L.; Ryan, Shannon

    2009-01-01

    Recent cut damages to crewmember extravehicular mobility unit (EMU) gloves during extravehicular activity (EVA) onboard the International Space Station (ISS) has been found to result from contact with sharp edges or pinch points rather than general wear or abrasion. One possible source of cut-hazards are protruding sharp edged crater lips from impact of micrometeoroid and orbital debris (MMOD) particles on external metallic handrails along EVA translation paths. During impact of MMOD particles at hypervelocity an evacuation flow develops behind the shock wave, resulting in the formation of crater lips that can protrude above the target surface. In this study, two methods were evaluated to limit EMU glove cut-hazards due to MMOD impact craters. In the first phase, four flexible overwrap configurations are evaluated: a felt-reusable surface insulation (FRSI), polyurethane polyether foam with beta-cloth cover, double-layer polyurethane polyether foam with beta-cloth cover, and multi-layer beta-cloth with intermediate Dacron netting spacers. These overwraps are suitable for retrofitting ground equipment that has yet to be flown, and are not intended to protect the handrail from impact of MMOD particles, rather to act as a spacer between hazardous impact profiles and crewmember gloves. At the impact conditions considered, all four overwrap configurations evaluated were effective in limiting contact between EMU gloves and impact crater profiles. The multi-layer beta-cloth configuration was the most effective in reducing the height of potentially hazardous profiles in handrail-representative targets. In the second phase of the study, four material alternatives to current aluminum and stainless steel alloys were evaluated: a metal matrix composite, carbon fiber reinforced plastic (CFRP), fiberglass, and a fiber metal laminate. Alternative material handrails are intended to prevent the formation of hazardous damage profiles during MMOD impact and are suitable for flight

  4. Mapping of Boulder Ejecta around Late Amazonian Impact Craters on Mars

    NASA Astrophysics Data System (ADS)

    Hood, D.; Karunatillake, S.; Fassett, C.

    2017-12-01

    Detailed mapping of boulders in Martian crater ejecta is lacking due to the large burden of manual boulder counting. Using a newly-developed boulder recognition algorithm, we map the ejected blocks of four Late Amazonian craters. These four craters: Tomini B (125° E, 15° N), Zumba (227° E, -9° N), Gratteri (200° E, -18° N), and an unnamed crater at 230° E, -23° N, have crater ages spanning from as young as 200 ka to as old as 17 Ma [Hartmann et al., 2010; Schon and Head, 2012]. Both Zumba and the unnamed crater are in Daedalia Planum but have very distinct ages making these ideal targets to examine boulder distribution variability within the same target material. Gratteri and Tomini B, by contrast, are in less distinct geologic settings with the impacted material being of mixed fluvial-volcanic origin. For these craters we locate and measure all meter-scale boulders outside of the crater rim and up to 3 crater radii away. Following the method described by Krishna and Kumar [Krishna and Kumar, 2016], we divide the area outside the crater basin into 36 angular sectors, each being 10° wide, and 30 radial sectors 1/10 crater radii wide up to 3 crater radii from the rim. These divisions enable investigation into the distribution of ejected boulders as a function of both direction and distance. We compute the cumulative size-frequency distribution, normalized to the surface area of the observed region, using an exponential fit, as N(a) = Ce-ab, where C is a constant equaling the total number of distinct boulders, a is the average diameter of each boulder, N(a) is the number of boulders of size not less than a, and b is the fit parameter (e.g.[Golombek and Rapp, 1997]). In addition, we also compute the spatial distribution of boulder shapes quantified as elongation: 1-width/height. With the distributions well-described, we compare the spatial distribution of boulders around these four craters to understand how target lithology and age affect the observed

  5. Doublet Crater

    NASA Image and Video Library

    2010-12-22

    This image from NASA Mars Odyssey is of a doublet crater located in Utopia Planitia, near the Elysium Volcanic region. Doublet craters are formed by simultaneous impact of a meteor that broke into two pieces prior to hitting the surface.

  6. Lunar crater volumes - Interpretation by models of impact cratering and upper crustal structure

    NASA Technical Reports Server (NTRS)

    Croft, S. K.

    1978-01-01

    Lunar crater volumes can be divided by size into two general classes with distinctly different functional dependence on diameter. Craters smaller than approximately 12 km in diameter are morphologically simple and increase in volume as the cube of the diameter, while craters larger than about 20 km are complex and increase in volume at a significantly lower rate implying shallowing. Ejecta and interior volumes are not identical and their ratio, Schroeters Ratio (SR), increases from about 0.5 for simple craters to about 1.5 for complex craters. The excess of ejecta volume causing the increase, can be accounted for by a discontinuity in lunar crust porosity at 1.5-2 km depth. The diameter range of significant increase in SR corresponds with the diameter range of transition from simple to complex crater morphology. This observation, combined with theoretical rebound calculation, indicates control of the transition diameter by the porosity structure of the upper crust.

  7. Paradigm lost: Venus crater depths and the role of gravity in crater modification

    NASA Technical Reports Server (NTRS)

    Sharpton, Virgil L.

    1992-01-01

    Previous to Magellan, a convincing case had been assembled that predicted that complex impact craters on Venus were considerably shallower than their counterparts on Mars, Mercury, the Moon, and perhaps even Earth. This was fueled primarily by the morphometric observation that, for a given diameter (D), crater depth (d) seems to scale inversely with surface gravity for the other planets in the inner solar system. The unpredicted depth of fresh impact craters on Venus argues against a simple inverse relationship between surface gravity and crater depth. Factors that could contribute to deep craters on Venus include (1) more efficient excavation on Venus, possibly reflecting rheological effects of the hot venusian environment; (2) more melting and efficient removal of melt from the crater cavity; and (3) enhanced ejection of material out of the crater, possibly as a result of entrainment in an atmosphere set in motion by the passage of the projectile. The broader issue raised by the venusian crater depths is whether surface gravity is the predominant influence on crater depths on any planet. While inverse gravity scaling of crater depths has been a useful paradigm in planetary cratering, the venusian data do not support this model and the terrestrial data are equivocal at best. The hypothesis that planetary gravity is the primary influence over crater depths and the paradigm that terrestrial craters are shallow should be reevaluated.

  8. Fresh Dark Ray Crater

    NASA Image and Video Library

    2011-10-15

    The crater on asteroid Vesta shown in this image from NASA Dawn spacecraft was emplaced onto the ejecta blanket of two large twin craters. Commonly, rays from impact craters are brighter than the surrounding surface.

  9. Discovering research value in the Campo del Cielo, Argentina, meteorite craters

    NASA Astrophysics Data System (ADS)

    Cassidy, William A.; Renard, Marc L.

    1996-07-01

    The Campo del Cielo meteorite crater field in Argentina contains at least 20 small meteorite craters, but a recent review of the field data and a remote sensing study suggest that there may be more. The fall occurred ˜4000 years ago into a uniform loessy soil, and the craters are well enough preserved so that some of their parameters of impact can be determined after excavation. The craters were formed by multi-ton fragments of a type IA meteoroid with abundant silicate inclusions. Relative to the horizontal, the angle of infall was ˜9°. Reflecting the low angle of infall, the crater field is elongated with apparent dimensions of 3 × 18.5 km. The largest craters are near the center of this ellipse. This suggests that when the parent meteoroid broke apart, the resulting fragments diverged from the original trajectory in inverse relation to their masses and did not undergo size sorting due to atmospheric deceleration. The major axis of the crater field as we know it extends along N63°E, but the azimuths of infall determined by excavation of Craters 9 and 10 are N83.5°E and N75.5°E, respectively. This suggests that the major axis of the crater field is not yet well determined. The three or four largest craters appear to have been formed by impacts that disrupted the projectiles, scattering fragments around the outsides of the craters and leaving no large masses within them; these are relatively symmetrical in shape. Other craters are elongated features with multi-ton masses preserved within them and no fragmentation products outside. There are two ways in which field research on the Campo del Cielo crater field is found to be useful. (1) Studies exist that have been used to interpret impact craters on planetary surfaces other than the Earth. This occurrence of a swarm of projectiles impacting at known angles and similar velocities into a uniform target material provides an excellent field site at which to test the applicability of those studies. (2) Individual

  10. Eastern rim of the Chesapeake Bay impact crater: Morphology, stratigraphy, and structure

    USGS Publications Warehouse

    Poag, C.W.

    2005-01-01

    This study reexamines seven reprocessed (increased vertical exaggeration) seismic reflection profiles that cross the eastern rim of the Chesapeake Bay impact crater. The eastern rim is expressed as an arcuate ridge that borders the crater in a fashion typical of the "raised" rim documented in many well preserved complex impact craters. The inner boundary of the eastern rim (rim wall) is formed by a series of raterfacing, steep scarps, 15-60 m high. In combination, these rim-wall scarps represent the footwalls of a system of crater-encircling normal faults, which are downthrown toward the crater. Outboard of the rim wall are several additional normal-fault blocks, whose bounding faults trend approximately parallel to the rim wall. The tops of the outboard fault blocks form two distinct, parallel, flat or gently sloping, terraces. The innermost terrace (Terrace 1) can be identified on each profile, but Terrace 2 is only sporadically present. The terraced fault blocks are composed mainly of nonmarine, poorly to moderately consolidated, siliciclastic sediments, belonging to the Lower Cretaceous Potomac Formation. Though the ridge-forming geometry of the eastern rim gives the appearance of a raised compressional feature, no compelling evidence of compressive forces is evident in the profiles studied. The structural mode, instead, is that of extension, with the clear dominance of normal faulting as the extensional mechanism. 

  11. Hypervelocity impacts into ice-topped layered targets: Investigating the effects of ice crust thickness and subsurface density on crater morphology

    NASA Astrophysics Data System (ADS)

    Harriss, Kathryn H.; Burchell, Mark J.

    2017-07-01

    Many bodies in the outer solar system are theorized to have an ice shell with a different subsurface material below, be it chondritic, regolith, or a subsurface ocean. This layering can have a significant influence on the morphology of impact craters. Accordingly, we have undertaken laboratory hypervelocity impact experiments on a range of multilayered targets, with interiors of water, sand, and basalt. Impact experiments were undertaken using impact speeds in the range of 0.8-5.3 km s-1, a 1.5 mm Al ball bearing projectile, and an impact incidence of 45°. The surface ice crust had a thickness between 5 and 50 mm, i.e., some 3-30 times the projectile diameter. The thickness of the ice crust as well as the nature of the subsurface layer (liquid, well consolidated, etc.) have a marked effect on the morphology of the resulting impact crater, with thicker ice producing a larger crater diameter (at a given impact velocity), and the crater diameter scaling with impact speed to the power 0.72 for semi-infinite ice, but with 0.37 for thin ice. The density of the subsurface material changes the structure of the crater, with flat crater floors if there is a dense, well-consolidated subsurface layer (basalt) or steep, narrow craters if there is a less cohesive subsurface (sand). The associated faulting in the ice surface is also dependent on ice thickness and the substrate material. We find that the ice layer (in impacts at 5 km s-1) is effectively semi-infinite if its thickness is more than 15.5 times the projectile diameter. Below this, the crater diameter is reduced by 4% for each reduction in ice layer thickness equal to the impactor diameter. Crater depth is also affected. In the ice thickness region, 7-15.5 times the projectile diameter, the crater shape in the ice is modified even when the subsurface layer is not penetrated. For ice thicknesses, <7 times the projectile diameter, the ice layer is breached, but the nature of the resulting crater depends heavily on the

  12. Pwyll Impact Crater: Perspective View of Topographic Model

    NASA Technical Reports Server (NTRS)

    1998-01-01

    This computer-generated perspective view of the Pwyll impact crater on Jupiter's moon Europa was created using images taken by NASA's Galileo spacecraft camera when the spacecraft flew past that moon on Feb. 20 and Dec. 16, 1997 during its 6th and 12th orbits of Jupiter. Images of the crater taken from different angles on the different orbits have been combined to generate a model of the topography of Pwyll and its surroundings. This simulated view is from the southwest at a 45 degree angle, with the vertical exaggerated four times the natural size. The colors represent different elevation levels with blue being the lowest and red the highest. Pwyll, about 26 kilometers (16 miles) across, is unusual among craters in the solar system, because its floor is at about the same elevation as the surrounding terrain. Moreover, its central peak, standing approximately 600 meters (almost 2,000 feet) above the floor, is much higher than its rim. This may indicate that the crater was modified shortly after its formation by the flow of underlying warm ice.

    The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC. JPL is an operating division of California Institute of Technology (Caltech).

    This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL http://www.jpl.nasa.gov/ galileo.

  13. Size-Frequency Distribution of Small Lunar Craters: Widening with Degradation and Crater Lifetime

    NASA Astrophysics Data System (ADS)

    Ivanov, B. A.

    2018-01-01

    The review and new measurements are presented for depth/diameter ratio and slope angle evolution during small ( D < 1 km) lunar impact craters aging (degradation). Comparative analysis of available data on the areal cratering density and on the crater degradation state for selected craters, dated with returned Apollo samples, in the first approximation confirms Neukum's chronological model. The uncertainty of crater retention age due to crater degradational widening is estimated. The collected and analyzed data are discussed to be used in the future updating of mechanical models for lunar crater aging.

  14. Mud volcanism and morphology of impact craters in Utopia Planitia on Mars: Evidence for the ancient ocean

    NASA Astrophysics Data System (ADS)

    Ivanov, Mikhail A.; Hiesinger, H.; Erkeling, G.; Reiss, D.

    2014-01-01

    Results of our detailed geological mapping and interpretation of the nature and relative and absolute model ages of units and structures in the SW portion of Utopia Planitia (20-45°N, 100-120°E) suggest the following. (1) The size-frequency distribution (SFD) of craters that both are buried by materials of the Vastitas Borealis units (VB) and superpose its surface indicate that the absolute model ages of terrain predating the emplacement of the VB is ˜3.7 Ga. (2) Lack of craters that are partly embayed by materials of the VB in the SW portion of Utopia Planitia implies that the emplacement of the VB was faster than the rate of accumulation of impact craters and is consistent with the geologically short time of emplacement of the VB due to catastrophic release of water from outflow channels (e.g., Carr, M.H. [1996]. Water on Mars. Oxford University Press, New York, p. 229). (3) The SFD of craters that superpose the surface of the VB indicates an absolute model age of ˜3.6-3.5 Ga. The absolute model ages of etched flows, which represent the upper stratigraphic limit of the VB, are estimated to be ˜3.5 Ga. (4) The majority of the larger (i.e., >1 km) impact craters show ejecta morphologies (rampart and pancake-like ejecta) that are indicative of the presence of ice/water in the target materials. The distal portions of the pancake-like ejecta are heavily degraded (not due to embayment). This suggests that these craters formed in targets that contained higher abundances of volatiles. (5) The diameter ranges of the craters with either rampart- or pancake-like ejecta are overlapping (from ˜2 to ˜60 km). Craters with pancake-like ejecta are concentrated within the central portion of the Utopia basin (less than ˜1000 km from the basin center) and rampart craters occur at the periphery of the basin. This pattern of the crater spatial distribution suggests that materials within the center of Utopia Planitia contained more ice/water. (6) Etched flows around the central

  15. Societal Implications of an Impact Crater - Chesapeake Bay Impact Structure, Virginia

    NASA Astrophysics Data System (ADS)

    Emry, S.; McFarland, R.; Powars, D.

    2002-05-01

    Ground water plays an important role in the economy and quality of life in the Coastal Plain of Virginia. In 1990, the aquifers in the Coastal Plain supplied over 100 million gallons of water per day to the citizens, businesses, and industries of Virginia. In southeastern Virginia, the thirteen public water utilities serve approximately 1.5 million people in the Hampton Roads area. The role of ground water resources in sustaining this area is more critical than ever due to the relatively low relief of the Coastal Plain Province, providing few new surface water sources to meet the growing population and expanding economy and the increased regulatory obstacles to obtaining a permit to build new reservoirs. A zone of salty ground water, referred to as the "inland salt water wedge," is well known to ground water resource planners and scientists, but until recently the phenomenon has not been satisfactorily explained. In 1996, the directors of the water utilities in Hampton Roads were introduced to the most dramatic geological event that ever took place in the Chesapeake Bay region. Geologists from the U.S. Geological Survey provided evidence of a meteor impact that formed a crater over 35 million years ago. The contours of the inland saltwater wedge conform well to the shape of the crater's outer rim. Prior to the discovery of the impact crater, it was presumed that the ground water flow in the Coastal Plain aquifer system was a relatively simple system described as "alternating layers of aquifers and confining units gradually dipping and thickening from the west to the east." With the discovery of the impact crater, the rules changed. In 1997, the USGS and the Hampton Roads Planning District Commission, representing the sixteen member jurisdictions, teamed up in a cooperative effort to redefine the hydrogeology of southeastern Virginia. In 1999, the Virginia Department of Environmental Quality and the Virginia Department of Mines, Minerals, and Energy joined the team

  16. Identification of Possible Interstellar Dust Impact Craters on Stardust Foil I033N,1

    NASA Astrophysics Data System (ADS)

    Ansari, A.; ISPE Team; 29,000 Stardust@home Dusters

    2011-12-01

    The Interstellar Dust Collector onboard NASA's Stardust Mission - the first to return solid extraterrestrial material to Earth from beyond the Moon - was exposed to the interstellar dust stream for a total of 229 days prior to the spacecraft's return in 2006 [1]. Aluminum foils and aerogel tiles on the collector may have captured the first samples of contemporary interstellar dust. Interstellar Preliminary Examination (ISPE) focuses in part on crater identification and analysis of residue within the craters to determine the nature and origin of the impacting particles. Thus far, ISPE has focused on nine foils and found a total of 20 craters. The number density of impact craters on the foils exceeds by far estimates made from interstellar flux calculations [2]. To identify craters, foil I1033N,1 was scanned with the Field Museum's Evo 60 Scanning Electron Microscope (SEM) at a resolution of 52 nm/pixel with a 15 kV and 170-240 pA beam. Contamination was monitored according to the ISPE protocol: four 4 μm × 3 μm areas of C layers of different thicknesses on a Stardust-type Al foil were irradiated 20 times for 50 s each, while the C and Al signals were recorded with energy-dispersive X-ray spectroscopy (EDS). The C/Al ratio did not increase after 20 repetitions on each of the four areas. The same experiment repeated 7 months later yielded identical results. Thus, analysis with the SEM results in no detectable contamination. Crater candidates were manually selected from SEM images, then reimaged at higher resolution (17 nm/pixel) in order to eliminate false detections. The foil was then sent to Washington University for Auger Nanoprobe elemental analysis of crater 11_175 (diam. 1.1 μm), and to the Naval Research Laboratory for focused ion beam work and transmission electron microscopy and EDS. Twelve crater candidates (diam. 0.28 - 1.1 μm), both elliptical and circular, were identified. The number density of craters on foil 1033N is 15.8 cm^-2. Auger measurements

  17. Is There any Relationship Between the Santa Elena Depression and Chicxulub Impact Crater, Northwestern Yucatan Peninsula, Mexico?

    NASA Astrophysics Data System (ADS)

    Lefticariu, L.

    2005-05-01

    The Terminal Cretaceous Chicxulub Impact Crater had a strong control on the depositional and diagenetic history of the northern Yucatan Platform during most of the Cenozoic Era. The Chicxulub Sedimentary Basin (henceforth Basin), which approximately coincides with the impact crater, is circumscribed by a concentration of karstic sinkholes known as the Ring of Cenotes. Santa Elena Depression (henceforth Depression) is the name proposed for the bowl-shaped buried feature, first contoured by geophysical studies, immediately south of the Basin, in the area where the Ticul 1 and UNAM 5 wells were drilled. Lithologic, petrographic, and biostratigraphic data on PEMEX, UNAM, and ICDP cores show that: 1) Cenozoic deposits are much thicker inside the Basin than inside the Depression, 2) in general, the Cenozoic formations from inside the Depression are the thickest among those outside the Basin, 3) variably dolomitized pelagic or outer-platform wackestone or mudstone occur both inside the Basin and Depression, 4) the age of the deeper-water sedimentary carbonate rocks is Paleocene-Eocene inside the Basin and Paleocene?-Early Eocene inside the Depression, 5) the oldest formations that crop out are of Middle Eocene age at the edge of the Basin and Early-Middle Eocene age inside the Depression, 6) saline lake deposits, that consist chiefly of anhydrite, gypsum, and fine carbonate, and also contain quartz, chert, clay, zeolite, potassium feldspar, pyrite, and fragments of wood, are present in the Cenozoic section of the UNAM 5 core between 282 and 198 m below the present land surface, 7) the dolomite, subaerial exposure features (subaerial crusts, vugs, karst, dedolomite), and vug-filling cement from the Eocene formations are more abundant inside the Depression than inside the Basin. The depositional environments that are proposed for explaining the Cenozoic facies succession within the Santa Elena Depression are: 1) deeper marine water (Paleocene?-Early Eocene), 2) relatively

  18. Martian Polar Impact Craters: A Preliminary Assessment Using Mars Orbiter Laser Altimeter (MOLA)

    NASA Technical Reports Server (NTRS)

    Sakimoto, S. E. H.; Garvin, J. B.

    1999-01-01

    Our knowledge of the age of the layered polar deposits and their activity in the volatile cycling and climate history of Mars is based to a large extent on their apparent ages as determined from crater counts. Interpretation of the polar stratigraphy (in terms of climate change) is complicated by reported differences in the ages of the northern and southern layered deposits. The north polar residual ice deposits are thought to be relatively young, based on the reported lack of any fresh impact craters in Viking Orbiter Images. Herkenhoff et al., report no craters at all on the North polar layered deposits or ice cap, and placed an upper bound on the surface age (or, alternatively, the vertical resurfacing rate) of 100 thousand years to 10 million years, suggesting that the north polar region is an active resurfacing site. In contrast, the southern polar region was found to have at least 15 impact craters in the layered deposits and cap. Plaut et al, concluded that the surface was less than or = 120 million years old. This reported age difference factor of 100 to 1000 increases complexity in climate and volatile modeling. Recent MOLA results for the topography of the northern polar cap document a handful or more of possible craters, which could result in revised age or resurfacing estimates for the northern cap. This study is a preliminary look at putative craters in both polar caps. Additional information is contained in the original extended abstract.

  19. Estimates of Comet Fragment Masses from Impact Crater Chains on Callisto and Ganymede

    NASA Technical Reports Server (NTRS)

    McKinnon, William B.; Schenk, Paul M.

    1995-01-01

    Chains of impact craters, or catenae, have been identified in Voyager images of Callisto and Ganymede. Although these resemble in some respects secondary crater chains, the source craters and basins for the catenae cannot be identified. The best explanation is a phenomenon similar to that displayed by former comet Shoemaker-Levy 9; tidal (or other) breakup close to Jupiter followed by gradual orbital separation of the fragments and collision with a Galilean satellite on the outbound leg of the trajectory. Because the trajectories must pass close to Jupiter, this constrains the impact geometry (velocity and impact angle) of the individual fragments. For the dominant classes of impactors, short period Jupiter-family comets and asteroids, velocities at Callisto and Ganymede are dominated by Jovian gravity and a satellite's orbital motion, and are insensitive to the pre-fragmentation heliocentric velocity; velocities are insensitive to satellite gravity for all impactor classes. Complex crater shapes on Callisto and Ganymede are determined from Voyager images and Schmidt-Holsapple scaling is used to back out individual fragment masses. We find that comet fragment radii are generally less than about 500 m (for ice densities) but can be larger. These estimates can be compared with those for the Shoemaker-Levy 9 impactors.

  20. Oudemans Crater

    NASA Technical Reports Server (NTRS)

    2008-01-01

    This image of the interior of Oudemans Crater was taken by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) at 1800 UTC (1:00 p.m. EDT) on October 2, 2006, near 9.8 degrees south latitude, 268.5 degrees east longitude. CRISM's image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 20 meters (66 feet) across.

    Oudemans Crater is located at the extreme western end of Valles Marineris in the Sinai Planum region of Mars. The crater measures some 124 kilometers (77 miles) across and sports a large central peak.

    Complex craters like Oudemans are formed when an object, such as an asteroid or comet, impacts the planet. The size, speed and angle at which the object hits all determine the type of crater that forms. The initial impact creates a bowl-shaped crater and flings material (known as ejecta) out in all directions along and beyond the margins of the bowl forming an ejecta blanket. As the initial crater cavity succumbs to gravity, it rebounds to form a central peak while material along the bowl's rim slumps back into the crater forming terraces along the inner wall. If the force of the impact is strong enough, a central peak forms and begins to collapse back into the crater basin, forming a central peak ring.

    The uppermost image in the montage above shows the location of CRISM data on a mosaic taken by the Mars Odyssey spacecraft's Thermal Emission Imaging System (THEMIS). The CRISM data was taken inside the crater, on the northeast slope of the central peak.

    The lower left image is an infrared false-color image that reveals several distinctive deposits. The center of the image holds a ruddy-brown deposit that appears to correlates with a ridge running southwest to northeast. Lighter, buff-colored deposits occupy low areas interspersed within the ruddy-brown deposit. The southeast corner holds small hills that form part of the central peak complex.

    The lower right image shows spectral

  1. Impact Crater Experiments for Introductory Physics and Astronomy Laboratories

    ERIC Educational Resources Information Center

    Claycomb, J. R.

    2009-01-01

    Activity-based collisional analysis is developed for introductory physics and astronomy laboratory experiments. Crushable floral foam is used to investigate the physics of projectiles undergoing completely inelastic collisions with a low-density solid forming impact craters. Simple drop experiments enable determination of the average acceleration,…

  2. Validation of numerical codes for impact and explosion cratering: Impacts on strengthless and metal targets

    NASA Astrophysics Data System (ADS)

    Pierazzo, E.; Artemieva, N.; Asphaug, E.; Baldwin, E. C.; Cazamias, J.; Coker, R.; Collins, G. S.; Crawford, D. A.; Davison, T.; Elbeshausen, D.; Holsapple, K. A.; Housen, K. R.; Korycansky, D. G.; Wünnemann, K.

    2008-12-01

    Over the last few decades, rapid improvement of computer capabilities has allowed impact cratering to be modeled with increasing complexity and realism, and has paved the way for a new era of numerical modeling of the impact process, including full, three-dimensional (3D) simulations. When properly benchmarked and validated against observation, computer models offer a powerful tool for understanding the mechanics of impact crater formation. This work presents results from the first phase of a project to benchmark and validate shock codes. A variety of 2D and 3D codes were used in this study, from commercial products like AUTODYN, to codes developed within the scientific community like SOVA, SPH, ZEUS-MP, iSALE, and codes developed at U.S. National Laboratories like CTH, SAGE/RAGE, and ALE3D. Benchmark calculations of shock wave propagation in aluminum-on-aluminum impacts were performed to examine the agreement between codes for simple idealized problems. The benchmark simulations show that variability in code results is to be expected due to differences in the underlying solution algorithm of each code, artificial stability parameters, spatial and temporal resolution, and material models. Overall, the inter-code variability in peak shock pressure as a function of distance is around 10 to 20%. In general, if the impactor is resolved by at least 20 cells across its radius, the underestimation of peak shock pressure due to spatial resolution is less than 10%. In addition to the benchmark tests, three validation tests were performed to examine the ability of the codes to reproduce the time evolution of crater radius and depth observed in vertical laboratory impacts in water and two well-characterized aluminum alloys. Results from these calculations are in good agreement with experiments. There appears to be a general tendency of shock physics codes to underestimate the radius of the forming crater. Overall, the discrepancy between the model and experiment results is

  3. Evidence for rapid topographic evolution and crater degradation on Mercury from simple crater morphometry

    NASA Astrophysics Data System (ADS)

    Fassett, Caleb I.; Crowley, Malinda C.; Leight, Clarissa; Dyar, M. Darby; Minton, David A.; Hirabayashi, Masatoshi; Thomson, Bradley J.; Watters, Wesley A.

    2017-06-01

    Examining the topography of impact craters and their evolution with time is useful for assessing how fast planetary surfaces evolve. Here, new measurements of depth/diameter (d/D) ratios for 204 craters of 2.5 to 5 km in diameter superposed on Mercury's smooth plains are reported. The median d/D is 0.13, much lower than expected for newly formed simple craters ( 0.21). In comparison, lunar craters that postdate the maria are much less modified, and the median crater in the same size range has a d/D ratio that is nearly indistinguishable from the fresh value. This difference in crater degradation is remarkable given that Mercury's smooth plains and the lunar maria likely have ages that are comparable, if not identical. Applying a topographic diffusion model, these results imply that crater degradation is faster by a factor of approximately two on Mercury than on the Moon, suggesting more rapid landform evolution on Mercury at all scales.Plain Language SummaryMercury and the Moon are both airless bodies that have experienced numerous <span class="hlt">impact</span> events over billions of years. These <span class="hlt">impacts</span> form <span class="hlt">craters</span> in a geologic instant. The question examined in this manuscript is how fast these <span class="hlt">craters</span> erode after their formation. To simplify the problem, we examined <span class="hlt">craters</span> of a particular size (2.5 to 5 km in diameter) on a particular geologic terrain type (volcanic smooth plains) on both the Moon and Mercury. We then measured the topography of hundreds of <span class="hlt">craters</span> on both bodies that met these criteria. Our results suggest that <span class="hlt">craters</span> on Mercury become shallower much more quickly than <span class="hlt">craters</span> on the Moon. We estimate that Mercury's topography erodes at a rate at least a factor of two faster than the Moon's.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA21915.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA21915.html"><span>Kokopelli <span class="hlt">Crater</span> on Ceres</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-12-14</p> <p>This image obtained by NASA's Dawn spacecraft shows a field of small <span class="hlt">craters</span> next to Kokopelli <span class="hlt">Crater</span>, seen at bottom right in this image, on dwarf planet Ceres. The small <span class="hlt">craters</span> overlay a smooth, wavy material that represents ejecta from nearby Dantu <span class="hlt">Crater</span>. The small <span class="hlt">craters</span> were formed by blocks ejected in the Dantu <span class="hlt">impact</span> event, and likely from the Kokopelli <span class="hlt">impact</span> as well. Kokopelli is named after the fertility deity who presides over agriculture in the tradition of the Pueblo people from the southwestern United States. The <span class="hlt">crater</span> measures 21 miles (34 kilometers) in diameter. Dawn took this image during its first extended mission on August 11, 2016, from its low-altitude mapping orbit, at about 240 miles (385 kilometers) above the surface. The center coordinates of this image are 20 degrees north latitude, 123 degrees east longitude. https://photojournal.jpl.nasa.gov/catalog/PIA21915</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=PIA00474&hterms=Butterfly&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DButterfly','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=PIA00474&hterms=Butterfly&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DButterfly"><span>Venus - <span class="hlt">Impact</span> <span class="hlt">Crater</span> in Eastern Navka Region</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1991-01-01</p> <p>This Magellan image, which is 50 kilometers (31 miles) in width and 80 kilometers (50 miles) in length, is centered at 11.9 degrees latitude, 352 degrees longitude in the eastern Navka Region of Venus. The <span class="hlt">crater</span>, which is approximately 8 kilometers (5 miles) in diameter, displays a butterfly symmetry pattern. The ejecta pattern most likely results from an oblique <span class="hlt">impact</span>, where the impactor came from the south and ejected material to the north.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930005117','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930005117"><span>Bright <span class="hlt">crater</span> outflows: Possible emplacement mechanisms</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Chadwick, D. John; Schaber, Gerald G.; Strom, Robert G.; Duval, Darla M.</p> <p>1992-01-01</p> <p>Lobate features with a strong backscatter are associated with 43 percent of the <span class="hlt">impact</span> <span class="hlt">craters</span> cataloged in Magellan's cycle 1. Their apparent thinness and great lengths are consistent with a low-viscosity material. The longest outflow yet identified is about 600 km in length and flows from the 90-km-diameter <span class="hlt">crater</span> Addams. There is strong evidence that the outflows are largely composed of <span class="hlt">impact</span> melt, although the mechanisms of their emplacement are not clearly understood. High temperatures and pressures of target rocks on Venus allow for more melt to be produced than on other terrestrial planets because lower shock pressures are required for melting. The percentage of <span class="hlt">impact</span> <span class="hlt">craters</span> with outflows increases with increasing <span class="hlt">crater</span> diameter. The mean diameter of <span class="hlt">craters</span> without outflows is 14.4 km, compared with 27.8 km for <span class="hlt">craters</span> with outflows. No <span class="hlt">craters</span> smaller than 3 km, 43 percent of <span class="hlt">craters</span> in the 10- to 30-km-diameter range, and 90 percent in the 80- to 100-km-diameter range have associated bright outflows. More melt is produced in the more energetic <span class="hlt">impact</span> events that produce larger <span class="hlt">craters</span>. However, three of the four largest <span class="hlt">craters</span> have no outflows. We present four possible mechanisms for the emplacement of bright outflows. We believe this 'shotgun' approach is justified because all four mechanisms may indeed have operated to some degree.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19800039547&hterms=lead+history&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dlead%2Bhistory','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19800039547&hterms=lead+history&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dlead%2Bhistory"><span><span class="hlt">Impact</span> melting early in lunar history</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Lange, M. A.; Ahrens, T. J.</p> <p>1979-01-01</p> <p>The total amount of <span class="hlt">impact</span> melt produced during early lunar history is examined in light of theoretically and experimentally determined relations between <span class="hlt">crater</span> diameter (D) and <span class="hlt">impact</span> melt volume. The time dependence of the melt production is given by the time dependent <span class="hlt">impact</span> rate as derived from <span class="hlt">cratering</span> statistics for two different <span class="hlt">crater</span>-size classes. Results show that small scale <span class="hlt">cratering</span> (D less than or equal to 30 km) leads to melt volumes which fit selected observations specifying the amount of <span class="hlt">impact</span> melt contained in the lunar regolith and in <span class="hlt">craters</span> with diameters less than 10 km. Larger <span class="hlt">craters</span> (D greater than 30 km) are capable of forming the <span class="hlt">abundant</span> <span class="hlt">impact</span> melt breccias found on the lunar surface. The group of large <span class="hlt">craters</span> (D greater than 30 km) produces nearly 10 times as much <span class="hlt">impact</span> melt as all the smaller <span class="hlt">craters</span>, and thus, the large <span class="hlt">impacts</span> dominate the modification of the lunar surface. A contradiction between the distribution of radiometric rock ages and a model of exponentially decreasing <span class="hlt">cratering</span> rate going back to 4.5 b.y. is reflected in uncertainty in the distribution of <span class="hlt">impact</span> melt as a function of time on the moon.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2011PhDT.........6R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2011PhDT.........6R"><span>Planetary Surface Properties, <span class="hlt">Cratering</span> Physics, and the Volcanic History of Mars from a New Global Martian <span class="hlt">Crater</span> Database</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Robbins, Stuart James</p> <p></p> <p><span class="hlt">Impact</span> <span class="hlt">craters</span> are arguably the primary exogenic planetary process contributing to the surface evolution of solid bodies in the solar system. <span class="hlt">Craters</span> appear across the entire surface of Mars, and they are vital to understanding its crustal properties as well as surface ages and modification events. They allow inferences into the ancient climate and hydrologic history, and they add a key data point for the understanding of <span class="hlt">impact</span> physics. Previously available databases of Mars <span class="hlt">impact</span> <span class="hlt">craters</span> were created from now antiquated datasets, automated algorithms with biases and inaccuracies, were limited in scope, and/or complete only to multikilometer diameters. This work presents a new global database for Mars that contains 378,540 <span class="hlt">craters</span> statistically complete for diameters D ≳ 1 km. This detailed database includes location and size, ejecta morphology and morphometry, interior morphology and degradation state, and whether the <span class="hlt">crater</span> is a secondary <span class="hlt">impact</span>. This database allowed exploration of global <span class="hlt">crater</span> type distributions, depth, and morphologies in unprecedented detail that were used to re-examine basic <span class="hlt">crater</span> scaling laws for the planet. The inclusion of hundreds of thousands of small, approximately kilometer-sized <span class="hlt">impacts</span> facilitated a detailed study of the properties of nearby fields of secondary <span class="hlt">craters</span> in relation to their primary <span class="hlt">crater</span>. It also allowed the discovery of vast distant clusters of secondary <span class="hlt">craters</span> over 5000 km from their primary <span class="hlt">crater</span>, Lyot. Finally, significantly smaller <span class="hlt">craters</span> were used to age-date volcanic calderas on the planet to re-construct the timeline of the last primary eruption events from 20 of the major Martian volcanoes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19810041820&hterms=evolution+rock&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Devolution%2Brock','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19810041820&hterms=evolution+rock&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Devolution%2Brock"><span>Infrared and radar signatures of lunar <span class="hlt">craters</span> - Implications about <span class="hlt">crater</span> evolution</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Thompson, T. W.; Cutts, J. A.; Shorthill, R. W.; Zisk, S. H.</p> <p>1980-01-01</p> <p>Geological models accounting for the strongly <span class="hlt">crater</span> size-dependent IR and radar signatures of lunar <span class="hlt">crater</span> floors are examined. The simplest model involves the formation and subsequent 'gardening' of an <span class="hlt">impact</span> melt layer on the <span class="hlt">crater</span> floor, but while adequate in accounting for the gradual fading of IR temperatures and echo strengths in <span class="hlt">craters</span> larger than 30 km in diameter, it is inadequate for smaller ones. It is concluded that quantitative models of the evolution of rock populations in regoliths and of the interaction of microwaves with regoliths are needed in order to understand <span class="hlt">crater</span> evolutionary processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70001158','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70001158"><span><span class="hlt">Crater</span> dimensions from apollo data and supplemental sources</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Pike, R.J.</p> <p>1976-01-01</p> <p>A catalog of <span class="hlt">crater</span> dimensions that were compiled mostly from the new Apollo-based Lunar Topographic Orthophotomaps is presented in its entirety. Values of <span class="hlt">crater</span> diameter, depth, rim height, flank width, circularity, and floor diameter (where applicable) are tabulated for a sample of 484 <span class="hlt">craters</span> on the Moon and 22 <span class="hlt">craters</span> on Earth. Systematic techniques of mensuration are detailed. The lunar <span class="hlt">craters</span> range in size from 400 m to 300 km across and include primary <span class="hlt">impact</span> <span class="hlt">craters</span> of the main sequence, secondary <span class="hlt">impact</span> <span class="hlt">craters</span>, craterlets atop domes and cones, and dark-halo <span class="hlt">craters</span>. The terrestrial <span class="hlt">craters</span> are between 10 m and 22.5 km in diameter and were formed by meteorite <span class="hlt">impact</span>. ?? 1976 D. Reidel Publishing Company.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=PIA04436&hterms=block+chain&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dblock%2Bchain','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=PIA04436&hterms=block+chain&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dblock%2Bchain"><span><span class="hlt">Crater</span> Chains</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2003-01-01</p> <p><p/> [figure removed for brevity, see original site] <p/>The large <span class="hlt">crater</span> at the top of this THEMIS visible image has several other <span class="hlt">craters</span> inside of it. Most noticeable are the <span class="hlt">craters</span> that form a 'chain' on the southern wall of the large <span class="hlt">crater</span>. These <span class="hlt">craters</span> are a wonderful example of secondary <span class="hlt">impacts</span>. They were formed when large blocks of ejecta from an <span class="hlt">impact</span> crashed back down onto the surface of Mars. Secondaries often form radial patterns around the <span class="hlt">impact</span> <span class="hlt">crater</span> that generated them, allowing researchers to trace them back to their origin.<p/>Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.<p/>NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.<p/>Image information: VIS instrument. Latitude 19.3, Longitude 347.5 East (12.5 West). 19 meter/pixel resolution.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017GeCoA.215..317K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017GeCoA.215..317K"><span>Hf isotope evidence for effective <span class="hlt">impact</span> melt homogenisation at the Sudbury <span class="hlt">impact</span> <span class="hlt">crater</span>, Ontario, Canada</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kenny, Gavin G.; Petrus, Joseph A.; Whitehouse, Martin J.; Daly, J. Stephen; Kamber, Balz S.</p> <p>2017-10-01</p> <p>We report on the first zircon hafnium-oxygen isotope and trace element study of a transect through one of the largest terrestrial <span class="hlt">impact</span> melt sheets. The differentiated melt sheet at the 1.85 Ga, originally ca. 200 km in diameter Sudbury <span class="hlt">impact</span> <span class="hlt">crater</span>, Ontario, Canada, yields a tight range of uniform zircon Hf isotope compositions (εHf(1850) of ca. -9 to -12). This is consistent with its well-established crustal origin and indicates differentiation from a single melt that was initially efficiently homogenised. We propose that the heterogeneity in other isotopic systems, such as Pb, in early-emplaced <span class="hlt">impact</span> melt at Sudbury is associated with volatility-related depletion during the <span class="hlt">impact</span> <span class="hlt">cratering</span> process. This depletion leaves the isotopic systems of more volatile elements more susceptible to contamination during post-<span class="hlt">impact</span> assimilation of country rock, whereas the systems of more refractory elements preserve initial homogeneities. Zircon oxygen isotope compositions in the melt sheet are also restricted in range relative to those in the <span class="hlt">impacted</span> target rocks. However, they display a marked offset approximately one-third up the melt sheet stratigraphy that is interpreted to be a result of post-<span class="hlt">impact</span> assimilation of 18O-enirched rocks into the base of the cooling <span class="hlt">impact</span> melt. Given that <span class="hlt">impact</span> <span class="hlt">cratering</span> was a more dominant process in the early history of the inner Solar System than it is today, and the possibility that <span class="hlt">impact</span> melt sheets were sources of ex situ Hadean zircon grains, these findings may have significance for the interpretation of the early zircon Hf record. We speculate that apparent εHf-time arrays observed in the oldest terrestrial and lunar zircon datasets may be related to <span class="hlt">impact</span> melting homogenising previously more diverse crust. We also show that spatially restricted partial melting of rocks buried beneath the superheated <span class="hlt">impact</span> melt at Sudbury provided a zircon crystallising environment distinct to the <span class="hlt">impact</span> melt sheet itself.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20160002655','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20160002655"><span>The Microstructure of Lunar Micrometeorite <span class="hlt">Impact</span> <span class="hlt">Craters</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Noble, S. K.; Keller, L. P.; Christoffersen, R.; Rahman, Z.</p> <p>2016-01-01</p> <p>The peak of the mass flux of impactors striking the lunar surface is made up of objects approximately 200 micrometers in diameter that erode rocks, comminute regolith grains, and produce agglutinates. The effects of these micro-scale <span class="hlt">impacts</span> are still not fully understood. Much effort has focused on evaluating the physical and optical effects of micrometeorite <span class="hlt">impacts</span> on lunar and meteoritic material using pulsed lasers to simulate the energy deposited into a substrate in a typical hypervelocity <span class="hlt">impact</span>. Here we characterize the physical and chemical changes that accompany natural micrometeorite <span class="hlt">impacts</span> into lunar rocks with long surface exposure to the space environment (12075 and 76015). Transmission electron microscope (TEM) observations were obtained from cross-sections of approximately 10-20 micrometers diameter <span class="hlt">craters</span> that revealed important micro-structural details of micrometeorite <span class="hlt">impact</span> processes, including the creation of npFe (sup 0) in the melt, and extensive deformation around the <span class="hlt">impact</span> site.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=PIA04678&hterms=under+armor&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dunder%2Barmor','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=PIA04678&hterms=under+armor&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dunder%2Barmor"><span>Pedestal <span class="hlt">Crater</span> and Yardangs</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2003-01-01</p> <p>MGS MOC Release No. MOC2-444, 6 August 2003<p/>This April 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a small meteor <span class="hlt">impact</span> <span class="hlt">crater</span> that has been modified by wind erosion. Two things happened after the <span class="hlt">crater</span> formed. First, the upper few meters of surface material into which the meteor <span class="hlt">impacted</span> was later eroded away by wind. The <span class="hlt">crater</span> ejecta formed a protective armor that kept the material under the ejecta from been blown away. This caused the <span class="hlt">crater</span> and ejecta to appear as if standing upon a raised platform--a feature that Mars geologists call a <i>pedestal <span class="hlt">crater</span>.</i> Next, the pedestal <span class="hlt">crater</span> was buried beneath several meters of new sediment, and then this material was eroded away by wind to form the array of sharp ridges that run across the pedestal <span class="hlt">crater</span>'s surface. These small ridges are known as <i>yardangs</i>. This picture is illuminated by sunlight from the upper left; it is located in west Daedalia Planum near 14.6oS, 131.9oW.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA20340.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA20340.html"><span>A Young, Fresh <span class="hlt">Crater</span> in Hellespontus</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2016-01-14</p> <p>This image from NASA Mars Reconnaissance Orbiter spacecraft is of a morphologically fresh and simple <span class="hlt">impact</span> <span class="hlt">crater</span> in the Hellespontus region. At 1.3 kilometers in diameter, this unnamed <span class="hlt">crater</span> is only slightly larger than Arizona's Barringer (aka Meteor) <span class="hlt">Crater</span>, by about 200 meters. Note the simple bowl shape and the raised <span class="hlt">crater</span> rim. Rock and soil excavated out of the <span class="hlt">crater</span> by the <span class="hlt">impacting</span> meteor -- called ejecta -- forms the ejecta deposit. It is continuous for about one <span class="hlt">crater</span> radius away from the rim and is likely composed of about 90 percent ejecta and 10 percent in-place material that was re-worked by both the <span class="hlt">impact</span> and the subsequently sliding ejecta. The discontinuous ejecta deposit extends from about one <span class="hlt">crater</span> radius outward. Here, high velocity ejecta that was launched from close to the <span class="hlt">impact</span> point -- and got the biggest kick -- flew a long way, landed, rolled, slid, and scoured the ground, forming long tendrils of ejecta and v-shaped ridges. http://photojournal.jpl.nasa.gov/catalog/PIA20340</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017P%26SS..145...71L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017P%26SS..145...71L"><span>Shape of boulders ejected from small lunar <span class="hlt">impact</span> <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Li, Yuan; Basilevsky, A. T.; Xie, Minggang; Ip, Wing-Huen</p> <p>2017-10-01</p> <p>The shape of ejecta boulders from 7 lunar <span class="hlt">impact</span> <span class="hlt">craters</span> <1 km in diameter of known absolute age was measured to explore whether it correlates with the <span class="hlt">crater</span> age and the boulder size. The boulders were mapped and then measured by rectangular fitting and the shape was represented by the axial ratio or aspect ratio (A) of the rectangle. The main conclusions from the analysis of our measurement results are: 1) the percentages of the number of boulders of studied <span class="hlt">craters</span> decrease with the increase of the axial ratio. Most (∼90%) of the boulders have the axial ratio in the range of 1-2; no boulder with axial ratio larger than 4 was found. 2) the axial ratios of mare ejecta boulders decrease with their exposure time, whereas that for highland ones show unchanged trend. This difference may be probably due to target properties. 3) The shape of ejecta boulders are influenced by mechanical strength of bedrocks and space erosion. 4) surface peak stresses caused by thermal fatigue maybe play a significant erosion role in the shape of boulders of various diameter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20040089287&hterms=aluminium&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Daluminium','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20040089287&hterms=aluminium&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Daluminium"><span>Fullerenes in an <span class="hlt">impact</span> <span class="hlt">crater</span> on the LDEF spacecraft</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Radicati di Brozolo, F.; Bunch, T. E.; Fleming, R. H.; Macklin, J.</p> <p>1994-01-01</p> <p>The fullerenes C60 and C70 have been found to occur naturally on Earth and have also been invoked to explain features in the absorption spectra of interstellar clouds. But no definitive spectroscopic evidence exists for fullerenes in space and attempts to find fullerenes in carbonaceous chondrites have been unsuccessful. Here we report the observation of fullerenes associated with carbonaceous <span class="hlt">impact</span> residue in a <span class="hlt">crater</span> on the Long Duration Exposure Facility (LDEF) spacecraft. Laser ionization mass spectrometry and Raman spectroscopy indicate the presence of fullerenes in the <span class="hlt">crater</span> and in adjacent ejecta. Man-made fullerenes survive experimental hypervelocity (approximately 6.1 km s-1) <span class="hlt">impacts</span> into aluminium targets, suggesting that space fullerenes contained in a carbonaceous micrometeorite could have survived the LDEF <span class="hlt">impact</span> at velocities towards the lower end of the natural particle encounter range (<13 km s-1). We also demonstrate that the fullerenes were unlikely to have formed as instrumental artefacts, nor are they present as contaminants. Although we cannot specify the origin of the fullerenes with certainty, the most plausible source is the chondritic impactor. If, alternatively, the <span class="hlt">impact</span> produced the fullerenes in situ on LDEF, then this suggests a viable mechanism for fullerene production in space.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890012008','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890012008"><span>Computer modeling of large asteroid <span class="hlt">impacts</span> into continental and oceanic sites: Atmospheric, <span class="hlt">cratering</span>, and ejecta dynamics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Roddy, D. J.; Schuster, S. H.; Rosenblatt, M.; Grant, L. B.; Hassig, P. J.; Kreyenhagen, K. N.</p> <p>1988-01-01</p> <p>Numerous <span class="hlt">impact</span> <span class="hlt">cratering</span> events have occurred on the Earth during the last several billion years that have seriously affected our planet and its atmosphere. The largest <span class="hlt">cratering</span> events, which were caused by asteroids and comets with kinetic energies equivalent to tens of millions of megatons of TNT, have distributed substantial quantities of terrestrial and extraterrestrial material over much or all of the Earth. In order to study a large-scale <span class="hlt">impact</span> event in detail, computer simulations were completed that model the passage of a 10 km-diameter asteroid through the Earth's atmosphere and the subsequent <span class="hlt">cratering</span> and ejecta dynamics associated with <span class="hlt">impact</span> of the asteroid into two different targets, i.e., an oceanic site and a continental site. The calcuations were designed to broadly represent giant <span class="hlt">impact</span> events that have occurred on the Earth since its formation and specifically represent an <span class="hlt">impact</span> <span class="hlt">cratering</span> event proposed to have occurred at the end of Cretaceous time. Calculation of the passage of the asteroid through a U.S. Standard Atmosphere showed development of a strong bow shock that expanded radially outward. Behind the shock front was a region of highly shock compressed and intensely heated air. Behind the asteroid, rapid expansion of this shocked air created a large region of very low density that also expanded away from the <span class="hlt">impact</span> area. Calculations of the <span class="hlt">cratering</span> events in both the continental and oceanic targets were carried to 120 s. Despite geologic differences, <span class="hlt">impacts</span> in both targets developed comparable dynamic flow fields, and by approx. 29 s similar-sized transient <span class="hlt">craters</span> approx. 39 km deep and approx. 62 km across had formed. For all practical purposes, the atmosphere was nearly completely removed from the <span class="hlt">impact</span> area for tens of seconds, i.e., air pressures were less than fractions of a bar out to ranges of over 50 km. Consequently, much of the asteroid and target materials were ejected upward into a near vacuum. Effects of secondary</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.P31E..05G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.P31E..05G"><span>IODP/ICDP Expedition 364-Drilling the Cretaceous-Paleogene Chicxulub <span class="hlt">impact</span> <span class="hlt">crater</span>: Insights into large <span class="hlt">craters</span> formation and their effect on life.</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gulick, S. P. S.; Morgan, J. V.; Fucugauchi, J. U.; Bralower, T. J.; Chenot, É.; Christeson, G. L.; Claeys, P.; Cockell, C. S.; Collins, G. S.; Coolen, M.; Gebhardt, C.; Goto, K.; Kring, D. A.; Xiao, L.; Lowery, C.; Mellett, C.; Ocampo-Torres, R.; Osinski, G. R.; Perez-Cruz, L. L.; Pickersgill, A.; Poelchau, M.; Rae, A.; Rasmussen, C.; Rebolledo-Vieyra, M.; Riller, U. P.; Sato, H.; Schmitt, D. R.; Smit, J.; Tikoo, S.; Tomioka, N.; Whalen, M. T.; Zylberman, W.; Jones, H.; Gareth, C.; Wittmann, A.; Lofi, J.; Yamaguchi, K. E.; Ferrière, L.</p> <p>2016-12-01</p> <p>An international project to drill the Chicxulub <span class="hlt">impact</span> <span class="hlt">crater</span> was conducted in April and May, 2016 as Expedition 364 of the International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Project (ICDP). Site M0077 is located offshore Yucatan in the southern Gulf of Mexico. The target was to core the only pristine terrestrial peak ring and to measure physical properties of the entire borehole. Specific questions included: What rocks comprise a topographic peak ring? How are peak rings formed? How are rocks weakened during large <span class="hlt">impacts</span> to allow them to collapse and form relatively wide, flat <span class="hlt">craters</span>? What insights arise from biologic recovery in the Paleogene within a potentially "toxic" ocean basin? Are <span class="hlt">impact</span> <span class="hlt">craters</span> (including peak rings) habitats for life? Coring occurred from 503 - 1334.7 mbsf with nearly 100% recovery. Wireline logs were collected from ultra slimline tools to total depth including gamma ray, magnetic susceptibility, sonic, borehole fluid temperature and conductivity, resistivity data, borehole images, and a finely spaced vertical seismic profile. Stratigraphy cored included 110 m of Eocene and Paleocene carbonates, 130 m of allochthonous impactites, and 590 m of crustal basement with dikes. All cores were measured using a shipboard core logger (density, gamma ray, magnetic susceptibility and resistivity) and shorebased dual energy, 0.3 mm resolution CT scanner. These data allow us to: 1) refine numerical models of the formation of the Chicxulub <span class="hlt">impact</span> structure; 2) place constraints on environmental perturbations that led to the K-Pg mass extinction; 3) improve simulations of <span class="hlt">impact</span> <span class="hlt">craters</span> on other planetary bodies; 4) examine deformation mechanisms for insights into how rocks weaken during <span class="hlt">impacts</span>; 5) study <span class="hlt">impact</span> generated hydrothermal systems and 6) understand the effects of <span class="hlt">impacts</span> on the deep biosphere including as a habitat for microbial life with implications for evolution on Earth and astrobiology. Key</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA00466.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA00466.html"><span>Venus - Large <span class="hlt">Impact</span> <span class="hlt">Crater</span> in the Eistla Region</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>1996-09-26</p> <p>This image from NASA Magellan spacecraft shows the central Eistla Region of the equatorial highlands of Venus. It is centered at 15 degrees north latitude and 5 degrees east longitude. The image is 76.8 kilometers (48 miles) wide. The <span class="hlt">crater</span> is slightly irregular in platform and approximately 6 kilometers (4 miles) in diameter. The walls appear terraced. Five or six lobes of radar-bright ejecta radiate up to 13.2 kilometers (8 miles) from the <span class="hlt">crater</span> rim. These lobes are up to 3.5 kilometers (2 miles) in width and form a "starfish" pattern against the underlying radar-dark plains. The asymmetric pattern of the ejecta suggests the angle of <span class="hlt">impact</span> was oblique. The alignment of two of the ejecta lobes along fractures in the underlying plains is apparently coincidental. http://photojournal.jpl.nasa.gov/catalog/PIA00466</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_15");'>15</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li class="active"><span>17</span></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_17 --> <div id="page_18" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="341"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20030018897&hterms=geology&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dgeology','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20030018897&hterms=geology&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D70%26Ntt%3Dgeology"><span>Geology of Lofn <span class="hlt">Crater</span>, Callisto</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Greeley, Ronald; Heiner, Sarah; Klemaszewski, James E.</p> <p>2001-01-01</p> <p>Lofn <span class="hlt">crater</span> is a 180-km-diameter <span class="hlt">impact</span> structure in the southern <span class="hlt">cratered</span> plains of Callisto and is among the youngest features seen on the surface. The Lofn area was imaged by the Galileo spacecraft at regional-scale resolutions (875 m/pixel), which enable the general geology to be investigated. The morphology of Lofn <span class="hlt">crater</span> suggests that (1) it is a class of <span class="hlt">impact</span> structure intermediate between complex <span class="hlt">craters</span> and palimpsests or (2) it formed by the <span class="hlt">impact</span> of a projectile which fragmented before reaching the surface, resulting in a shallow <span class="hlt">crater</span> (even for Callisto). The asymmetric pattern of the rim and ejecta deposits suggests that the impactor entered at a low angle from the northwest. The albedo and other characteristics of the ejecta deposits from Lofn also provide insight into the properties of the icy lithosphere and subsurface configuration at the time of <span class="hlt">impact</span>. The "target" for the Lofn <span class="hlt">impact</span> is inferred to have included layered materials associated with the Adlinda multiring structure northwest of Loh and ejecta deposits from the Heimdall <span class="hlt">crater</span> area to the southeast. The Lofn <span class="hlt">impact</span> might have penetrated through these materials into a viscous substrate of ductile ice or possibly liquid water. This interpretation is consistent with models of the current interior of Callisto based on geophysical information obtained from the Galileo spacecraft.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003icbg.conf...20D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003icbg.conf...20D"><span>WIRGO in TIC's? [What (on Earth) is Really Going On in Terrestrial <span class="hlt">Impact</span> <span class="hlt">Craters</span>?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dence, Michael R.</p> <p>2003-02-01</p> <p>Canada is well endowed with <span class="hlt">impact</span> <span class="hlt">craters</span> formed in crystalline rocks with relatively homogeneous physical properties. They exhibit all the main morphological-structural variations with <span class="hlt">crater</span> size seen in <span class="hlt">craters</span> on other rocky planets, from small simple bowl to large peak and ring forms. Lacking stratigraphy, analysis is based on the imprint of shock melting and metamorphism, the position of the GPL (limit of initial Grady-Kipp fracturing due to shock wave reverberations) relative to shock level, the geometry of late stage shears and breccias and the volume of shocked material beyond the GPL. Simple <span class="hlt">craters</span>, exemplified by Brent (D = 3.7 km) allow direct comparison with models and experimental data. Results of interest include: 1. The central pool of <span class="hlt">impact</span> melt and underlying breccia at the base of the <span class="hlt">crater</span> fill is interpreted as the remnant of the transient <span class="hlt">crater</span> lining; 2. The overlying main mass of breccias filling the final apparent <span class="hlt">crater</span> results from latestage slumping of large slabs bounded by a primary shear surface that conforms to a sphere segment of radius, rs approx. = 2dtc, where dtc is the transient <span class="hlt">crater</span> depth; 3. The foot of the primary shear intersects above the GPL at the centre of the melt pool and the rapid emplacement of slumped slabs produces further brecciation while suppressing any tendency for the centre to rise. In the autochthonous breccias below the melt and in the underlying para-allochthone below the GPL, shock metamorphism weakens with depth. The apparent attenuation of the shock pulse can be compared with experimentally derived rates of attenuation to give a measure of displacements down axis and estimates of the size of a nominal bolide of given velocity, the volume of <span class="hlt">impact</span> melt and the energy released on <span class="hlt">impact</span>. In larger complex <span class="hlt">craters</span> (e.g. Charlevoix, D = 52 km) apparent shock attenuation is low near the centre but is higher towards the margin. The inflection point marks the change from uplift of deep material in the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018LPICo2066.7030P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018LPICo2066.7030P"><span>Enigmatic Sedimentary Deposits Within Partially Exhumed <span class="hlt">Impact</span> <span class="hlt">Craters</span> in the Aeolis Dorsa Region, Mars: Evidence for Past <span class="hlt">Crater</span> Lakes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Peel, S. E.; Burr, D. M.</p> <p>2018-06-01</p> <p>We mapped enigmatic sedimentary deposits within five partially exhumed <span class="hlt">impact</span> <span class="hlt">craters</span> within the Aeolis Dorsa Region of Mars. Ten units have been identified and are found to be consistent with deposition within and adjacent to lacustrine systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1990GeCoA..54.3247R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1990GeCoA..54.3247R"><span>A discussion of 'Anomalous quartz from the Roter Kamm <span class="hlt">impact</span> <span class="hlt">crater</span>, Namibia - Evidence for post-<span class="hlt">impact</span> hydrothermal activity?'</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Roedder, Edwin</p> <p>1990-11-01</p> <p>This paper presents arguments against the statement made by Koeberl et al. (1989) to the effect that various differences between the quartz of the three quartz pebbles from the Roter Kamm <span class="hlt">impact</span> <span class="hlt">crater</span> (Namibia) and the quartz of the pegmatites present in the basement rocks of this <span class="hlt">crater</span> can be best interpreted as evidence that the pebbles were formed (or 'recrystallized') by a post-<span class="hlt">impact</span> hydrothermal system. Arguments are presented that suggest that the three quartz pebbles are, most likely, fragments of a preimpact vein quartz of hydrothermal origin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015P%26SS..117...45I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015P%26SS..117...45I"><span>Landing site selection for Luna-Glob mission in <span class="hlt">crater</span> Boguslawsky</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ivanov, M. A.; Hiesinger, H.; Abdrakhimov, A. M.; Basilevsky, A. T.; Head, J. W.; Pasckert, J.-H.; Bauch, K.; van der Bogert, C. H.; Gläser, P.; Kohanov, A.</p> <p>2015-11-01</p> <p>Boguslawsky <span class="hlt">crater</span> (72.9°S, 43.3°E, ~100 km in diameter) is a primary target for the Luna-Glob mission. The <span class="hlt">crater</span> has a morphologically smooth (at the resolution of WAC images), flat, and horizontal floor, which is about 55-60 km in diameter. Two ellipses were selected as specific candidate landing areas on the floor: the western ellipse is centered at 72.9°S, 41.3°E and the eastern ellipse is centered at 73.9°S, 43.9°E. Both ellipses represent areas from which Earth is visible during the entire year of 2016 and lack permanently shadowed areas. Boguslawsky <span class="hlt">crater</span> is located on or near the rim of the South Pole-Aitken basin, which provides the unique possibility to sample some of the most ancient rocks on the Moon that probably pre-date the SPA <span class="hlt">impact</span> event. The low depth/diameter ratio of Boguslawsky suggests that the <span class="hlt">crater</span> has been partly filled after its formation. Although volcanic flooding of the <span class="hlt">crater</span> cannot be ruled out, the more likely process of filling of Boguslawsky is the emplacement of ejecta from nearby and remote large <span class="hlt">craters</span>/basins. Three morphologically distinctive units are the most <span class="hlt">abundant</span> within the selected landing ellipses: rolling plains (rpc), flat plains (fp), and ejecta from <span class="hlt">crater</span> Boguslawsky-D (ejf), which occurs on the eastern wall of Boguslawsky. The possible contribution of materials from unknown sources makes the flat and rolling plains less desirable targets for landing. In contrast, ejecta from Boguslawsky-D represents local materials re-distributed by the Boguslawsky-D <span class="hlt">impact</span> from the wall onto the floor of Boguslawsky. Thus, this unit, which constitutes about 50% of the eastern landing ellipse, represents a target of clearer provenance and a higher scientific priority.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20130001619','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20130001619"><span>Characterization of the Morphometry of <span class="hlt">Impact</span> <span class="hlt">Craters</span> Hosting Polar Deposits in Mercury's North Polar Region</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Talpe Matthieu; Zuber, Maria T.; Yang, Di; Neumann, Gregory A.; Solomon, Sean C.; Mazarico, Erwan; Vilas, Faith</p> <p>2012-01-01</p> <p>Earth-based radar images of Mercury show radar-bright material inside <span class="hlt">impact</span> <span class="hlt">craters</span> near the planet s poles. A previous study indicated that the polar-deposit-hosting <span class="hlt">craters</span> (PDCs) at Mercury s north pole are shallower than <span class="hlt">craters</span> that lack such deposits. We use data acquired by the Mercury Laser Altimeter on the MESSENGER spacecraft during 11 months of orbital observations to revisit the depths of <span class="hlt">craters</span> at high northern latitudes on Mercury. We measured the depth and diameter of 537 <span class="hlt">craters</span> located poleward of 45 N, evaluated the slopes of the northern and southern walls of 30 PDCs, and assessed the floor roughness of 94 <span class="hlt">craters</span>, including nine PDCs. We find that the PDCs appear to have a fresher <span class="hlt">crater</span> morphology than the non-PDCs and that the radar-bright material has no detectable influence on <span class="hlt">crater</span> depths, wall slopes, or floor roughness. The statistical similarity of <span class="hlt">crater</span> depth-diameter relations for the PDC and non-PDC populations places an upper limit on the thickness of the radar-bright material (< 170 m for a <span class="hlt">crater</span> 11 km in diameter) that can be refined by future detailed analysis. Results of the current study are consistent with the view that the radar-bright material constitutes a relatively thin layer emplaced preferentially in comparatively young <span class="hlt">craters</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1615331D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1615331D"><span><span class="hlt">Impact</span> <span class="hlt">craters</span> and landslide volume distribution in Valles Marineris, Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>De Blasio, Fabio</p> <p>2014-05-01</p> <p>The landslides in the wide gorge system of Valles Marineris (Mars) exhibit volumes of the or-der of several hundred 1,000 km3 and runouts often in the excess of 80 km. Most landslides have occurred at the borders of the valleys, where the unbalanced weight of the 5-8 km high headwalls has been evidently sufficient to cause instability. Previous analysis has shown that the mechanical conditions of instability would not have been reached without external triggering fac-tors, if the wallslope consisted of intact rock. Among the factors that have likely promoted instability, we are currently analyzing: i) the possibility of rock weakening due to weathering; ii) the alternation of weak layers within more massive rock; weak layers might for example due to evaporites, the possible presence of ice table at some depth, or water; iii) weakening due to <span class="hlt">impact</span> damage prior to the formation of Valles Marineris; studies of <span class="hlt">impact</span> <span class="hlt">craters</span> on Earth show that the volumes of damaged rock extends much deeper than the <span class="hlt">crater</span> itself; iv) direct triggering of a landslide due to the seismic waves generated by a large meteoroid <span class="hlt">impact</span> in the vicinity, and v) direct triggering of a landslide con-sequent to <span class="hlt">impact</span> at the headwall, with impulsive release of momentum and short but intense increase of the triggering force. We gathered a large database for about 3000 Martian landslides that allow us to infer some of their statistical properties supporting our analyses, and especially to discriminate among some of the above listed predisposing and triggering factors. In particular, we analyse in this contribution the frequency distribution of landslide volumes starting from the assumption that these events are controlled by the extent of the shock damage zones. Relative position of the <span class="hlt">impact</span> point and damage zones with respect to the Valles Marineris slopes could in fact control the released volumes. We perform 3D slope stability analy-sis under different geometrical constraints (e.g. <span class="hlt">crater</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140012822','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140012822"><span>The Gale <span class="hlt">Crater</span> Mound in a Regional Geologic Setting: Comparison Study of Wind Erosion in Gale <span class="hlt">Crater</span> and Within a 1000 KM Radius</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dapremont. A.; Allen, C.; Runyon, C.</p> <p>2014-01-01</p> <p>Gale is a Late Noachian/Early Hesperian <span class="hlt">impact</span> <span class="hlt">crater</span> located on the dichotomy boundary separating the southern highlands and the northern lowlands of Mars. NASA's Curiosity Rover is currently exploring Gale, searching for evidence of habitability early in Mars history. With an approximate diameter of 155 km, and a approx. 5 km central mound informally titled Mt. Sharp, Gale represents a region of geologic interest due to the <span class="hlt">abundance</span> of knowledge that can be derived, through its sedimentary deposits, pertaining to the environmental evolution of Mars. This study was undertaken to compare wind erosional features in Gale <span class="hlt">Crater</span> and within sediments in a 1000 km radial area. The ultimate objective of this comparison was to determine if or how Gale relates to the surrounding region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017RAA....17...24J','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017RAA....17...24J"><span>Physical properties of lunar <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Joshi, Maitri P.; Bhatt, Kushal P.; Jain, Rajmal</p> <p>2017-02-01</p> <p>The surface of the Moon is highly <span class="hlt">cratered</span> due to <span class="hlt">impacts</span> of meteorites, asteroids, comets and other celestial objects. The origin, size, structure, age and composition vary among <span class="hlt">craters</span>. We study a total of 339 <span class="hlt">craters</span> observed by the Lunar Reconnaissance Orbiter Camera (LROC). Out of these 339 <span class="hlt">craters</span>, 214 <span class="hlt">craters</span> are known (named <span class="hlt">craters</span> included in the IAU Gazetteer of Planetary Nomenclature) and 125 <span class="hlt">craters</span> are unknown (<span class="hlt">craters</span> that are not named and objects that are absent in the IAU Gazetteer). We employ images taken by LROC at the North and South Poles and near side of the Moon. We report for the first time the study of unknown <span class="hlt">craters</span>, while we also review the study of known <span class="hlt">craters</span> conducted earlier by previous researchers. Our study is focused on measurements of diameter, depth, latitude and longitude of each <span class="hlt">crater</span> for both known and unknown <span class="hlt">craters</span>. The diameter measurements are based on considering the Moon to be a spherical body. The LROC website also provides a plot which enables us to measure the depth and diameter. We found that out of 214 known <span class="hlt">craters</span>, 161 <span class="hlt">craters</span> follow a linear relationship between depth (d) and diameter (D), but 53 <span class="hlt">craters</span> do not follow this linear relationship. We study physical dimensions of these 53 <span class="hlt">craters</span> and found that either the depth does not change significantly with diameter or the depths are extremely high relative to diameter (conical). Similarly, out of 125 unknown <span class="hlt">craters</span>, 78 <span class="hlt">craters</span> follow the linear relationship between depth (d) and diameter (D) but 47 <span class="hlt">craters</span> do not follow the linear relationship. We propose that the <span class="hlt">craters</span> following the scaling law of depth and diameter, also popularly known as the linear relationship between d and D, are formed by the <span class="hlt">impact</span> of meteorites having heavy metals with larger dimension, while those with larger diameter but less depth are formed by meteorites/celestial objects having low density material but larger diameter. The <span class="hlt">craters</span> with very high depth and with very small</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EPSC...10..466P','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EPSC...10..466P"><span>Dawn Framing Camera: Morphology and morphometry of <span class="hlt">impact</span> <span class="hlt">craters</span> on Ceres</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Platz, T.; A; Nathues; Schäfer, M.; Hoffmann, M.; Kneissl, T.; Schmedemann, N.; Vincent, J.-B.; Büttner, I.; Gutierrez-Marques, P.; Ripken, J.; Russell, C. T.; Schäfer, T.; Thangjam, G. S.</p> <p>2015-10-01</p> <p>In the first approach images of Ceres we tried to discern the simple-to-complex transition diameter of <span class="hlt">impact</span> <span class="hlt">craters</span>. Limited by spatial resolution we found the smallest complex <span class="hlt">crater</span> without central peak development to be around 21.4 km in diameter. Hence, the transition diameter is expected to be between 21.4 km and 10.6 km, the predicted transition diameter for an icy target. It appears likely that either Ceres' surface material contains a rocky component or has a laterally inhomogeneous composition ranging from icy to ice-rocky</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19900061677&hterms=barlow&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dbarlow','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19900061677&hterms=barlow&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D80%26Ntt%3Dbarlow"><span>Martian <span class="hlt">impact</span> <span class="hlt">craters</span> - Correlations of ejecta and interior morphologies with diameter, latitude, and terrain</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Barlow, Nadine G.; Bradley, Tracy L.</p> <p>1990-01-01</p> <p>An effort is made to establish the ability of a correlation between <span class="hlt">crater</span> morphology and latitude, diameter, and terrain, to discriminate among the effects of <span class="hlt">impact</span> energy, atmosphere, and subsurface volatiles in 3819 larger-than-8 km diameter <span class="hlt">craters</span> distributed over the Martian surface. It is noted that changes in ejecta and interior morphology correlate with increases in <span class="hlt">crater</span> diameter, and that while many of the interior structures exhibit distributions interpretable as terrain-dependent, central peak and peak ring interior morphologies exhibit minimal relationships with planetary properties.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA12935.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA12935.html"><span>Fresh Copernican <span class="hlt">Crater</span></span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2009-12-21</p> <p>A subset of NAC Image M112162602L showing landslides bottom covering <span class="hlt">impact</span> melt on the floor top of a fresh Copernican-age <span class="hlt">crater</span> at the edge of Oceanus Procellarum and west of Balboa <span class="hlt">crater</span> taken by NASA Lunar Reconnaissance Orbiter.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19850047917&hterms=dg&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Ddg','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19850047917&hterms=dg&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D90%26Ntt%3Ddg"><span>The scaling of complex <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Croft, S. K.</p> <p>1985-01-01</p> <p>The empirical relation between the transient <span class="hlt">crater</span> diameter (Dg) and final <span class="hlt">crater</span> diameter (Dr) of complex <span class="hlt">craters</span> and basins is estimated using cumulative terrace widths, central uplift diameters, continuous ejecta radii, and transient <span class="hlt">crater</span> reconstructions determined from lunar and terrestrial <span class="hlt">impact</span> structures. The ratio Dg/Dr is a power law function of Dr, decreasing uniformly from unity at the diameter of the simple-complex <span class="hlt">crater</span> morphology transition to about 0.5 for large multiring basins like Imbrium on the moon. The empirical constants in the Dg/Dr relation are interpreted physically to mean that the position of the final rim relative to the transient <span class="hlt">crater</span>, and hence the extent of collapse, is controlled or greatly influenced by the properties of the zone of dissociated material produced by the <span class="hlt">impact</span> shock. The continuity of the Dg/Dr relation over the entire spectrum of morphologic types from complex <span class="hlt">craters</span> to multiring basins implies that the rims of all these structures form in the same tectonic environment despite morphologic differences.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=PIA04904&hterms=Northeast&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DNortheast','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=PIA04904&hterms=Northeast&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DNortheast"><span>Exhuming <span class="hlt">Crater</span> in Northeast Arabia</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2003-01-01</p> <p>MGS MOC Release No. MOC2-563, 3 December 2003<p/>The upper crust of Mars is layered, and interbedded with these layers are old, filled and buried meteor <span class="hlt">impact</span> <span class="hlt">craters</span>. In a few places on Mars, such as Arabia Terra, erosion has re-exposed some of the filled and buried <span class="hlt">craters</span>. This October 2003 Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows an example. The larger circular feature was once a meteor <span class="hlt">crater</span>. It was filled with sediment, then buried beneath younger rocks. The smaller circular feature is a younger <span class="hlt">impact</span> <span class="hlt">crater</span> that formed in the surface above the rocks that buried the large <span class="hlt">crater</span>. Later, erosion removed all of the material that covered the larger, buried <span class="hlt">crater</span>, except in the location of the small <span class="hlt">crater</span>. This pair of martian landforms is located near 17.6oN, 312.8oW. The image covers an area 3 km (1.9 mi) wide and is illuminated from the lower left.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=PIA00094&hterms=namesake&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dnamesake','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=PIA00094&hterms=namesake&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dnamesake"><span>Limb of Copernicus <span class="hlt">Impact</span> <span class="hlt">Crater</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>1991-01-01</p> <p>Copernicus is 93 km wide and is located within the Mare Imbrium Basin, northern nearside of the Moon (10 degrees N., 20 degrees W.). Image shows <span class="hlt">crater</span> floor, floor mounds, rim, and rayed ejecta. Rays from the ejecta are superposed on all other surrounding terrains which places the <span class="hlt">crater</span> in its namesake age group: the Copernican system, established as the youngest assemblage of rocks on the Moon (Shoemaker and Hackman, 1962, The Moon: London, Academic Press, p.289- 300).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA00474.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA00474.html"><span>Venus - <span class="hlt">Impact</span> <span class="hlt">Crater</span> in Eastern Navka Region</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>1996-11-20</p> <p>This Magellan image, which is 50 kilometers (31 miles) in width and 80 kilometers (50 miles) in length, is centered at 11.9 degrees latitude, 352 degrees longitude in the eastern Navka Region of Venus. The <span class="hlt">crater</span>, which is approximately 8 kilometers (5 miles) in diameter, displays a butterfly symmetry pattern. The ejecta pattern most likely results from an oblique <span class="hlt">impact</span>, where the impactor came from the south and ejected material to the north. http://photojournal.jpl.nasa.gov/catalog/PIA00474</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA21591.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA21591.html"><span>Secondary <span class="hlt">Craters</span> in Bas Relief</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-04-17</p> <p>NASA's Mars Reconnaissance Orbiter (MRO) captured this region of Mars, sprayed with secondary <span class="hlt">craters</span> from 10-kilometer Zunil <span class="hlt">Crater</span> to the northwest. Secondary <span class="hlt">craters</span> form from rocks ejected at high speed from the primary <span class="hlt">crater</span>, which then <span class="hlt">impact</span> the ground at sufficiently high speed to make huge numbers of much smaller <span class="hlt">craters</span> over a large region. In this scene, however, the secondary <span class="hlt">crater</span> ejecta has an unusual raised-relief appearance like bas-relief sculpture. How did that happen? One idea is that the region was covered with a layer of fine-grained materials like dust or pyroclastics about 1 to 2 meters thick when the Zunil <span class="hlt">impact</span> occurred (about a million years ago), and the ejecta served to harden or otherwise protect the fine-grained layer from later erosion by the wind. https://photojournal.jpl.nasa.gov/catalog/PIA21591</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016Icar..267...86D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016Icar..267...86D"><span>Changes in blast zone albedo patterns around new martian <span class="hlt">impact</span> <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Daubar, I. J.; Dundas, C. M.; Byrne, S.; Geissler, P.; Bart, G. D.; McEwen, A. S.; Russell, P. S.; Chojnacki, M.; Golombek, M. P.</p> <p>2016-03-01</p> <p>"Blast zones" (BZs) around new martian <span class="hlt">craters</span> comprise various albedo features caused by the initial <span class="hlt">impact</span>, including diffuse halos, extended linear and arcuate rays, secondary <span class="hlt">craters</span>, ejecta patterns, and dust avalanches. We examined these features for changes in repeat images separated by up to four Mars years. Here we present the first comprehensive survey of the qualitative and quantitative changes observed in <span class="hlt">impact</span> blast zones over time. Such changes are most likely due to airfall of high-albedo dust restoring darkened areas to their original albedo, the albedo of adjacent non-<span class="hlt">impacted</span> surfaces. Although some sites show drastic changes over short timescales, nearly half of the sites show no obvious changes over several Mars years. Albedo changes are more likely to occur at higher-latitude sites, lower-elevation sites, and at sites with smaller central <span class="hlt">craters</span>. No correlation was seen between amount of change and Dust Cover Index, relative halo size, or historical regional albedo changes. Quantitative albedo measurements of the diffuse dark halos relative to their surroundings yielded estimates of fading lifetimes for these features. The average lifetime among sites with measurable fading is ∼15 Mars years; the median is ∼8 Mars years for a linear brightening. However, at approximately half of sites with three or more repeat images, a nonlinear function with rapid initial fading followed by a slow increase in albedo provides a better fit to the fading behavior; this would predict even longer lifetimes. The predicted lifetimes of BZs are comparable to those of slope streaks, and considered representative of fading by global atmospheric dust deposition; they last significantly longer than dust devil or rover tracks, albedo features that are erased by different processes. These relatively long lifetimes indicate that the measurement of the current <span class="hlt">impact</span> rate by Daubar et al. (Daubar, I.J. et al. [2013]. Icarus 225, 506-516. http://dx.doi.org/10.1016/j</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70197971','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70197971"><span>Changes in blast zone albedo patterns around new martian <span class="hlt">impact</span> <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Daubar, Ingrid J.; Dundas, Colin; Byrne, Shane; Geissler, Paul; Bart, Gwen; McEwen, Alfred S.; Russell, Patrick; Chojnacki, Matthew; Golombek, M.P.</p> <p>2016-01-01</p> <p>“Blast zones” (BZs) around new martian <span class="hlt">craters</span> comprise various albedo features caused by the initial <span class="hlt">impact</span>, including diffuse halos, extended linear and arcuate rays, secondary <span class="hlt">craters</span>, ejecta patterns, and dust avalanches. We examined these features for changes in repeat images separated by up to four Mars years. Here we present the first comprehensive survey of the qualitative and quantitative changes observed in <span class="hlt">impact</span> blast zones over time. Such changes are most likely due to airfall of high-albedo dust restoring darkened areas to their original albedo, the albedo of adjacent non-<span class="hlt">impacted</span> surfaces. Although some sites show drastic changes over short timescales, nearly half of the sites show no obvious changes over several Mars years. Albedo changes are more likely to occur at higher-latitude sites, lower-elevation sites, and at sites with smaller central <span class="hlt">craters</span>. No correlation was seen between amount of change and Dust Cover Index, relative halo size, or historical regional albedo changes. Quantitative albedo measurements of the diffuse dark halos relative to their surroundings yielded estimates of fading lifetimes for these features. The average lifetime among sites with measurable fading is ∼15 Mars years; the median is ∼8 Mars years for a linear brightening. However, at approximately half of sites with three or more repeat images, a nonlinear function with rapid initial fading followed by a slow increase in albedo provides a better fit to the fading behavior; this would predict even longer lifetimes. The predicted lifetimes of BZs are comparable to those of slope streaks, and considered representative of fading by global atmospheric dust deposition; they last significantly longer than dust devil or rover tracks, albedo features that are erased by different processes. These relatively long lifetimes indicate that the measurement of the current <span class="hlt">impact</span> rate by Daubar et al. (Daubar, I.J. et al. [2013]. Icarus 225, 506–516. http://dx.doi.org/10</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19780060124&hterms=Nuclear+explosion&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DNuclear%2Bexplosion','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19780060124&hterms=Nuclear+explosion&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DNuclear%2Bexplosion"><span>Application of high explosion <span class="hlt">cratering</span> data to planetary problems</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Oberbeck, V. R.</p> <p>1977-01-01</p> <p>The present paper deals with the conditions of explosion or nuclear <span class="hlt">cratering</span> required to simulate <span class="hlt">impact</span> <span class="hlt">crater</span> formation. Some planetary problems associated with three different aspects of <span class="hlt">crater</span> formation are discussed, and solutions based on high-explosion data are proposed. Structures of <span class="hlt">impact</span> <span class="hlt">craters</span> and some selected explosion <span class="hlt">craters</span> formed in layered media are examined and are related to the structure of lunar basins. The mode of ejection of material from <span class="hlt">impact</span> <span class="hlt">craters</span> is identified using explosion analogs. The ejection mode is shown to have important implications for the origin of material in <span class="hlt">crater</span> and basin deposits. Equally important are the populations of secondary <span class="hlt">craters</span> on lunar and planetary surfaces.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_16");'>16</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li class="active"><span>18</span></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_18 --> <div id="page_19" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="361"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030014839','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030014839"><span><span class="hlt">Impact</span> <span class="hlt">Cratering</span>: Bridging the Gap Between Modeling and Observations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2003-01-01</p> <p>This volume contains abstracts that have been accepted for presentation at the workshop on <span class="hlt">Impact</span> <span class="hlt">Cratering</span>: Bridging the Gap Between Modeling and Observations, February 7-9, 2003, in Houston, Texas. Logistics, onsite administration, and publications for this workshop were provided by the staff of the Publications and Program Services Department at the Lunar and Planetary Institute.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA15121.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA15121.html"><span>Vesta <span class="hlt">Cratered</span> Landscape: Double <span class="hlt">Crater</span> and <span class="hlt">Craters</span> with Bright Ejecta</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2011-11-23</p> <p>This image from NASA Dawn spacecraft is dominated by a double <span class="hlt">crater</span> which may have been formed by the simultaneous <span class="hlt">impact</span> of a binary asteroid. Binary asteroids are asteroids that orbit their mutual center of mass.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920001657','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920001657"><span>Chemical fractionation of siderophile elements in impactites from Australian meteorite <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Attrep, A., Jr.; Orth, C. J.; Quintana, L. R.; Shoemaker, C. S.; Shoemaker, E. M.; Taylor, S. R.</p> <p>1991-01-01</p> <p>The <span class="hlt">abundance</span> pattern of siderophile elements in terrestrial and lunar <span class="hlt">impact</span> melt rocks was used extensively to infer the nature of the <span class="hlt">impacting</span> projectiles. An implicit assumption made is that the siderophile <span class="hlt">abundance</span> ratios of the projectiles are approximately preserved during mixing of the projectile constituents with the <span class="hlt">impact</span> melts. As this mixture occurs during flow of strongly shocked materials at high temperatures, however there are grounds for suspecting that the underlying assumption is not always valid. In particular, fractionation of the melted and partly vaporized material of the projectile might be expected because of differences in volatility, solubility in silicate melts, and other characteristics of the constituent elements. Impactites from <span class="hlt">craters</span> with associated meteorites offer special opportunities to test the assumptions on which projectile identifications are based and to study chemical fractionation that occurred during the <span class="hlt">impact</span> process.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008CRGeo.340..801U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008CRGeo.340..801U"><span><span class="hlt">Impact</span> ejecta and carbonate sequence in the eastern sector of the Chicxulub <span class="hlt">crater</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Urrutia-Fucugauchi, Jaime; Chavez-Aguirre, Jose Maria; Pérez-Cruz, Ligia; De la Rosa, Jose Luis</p> <p>2008-12-01</p> <p>The Chicxulub 200 km diameter <span class="hlt">crater</span> located in the Yucatan platform of the Gulf of Mexico formed 65 Myr ago and has since been covered by Tertiary post-<span class="hlt">impact</span> carbonates. The sediment cover and absence of significant volcanic and tectonic activity in the carbonate platform have protected the <span class="hlt">crater</span> from erosion and deformation, making Chicxulub the only large multi-ring <span class="hlt">crater</span> in which ejecta is well preserved. Ejecta deposits have been studied by drilling/coring in the southern <span class="hlt">crater</span> sector and at outcrops in Belize, Quintana Roo and Campeche; little information is available from other sectors. Here, we report on the drilling/coring of a section of ˜34 m of carbonate breccias at 250 m depth in the Valladolid area (120 km away from <span class="hlt">crater</span> center), which are interpreted as Chicxulub proximal ejecta deposits. The Valladolid breccias correlate with the carbonate breccias cored in the Peto and Tekax boreholes to the south and at similar radial distance. This constitutes the first report of breccias in the eastern sector close to the <span class="hlt">crater</span> rim. Thickness of the Valladolid breccias is less than that at the other sites, which may indicate erosion of the ejecta deposits before reestablishment of carbonate deposition. The region east of the <span class="hlt">crater</span> rim appears different from regions to the south and west, characterized by high density and scattered distribution of sinkholes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/5166708-impact-craters-importance-geologic-record-implications-natural-resource-development','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/5166708-impact-craters-importance-geologic-record-implications-natural-resource-development"><span><span class="hlt">Impact</span> <span class="hlt">craters</span>: their importance in geologic record and implications for natural resource development</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Levie, D. Jr.</p> <p>1986-05-01</p> <p><span class="hlt">Impacting</span> bodies of sufficient size traveling at hypervelocities carry tremendous potential energy. This relatively infrequent process results in the instantaneous formation of unique structures that are characterized by extensive fracturing and brecciation of the target material. <span class="hlt">Impacts</span> onto continental shield areas can create rich ore deposits, such as the Sudbury mining district in Canada. <span class="hlt">Impacts</span> into the sedimentary column can instantaneously create hydrocarbon reservoirs out of initially nonporous rocks, such as at Red Wing Creek and Viewfield in the Williston basin. Associated reservoirs are usually limited to a highly deformed central uplift in larger <span class="hlt">craters</span>, or to the fractured rimmore » facies in smaller <span class="hlt">craters</span>. The presence of reservoirs and trapping mechanisms is largely dependent, however, upon the preservation state of the <span class="hlt">crater</span> in the subsurface. A catastrophic extraterrestrial event (a large asteroid <span class="hlt">impact</span>) has also been suggested as the cause for the extinction of the dinosaurs, but the latest theory proposes a companion star with a 26 m.y. periodicity as the cause for numerous lifeform extinctions over a similar time interval. Regardless of their magnitude and distribution over the earth, it is clear that catastrophic extraterrestrial events have been responsible for altering the geologic column locally, regionally, and quite possibly on a global scale.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19880033068&hterms=keefe&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAuthor-Name%26N%3D0%26No%3D50%26Ntt%3Dkeefe','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19880033068&hterms=keefe&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAuthor-Name%26N%3D0%26No%3D50%26Ntt%3Dkeefe"><span>The size distributions of fragments ejected at a given velocity from <span class="hlt">impact</span> <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>O'Keefe, John D.; Ahrens, Thomas J.</p> <p>1987-01-01</p> <p>The mass distribution of fragments that are ejected at a given velocity for <span class="hlt">impact</span> <span class="hlt">craters</span> is modeled to allow extrapolation of laboratory, field, and numerical results to large scale planetary events. The model is semi-empirical in nature and is derived from: (1) numerical calculations of <span class="hlt">cratering</span> and the resultant mass versus ejection velocity, (2) observed ejecta blanket particle size distributions, (3) an empirical relationship between maximum ejecta fragment size and <span class="hlt">crater</span> diameter, (4) measurements and theory of maximum ejecta size versus ejecta velocity, and (5) an assumption on the functional form for the distribution of fragments ejected at a given velocity. This model implies that for planetary <span class="hlt">impacts</span> into competent rock, the distribution of fragments ejected at a given velocity is broad, e.g., 68 percent of the mass of the ejecta at a given velocity contains fragments having a mass less than 0.1 times a mass of the largest fragment moving at that velocity. The broad distribution suggests that in <span class="hlt">impact</span> processes, additional comminution of ejecta occurs after the upward initial shock has passed in the process of the ejecta velocity vector rotating from an initially downward orientation. This additional comminution produces the broader size distribution in <span class="hlt">impact</span> ejecta as compared to that obtained in simple brittle failure experiments.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19770054896&hterms=conversion+rate&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dconversion%2Brate%2527','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19770054896&hterms=conversion+rate&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dconversion%2Brate%2527"><span>Relative <span class="hlt">crater</span> production rates on planets</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hartmann, W. K.</p> <p>1977-01-01</p> <p>The relative numbers of <span class="hlt">impacts</span> on different planets, estimated from the dynamical histories of planetesimals in specified orbits (Wetherill, 1975), are converted by a described procedure to <span class="hlt">crater</span> production rates. Conversions are dependent on <span class="hlt">impact</span> velocity and surface gravity. <span class="hlt">Crater</span> retention ages can then be derived from the ratio of the <span class="hlt">crater</span> density to the <span class="hlt">crater</span> production rate. The data indicate that the terrestrial planets have <span class="hlt">crater</span> production rates within a factor ten of each other. As an example, for the case of Mars, least-squares fits to <span class="hlt">crater</span>-count data suggest an average age of 0.3 to 3 billion years for two types of channels. The age of Olympus Mons is discussed, and the effect of Tharsis volcanism on channel formation is considered.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015JGRB..120.6141S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015JGRB..120.6141S"><span>Scaling multiblast <span class="hlt">craters</span>: General approach and application to volcanic <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Sonder, I.; Graettinger, A. H.; Valentine, G. A.</p> <p>2015-09-01</p> <p>Most volcanic explosions leave a <span class="hlt">crater</span> in the surface around the center of the explosions. Such <span class="hlt">craters</span> differ from products of single events like meteorite <span class="hlt">impacts</span> or those produced by military testing because they typically result from multiple, rather than single, explosions. Here we analyze the evolution of experimental <span class="hlt">craters</span> that were created by several detonations of chemical explosives in layered aggregates. An empirical relationship for the scaled <span class="hlt">crater</span> radius as a function of scaled explosion depth for single blasts in flat test beds is derived from experimental data, which differs from existing relations and has better applicability for deep blasts. A method to calculate an effective explosion depth for nonflat topography (e.g., for explosions below existing <span class="hlt">craters</span>) is derived, showing how multiblast <span class="hlt">crater</span> sizes differ from the single-blast case: Sizes of natural caters (radii and volumes) are not characteristic of the number of explosions, nor therefore of the total acting energy, that formed a <span class="hlt">crater</span>. Also, the <span class="hlt">crater</span> size is not simply related to the largest explosion in a sequence but depends upon that explosion and the energy of that single blast and on the cumulative energy of all blasts that formed a <span class="hlt">crater</span>. The two energies can be combined to form an effective number of explosions that is characteristic for the <span class="hlt">crater</span> evolution. The multiblast <span class="hlt">crater</span> size evolution has implications on the estimates of volcanic eruption energies, indicating that it is not correct to estimate explosion energy from <span class="hlt">crater</span> size using previously published relationships that were derived for single-blast cases.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA21454.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA21454.html"><span>A Dragonfly-Shaped <span class="hlt">Crater</span></span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-02-10</p> <p>The broader scene for this image is the fluidized ejecta from Bakhuysen <span class="hlt">Crater</span> to the southwest, but there's something very interesting going on here on a much smaller scale. A small <span class="hlt">impact</span> <span class="hlt">crater</span>, about 25 meters in diameter, with a gouged-out trench extends to the south. The ejecta (rocky material ejected from the <span class="hlt">crater</span>) mostly extends to the east and west of the <span class="hlt">crater</span>. This "butterfly" ejecta is very common for <span class="hlt">craters</span> formed at low <span class="hlt">impact</span> angles. Taken together, these observations suggest that the <span class="hlt">crater</span>-forming impactor came in at a low angle from the north, hit the ground and ejected material to the sides. The top of the impactor may have sheared off ("decapitating" the impactor) and continued downrange, forming the trench. We can't prove that's what happened, but this explanation is consistent with the observations. Regardless of how it formed, it's quite an interesting-looking "dragonfly" <span class="hlt">crater</span>. The map is projected here at a scale of 50 centimeters (19.69 inches) per pixel. [The original image scale is 55.7 centimeters (21.92 inches) per pixel (with 2 x 2 binning); objects on the order of 167 centimeters (65.7 inches) across are resolved.] North is up. http://photojournal.jpl.nasa.gov/catalog/PIA21454</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013M%26PS...48...87M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013M%26PS...48...87M"><span>Application of nondestructive testing methods to study the damage zone underneath <span class="hlt">impact</span> <span class="hlt">craters</span> of MEMIN laboratory experiments</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Moser, Dorothee; Poelchau, Michael H.; Stark, Florian; Grosse, Christian</p> <p>2013-01-01</p> <p>Within the framework of the Multidisciplinary Experimental and Modeling <span class="hlt">Impact</span> Research Network (MEMIN) research group, the damage zones underneath two experimentally produced <span class="hlt">impact</span> <span class="hlt">craters</span> in sandstone targets were investigated using several nondestructive testing (NDT) methods. The 20 × 20 × 20 cm sandstones were <span class="hlt">impacted</span> by steel projectiles with a radius of 1.25 mm at approximately 5 km s-1, resulting in <span class="hlt">craters</span> with approximately 6 cm diameter and approximately 1 cm depth. Ultrasound (US) tomography and vibrational analysis were applied before and after the <span class="hlt">impact</span> experiments to characterize the damage zone, and micro-computer tomography (μ-CT) measurements were performed to visualize subsurface fractures. The newly obtained experimental data can help to quantify the extent of the damage zone, which extends to about 8 cm depth in the target. The <span class="hlt">impacted</span> sandstone shows a local p-wave reduction of 18% below the <span class="hlt">crater</span> floor, and a general reduction in elastic moduli by between approximately 9 and approximately 18%, depending on the type of elastic modulus. The results contribute to a better empirical and theoretical understanding of hypervelocity events and simulations of <span class="hlt">cratering</span> processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017PhDT........28V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017PhDT........28V"><span>Expanded <span class="hlt">Craters</span> on Mars: Implications for Shallow, Mid-latitude Excess Ice</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Viola, Donna</p> <p></p> <p>Understanding the age and distribution of shallow ice on Mars is valuable for interpreting past and present climate conditions, and has implications on habitability and future in situ resource utilization. Many ice-related features, such as lobate debris aprons and concentric <span class="hlt">crater</span> fill, have been studied using a range of remote sensing techniques. Here, I explore the distribution of expanded <span class="hlt">craters</span>, a form of sublimation thermokarst where shallow, excess ice has been destabilized and sublimated following an <span class="hlt">impact</span> event. This leads to the collapse of the overlying dry regolith to produce the appearance of diameter widening. The modern presence of these features suggests that excess ice has remained preserved in the terrain immediately surrounding the <span class="hlt">craters</span> since the time of their formation in order to maintain the surface. High-resolution imagery is ideal for observing thermokarst features, and much of the work described here will utilize data from the Context Camera (CTX) and High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO). Expanded <span class="hlt">craters</span> tend to be found in clusters that emanate radially from at least four primary <span class="hlt">craters</span> in Arcadia Planitia, and are interpreted as secondary <span class="hlt">craters</span> that formed nearly simultaneously with their primaries. <span class="hlt">Crater</span> age dates of the primaries indicate that the expanded secondaries, as well as the ice layer into which they <span class="hlt">impacted</span>, must be at least tens of millions of years old. Older double-layer ejecta <span class="hlt">craters</span> in Arcadia Planitia commonly have expanded <span class="hlt">craters</span> superposed on their ejecta - and they tend to be more expanded (with larger diameters) in the inner ejecta layer. This has implications on the formation mechanisms for <span class="hlt">craters</span> with this unique ejecta morphology. Finally, I explore the distribution of expanded <span class="hlt">craters</span> south of Arcadia Planitia and across the southern mid-latitudes, along with scalloped depressions (another form of sublimation thermokarst), in order to identify</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA01147.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA01147.html"><span><span class="hlt">Craters</span> on <span class="hlt">Crater</span></span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2006-10-10</p> <p>Several <span class="hlt">craters</span> were formed on the rim of this large <span class="hlt">crater</span>. The movement of material downhill toward the floor of the large <span class="hlt">crater</span> has formed interesting patterns on the floors of the smaller <span class="hlt">craters</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2012LPI....43.2579H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2012LPI....43.2579H"><span>Investigation of Secondary <span class="hlt">Craters</span> in the Saturnian System</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hoogenboom, T.; Schenk, P.; White, O. L.</p> <p>2012-03-01</p> <p>To derive accurate ages using <span class="hlt">impact</span> <span class="hlt">craters</span>, the <span class="hlt">impact</span> source must be determined. We investigate secondary <span class="hlt">crater</span> size, frequency, distribution, formation, and <span class="hlt">crater</span> chain formation on icy satellites throughout the Jupiter and Saturn systems.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010cosp...38..532S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010cosp...38..532S"><span>Method for evaluation of laboratory <span class="hlt">craters</span> using <span class="hlt">crater</span> detection algorithm for digital topography data</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Salamunićcar, Goran; Vinković, Dejan; Lončarić, Sven; Vučina, Damir; Pehnec, Igor; Vojković, Marin; Gomerčić, Mladen; Hercigonja, Tomislav</p> <p></p> <p>In our previous work the following has been done: (1) the <span class="hlt">crater</span> detection algorithm (CDA) based on digital elevation model (DEM) has been developed and the GT-115225 catalog has been assembled [GRS, 48 (5), in press, doi:10.1109/TGRS.2009.2037750]; and (2) the results of comparison between explosion-induced laboratory <span class="hlt">craters</span> in stone powder surfaces and GT-115225 have been presented using depth/diameter measurements [41stLPSC, Abstract #1428]. The next step achievable using the available technology is to create 3D scans of such labo-ratory <span class="hlt">craters</span>, in order to compare different properties with simple Martian <span class="hlt">craters</span>. In this work, we propose a formal method for evaluation of laboratory <span class="hlt">craters</span>, in order to provide objective, measurable and reproducible estimation of the level of achieved similarity between these laboratory and real <span class="hlt">impact</span> <span class="hlt">craters</span>. In the first step, the section of MOLA data for Mars (or SELENE LALT for Moon) is replaced with one or several 3D-scans of laboratory <span class="hlt">craters</span>. Once embedment was done, the CDA can be used to find out whether this laboratory <span class="hlt">crater</span> is similar enough to real <span class="hlt">craters</span>, as to be recognized as a <span class="hlt">crater</span> by the CDA. The CDA evaluation using ROC' curve represents how true detection rate (TDR=TP/(TP+FN)=TP/GT) depends on the false detection rate (FDR=FP/(TP+FP)). Using this curve, it is now possible to define the measure of similarity between laboratory and real <span class="hlt">impact</span> <span class="hlt">craters</span>, as TDR or FDR value, or as a distance from the bottom-right origin of the ROC' curve. With such an approach, the reproducible (formally described) method for evaluation of laboratory <span class="hlt">craters</span> is provided.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050201864','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050201864"><span>Characteristics of <span class="hlt">Impact</span> <span class="hlt">Craters</span> and Interior Deposits: Analysis of the Spatial and Temporal Distribution of Volatiles in the Highlands of Mars</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mest, S. C.</p> <p>2005-01-01</p> <p>The martian southern highlands contain <span class="hlt">impact</span> <span class="hlt">craters</span> that display pristine to degraded morphologies, and preserve a record of degradation that can be attributed to fluvial, eolian, mass wasting, volcanic and <span class="hlt">impact</span>-related processes. However, the relative degree of modification by these processes and the amounts of material contributed to <span class="hlt">crater</span> interiors are not well constrained. <span class="hlt">Impact</span> <span class="hlt">craters</span> (D>10 km) within Terra Cimmeria (0deg-60degS, 190deg-240degW), Terra Tyrrhena (0deg-30degS, 260deg-310degW) and Noachis Terra (20deg-50degS, 310deg-340degW) are being examined to better understand the degradational history and evolution of highland terrains. The following scientific objectives will be accomplished. 1) Determine the geologic processes that modified <span class="hlt">impact</span> <span class="hlt">craters</span> (and surrounding highland terrains). 2) Determine the sources (e.g. fluvial, lacustrine, eolian, mass wasting, volcanic, <span class="hlt">impact</span> melt) and relative amounts of material composing <span class="hlt">crater</span> interior deposits. 3) Document the relationships between <span class="hlt">impact</span> <span class="hlt">crater</span> degradation and highland fluvial systems. 4) Determine the spatial and temporal relationships between degradational processes on local and regional scales. And 5) develop models of <span class="hlt">impact</span> <span class="hlt">crater</span> (and highland) degradation that can be applied to these and other areas of the martian highlands. The results of this study will be used to constrain the geologic, hydrologic and climatic evolution of Mars and identify environments in which subsurface water might be present or evidence for biologic activity might be preserved.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20010044700&hterms=Xxxii&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DXxxii','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20010044700&hterms=Xxxii&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3DXxxii"><span>Availability of Heat to Drive Hydrothermal Systems in Large Martian <span class="hlt">Impact</span> <span class="hlt">Craters</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Thorsos, I. E.; Newsom, H. E.; Davies, A. G.</p> <p>2001-01-01</p> <p>The central uplift in large <span class="hlt">craters</span> on Mars can provide a substantial source of heat, equivalent to heat produced by the <span class="hlt">impact</span> melt sheet. The heat generated in large <span class="hlt">impacts</span> could play a significant role in hydrothermal systems on Mars. Additional information is contained in the original extended abstract.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2008GeoRL..3523206K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2008GeoRL..3523206K"><span>Ring-mold <span class="hlt">craters</span> in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kress, Ailish M.; Head, James W.</p> <p>2008-12-01</p> <p>Ring-mold <span class="hlt">craters</span> (RMCs), concentric <span class="hlt">crater</span> forms shaped like a truncated torus and named for their similarity to the cooking implement, are <span class="hlt">abundant</span> in lobate debris aprons (LDA) and lineated valley fill (LVF) in the northern mid-latitudes on Mars, but are not seen in surrounding terrain. LDA and LVF have been interpreted to form by flow of debris, but uncertainty remains concerning the mechanism of flow, with hypotheses ranging from pore-ice-assisted creep of talus to debris-covered glaciers. RMCs average less than a few hundred meters in diameter and occur in association with normal bowl-shaped <span class="hlt">impact</span> <span class="hlt">craters</span> whose average diameters are commonly less than RMCs. On the basis of their morphologic similarities to laboratory <span class="hlt">impact</span> <span class="hlt">craters</span> formed in ice and the physics of <span class="hlt">impact</span> <span class="hlt">cratering</span> into layered material, we interpret the unusual morphology of RMCs to be the result of <span class="hlt">impact</span> into a relatively pure ice substrate below a thin regolith, with strength-contrast properties, spallation, viscous flow and sublimation being factors in the development of the ring-mold shape. Associated smaller bowl-shaped <span class="hlt">craters</span> are interpreted to have formed within a layer of regolith-like sublimation till overlying the ice substrate. Estimates of <span class="hlt">crater</span> depths of excavation between populations of bowl-shaped and ring-mold <span class="hlt">craters</span> suggest that the debris layer is relatively thin. These results support the hypothesis that LDA and LVF formed as debris-covered glaciers and predict that many hundreds of meters of ice remain today in LDA and LVF deposits, beneath a veneer of sublimation till. RMCs can be used in other parts of Mars to predict and assess the presence of ancient ice-related deposits.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014DPS....4641310H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014DPS....4641310H"><span>Modeling the Provenance of <span class="hlt">Crater</span> Ejecta</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Huang, Ya-Huei; Minton, David A.</p> <p>2014-11-01</p> <p>The <span class="hlt">cratering</span> history of the Moon provides a way to study the violent early history of our early solar system. Nevertheless, we are still limited in our ability to interpret the lunar <span class="hlt">cratering</span> history because the complex process of generation and subsequent transportation and destruction of <span class="hlt">impact</span> melt products is relatively poorly understood. Here we describe a preliminary model for the transport of datable <span class="hlt">impact</span> melt products by <span class="hlt">craters</span> over Gy timescales on the lunar surface. We use a numerical model based on the Maxwell Z-model to model the exhumation and transport of ejecta material from within the excavation flow of a transient <span class="hlt">crater</span>. We describe our algorithm for rapidly estimating the provenance of ejecta material for use in a Monte Carlo <span class="hlt">cratering</span> code capable of simulating lunar <span class="hlt">cratering</span> over Gy timescales.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.P33D2906S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.P33D2906S"><span>Terrestrial Palynology of Paleocene and Eocene Sediments Above the Chicxulub <span class="hlt">Impact</span> <span class="hlt">Crater</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Smith, V.; Warny, S.; Bralower, T. J.; Jones, H.; Lowery, C. M.; Smit, J.; Vajda, V.; Vellekoop, J.; 364 Scientists, E.</p> <p>2017-12-01</p> <p>International Ocean Discovery Program (IODP) Expedition 364, with support from the International Continental Scientific Drilling Program, cored through Paleocene and Eocene sediments and into the <span class="hlt">impact</span> structure of the Chicxulub <span class="hlt">impact</span> <span class="hlt">crater</span>. Three palynological studies of the post-<span class="hlt">impact</span> section are currently underway. The two other studies are investigating the dinoflagellate palynology and terrestrial palynology of the K/Pg boundary section, while this study focuses on the early Eocene terrestrial palynology of the IODP 364 core, which has yielded a diverse and well preserved pollen assemblage. A few samples from the Early Paleocene have also been examined but organic microfossil preservation is quite poor. Samples from this core are the oldest palynological record from the Yucatan peninsula. Sample preparation and detailed <span class="hlt">abundance</span> counts of sixty samples throughout the post-<span class="hlt">impact</span> section are in progress, with a particular focus on the Paleocene-Eocene Thermal Maximum (PETM) and the Early Eocene Climatic Optimum (EECO). Terrestrial palynomorph assemblages will be used to reconstruct paleoclimatological conditions throughout this time period. Floral response to hyperthermal events in the IODP 364 core will be compared with records from other Gulf of Mexico and Caribbean sections. In addition to the biological and paleoclimatological implications of this research, age control from foraminiferal and nannofossil biostratigraphy, paleomagnetism, and radiometric dating will provide a chronological framework for the terrestrial pollen biostratigraphy, with applications to hydrocarbon exploration in the Wilcox Formation and age equivalent sections in the Gulf of Mexico.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016AGUFM.P41C..03S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016AGUFM.P41C..03S"><span><span class="hlt">Impact</span> <span class="hlt">crater</span> morphology and the Central Pit/Dome of Occator: Ceres as an Ice-rich Body</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schenk, P.; Marchi, S.; O'Brien, D. P.; Platz, T.; Bland, M. T.; Buczkowski, D.; Scully, J. E. C.; Ammannito, E.; Raymond, C. A.; Russell, C. T.</p> <p>2016-12-01</p> <p>Pristine <span class="hlt">crater</span> morphologies on Ceres (at D <40 km) are astonishingly similar to those on midsize icy bodies (e.g., moons of Saturn) but very different from those on silicate-rich Vesta. All these bodies have similar gravity and broadly similar <span class="hlt">impact</span> velocities, and these patterns reveal that the upper 10s of km of Ceres are much weaker than on silicate-rich Vesta. This stands in contrast to the lack of viscous relaxation (Bland et al., 2016), which implies an upper layer on Ceres capable of resisting flow despite the relatively high surface temperatures. This can be explained as distinct responses of an outer layer partially composed of weak ices and strong silicates that fail during high-strain <span class="hlt">impact</span> processes (which are apparently controlled by the weak phase) but does not flow under low-strain creep (which is apparently controlled more by the strong phase). Furthermore, comparison with Martian <span class="hlt">craters</span> indicates that, in contrast to Ceres, the amount of water ice in the crust of Mars results in hybrid morphologies only midway between silicate and ice worlds, indicating that the upper layers of Ceres must have more ice than does Mars. The presence of apparent <span class="hlt">impact</span> melt deposits and central pits in larger <span class="hlt">craters</span> (D>40 km and D>75 km, respectively) on Ceres implies either warmer conditions than at Saturn, or the presence of a deeper layer enriched in (weaker) ice at comparable depths, also consistent with partial relaxation in larger <span class="hlt">craters</span>. The formation of a fractured dome 3-km-wide and 0.75-km-high within recently formed Occator <span class="hlt">crater</span> may be due to refreezing of a water zone melted after <span class="hlt">impact</span>, or mobilization of carbonates or ice in the <span class="hlt">crater</span> center, possibly from such deeper layers.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_17");'>17</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li class="active"><span>19</span></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_19 --> <div id="page_20" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="381"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920019775&hterms=graduation+rates&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dgraduation%2Brates','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920019775&hterms=graduation+rates&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dgraduation%2Brates"><span>Styles of <span class="hlt">crater</span> gradation in Southern Ismenius Lacus, Mars: Clues from Meteor <span class="hlt">Crater</span>, Arizona</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grant, J. A.; Schultz, P. H.</p> <p>1992-01-01</p> <p><span class="hlt">Impact</span> <span class="hlt">craters</span> on the Earth and Mars provide a unique opportunity to quantify the gradational evolution of instantaneously created landforms in a variety of geologic settings. Unlike most landforms, the initial morphology associated with <span class="hlt">impact</span> <span class="hlt">craters</span> on both planets is uncomplicated by competition between construction and degradation during formation. Furthermore, pristine morphologies are both well-constrained and similar to a first order. The present study compares styles of graduation at Meteor <span class="hlt">Crater</span> with those around selected <span class="hlt">craters</span> (greater than 1-2 km in diameter) in southern Ismenius Lacus. Emphasis is placed on features visible in images near LANDSAT TM resolution (30-50 m/pixel) which is available for both areas. In contrast to Mars, vegetation on the Earth can modify gradation, but appears to influence overall rates and styles by 2X-3X rather than orders of magnitude. Further studies of additional <span class="hlt">craters</span> in differing settings will refine the effects of this and other factors (e.g., substrate). Finally, by analogy with results from other terrestrial gradational surfaces this study should help provide constraints on climate over <span class="hlt">crater</span> histories.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA04410.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA04410.html"><span><span class="hlt">Crater</span> Wall and Floor</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2003-02-18</p> <p>The <span class="hlt">impact</span> <span class="hlt">crater</span> observed in this NASA Mars Odyssey image taken in Terra Cimmeria suggests sediments have filled the <span class="hlt">crater</span> due to the flat and smooth nature of the floor compared to rougher surfaces at higher elevations.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017M%26PS...52.2067B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017M%26PS...52.2067B"><span>The fourth Arab <span class="hlt">Impact</span> <span class="hlt">Cratering</span> and Astrogeology Conference (AICAC IV), April 9-12, 2017, Algiers (Algeria)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Belhaï, D.; Chennaoui-Aoudjehane, H.; Baratoux, D.; Ferrière, L.; Lamali, A.; Sahoui, R.; Lambert, P.; Ayadi, A.</p> <p>2017-09-01</p> <p>We present a report about the fourth Arab <span class="hlt">Impact</span> <span class="hlt">Cratering</span> and Astrogeology Conference (AICAC IV) that took place in Algiers at the USTHB (Université des Sciences et Technologie Houari Boumedienne, Algiers, Algeria) in the presence of the presidents of the USTHB and Boumerdès Universities, the Director of CRAAG (Centre de Recherche en Astronomie, Astrophysique et Géophysique), and the General Director of the National Administration for Scientific Research (NASR/DGRSDT). This series of conferences aims to promote research interest for <span class="hlt">impact</span> <span class="hlt">cratering</span> in the Arab world and beyond, including for instance in African countries. In spite of persistently restraining travel measures to Algeria, the fourth edition held in Algiers was marked by continuous international participation, with participants from seven different countries. This conference focused on presentations of scientific results in the research fields related to planetology, meteorites, and <span class="hlt">impact</span> <span class="hlt">craters</span>. In particular, the Algerian <span class="hlt">impact</span> structures were under the spotlights during both oral and poster sessions. During this conference, the presence of freshly graduated Ph.D. students and new Ph.D. projects related to <span class="hlt">impact</span> <span class="hlt">cratering</span> or meteoritic science was a positive sign for the consolidation of research groups in this domain in the Arab world and Africa. Therefore, international cooperation or external support and funding are still needed to ensure the development of this scientific discipline in this part of the world.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2004EOSTr..85..378N','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2004EOSTr..85..378N"><span><span class="hlt">Cratering</span> in Marine Environments and on Ice</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Newsom, Horton E.</p> <p>2004-09-01</p> <p>Since the discovery of plate tectonics, <span class="hlt">impact</span> <span class="hlt">cratering</span> is arguably the most significant geologic process now recognized as an important process on Earth. <span class="hlt">Impacts</span> into ice, another main topic covered in this book, may be important on other worlds. Large numbers of <span class="hlt">impact</span> <span class="hlt">craters</span> that formed in marine environments on Earth have only been discovered in the last 10 years. Twenty-five <span class="hlt">craters</span> that formed in marine environments have been documented, according to the first chapter of this book, although none are known that excavated oceanic crust. The papers in <span class="hlt">Cratering</span> in Marine Environments and on Ice will whet your appetite for the exciting and ambitious range of topics implied by the title, which stems from a conference in Svalbard, Norway, in September 2001. This book provides a flavor of the rapidly advancing and diverse field of <span class="hlt">impact</span> <span class="hlt">cratering</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014CRGeo.346...82I','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014CRGeo.346...82I"><span>Tectonic-karstic origin of the alleged "<span class="hlt">impact</span> <span class="hlt">crater</span>" of Lake Isli (Imilchil district, High Atlas, Morocco)</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ibouh, Hassan; Michard, André; Charrière, André; Benkaddour, Abdelfattah; Rhoujjati, Ali</p> <p>2014-03-01</p> <p>The scenic lakes Tislit and Isli of the Imilchil area in the central High Atlas of Morocco have been recently promoted to the rank of "dual <span class="hlt">impact</span> <span class="hlt">crater</span>" by a group of geoscientists. This was promptly denied by a group of meteorite specialists, but the first team reiterated their <span class="hlt">impact</span> <span class="hlt">crater</span> interpretation, now restricted to Lake Isli. This alleged 40-kyr-old <span class="hlt">impact</span> <span class="hlt">crater</span> would be associated with the Agoudal meteorite recognized further in the southeast. Here, we show that the lake formed during the Lowe-Middle Pleistocene in a small Pliocene (?) pull-apart basin through additional collapsing due to karst phenomena in the underlying limestones. This compares with the formation of a number of lakes of the Atlas Mountains. None of the "proofs" produced in support of a meteoritic origin of Lake Isli coincides with the geology of the area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFMPP31D..01G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFMPP31D..01G"><span>IODP-ICDP Expedition 364: Drilling the Chicxulub <span class="hlt">impact</span> <span class="hlt">crater</span> to understand planetary evolution and mass extinction</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gulick, S. P. S.; Morgan, J. V.</p> <p>2017-12-01</p> <p>The most recent of Earth's five largest mass extinction events occurred 66 Ma, coeval with the <span class="hlt">impact</span> of a 12 km asteroid, striking at 60 degrees into what is today the Yucatán Peninsula, México, producing the 200 km-wide Chicxulub <span class="hlt">crater</span>. This <span class="hlt">impact</span>, by some estimations, drove the extinction of 75% of life on Earth at the genus level. The mass extinction event marks the boundary between the Cretaceous and Paleogene. Proposed kill mechanisms include thermal effects caused by the reentry of fast ejecta into Earth's atmosphere, dust and sulfate aerosols reducing Earth's solar insolation, ocean acidification, and metal toxicity due to the chemical make-up of the impactor. The magnitude and duration of these processes is still debated, and further evaluation of the proposed kill mechanisms requires an understanding of the mechanics of the Chicxulub <span class="hlt">impact</span> as well as the resulting global environmental perturbations. In April and May 2016, the International Ocean Discovery Program, with co-funding from the International Continental Scientific Drilling Program, successfully cored into the Chicxulub <span class="hlt">impact</span> <span class="hlt">crater</span> with nearly 100% recovery. These cores include the first-ever samples of the transition from an intact peak ring through post-<span class="hlt">impact</span> sediments. A peak ring is a discontinuous ring of mountains observed within the central basin of all large <span class="hlt">impact</span> <span class="hlt">craters</span> on rocky planets. Newly drilled cores include the uplifted target rocks, melt-rich impactites, hydrothermal deposits, a possible settling layer, and the resumption of carbonate sedimentation. The discovery that Chicxulub's peak ring consists of largely granitic crust uplifted by 10 km calibrates <span class="hlt">impact</span> models and allows for observation of <span class="hlt">impact</span> processes. At the top of the peak ring, the K-Pg boundary deposit includes a impactite sequence 130 m thick deposited by processes that range from minutes to likely years post-<span class="hlt">impact</span>. This sequence is then overprinted by hydrothermal processes that lasted at least 100s</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017APS..DFDG39010B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017APS..DFDG39010B"><span>Investigating large-scale secondary circulations within <span class="hlt">impact</span> <span class="hlt">crater</span> topographies in a refractive index-matched facility</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Blois, Gianluca; Kim, Taehoon; Bristow, Nathan; Day, Mackenzie; Kocurek, Gary; Anderson, William; Christensen, Kenneth</p> <p>2017-11-01</p> <p><span class="hlt">Impact</span> <span class="hlt">craters</span>, common large-scale topographic features on the surface of Mars, are circular depressions delimited by a sharp ridge. A variety of <span class="hlt">crater</span> fill morphologies exist, suggesting that complex intracrater circulations affect their evolution. Some large <span class="hlt">craters</span> (diameter >10 km), particularly at mid latitudes on Mars, exhibit a central mound surrounded by circular moat. Foremost among these examples is Gale <span class="hlt">crater</span>, landing site of NASA's Curiosity rover, since large-scale climatic processes early in in the history of Mars are preserved in the stratigraphic record of the inner mound. Investigating the intracrater flow produced by large scale winds aloft Mars <span class="hlt">craters</span> is key to a number of important scientific issues including ongoing research on Mars paleo-environmental reconstruction and the planning of future missions (these results must be viewed in conjunction with the affects of radial katabatibc flows, the importance of which is already established in preceding studies). In this work we consider a number of <span class="hlt">crater</span> shapes inspired by Gale morphology, including idealized <span class="hlt">craters</span>. Access to the flow field within such geometrically complex topography is achieved herein using a refractive index matched approach. Instantaneous velocity maps, using both planar and volumetric PIV techniques, are presented to elucidate complex three-dimensional flow within the <span class="hlt">crater</span>. In addition, first- and second-order statistics will be discussed in the context of wind-driven (aeolian) excavation of <span class="hlt">crater</span> fill.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.P41F1980R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.P41F1980R"><span><span class="hlt">Impact</span>-induced compositional variations on Mercury</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rivera-Valentin, E. G.; Barr, A. C.</p> <p>2013-12-01</p> <p>The surface of Mercury shows unexpected spectral variations spatially associated with <span class="hlt">crater</span> and basin ejecta (the so-called 'low-reflectance material' or LRM; [1]). The low reflectance is suggested to be caused by a native darkening agent at depth that has been excavated and redeposited onto the surface [1]. Although LRM is generally associated with <span class="hlt">crater</span> ejecta, it is not found within the ejecta blankets of many large <span class="hlt">impact</span> <span class="hlt">craters</span>, perhaps suggesting that the subsurface source is heterogeneous [2]. We have developed a 3-D Monte Carlo model of <span class="hlt">impact</span> <span class="hlt">cratering</span>, excavation, and ejecta blanket deposition. Our simulations of the effect of early <span class="hlt">impacts</span> onto Mercury show that if the LRM originates from depth to cover ~15% of Mercury's surface [2], its source is ~30 km deep. Considering the estimated mercurian crustal thickness of 50 km [3] this implies the darkening agent is most probably located within a chemically distinct lower crust. Simulations show that repeated and overlapping <span class="hlt">impacts</span> redistribute the darkening agent away from the basin source and create a weak association between <span class="hlt">crater</span> size and LRM <span class="hlt">abundance</span>. Thus subsurface heterogeneity is not required to produce the weak association between <span class="hlt">crater</span> size and LRM <span class="hlt">abundance</span> within <span class="hlt">crater</span> ejecta; this is a natural consequence of overlapping <span class="hlt">impacts</span>. Our results can elucidate the new high-resolution compositional mapping of Mercury's heavily <span class="hlt">cratered</span> terrain and provide insight into subsurface composition. Acknowledgements: This work is supported by the Center for Lunar Origin and Evolution through the NASA Lunar Science Institute NNA09DB32A. References: [1] Denevi and Robinson, 2008, Icarus 197, 239-246. [2] Denevi et al., 2009, Science 324, 613-618. [3] Smith et al., 2012, Science 336, 214-217.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA04018.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA04018.html"><span>Buried <span class="hlt">Crater</span></span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2002-12-04</p> <p>With a location roughly equidistant between two of the largest volcanic constructs on the planet, the fate of the approximately 50 km 31 mile <span class="hlt">impact</span> <span class="hlt">crater</span> in this image from NASA Mars Odyssey was sealed. It has been buried to the rim by lava flows. The MOLA context image shows pronounced flow lobes surrounding the <span class="hlt">crater</span>, a clear indication of the most recent episode of volcanism that could have contributed to its infilling. Breaches in the rim are clearly evident in the image and suggest locations through which lavas could have flowed. These openings appear to be limited to the west side of the <span class="hlt">crater</span>. Other <span class="hlt">craters</span> in the area are nearly obliterated by the voluminous lava flows, further demonstrating one of the means by which Mars renews its surface. The MOLA context image shows pronounced flow lobes surrounding the <span class="hlt">crater</span>, a clear indication of the most recent episode of volcanism that could have contributed to its infilling. Breaches in the rim are clearly evident in the image and suggest locations through which lavas could have flowed. These openings appear to be limited to the west side of the <span class="hlt">crater</span>. Other <span class="hlt">craters</span> in the area are nearly obliterated by the voluminous lava flows, further demonstrating one of the means by which Mars renews its surface. http://photojournal.jpl.nasa.gov/catalog/PIA04018</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2003icbg.conf...15C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2003icbg.conf...15C"><span><span class="hlt">Cratering</span> on Small Bodies: Lessons from Eros</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Chapman, C. R.</p> <p>2003-01-01</p> <p><span class="hlt">Cratering</span> and regolith processes on small bodies happen continuously as interplanetary debris rains down on asteroids, comets, and planetary satellites. Butthey are very poorly observed and not well understood. On the one hand, we have laboratory experimentation at small scales and we have examination of large <span class="hlt">impact</span> <span class="hlt">craters</span> (e.g. Meteor <span class="hlt">Crater</span> on Earth and imaging of <span class="hlt">abundant</span> <span class="hlt">craters</span> on terrestrial planets and outer planet moons). Understanding <span class="hlt">cratering</span> on bodies of intermediate scales, tens of meters to hundreds of km in size, involves either extrapolation from our understanding of <span class="hlt">cratering</span> phenomena at very different scales or reliance on very preliminary, incomplete examination of the observational data we now have for a few small bodies. I review the latter information here. It has been generally understood that the role of gravity is greatly diminished for smaller bodies, so a lot of <span class="hlt">cratering</span> phenomena studied for larger bodies is less applicable. But it would be a mistake to imagine that laboratory experiments on gravitationless rocks (usually at 1 g) are directly applicable, except perhaps to those monolithic Near Earth Asteroids (NEAs) some tens of meters in size that spin very rapidly and can be assumed to be "large bare rocks" with "negative gravity". Whereas it had once been assumed that asteroids smaller than some tens of km diameter would retain little regolith, it is increasingly apparent that regolith and megoregolith processes extend down to bodies only hundreds of meters in size, perhaps smaller. Yet these processes are very different from those that pertain to the Moon, which is our chief prototype of regolith processes. The NEAR Shoemaker spacecraft's studies of Eros provide the best evidence to date about small-body <span class="hlt">cratering</span> processes, as well as a warning that our theoretical understanding requires anchoring by direct observations. Eros: "Ponds", Paucity of Small <span class="hlt">Craters</span>, and Other Mysteries. Although Eros is currently largely detached</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11543120','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11543120"><span>The Cretaceous-Tertiary <span class="hlt">impact</span> <span class="hlt">crater</span> and the cosmic projectile that produced it.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Sharpton, V L; Marin, L E</p> <p>1997-05-30</p> <p>Evidence gathered to date from topographic data, geophysical data, well logs, and drill-core samples indicates that the buried Chicxulub basin, the source <span class="hlt">crater</span> for the approximately 65 Ma Cretaceous-Tertiary (K/T) boundary deposits, is approximately 300 km in diameter. A prominent topographic ridge and a ring of gravity anomalies mark the position of the basin rim at approximately 150 km from the center. Wells in this region recovered thick sequences of <span class="hlt">impact</span>-generated breccias at 200-300 m below present sea level. Inside the rim, which has been severely modified by erosion following <span class="hlt">impact</span>, the subsurface basin continues to deepen until near the center it is approximately 1 km deep. The best planetary analog for this <span class="hlt">crater</span> appears to be the 270 km-diameter Mead basin on Venus. Seismic reflection data indicate that the central zone of downward displacement and excavation (the transient <span class="hlt">crater</span> is approximately 130 km in diameter, consistent with previous studies of gravity anomaly data). Our analysis of projectile characteristics utilizes this information, coupled with conventional scaling relationships, and geochemical constraints on the mass of extraterrestrial material deposited within the K/T boundary layer. Results indicate that the Chicxulub <span class="hlt">crater</span> would most likely be formed by a long-period comet composed primarily of nonsilicate materials (ice, hydrocarbons, etc.) and subordinate amounts (< or = 50%) primitive chondritic material. This collision would have released the energy equivalent to between 4 x 10(8) and 4 x 10(9) megatons of TNT. Studies of terrestrial <span class="hlt">impact</span> rates suggest that such an event would have a mean production rate of approximately 1.25 x 10(-9) y-1. This rate is considerably lower than that of the major mass extinctions over the last 250 million years (approximately 5 x 10(-7) y-1). Consequently, while there is substantial circumstantial evidence establishing the cause-effect link between the Chicxulub basin forming event and the K</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016EGUGA..1810317L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016EGUGA..1810317L"><span>Wildfires Caused by Formation of Small <span class="hlt">Impact</span> <span class="hlt">Craters</span>: A Kaali <span class="hlt">Crater</span> Case</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Losiak, Anna; Belcher, Claire; Hudspith, Victoria; Zhu, Menghua; Bronikowska, Malgorzata; Jõeleht, Argo; Plado, Juri</p> <p>2016-04-01</p> <p>Formation of ~200-km Chicxulub 65 Ma ago was associated with release of significant amount of thermal energy [1,2,3] which was sufficient to start wildfires that had either regional [4] or global [5] range. The evidence for wildfires caused by <span class="hlt">impacts</span> smaller than Chicxulub is inconclusive. On one hand, no signs of fires are associated with the formation of 24-km Ries <span class="hlt">crater</span> [6]. On the other hand, the Tunguska site was burned after the <span class="hlt">impact</span> and the numerical models of the bolide-produced thermal radiation suggest that the Tunguska-like event would produce a thermal flux to the surface that is sufficient to ignite pine needles [7]. However, in case of Tunguska the only proof for the bolide starting the fire comes from an eyewitness description collected many years after the event. Some authors [8] suggest that this fire might have been caused "normaly" later during the same year, induced on dead trees killed by the Tunguska fall. More recently it was observed that the Chelyabinsk meteor [9] - smaller than Tunguska event - did not produced a fire. In order to explore this apparent relationship in more detail, we have studied the proximal ejecta from a 100-m in diameter, ~3500 years old [10] Kaali <span class="hlt">crater</span> (Estonia) within which we find pieces of charred organic material. Those pieces appear to have been produced during the <span class="hlt">impact</span>, according to their stratigraphic location and following 14C analysis [19] as opposed to pre- or post-<span class="hlt">impact</span> forest fires. In order to determine the most probable formation mechanism of the charred organic material found within Kaali proximal ejecta blanket, we: 1) Analyzed charcoal under SEM to identify the charred plants and determine properties of the charcoal related to the temperature of its formation [11]. Detected homogenization of cell walls suggests that at least some pieces of charcoal were formed at >300 °C [11]. 2) Analyzed the reflectance properties of the charred particles in order to determine the intensity with which</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100017206','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100017206"><span>Topography of the Martian <span class="hlt">Impact</span> <span class="hlt">Crater</span> Tooting</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mouginis-Mark, P. J.; Garbeil, H.; Boyce, J. M.</p> <p>2009-01-01</p> <p>Tooting <span class="hlt">crater</span> is approx.29 km in diameter, is located at 23.4degN, 207.5degE, and is classified as a multi-layered ejecta <span class="hlt">crater</span> [1]. Our mapping last year identified several challenges that can now be addressed with HiRISE and CTX images, but specifically the third dimension of units. To address the distribution of ponded sediments, lobate flows, and volatile-bearing units within the <span class="hlt">crater</span> cavity, we have focused this year on creating digital elevation models (DEMs) for the <span class="hlt">crater</span> and ejecta blanket from stereo CTX and HiRISE images. These DEMs have a spatial resolution of approx.50 m for CTX data, and 2 m for HiRISE data. Each DEM is referenced to all of the available individual MOLA data points within an image, which number approx.5,000 and 800 respectively for the two data types</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19870043241&hterms=Mexico+sonora&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DMexico%2Bsonora','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19870043241&hterms=Mexico+sonora&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3DMexico%2Bsonora"><span>Radar characteristics of small <span class="hlt">craters</span> - Implications for Venus</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Greeley, Ronald; Christensen, Philip R.; Mchone, John F.</p> <p>1987-01-01</p> <p>Shuttle radar images (SIR-A) of volcanic and <span class="hlt">impact</span> <span class="hlt">craters</span> were examined to assess their appearance on radar images. Radar characteristics were determined for (1) nine maarlikie <span class="hlt">craters</span> in the Pinacate volcanic field, Sonora, Mexico; (2) the caldera of Cerro Volcan Quemado, in the Bolivian Andes; (3) Talemzane <span class="hlt">impact</span> <span class="hlt">crater</span>, Algeria; and (4) Al Umchaimin, a possible <span class="hlt">impact</span> structure in Iraq. SIR-A images were compared with conventional photographs and with results from field studies. Consideration was then given to radar images available for Venus, or anticipated from the Magellan mission. Of the criteria ordinarily used to identify <span class="hlt">impact</span> <span class="hlt">craters</span>, some can be assessed with radar images and others cannot be used; planimetric form, expressed as circularity, and ejecta-block distribution can be assessed on radar images, but rim and floor elevations relative to the surrounding plain and disposition of rim strata are difficult or impossible to determine. It is concluded that it will be difficult to separate small <span class="hlt">impact</span> <span class="hlt">craters</span> from small volcanic <span class="hlt">craters</span> on Venus using radar images and is suggested that it will be necessary to understand the geological setting of the areas containing the <span class="hlt">craters</span> in order to determine their origin.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996GeoRL..23.1565U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996GeoRL..23.1565U"><span>UNAM Scientific Drilling Program of Chicxulub <span class="hlt">Impact</span> Structure-Evidence for a 300 kilometer <span class="hlt">crater</span> diameter</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Urrutia-Fucugauchi, J.; Marin, L.; Trejo-Garcia, A.</p> <p></p> <p>As part of the UNAM drilling program at the Chicxulub structure, two 700 m deep continuously cored boreholes were completed between April and July, 1995. The Peto UNAM-6 and Tekax UNAM-7 drilling sites are ˜150 km and 125 km, respectively, SSE of Chicxulub Puerto, near the <span class="hlt">crater</span>'s center. Core samples from both sites show a sequence of post-<span class="hlt">crater</span> carbonates on top of a thick <span class="hlt">impact</span> breccia pile covering the disturbed Mesozoic platform rocks. At UNAM-7, two <span class="hlt">impact</span> breccia units were encountered: (1) an upper breccia, mean magnetic susceptibility is high (˜55 × 10-6 SI units), indicating a large component of silicate basement has been incorporated into this breccia, and (2) an evaporite-rich, low susceptibility <span class="hlt">impact</span> breccia similar in character to the evaporite-rich breccias observed at the PEMEX drill sites further out. The upper breccia was encountered at ˜226 m below the surface and is ˜125 m thick; the lower breccia is immediately subjacent and is >240 m thick. This two-breccia sequence is typical of the suevite-Bunte breccia sequence found within other well preserved <span class="hlt">impact</span> <span class="hlt">craters</span>. The suevitic upper unit is not present at UNAM-6. Instead, a >240 m thick evaporite-rich breccia unit, similar to the lower breccia at UNAM-7, was encountered at a depth of ˜280 m. The absence of an upper breccia equivalent at UNAM-6 suggests some portion of the breccia sequence has been removed by erosion. This is consistent with interpretations that place the high-standing <span class="hlt">crater</span> rim at 130-150 km from the center. Consequently, the stratigraphic observations and magnetic susceptibiity records on the upper and lower breccias (depth and thickness) support a ˜300 km diameter <span class="hlt">crater</span> model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19980111118','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19980111118"><span>Breccia Formation at a Complex <span class="hlt">Impact</span> <span class="hlt">Crater</span>: Slate Islands, Lake Superior, Ontario, Canada</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dressler, B. O.; Sharpton, V. L.</p> <p>1997-01-01</p> <p>The Slate Islands <span class="hlt">impact</span> structure is the eroded remnant of a approximately 30-32 km-diameter complex <span class="hlt">impact</span> structure located in northern Lake Superior, Ontario, Canada. Target rocks are Archean supracrustal and igneous rocks and Proterozoic metavolcanics, metasediments, and diabase. A wide variety of breccias occurs on the islands, many of which contain fragments exhibiting shock metamorphic features. Aphanitic, narrow and inclusion-poor pseudotachylite veins, commonly with more or less parallel boundaries and apophyses branching off them, represent the earliest breccias formed during the compression stage of the <span class="hlt">impact</span> process. Coarse-grained, polymictic elastic matrix breccias form small to very large, inclusion-rich dikes and irregularly shaped bodies that may contain altered glass fragments. These breccias have sharp contacts with their host rocks and include a wide range of fragment types some of which were transported over minimum distances of approximately 2 km away from the center of the structure. They cut across pseudotachylite veins and contain inclusions of them. Field and petrographic evidence indicate that these polymictic breccias formed predominantly during the excavation and central uplift stages of the <span class="hlt">impact</span> process. Monomictic breccias, characterized by angular fragments and transitional contacts with their host rocks, occur in parautochthonous target rocks, mainly on the outlying islands of the Slate Islands archipelago. A few contain fragmented and disrupted, coarse-grained, polymictic clastic matrix breccia dikes. This is an indication that at least some of these monomictic breccias formed late in the <span class="hlt">impact</span> process and that they are probably related to a late <span class="hlt">crater</span> modification stage. A small number of relatively large occurrences of glass-poor, suevitic breccias occur at the flanks of the central uplift and along the inner flank of the outer ring of the Slate Islands complex <span class="hlt">crater</span>. A coarse, glass-free, allogenic breccia, containing</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2013AGUFM.P51G1810B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2013AGUFM.P51G1810B"><span>How Small Can <span class="hlt">Impact</span> <span class="hlt">Craters</span> Be Detected at Large Scale by Automated Algorithms?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Bandeira, L.; Machado, M.; Pina, P.; Marques, J. S.</p> <p>2013-12-01</p> <p> intended to be detected: the lower this limit is, the higher the false detection rates are. A detailed evaluation is performed with breakdown results by <span class="hlt">crater</span> dimension and image or surface type, permitting to realize that automated detections in large <span class="hlt">crater</span> datasets in HiRISE imagery datasets with 25cm/pixel resolution can be successfully done (high correct and low false positive detections) until a <span class="hlt">crater</span> dimension of about 8-10 m or 32-40 pixels. [1] Martins L, Pina P. Marques JS, Silveira M, 2009, <span class="hlt">Crater</span> detection by a boosting approach. IEEE Geoscience and Remote Sensing Letters 6: 127-131. [2] Salamuniccar G, Loncaric S, Pina P. Bandeira L., Saraiva J, 2011, MA130301GT catalogue of Martian <span class="hlt">impact</span> <span class="hlt">craters</span> and advanced evaluation of <span class="hlt">crater</span> detection algorithms using diverse topography and image datasets. Planetary and Space Science 59: 111-131. [3] Bandeira L, Ding W, Stepinski T, 2012, Detection of sub-kilometer <span class="hlt">craters</span> in high resolution planetary images using shape and texture features. Advances in Space Research 49: 64-74.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.4564E','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.4564E"><span>Lake sedimentological and plant ecological development across the Early Danian hyperthermal, Boltysh <span class="hlt">Impact</span> <span class="hlt">Crater</span>, Ukraine</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Ebinghaus, Alena; Jolley, David; Andrews, Steven; Kemp, David</p> <p>2017-04-01</p> <p>Past hyperthermals and associated negative carbon isotope excursions (CIEs) are inferred to have had significant <span class="hlt">impact</span> on marine environments; however the formation and changes of terrestrial ecosystems across hyperthermals are less well constrained due to the lack of complete and high-resolution data. The Boltysh <span class="hlt">impact</span> <span class="hlt">crater</span>, Ukraine, which formed at the Cretaceous/Palaeogene (K/Pg) boundary at the northern margin of the Tethys Ocean, contains a >400 m thick unique and detailed lacustrine rock record of the Early Danian Dan-C2 hyperthermal. Based on a borehole (hole 42/11) drilled in the central part of the <span class="hlt">crater</span>, we use a combination of sedimentological, palynological and carbon isotope data to 1) characterise and reconstruct lake formation and associated plant ecosystems, and 2) to assess lake sedimentological and ecological response to climatic variabilities during warming. Based on detailed facies analysis, 3 major gradual stages of lake formation are identified, indicating a strong relationship to carbon isotope shifts and associated climatic trends. Initial pre-excursion sedimentation was controlled by <span class="hlt">crater</span> morphology and <span class="hlt">crater</span> rim erosion transporting high amount of sediment into a shallow fresh water lake. During the negative excursion, sediment supply was increasingly characterised by inflow-evaporation ratio variabilities which affected seasonal stratification patterns and longer-term lake levels. An inferred increase in atmospheric pCO2 during the CIE, together with increasing mean annual temperatures, was likely responsible for periodic increases in bioproductivity. Palynological analyses demonstrate a gradual shift from mesic humid dominated vegetation to winterwet savannah-type vegetation at this stage, associated with an increase in mean annual temperatures and decrease in moisture availability. The positive excursion (recovery) and post-excursion stage is characterised by increased <span class="hlt">abundance</span> of temperate mesic humid taxa. This cooling trend</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19800039557&hterms=depression+mexico&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Ddepression%2Bmexico','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19800039557&hterms=depression+mexico&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Ddepression%2Bmexico"><span>Endogenic <span class="hlt">craters</span> on basaltic lava flows - Size frequency distributions</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Greeley, R.; Gault, D. E.</p> <p>1979-01-01</p> <p>Circular <span class="hlt">crater</span> forms, termed collapse depressions, which occur on many basalt flows on the earth have also been detected on the moon and Mars and possibly on Mercury and Io. The admixture of collapse <span class="hlt">craters</span> with <span class="hlt">impact</span> <span class="hlt">craters</span> would affect age determinations of planetary surface units based on <span class="hlt">impact</span> <span class="hlt">crater</span> statistics by making them appear anomalously old. In the work described in the present paper, the techniques conventionally used in planetary <span class="hlt">crater</span> counting were applied to the determination of the size range and size frequency distribution of collapse <span class="hlt">craters</span> on lava flows in Idaho, California, and New Mexico. Collapse depressions range in size from 3 to 80 m in diameter; their cumulative size distributions are similar to those of small <span class="hlt">impact</span> <span class="hlt">craters</span> on the moon.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030079993','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030079993"><span>Results of the Workshop on <span class="hlt">Impact</span> <span class="hlt">Cratering</span>: Bridging the Gap Between Modeling and Observations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Herrick, Robert (Editor); Pierazzo, Elisabetta (Editor)</p> <p>2003-01-01</p> <p>On February 7-9,2003, approximately 60 scientists gathered at the Lunar and Planetary Institute in Houston, Texas, for a workshop devoted to improving knowledge of the <span class="hlt">impact</span> <span class="hlt">cratering</span> process. We (co-conveners Elisabetta Pierazzo and Robert Herrick) both focus research efforts on studying the <span class="hlt">impact</span> <span class="hlt">cratering</span> process, but the former specializes in numerical modeling while the latter draws inferences from observations of planetary <span class="hlt">craters</span>. Significant work has been done in several key areas of <span class="hlt">impact</span> studies over the past several years, but in many respects there seem to be a disconnect between the groups employing different approaches, in particular modeling versus observations. The goal in convening this workshop was to bring together these disparate groups to have an open dialogue for the purposes of answering outstanding questions about the <span class="hlt">impact</span> process and setting future research directions. We were successful in getting participation from most of the major research groups studying the <span class="hlt">impact</span> process. Participants gathered from five continents with research specialties ranging from numerical modeling to field geology, and from small-scale experimentation and geochemical sample analysis to seismology and remote sensing.With the assistance of the scientific advisory committee (Bevan French, Kevin Housen, Bill McKinnon, Jay Melosh, and Mike Zolensky), the workshop was divided into a series of sessions devoted to different aspects of the <span class="hlt">cratering</span> process. Each session was opened by two invited t a b , one given by a specialist in numerical or experimental modeling approaches, and the other by a specialist in geological, geophysical, or geochemical observations. Shorter invited and contributed talks filled out the sessions, which were then concluded with an open discussion time. All modelers were requested to address the question of what observations would better constrain their models, and all observationists were requested to discuss how their observations can</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_18");'>18</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li class="active"><span>20</span></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_20 --> <div id="page_21" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="401"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AIPC.1653b0018A','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AIPC.1653b0018A"><span>Delineating Bukit Bunuh <span class="hlt">impact</span> <span class="hlt">crater</span> boundary by geophysical and geotechnical investigation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Azwin, I. N.; Rosli, S.; Mokhtar, S.; Nordiana, M. M.; Ragu, R. R.; Mark, J.</p> <p>2015-03-01</p> <p>Evidences of <span class="hlt">crater</span> morphology and shock metamorphism in Bukit Bunuh, Lenggong, Malaysia were found during the archaeological research conducted by the Centre for Global Archaeological Research Malaysia, Universiti Sains Malaysia. In order to register Bukit Bunuh as one of the world meteorite <span class="hlt">impact</span> site, detailed studies are needed to verify the boundary of the <span class="hlt">crater</span> accordingly. Geophysical study was conducted utilising the seismic refraction and 2-D electrical resistivity method. Seismic refraction survey was done using ABEM MK8 24 channel seismograph with 14Hz geophones and 40kg weight drop while 2-D electrical resistivity survey was performed using ABEM SAS4000 Terrameter and ES10-64C electrode selector with pole-dipole array. Bedrock depths were digitized from the sections obtained. The produced bedrock topography map shows that there is low bedrock level circulated by high elevated bedrock and interpreted as <span class="hlt">crater</span> and rim respectively with diameter approximately 8km. There are also few spots of high elevated bedrock appear at the centre of the <span class="hlt">crater</span> which interpreted as rebounds zone. Generally, the research area is divided into two layers where the first layer with velocity 400-1100 m/s and resistivity value of 10-800 Om predominantly consists of alluvium mix with gravel and boulders. Second layer represents granitic bedrock with depth of 5-50m having velocity >2100 m/s and resistivity value of >1500 Om. This research is strengthen by good correlation between geophysical data and geotechnical borehole records executed inside and outside of the <span class="hlt">crater</span>, on the rim, as well as at the rebound area.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20030064018&hterms=Impact+environmental&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DImpact%2Benvironmental','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20030064018&hterms=Impact+environmental&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3DImpact%2Benvironmental"><span>Oceanic <span class="hlt">Impact</span>: Mechanisms and Environmental Perturbations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Gersonde, Rainer (Editor); Deutsch, Alex (Editor); Ivanov, Boris A. (Editor); Kyte, Frank T. (Editor)</p> <p>2002-01-01</p> <p>The contents include the following: Oceanic <span class="hlt">impacts</span>-a growing field of fundamental geoscience. Shock metamorphism on the ocean floor (numerical simulations). Numerical modeling of <span class="hlt">impact</span>-induced modifications of the deep-sea floor. Computer modelling of the water resurge at a marine <span class="hlt">impact</span>: the Lockne <span class="hlt">crater</span>, Sweden. Experimental investigation of the role of water in <span class="hlt">impact</span> vaporization chemistry. Calcareous plankton stratigraphy around the Pliocene Eltanin asteroid <span class="hlt">impact</span> area (SE Pacific): documentation and application for geological and paleoceanographic reconstruction. Composition of <span class="hlt">impact</span> melt debris from the Eltanin <span class="hlt">impact</span> strewn field, Bellingshausen Sea. Iridium concentrations and <span class="hlt">abundances</span> of meteoritic ejecta from the Eltanin <span class="hlt">impact</span> in sediment cores from Polarstern expedition ANT XII/4. Unmelted meteoritic debris collected from Eltanin ejecta in Polarstern cores from expedition ANT XII/4. <span class="hlt">Impact</span> tsunami-Eltanin. Ancient <span class="hlt">impact</span> structures on modern continental shelves: The Chesapeake Bay, Montagnais, and Toms Canyon <span class="hlt">craters</span>, Atlantic margin of North America. The Mjolnir marine <span class="hlt">impact</span> <span class="hlt">crater</span> porosity anomaly. Kardla (Hiiu-maa Island, Estonia) - the buried and well-preserved Ordovician marine <span class="hlt">impact</span> structure. Long-term effect of the Kardla <span class="hlt">crater</span> (Hiiu-maa, Estonia) on Late Ordovician carbonate sedimentation. The middle Devonian Kaluga <span class="hlt">impact</span> <span class="hlt">crater</span> (Russia): new interpretation of marine setting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EPSC....9..454R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EPSC....9..454R"><span>The Variability of <span class="hlt">Crater</span> Identification Among Expert and Community <span class="hlt">Crater</span> Analysts</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Robbins, S. J.; Antonenko, I.; Kirchoff, M. R.; Chapman, C. R.; Fassett, C. I.; Herrick, R. R.; Singer, K.; Zanetti, M.; Lehan, C.; Huang, D.; Gay, P.</p> <p>2014-04-01</p> <p>Statistical studies of <span class="hlt">impact</span> <span class="hlt">crater</span> populations have been used to model ages of planetary surfaces for several decades [1]. This assumes that <span class="hlt">crater</span> counts are approximately invariant and a "correct" population will be identified if the analyst is skilled and diligent. However, the reality is that <span class="hlt">crater</span> identification is somewhat subjective, so variability between analysts, or even a single analyst's variation from day-to-day, is expected [e.g., 2, 3]. This study was undertaken to quantify that variability within an expert analyst population and between experts and minimally trained volunteers.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20020073439','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20020073439"><span>Major Element Analysis of the Target Rocks at Meteor <span class="hlt">Crater</span>, Arizona</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>See, Thomas H.; Hoerz, Friedrich; Mittlefehldt, David W.; Varley, Laura; Mertzman, Stan; Roddy, David</p> <p>2002-01-01</p> <p>We collected approximately 400 rock chips in continuous vertical profile at Meteor <span class="hlt">Crater</span>, Arizona, representing, from bottom to top, the Coconino, Toroweap, Kaibab, and Moenkopi Formations to support ongoing compositional analyses of the <span class="hlt">impact</span> melts and their stratigraphic source depth(s) and other studies at Meteor <span class="hlt">Crater</span> that depend on the composition of the target rocks. These rock chips were subsequently pooled into 23 samples for compositional analysis by XRF (x ray fluorescence) methods, each sample reflecting a specific stratigraphic "subsection" approximately 5-10 in thick. We determined the modal <span class="hlt">abundance</span> of quartz, dolomite, and calcite for the entire Kaibab Formation at vertical resolutions of 1-2 meters. The Coconino Formation composes the lower half of the <span class="hlt">crater</span> cavity. It is an exceptionally pure sandstone. The Toroweap is only two inches thick and compositionally similar to Coconino, therefore, it is not a good compositional marker horizon. The Kaibab Formation is approximately 80 in thick. XRD (x ray diffraction) studies show that the Kaibab Formation is dominated by dolomite and quartz, albeit in highly variable proportions; calcite is a minor phase at best. The Kaibab at Meteor <span class="hlt">Crater</span> is therefore a sandy dolomite rather than a limestone, consistent with pronounced facies changes in the Permian of SE Arizona over short vertical and horizontal distances. The Moenkopi forms the 12 in thick cap rock and has the highest Al2O3 and FeO concentrations of all target rocks. With several examples, we illustrate how this systematic compositional and modal characterization of the target ideologies may contribute to an understanding of Meteor <span class="hlt">Crater</span>, such as the depth of its melt zone, and to <span class="hlt">impact</span> <span class="hlt">cratering</span> in general, such as the liberation of CO2 from shocked carbonates.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=PIA09369&hterms=block+chain&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dblock%2Bchain','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=PIA09369&hterms=block+chain&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dblock%2Bchain"><span>Rayed Gratteri <span class="hlt">Crater</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2006-01-01</p> <p><p/> [figure removed for brevity, see original site] Click on image for larger version <p/> This HiRISE image covers the western portion of the primary cavity of Gratteri <span class="hlt">crater</span> situated in the Memnonia Fossae region. Gratteri <span class="hlt">crater</span> is one of five definitive large rayed <span class="hlt">craters</span> on Mars. Gratteri <span class="hlt">crater</span> has a diameter of approximately 6.9 kilometers. <span class="hlt">Crater</span> rays are long, linear features formed from the high-velocity ejection of blocks of material that re-<span class="hlt">impact</span> the surface in linear clusters or chains that appear to emanate from the main or primary cavity. Such <span class="hlt">craters</span> have been long recognized as the 'brightest' and 'freshest' <span class="hlt">craters</span> on the Moon. However, Martian rays differ from lunar rays in that they are not 'bright,' but best recognized by their thermal signature (at night) in 100 meter/pixel THEMIS thermal infrared images. The HiRISE image shows that Gratteri <span class="hlt">crater</span> has well-developed and sharp <span class="hlt">crater</span> morphologic features with no discernable superimposed <span class="hlt">impact</span> <span class="hlt">craters</span>. The HiRISE sub-image shows that this is true for the ejecta and <span class="hlt">crater</span> floor up to the full resolution of the image. Massive slumped blocks of materials on the <span class="hlt">crater</span> floor and the 'spur and gully' morphology with the <span class="hlt">crater</span> wall may suggest that the subsurface in this area may be thick and homogenous. Gratteri <span class="hlt">crater</span>'s ejecta blanket (as seen in THEMIS images) can be described as 'fluidized,' which may be suggestive of the presence of ground-ice that may have helped to 'liquefy' the ejecta as it was deposited near the <span class="hlt">crater</span>. Gratteri's ejecta can be observed to have flowed in and around obstacles including an older, degraded <span class="hlt">crater</span> lying immediately to the SW of Gratteri's primary cavity. <p/> Image PSP_001367_1620 was taken by the High Resolution Imaging Science Experiment (HiRISE) camera onboard the Mars Reconnaissance Orbiter spacecraft on November 10, 2006. The complete image is centered at -17.7 degrees latitude, 199.9 degrees East longitude. The range to the target site was 257.1 km</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009AGUFM.P43B1435D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009AGUFM.P43B1435D"><span>“FRIED EGG”: AN OCEANIC <span class="hlt">IMPACT</span> <span class="hlt">CRATER</span> IN THE MID-ATLANTIC?</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Dias, F. C.; Lourenco, N.; Lobo, A.; Santos de Campos, A.; Pinto de Abreu, M.</p> <p>2009-12-01</p> <p>Analysis of a multibeam echosounder hydrographic survey performed in the Southern Azores Platform under the scope of the Portuguese Continental Shelf Project has revealed a large scale bathymetric structure nicknamed “Fried Egg” due to its well defined morphology. Laying at about 2km depth, this structure consists of a roughly circular 6km wide depression 110m below the surrounding ocean bottom, with a circular dome shaped central uplift 3km in diameter and with a base to top height of 300m. The associated backscatter signal presents a distinctive ring-like signature corresponding to the lower flank section of the dome, suggesting the outcrop of hard rock material. The remaining backscatter signal seems to correspond to widespread sediments. No lava flows are apparent either within the structure or on its surroundings. All these properties are compatible with the record of terrestrial <span class="hlt">impact</span> <span class="hlt">craters</span>, thus making of “Fried Egg” a potential oceanic <span class="hlt">impact</span> <span class="hlt">crater</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19890012013','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19890012013"><span>Non-random <span class="hlt">cratering</span> flux in recent time</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schultz, P. H.</p> <p>1988-01-01</p> <p>Proposed periodic cycles of mass mortality have been linked to periodic changes in the <span class="hlt">impact</span> flux on Earth. Such changes in the <span class="hlt">impact</span> flux, however, also should be recorded on the Moon. Previous studies have concluded that the <span class="hlt">impact</span> flux on the Moon over the last 1 to 2 billion years has been reasonably constant, but sudden changes in the <span class="hlt">impact</span> flux over time intervals as short as 30 my could not be detected in these studies unless the added <span class="hlt">crater</span> population greatly exceeded the cumulative <span class="hlt">cratering</span> record. Consequently this study focuses only on bright-rayed <span class="hlt">craters</span> larger than 1 km thereby not only limiting the study to recent <span class="hlt">craters</span> but also largely eliminating contamination by secondary <span class="hlt">craters</span>. Preservation of ray patterns and other fine-scale surface textures in the ejecta provides first-order culling of <span class="hlt">craters</span> younger than Tycho, i.e., about 100 my. Although a periodic change in the <span class="hlt">impact</span> flux in the Earth-Moon system cannot yet be confirmed from the data, a non-random component appears to exist with an increased flux around 7 and 15 my. The concentrations in different quadrants of the lunar hemisphere would be consistent with a shower of debris generally smaller than 0.5 km.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007M%26PS...42..709K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007M%26PS...42..709K"><span>Uppermost <span class="hlt">impact</span> fallback layer in the Bosumtwi <span class="hlt">crater</span> (Ghana): Mineralogy, geochemistry, and comparison with Ivory Coast tektites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Koeberl, Christian; Brandstätter, Franz; Glass, Billy P.; Hecht, Lutz; Mader, Dieter; Reimold, Wolf Uwe</p> <p></p> <p>In 2004, an International Continental Scientific Drilling Program (ICDP) drilling project at the Bosumtwi <span class="hlt">impact</span> <span class="hlt">crater</span>, Ghana (10.5 km in diameter, 1.07 Myr old), was performed to study the sediments that fill the lake as well as the underlying impactites. In one (LB-05) of 16 cores drilled into the lake sediments, the zone between the <span class="hlt">impact</span> breccias and the post-<span class="hlt">impact</span> sediments was penetrated, preserving the final, fine-grained <span class="hlt">impact</span> fallback layer. This ~30 cm thick layer contains in the top 10 cm “accretionary” lapilli, microtektite-like glass spherules, and shocked quartz grains. Glass particles -- mostly of splash form less than 1 mm size -- make up the bulk of the grains (~70-78% by number) in the coarser size fraction (>125 μm) of the top of the fallback layer. About one-third of all quartz grains in the uppermost part of the layer are shocked, with planar deformation features (PDFs); almost half of these grains are highly shocked, with 3 or more sets of PDFs. K-feldspar grains also occur and some show shock deformation. The <span class="hlt">abundance</span> of shocked quartz grains and the average shock level as indicated by the number of sets of PDFs, for both quartz and K-feldspar, decrease with depth into the layer. The well-preserved glass spherules and fragments are chemically rather homogeneous within each particle, and also show relatively small variations between the various particles. On average, the composition of the fallback spherules from core LB-5B is very similar to the composition of Ivory Coast tektites and microtektites, with the exception of CaO contents, which are about 1.5 to 2 times higher in the fallback spherules. This is a rare case in which the uppermost fallback layer and the transition to the post-<span class="hlt">impact</span> sediments has been preserved in an <span class="hlt">impact</span> structure; its presence indicates that the impactite sequence at Bosumtwi is complete and that Bosumtwi is a very well-preserved <span class="hlt">impact</span> <span class="hlt">crater</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150001944','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150001944"><span>Mineralogy and Genesis of the Windjana Sandstone, Kimberley Area, Gale <span class="hlt">Crater</span>, Mars</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Treiman, A. H.; Bish, D.; Ming, D. W.; Grotzinger, J.; Vaniman, D. T.; Baker, M. B.; Farmer, J.; Chipera, S.; Downs, R. T.; Morris, R. V.; <a style="text-decoration: none; " href="javascript:void(0); " onClick="displayelement('author_20150001944'); toggleEditAbsImage('author_20150001944_show'); toggleEditAbsImage('author_20150001944_hide'); "> <img style="display:inline; width:12px; height:12px; " src="images/arrow-up.gif" width="12" height="12" border="0" alt="hide" id="author_20150001944_show"> <img style="width:12px; height:12px; display:none; " src="images/arrow-down.gif" width="12" height="12" border="0" alt="hide" id="author_20150001944_hide"></p> <p>2015-01-01</p> <p>MSL Curiosity investigated the Windjana sandstone outcrop, in the Kimberley area of Gale <span class="hlt">Crater</span>, and obtained mineralogical analyses with the CheMin XRD instrument. Windjana is remarkable in containing an <span class="hlt">abundance</span> of potassium feldspar (and thus K in its bulk chemistry) combined with a low <span class="hlt">abundance</span> of plagioclase (and low Na/K in its chemistry). The source of this enrichment in K is not clear, but has significant implications for the geology of Gale <span class="hlt">Crater</span> and of Mars. The high K could be intrinsic to the sediment and imply that the sediment source area (Gale <span class="hlt">Crater</span> rim) includes K-rich basalts and possibly more evolved rocks derived from alkaline magmas. Alternatively, the high K could be diagenetic and imply that the Gale <span class="hlt">Crater</span> sediments were altered by K-rich aqueous fluids after deposition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70014824','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70014824"><span>Computer simulations of large asteroid <span class="hlt">impacts</span> into oceanic and continental sites--preliminary results on atmospheric, <span class="hlt">cratering</span> and ejecta dynamics</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Roddy, D.J.; Schuster, S.H.; Rosenblatt, M.; Grant, L.B.; Hassig, P.J.; Kreyenhagen, K.N.</p> <p>1987-01-01</p> <p>Computer simulations have been completed that describe passage of a 10-km-diameter asteroid through the Earth's atmosphere and the subsequent <span class="hlt">cratering</span> and ejecta dynamics caused by <span class="hlt">impact</span> of the asteroid into both oceanic and continental sites. The asteroid was modeled as a spherical body moving vertically at 20 km/s with a kinetic energy of 2.6 ?? 1030 ergs (6.2 ?? 107 Mt ). Detailed material modeling of the asteroid, ocean, crustal units, sedimentary unit, and mantle included effects of strength and fracturing, generic asteroid and rock properties, porosity, saturation, lithostatic stresses, and geothermal contributions, each selected to simulate <span class="hlt">impact</span> and geologic conditions that were as realistic as possible. Calculation of the passage of the asteroid through a U.S. Standard Atmosphere showed development of a strong bow shock wave followed by a highly shock compressed and heated air mass. Rapid expansion of this shocked air created a large low-density region that also expanded away from the <span class="hlt">impact</span> area. Shock temperatures in air reached ???20,000 K near the surface of the uplifting <span class="hlt">crater</span> rim and were as high as ???2000 K at more than 30 km range and 10 km altitude. Calculations to 30 s showed that the shock fronts in the air and in most of the expanding shocked air mass preceded the formation of the <span class="hlt">crater</span>, ejecta, and rim uplift and did not interact with them. As <span class="hlt">cratering</span> developed, uplifted rim and target material were ejected into the very low density, shock-heated air immediately above the forming <span class="hlt">crater</span>, and complex interactions could be expected. Calculations of the <span class="hlt">impact</span> events showed equally dramatic effects on the oceanic and continental targets through an interval of 120 s. Despite geologic differences in the targets, both <span class="hlt">cratering</span> events developed comparable dynamic flow fields and by ???29 s had formed similar-sized transient <span class="hlt">craters</span> ???39 km deep and ???62 km across. Transient-rim uplift of ocean and crust reached a maximum altitude of nearly</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA21636.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA21636.html"><span>A South Polar Pit or an <span class="hlt">Impact</span> <span class="hlt">Crater</span>?</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-05-30</p> <p>This observation from NASA's Mars Reconnaissance Orbiter show it is late summer in the Southern hemisphere, so the Sun is low in the sky and subtle topography is accentuated in orbital images. We see many shallow pits in the bright residual cap of carbon dioxide ice (also called "Swiss cheese terrain"). There is also a deeper, circular formation that penetrates through the ice and dust. This might be an <span class="hlt">impact</span> <span class="hlt">crater</span> or it could be a collapse pit. https://photojournal.jpl.nasa.gov/catalog/PIA21636</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19780060135&hterms=model+geological&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dmodel%2Bgeological','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19780060135&hterms=model+geological&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dmodel%2Bgeological"><span><span class="hlt">Impact</span> <span class="hlt">cratering</span> phenomenon for the Ries multiring structure based on constraints of geological, geophysical, and petrological studies and the nature of the <span class="hlt">impacting</span> body</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Chao, E. C. T.; Minkin, J. A.</p> <p>1977-01-01</p> <p>In the present paper, an attempt is made to delineate, on the basis of field and laboratory data, the phenomenon of formation of the Ries multiring basin - the best preserved very large terrestrial <span class="hlt">impact</span> structure. The model proposed conforms to constraints imposed by geological, geophysical, and petrological studies and by the nature of the postulated <span class="hlt">impacting</span> body. It is also based on the <span class="hlt">impact</span> features of a stony meteorite measuring 3 km in diameter at an <span class="hlt">impact</span> velocity of 15 km/sec. The schematic reconstruction shows that critical to the production of a shallow <span class="hlt">crater</span> is shallow <span class="hlt">impact</span> penetration (shallow depth of burst). This and the nonballistic ejection of excavated material appear to be genetically related, i.e., if extensive nonballistic transport is recognized, then the associated <span class="hlt">crater</span> must be a shallow structure and vice versa. This also means the shallow configuration of a <span class="hlt">crater</span> may not have anything to do with postcratering readjustment.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920001565','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920001565"><span>Gradational evolution of young, simple <span class="hlt">impact</span> <span class="hlt">craters</span> on the Earth</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grant, J. A.; Schultz, P. H.</p> <p>1991-01-01</p> <p>From these three <span class="hlt">craters</span>, a first order gradational evolutionary sequence can be proposed. As <span class="hlt">crater</span> rims are reduced by backwasting and downwasting through fluvial and mass wasting processes, <span class="hlt">craters</span> are enlarged by approx. 10 pct. Enlargement of drainages inside the <span class="hlt">crater</span> eventually forms rim breaches, thereby capturing headward portions of exterior drainages. At the same time, the relative importance of gradational processes may reverse on the ejecta: aeolian activity may supersede fluvial incisement and fan formation at late stages of modification. Despite actual high drainage densities on the <span class="hlt">crater</span> exterior during early stages of gradation, the subtle scale of these systems results in low density estimates from air photos and satellite images. Because signatures developed on surfaces around all three <span class="hlt">craters</span> appear to be mostly gradient dependent, they may not be unique to simple <span class="hlt">crater</span> morphologies. Similar signatures may develop on portions of complex <span class="hlt">craters</span> as well; however, important differences may also occur.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050174579','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050174579"><span>Distant Secondary <span class="hlt">Craters</span> and Age Constraints on Young Martian Terrains</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>McEwen, A.; Preblich, B.; Turtle, E.; Studer, D.; Artemieva, N.; Golombek, M.; Hurst, M.; Kirk, R.; Burr, D.</p> <p>2005-01-01</p> <p>Are small (less than approx. 1 km diameter) <span class="hlt">craters</span> on Mars and the Moon dominated by primary <span class="hlt">impacts</span>, by secondary <span class="hlt">impacts</span> of much larger primary <span class="hlt">craters</span>, or are both primaries and secondaries significant? This question is critical to age constraints for young terrains and for older terrains covering small areas, where only small <span class="hlt">craters</span> are superimposed on the unit. If the martian rayed <span class="hlt">crater</span> Zunil is representative of large <span class="hlt">impact</span> events on Mars, then the density of secondaries should exceed the density of primaries at diameters a factor of 1000 smaller than that of the largest contributing primary <span class="hlt">crater</span>. On the basis of morphology and depth/diameter measurements, most small <span class="hlt">craters</span> on Mars could be secondaries. Two additional observations (discussed below) suggest that the production functions of Hartmann and Neukum predict too many primary <span class="hlt">craters</span> smaller than a few hundred meters in diameter. Fewer small, high-velocity <span class="hlt">impacts</span> may explain why there appears to be little <span class="hlt">impact</span> regolith over Amazonian terrains. Martian terrains dated by small <span class="hlt">craters</span> could be older than reported in recent publications.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20090033478','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20090033478"><span><span class="hlt">Cratering</span> Equations for Zinc Orthotitanate Coated Aluminum</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hyde, James; Christiansen, Eric; Liou, Jer-Chyi; Ryan, Shannon</p> <p>2009-01-01</p> <p>The final STS-125 servicing mission (SM4) to the Hubble Space Telescope (HST) in May of 2009 saw the return of the 2nd Wide Field Planetary Camera (WFPC2) aboard the shuttle Discovery. This hardware had been in service on HST since it was installed during the SM1 mission in December of 1993 yielding one of the longest low Earth orbit exposure times (15.4 years) of any returned space hardware. The WFPC2 is equipped with a 0.8 x 2.2 m radiator for thermal control of the camera electronics (Figure 1). The space facing surface of the 4.1 mm thick aluminum radiator is coated with Z93 zinc orthotitanate thermal control paint with a nominal thickness of 0.1 0.2 mm. Post flight inspections of the radiator panel revealed hundreds of micrometeoroid/orbital debris (MMOD) <span class="hlt">impact</span> <span class="hlt">craters</span> ranging in size from less than 300 to nearly 1000 microns in diameter. The Z93 paint exhibited large spall areas around the larger <span class="hlt">impact</span> sites (Figure 2) and the <span class="hlt">craters</span> observed in the 6061-T651 aluminum had a different shape than those observed in uncoated aluminum. Typical hypervelocity <span class="hlt">impact</span> <span class="hlt">craters</span> in aluminum have raised lips around the <span class="hlt">impact</span> site. The <span class="hlt">craters</span> in the HST radiator panel had suppressed <span class="hlt">crater</span> lips, and in some cases multiple <span class="hlt">craters</span> were present instead of a single individual <span class="hlt">crater</span>. Humes and Kinard observed similar behavior after the WFPC1 post flight inspection and assumed the Z93 coating was acting like a bumper in a Whipple shield. Similar paint behavior (spall) was also observed by Bland2 during post flight inspection of the International Space Station (ISS) S-Band Antenna Structural Assembly (SASA) in 2008. The SASA, with similar Z93 coated aluminum, was inspected after nearly 4 years of exposure on the ISS. The multi-<span class="hlt">crater</span> phenomena could be a function of the density, composition, or <span class="hlt">impact</span> obliquity angle of the <span class="hlt">impacting</span> particle. For instance, a micrometeoroid particle consisting of loosely bound grains of material could be responsible for creating the</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2009EGUGA..11.7702S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2009EGUGA..11.7702S"><span>Comparison of <span class="hlt">Impact</span> <span class="hlt">Crater</span> Size-Frequency Distributions (SFD) on Saturnian Satellites with Other Solar-System Bodies</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmedemann, N.; Neukum, G.; Denk, T.; Wagner, R.; Hartmann, O.</p> <p>2009-04-01</p> <p>The examination of the geologic history of the saturnian satellites is a major goal of the Cassini imaging experiment (ISS) [5]. The study of the <span class="hlt">impact</span> <span class="hlt">crater</span>-SFD is necessary to derive ages of the saturnian satellite surface units. Furthermore it can be used for resolving the main impactor source and the impactor orbital characteristics for understanding the nature of the bombardment. While large and old areas are suited to measure the branch of large <span class="hlt">crater</span> sizes, smaller <span class="hlt">craters</span> can be found in a state of production only at relatively young areas on the saturnian satellites. The <span class="hlt">impact-crater</span> SFD is derived only from such <span class="hlt">crater</span> populations which are in production. Hence the measurement of the whole production function in one specific area is impossible. Therefore we have to measure it piece-wise in <span class="hlt">crater</span> size range in a number of suitable areas. On Iapetus the production function has been measured in seven <span class="hlt">crater</span> size range pieces, covering a <span class="hlt">crater</span> size range from 0.15 km to 700 km. At the same <span class="hlt">crater</span> size, these areas have somewhat different <span class="hlt">crater</span> frequencies, since they are of different ages. The <span class="hlt">crater</span> frequency differences of the respective pieces to each other have to be taken out, in order to obtain continuous curves. We have achieved that by normalizing the frequencies measured on the older surface units at the respective smallest <span class="hlt">crater</span> sizes to the tail ends of the <span class="hlt">crater</span> frequencies for the largest <span class="hlt">craters</span> on the younger surface units. The resulting continuous curves give us a reliable production SFD over the whole accessible range. Doing so, we assumed that the production SFD has not changed over time in the parts of the SFD not directly accessible by measurement. Hence the resulting SFD curve is a consequence of a compilation of measurements taken in different areas. Intensive analyses of the <span class="hlt">crater</span> diameter SFD of the lunar surface have revealed a characteristic W-shaped curve, when it is R-plotted. <span class="hlt">Crater</span> counting on other planetary surfaces</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70178874','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70178874"><span><span class="hlt">Cratering</span> on Ceres: Implications for its crust and evolution</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Hiesinger, H.; Marchi, S.; Schmedemann, N.; Schenk, P.; Pasckert, J. H.; Neesemann, A.; O'Brien, D. P.; Kneissl, T.; Ermakov, A.; Fu, R.R.; Bland, M. T.; Nathues, A.; Platz, T.; Williams, D.A.; Jaumann, R.; Castillo-Rogez, J. C.; Ruesch, O.; Schmidt, B.; Park, R.S.; Preusker, F.; Buczkowski, D.L.; Russell, C.T.; Raymond, C.A.</p> <p>2016-01-01</p> <p>Thermochemical models have predicted that Ceres, is to some extent, differentiated and should have an icy crust with few or no <span class="hlt">impact</span> <span class="hlt">craters</span>. We present observations by the Dawn spacecraft that reveal a heavily <span class="hlt">cratered</span> surface, a heterogeneous <span class="hlt">crater</span> distribution, and an apparent absence of large <span class="hlt">craters</span>. The morphology of some <span class="hlt">impact</span> <span class="hlt">craters</span> is consistent with ice in the subsurface, which might have favored relaxation, yet large unrelaxed <span class="hlt">craters</span> are also present. Numerous <span class="hlt">craters</span> exhibit polygonal shapes, terraces, flowlike features, slumping, smooth deposits, and bright spots. <span class="hlt">Crater</span> morphology and simple-to-complex <span class="hlt">crater</span> transition diameters indicate that the crust of Ceres is neither purely icy nor rocky. By dating a smooth region associated with the Kerwan <span class="hlt">crater</span>, we determined absolute model ages (AMAs) of 550 million and 720 million years, depending on the applied chronology model.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014EGUGA..1610109H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014EGUGA..1610109H"><span>Boguslawsky <span class="hlt">crater</span>, Moon: Geology of the Luna-Glob Landing Site</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hiesinger, Harald; Ivanov, Mikhail; Hendrik Paskert, Jan; Bauch, Karin; Howes van der Bogert, Carolyn</p> <p>2014-05-01</p> <p> associated with small <span class="hlt">impact</span> <span class="hlt">craters</span> (mostly <500 m diameter) can be up to 45 degrees. Using LRO Diviner data, our thermal model [4] indicates several areas with higher thermal inertia and, thus, rock <span class="hlt">abundances</span>. However, many of those areas likely can be attributed to temperature differences caused by insufficient topographic correction. However, we found several areas with high rock <span class="hlt">abundances</span> that are clearly not affected by topography and are associated with the morphologically freshest <span class="hlt">craters</span>. Manual boulder counts for those areas on LRO NAC images confirm a large number of boulders on the surface. For example, in an area of about 4 km2, we counted more than 16,000 boulders between ~0.5 m and up to 13 m in size around a small <span class="hlt">crater</span> at the eastern edge of the western landing ellipse. References: [1] Neukum et al. (2001), Space Sci. Rev. 96; [2] Wilhelms (1987) USGS Prof. Paper 1348; [3] Wilhelms et al. (1979) USGS I-1162; [4] Bauch et al. (2014), Submitted to PSS.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/22391293-delineating-bukit-bunuh-impact-crater-boundary-geophysical-geotechnical-investigation','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/22391293-delineating-bukit-bunuh-impact-crater-boundary-geophysical-geotechnical-investigation"><span>Delineating Bukit Bunuh <span class="hlt">impact</span> <span class="hlt">crater</span> boundary by geophysical and geotechnical investigation</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Azwin, I. N., E-mail: nurazwinismail@yahoo.com; Rosli, S.; Nordiana, M. M.</p> <p>2015-03-30</p> <p>Evidences of <span class="hlt">crater</span> morphology and shock metamorphism in Bukit Bunuh, Lenggong, Malaysia were found during the archaeological research conducted by the Centre for Global Archaeological Research Malaysia, Universiti Sains Malaysia. In order to register Bukit Bunuh as one of the world meteorite <span class="hlt">impact</span> site, detailed studies are needed to verify the boundary of the <span class="hlt">crater</span> accordingly. Geophysical study was conducted utilising the seismic refraction and 2-D electrical resistivity method. Seismic refraction survey was done using ABEM MK8 24 channel seismograph with 14Hz geophones and 40kg weight drop while 2-D electrical resistivity survey was performed using ABEM SAS4000 Terrameter and ES10-64Cmore » electrode selector with pole-dipole array. Bedrock depths were digitized from the sections obtained. The produced bedrock topography map shows that there is low bedrock level circulated by high elevated bedrock and interpreted as <span class="hlt">crater</span> and rim respectively with diameter approximately 8km. There are also few spots of high elevated bedrock appear at the centre of the <span class="hlt">crater</span> which interpreted as rebounds zone. Generally, the research area is divided into two layers where the first layer with velocity 400-1100 m/s and resistivity value of 10-800 Om predominantly consists of alluvium mix with gravel and boulders. Second layer represents granitic bedrock with depth of 5-50m having velocity >2100 m/s and resistivity value of >1500 Om. This research is strengthen by good correlation between geophysical data and geotechnical borehole records executed inside and outside of the <span class="hlt">crater</span>, on the rim, as well as at the rebound area.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70010404','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70010404"><span>Moon-Mercury: Relative preservation states of secondary <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Scott, D.H.</p> <p>1977-01-01</p> <p>Geologic mapping of the Kuiper quadrangle of Mercury and other geologic studies of the planet indicate that secondary <span class="hlt">craters</span> are much better preserved than those on the moon around primary <span class="hlt">craters</span> of similar size and morphology. Among the oldest recognized secondary <span class="hlt">craters</span> on the moon associated with <span class="hlt">craters</span> 100 km across or less are those of Posidonius, Atlas and Plato; these <span class="hlt">craters</span> have been dated as middle to late Imbrian in age. Many <span class="hlt">craters</span> on Mercury with dimensions, morphologies and superposed <span class="hlt">crater</span> densities similar to these lunar <span class="hlt">craters</span> have fields and clusters of fresher appearing secondary <span class="hlt">craters</span>. The apparent differences between secondary-<span class="hlt">crater</span> morphology and parent <span class="hlt">crater</span> may be due in part to: (1) rapid isostatic adjustment of the parent <span class="hlt">crater</span>; (2) different <span class="hlt">impact</span> fluxes between the two planets; and (or) (3) to the greater concentration of Mercurian secondaries around <span class="hlt">impact</span> areas, thereby accentuating <span class="hlt">crater</span> forms. Another factor which may contribute to the better state of preservation of Mercurian secondaries relative to the moon is the difference in <span class="hlt">crater</span> ejecta velocities on both bodies. These velocities have been calculated for fields of secondary <span class="hlt">craters</span> at about equal ranges from lunar and Mercurian parent <span class="hlt">craters</span>. Results show that ejection velocities of material producing most of the secondary <span class="hlt">craters</span> are rather low (<1 km/s) but velocities on Mercury are about 50% greater than those on the moon for equivalent ranges. Higher velocities may produce morphologically enhanced secondary <span class="hlt">craters</span> which may account for their better preservation with time. ?? 1977.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_19");'>19</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li class="active"><span>21</span></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_21 --> <div id="page_22" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="421"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018P%26SS..153..142S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018P%26SS..153..142S"><span>Global and local re-<span class="hlt">impact</span> and velocity regime of ballistic ejecta of boulder <span class="hlt">craters</span> on Ceres</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schulzeck, F.; Schröder, S. E.; Schmedemann, N.; Stephan, K.; Jaumann, R.; Raymond, C. A.; Russell, C. T.</p> <p>2018-04-01</p> <p>Imaging by the Dawn-spacecraft reveals that fresh <span class="hlt">craters</span> on Ceres below 40 km often exhibit numerous boulders. We investigate how the fast rotating, low-gravity regime on Ceres influences their deposition. We analyze size-frequency distributions of ejecta blocks of twelve boulder <span class="hlt">craters</span>. Global and local landing sites of boulder <span class="hlt">crater</span> ejecta and boulder velocities are determined by the analytical calculation of elliptic particle trajectories on a rotating body. The cumulative distributions of boulder diameters follow steep-sloped power-laws. We do not find a correlation between boulder size and the distance of a boulder to its primary <span class="hlt">crater</span>. Due to Ceres' low gravitational acceleration and fast rotation, ejecta of analyzed boulder <span class="hlt">craters</span> (8-31 km) can be deposited across the entire surface of the dwarf planet. The particle trajectories are strongly influenced by the Coriolis effect as well as the <span class="hlt">impact</span> geometry. Fast ejecta of high-latitude <span class="hlt">craters</span> accumulate close to the pole of the opposite hemisphere. Fast ejecta of low-latitude <span class="hlt">craters</span> wraps around the equator. Rotational effects are also relevant for the low-velocity regime. Boulders are ejected at velocities up to 71 m/s.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA00479.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA00479.html"><span>Venus - Complex <span class="hlt">Crater</span> Dickinson in NE Atalanta Region</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>1996-11-26</p> <p>This Magellan image is centered at 74.6 degrees north latitude and 177.3 east longitude, in the northeastern Atalanta Region of Venus. The image is approximately 185 kilometers (115 miles) wide at the base and shows Dickinson, an <span class="hlt">impact</span> <span class="hlt">crater</span> 69 kilometers (43 miles) in diameter. The <span class="hlt">crater</span> is complex, characterized by a partial central ring and a floor flooded by radar-dark and radar-bright materials. Hummocky, rough-textured ejecta extend all around the <span class="hlt">crater</span>, except to the west. The lack of ejecta to the west may indicate that the impactor that produced the <span class="hlt">crater</span> was an oblique <span class="hlt">impact</span> from the west. Extensive radar-bright flows that emanate from the <span class="hlt">crater</span>'s eastern walls may represent large volumes of <span class="hlt">impact</span> melt, or they may be the result of volcanic material released from the subsurface during the <span class="hlt">cratering</span> event. http://photojournal.jpl.nasa.gov/catalog/PIA00479</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016GeCoA.180...33F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016GeCoA.180...33F"><span>Target-projectile interaction during <span class="hlt">impact</span> melting at Kamil <span class="hlt">Crater</span>, Egypt</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fazio, Agnese; D'Orazio, Massimo; Cordier, Carole; Folco, Luigi</p> <p>2016-05-01</p> <p>In small meteorite <span class="hlt">impacts</span>, the projectile may survive through fragmentation; in addition, it may melt, and chemically and physically interact with both shocked and melted target rocks. However, the mixing/mingling between projectile and target melts is a process still not completely understood. Kamil <span class="hlt">Crater</span> (45 m in diameter; Egypt), generated by the hypervelocity <span class="hlt">impact</span> of the Gebel Kamil Ni-rich ataxite on sandstone target, allows to study the target-projectile interaction in a simple and fresh geological setting. We conducted a petrographic and geochemical study of macroscopic <span class="hlt">impact</span> melt lapilli and bombs ejected from the <span class="hlt">crater</span>, which were collected during our geophysical campaign in February 2010. Two types of glasses constitute the <span class="hlt">impact</span> melt lapilli and bombs: a white glass and a dark glass. The white glass is mostly made of SiO2 and it is devoid of inclusions. Its negligible Ni and Co contents suggest derivation from the target rocks without interaction with the projectile (<0.1 wt% of projectile contamination). The dark glass is a silicate melt with variable contents of Al2O3 (0.84-18.7 wt%), FeOT (1.83-61.5 wt%), and NiO (<0.01-10.2 wt%). The dark glass typically includes fragments (from few μm to several mm in size) of shocked sandstone, diaplectic glass, lechatelierite, and Ni-Fe metal blebs. The metal blebs are enriched in Ni compared to the Gebel Kamil meteorite. The dark glass is thus a mixture of target and projectile melts (11-12 wt% of projectile contamination). Based on recently proposed models for target-projectile interaction and for <span class="hlt">impact</span> glass formation, we suggest a scenario for the glass formation at Kamil. During the transition from the contact and compression stage and the excavation stage, projectile and target liquids formed at their interface and chemically interact in a restricted zone. Projectile contamination affected only a shallow portion of the target rocks. The SiO2 melt that eventually solidified as white glass behaved as</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014JGRE..119.1914F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014JGRE..119.1914F"><span>Regolith thickness over Sinus Iridum: Results from morphology and size-frequency distribution of small <span class="hlt">impact</span> <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fa, Wenzhe; Liu, Tiantian; Zhu, Meng-Hua; Haruyama, Junichi</p> <p>2014-08-01</p> <p>High-resolution optical images returned from recent lunar missions provide a new chance for estimation of lunar regolith thickness using morphology and the size-frequency distribution of small <span class="hlt">impact</span> <span class="hlt">craters</span>. In this study, regolith thickness over the Sinus Iridum region is estimated using Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Cameras (NACs) images. A revised relationship between <span class="hlt">crater</span> geometry and regolith thickness is proposed based on old experimental data that takes into considering the effect of the illumination angle of the images. In total, 227 high-resolution LROC NAC images are used, and 378,556 <span class="hlt">impact</span> <span class="hlt">craters</span> with diameters from 4.2 to 249.8 m are counted, and their morphologies are identified. Our results show that 50% of the Sinus Iridum region has a regolith thickness between 5.1 and 10.7 m, and the mean and median regolith thicknesses are 8.5 and 8.0 m, respectively. There are substantial regional variations in the regolith thickness, with its median value varying from 2.6 to 12.0 m for most regions. Local variations of regolith thickness are found to be correlated with the lunar surface age: the older the surface, the greater the thickness. In addition, sporadically distributed <span class="hlt">impact</span> ejecta and <span class="hlt">crater</span> rays are associated with relatively larger regolith thickness, which might result from excavation and transport of materials during the formation of the secondaries of Copernican-aged <span class="hlt">craters</span>. Our estimated regolith thickness can help with future analysis of Chang'E-3 lunar penetrating radar echoes and studies of the subsurface stratigraphic structure of the Moon.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20170003184&hterms=moon&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dmoon','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20170003184&hterms=moon&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3Dmoon"><span>Secondary <span class="hlt">Crater</span>-Initiated Debris Flow on the Moon</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Martin-Wells, K. S.; Campbell, D. B.; Campbell, B. A.; Carter, L. M.; Fox, Q.</p> <p>2016-01-01</p> <p>In recent work, radar circular polarization echo properties have been used to identify "secondary" <span class="hlt">craters</span> without distinctive secondary morphologies. Because of the potential for this method to improve our knowledge of secondary <span class="hlt">crater</span> population-in particular the effect of secondary populations on <span class="hlt">crater</span>- derived ages based on small <span class="hlt">craters</span>-it is important to understand the origin of radar polarization signatures associated with secondary <span class="hlt">impacts</span>. In this paper, we utilize Lunar Reconnaissance Orbiter Camera photographs to examine the geomorphology of secondary <span class="hlt">craters</span> with radar circular polarization ratio enhancements. Our investigation reveals evidence of dry debris flow with an <span class="hlt">impact</span> melt component at such secondary <span class="hlt">craters</span>. We hypothesize that these debris flows were initiated by the secondary <span class="hlt">impacts</span> themselves, and that they have entrained blocky material ejected from the secondaries. By transporting this blocky material downrange, we propose that these debris flows (rather than solely ballistic emplacement) are responsible for the tail-like geometries of enhanced radar circular polarization ratio associated with the secondary <span class="hlt">craters</span> investigated in this work. Evidence of debris flow was observed at both clustered and isolated secondary <span class="hlt">craters</span>, suggesting that such flow may be a widespread occurrence, with important implications for the mixing of primary and local material in <span class="hlt">crater</span> rays.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA21021.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA21021.html"><span>Small Expanded <span class="hlt">Craters</span> in the Northern Lowlands</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2016-08-24</p> <p>This image shows many small <span class="hlt">craters</span> over a larger degraded one in the northern lowlands. These small <span class="hlt">craters</span> are smoother and shallower than their counterparts closer to the equator. Scientists believe this difference is a result of <span class="hlt">impact</span> into a region with subsurface ice, which sublimates when exposed to the Martian atmosphere. This causes the <span class="hlt">crater</span> to gradually expand and flatten after <span class="hlt">impact</span>. http://photojournal.jpl.nasa.gov/catalog/PIA21021</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19970030228&hterms=TNT&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DTNT','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19970030228&hterms=TNT&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DTNT"><span>The Cretaceous-Tertiary <span class="hlt">Impact</span> <span class="hlt">Crater</span> and the Cosmic Projectile that Produced it</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sharpton, Virgil L.; Marin, Luis E.</p> <p>1997-01-01</p> <p>Evidence gathered to date from topographic data, geophysical data, well logs, and drill-core samples indicates that the buried Chicxulub basin, the source <span class="hlt">crater</span> for the approximately 65 Ma Cretaceous-Tertiary (K/T) boundary deposits, is approximately 300 km in diameter. A prominent topographic ridge and a ring of gravity anomalies mark the position of the basin rim at approximately 150 km from the center. Wells in this region recovered thick sequences of <span class="hlt">impact</span>-generated breccias at 200-300 m below present sea level. Inside the rim, which has been severely modified by erosion following <span class="hlt">impact</span>, the subsurface basin continues to deepen until near the center it is approximately 1 km deep. The best planetary analog for this <span class="hlt">crater</span> appears to be the 270 km-diameter Mead basin on Venus. Seismic reflection data indicate that the central zone of downward displacement and excavation (the transient <span class="hlt">crater</span> is approximately 130 km in diameter, consistent with previous studies of gravity anomaly data). Our analysis of projectile characteristics utilizes this information, coupled with conventional scaling relationships, and geochemical constraints on the mass of extraterrestrial material deposited within the K/T boundary layer. Results indicate that the Chicxulub <span class="hlt">crater</span> would most likely be formed by a long-period comet composed primarily of nonsilicate materials (ice, hydrocarbons, etc.) and subordinate amounts (less than or equal to 50 percent) primitive chondritic material. This collision would have released the energy equivalent to between 4 x 10(exp 8) and 4 x 10(exp 9) megatons of TNT. Studies of terrestrial <span class="hlt">impact</span> rates suggest that such an event would have a mean production rate of approximately 1.25 x 10(exp -9) y(exp -1). This rate is considerably lower than that of the major mass extinctions over the last 250 million years (approximately 5 x 10(exp -7) y(exp -1). Consequently, while there is substantial circumstantial evidence establishing the cause-effect link</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20030110948&hterms=Preservation&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DPreservation','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20030110948&hterms=Preservation&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DPreservation"><span><span class="hlt">Impact</span> <span class="hlt">Craters</span> of Venus with D Greater Than 5 km Classified Based on Degree of Preservation of the Associated Radar-Dark Deposits</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Basilevsky, A. T.; Head, J. W.; Setyaeva, I. V.</p> <p>2003-01-01</p> <p>This is a further continuation of work, which studied <span class="hlt">craters</span> greater than or equal to 30 km in diameter. That work subdivided <span class="hlt">craters</span> based on character of the associated radar dark deposits. It was suggested and then confirmed that the most pristine deposits of that sort are radar-dark parabolas. Non-parabolic radar-dark halos represent the next stage of the deposit evolution and then with time they disappear. So presence and character of <span class="hlt">crater</span>-associated dark deposit can be used for estimates of the <span class="hlt">crater</span> age and then for dating other features. Previous work classified <span class="hlt">craters</span> into: 1) <span class="hlt">craters</span> with dark parabola (DP), 2) with clear dark halo (CH), 3) with faint halo (FH) and 4) with no dark halo (NH). It was found that <span class="hlt">abundances</span> of <span class="hlt">craters</span> superposed on regional plains (whose mean age is close to the planet mean surface age T) and belonging to DP, CH, FH and NH classes were correspondingly 15, 30, 30 and 25%. From that it was concluded that DP <span class="hlt">craters</span> are not older than 0.1-0.15T; CH <span class="hlt">craters</span> formed during the time interval from approx. 0.5T until 0.1-0.15T ago, and the FH and NH <span class="hlt">craters</span> formed prior to approx. 0.5T ago. It was shown that the DP, CH, FH and NH percentages show only slight apparent dependence on the <span class="hlt">crater</span> geographic latitudes and no noticeable dependence on the <span class="hlt">crater</span> size. The present study analyzes a much larger population (all D greater than or equal to 5 km <span class="hlt">craters</span>) to investigate better the latitude effect and to study if within this larger <span class="hlt">crater</span> population the size effect exists.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19840035671&hterms=pit+final&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dpit%2Bfinal','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19840035671&hterms=pit+final&qs=N%3D0%26Ntk%3DAll%26Ntx%3Dmode%2Bmatchall%26Ntt%3Dpit%2Bfinal"><span>A proposed origin for palimpsests and anomalous pit <span class="hlt">craters</span> on Ganymede and Callisto</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Croft, S. K.</p> <p>1983-01-01</p> <p>The hypothesis that palimpsests and anomalous pit <span class="hlt">craters</span> are essentially pristine <span class="hlt">crater</span> forms derived from high-velocity <span class="hlt">impacts</span> and/or <span class="hlt">impacts</span> into an ice crust with preimpact temperatures near melting is explored. The observational data are briefly reviewed, and an <span class="hlt">impact</span> model is proposed for the direct formation of a palimpsest from an <span class="hlt">impact</span> when the modification flow which produces the final <span class="hlt">crater</span> is dominated by 'wet' fluid flow, as opposed to the 'dry' granular flow which produces normal <span class="hlt">craters</span>. Conditions of 'wet' modification occur when the volume of <span class="hlt">impact</span> melt remaining in the transient <span class="hlt">crater</span> attains a volume comparable to the transient <span class="hlt">crater</span>. The normal <span class="hlt">crater</span>-palimpsest transition is found to occur for sufficiently large <span class="hlt">impacts</span> or sufficiently fast impactors. The range of <span class="hlt">crater</span> diameters and morphological characteristics inferred from the <span class="hlt">impact</span> model is consistent with the observed characteristics of palimpsests and anomalous pit <span class="hlt">craters</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA15083.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA15083.html"><span>Dark Material Associated with and between <span class="hlt">Craters</span></span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2011-11-18</p> <p>This image from NASA Dawn spacecraft shows areas of dark material which are both associated with <span class="hlt">impact</span> <span class="hlt">craters</span> and between these <span class="hlt">craters</span> on asteroid Vesta. Dark material is seen cropping out of the rims and sides of the larger <span class="hlt">craters</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70037501','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70037501"><span>The sedimentology and dynamics of <span class="hlt">crater</span>-affiliated wind streaks in western Arabia Terra, Mars and Patagonia, Argentina</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Rodriguez, J.A.P.; Tanaka, K.L.; Yamamoto, A.; Berman, D.C.; Zimbelman, J.R.; Kargel, J.S.; Sasaki, S.; Jinguo, Y.; Miyamoto, H.</p> <p>2010-01-01</p> <p>Wind streaks comprise recent aeolian deposits that have been extensively documented on Venus, Earth and Mars. Martian wind streaks are among the most <span class="hlt">abundant</span> surface features on the planet and commonly extend from the downwind margins of <span class="hlt">impact</span> <span class="hlt">craters</span>. Previous studies of wind streaks emerging from <span class="hlt">crater</span> interior deposits suggested that the mode of emplacement was primarily related to the deposition of silt-sized particles as these settled from plumes. We have performed geologic investigations of two wind streaks clusters; one situated in western Arabia Terra, a region in the northern hemisphere of Mars, and another in an analogous terrestrial site located in southern Patagonia, Argentina, where occurrences of wind streaks emanate from playas within maar <span class="hlt">craters</span>. In both these regions we have identified bedforms in sedimentary deposits on <span class="hlt">crater</span> floors, along wind-facing interior <span class="hlt">crater</span> margins, and along wind streaks. These observations indicate that these deposits contain sand-sized particles and that sediment migration has occurred via saltation from <span class="hlt">crater</span> interior deposits to wind streaks. In Arabia Terra and in Patagonia wind streaks initiate from <span class="hlt">crater</span> floors that contain lithic and evaporitic sedimentary deposits, suggesting that the composition of wind streak source materials has played an important role in development. Spatial and topographic analyses suggest that regional clustering of wind streaks in the studied regions directly correlates to the areal density of <span class="hlt">craters</span> with interior deposits, the degree of proximity of these deposits, and the <span class="hlt">craters</span>' rim-to-floor depths. In addition, some (but not all) wind streaks within the studied clusters have propagated at comparable yearly (Earth years) rates. Extensive saltation is inferred to have been involved in its propagation based on the studied terrestrial wind streak that shows ripples and dunes on its surface and the Martian counterpart changes orientation toward the downslope direction where it</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140000236','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140000236"><span>Pyroclastic Deposits in the Floor-fractured <span class="hlt">Crater</span> Alphonsus</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Allen, Carlton C.; Donaldson-Hanna, Kerri L.; Pieters, Carle M.; Moriarty, Daniel P.; Greenhagen, Benjamin T.; Bennett, Kristen A.; Kramer, Georgiana Y.; Paige, David A.</p> <p>2013-01-01</p> <p>Alphonsus, the 118 km diameter floor-fractured <span class="hlt">crater</span>, is located immediately east of Mare Nubium. Eleven pyroclastic deposits have been identified on the <span class="hlt">crater</span>'s floor. Early telescopic spectra suggest that the floor of Alphonsus is noritic, and that the pyroclastic deposits contain mixtures of floor material and a juvenile component including basaltic glass. Head and Wilson contend that Nubium lavas intruded the breccia zone beneath Alphonsus, forming dikes and fractures on the <span class="hlt">crater</span> floor. In this model, the magma ascended to the level of the mare but cooled underground, and a portion broke thru to the surface in vulcanian (explosive) eruptions. Alternatively, the erupted material could be from a source unrelated to the mare, in the style of regional pyroclastic deposits. High-resolution images and spectroscopy from the Moon Mineralogy Mapper (M3), Diviner Lunar Radiometer, and Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (NAC) provide data to test these formation models. Spectra from M3 confirm that the <span class="hlt">crater</span> floor is primarily composed of noritic material, and that the Nubium lavas are basaltic. Spectra from the three largest pyroclastic deposits in Alphonsus are consistent with a minor low- Ca pyroxene component in a glass-rich matrix. The centers of the 2 micron absorption bands have wavelengths too short to be of the same origin as the Nubium basalts. Diviner Christiansen feature (CF) values were used to estimate FeO <span class="hlt">abundances</span> for the <span class="hlt">crater</span> floor, Nubium soil, and pyroclastic deposits. The estimated <span class="hlt">abundance</span> for the <span class="hlt">crater</span> floor (7.5 +/- 1.4 wt.%) is within the range of FeO values for Apollo norite samples. However, the estimated FeO <span class="hlt">abundance</span> for Nubium soil (13.4 +/- 1.4 wt.%) is lower than those measured in most mare samples. The difference may reflect contamination of the mare soil by highland ejecta. The Diviner-derived FeO <span class="hlt">abundance</span> for the western pyroclastic deposit is 13.8 +/- 3.3 wt.%. This is lower than the values for mare soil</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA21881.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA21881.html"><span>The Case of the Missing <span class="hlt">Crater</span> Rim</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-08-21</p> <p>In this observation from NASA's Mars Reconnaissance Orbiter, these two <span class="hlt">craters</span> perched at the edge of an outflow channel, appear to have lost a portion of their <span class="hlt">crater</span> rims during a flood event. Alternatively, it is also possible that the <span class="hlt">craters</span> <span class="hlt">impacted</span> the edge of the outflow channel after the flood occurred and we are seeing the difference in the strength of the material <span class="hlt">impacted</span>. https://photojournal.jpl.nasa.gov/catalog/PIA21881</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016JGRE..121.1900F','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016JGRE..121.1900F"><span>Analysis of <span class="hlt">impact</span> <span class="hlt">crater</span> populations and the geochronology of planetary surfaces in the inner solar system</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Fassett, Caleb I.</p> <p>2016-10-01</p> <p>Analyzing the density of <span class="hlt">impact</span> <span class="hlt">craters</span> on planetary surfaces is the only known technique for learning their ages remotely. As a result, <span class="hlt">crater</span> statistics have been widely analyzed on the terrestrial planets, since the timing and rates of activity are critical to understanding geologic process and history. On the Moon, the samples obtained by the Apollo and Luna missions provide critical calibration points for <span class="hlt">cratering</span> chronology. On Mercury, Venus, and Mars, there are no similarly firm anchors for <span class="hlt">cratering</span> rates, but chronology models have been established by extrapolating from the lunar record or by estimating their impactor fluxes in other ways. This review provides a current perspective on <span class="hlt">crater</span> population measurements and their chronological interpretation. Emphasis is placed on how ages derived from <span class="hlt">crater</span> statistics may be contingent on assumptions that need to be considered critically. In addition, ages estimated from <span class="hlt">crater</span> populations are somewhat different than ages from more familiar geochronology tools (e.g., radiometric dating). Resurfacing processes that remove <span class="hlt">craters</span> from the observed population are particularly challenging to account for, since they can introduce geologic uncertainty into results or destroy information about the formation age of a surface. Regardless of these challenges, <span class="hlt">crater</span> statistics measurements have resulted in successful predictions later verified by other techniques, including the age of the lunar maria, the existence of a period of heavy bombardment in the Moon's first billion years, and young volcanism on Mars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017EGUGA..19.9612S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017EGUGA..19.9612S"><span>The <span class="hlt">Crater</span> Ejecta Distribution on Ceres</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Schmedemann, Nico; Neesemann, Adrian; Schulzeck, Franziska; Krohn, Katrin; Gathen, Isabel; Otto, Katharina; Jaumann, Ralf; Michael, Gregory; Raymond, Carol; Russell, Christopher</p> <p>2017-04-01</p> <p>Since March 6 2015 the Dawn spacecraft [1] has been in orbit around the dwarf planet Ceres. At small <span class="hlt">crater</span> diameters Ceres appears to be peppered with secondary <span class="hlt">craters</span> that often align in chains or form clusters. Some of such possible <span class="hlt">crater</span> chains follow curved geometries and are not in a radial orientation with respect to possible source <span class="hlt">craters</span> [2]. Ceres is a fast rotating body ( 9 h per revolution) with comparatively low surface gravity ( 0.27 m/s2). A substantial fraction of <span class="hlt">impact</span> ejecta may be launched with velocities similar to Ceres' escape velocity (510 m/s), which implies that many ejected particles follow high and long trajectories. Thus, due to Ceres' fast rotation the distribution pattern of the reimpacting ejected material is heavily affected by Coriolis forces that results in a highly asymmetrical and curved pattern of secondary <span class="hlt">crater</span> chains. In order to simulate flight trajectories and distribution of <span class="hlt">impact</span> ejected material for individual <span class="hlt">craters</span> on Ceres we used the scaling laws by [3] adjusted to the Cerean <span class="hlt">impact</span> conditions [4] and the <span class="hlt">impact</span> ejecta model by [5]. These models provide the starting conditions for tracer particles in the simulation. The trajectories of the particles are computed as n-body simulation. The simulation calculates the positions and <span class="hlt">impact</span> velocities of each <span class="hlt">impacting</span> tracer particle with respect to the rotating surface of Ceres, which is approximated by a two-axis ellipsoid. Initial results show a number of interesting features in the simulated deposition geometries of specific <span class="hlt">crater</span> ejecta. These features are roughly in agreement with features that can be observed in Dawn imaging data of the Cerean surface. For example: ray systems of fresh <span class="hlt">impact</span> <span class="hlt">craters</span>, non-radial <span class="hlt">crater</span> chains and global scale border lines of higher and lower color ratio areas. Acknowledgment: This work has been supported by the German Space Agency (DLR) on behalf of the Federal Ministry for Economic Affairs and Energy, Germany, grants 50 OW</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19920033269&hterms=slump&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dslump','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19920033269&hterms=slump&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dslump"><span>Terrace width variations in complex Mercurian <span class="hlt">craters</span> and the transient strength of <span class="hlt">cratered</span> Mercurian and lunar crust</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Leith, Andrew C.; Mckinnon, William B.</p> <p>1991-01-01</p> <p>The effective cohesion of the <span class="hlt">cratered</span> region during <span class="hlt">crater</span> collapse is determined via the widths of slump terraces of complex <span class="hlt">craters</span>. Terrace widths are measured for complex <span class="hlt">craters</span> on Mercury; these generally increase outward toward the rim for a given <span class="hlt">crater</span>, and the width of the outermost major terrace is generally an increasing function of <span class="hlt">crater</span> diameter. The terrace widths on Mercury and a gravity-driven slump model are used to estimate the strength of the <span class="hlt">cratered</span> region immediately after <span class="hlt">impact</span> (about 1-2 MPa). A comparison with the previous study of lunar complex <span class="hlt">craters</span> by Pearce and Melosh (1986) indicates that the transient strength of <span class="hlt">cratered</span> Mercurian crust is no greater than that of the moon. The strength estimates vary only slightly with the geometric model used to restore the outermost major terrace to its precollapse configuration and are consistent with independent strength estimates from the simple-to-complex <span class="hlt">crater</span> depth/diameter transition.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19780033374&hterms=Two+planets+moon&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DTwo%2Bplanets%2Bmoon.','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19780033374&hterms=Two+planets+moon&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3DTwo%2Bplanets%2Bmoon."><span>Moon-Mercury - Relative preservation states of secondary <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Scott, D. H.</p> <p>1977-01-01</p> <p>Geologic studies including mapping of the Kuiper quadrangle of Mercury suggest that secondary <span class="hlt">craters</span> are much better preserved than those on the moon. Factors which may account for the apparent differences between lunar and Mercurian secondary <span class="hlt">crater</span> morphology include: (1) the rapid isostatic adjustment of the parent <span class="hlt">crater</span>, (2) different <span class="hlt">impact</span> fluxes of the two planets, (3) the greater concentration of Mercurian secondaries around <span class="hlt">impact</span> areas, and (4) differences in <span class="hlt">crater</span> ejection velocities. It has been shown that the ejection velocities on Mercury are about 50% greater than those on the moon at equivalent ranges. This may account for morphologically enhanced secondary <span class="hlt">craters</span>, and may explain their better preservation with time.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930002186','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930002186"><span>Compositional analysis and classification of projectile residues in LDEF <span class="hlt">impact</span> <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Horz, Friedrich; Bernhard, Ronald P.</p> <p>1992-01-01</p> <p>This catalog contains preliminary analyses of residues of hypervelocity projectiles that encountered gold substrates exposed by instrument A0187-1 on the Long Duration Exposure Facility (LDEF). This instrument was on LDEF's trailing edge where relative encounter speeds should be lowest for any non-spinning platform in low Earth orbit (LEO). Approximately 0.6 m(exp 2) of Au substrates yielded 198 <span class="hlt">impact</span> <span class="hlt">craters</span> greater than 20 micrometers in diameter. Some 30 percent of the <span class="hlt">craters</span> were made by natural cosmic dust particles and some 15 percent by man-made objects. Some 50 percent of all features, however, have residues, if any, that are beyond the detection threshold of the SEM-EDXA method used. The purpose of this catalog is to provide detailed evidence and criteria that may be used to arrive at specific particle types on a case-by-case basis and to group such particles into compositional classes. Clearly this is a somewhat interpretative undertaking. For that reason, we encourage and solicit critique and comments from those interested in the systematic analysis of all <span class="hlt">impact</span> features on LDEF.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20150002911','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20150002911"><span>Noachian <span class="hlt">Impact</span> Ejecta on Murray Ridge and Pre-<span class="hlt">impact</span> Rocks on Wdowiak Ridge, Endeavour <span class="hlt">Crater</span>, Mars: Opportunity Observations</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Mittlefehldt, D. W.; Gellert, R.; Ming, D. W.; Morris, R. V.; Schroeder, C.; Yen, A. S.; Farrand, W. H.; Arvidson, R. E.; Franklin, B. J.; Grant, J. A.; <a style="text-decoration: none; " href="javascript:void(0); " onClick="displayelement('author_20150002911'); toggleEditAbsImage('author_20150002911_show'); toggleEditAbsImage('author_20150002911_hide'); "> <img style="display:inline; width:12px; height:12px; " src="images/arrow-up.gif" width="12" height="12" border="0" alt="hide" id="author_20150002911_show"> <img style="width:12px; height:12px; display:none; " src="images/arrow-down.gif" width="12" height="12" border="0" alt="hide" id="author_20150002911_hide"></p> <p>2015-01-01</p> <p>Mars Exploration Rover Opportunity has been exploring Meridiani Planum since January 2004, and has completed 4227% of its primary mission. Opportunity has been investigating the geology of the rim of 22 km diameter Endeavour <span class="hlt">crater</span>, first on the Cape York segment and now on Cape Tribulation. The outcrops are divided York; (ii) the Shoemaker fm, <span class="hlt">impact</span> breccias representing ejecta from the <span class="hlt">crater</span>; into three formations: (i) the lower Matijevic fm, a pre-<span class="hlt">impact</span> lithology on Cape and (iii) the upper Grasberg fm, a post-<span class="hlt">impact</span> deposit that drapes the lower portions of the eroded rim segments. On the Cape Tribulation segment Opportunity has been studying the rocks on Murray Ridge, with a brief sojourn to Wdowiak Ridge west of the rim segment. team member Thomas Wdowiak, who died in 2013.) One region of Murray Ridge has distinctive CRISM spectral characteristics indicating the presence of a small concentration of aluminous smectite based on a 2.2 micron Al-OH combination band (hereafter, the Al-OH region).</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20030067009&hterms=TURTLES&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DTURTLES','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20030067009&hterms=TURTLES&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DTURTLES"><span>Numerical Simulations of Silverpit <span class="hlt">Crater</span> Collapse</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Collins, G. S.; Ivanov, B. A.; Turtle, E. P.; Melosh, H. J.</p> <p>2003-01-01</p> <p>The Silverpit <span class="hlt">crater</span> is a recently discovered, 60-65 Myr old complex <span class="hlt">crater</span>, which lies buried beneath the North Sea, about 150 km east of Britain. High-resolution images of Silverpit's subsurface structure, provided by three-dimensional seismic reflection data, reveal an inner-<span class="hlt">crater</span> morphology similar to that expected for a 5-8 km diameter terrestrial <span class="hlt">crater</span>. The <span class="hlt">crater</span> walls show evidence of terrace-style slumping and there is a distinct central uplift, which may have produced a central peak in the pristine <span class="hlt">crater</span> morphology. However, Silverpit is not a typical 5-km diameter terrestrial <span class="hlt">crater</span>, because it exhibits multiple, concentric rings outside the main cavity. External concentric rings are normally associated with much larger <span class="hlt">impact</span> structures, for example Chicxulub on Earth, or Orientale on the Moon. Furthermore, external rings associated with large <span class="hlt">impacts</span> on the terrestrial planets and moons are widely-spaced, predominantly inwardly-facing, asymmetric scarps. However, the seismic data show that the external rings at Silverpit represent closely-spaced, concentric faultbound graben, with both inwardly and outwardly facing fault-scarps. This type of multi-ring structure directly analogous to the Valhalla-type multi-ring basins found on the icy satellites. Thus, the presence and style of the multiple rings at Silverpit is surprising given both the size of the <span class="hlt">crater</span> and its planetary setting. A further curiosity of the Silverpit structure is that the external concentric rings appear to be extensional features on the West side of the <span class="hlt">crater</span> and compressional features on the East side. The <span class="hlt">crater</span> also lies in a local depression, thought to be created by postimpact movement of a salt layer buried beneath the <span class="hlt">crater</span>.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_20");'>20</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li class="active"><span>22</span></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_22 --> <div id="page_23" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="441"> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70035006','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70035006"><span>Exploration of Victoria <span class="hlt">crater</span> by the mars rover opportunity</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Squyres, S. W.; Knoll, A.H.; Arvidson, R. E.; Ashley, James W.; Bell, J.F.; Calvin, W.M.; Christensen, P.R.; Clark, B. C.; Cohen, B. A.; De Souza, P.A.; Edgar, L.; Farrand, W. H.; Fleischer, I.; Gellert, Ralf; Golombek, M.P.; Grant, J.; Grotzinger, J.; Hayes, A.; Herkenhoff, K. E.; Johnson, J. R.; Jolliff, B.; Klingelhofer, G.; Knudson, A.; Li, R.; McCoy, T.J.; McLennan, S.M.; Ming, D. W.; Mittlefehldt, D. W.; Morris, R.V.; Rice, J. W.; Schroder, C.; Sullivan, R.J.; Yen, A.; Yingst, R.A.</p> <p>2009-01-01</p> <p>The Mars rover Opportunity has explored Victoria <span class="hlt">crater</span>, a ???750-meter eroded <span class="hlt">impact</span> <span class="hlt">crater</span> formed in sulfate-rich sedimentary rocks. <span class="hlt">Impact</span>-related stratigraphy is preserved in the <span class="hlt">crater</span> walls, and meteoritic debris is present near the <span class="hlt">crater</span> rim. The size of hematite-rich concretions decreases up-section, documenting variation in the intensity of groundwater processes. Layering in the <span class="hlt">crater</span> walls preserves evidence of ancient wind-blown dunes. Compositional variations with depth mimic those ???6 kilometers to the north and demonstrate that water-induced alteration at Meridiani Planum was regional in scope.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/19461001','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/19461001"><span>Exploration of Victoria <span class="hlt">crater</span> by the Mars rover Opportunity.</span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Squyres, S W; Knoll, A H; Arvidson, R E; Ashley, J W; Bell, J F; Calvin, W M; Christensen, P R; Clark, B C; Cohen, B A; de Souza, P A; Edgar, L; Farrand, W H; Fleischer, I; Gellert, R; Golombek, M P; Grant, J; Grotzinger, J; Hayes, A; Herkenhoff, K E; Johnson, J R; Jolliff, B; Klingelhöfer, G; Knudson, A; Li, R; McCoy, T J; McLennan, S M; Ming, D W; Mittlefehldt, D W; Morris, R V; Rice, J W; Schröder, C; Sullivan, R J; Yen, A; Yingst, R A</p> <p>2009-05-22</p> <p>The Mars rover Opportunity has explored Victoria <span class="hlt">crater</span>, an approximately 750-meter eroded <span class="hlt">impact</span> <span class="hlt">crater</span> formed in sulfate-rich sedimentary rocks. <span class="hlt">Impact</span>-related stratigraphy is preserved in the <span class="hlt">crater</span> walls, and meteoritic debris is present near the <span class="hlt">crater</span> rim. The size of hematite-rich concretions decreases up-section, documenting variation in the intensity of groundwater processes. Layering in the <span class="hlt">crater</span> walls preserves evidence of ancient wind-blown dunes. Compositional variations with depth mimic those approximately 6 kilometers to the north and demonstrate that water-induced alteration at Meridiani Planum was regional in scope.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20030068028','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20030068028"><span>Russian-US Partnership to Study the 23-km-diameter El'gygtgyn <span class="hlt">Impact</span> <span class="hlt">Crater</span>, Northeast Russia</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Sharpton, Virgil L.; Minyuk, Pavel S.; Brigham-Grette, Julie; Glushkova, Olga; Layer, Paul; Raikevich, Mikhail; Stone, David; Smirnov, Valdimir</p> <p>2002-01-01</p> <p>El'gygytgyn <span class="hlt">crater</span>, located within Eastern Siberia, is a Pliocene-aged (3.6 Ma), well-preserved <span class="hlt">impact</span> <span class="hlt">crater</span> with a rim diameter of roughly 23 km. The target rocks are a coherent assemblage of crystalline rocks ranging from andesite to basalt. At the time of <span class="hlt">impact</span> the region was forested and the Arctic Ocean was nearly ice-free. A 15-km lake fills the center of the feature and water depths are approximately 175 m. Evidence of shock metamorphism, -- including coesite, fused mineral glasses, and planar deformation features in quartz -- has been reported. This feature is one of the youngest and best preserved complex <span class="hlt">craters</span> on Earth. Because of its remote Arctic setting, however, El gygytgyn <span class="hlt">crater</span> remains poorly investigated. The objectives of this three-year project are to establish and maintain a research partnership between scientists from Russia and the United States interested in the El gygytgyn <span class="hlt">crater</span>. The principal institutions in the U.S. will be the Geophysical Institute, University of Alaska Fairbanks and the University of Massachusetts Amherst. The principal institution in Russia will be the North East Interdisciplinary Scientific Research Institute (NEISRI), which is the Far-East Branch of the Russian Academy of Science. Three science tasks are identified for the exchange program: (1) Evaluate impactite samples collected during previous field excursions for evidence of and level of shock deformation. (2) Build a high-resolution digital elevation model for the <span class="hlt">crater</span> and its surroundings using interferometric synthetic aperture radar techniques on JERS-1, ERS-1, ERS-2, and/or RadarSat range-doppler data. (3) Gather all existing surface data available from Russian and U.S. institutions (DEM, remote sensing image data, field-based lithological and sample maps, and existing geophysical data) and assemble into a Geographic Information Systems database.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA03785.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA03785.html"><span><span class="hlt">Cratered</span> terrain in Terra Meridiani</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2002-05-23</p> <p>This region of Terra Meridiani, imaged by NASA Mars Odyssey, shows an old, heavily degraded channel that appears to terminate abruptly at the rim of a 10 km diameter <span class="hlt">crater</span>, suggesting that the <span class="hlt">impact</span> <span class="hlt">crater</span> was created after the channel was formed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017M%26PS...52.1330R','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017M%26PS...52.1330R"><span>Complex <span class="hlt">crater</span> formation: Insights from combining observations of shock pressure distribution with numerical models at the West Clearwater Lake <span class="hlt">impact</span> structure</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Rae, A. S. P.; Collins, G. S.; Grieve, R. A. F.; Osinski, G. R.; Morgan, J. V.</p> <p>2017-07-01</p> <p>Large <span class="hlt">impact</span> structures have complex morphologies, with zones of structural uplift that can be expressed topographically as central peaks and/or peak rings internal to the <span class="hlt">crater</span> rim. The formation of these structures requires transient strength reduction in the target material and one of the proposed mechanisms to explain this behavior is acoustic fluidization. Here, samples of shock-metamorphosed quartz-bearing lithologies at the West Clearwater Lake <span class="hlt">impact</span> structure, Canada, are used to estimate the maximum recorded shock pressures in three dimensions across the <span class="hlt">crater</span>. These measurements demonstrate that the currently observed distribution of shock metamorphism is strongly controlled by the formation of the structural uplift. The distribution of peak shock pressures, together with apparent <span class="hlt">crater</span> morphology and geological observations, is compared with numerical <span class="hlt">impact</span> simulations to constrain parameters used in the block-model implementation of acoustic fluidization. The numerical simulations produce <span class="hlt">craters</span> that are consistent with morphological and geological observations. The results show that the regeneration of acoustic energy must be an important feature of acoustic fluidization in <span class="hlt">crater</span> collapse, and should be included in future implementations. Based on the comparison between observational data and <span class="hlt">impact</span> simulations, we conclude that the West Clearwater Lake structure had an original rim (final <span class="hlt">crater</span>) diameter of 35-40 km and has since experienced up to 2 km of differential erosion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2010avh..confE..55U','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2010avh..confE..55U"><span>The Chicxulub Multiring <span class="hlt">Impact</span> <span class="hlt">Crater</span> and the Cretaceous/Paleogene Boundary: Results From Geophysical Surveys and Drilling</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Urrutia-Fucugauchi, J.; Perez-Cruz, Ligia</p> <p>2010-03-01</p> <p>The Chicxulub <span class="hlt">crater</span> has attracted considerable attention as one of the three largest terrestrial <span class="hlt">impact</span> structures and its association with the Cretaceous/Paleogene boundary (K/Pg). Chicxulub is a 200 km-diameter multi-ring structure formed 65.5 Ma ago in the Yucatan carbonate platform in the southern Gulf of Mexico and which has since been buried by Paleogene and Neogene carbonates. Chicxulub is one of few large <span class="hlt">craters</span> with preserved ejecta deposits, which include the world-wide K/Pg boundary clay layer. The <span class="hlt">impact</span> has been related to the global major environmental and climatic effects and the organism mass extinction that mark the K/Pg boundary, which affected more than 70 % of organisms, including the dinosaurs, marine and flying reptiles, ammonites and a large part of the marine microorganisms. The <span class="hlt">impact</span> and <span class="hlt">crater</span> formation occur instantaneously, with excavation of the crust down to 25 km depths in fractions of second and lower crust uplift and <span class="hlt">crater</span> formation in a few hundreds of seconds. Energy released by <span class="hlt">impact</span> and crustal deformation generates seismic waves traveling the whole Earth, and resulting in intense fracturing and deformation at the target site. Understanding of the physics of <span class="hlt">impacts</span> on planetary surfaces and modeling of processes of crustal deformation, rheological behavior of materials at high temperatures and pressures remain a major challenge in geosciences. Study of the Chicxulub <span class="hlt">crater</span> and the global effects and mass extinction requires inter- and multidisciplinary approaches, with researchers from many diverse fields beyond the geosciences. With no surface exposures, geophysical surveys and drilling are required to study the <span class="hlt">crater</span>. Differential compaction between the <span class="hlt">impact</span> breccias and the surrounding carbonate rocks has produced a ring-fracture structure that at the surface reflects in a small topographic depression and the karstic cenote ring. The <span class="hlt">crater</span> structure, located half offshore and half on-land, has been imaged by</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=20030111111&hterms=TURTLES&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DTURTLES','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=20030111111&hterms=TURTLES&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3DTURTLES"><span>Numerical Simulations of Silverpit <span class="hlt">Crater</span> Collapse</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Collins, G. S.; Turtle, E. P.; Melosh, H. J.</p> <p>2003-01-01</p> <p>The Silverpit <span class="hlt">crater</span> is a recently discovered, 60-65 Myr old complex <span class="hlt">crater</span>, which lies buried beneath the North Sea, about 150 km east of Britain. High-resolution images of Silverpit's subsurface structure, provided by three-dimensional seismic reflection data, reveal an inner-<span class="hlt">crater</span> morphology similar to that expected for a 5-8 km diameter terrestrial <span class="hlt">crater</span>. The <span class="hlt">crater</span> walls show evidence of terracestyle slumping and there is a distinct central uplift, which may have produced a central peak in the pristine <span class="hlt">crater</span> morphology. However, Silverpit is not a typical 5-km diameter terrestrial <span class="hlt">crater</span>, because it exhibits multiple, concentric rings outside the main cavity. External concentric rings are normally associated with much larger <span class="hlt">impact</span> structures, for example Chicxulub on Earth, or Orientale on the Moon. Furthermore, external rings associated with large <span class="hlt">impacts</span> on the terrestrial planets and moons are widely-spaced, predominantly inwardly-facing, asymmetric scarps. However, the seismic data show that the external rings at Silverpit represent closely-spaced, concentric fault-bound graben, with both inwardly and outwardly facing faults-carps. This type of multi-ring structure is directly analogous to the Valhalla-type multi-ring basins found on the icy satellites. Thus, the presence and style of the multiple rings at Silverpit is surprising given both the size of the <span class="hlt">crater</span> and its planetary setting.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70012720','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70012720"><span>STRAWBERRY <span class="hlt">CRATER</span> ROADLESS AREAS, ARIZONA.</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Wolfe, Edward W.; Light, Thomas D.</p> <p>1984-01-01</p> <p>The results of a mineral survey conducted in the Strawberry <span class="hlt">Crater</span> Roadless Areas, Arizona, indicate little promise for the occurrence of metallic mineral or fossil fuel resources in the area. The area contains deposits of cinder, useful for the production of aggregate block, and for deposits of decorative stone; however, similar deposits occur in great <span class="hlt">abundance</span> throughout the San Francisco volcanic field outside the roadless areas. There is a possibility that the Strawberry <span class="hlt">Crater</span> Roadless Areas may overlie part of a crustal magma chamber or still warm pluton related to the San Francisco Mountain stratovolcano or to basaltic vents of late Pleistocene or Holocene age. Such a magma chamber or pluton beneath the Strawberry <span class="hlt">Crater</span> Roadless Areas might be an energy source from which a hot-, dry-rock geothermal energy system could be developed, and a probable geothermal resource potential is therefore assigned to these areas. 9 refs.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930020173','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930020173"><span>Derivation of particulate directional information from analysis of elliptical <span class="hlt">impact</span> <span class="hlt">craters</span> on LDEF</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Newman, P. J.; Mackay, N.; Deshpande, S. P.; Green, S. F.; Mcdonnell, J. A. M.</p> <p>1993-01-01</p> <p>The Long Duration Exposure Facility provided a gravity gradient stabilized platform which allowed limited directional information to be derived from particle <span class="hlt">impact</span> experiments. The morphology of <span class="hlt">impact</span> <span class="hlt">craters</span> on semi-infinite materials contains information which may be used to determine the direction of <span class="hlt">impact</span> much more accurately. We demonstrate the applicability of this technique and present preliminary results of measurements from LDEF and modelling of interplanetary dust and space debris.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19990028625&hterms=images+mars&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dimages%2Bmars','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19990028625&hterms=images+mars&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dimages%2Bmars"><span>Mid-Latitude versus Polar-Latitude Transitional <span class="hlt">Impact</span> <span class="hlt">Craters</span>: Geometric Properties from Mars Orbiter Laser Altimeter (MOLA) Observations and Viking Images</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Matias, A.; Garvin, J. B.; Sakimoto, S. E. H.</p> <p>1998-01-01</p> <p>One intriguing aspect of martian <span class="hlt">impact</span> <span class="hlt">crater</span> morphology is the change of <span class="hlt">crater</span> cavity and ejecta characteristics from the mid-latitudes to the polar regions. This is thought to reflect differences in target properties such as an increasing presence of ice in the polar regions. Previous image-based efforts concerning martian <span class="hlt">crater</span> morphology has documented some aspects of this, but has been hampered by the lack of adequate topography data. Recent Mars Orbiter Laser Altimeter (MOLA) topographic profiles provide a quantitative perspective for interpreting the detailed morphologies of martian <span class="hlt">crater</span> cavities and ejecta morphology. This study is a preliminary effort to quantify the latitude-dependent differences in morphology with the goal of identifying target-dependent and <span class="hlt">crater</span> modification effects from the combined of images and MOLA topography. We combine the available MOLA profiles and the corresponding Viking Mars Digital Image Mosaics (MDIMS), and high resolution Viking Orbiter images to focus on two transitional <span class="hlt">craters</span>; one on the mid-latitudes, and one in the North Polar region. One MOLA pass (MGS Orbit 34) traverses the center of a 15.9 km diameter fresh complex <span class="hlt">crater</span> located at 12.8degN 83.8degE on the Hesperian ridge plains unit (Hvr). Viking images, as well as MOLA data, show that this <span class="hlt">crater</span> has well developed wall terraces and a central peak with 429 m of relative relief. Three MOLA passes have been acquired for a second <span class="hlt">impact</span> <span class="hlt">crater</span>, which is located at 69.5degN 41degE on the Vastitas Borealis Formation. This fresh rampart <span class="hlt">crater</span> lacks terraces and central peak structures and it has a depth af 579 m. Correlation between images and MOLA topographic profiles allows us to construct basic facies maps of the <span class="hlt">craters</span>. Eight main units were identified, four of which are common on both <span class="hlt">craters</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20100003189','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20100003189"><span>Creation of High Resolution Terrain Models of Barringer Meteorite <span class="hlt">Crater</span> (Meteor <span class="hlt">Crater</span>) Using Photogrammetry and Terrestrial Laser Scanning Methods</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Brown, Richard B.; Navard, Andrew R.; Holland, Donald E.; McKellip, Rodney D.; Brannon, David P.</p> <p>2010-01-01</p> <p>Barringer Meteorite <span class="hlt">Crater</span> or Meteor <span class="hlt">Crater</span>, AZ, has been a site of high interest for lunar and Mars analog <span class="hlt">crater</span> and terrain studies since the early days of the Apollo-Saturn program. It continues to be a site of exceptional interest to lunar, Mars, and other planetary <span class="hlt">crater</span> and <span class="hlt">impact</span> analog studies because of its relatively young age (est. 50 thousand years) and well-preserved structure. High resolution (2 meter to 1 decimeter) digital terrain models of Meteor <span class="hlt">Crater</span> in whole or in part were created at NASA Stennis Space Center to support several lunar surface analog modeling activities using photogrammetric and ground based laser scanning techniques. The dataset created by this activity provides new and highly accurate 3D models of the inside slope of the <span class="hlt">crater</span> as well as the downslope rock distribution of the western ejecta field. The data are presented to the science community for possible use in furthering studies of Meteor <span class="hlt">Crater</span> and <span class="hlt">impact</span> <span class="hlt">craters</span> in general as well as its current near term lunar exploration use in providing a beneficial test model for lunar surface analog modeling and surface operation studies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017P%26SS..148...12K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017P%26SS..148...12K"><span>Characteristics of small young lunar <span class="hlt">impact</span> <span class="hlt">craters</span> focusing on current production and degradation on the Moon</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kereszturi, Akos; Steinmann, Vilmos</p> <p>2017-11-01</p> <p>Analysing the size-frequency distribution of very small lunar <span class="hlt">craters</span> (sized below 100 m including ones below 10 m) using LROC images, spatial density and related age estimations were calculated for mare and terra terrains. Altogether 1.55 km2 area was surveyed composed of 0.1-0.2 km2 units, counting 2784 <span class="hlt">craters</span>. The maximal areal density was present at the 4-8 m diameter range at every analysed terrain suggesting the bombardment is areally relatively homogeneous. Analysing the similarities and differences between various areas, the mare terrains look about two times older than the terra terrains using <100 m diameter <span class="hlt">craters</span>. The calculated ages ranged between 13 and 20 Ma for mare, 4-6 Ma for terra terrains. Substantial fluctuation (min: 936 <span class="hlt">craters</span>/km2, max: 2495 <span class="hlt">craters</span>/km2) was observed without obvious source of nearby secondaries or fresh ejecta blanket produced fresh <span class="hlt">crater</span>. Randomness analysis and visual inspection also suggested no secondary <span class="hlt">craters</span> or ejecta blanket from fresh <span class="hlt">impact</span> could contribute substantially in the observed heterogeneity of the areal distribution of small <span class="hlt">craters</span> - thus distant secondaries or even other, poorly known resurfacing processes should be considered in the future. The difference between the terra/mare ages might come only partly from the easier identification of small <span class="hlt">craters</span> on smooth mare terrains, as the differences were observed for larger (30-60 m diameter) <span class="hlt">craters</span> too. Difference in the target hardness could more contribute in this effect. It was possible to separate two groups of small <span class="hlt">craters</span> based on their appearance: a rimmed thus less eroded, and a rimless thus more eroded one. As the separate usage of different morphology groups of <span class="hlt">craters</span> for age estimation at the same area is not justifiable, this was used only for comparison. The SFD curves of these two groups showed characteristic differences: the steepness of the fresh <span class="hlt">craters</span>' SFD curves are similar to each other and were larger than the isochrones. The</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=PIA05281&hterms=swiss+cheese&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dswiss%2Bcheese','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=PIA05281&hterms=swiss+cheese&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dswiss%2Bcheese"><span>Exhuming South Polar <span class="hlt">Crater</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2004-01-01</p> <p>7 February 2004 The large, circular feature in this image is an old meteor <span class="hlt">impact</span> <span class="hlt">crater</span>. The <span class="hlt">crater</span> is larger than the 3 kilometers-wide (1.9 miles-wide) Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image, thus only part of the <span class="hlt">crater</span> is seen. The bright mesas full of pits and holes--in some areas resembling swiss cheese--are composed of frozen carbon dioxide. In this summertime view, the mesa slopes and pit walls are darkened as sunlight causes some of the ice to sublime away. At one time in the past, the <span class="hlt">crater</span> shown here may have been completely covered with carbon dioxide ice, but, over time, it has been exhumed as the ice sublimes a little bit more each summer. The <span class="hlt">crater</span> is located near 86.8oS, 111.6oW. Sunlight illuminates this scene from the upper left.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19920009568','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19920009568"><span>Planetary <span class="hlt">cratering</span> mechanics</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Okeefe, John D.; Ahrens, Thomas J.</p> <p>1992-01-01</p> <p>To obtain a quantitative understanding of the <span class="hlt">cratering</span> process over a broad range of conditions, we have numerically computed the evolution of <span class="hlt">impact</span> induced flow fields and calculated the time histories of the major measures of <span class="hlt">crater</span> geometry (e.g., depth diameter, lip height ...) for variations in planetary gravity (0 to 10 exp 9 cm/sq seconds), material strength (0 to 140 kbar), thermodynamic properties, and impactor radius (0.05 to 5000 km). These results were fit into the framework of the scaling relations of Holsapple and Schmidt (1987). We describe the <span class="hlt">impact</span> process in terms of four regimes: (1) penetration; (2) inertial; (3) terminal; and (4) relaxation.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940016252&hterms=origin+military&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dorigin%2Bmilitary','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940016252&hterms=origin+military&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dorigin%2Bmilitary"><span>Named Venusian <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Russell, Joel F.; Schaber, Gerald G.</p> <p>1993-01-01</p> <p>Schaber et al. compiled a database of 841 <span class="hlt">craters</span> on Venus, based on Magellan coverage of 89 percent of the planet's surface. That database, derived from coverage of approximately 98 percent of Venus' surface, has been expanded to 912 <span class="hlt">craters</span>, ranging in diameter from 1.5 to 280 km. About 150 of the larger <span class="hlt">craters</span> were previously identified by Pioneer Venus and Soviet Venera projects and subsequently formally named by the International Astronomical Union (IAU). Altogether, the <span class="hlt">crater</span> names submitted to the IAU for approval to date number about 550, a little more than half of the number of <span class="hlt">craters</span> identified on Magellan images. The IAU will consider more names as they are submitted for approval. Anyone--planetary scientist or layman--may submit names; however, candidate names must conform to IAU rules. The person to be honored must be deceased for at least three years, must not be a religious figure or a military or political figure of the 19th or 20th century, and, for Venus, must be a woman. All formally and provisionally approved names for Venusian <span class="hlt">impact</span> <span class="hlt">craters</span>, along with their latitude, longitude, size, and origin of their name, will be presented at LPSC and will be available as handouts.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018P%26SS..153...22S','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018P%26SS..153...22S"><span>Characterizing dark mantle deposits in the lunar <span class="hlt">crater</span> Alphonsus</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Shkuratov, Y. G.; Ivanov, M. A.; Korokhin, V. V.; Kaydash, V. G.; Basilevsky, A. T.; Videen, G.; Hradyska, L. V.; Velikodsky, Y. I.; Marchenko, G. P.</p> <p>2018-04-01</p> <p>We analyze available remote-sensing data of the <span class="hlt">crater</span> Alphonsus, focusing on the analysis of the <span class="hlt">crater</span>'s dark mantle deposits (DMDs), which includes images from NASA Clementine and Lunar Reconnaissance Orbiter (LRO), Japanese Selene (Kaguya), and Indian Chandrayaan-1 missions. The Alphonsus DMDs are gentle-sloped flat hills with typical heights of several meters, which are presented with pyroclastic materials. Our determination of the absolute ages of the Alphonsus DMDs by the technique of <span class="hlt">crater</span> size-frequency distributions shows that they are ∼200-400 m.y. old. However, being geologically young, the Alphonsus DMDs are not seen in OMAT maps. The DMDs have noticeably lower content of TiO2 (2-3%) than the mare regions to the west (>4%). The assessment of total pyroxene shows it has a higher <span class="hlt">abundance</span> in the DMDs, although LRO Diviner measurements of the Chirstiansen feature suggest, rather, a high <span class="hlt">abundance</span> of olivine. The DMDs pyroclastic material has no signs of OH/H2O compounds. We may suggest that this characteristic of the DMDs either relates to their <span class="hlt">impact</span> reworking and loss of the OH/H2O compounds or to the non-water volatiles as the driving agent of the pyroclastic activity. The compositional assessments of the DMDs may be flawed from contamination with the surrounding material due to horizontal and vertical transportation due to <span class="hlt">impacts</span>. This effect probably can be observed in LROC NAC images of high resolution. A very dark material outcropping on the slopes of the vent depression is seen due to renovation of the regolith on the steep walls of the depression. Thus, at smaller phase angles, the pyroclastic material is dark and at larger phase angles it appears almost like the surrounding material. This means that the phase dependence of the outcropping dark material is shallow; i.e. the dark surface is smoother than its surroundings. This may suggest venting of gases resulting in fluidization of the granular pyroclastic material of the deposit.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2007P%26SS...55...70M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2007P%26SS...55...70M"><span>Ejecta velocity distribution for <span class="hlt">impact</span> <span class="hlt">cratering</span> experiments on porous and low strength targets</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Michikami, Tatsuhiro; Moriguchi, Kouichi; Hasegawa, Sunao; Fujiwara, Akira</p> <p>2007-01-01</p> <p><span class="hlt">Impact</span> <span class="hlt">cratering</span> experiments on porous targets with various compressive strength ranging from ˜0.5 to ˜250 MPa were carried out in order to investigate the relationship between the ejecta velocity, and material strength or porosity of the target. A spherical alumina projectile (diameter ˜1 mm) was shot perpendicularly into the target surface with velocity ranging from 1.2 to 4.5 km/s (nominal 4 km/s), using a two-stage light-gas gun. The ejecta velocity was estimated from the fall point distance of ejecta. The results show that there are in fact a large fraction of ejecta with very low velocities when the material strength of the target is small and the porosity is high. As an example, in the case of one specific target (compressive strength ˜0.5 MPa and porosity 43%), the amount of ejecta with velocities lower than 1 m/s is about 40% of the total mass. The average velocity of the ejecta decreases with decreasing material strength or increasing the porosity of the target. Moreover, in our experiments, the ejecta velocity distributions normalized to total ejecta mass seem to be mainly dependent on the material strength of the target, and not so greatly on the porosity. We also compare our experimental results with those of Gault et al. [1963. Spray ejected from the lunar surface by meteoroid <span class="hlt">impact</span>. NASA Technical Note D-1767] and Housen [1992. <span class="hlt">Crater</span> ejecta velocities for <span class="hlt">impacts</span> on rocky bodies. LPSC XXIII, 555-556] for the ejecta velocity distribution using Housen's nondimensional scaling parameter. The ejecta velocity distributions of our experiments are lower than those of Gault et al. [1963. Spray ejected from the lunar surface by meteoroid <span class="hlt">impact</span>. NASA Technical Note D-1767] and Housen [1992. <span class="hlt">Crater</span> ejecta velocities for <span class="hlt">impacts</span> on rocky bodies. LPSC XIII, 555-556].</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19780042894&hterms=gardening&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dgardening','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19780042894&hterms=gardening&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D50%26Ntt%3Dgardening"><span><span class="hlt">Impact</span> <span class="hlt">cratering</span> and regolith dynamics. [on moon</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hoerz, F.</p> <p>1977-01-01</p> <p>The most recent models concerning mechanical aspects of lunar regolith dynamics related to <span class="hlt">impact</span> <span class="hlt">cratering</span> use probabilistic approaches to account for the randomness of the meteorite environment in both space and time. Accordingly the absolute regolith thickness is strictly a function of total bombardment intensity and absolute regolith growth rate in nonlinear through geologic time. Regoliths of increasing median thickness will have larger and larger proportions of more and more deep seated materials. An especially active zone of reworking on the lunar surface of about 1 mm depth has been established. With increasing depth, the probability of excavation and regolith turnover decreases very rapidly. Thus small scale stratigraphy - observable in lunar core materials - is perfectly compatible with regolith gardening, though it is also demonstrated that any such stratigraphy does not necessarily present a complete record of the regolith's depositional history. At present, the lifetimes of exposed lunar rocks against comminution by <span class="hlt">impact</span> processes can be modeled; it appears that catastrophic rupture dominates over single particle abrasion.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19890062572&hterms=slump&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dslump','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19890062572&hterms=slump&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dslump"><span>Test of a geometric model for the modification stage of simple <span class="hlt">impact</span> <span class="hlt">crater</span> development</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Grieve, R. A. F.; Coderre, J. M.; Rupert, J.; Garvin, J. B.</p> <p>1989-01-01</p> <p>This paper presents a geometric model describing the geometry of the transient cavity of an <span class="hlt">impact</span> <span class="hlt">crater</span> and the subsequent collapse of its walls to form a <span class="hlt">crater</span> filled by an interior breccia lens. The model is tested by comparing the volume of slump material calculated from known dimensional parameters with the volume of the breccia lens estimated on the basis of observational data. Results obtained from the model were found to be consistent with observational data, particularly in view of the highly sensitive nature of the model to input parameters.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018JPhCS1015c2131M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018JPhCS1015c2131M"><span>Experience of modeling relief of <span class="hlt">impact</span> lunar <span class="hlt">crater</span> Aitken based on high-resolution orbital images</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Mukhametshin, Ch R.; Semenov, A. A.; Shpekin, M. I.</p> <p>2018-05-01</p> <p>The paper presents the author’s results of modeling the relief of lunar Aitken <span class="hlt">crater</span> on the basis of high-resolution orbital images. The images were taken in the frame of the “Apollo” program in 1971-1972 and delivered to the Earth by crews of “Apollo-15” and “Apollo-17”. The authors used the images obtained by metric and panoramic cameras. The main result is the careful study of the unusual features of Aitken <span class="hlt">crater</span> on models created by the authors with the computer program, developed by “Agisoft Photoscan”. The paper shows what possibilities are opened with 3D models in the study of the structure of <span class="hlt">impact</span> <span class="hlt">craters</span> on the Moon. In particular, for the first time, the authors managed to show the structure of the glacier-like tongue in Aitken <span class="hlt">crater</span>, which is regarded as one of the promising areas of the Moon for the forthcoming expeditions.</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li class="active"><span>23</span></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_23 --> <div id="page_24" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="461"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2016M%26PS...51.1762W','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2016M%26PS...51.1762W"><span><span class="hlt">Impacts</span> into quartz sand: <span class="hlt">Crater</span> formation, shock metamorphism, and ejecta distribution in laboratory experiments and numerical models</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Wünnemann, Kai; Zhu, Meng-Hua; Stöffler, Dieter</p> <p>2016-10-01</p> <p>We investigated the ejection mechanics by a complementary approach of <span class="hlt">cratering</span> experiments, including the microscopic analysis of material sampled from these experiments, and 2-D numerical modeling of vertical <span class="hlt">impacts</span>. The study is based on <span class="hlt">cratering</span> experiments in quartz sand targets performed at the NASA Ames Vertical Gun Range. In these experiments, the preimpact location in the target and the final position of ejecta was determined by using color-coded sand and a catcher system for the ejecta. The results were compared with numerical simulations of the <span class="hlt">cratering</span> and ejection process to validate the iSALE shock physics code. In turn the models provide further details on the ejection velocities and angles. We quantify the general assumption that ejecta thickness decreases with distance according to a power-law and that the relative proportion of shocked material in the ejecta increase with distance. We distinguish three types of shock metamorphic particles (1) melt particles, (2) shock lithified aggregates, and (3) shock-comminuted grains. The agreement between experiment and model was excellent, which provides confidence that the models can predict ejection angles, velocities, and the degree of shock loading of material expelled from a <span class="hlt">crater</span> accurately if <span class="hlt">impact</span> parameters such as <span class="hlt">impact</span> velocity, impactor size, and gravity are varied beyond the experimental limitations. This study is relevant for a quantitative assessment of <span class="hlt">impact</span> gardening on planetary surfaces and the evolution of regolith layers on atmosphereless bodies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930000980','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930000980"><span>A history of the Lonar <span class="hlt">crater</span>, India: An overview</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Nayak, V. K.</p> <p>1992-01-01</p> <p>The origin of the circular structure at Lonar, India, described variously as cauldron, pit, hollow, depression, and <span class="hlt">crater</span>, has been a controversial subject since the early nineteenth century. A history of its origin and other aspects from 1823 to 1990 are overviewed. The structure in the Deccan Trap Basalt is nearly circular with a breach in the northeast, 1830 m in diameter, 150 m deep, with a saline lake in the <span class="hlt">crater</span> floor. Over the years, the origin of the Lonar structure has risen from volcanism, subsidence, and cryptovolcanism to an authentic meteorite <span class="hlt">impact</span> <span class="hlt">crater</span>. Lonar is unique because it is probably the only terrestrial <span class="hlt">crater</span> in basalt and is the closest analog with the Moon's <span class="hlt">craters</span>. Some unresolved questions are suggested. The proposal is made that the young Lonar <span class="hlt">impact</span> <span class="hlt">crater</span>, which is less than 50,000 years old, should be considered as the best <span class="hlt">crater</span> laboratory analogous to those of the Moon, be treated as a global monument, and preserved for scientists to comprehend more about the mysteries of nature and <span class="hlt">impact</span> <span class="hlt">cratering</span>, which is now emerging as a fundamental ubiquitous geological process in the evolution of the planets.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19820038854&hterms=TNT&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DTNT','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19820038854&hterms=TNT&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D40%26Ntt%3DTNT"><span>The equivalent depth of burst for <span class="hlt">impact</span> <span class="hlt">cratering</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Holsapple, K. A.</p> <p>1980-01-01</p> <p>The concept of modeling an <span class="hlt">impact</span> <span class="hlt">cratering</span> event with an explosive event with the explosive buried at some equivalent depth of burst (d.o.b.) is discussed. Various and different ways to define this equivalent d.o.b. are identified. Recent experimental results for a dense quartz sand are used to determine the equivalent d.o.b. for various conditions of charge type, event size, and <span class="hlt">impact</span> conditions. The results show a decrease in equivalent d.o.b. with increasing energy for fixed <span class="hlt">impact</span> velocity and a decrease in equivalent d.o.b. with increasing velocity for fixed energy. The values for an iron projectile are on the order of 2-3 projectile radii for energy equal to one ton of TNT, decreasing to about 1.5 radii at a megaton of TNT. The dependence on projectile and target mass density matches that included in common jet-penetration formulas for projectile densities greater than target densities and for the higher energies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70194928','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70194928"><span>Seismic expression of the Chesapeake Bay <span class="hlt">impact</span> <span class="hlt">crater</span>: Structural and morphologic refinements based on new seismic data</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Poag, C. Wylie; Hutchinson, Deborah R.; Colman, Steve M.; Lee, Myung W.; Dressler, B.O.; Sharpton, V.L.</p> <p>1999-01-01</p> <p>This work refines previous interpretations of the structure and morphology of the Chesapeake Bay <span class="hlt">impact</span> <span class="hlt">crater</span> on the basis of more than 1,200 km of multichannel and single-channel seismic reflection profiles collected in the bay and on the adjacent continental shelf. The outer rim, formed in sedimentary rocks, is irregularly circular, with an average diameter of ~85 km. A 20–25-km-wide annular trough separates the outer rim from an ovate, crystalline peak ring of ~200 m of maximum relief. The inner basin is 35–40 km in diameter, and at least 1.26 km deep. A crystalline(?) central peak, approximately 1 km high, is faintly imaged on three profiles, and also is indicated by a small positive Bouguer gravity anomaly. These features classify the <span class="hlt">crater</span> as a complex peak-ring/central peak <span class="hlt">crater</span>. Chesapeake Bay <span class="hlt">Crater</span> is most comparable to the Ries and Popigai <span class="hlt">Craters</span> on Earth; to protobasins on Mars, Mercury, and the Moon; and to type D <span class="hlt">craters</span> on Venus.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930020179','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930020179"><span><span class="hlt">Cratering</span> in glasses <span class="hlt">impacted</span> by debris or micrometeorites</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Wiedlocher, David E.; Kinser, Donald L.</p> <p>1993-01-01</p> <p>Mechanical strength measurements on five glasses and one glass-ceramic exposed on LDEF revealed no damage exceeding experimental limits of error. The measurement technique subjected less than 5 percent of the sample surface area to stresses above 90 percent of the failure strength. Seven micrometeorite or space debris <span class="hlt">impacts</span> occurred at locations which were not in that portion of the sample subjected to greater than 90 percent of the applied stress. As a result of this, the <span class="hlt">impact</span> events on the sample were not detected in the mechanical strength measurements. The physical form and structure of the <span class="hlt">impact</span> sites was carefully examined to determine the influence of those events upon stress concentration associated with the <span class="hlt">impact</span> and the resulting mechanical strength. The size of the <span class="hlt">impact</span> site, insofar as it determines flaw size for fracture purposes, was examined. Surface topography of the <span class="hlt">impacts</span> reveals that six of the seven sites display <span class="hlt">impact</span> melting. The classical melt <span class="hlt">crater</span> structure is surrounded by a zone of fractured glass. Residual stresses arising from shock compression and from cooling of the fused zone cannot be included in the fracture mechanics analyses based on simple flaw size measurements. Strategies for refining estimates of mechanical strength degradation by <span class="hlt">impact</span> events are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015AGUFMNH11A1886M','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015AGUFMNH11A1886M"><span>The shapes of fragments in hypervelocity <span class="hlt">impact</span> experiments ranging from <span class="hlt">cratering</span> to catastrophic disruption</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Michikami, T.; Hagermann, A.; Kadokawa, T.; Yoshida, A.; Shimada, A.; Hasegawa, S.; Tsuchiyama, A.</p> <p>2015-12-01</p> <p>Laboratory <span class="hlt">impact</span> experiments have found that the shapes of <span class="hlt">impact</span> fragments as defined by axes a, b and c, these being the maximum dimensions of the fragment in three mutually orthogonal planes (a ≥ b ≥ c) are distributed around mean values of the axial ratios b/a ~0.7 and c/a ~0.5, i.e., corresponding to a : b: c in the simple proportion 2: √2: 1. The shape distributions of some boulders on asteroid Eros, the small- and fast-rotating asteroids (diameter < 200 m and rotation period < 1 h), and asteroids in young families, are similar to those of laboratory fragments in catastrophic disruption. However, the shapes of laboratory fragments were obtained from the experiments that resulted in catastrophic disruption, a process that is different from <span class="hlt">impact</span> <span class="hlt">cratering</span>. In order to systematically investigate the shapes of fragments in the range from <span class="hlt">impact</span> <span class="hlt">cratering</span> to catastrophic disruption, <span class="hlt">impact</span> experiments for basalt targets 5 to 15 cm in size were performed. A total of 28 <span class="hlt">impact</span> experiments were carried out by a spherical nylon projectile (diameter 7.14 mm) perpendicularly into the target surface at velocities of 1.6 to 7.0 km/s. More than 13,000 fragments with b ≥ 4 mm generated in the <span class="hlt">impact</span> experiments were measured. In the experiments, the mean value of c/a in each <span class="hlt">impact</span> decreases with decreasing <span class="hlt">impact</span> energy per unit target mass. For instance, the mean value of c/a in an <span class="hlt">impact</span> <span class="hlt">cratering</span> event is nearly 0.2, which is less than that c/a in a catastrophic disruption (~0.5). To apply the experimental results to real collisions on asteroids, we investigated the shapes of 21 arbitrarily selected boulders (> 8 m) on asteroid Itokawa. The mean value of c/a of these boulders is 0.46, which is similar to the value for catastrophic disruption. This implies that the parent body of Itokawa could have experienced a catastrophic disruption.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA00280.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA00280.html"><span>Ganymede - Mixture of Terrains and Large <span class="hlt">Impact</span> <span class="hlt">Crater</span> in Uruk Sulcus Region</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>1997-09-07</p> <p>A mixture of terrains studded with a large <span class="hlt">impact</span> <span class="hlt">crater</span> is shown in this view of the Uruk Sulcus region of Jupiter moon Ganymede taken by NASA Galileo spacecraft during its first flyby of the planet-sized moon on June 27, 1996. http://photojournal.jpl.nasa.gov/catalog/PIA00280</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018ISPAnIV-3..127K','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018ISPAnIV-3..127K"><span>Generating <span class="hlt">Impact</span> Maps from Automatically Detected Bomb <span class="hlt">Craters</span> in Aerial Wartime Images Using Marked Point Processes</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Kruse, Christian; Rottensteiner, Franz; Hoberg, Thorsten; Ziems, Marcel; Rebke, Julia; Heipke, Christian</p> <p>2018-04-01</p> <p>The aftermath of wartime attacks is often felt long after the war ended, as numerous unexploded bombs may still exist in the ground. Typically, such areas are documented in so-called <span class="hlt">impact</span> maps which are based on the detection of bomb <span class="hlt">craters</span>. This paper proposes a method for the automatic detection of bomb <span class="hlt">craters</span> in aerial wartime images that were taken during the Second World War. The object model for the bomb <span class="hlt">craters</span> is represented by ellipses. A probabilistic approach based on marked point processes determines the most likely configuration of objects within the scene. Adding and removing new objects to and from the current configuration, respectively, changing their positions and modifying the ellipse parameters randomly creates new object configurations. Each configuration is evaluated using an energy function. High gradient magnitudes along the border of the ellipse are favored and overlapping ellipses are penalized. Reversible Jump Markov Chain Monte Carlo sampling in combination with simulated annealing provides the global energy optimum, which describes the conformance with a predefined model. For generating the <span class="hlt">impact</span> map a probability map is defined which is created from the automatic detections via kernel density estimation. By setting a threshold, areas around the detections are classified as contaminated or uncontaminated sites, respectively. Our results show the general potential of the method for the automatic detection of bomb <span class="hlt">craters</span> and its automated generation of an <span class="hlt">impact</span> map in a heterogeneous image stock.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA21911.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA21911.html"><span>Emesh <span class="hlt">Crater</span> on Ceres</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-11-02</p> <p>This image taken by NASA's Dawn spacecraft shows Emesh, a <span class="hlt">crater</span> on Ceres. Emesh, named after the Sumerian god of vegetation and agriculture, is 12 miles (20 kilometers) wide. Located at the edge of the Vendimia Planitia, the floor of this <span class="hlt">crater</span> is asymmetrical with terraces distributed along the eastern rim. Additionally, this image shows many subtle linear features that are likely the surface expressions of faults. These faults play a big role in shaping Ceres' <span class="hlt">craters</span>, leading to non-circular <span class="hlt">craters</span> such as Emesh. To the left of Emesh in this view, a much older <span class="hlt">crater</span> of similar size has mostly been erased by <span class="hlt">impacts</span> and their ejecta. Dawn took this image on May 11, 2016, from its low-altitude mapping orbit, at a distance of about 240 miles (385 kilometers) above the surface. The center coordinates of this image are 11 degrees north latitude, 158 degrees east longitude. https://photojournal.jpl.nasa.gov/catalog/PIA21911</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70194853','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70194853"><span>Underwater research methods for study of nuclear bomb <span class="hlt">craters</span>, Enewetak, Marshall Islands</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>Shinn, E.A.; Halley, R.B.; Kindinger, J.L.; Hudson, J.H.; Slate, R.A.</p> <p>1990-01-01</p> <p>Three <span class="hlt">craters</span>, created by the explosion of nuclear fusion devices, were mapped, sampled, core drilled and excavated with airlifts at Enewetak Atoll in the Marshall Islands by using scuba and a research submersible. The <span class="hlt">craters</span> studied were Mike, Oak, and Koa. Tests took place near sea level at the transition between lithified reef flat and unlithified lagoonal sediments, where water depth ranged from 1 to 4 m. <span class="hlt">Craters</span> produced by the blasts ranged from 30 to 60 m in depth. The purpose of our study was to determine <span class="hlt">crater</span> diameter and depth immediately after detonation. Observations of submerged roadways and testing structures and upturned <span class="hlt">crater</span> rims similar to those characteristic of meteor <span class="hlt">impacts</span> indicate that the initial, or transient, <span class="hlt">craters</span> were smaller than their present size. At some later time, while the area was too radioactive for direct examination, the sides of the <span class="hlt">craters</span> slumped owing to dewatering of under lying pulverized rock. Core drilling of <span class="hlt">crater</span> margins with a diver-operated hydraulic coring device provided additional data. On the seaward margin of the atoll, opposite Mike, a large portion of the atoll rim approximately the size of a city block had slumped into the deep ocean, leaving a clean vertical rock section more than 400m high. An <span class="hlt">abundance</span> of aggressive grey reef sharks displaying classic territorial behavior prevented use of scuba at the Mike slump site. The two-person submersible R.V. Delta provided protection and allowed observations down to 300 m. During the 6-week period of study, we made more than 300 scuba and 275 submersible dives. Mapping was with side scan sonar and continuous video sweeps supplemented by tape-recorded verbal descriptions made from within the submersible. A mini-ranger navigation system linked to the submersible allowed plotting of bottom features, depth and sediment type with spatial accuracy to within 2 m.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.ncbi.nlm.nih.gov/pubmed/11539331','PUBMED'); return false;" href="https://www.ncbi.nlm.nih.gov/pubmed/11539331"><span>Surface expression of the Chicxulub <span class="hlt">crater</span></span></a></p> <p><a target="_blank" href="https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?DB=pubmed">PubMed</a></p> <p>Pope, K O; Ocampo, A C; Kinsland, G L; Smith, R</p> <p>1996-06-01</p> <p>Analyses of geomorphic, soil, and topographic data from the northern Yucatan Peninsula, Mexico, confirm that the buried Chicxulub <span class="hlt">impact</span> <span class="hlt">crater</span> has a distinct surface expression and that carbonate sedimentation throughout the Cenozoic has been influenced by the <span class="hlt">crater</span>. Late Tertiary sedimentation was mostly restricted to the region within the buried <span class="hlt">crater</span>, and a semicircular moat existed until at least Pliocene time. The topographic expression of the <span class="hlt">crater</span> is a series of features concentric with the <span class="hlt">crater</span>. The most prominent is an approximately 83-km-radius trough or moat containing sinkholes (the Cenote ring). Early Tertiary surfaces rise abruptly outside the moat and form a stepped topography with an outer trough and ridge crest at radii of approximately 103 and approximately 129 km, respectively. Two discontinuous troughs lie within the moat at radii of approximately 41 and approximately 62 km. The low ridge between the inner troughs corresponds to the buried peak ring. The moat corresponds to the outer edge of the <span class="hlt">crater</span> floor demarcated by a major ring fault. The outer trough and the approximately 62-km-radius inner trough also mark buried ring faults. The ridge crest corresponds to the topographic rim of the <span class="hlt">crater</span> as modified by postimpact processes. These interpretations support previous findings that the principal <span class="hlt">impact</span> basin has a diameter of approximately 180 km, but concentric, low-relief slumping extends well beyond this diameter and the eroded <span class="hlt">crater</span> rim may extend to a diameter of approximately 260 km.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19870008162','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19870008162"><span>Zhamanshin meteor <span class="hlt">crater</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Florenskiy, P. V.; Dabizha, A. I.</p> <p>1987-01-01</p> <p>A historical survey and geographic, geologic and geophysical characteristics, the results of many years of study of the Zhamanshin meteor <span class="hlt">crater</span> in the Northern Aral region, are reported. From this data the likely initial configuration and cause of formation of the <span class="hlt">crater</span> are reconstructed. Petrographic and mineralogical analyses are given of the brecciated and remelted rocks, of the zhamanshinites and irgizite tektites in particular. The <span class="hlt">impact</span> melting, dispersion and quenching processes resulting in tektite formation are discussed.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://www.osti.gov/biblio/6966739-strawberry-crater-roadless-areas-arizona','SCIGOV-STC'); return false;" href="https://www.osti.gov/biblio/6966739-strawberry-crater-roadless-areas-arizona"><span>Strawberry <span class="hlt">Crater</span> Roadless Areas, Arizona</span></a></p> <p><a target="_blank" href="http://www.osti.gov/search">DOE Office of Scientific and Technical Information (OSTI.GOV)</a></p> <p>Wolfe, E.W.; Light, T.D.</p> <p>1984-01-01</p> <p>The results of a mineral survey conducted in 1980 in the Strawberry <span class="hlt">Crater</span> Roadless Areas, Arizona, indicate little promise for the occurrence of metallic mineral or fossil fuel resources in the area. The area contains deposits of cinder, useful for the production of aggregate block, and for deposits of decorative stone; however, similar deposits occur in great <span class="hlt">abundance</span> throughout the San Francisco volcanic field outside the roadless areas. There is a possibility that the Strawberry <span class="hlt">Crater</span> Roadless Areas may overlie part of a crustal magma chamber or still warm pluton related to the San Francisco Mountain stratovolcano or to basalticmore » vents of late Pleistocene or Holocene age. Such a magma chamber or pluton beneath the Strawberry <span class="hlt">Crater</span> Roadless Areas might be an energy source from which a hot-, dry-rock geothermal energy system could be developed, and a probable geothermal resource potential is therefore assigned to these areas.« less</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2017AGUFM.P43D2913D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2017AGUFM.P43D2913D"><span><span class="hlt">Crater</span> Morphology of Engineered and Natural Impactors into Planetary Ice</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Danner, M.; Winglee, R.; Koch, J.</p> <p>2017-12-01</p> <p><span class="hlt">Crater</span> morphology of engineered impactors, such as those proposed for the Europa Kinetic Ice Penetrator (EKIP) mission, varies drastically from that of natural impactors (i.e. Asteroids, meteoroids). Previous work of natural <span class="hlt">impact</span> <span class="hlt">craters</span> in ice have been conducted with the intent to bound the thickness of Europa's ice crust; this work focuses on the depth, size, and compressional effects caused by various impactor designs, and the possible effects to the Europan surface. The present work details results from nine projectiles that were dropped on the Taku Glacier, AK at an altitude of 775 meters above surface; three rocks to simulate natural impactors, and six iterations of engineered steel and aluminum penetrator projectiles. Density measurements were taken at various locations within the <span class="hlt">craters</span>, as well as through a cross section of the <span class="hlt">crater</span>. Due to altitude restrictions, projectiles remained below terminal velocity. The natural/rock <span class="hlt">impact</span> <span class="hlt">craters</span> displayed typical <span class="hlt">cratering</span> characteristics such as shallow, half meter scale depth, and orthogonal compressional forcing. The engineered projectiles produced <span class="hlt">impact</span> <span class="hlt">craters</span> with depths averaging two meters, with <span class="hlt">crater</span> widths matching the impactor diameters. Compressional waves from the engineered impactors propagated downwards, parallel to direction of <span class="hlt">impact</span>. Engineered impactors create significantly less lateral fracturing than natural impactors. Due to the EKIP landing mechanism, sampling of pristine ice closer to the lander is possible than previously thought with classical <span class="hlt">impact</span> theory. Future work is planned to penetrate older, multiyear ice with higher velocity <span class="hlt">impacts</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018LPICo2047.6018D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018LPICo2047.6018D"><span><span class="hlt">Impact</span> Melt Emplacement on Mercury</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Daniels, J. W.; Neish, C. D.</p> <p>2018-05-01</p> <p>This work proposes that fresh <span class="hlt">craters</span> on rocky bodies may deposit <span class="hlt">impact</span> melt externally ultimately according to the strength of its surface gravity, regardless of the body's surface topography and melt <span class="hlt">abundance</span>.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940015911&hterms=barlow&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dbarlow','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940015911&hterms=barlow&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D60%26Ntt%3Dbarlow"><span>Morphologic and morphometric studies of <span class="hlt">impact</span> <span class="hlt">craters</span> in the northern plains of Mars</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Barlow, N. G.</p> <p>1993-01-01</p> <p>Fresh <span class="hlt">impact</span> <span class="hlt">craters</span> in the northern plains of Mars display a variety of morphologic and morphometric properties. Ejecta morphologies range from radial to fluidized, interior features include central peaks and central pits, fluidized morphologies display a range of sinuosities, and depth-diameter ratios are being measured to determine regional variations. Studies of the martian northern plains over the past five years have concentrated in three areas: (1) determining correlations of ejecta morphologies with <span class="hlt">crater</span> diameter, latitude, and underlying terrain; (2) determining variations in fluidized ejecta blanket sinuosity across the planet; and (3) measurement of depth-diameter ratios and determination of regional variations in this ratio.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19730050944&hterms=ghosts&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dghosts','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19730050944&hterms=ghosts&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D10%26Ntt%3Dghosts"><span>Moon - 'Ghost' <span class="hlt">craters</span> formed during Mare filling.</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Cruikshank, D. P.; Hartmann, W. K.; Wood, C. A.</p> <p>1973-01-01</p> <p>This paper discusses formation of 'pathological' cases of <span class="hlt">crater</span> morphology due to interaction of <span class="hlt">craters</span> with molten lavas. Terrestrial observations of such a process are discussed. In lunar maria, a number of small <span class="hlt">impact</span> <span class="hlt">craters</span> (D less than 10 km) may have been covered by thin layers of fluid lavas, or formed in molten lava. Some specific lunar examples are discussed, including unusual shallow rings resembling experimental <span class="hlt">craters</span> deformed by isostatic filling.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996LPI....27..719L','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996LPI....27..719L"><span>The Distribution of Subsurface Water at Hadriaca and Tyrrhena Paterae and Surrounding Areas on Mars from <span class="hlt">Impact</span> <span class="hlt">Crater</span> Morphology</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Lancaster, M. G.; Guest, J. E.</p> <p>1996-03-01</p> <p>It is well established that the surface of Mars exhibits <span class="hlt">abundant</span> evidence for the presence of either liquid or frozen water during the course of Martian history. The origin, location, extent and transport of this water is of critical importance in the understanding of Martian geology and climate. In particular, the fluid appearance of rampart <span class="hlt">crater</span> ejecta has been cited as evidence for subsurface ice at the time of <span class="hlt">impact</span>. Ejecta morphology has proven to be a useful tool for studying the distribution of subsurface ice on Mars. It is possible that in some regions the concentration and distribution of subsurface ice has been affected by volcanic processes, either in the melting and/or mobilisation of existing subsurface water, and/or in the injection of juvenile water into the martian crust. The presence of water may also have affected the style of volcanic eruptions on Mars, increasing the volatile content of rising magmas and generating explosive activity. We are currently investigating the <span class="hlt">abundance</span> and role of water in the evolution of the volcanoes Hadriaca and Tyrrhena Patera and surrounding highlands northeast of the Hellas Basin. The morphology of these volcanoes has been attributed to explosive volcanism, and to the presence of substantial amounts of water in the regolith at the time of their eruption. The location of Hadriaca Patera in a region containing channelled plains, debris flows, and pitted plains, together with the style of erosion of the volcano flanks suggests presence of volatile-rich surface materials or fluvial or periglacial activity. This work is a continuation of research undertaken by Cave in the Elysium Mons Region, where ice was found to be enriched at depth in the Elysium Lavas. We are performing a similar analysis for the volcanics of Hadriaca and Tyrrhena Paterae. A database containing information on the location, size, morphology, ejecta characteristics and degradation state of several hundred <span class="hlt">impact</span> <span class="hlt">craters</span> displaying ejecta in</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-GSFC_20171208_Archive_e002031.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-GSFC_20171208_Archive_e002031.html"><span>Einstein and Einstein A: A Study in <span class="hlt">Crater</span> Morphology</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-12-08</p> <p>NASA image release May 14, 2010 Einstein and Einstein A: A Study in <span class="hlt">Crater</span> Morphology Located on the western limb of the Moon, Einstein and Einstein A <span class="hlt">craters</span> (16.3oN, 271.3oE ) are only visible to Earth-based observers during certain lunar lighting and orientation conditions. Einstein A is younger than Einstein, as indicated by the fact that it lies squarely in the middle of the floor of Einstein. When viewed in topographic data, these two <span class="hlt">craters</span> reveal much about the relative age and shape of an <span class="hlt">impact</span> <span class="hlt">crater</span>. To understand further, let's first take a look at Einstein. Einstein is a fairly large <span class="hlt">crater</span> that spans 198 km across. A <span class="hlt">crater</span>'s size alone however cannot reveal much about age. ÊEinstein's relative age can be determined by examining the frequency and distribution of <span class="hlt">impact</span> <span class="hlt">craters</span> overprinted on its rim and floor. Younger <span class="hlt">craters</span> have had fewer <span class="hlt">impacts</span>, which enables them to retain their original morphology. Einstein A reveals most of its original structure, including a raised rim and ejecta blanket, and is therefore a relatively young <span class="hlt">crater</span> as compared to Einstein, whose original structure has been somewhat degraded over time by smaller <span class="hlt">impacts</span>. The Einstein <span class="hlt">craters</span> were named after famed physicist, philosopher, and scientist Albert Einstein (1879-1955). To learn more go to: www.nasa.gov/mission_pages/LRO/multimedia/lroimages/lola-... NASA Goddard Space Flight Center is home to the nation's largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA08185.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA08185.html"><span><span class="hlt">Cratered</span> Crescent</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2006-05-25</p> <p>Quiet and cold, a crescent Tethys floats above the nearly edge-on rings of Saturn. The only surface features visible on Tethys 1,071 kilometers, or 665 miles across from this distance are a few <span class="hlt">impact</span> <span class="hlt">craters</span></p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li class="active"><span>24</span></li> <li><a href="#" onclick='return showDiv("page_25");'>25</a></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_24 --> <div id="page_25" class="hiddenDiv"> <div class="row"> <div class="col-sm-12"> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div> </div> <div class="row"> <div class="col-sm-12"> <ol class="result-class" start="481"> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018PhDT.........9D','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018PhDT.........9D"><span><span class="hlt">Cratering</span> Characteristics of the Europa Kinetic Ice Penetrator</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Danner, Mariah L.</p> <p></p> <p>This thesis further develops the Europa Kinetic Ice Penetrator (EKIP) landing technique for airless bodies, as well as characterizes the effect EKIP would have on Europa's surface. Damage to the extremophile Planococcus Halocryophilus OR1 (PHOR1) during a laboratory hypervelocity <span class="hlt">impact</span> test was studied the effect of rapid application of pressure to microbes frozen in ice. Significant die-off occurred, however PHOR1 microbes survived a 2.2km/s <span class="hlt">impact</span>. Field testing the second-stage deployment, as well as to characterize <span class="hlt">crater</span> morphology of the EKIP system was conducted. With low <span class="hlt">impact</span> velocities, penetrators consistently had deeper, narrower <span class="hlt">craters</span> than natural impactors (rocks), and showed less radial and sub-impactor compression. This, and future <span class="hlt">crater</span> data into harder substrates, will create a <span class="hlt">cratering</span> hardness curve for this design impactor into airless bodies. This curve, used with the eventual in situ <span class="hlt">craters</span>, can be used to constrain the hardness and other physical properties of the surface of icy-bodies.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19940016391&hterms=laws+physics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dlaws%2Bphysics','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19940016391&hterms=laws+physics&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D20%26Ntt%3Dlaws%2Bphysics"><span>A fresh look at <span class="hlt">crater</span> scaling laws for normal and oblique hypervelocity <span class="hlt">impacts</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Watts, A. J.; Atkinson, D. R.; Rieco, S. R.; Brandvold, J. B.; Lapin, S. L.; Coombs, C. R.</p> <p>1993-01-01</p> <p>With the concomitant increase in the amount of man-made debris and an ever increasing use of space satellites, the issue of accidental collisions with particles becomes more severe. While the natural micrometeoroid population is unavoidable and assumed constant, continued launches increase the debris population at a steady rate. Debris currently includes items ranging in size from microns to meters which originated from spent satellites and rocket cases. To understand and model these environments, <span class="hlt">impact</span> damage in the form of <span class="hlt">craters</span> and perforations must be analyzed. Returned spacecraft materials such as those from LDEF and Solar Max have provided such a testbed. From these space-aged samples various <span class="hlt">impact</span> parameters (i.e., particle size, particle and target material, particle shape, relative <span class="hlt">impact</span> speed, etc.) may be determined. These types of analyses require the use of generic analytic scaling laws which can adequately describe the <span class="hlt">impact</span> effects. Currently, most existing analytic scaling laws are little more than curve-fits to limited data and are not based on physics, and thus are not generically applicable over a wide range of <span class="hlt">impact</span> parameters. During this study, a series of physics-based scaling laws for normal and oblique <span class="hlt">crater</span> and perforation formation has been generated into two types of materials: aluminum and Teflon.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950017423','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950017423"><span>Dimensional scaling for <span class="hlt">impact</span> <span class="hlt">cratering</span> and perforation</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Watts, Alan J.; Atkinson, Dale</p> <p>1995-01-01</p> <p>POD Associates have revisited the issue of generic scaling laws able to adequately predict (within better than 20 percent) <span class="hlt">cratering</span> in semi-infinite targets and perforations through finite thickness targets. The approach used was to apply physical logic for hydrodynamics in a consistent manner able to account for chunky-body <span class="hlt">impacts</span> such that the only variables needed are those directly related to known material properties for both the impactor and target. The analyses were compared and verified versus CTH hydrodynamic code calculations and existing data. Comparisons with previous scaling laws were also performed to identify which (if any) were good for generic purposes. This paper is a short synopsis of the full report available through the NASA Langley Research Center, LDEF Science Office.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1983LPSC...14..353H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1983LPSC...14..353H"><span>Morphology and chemistry of projectile residue in small experimental <span class="hlt">impact</span> <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Horz, F.; Fechtig, H.; Janicke, J.; Schneider, E.</p> <p>1983-11-01</p> <p>Small-scale <span class="hlt">impact</span> <span class="hlt">craters</span> (5-7 mm in diameter) were produced with a light gas gun in high purity Au and Cu targets using soda lime glass (SL) and man-made basalt glass (BG) as projectiles. Maximum <span class="hlt">impact</span> velocity was 6.4 km/s resulting in peak pressures of approximately 120-150 GPa. Copious amounts of projectile melts are preserved as thin glass liners draping the entire <span class="hlt">crater</span> cavity; some of this liner may be lost by spallation, however. SEM investigations reveal complex surface textures including multistage flow phenomena and distinct temporal deposition sequences of small droplets. Inasmuch as some of the melts were generated at peak pressures greater than 120 GPa, these glasses represent the most severely shocked silicates recovered from laboratory experiments to date. Major element analyses reveal partial loss of alkalis; Na2O loss of 10-15 percent is observed, while K2O loss may be as high as 30-50 percent. Although the observed volatile loss in these projectile melts is significant, it still remains uncertain whether target melts produced on planetary surfaces are severely fractionated by selective volatilization processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/1996LPI....27..473G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/1996LPI....27..473G"><span>The Group of Macha <span class="hlt">Craters</span> in Western Yakutia</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gurov, E. P.</p> <p>1996-03-01</p> <p>The group of Macha <span class="hlt">craters</span> is placed in the marginal part of Aldan Anteclise in Macha river basin, the left tributary of Lena river. Coordinates of the <span class="hlt">craters</span>: 60 degrees 06 minutes N, 117 degrees 35 minutes E. The Macha <span class="hlt">craters</span> were discovered by aerovisual observations of Aldan Shield and Aldan Anteclise during the <span class="hlt">impact</span> <span class="hlt">craters</span> search in this region.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://ntrs.nasa.gov/search.jsp?R=19790055292&hterms=gravity+anomaly&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dgravity%2Banomaly','NASA-TRS'); return false;" href="https://ntrs.nasa.gov/search.jsp?R=19790055292&hterms=gravity+anomaly&qs=Ntx%3Dmode%2Bmatchall%26Ntk%3DAll%26N%3D0%26No%3D30%26Ntt%3Dgravity%2Banomaly"><span>Lunar Bouguer gravity anomalies - Imbrian age <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Dvorak, J.; Phillips, R. J.</p> <p>1978-01-01</p> <p>The Bouguer gravity of mass anomalies associated with four Imbrian age <span class="hlt">craters</span>, analyzed in the present paper, are found to differ considerably from the values of the mass anomalies associated with some young lunar <span class="hlt">craters</span>. Of the Imbrian age <span class="hlt">craters</span>, only Piccolomini exhibits a negative gravity anomaly (i.e., a low density region) which is characteristic of the young <span class="hlt">craters</span> studied. The Bouguer gravity anomalies are zero for each of the remaining Imbrian age <span class="hlt">craters</span>. Since, Piccolomini is younger, or at least less modified, than the other Imbrian age <span class="hlt">craters</span>, it is suggested that the processes responsible for the post-<span class="hlt">impact</span> modification of the Imbrian age <span class="hlt">craters</span> may also be responsible for removing the negative mass anomalies initially associated with these features.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA21410.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA21410.html"><span>Yalode <span class="hlt">Crater</span> on Ceres</span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>2017-06-28</p> <p>Yalode <span class="hlt">crater</span> is so large -- at 162 miles, 260 kilometers in diameter -- that a variety of vantage points is necessary to understand its geological context. This view of the northern portion of Yalode is one of many images NASA's Dawn spacecraft has taken of this <span class="hlt">crater</span>. The large <span class="hlt">impact</span> that formed the <span class="hlt">crater</span> likely involved a lot of heat, which explains the relatively smooth <span class="hlt">crater</span> floor punctuated by smaller <span class="hlt">craters</span>. A couple of larger <span class="hlt">craters</span> in Yalode have polygonal shapes. This type of <span class="hlt">crater</span> shape is frequently found on Ceres and may be indicative of extensive underground fractures. The larger <span class="hlt">crater</span> to the right of center in this image is called Lono (12 miles, 20 kilometers in diameter) and the one below it is called Besua (11 miles, 17 kilometers). Some of the small <span class="hlt">craters</span> are accompanied by ejecta blankets that are more reflective than their surroundings. The strange Nar Sulcus fractures can be seen in the bottom left corner of the picture. Linear features seen throughout the image may have formed when material collapsed above empty spaces underground. These linear features include linear chains of <span class="hlt">craters</span> called catenae. Dawn took this image on September 27, 2015, from 915 miles (1,470 kilometers) altitude. The center coordinates of this image are 32 degrees south latitude and 300 degrees east longitude. Yalode gets its name from a goddess worshipped by women at the harvest rites in the Dahomey culture of western Africa. Besua takes its name from the Egyptian grain god, and Lono from the Hawaiian god of agriculture. https://photojournal.jpl.nasa.gov/catalog/PIA21410</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19950017405','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19950017405"><span>Small <span class="hlt">craters</span> on the meteoroid and space debris <span class="hlt">impact</span> experiment</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Humes, Donald H.</p> <p>1995-01-01</p> <p>Examination of 9.34 m(exp 2) of thick aluminum plates from the Long Duration Exposure Facility (LDEF) using a 25X microscope revealed 4341 <span class="hlt">craters</span> that were 0.1 mm in diameter or larger. The largest was 3 mm in diameter. Most were roughly hemispherical with lips that were raised above the original plate surface. The <span class="hlt">crater</span> diameter measured was the diameter at the top of the raised lips. There was a large variation in the number density of <span class="hlt">craters</span> around the three-axis gravity-gradient stabilized spacecraft. A model of the near-Earth meteoroid environment is presented which uses a meteoroid size distribution based on the <span class="hlt">crater</span> size distribution on the space end of the LDEF. An argument is made that nearly all the <span class="hlt">craters</span> on the space end must have been caused by meteoroids and that very few could have been caused by man-made orbital debris. However, no chemical analysis of impactor residue that will distinguish between meteoroids and man-made debris is yet available. A small area (0.0447 m(exp 2)) of one of the plates on the space end was scanned with a 200X microscope revealing 155 <span class="hlt">craters</span> between 10 micron and 100 micron in diameter and 3 <span class="hlt">craters</span> smaller than 10 micron. This data was used to extend the size distribution of meteoroids down to approximately 1 micron. New penetration equations developed by Alan Watts were used to relate <span class="hlt">crater</span> dimensions to meteoroid size. The equations suggest that meteoroids must have a density near 2.5 g/cm(exp 3) to produce <span class="hlt">craters</span> of the shape found on the LDEF. The near-Earth meteoroid model suggests that about 80 to 85 percent of the 100 micron to 1 mm diameter <span class="hlt">craters</span> on the twelve peripheral rows of the LDEF were caused by meteoroids, leaving 15 to 20 percent to be caused by man-made orbital debris.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2018E%26ES..134a2022G','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2018E%26ES..134a2022G"><span>Calculation of <span class="hlt">craters</span> resulting from <span class="hlt">impact</span> rupture of rock mass using pulse hydrodynamic problem formulation</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Gorodilov, LV; Rasputina, TB</p> <p>2018-03-01</p> <p>A liquid–solid hydrodynamic model is used to determine shapes and sizes of <span class="hlt">craters</span> generated by <span class="hlt">impact</span> rupture of rocks. Near the <span class="hlt">impact</span> location, rock is modeled by an ideal incompressible liquid, in the distance—by an absolute solid. The calculated data are compared with the experimental results obtained under <span class="hlt">impact</span> treatment of marble by a wedge-shaped tool.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19940011772','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19940011772"><span>Trace-element composition of Chicxulub <span class="hlt">crater</span> melt rock, K/T tektites and Yucatan basement</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Hildebrand, A. R.; Gregoire, D. C.; Attrep, M., Jr.; Claeys, P.; Thompson, C. M.; Boynton, W. V.</p> <p>1993-01-01</p> <p>The Cretaceous/Tertiary (K/T) boundary Chicxulub <span class="hlt">impact</span> is the best preserved large <span class="hlt">impact</span> in the geologic record. The Chicxulub <span class="hlt">crater</span> has been buried with no apparent erosion of its intracrater deposits, and its ejecta blanket is known and is well preserved at hundreds of localities globally. Although most of the molten material ejected from the <span class="hlt">crater</span> has been largely altered, a few localities still preserve tektite glass. Availability of intra- and extracrater <span class="hlt">impact</span> products as well as plausible matches to the targeted rocks allows the comparison of compositions of the different classes of <span class="hlt">impact</span> products to those of the <span class="hlt">impacted</span> lithologies. Determination of trace-element compositions of the K/T tektites, Chicxulub melt rock, and the targeted Yucatan silicate basement and carbonate/evaporite lithologies have been made using instrumental neutron activation analysis (INAA) and inductively coupled plasma mass spectrometry (ICP-MS). Some sample splits were studied with both techniques to ensure that inter-laboratory variation was not significant or could be corrected. The concentration of a few major and minor elements was also checked against microprobe results. Radiochemical neutron activation analysis (RNAA) was used to determine Ir <span class="hlt">abundances</span> in some samples.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20170001953','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20170001953"><span>Constraining the Origin of Basaltic Volcanic Rocks Observed by Opportunity Along the Rim of Endeavour <span class="hlt">Crater</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Bouchard, M. C.; Jolliff, B. L.; Farrand, W. H.; Mittlefehldt, D. W.</p> <p>2017-01-01</p> <p>The Mars Exploration Rover (MER) Opportunity continues its exploration along the rim of Endeavour <span class="hlt">Crater</span>. While the primary focus for investigation has been to seek evidence of aqueous alteration, Opportunity has observed a variety of rock types, including some that are hard and relatively unaltered. These rocks tend to occur most commonly as "float rocks" or "erratics" where the geologic setting does not clearly reveal their origin. Along the rim of Endeavour <span class="hlt">crater</span> (Fig. 1), such rocks, commonly noted in Panoramic Camera (Pancam) left eye composites as "blue rocks", are <span class="hlt">abundant</span> components of some of the Endeavour <span class="hlt">crater</span> rim deposits, scree slopes, and colluvium deposits. In this abstract, we examine the similarity of several of these rocks analyzed using Opportunity's Alpha Particle X-Ray Spectrometer (APXS), images and color from the Pancam, and textures observed with the Microscopic Imager (MI. At issue is the blue rocks origin; are they <span class="hlt">impact</span> melt or volcanic, what is their age relative to Endeavour <span class="hlt">crater</span>, and how they are related to each other?</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014Icar..239..186B','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014Icar..239..186B"><span>Martian Low-Aspect-Ratio Layered Ejecta (LARLE) <span class="hlt">craters</span>: Distribution, characteristics, and relationship to pedestal <span class="hlt">craters</span></span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Barlow, Nadine G.; Boyce, Joseph M.; Cornwall, Carin</p> <p>2014-09-01</p> <p>Low-Aspect-Ratio Layered Ejecta (LARLE) <span class="hlt">craters</span> are a unique landform found on Mars. LARLE <span class="hlt">craters</span> are characterized by a <span class="hlt">crater</span> and normal layered ejecta pattern surrounded by an extensive but thin outer deposit which terminates in a sinuous, almost flame-like morphology. We have conducted a survey to identify all LARLE <span class="hlt">craters</span> ⩾1-km-diameter within the ±75° latitude zone and to determine their morphologic and morphometric characteristics. The survey reveals 140 LARLE <span class="hlt">craters</span>, with the majority (91%) located poleward of 40°S and 35°N and all occurring within thick mantles of fine-grained deposits which are likely ice-rich. LARLE <span class="hlt">craters</span> range in diameter from the cut-off limit of 1 km up to 12.2 km, with 83% being smaller than 5 km. The radius of the outer LARLE deposit displays a linear trend with the <span class="hlt">crater</span> radius and is greatest at higher polar latitudes. The LARLE deposit ranges in length between 2.56 and 14.81 <span class="hlt">crater</span> radii in average extent, with maximum length extending up to 21.4 <span class="hlt">crater</span> radii. The LARLE layer is very sinuous, with lobateness values ranging between 1.45 and 4.35. LARLE <span class="hlt">craters</span> display a number of characteristics in common with pedestal <span class="hlt">craters</span> and we propose that pedestal <span class="hlt">craters</span> are eroded versions of LARLE <span class="hlt">craters</span>. The distribution and characteristics of the LARLE <span class="hlt">craters</span> lead us to propose that <span class="hlt">impact</span> excavation into ice-rich fine-grained deposits produces a dusty base surge cloud (like those produced by explosion <span class="hlt">craters</span>) that deposits dust and ice particles to create the LARLE layers. Salts emplaced by upward migration of water through the LARLE deposit produce a surficial duricrust layer which protects the deposit from immediate removal by eolian processes.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2014AGUFM.P43B3985H','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2014AGUFM.P43B3985H"><span>The Global Contribution of Secondary <span class="hlt">Craters</span> on the Icy Satellites</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Hoogenboom, T.; Johnson, K. E.; Schenk, P.</p> <p>2014-12-01</p> <p>At present, surface ages of bodies in the Outer Solar System are determined only from <span class="hlt">crater</span> size-frequency distributions (a method dependent on an understanding of the projectile populations responsible for <span class="hlt">impact</span> <span class="hlt">craters</span> in these planetary systems). To derive accurate ages using <span class="hlt">impact</span> <span class="hlt">craters</span>, the impactor population must be understood. <span class="hlt">Impact</span> <span class="hlt">craters</span> in the Outer Solar System can be primary, secondary or sesquinary. The contribution of secondary <span class="hlt">craters</span> to the overall population has recently become a "topic of interest." Our objective is to better understand the contribution of dispersed secondary <span class="hlt">craters</span> to the small <span class="hlt">crater</span> populations, and ultimately that of small comets to the projectile flux on icy satellites in general. We measure the diameters of obvious secondary <span class="hlt">craters</span> (determined by e.g. irregular <span class="hlt">crater</span> shape, small size, clustering) formed by all primary <span class="hlt">craters</span> on Ganymede for which we have sufficiently high resolution data to map secondary <span class="hlt">craters</span>. Primary <span class="hlt">craters</span> mapped range from approximately 40 km to 210 km. Image resolution ranges from 45 to 440 m/pixel. Bright terrain on Ganymede is our primary focus. These resurfaced terrains have relatively low <span class="hlt">crater</span> densities and serve as a basis for characterizing secondary populations as a function of primary size on an icy body for the first time. Although focusing on Ganymede, we also investigate secondary <span class="hlt">crater</span> size, frequency, distribution, and formation, as well as secondary <span class="hlt">crater</span> chain formation on icy satellites throughout the Saturnian and Jovian systems principally Rhea. We compare our results to similar studies of secondary <span class="hlt">cratering</span> on the Moon and Mercury. Using Galileo and Voyager data, we have identified approximately 3,400 secondary <span class="hlt">craters</span> on Ganymede. In some cases, we measured <span class="hlt">crater</span> density as a function of distance from a primary <span class="hlt">crater</span>. Because of the limitations of the Galileo data, it is necessary to extrapolate from small data sets to the global population of secondary <span class="hlt">craters</span></p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2001LPI....32.1340C','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2001LPI....32.1340C"><span>Microbial Mats of the Tswaing <span class="hlt">Impact</span> <span class="hlt">Crater</span>: Results of a South African Exobiology Expedition and Implications for the Search for Biological Molecules on Mars</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Cockell, C. S.; Brandt, D.; Hand, K.; Lee, P.</p> <p>2001-03-01</p> <p>We describe microbial mats from the Tswaing <span class="hlt">impact</span> <span class="hlt">crater</span> in South Africa. The mats provide insights into the unique biological characteristics of <span class="hlt">impact</span> <span class="hlt">craters</span> and can help strategies for the search for biomolecules on Mars.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://adsabs.harvard.edu/abs/2015EGUGA..17.1231V','NASAADS'); return false;" href="http://adsabs.harvard.edu/abs/2015EGUGA..17.1231V"><span>3d morphometric analysis of lunar <span class="hlt">impact</span> <span class="hlt">craters</span>: a tool for degradation estimates and interpretation of maria stratigraphy</span></a></p> <p><a target="_blank" href="http://adsabs.harvard.edu/abstract_service.html">NASA Astrophysics Data System (ADS)</a></p> <p>Vivaldi, Valerio; Massironi, Matteo; Ninfo, Andrea; Cremonese, Gabriele</p> <p>2015-04-01</p> <p>In this study we have applied 3D morphometric analysis of <span class="hlt">impact</span> <span class="hlt">craters</span> on the Moon by means of high resolution DTMs derived from LROC (Lunar Reconnaissance Orbiter Camera) NAC (Narrow Angle Camera) (0.5 to 1.5 m/pixel). The objective is twofold: i) evaluating <span class="hlt">crater</span> degradation and ii) exploring the potential of this approach for Maria stratigraphic interpretation. In relation to the first objective we have considered several <span class="hlt">craters</span> with different diameters representative of the four classes of degradation being C1 the freshest and C4 the most degraded ones (Arthur et al., 1963; Wilhelms, 1987). DTMs of these <span class="hlt">craters</span> were elaborated according to a multiscalar approach (Wood, 1996) by testing different ranges of kernel sizes (e.g. 15-35-50-75-100), in order to retrieve morphometric variables such as slope, curvatures and openness. In particular, curvatures were calculated along different planes (e.g. profile curvature and plan curvature) and used to characterize the different sectors of a <span class="hlt">crater</span> (rim crest, floor, internal slope and related boundaries) enabling us to evaluate its degradation. The gradient of the internal slope of different <span class="hlt">craters</span> representative of the four classes shows a decrease of the slope mean value from C1 to C4 in relation to <span class="hlt">crater</span> age and diameter. Indeed degradation is influenced by gravitational processes (landslides, dry flows), as well as space weathering that induces both smoothing effects on the morphologies and infilling processes within the <span class="hlt">crater</span>, with the main results of lowering and enlarging the rim crest, and shallowing the <span class="hlt">crater</span> depth. As far as the stratigraphic application is concerned, morphometric analysis was applied to recognize morphologic features within some simple <span class="hlt">craters</span>, in order to understand the stratigraphic relationships among different lava layers within Mare Serenitatis. A clear-cut rheological boundary at a depth of 200 m within the small fresh Linnè <span class="hlt">crater</span> (diameter: 2.22 km), firstly hypothesized</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://images.nasa.gov/#/details-PIA00094.html','SCIGOVIMAGE-NASA'); return false;" href="https://images.nasa.gov/#/details-PIA00094.html"><span>Limb of Copernicus <span class="hlt">Impact</span> <span class="hlt">Crater</span></span></a></p> <p><a target="_blank" href="https://images.nasa.gov/">NASA Image and Video Library</a></p> <p></p> <p>1998-06-03</p> <p>Copernicus is 93 km wide and is located within the Mare Imbrium Basin, northern nearside of the Moon 10 degrees N., 20 degrees W.. This image from NASA's Lunar Orbiter shows <span class="hlt">crater</span> floor, floor mounds, rim, and rayed ejecta. http://photojournal.jpl.nasa.gov/catalog/PIA00094</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20050201815','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20050201815"><span>Workshop on The Role of Volatile and Atmospheres on Martian <span class="hlt">Impact</span> <span class="hlt">Craters</span></span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p></p> <p>2005-01-01</p> <p>This volume contains abstracts that have been accepted for presentation at the Workshop on the Role of Volatiles and Atmospheres on Martian <span class="hlt">Impact</span> <span class="hlt">Craters</span>, July 11-14,2005, Laurel, Maryland. Administration and publications support for this meeting were provided by the staff of the Publications and Program Services Department at the Lunar and Planetary Institute.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/19930000989','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/19930000989"><span>Search for the 700,000-year-old source <span class="hlt">crater</span> of the Australasian tektite strewn field</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Schnetzler, C. C.; Garvin, J. B.</p> <p>1992-01-01</p> <p>Many tektite investigations have hypothesized that the <span class="hlt">impact</span> <span class="hlt">crater</span> that was the source of the extensive Australasian strewn field lies somewhere in or near Indochina. This is due to variations in <span class="hlt">abundance</span> and size of tektites across the strewn field, variation of thickness of microtektite layers in ocean cores, nature and ablation characteristics across the field, and, above all, the occurrence of the large, blocky, layered Muong Nong-type tektites in Indochina. A recent study of the location and chemistry of Muong Nong-type and splash-form tektites suggests that the source region can be further narrowed to a limited area in eastern Thailand and southern Loas. Satellite multispectral imagery, a digital elevation dataset, and maps showing drainage patterns were used to search within this area for possible anomalous features that may be large degraded <span class="hlt">impact</span> <span class="hlt">craters</span>. Four interesting structures were identified from these datasets, and they are presented.</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('https://pubs.er.usgs.gov/publication/70019214','USGSPUBS'); return false;" href="https://pubs.er.usgs.gov/publication/70019214"><span>The phanerozoic <span class="hlt">impact</span> <span class="hlt">cratering</span> rate: Evidence from the farside of the Moon</span></a></p> <p><a target="_blank" href="http://pubs.er.usgs.gov/pubs/index.jsp?view=adv">USGS Publications Warehouse</a></p> <p>McEwen, A.S.; Moore, Johnnie N.; Shoemaker, E.M.</p> <p>1997-01-01</p> <p>The relatively recent (< 1 b.y.) flux of asteroids and comets forming large <span class="hlt">craters</span> on the Earth and Moon may be accurately recorded by <span class="hlt">craters</span> with bright rays on the Moon's farside. Many previously unknown farside rayed <span class="hlt">craters</span> are clearly distinguished in the low-phase-angle images returned by the Clementine spacecraft. Some large rayed <span class="hlt">craters</span> on the lunar nearside are probably significantly older than 1 Ga; rays remain visible over the maria due to compositional contrasts long after soils have reached optical maturity. Most of the farside crust has a more homogeneous composition and only immature rays are visible. The size-frequency distribution of farside rayed <span class="hlt">craters</span> is similar to that measured for Eratosthenian <span class="hlt">craters</span> (up to 3.2 b.y.) at diameters larger than 15 km. The areal density of farside rayed <span class="hlt">craters</span> matches that of a corrected tabulation of nearside Copernican <span class="hlt">craters</span>. Hence the presence of bright rays due to immature soils around large <span class="hlt">craters</span> provides a consistent time-stratigraphic basis for defining the base of the Copernican System. The density of large <span class="hlt">craters</span> less than ???3.2 b.y. old is ???3.2 times higher than that of large farside rayed <span class="hlt">craters</span> alone. This observation can be interpreted in two ways: (1) the average <span class="hlt">cratering</span> rate has been constant over the past 3.2 b.y. and the base of the Copernican is ???1 Ga, or (2) the <span class="hlt">cratering</span> rate has increased in recent geologic time and the base of the Copernican is less than 1 Ga. We favor the latter interpretation because the rays of Copernicus (800-850 m.y. old) appear to be very close to optical maturity, suggesting that the average Copernican <span class="hlt">cratering</span> rate was ???35% higher than the average Eratosthenian rate. Other lines of evidence for an increase in the Phanerozoic (545 Ga) <span class="hlt">cratering</span> rate are (1) the densities of small <span class="hlt">craters</span> superimposed on Copernicus and Apollo landing sites, (2) the rates estimated from well-dated terrestrial <span class="hlt">craters</span> (??? 120 m.y.) and from present-day astronomical</p> </li> <li> <p><a target="_blank" onclick="trackOutboundLink('http://hdl.handle.net/2060/20140004932','NASA-TRS'); return false;" href="http://hdl.handle.net/2060/20140004932"><span>LU60645GT and MA132843GT Catalogues of Lunar and Martian <span class="hlt">Impact</span> <span class="hlt">Craters</span> Developed Using a <span class="hlt">Crater</span> Shape-based Interpolation <span class="hlt">Crater</span> Detection Algorithm for Topography Data</span></a></p> <p><a target="_blank" href="http://ntrs.nasa.gov/search.jsp">NASA Technical Reports Server (NTRS)</a></p> <p>Salamuniccar, Goran; Loncaric, Sven; Mazarico, Erwan Matias</p> <p>2012-01-01</p> <p>For Mars, 57,633 <span class="hlt">craters</span> from the manually assembled catalogues and 72,668 additional <span class="hlt">craters</span> identified using several <span class="hlt">crater</span> detection algorithms (CDAs) have been merged into the MA130301GT catalogue. By contrast, for the Moon the most complete previous catalogue contains only 14,923 <span class="hlt">craters</span>. Two recent missions provided higher-quality digital elevation maps (DEMs): SELENE (in 1/16° resolution) and Lunar Reconnaissance Orbiter (we used up to 1/512°). This was the main motivation for work on the new <span class="hlt">Crater</span> Shape-based interpolation module, which improves previous CDA as follows: (1) it decreases the number of false-detections for the required number of true detections; (2) it improves detection capabilities for very small <span class="hlt">craters</span>; and (3) it provides more accurate automated measurements of <span class="hlt">craters</span>' properties. The results are: (1) LU60645GT, which is currently the most complete (up to D>=8 km) catalogue of Lunar <span class="hlt">craters</span>; and (2) MA132843GT catalogue of Martian <span class="hlt">craters</span> complete up to D>=2 km, which is the extension of the previous MA130301GT catalogue. As previously achieved for Mars, LU60645GT provides all properties that were provided by the previous Lunar catalogues, plus: (1) correlation between morphological descriptors from used catalogues; (2) correlation between manually assigned attributes and automated measurements; (3) average errors and their standard deviations for manually and automatically assigned attributes such as position coordinates, diameter, depth/diameter ratio, etc; and (4) a review of positional accuracy of used datasets. Additionally, surface dating could potentially be improved with the exhaustiveness of this new catalogue. The accompanying results are: (1) the possibility of comparing a large number of Lunar and Martian <span class="hlt">craters</span>, of e.g. depth/diameter ratio and 2D profiles; (2) utilisation of a method for re-projection of datasets and catalogues, which is very useful for <span class="hlt">craters</span> that are very close to poles; and (3) the extension of the</p> </li> </ol> <div class="pull-right"> <ul class="pagination"> <li><a href="#" onclick='return showDiv("page_1");'>«</a></li> <li><a href="#" onclick='return showDiv("page_21");'>21</a></li> <li><a href="#" onclick='return showDiv("page_22");'>22</a></li> <li><a href="#" onclick='return showDiv("page_23");'>23</a></li> <li><a href="#" onclick='return showDiv("page_24");'>24</a></li> <li class="active"><span>25</span></li> <li><a href="#" onclick='return showDiv("page_25");'>»</a></li> </ul> </div> </div><!-- col-sm-12 --> </div><!-- row --> </div><!-- page_25 --> <div class="footer-extlink text-muted" style="margin-bottom:1rem; text-align:center;">Some links on this page may take you to non-federal websites. Their policies may differ from this site.</div> </div><!-- container --> <footer><a id="backToTop" href="#top"> </a><nav><a id="backToTop" href="#top"> </a><ul class="links"><a id="backToTop" href="#top"> </a><li><a id="backToTop" href="#top"></a><a href="/sitemap.html">Site Map</a></li> <li><a href="/members/index.html">Members Only</a></li> <li><a href="/website-policies.html">Website Policies</a></li> <li><a href="https://doe.responsibledisclosure.com/hc/en-us" target="_blank">Vulnerability Disclosure Program</a></li> <li><a href="/contact.html">Contact Us</a></li> </ul> <div class="small">Science.gov is maintained by the U.S. Department of Energy's <a href="https://www.osti.gov/" target="_blank">Office of Scientific and Technical Information</a>, in partnership with <a href="https://www.cendi.gov/" target="_blank">CENDI</a>.</div> </nav> </footer> <script type="text/javascript"><!-- // var lastDiv = ""; function showDiv(divName) { // hide last div if (lastDiv) { document.getElementById(lastDiv).className = "hiddenDiv"; } //if value of the box is not nothing and an object with that name exists, then change the class if (divName && document.getElementById(divName)) { document.getElementById(divName).className = "visibleDiv"; lastDiv = divName; } } //--> </script> <script> /** * Function that tracks a click on an outbound link in Google Analytics. * This function takes a valid URL string as an argument, and uses that URL string * as the event label. */ var trackOutboundLink = function(url,collectionCode) { try { h = window.open(url); setTimeout(function() { ga('send', 'event', 'topic-page-click-through', collectionCode, url); }, 1000); } catch(err){} }; </script> <!-- Google Analytics --> <script> (function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){ (i[r].q=i[r].q||[]).push(arguments)},i[r].l=1*new Date();a=s.createElement(o), m=s.getElementsByTagName(o)[0];a.async=1;a.src=g;m.parentNode.insertBefore(a,m) })(window,document,'script','//www.google-analytics.com/analytics.js','ga'); ga('create', 'UA-1122789-34', 'auto'); ga('send', 'pageview'); </script> <!-- End Google Analytics --> <script> showDiv('page_1') </script> </body> </html>