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Sample records for interpreting impact crater

  1. The rayed crater Zunil and interpretations of small impact craters on Mars

    NASA Astrophysics Data System (ADS)

    McEwen, Alfred S.; Preblich, Brandon S.; Turtle, Elizabeth P.; Artemieva, Natalia A.; Golombek, Matthew P.; Hurst, Michelle; Kirk, Randolph L.; Burr, Devon M.; Christensen, Philip R.

    2005-08-01

    A 10-km diameter crater named Zunil in the Cerberus Plains of Mars created ˜10 secondary craters 10 to 200 m in diameter. Many of these secondary craters are concentrated in radial streaks that extend up to 1600 km from the primary crater, identical to lunar rays. Most of the larger Zunil secondaries are distinctive in both visible and thermal infrared imaging. MOC images of the secondary craters show sharp rims and bright ejecta and rays, but the craters are shallow and often noncircular, as expected for relatively low-velocity impacts. About 80% of the impact craters superimposed over the youngest surfaces in the Cerberus Plains, such as Athabasca Valles, have the distinctive characteristics of Zunil secondaries. We have not identified any other large (⩾10 km diameter) impact crater on Mars with such distinctive rays of young secondary craters, so the age of the crater may be less than a few Ma. Zunil formed in the apparently youngest (least cratered) large-scale lava plains on Mars, and may be an excellent example of how spallation of a competent surface layer can produce high-velocity ejecta (Melosh, 1984, Impact ejection, spallation, and the origin of meteorites, Icarus 59, 234-260). It could be the source crater for some of the basaltic shergottites, consistent with their crystallization and ejection ages, composition, and the fact that Zunil produced abundant high-velocity ejecta fragments. A 3D hydrodynamic simulation of the impact event produced 10 10 rock fragments ⩾10 cm diameter, leading to up to 10 9 secondary craters ⩾10 m diameter. Nearly all of the simulated secondary craters larger than 50 m are within 800 km of the impact site but the more abundant smaller (10-50 m) craters extend out to 3500 km. If Zunil is representative of large impact events on Mars, then secondaries should be more abundant than primaries at diameters a factor of ˜1000 smaller than that of the largest primary crater that contributed secondaries. As a result, most small

  2. 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.

  3. 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

  4. 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.

  5. Impact crater scaling laws

    NASA Technical Reports Server (NTRS)

    Holsapple, K. A.

    1987-01-01

    Impact craters are numerous on planetary bodies and furnish important information about the composition and past histories of those bodies. The interpretation of that information requires knowledge about the fundamental aspects of impact cratering mechanics. Since the typical conditions of impacts are at a size scale and velocity far in excess of experimental capabilities, direct simulations are precluded. Therefore, one must rely on extrapolation from experiments of relatively slow impacts of very small bodies, using physically based scaling laws, or must study the actual cases of interest using numerical code solutions of the fundamental physical laws that govern these processes. A progress report is presented on research on impact cratering scaling laws, on numerical studies that were designed to investigate those laws, and on various applications of the scaling laws developed by the author and his colleagues. These applications are briefly reviewed.

  6. Impact Crater

    NASA Technical Reports Server (NTRS)

    2002-01-01

    [figure removed for brevity, see original site]

    The layering of material observed at the bottom of this impact crater suggests multiple depositional and erosional episodes in a changing environment.

    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 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.

  7. 3d morphometric analysis of lunar impact craters: a tool for degradation estimates and interpretation of maria stratigraphy

    NASA Astrophysics Data System (ADS)

    Vivaldi, Valerio; Massironi, Matteo; Ninfo, Andrea; Cremonese, Gabriele

    2015-04-01

    In this study we have applied 3D morphometric analysis of impact craters 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 crater degradation and ii) exploring the potential of this approach for Maria stratigraphic interpretation. In relation to the first objective we have considered several craters 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 craters 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 crater (rim crest, floor, internal slope and related boundaries) enabling us to evaluate its degradation. The gradient of the internal slope of different craters representative of the four classes shows a decrease of the slope mean value from C1 to C4 in relation to crater 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 crater, with the main results of lowering and enlarging the rim crest, and shallowing the crater depth. As far as the stratigraphic application is concerned, morphometric analysis was applied to recognize morphologic features within some simple craters, 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 crater (diameter: 2.22 km), firstly hypothesized

  8. Analytical Scanning and Transmission Electron Microscopy of Laboratory Impacts on Stardust Aluminium Foils: Interpreting Impact Crater Morphology and the Composition of Impact Residues.

    SciTech Connect

    Kearsley, A T; Graham, G A; Burchell, M J; Cole, M J; Dai, Z R; Teslich, N; Chater, R; Wozniakiewicz, P A; Spratt, J; Jones, G

    2006-10-19

    The known encounter velocity (6.1kms{sup -1}) between the Stardust spacecraft and the dust emanating from the nucleus of comet Wild 2 has allowed realistic simulation of dust collection in laboratory experiments designed to validate analytical methods for the interpretation of dust impacts on the aluminium foil components of the Stardust collector. In this report we present information on crater gross morphology, the pre-existing major and trace element composition of the foil, geometrical issues for energy dispersive X-ray analysis of the impact residues in scanning electron microscopes, and the modification of dust chemical composition during creation of impact craters as revealed by analytical transmission electron microscopy. Together, these observations help to underpin the interpretation of size, density and composition for particles impacted upon the Stardust aluminium foils.

  9. Paleontological interpretations of crater processes and infilling of synimpact sediments from the Chesapeake Bay impact structure

    USGS Publications Warehouse

    Self-Trail J.M.; Edwards, L.E.; Litwin, R.J.

    2009-01-01

    Biostratigraphic analysis of sedimentary breccias and diamictons in the Chesapeake Bay impact structure provides information regarding the timing and processes of late-stage gravitational crater collapse and ocean resurge. Studies of calcareous nannofossil and palynomorph assemblages in the International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B cores show the mixed-age, mixed-preservation microfossil assemblages that are typical of deposits from the upper part of the Chesapeake Bay impact structure. Sparse, poorly preserved, possibly thermally altered pollen is present within a gravelly sand interval below the granite slab at 1392 m in Eyreville core B, an interval that is otherwise barren of calcareous nannofossils and dinocysts. Gravitational collapse of watersaturated sediments from the transient crater wall resulted in the deposition of sediment clasts primarily derived from the nonmarine Cretaceous Potomac Formation. Collapse occurred before the arrival of resurge. Low pollen Thermal Alteration Index (TAI) values suggest that these sediments were not thermally altered by contact with the melt sheet. The arrival of resurge sedimentation is identified based on the presence of diamicton zones and stringers rich in glauconite and marine microfossils at 866.7 m. This horizon can be traced across the crater and can be used to identify gravitational collapse versus ocean-resurge sedimentation. Glauconitic quartz sand diamicton dominates the sediments above 618.2 m. Calcareous nannofossil and dinoflagellate data from this interval suggest that the earliest arriving resurge from the west contained little or no Cretaceous marine input, but later resurge pulses mined Cretaceous sediments east of the Watkins core in the annular trough. Additionally, the increased distance traveled by resurge to the central crater in turbulent flow conditions resulted in the disaggregation of Paleogene unconsolidated sediments. As a

  10. Paleontological interpretations of crater processes and infilling of synimpact sediments from the Chesapeake Bay impact structure

    USGS Publications Warehouse

    Self-Trail, Jean M.; Edwards, Lucy E.; Litwin, Ronald J.

    2009-01-01

    Biostratigraphic analysis of sedimentary breccias and diamictons in the Chesapeake Bay impact structure provides information regarding the timing and processes of late-stage gravitational crater collapse and ocean resurge. Studies of calcareous nannofossil and palynomorph assemblages in the International Continental Scientific Drilling Program (ICDP)–U.S. Geological Survey (USGS) Eyreville A and B cores show the mixed-age, mixed-preservation microfossil assemblages that are typical of deposits from the upper part of the Chesapeake Bay impact structure. Sparse, poorly preserved, possibly thermally altered pollen is present within a gravelly sand interval below the granite slab at 1392 m in Eyreville core B, an interval that is otherwise barren of calcareous nannofossils and dinocysts. Gravitational collapse of water- saturated sediments from the transient crater wall resulted in the deposition of sediment clasts primarily derived from the nonmarine Cretaceous Potomac Formation. Collapse occurred before the arrival of resurge. Low pollen Thermal Alteration Index (TAI) values suggest that these sediments were not thermally altered by contact with the melt sheet. The arrival of resurge sedimentation is identified based on the presence of diamicton zones and stringers rich in glauconite and marine microfossils at 866.7 m. This horizon can be traced across the crater and can be used to identify gravitational collapse versus ocean-resurge sedimentation. Glauconitic quartz sand diamicton dominates the sediments above 618.2 m. Calcareous nannofossil and dino-flagellate data from this interval suggest that the earliest arriving resurge from the west contained little or no Cretaceous marine input, but later resurge pulses mined Cretaceous sediments east of the Watkins core in the annular trough. Additionally, the increased distance traveled by resurge to the central crater in turbulent flow conditions resulted in the disaggregation of Paleogene unconsolidated sediments. As

  11. The terrestrial impact cratering record.

    NASA Astrophysics Data System (ADS)

    Grieve, R. A. F.; Pesonen, L. J.

    1992-12-01

    Approximately 130 terrestrial hypervelocity impact craters are currently known. The rate of discovery of new craters is 3 - 5 craters per year. Although modified by erosion, terrestrial impact craters exhibit the range of morphologies observed for craters on other terrestrial planetary bodies. Due to erosion and its effects on form, terrestrial craters are recognized primarily by the occurrence of shock metamorphic effects. Terrestrial craters have a set of geophysical characteristics which are largely the result of the passage of a shock wave and impact-induced fracturing. Much current work is focused on the effects of impact on Earth evolution. Previous work on shock metamorphism and the contamination of impact melt rocks by meteoritic siderophile elements provides a basis for the interpretation of the physical and chemical evidence from Cretaceous-Tertiary boundary sites as resulting from a major impact. By analogy with the lunar record and modelling of the effects of very large impacts, it has been proposed that biological and atmospheric evolution of the Earth could not stabilize before the end of the late heavy bombardment ≡3.8 Ga ago. The present terrestrial cratering rate is 5.4±2.7×10-15 km-2a-1 for a diameter ≥20 km. On a gobal scale, a major impact sufficient to cripple human civilization severely will occur on time scales of ≡106a.

  12. Impact craters on Titan

    USGS Publications Warehouse

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

    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.

  13. 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.

  14. Impact craters on Venus

    NASA Technical Reports Server (NTRS)

    Schaber, G. G.

    1991-01-01

    Compared with volcanism and tectonism, impact cratering on Venus has played an overall minor role in sculpting the present-day landscape. The study of Venus impact craters is vital to help place the chronology of the geologic features on the surface in the context of the planet's geological evolution. The degradation of impact craters also provides information on surface and interior processes, particularly alteration by tectonism and volcanism. Through orbit 1422, Magellan mapped about 450 impact craters, with diameters ranging from 2 to 275 km, within an area of about 226 million sq km, or 49 percent of the planet's surface. These craters and their associated deposits show surprisingly little evidence of degradation at the 75 m/pixel resolution of the Magellan SAR. Remarkably few craters in the Magellan images appear to be in the process of being buried by volcanic deposits or destroyed by tectonic activity.

  15. Interpreting the cratering record - Mercury to Ganymede and Callisto

    NASA Technical Reports Server (NTRS)

    Woronow, A.; Strom, R. G.; Gurnis, M.

    1982-01-01

    A first analysis is presented of what the Galilean satellites' crater production function is, along with some interpretations of the conclusion. The basic premise is that the larger crater population of the lunar highlands is not at saturation density. The saturation issue is addressed, showing why the concept of saturation of lunar highlands can no longer be regarded as the best hypothesis, at least for large craters. The cratering records of Mars, Mercury, and the moon are reviewed and synthesized, and crater characteristics and statistics for Callisto and Ganymede are discussed and interpreted. It is shown that even the very densely cratered lunar highlands still retain considerable information about their production function; that remarkable similarities exist among the cratering histories of all of the terrestrial planets, both in terms of their production functions and of their total crater densities; and that the Gallilean satellites seem to have experienced quite a different impact history from that of the terrestrial planets.

  16. 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

  17. 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.

  18. Problems in the interpretation of lunar mare stratigraphy and relative ages indicated by ejecta from small impact craters

    NASA Technical Reports Server (NTRS)

    Young, R. A.; Brennan, W. J.; Nichols, D. J.

    1974-01-01

    The numbers of large ejecta blocks in excess of several meters in diameter ('blockiness') around the rims of small craters in southeastern Mare Serenitatis exceed those around similar craters in southern Mare Imbrium (and some other regions) at all but the final stages of crater degradation. Terrestrial explosion crater analogs, studies of impact processes, and a layered mare model suggest that the nature of the layering in the subsurface, including lavas, ejecta and buried regolith horizons, could account for the variable blockiness of crater ejecta and, possibly, for some variation in crater size-frequency distributions. Such effects would limit the reliability and utility of counting postmare craters for the purpose of estimating the relative ages of mare surfaces. Similarly, comparisons of the effects of progressive degradation on small impact craters to determine relative or absolute ages of individual craters may be limited by the influence of stratigraphy on ejecta fragment size distributions, which would in turn affect micrometeorite erosion rates and regolith production models.

  19. 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

  20. Fresh, Rayed Impact Crater

    NASA Technical Reports Server (NTRS)

    2003-01-01

    MGS MOC Release No. MOC2-416, 9 July 2003

    This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a fresh, young meteor impact crater on the martian surface. It is less than 400 meters (less than 400 yards) across. While there is no way to know the exact age of this or any other martian surface feature, the rays are very well preserved. On a planet where wind can modify surface features at the present time, a crater with rayed ejecta patterns must be very young indeed. Despite its apparent youth, the crater could still be many hundreds of thousands, if not several million, of years old. This impact scar is located within the much larger Crommelin Crater, near 5.6oN, 10.0oW. Sunlight illuminates the scene from the left.

  1. Venus - Impact Crater 'Isabella

    NASA Technical Reports Server (NTRS)

    1992-01-01

    Crater Isabella, with a diameter of 175 kilometers (108 miles), seen in this Magellan radar image, is the second largest impact crater on Venus. The feature is named in honor of the 15th Century queen of Spain, Isabella of Castile. Located at 30 degrees south latitude, 204 degrees east longitude, the crater has two extensive flow-like structures extending to the south and to the southeast. The end of the southern flow partially surrounds a pre-existing 40 kilometer (25 mile) circular volcanic shield. The southeastern flow shows a complex pattern of channels and flow lobes, and is overlain at its southeastern tip by deposits from a later 20 kilometer (12 mile) diameter impact crater, Cohn (for Carola Cohn, Australian artist, 1892-1964). The extensive flows, unique to Venusian impact craters, are a continuing subject of study for a number of planetary scientists. It is thought that the flows may consist of 'impact melt,' rock melted by the intense heat released in the impact explosion. An alternate hypothesis invokes 'debris flows,' which may consist of clouds of hot gases and both melted and solid rock fragments that race across the landscape during the impact event. That type of emplacement process is similar to that which occurs in violent eruptions on Earth, such as the 1991 Mount Pinatubo eruption in the Philippines.

  2. 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

  3. Visualization and Interpretation in 3D Virtual Reality of Topographic and Geophysical Data from the Chicxulub Impact Crater

    NASA Astrophysics Data System (ADS)

    Rosen, J.; Kinsland, G. L.; Borst, C.

    2011-12-01

    We have assembled Shuttle Radar Topography Mission (SRTM) data (Borst and Kinsland, 2005), gravity data (Bedard, 1977), horizontal gravity gradient data (Hildebrand et al., 1995), magnetic data (Pilkington et al., 2000) and GPS topography data (Borst and Kinsland, 2005) from the Chicxulub Impact Crater buried on the Yucatan Peninsula of Mexico. These data sets are imaged as gridded surfaces and are all georegistered, within an interactive 3D virtual reality (3DVR) visualization and interpretation system created and maintained in the Center for Advanced Computer Studies at the University of Louisiana at Lafayette. We are able to view and interpret the data sets individually or together and to scale and move the data or to move our physical head position so as to achieve the best viewing perspective for interpretation. A feature which is especially valuable for understanding the relationships between the various data sets is our ability to "interlace" the 3D images. "Interlacing" is a technique we have developed whereby the data surfaces are moved along a common axis so that they interpenetrate. This technique leads to rapid and positive identification of spatially corresponding features in the various data sets. We present several images from the 3D system, which demonstrate spatial relationships amongst the features in the data sets. Some of the anomalies in gravity are very nearly coincident with anomalies in the magnetic data as one might suspect if the causal bodies are the same. Other gravity and magnetic anomalies are not spatially coincident indicating different causal bodies. Topographic anomalies display a strong spatial correspondence with many gravity anomalies. In some cases small gravity anomalies and topographic valleys are caused by shallow dissolution within the Tertiary cover along faults or fractures propagated upward from the buried structure. In other cases the sources of the gravity anomalies are in the more deeply buried structure from which

  4. 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).

  5. 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

  6. Lunar Simple Crater Impact Melt Volumes

    NASA Technical Reports Server (NTRS)

    Plescia, Jeffrey B.; Barnouin, O. S.; Cintala, Mark J.

    2013-01-01

    Impact melt is observed in simple lunar craters having diameters as small as less than 200 m. The presence of ponds of impact melt on the floor of such small craters is interpreted to indicate vertical impacts. Data from the LRO LROC and LOLA experiments allow quantitative estimates of the volume of impact melt in simple crater. Such estimates allow for validation of theoretical models of impact melt generation and examination of target effects. Preliminary data have considerable scatter but are broadly consistent with the models.

  7. 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.

  8. 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; Gurrola, Eric; Harcke, Leif

    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

  9. 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.

  10. Impact crater degradation on venusian plains

    NASA Astrophysics Data System (ADS)

    Izenberg, N. R.; Arvidson, R. E.; Phillips, R. J.

    1994-02-01

    In venusian plains, impact craters without extensive low backscatter ejecta deposits are more likely to have low backscatter floors, be embayed by volcanic deposits, and exhibit fractures as compared to craters with extensive low backscatter ejecta. We interpret these trends as evidence of ongoing degradation of low backscatter ejecta by aeolian activity, weathering, and volcanism. Using a crater age sequence based on extent of preservation of low backscatter ejecta, together with Monte Carlo simulations, we find that tectonic activity has extended over a longer time period than volcanism.

  11. 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.

  12. Venus - Multiple-Floored, Irregular Impact Crater

    NASA Technical Reports Server (NTRS)

    1991-01-01

    Magellan 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.

  13. Largest impact craters on Venus

    NASA Technical Reports Server (NTRS)

    Ivanov, B. A.; Weitz, C. M.; Basilevsky, A. T.

    1992-01-01

    High-resolution radar images from the Magellan spacecraft have allowed us to perform a detailed study on 25 large impact craters on Venus with diameters from 70 to 280 km. The dimension of these large craters is comparable with the characteristic thickness of the venusian lithosphere and the atmospheric scale height. Some physical parameters for the largest impact craters on Venus (LICV), such as depth, ring/diameter ratio, and range of ballistic ejecta deposits, have been obtained from the SAR images and the altimetry dataset produced by MIT. Data related to each of these parameters is discussed.

  14. Craters! A Multi-Science Approach to Cratering and Impacts.

    ERIC Educational Resources Information Center

    Hartmann, William K.; Cain, Joe

    This book provides a complete Scope Sequence and Coordination teaching module. First, craters are introduced as a generally observable phenomena. Then, by making craters and by investigating the results, students gain close-up, hands-on experience with impact events and their products. Real crater examples from the Moon and elsewhere are included…

  15. 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).

  16. 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.

  17. 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.

  18. Venus - Lavinia Region Impact Craters

    NASA Technical Reports Server (NTRS)

    1990-01-01

    Three large meteorite impact craters, with diameters that range from 37 to 50 kilometers (23 to 31 miles), are seen in this image of the Lavinia region of Venus. The image is centered at 27 degrees south latitude and 339 degrees east longitude (longitude on Venus is measured from 0 degrees to 360 degrees east), and covers an area 550 kilometers (342 miles) wide by about 500 kilometers (311 miles) long. Situated in a region of fractured plains, the craters show many features typical of meteorite impact craters, including rough (bright) material around the rim, terraced inner walls and central peaks. Numerous domes, probably caused by volcanic activity, are seen in the southeastern corner of the mosaic. The domes range in diameter from 1 to 12 kilometers (0.6 to 7 miles). Some of the domes have central pits that are typical of some types of volcanoes. North is at the top of the image.

  19. Structural and Geological Interpretation of Posidonius Crater on the Moon

    NASA Astrophysics Data System (ADS)

    Ishihara, Y.; Chiba, T.; Haruyama, J.; Otake, H.; Ohtake, M.

    2015-12-01

    Posidonius crater locates on northeastern rim parts of the Serenitatis basin and is a typical floor-fractured crater. Because of Posidonius is located lunar central nearside and easily observed by ground-base telescope, the complex texture of crater floor attracted planetary scientist attention from before lunar exportation era. However, origin or formation histories of floor fractures are not fully resolved yet. In this study, we try to estimate geologic histories of Posidonius crater based on topographic data and multiband image data obtained by Terrain Camera (TC) and Multiband Imager (MI) onboard Kaguya. A part of crater floor of Posidonius is flooded by mare basalt. Previous studies interpreted that the source of mare basalt is located somewhere at Mare Serenitatis and flooded into Posidonius crater, then sinuous rill (Rimae Posidonius) is the resulting structure of flooded basalt flow. However, based on TC topographic data, sinuous rill feature indicate opposite flow direction to previous interpretations. Based on TC topographic data, we could interpret topographic features as follows; Rimare Posidonius flow from volcanic vent located at northern edge of Posidonius crater floor and flow out to Mare Serenitatis at western rim, the central part of crater floor slightly leaned to west and broken in several regions. From band depth of MI data, eastern part of crater floor is mostly consisted by highland materials and complex rills are basically not showing the basaltic feature. Combined both analysis results, we interpret the cause of complex structure of Posidonius crater is as follows; after crater formation, large sill intruded below crater floor and uppermost layer of crater floor is delaminated from the basement then floats on basaltic intrusion as "otoshibuta" (Japanese style lid for stew). Complex fracture was probably formed delamination and flotation stage by mechanical stress.

  20. Venusian impact basins and cratered terrains

    NASA Technical Reports Server (NTRS)

    Hamilton, Warren B.

    1992-01-01

    The consensus regarding interpretation of Magellan radar imagery assigns Venus a young volcanic surface subjected in many areas to moderate crustal shortening. I infer that, on the contrary, ancient densely cratered terrain and large impact basins may be preserved over more than half the planet and that crustal shortening has been much overestimated. I see wind erosion and deposition as far more effective in modifying old structures. Integration with lunar chronology suggests that most of the surface of Venus may be older than 3.0 Ga and much may be older than 3.8 Ga. Broad volcanos, hug volcanic domes, plains preserving lobate flow patterns, and numerous lesser volcanic features, pocked sparsely by impact craters, are indeed obvious on Magellan imagery. Some of these postvolcanic impact craters have been slightly extended, but only a small portion has been flooded by still younger lavas. Relative ages of the young craters are indicated by the varying eolian removal of their forms and ejecta blankets and flow lobes, and the oldest are much subdued. If these young impact craters, maximum diameter 275 km, include all preserved impact structures, then their quantity and distribution indicate that Venus was largely resurfaced by volcanism approx. 0.5 Ga, subsequent eruptions having been at a much reduced rate. Away from the approx. 0.5 Ga volcanic features, much of Venus is, however, dominated by circular and subcircular features, 50-2000 km in diameter, many of them multiring, that may be mostly older impact and impact-melt structures substantially modified by wind action. Eolian erosion scoured to bedrock old ridges and uplands, including those that may be cratered terrains and the rims and outer-ring depressions of large impact basins, and removed all surficial deposits to the limits of resolution of the imagery. The complementary eolian deposits form not only dunes, wind streaks, and small plains, but also broad radar-dark plains, commonly assumed to be volcanic

  1. Impacts into Sandstone: Crater Morphology, Crater Scaling and the Effects of Porosity

    NASA Astrophysics Data System (ADS)

    Poelchau, M. H.; Dufresne, A.; Kenkmann, T.

    2011-03-01

    Crater morphology results from impact cratering experiments in sandstone within the MEMIN program are presented and compared to other brittle materials. The effects of porosity on crater shape, volume and cratering efficiency are analyzed.

  2. 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

  3. Keeping that youthful look. [impact cratering of Venus

    NASA Technical Reports Server (NTRS)

    Solomon, Sean C.

    1993-01-01

    The record of impact cratering on Venus, recently revealed from high-resolution radar imaging by the Magellan spacecraft, has been interpreted as indicating that the planet underwent catastrophic global resurfacing about 500 million years ago. Although other interpretations of the crater characteristics have been suggested, the possibility of geologically rapid global resurfacing on the planet that most resembles our own in terms of mass, density, and bulk composition has generated widespread interest. The mechanisms that could cause such a catastrophe are discussed.

  4. 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.

  5. Backyard bolides: finding a buried impact crater.

    NASA Astrophysics Data System (ADS)

    Poag, C. W.

    1998-10-01

    The author reports the scientific activities that led to his discovery of a huge submerged impact crater in Chesapeake Bay, some 140 km east of Atlantic City, New Jersey. This crater, buried under 350 m of sediment is 80 km wide and almost 1 km deep. Microfossil evidence shows that the crater is approximately 35 million years old. The author futher identified 14 small secondary craters with diamters of 0.4 to 0.5 km diameter within 60 km of the primary crater. These were caused by the impact of huge blocks of material ejected by the primary impact event. In addition, the author identified an intermediate-size primary crater (19 km diameter) in Toms Canyon, some 300 km from the Chesapeake crater and, again from microfossil evidence, identical in age.

  6. 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

  7. 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

    2010-07-01

    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

  8. 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.

  9. 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.

  10. The LCROSS Impact Cratering Experiment

    NASA Astrophysics Data System (ADS)

    Schultz, P. H.; Hermalyn, B.; Ernst, C. M.; Colaprete, A.

    2009-12-01

    The large Earth-Departure-Upper Stage (the “EDUS”) and the LCROSS Shepherding Spacecraft (SSc) will both slam into the permanently shadowed regions near the lunar south pole on October 9, 2009. The goal of this mission is to excavate possible ice buried below the surface, thereby providing a measure of potential reservoirs of water for future human exploration. Impact experiments at the NASA Ames Vertical Gun Range (AVGR) have contributed to the mission design and planning. These experiments have included predictions for target selection (Schultz, 2006), a re-assessment of excavation at early times (Hermalyn and Schultz, 2009), and excavation depths (this study). Such predictions are critical for designing instrument sensitivity/selection for the SSc and earth-based telescopic observing campaigns. Because the EDUS has an effective low density (with concentrations at two ends), we have explored the effects of impactor density and configuration (hollow, solid) on the early-stage cratering process, including excavation depths. Most ejecta scaling studies use loose quartz or flint-shot sand in order to track late-stage excavation scaling. This approach does not work well at earlier stages, which comprise a greater fraction of growth at larger scales (see Hermalyn and Schultz, 2009; Hermalyn and Schultz, this volume). Experiments using solid and hollow aluminum spheres impacted a variety of target types (fine and coarse sand, fine pumice, and JSC-1a) in order to assess their effect on this earlier stage of crater growth. Tracers were placed at different depths allowed tracking of excavation. Results have direct implications to the LCROSS experiment and observations (after appropriate scaling). First, the effective low-density impactor significantly reduces excavation depths to a projectile diameter or less, even in sand. This becomes more important for regolith-like targets since the hollow projectile collapses and target compression prevents deep penetration

  11. 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.

  12. 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.

  13. Impact Crater Size and Evolution: Expectations for Deep Impact

    NASA Technical Reports Server (NTRS)

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

    2002-01-01

    Deep Impact will involve a unique cratering experiment designed to probe below the surface of a comet. Laboratory experiments provide critical data for crater scaling and evolution of the ejecta curtain. Additional information is contained in the original extended abstract.

  14. The Deep Impact oblique impact cratering experiment

    NASA Astrophysics Data System (ADS)

    Schultz, Peter H.; Eberhardy, Clara A.; Ernst, Carolyn M.; A'Hearn, Michael F.; Sunshine, Jessica M.; Lisse, Carey M.

    The Deep Impact probe collided with 9P Tempel 1 at an angle of about 30° from the horizontal. This impact angle produced an evolving ejecta flow field very similar to much smaller scale oblique-impact experiments in porous particulate targets in the laboratory. Similar features and phenomena include a decoupled vapor/dust plume at the earliest times, a pronounced downrange bias of the ejecta, an uprange “zone of avoidance” (ZoA), heart-shaped ejecta ray system (cardioid pattern), and a conical (but asymmetric) ejecta curtain. Departures from nominal cratering evolution, however, provide clues on the nature of the impact target. These departures include: fainter than expected flash at first contact, delayed emergence of the self-luminous vapor/dust plume, uprange-directed plume, narrow early-time uprange ray followed by a late-stage uprange plume, persistence of ejecta asymmetries (and the uprange ZoA) throughout the approach sequence, emergence of a downrange ZoA at late times, detachment of uprange curved rays, very long lasting non-radial ejecta rays, and high-angle ejecta plume lasting over the entire encounter. The first second of crater formation most closely resembles the consequences of a highly porous target, while later evolution indicates that the target may be layered as well. Experiments also reveal that impacts into highly porous targets produce a vapor/dust plume directed back up the incoming trajectory. This uprange plume is attributed to cavitation within a narrow penetration funnel. The observed lateral expansion speed of the initial vapor plume downrange provides an estimate for the total vaporized mass equal to ˜5m (projectile masses) of water ice or 6m of CO2. The downrange plume speed is consistent with the gas expansion added to the downrange horizontal component of the DI probe. Based on high-speed spectroscopy of experimental impacts, the observed delay in brightening of the DI plume may be the result of delayed condensation of carbon

  15. The Deep Impact oblique impact cratering experiment

    NASA Astrophysics Data System (ADS)

    Schultz, Peter H.; Eberhardy, Clara A.; Ernst, Carolyn M.; A'Hearn, Michael F.; Sunshine, Jessica M.; Lisse, Carey M.

    2007-10-01

    The Deep Impact probe collided with 9P Tempel 1 at an angle of about 30° from the horizontal. This impact angle produced an evolving ejecta flow field very similar to much smaller scale oblique-impact experiments in porous particulate targets in the laboratory. Similar features and phenomena include a decoupled vapor/dust plume at the earliest times, a pronounced downrange bias of the ejecta, an uprange "zone of avoidance" (ZoA), heart-shaped ejecta ray system (cardioid pattern), and a conical (but asymmetric) ejecta curtain. Departures from nominal cratering evolution, however, provide clues on the nature of the impact target. These departures include: fainter than expected flash at first contact, delayed emergence of the self-luminous vapor/dust plume, uprange-directed plume, narrow early-time uprange ray followed by a late-stage uprange plume, persistence of ejecta asymmetries (and the uprange ZoA) throughout the approach sequence, emergence of a downrange ZoA at late times, detachment of uprange curved rays, very long lasting non-radial ejecta rays, and high-angle ejecta plume lasting over the entire encounter. The first second of crater formation most closely resembles the consequences of a highly porous target, while later evolution indicates that the target may be layered as well. Experiments also reveal that impacts into highly porous targets produce a vapor/dust plume directed back up the incoming trajectory. This uprange plume is attributed to cavitation within a narrow penetration funnel. The observed lateral expansion speed of the initial vapor plume downrange provides an estimate for the total vaporized mass equal to ˜5m (projectile masses) of water ice or 6m of CO 2. The downrange plume speed is consistent with the gas expansion added to the downrange horizontal component of the DI probe. Based on high-speed spectroscopy of experimental impacts, the observed delay in brightening of the DI plume may be the result of delayed condensation of carbon, in

  16. 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

  17. 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

  18. Impact Craters in North America

    NASA Astrophysics Data System (ADS)

    Grieve, R. A. F.; Wood, C. A.; Garvin, J. B.; McLaughlin, G.; McHone, J. F.

    1988-03-01

    Meteor Crater Upheaval Dome Sierra Madera Middlesboro Pilot Lake Carswell Gow Lake Deep Bay Nicholson Lake West Hawk Lake Haughton Sudbury Wanapitei Brent Lac Couture New Quebec Clearwater Lakes Manicouagan Charlevoix Lac La Moinerie Mistastin

  19. 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.

  20. Limb of Copernicus Impact Crater

    NASA Technical Reports Server (NTRS)

    1991-01-01

    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 crater floor, floor mounds, rim, and rayed ejecta. Rays from the ejecta are superposed on all other surrounding terrains which places the crater 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).

  1. Research on lunar Mare emplacement and impact cratering experiments

    NASA Technical Reports Server (NTRS)

    Greeley, R.; Schultz, P. H.; Gault, D. E.

    1980-01-01

    A model was derived enabling the interpretation of lunar styles of volcanism through the analysis of various surface features. The model was applied to several areas on the Moon, including the Orientale Basin, the Smythii Basin, the Herigonious region, and several highland areas. Concurrent with the application of the model, several topical studies of various aspects of lunar volcanism were completed. A series of impact crater experiments was conducted at NASA Ames in order to determine the effect that viscous targets would have on cratering mechanics and morphology for application in studies of Martian ejecta flow craters. The results of the experiments led to a model that can account for the formation of multiple flow lobes and the general morphology of some aspects of Martian craters.

  2. Lunar and Planetary Science XXXV: Mars Impact Cratering

    NASA Technical Reports Server (NTRS)

    2004-01-01

    This document discusses the following topics: High Resolution Digital Elevation Models of Pristine Explosion Craters; Crater Degradation in the Martian Highlands: Morphometric Analysis of the Sinus Sabaeus Region and Simulation Modeling Suggest Fluvial Processes; Analysis of Impact Crater Preservation on Mars Using THEMIS Data; Atmospheric Entry Studies and the Smallest Impact Craters on Mars; Updating the Crater Count Chronology System for Mars; Control of Impact Crater-related Fracture Systems on the Subsurface Hydrology and Ground Collapse; Quantitative Analyses of Terrestrial Crater Deposits: Constraining Formation and Sediment Transport Processes on Mars; and Predicted Effects of Surface Processes on Martian Impact Crater Depth/Diameter Relationships

  3. The missing large impact craters on Ceres

    NASA Astrophysics Data System (ADS)

    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.

    2016-07-01

    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.

  4. 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.

  5. Crater and cavity depth in hypervelocity impact

    NASA Astrophysics Data System (ADS)

    Kadono, T.; Fujiwara, A.

    2003-04-01

    Hypervelocity impact experiments with low-density mediums (e.g., foams) have been so far carried out to develop the instruments for intact capture of interplanetary dust particles. The results show that the impact leads a "cavity", a cylindrical or carrot (spindle) shaped vestige. Its shape depends on the condition of projectiles; when impact velocity is so low that projectiles are intact, the depth increases with impact velocity, while it decreases or is constant with impact velocity when the impact velocity is so high that projectiles are broken (e.g., Kadono, Planet. Space Sci. 47, 305--318, 1999). On the other hand, as described by Summers (NASA TN D-94, 1959), crater shape with high density targets (comparable to projectile density) also changes with impact velocity. At low velocities, the strength of projectile's materials is greater than the dynamic impact pressure and the projectile penetrates the target intact. The crater produced is deep and narrow. With increase in impact velocity, a point is reached at which the impact pressure is sufficient to cause the projectile to fragment into a few large pieces at impact. Then as the impact velocity is increased further, the projectile shatters into numerous small pieces and the penetration actually decreases. Finally a velocity is reached at which the typical fluid impact occurs, the crater formed is nearly hemispherical in shape. It appears that the situation in cavity formation with low density targets is quite similar to that in cratering with high density targets at low impact velocity. This similarity allows us to discuss cavity formation and cratering in a unified view. As described above, the previous experiments clearly suggest that the condition of projectiles plays important roles in both cratering and cavity formation. Hence here, by introducing a parameter that characterizes the condition of projectiles at the instance of impact, cratering processes such as projectile penetration and shock wave

  6. Impact Crater Particulates: Microscopic Meteoritic Material Surrounding Meteorite Craters

    NASA Astrophysics Data System (ADS)

    Smith, Toby Russell

    1995-01-01

    The influx of extraterrestrial matter onto the Earth is a ongoing process. Every year 40,000 metric tons of extraterrestrial matter is accreted by the Earth (Love 1993). A small fraction of this material arrives at Earth as objects large enough to survive the passage through atmosphere. Some of this material is completely melted as it passes through the atmosphere and arrives at the surface of the Earth as cosmic spherules. Cosmic spherules formed from metallic cosmic material undergoes changes in its elemental abundance as it passes through the atmosphere. The oxidation of the spherules results in the concentration of more refractory elements like Ni and Co into the metallic phase. Cosmic spherules are also formed by the passage of large meteorites through the atmosphere and their resulting impact onto the Earth. I found that the cosmic spherules from a wide variety of sources show a very similar trend in the elemental abundance patterns of their metallic phases. This trend is most obvious in the spherules recovered from the deep -sea and the spherules imbedded in impactite glass recovered from iron meteorite impact crater sites. The metallic spherules recovered from the soil surrounding impact craters do not show the high degree of elemental fractionation found in the deep-sea and impactite spherules. The composition of these spherules indicate that they are a mixture of meteoritic and target material. Metallic spherules are not the only meteoritic material to be found in the soil surrounding meteorite craters. I found that small fragments of the parent meteorite are an ubiquitous component of the soil surrounding the Odessa and Dalgaranga meteorite craters. These fragments occurred as small (most less than 400 mu m in size) heavily weathered fragments of meteoritic metal. The total calculated mass of these fragments is an order of magnitude larger than the mass of ponderable meteorites recovered from the site but 1 to 2 orders of magnitude smaller than the

  7. 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.

  8. Venus impact craters: Implications for atmospheric and resurfacing processes from Magellan observations

    NASA Technical Reports Server (NTRS)

    Phillips, Roger J.

    1991-01-01

    Observations of impact craters on Venus by Magellan yield important insights into: (1) atmospheric effects on the formation of impact craters and their attendant ejecta deposits and (2) the resurfacing history of the planet. Most craters smaller than 15 km are classified as irregular; they possess irregularly shaped rims, and multiple hummocky floors. The irregular nature of these craters is interpreted to be the consequence of breakup and dispersion of incoming meteoroids by the dense atmosphere. Two major ejecta facies of venusian impact craters are hummocky ejecta and outer ejecta. A number of craters documented in the Magellan images possess often non-radial, flow-like ejecta indicative of a low viscosity materials. Approximately half of the impact craters observed with the Magellan radar are partially or wholly surrounded by areas with low radar backscatter cross sections.

  9. A suspected impact crater near Duckwater, Nevada.

    NASA Astrophysics Data System (ADS)

    Schmude, R. W., Jr.; Westfall, J. E.

    1998-07-01

    Results of recent expeditions to a possible impact crater in central Nevada are summarized in this report. This feature has a mean diameter of 91.3 m, a mean depth of 5.1±0.1 m, a volume of 24560 m3 and a rim height of up to 0.6 m). Preliminary geological and topographic maps of this crater are presented.

  10. Impact Cratering on Small Asteroids and into Coarse Regoliths

    NASA Astrophysics Data System (ADS)

    Durda, D. D.

    2012-12-01

    Impact cratering on the smallest asteroids can result in crater and other associated impact scar morphologies that we do not usually see exhibited in imagery of larger main-belt asteroids and airless moons. The NEAR-Shoemaker spacecraft at (433) Eros and the Hayabusa spacecraft at (25143) Itokawa showed the surfaces of these near-Earth asteroids to be relatively depleted in smaller craters. 'Armoring' of the surface by the presence of boulders larger than the size of the projectiles needed to form the missing craters has been proposed as one possible contributing factor in the observed depletion. Indeed, a number of bright spots observed on the surfaces of some boulders on Itokawa appear to have a size distribution consistent with small projectiles and have been interpreted as impact scars - an extreme end member example of the armoring hypothesis. Several research teams have conducted a number of laboratory impact experiments focusing on the range of morphological expression of craters formed in coarse regoliths where the impacting projectiles are comparable in size to the regolith grains. The results of these experiments suggest that craters become less well defined and more irregular in shape as soon as the regolith target grains are larger than the projectiles. I will give an overview of the range of visual appearance of impact features on small asteroids, review the results of some previous laboratory experiments relevant to the armoring hypothesis, and present results of our own new impact experiments conducted at the Ames Vertical Gun Range to examine the range of morphological expression of impacts onto blocks on and in the regolith of small airless bodies.

  11. 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.

  12. Structure of the Chesapeake Bay Impact Crater from Wide-Angle Seismic Waveform Tomography

    NASA Astrophysics Data System (ADS)

    Lester, W. R.; Hole, J. A.; Catchings, R. D.; Bleibinhaus, F.

    2006-12-01

    The 35 million year old Chesapeake Bay impact structure is one of the largest and most well preserved meteor/comet impact structures on Earth. As a marine impact on a continental shelf, its morphology consists of a deep inner crater penetrating pre-existing crystalline basement surrounded by a much wider, shallower crater within the overlying sediments. In 2004, the U.S. Geological Survey conducted a combined refraction and low-fold reflection seismic survey across the northern part of the inner crater with the goals of constraining crater structure and identifying an ideal drill site for a deep borehole. Waveform inversion was applied to the seismic data to produce a high-resolution seismic velocity model of the inner crater. This significantly improved the spatial resolution over previous images based on travel times. Under the northeastern part of the outer crater, eastward-sloping, relatively intact crystalline basement is at a depth of ~1.5 km. The edge of the inner crater is at ~17 km radius and slopes gradually inward to penetrate pre-existing crystalline basement. The top of crystalline rock on the central uplift is about 0.8 km higher than its surroundings. Seismic velocity of crystalline rocks under the inner crater is much lower than under the outer crater, suggesting strong fracturing/brecciation of the inner crater floor and even stronger brecciation of the central uplift. A basement uplift and lateral change of basement velocity occurs at a radius of ~12 km and is interpreted as possibly indicating the edge of the transient crater caused by impact excavation prior to collapse. Assuming a 24 km diameter transient crater, scaling laws based on extraterrestrial craters and numerical models predict the observed inner crater diameter, central uplift diameter, and inner crater depth. This suggests that the crater collapse processes that created the inner crater in crystalline rocks were unaffected by the much weaker rheology of the overlying sediments.

  13. Dark halos and rays of young lunar craters: A new insight into interpretation

    NASA Astrophysics Data System (ADS)

    Kaydash, Vadym; Shkuratov, Yuriy; Videen, Gorden

    2014-03-01

    Images acquired by the Narrow Angle Camera of the Lunar Reconnaissance Orbiter allow phase-ratio imagery of young lunar craters surrounded by dark halos. Such imaging is a new optical remote-sensing technique that is sensitive to the degree of surface roughness. We apply the phase-ratio technique to LRO images of young dark-halo craters near the crater Denning and in the Balmer basin, in addition to craters created by the impacts of the Ranger-6 spacecraft and Saturn-5 sections of Apollo-13 and Apollo-17. We suggest an alternative explanation of the dark halos and rays seen near the craters at large phase angles. Phase-ratio imaging suggests that these features result from higher surface roughness. Thus, the interpretation of dark crater halos and rays as a composition/maturity variance should be used with caution. The composition and structure factors can be effectively discriminated only using images acquired in a wide range of phase angles including small angles.

  14. 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.

  15. 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.

  16. Impact craters: An ice study on Rhea

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

    The goal of this project is to study the properties of H2O ice in the environment of the Saturn satellites and in particular to measure the relative amounts of crystalline and amorphous H2O ice in and around two craters on Rhea. The craters are remnants of cataclysmic events that, by raising the local temperature, melted the ice, which subsequently crystallized. Based on laboratory experiments it is expected that, when exposed to ion bombardment at the temperatures typical of the Saturn satellites, the crystalline structure of the ice will be broken, resulting in the disordered, amorphous phase. We therefore expect the ice in and around the craters to be partially crystalline and partially amorphous. We have designed a technique that estimates the relative amounts of crystalline and amorphous H2O ice based on measurements of the distortion of the 2-μm spectral absorption band. The technique is best suited for planetary surfaces that are predominantly icy, but works also for surfaces slightly contaminated with other ices and non-ice components. We apply the tool to two areas around the Inktomi and the Obatala craters. The first is a young impact crater on the leading hemisphere of Rhea, the second is an older one on the trailing hemisphere. For each crater we obtain maps of the fraction of crystalline ice, which were overlain onto Imaging Science Subsystem (ISS) images of the satellite searching for correlations between crystallinity and geography. For both craters the largest fractions of crystalline ice are in the center, as would be intuitively expected since the 'ground zero' areas should be most affected by the effects of the impact. The overall distribution of the crystalline ice fraction maps the shape of the crater and, in the case of Inktomi, of the rays. The Inktomi crater ranges between a maximum fraction of 67% crystalline ice to a minimum of 39%. The Obatala crater varies between a maximum of 51% and a minimum of 33%. Based on simplifying assumptions

  17. Impact Materials of Takamatsu Crater in Japan

    NASA Astrophysics Data System (ADS)

    Miura, Y.; Okamoto, M.; Fukuchi, T.

    1995-09-01

    Shocked quartz materials have been found in Japanese K.T boundary (Hokkaido) and mountains of middle main-islands of Japan, though there are few direct evidence of "natural circular structure" on the surface in Japan. However circular structure has been recently found as a buried crater(up to 150m deep) [1] which is ca. 4km in diameter with -10 mgal of Bouguer gravity anomaly from surrounding Rhyoke granitic region of the southern part of Takamatsu City, Kagawa Prefecture, northeast Shikoku, Japan [1,2,3]. Two boring cores of 300m deep near small mountains inside the crater could not reach the bottom of the crater so far. From model calculation of the negative gravity anomaly, the Takamatsu crater shows deep basin structure up to 1.4km. If the Takamatsu crater is considered to be only impact crater, it is difficult to discuss only surface materials on the crater. But anomalous minerals are found only around small volcanic intrusions inside the crater, which the mixed minerals are clearly different with those of other volcanic intrusions of the Yashima and Goshikidai outside the crater [1,2,3]. The small volcanic intrusions are not origin of large Takamatsu crater, because the small volcanic intrusions are found on whole areas of Kagawa Prefecture. Major different activity of the small intrusions inside the crater is to bring the brecciated materials of the interior (esp. crater sediments). The xenolith materials around only volcanic intrusion of andesite are divided into the following four major mineral materials:(a) round pebble fragments from the Rhyoke granitic basement (Sampling No.15), (b) rock fragments from intruded biotite andesites (Nos. 2,15), (c) impact-induced fragments of shocked Quartz grains (Nos. 2,3,6,15), diaplectic feldspars (Nos. 2,3,6,15), silica glasses (Nos. 2,15) and small Fe-Ni metallic grains (No.15), and (d) small sedimentary fragments of halite and mordenite, as listed in Table 1. Table I, showing the characterization of surface samples

  18. Cratering on a Comet: Expectations for Deep Impact

    NASA Astrophysics Data System (ADS)

    Schultz, P. H.

    2001-11-01

    In 2005, the Deep Impact Mission will witness the collision of a 350kg impactor into Comet P-Temple 1. Laboratory impact experiments provide scaling laws that relate impactor mass to crater diameter and depth for various target and impactor properties. A series of experiments have been performed at the NASA Ames Vertical Gun Range in order to assess the effects of the density and impedance ratio between target and impactor, target compressibility, target porosity, and impact angle. Although the maximum velocity achievable in the laboratory is below that for Deep Impact (7km/sec versus 10.3 km/sec), varying impactor diameter and velocity allows extrapolating beyond this range, for certain assumptions. This approach has been used for various particulate targets including pumice (1.1 to 1.5 g/cc, sand (1.7g/cc), vermiculite (0.09 g/cc), and micro-spheres (0.05g/cc), which provide the maximum possible diameter produced on Temple 1. Smaller sizes are expected if strength, rather than gravity, controls limits of crater growth or if internal energy losses (e.g., pore-space collapse) reduce the coupling efficiency. Crater size also can be augmented through back pressures created by vapor expansion within the crater cavity. The maximum predicted crater diameters (without back pressure) for the DI impact into a 0.3 g/cc porous target are: 89 m (pumice), 124 m (fine sand), 98m (fine sand with compaction losses). Formation times approach 200 seconds. Crater size, plume evolution (size and photometry), formation time, ejection (curtain) angle, and the ejecta deposit will all contribute to meaningful interpretations of the near-surface properties.

  19. 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.

  20. The size-frequency distribution of elliptical impact craters

    NASA Astrophysics Data System (ADS)

    Collins, G. S.; Elbeshausen, D.; Davison, T. M.; Robbins, S. J.; Hynek, B. M.

    2011-10-01

    Impact craters are elliptical in planform if the impactor's trajectory is below a threshold angle of incidence. Laboratory experiments and 3D numerical simulations demonstrate that this threshold angle decreases as the ratio of crater size to impactor size increases. According to impact cratering scaling laws, this implies that elliptical craters occur at steeper impact angles as crater size or target strength increases. Using a standard size-frequency distribution for asteroids impacting the terrestrial planets we estimate the fraction of elliptical craters as a function of crater size on the Moon, Mars, Earth, Venus and Mercury. In general, the expected fraction of elliptical craters is ~ 2-4% for craters between 5 and 100-km in diameter, consistent with the observed population of elliptical craters on Mars. At larger crater sizes both our model and observations suggest a dramatic increase in the fraction of elliptical craters with increasing crater diameter. The observed fraction of elliptical craters larger than 100-km diameter is significantly greater than our model predictions, which may suggest that there is an additional source of large elliptical craters other than oblique impact.

  1. 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; 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.

  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

    2016-01-01

    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

  4. Meteoritic material at five large impact craters

    NASA Technical Reports Server (NTRS)

    Palme, H.; Janssens, M.-J.; Takahashi, H.; Anders, E.; Hertogen, J.

    1978-01-01

    The paper analyzes the meteoritic material at five multikilometer craters: Clearwater (Lac a l'Eau Claire) East and West (22 and 32 km), Manicouagan (70 km) and Mistastin (28 km), all in Canada; and Lake Bosumtwi (10.5 km), Ghana, which is associated with Ivory Coast tektites. Radiochemical neutron activation analysis is applied to 16 crater samples for the siderophile trace elements Ir, Os, Pd, Ni, Ge, and Re, which are depleted to varying degrees in the earth's crust but are abundant in all meteorites except achondrites. It is found that only two samples, both from Clearwater, exhibit a strong meteoritic signal. The remaining ones fall within or slightly above the range for terrestrial rocks, and therefore at best contain only small meteoritic components. Clearwater East is the first terrestrial impact crater to be associated with a stony meteorite (a C1 or C2 chondrite).

  5. Damage areas due to impact craters on LDEF aluminum panels

    NASA Technical Reports Server (NTRS)

    Coombs, Cassandra R.; Atkinson, Dale R.; Allbrooks, Martha; Wagner, J. D.

    1992-01-01

    Because of its exposure time and total exposed surface area, the LDEF provides a unique opportunity to analyze the effects of the natural and man-made particle populations in low earth orbit (LEO). This study concentrated on collecting and analyzing measurements of impact craters from seven painted aluminum surfaces at different locations on the satellite. These data are being used to: (1) update the current theoretical micrometeoroid and debris models for LEO; (2) characterize the effects of the LEO micrometeoroid and debris environment of satellite components and designs; (3) help assess the probability of collision between spacecraft in LEO and already resident debris and the survivability of those spacecraft that must travel through, or reside in, LEO; and (4) help define and evaluate future debris mitigation and disposal methods. Measurements were collected from one aluminum experiment tray cover (Bay C-12), two aluminum grapple plates (Bays C-01, C-10), and four aluminum experiment sun-shields (Bay E-09), all of which were coated with thermal paint. These measurements were taken at the Facility for Optical Interpretation of Large Surfaces (FOILS) Lab at JSC. Virtually all features greater than 0.2 mm in diameter possessed a spall zone in which all of the paint was removed from the aluminum surface, and which varied in size from 2-5 crater diameters. The actual craters vary from central pits without raised rims to morphologies more typical of craters formed in aluminum under hypervelocity impact conditions for larger features. Most craters exhibit a shock zone that varies in size from approximately 1-20 crater diameters. In general, only the outermost layer of paint was affected by this impact-related phenomenon, with several impacts possessing ridge-like structures encircling the area in which this outer-most paint layer was removed. Overall, there were no noticeable penetrations or bulges on the underside of the trays. One tray from the E-09 bay exhibited a

  6. Interpretation of Wild 2 Dust Fine Structure: Comparison of Stardust Aluminium Foil Craters to the Three-Dimensional Shape of Experimental Impacts by Artificial Aggregate Particles and Meteorite Powders

    SciTech Connect

    Kearsley, A T; Burchell, M J; Price, M C; Graham, G A; Wozniakiewicz, P J; Cole, M J; Foster, N J; Teslich, N

    2009-12-10

    New experimental results show that Stardust crater morphology is consistent with interpretation of many larger Wild 2 dust grains being aggregates, albeit most of low porosity and therefore relatively high density. The majority of large Stardust grains (i.e. those carrying most of the cometary dust mass) probably had density of 2.4 g cm{sup -3} (similar to soda-lime glass used in earlier calibration experiments) or greater, and porosity of 25% or less, akin to consolidated carbonaceous chondrite meteorites, and much lower than the 80% suggested for fractal dust aggregates. Although better size calibration is required for interpretation of the very smallest impacting grains, we suggest that aggregates could have dense components dominated by {micro}m-scale and smaller sub-grains. If porosity of the Wild 2 nucleus is high, with similar bulk density to other comets, much of the pore-space may be at a scale of tens of micrometers, between coarser, denser grains. Successful demonstration of aggregate projectile impacts in the laboratory now opens the possibility of experiments to further constrain the conditions for creation of bulbous (Type C) tracks in aerogel, which we have observed in recent shots. We are also using mixed mineral aggregates to document differential survival of pristine composition and crystalline structure in diverse fine-grained components of aggregate cometary dust analogues, impacted onto both foil and aerogel under Stardust encounter conditions.

  7. The Wabar impact craters, Saudi Arabia, revisited

    NASA Astrophysics Data System (ADS)

    Gnos, E.; Hofmann, B. A.; Halawani, M. A.; Tarabulsi, Y.; Hakeem, M.; Al Shanti, M.; Greber, N. D.; Holm, S.; Alwmark, C.; Greenwood, R. C.; Ramseyer, K.

    2013-10-01

    The very young Wabar craters formed by impact of an iron meteorite and are known to the scientific community since 1933. We describe field observations made during a visit to the Wabar impact site, provide analytical data on the material collected, and combine these data with poorly known information discovered during the recovery of the largest meteorites. During our visit in March 2008, only two craters (Philby-B and 11 m) were visible; Philby-A was completely covered by sand. Mapping of the ejecta field showed that the outcrops are strongly changing over time. Combining information from different visitors with our own and satellite images, we estimate that the large seif dunes over the impact site migrate by approximately 1.0-2.0 m yr-1 southward. Shock lithification took place even at the smallest, 11 m crater, but planar fractures (PFs) and undecorated planar deformation features (PDFs), as well as coesite and stishovite, have only been found in shock-lithified material from the two larger craters. Shock-lithified dune sand material shows perfectly preserved sedimentary structures including cross-bedding and animal burrows as well as postimpact structures such as open fractures perpendicular to the bedding, slickensides, and radiating striation resembling shatter cones. The composition of all impact melt glasses can be explained as mixtures of aeolian sand and iron meteorite. We observed a partial decoupling of Fe and Ni in the black impact glass, probably due to partitioning of Ni into unoxidized metal droplets. The absence of a Ca-enriched component demonstrates that the craters did not penetrate the bedrock below the sand sheet, which has an estimated thickness of 20-30 m.

  8. 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.

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

    USGS Publications Warehouse

    Horton, J.W., Jr.; 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.

  10. Hydrogeology associated to faulting of the Chicxulub Impact Crater rim

    NASA Astrophysics Data System (ADS)

    Rebolledo-Vieyra, M.; Hernandez-Terrones, L.; Almazan-Becerril, A.; Valadez-Cruz, F.

    2011-12-01

    The only surface expression of the Chicxulub Impact Crater is a Ring of Cenotes (sinkholes) whose density varies from several cenotes per kilometer, to several kilometers between each cenote. This ring has a radius of approximately 90 km and it is centered at Chicxulub Puerto. It is not known today whether the Ring of Cenotes is the surface expression of the transient cavity as some authors have suggested, or whether it is the outer rim of the impact structure. The center of the ring is approximately coincident with the center of the Chicxulub Impact Crater. Reactivation of K/T rim faults had been associated to the formation of the ring of cenotes. However, none of these models project such faults to the Tertiary sedimentary sequence; therefore we can only infer that the cenotes are associated to these faults. Other hypotheses include "post impact subsidence induced by slumping and viscous relaxation in the rim" and "slumping in the rim of the buried crater, differential thickness in the rocks overlying the crater, or solution collapse within porous impact deposits", others suggest duration of subaerial exposure and weathering as a principal reason both for difference in permeability and cenote density inside and outside the Ring. This is consistent with the evolution of surface features reported. While sedimentation occurred in the basin outlined by the Ring, erosion and karst weathering were taking place outside the Ring. The karst features are associated with gravity gradients, which have been interpreted as corresponding to peripheral faults of the buried crater. We conducted geoelectric tomography perpendicular to the ring of cenotes, where we mapped the karstic features in the area and we interpret the high permeability in this area, to be associated to the faults generated by the differential compaction of the sedimentary sequence within the crater. This fault system generates a secondary porosity with high permeability that allows the circulation of water

  11. Impact cratering at geologic stage boundaries

    NASA Technical Reports Server (NTRS)

    Stothers, Richard B.

    1993-01-01

    The largest known Cenozoic impact craters with the most accurately measured ages are found to correlate very closely with geologic stage boundaries. The level of confidence in this result is 98-99 percent even under the most pessimistic assumptions concerning dating errors. One or more large impacts may have led, in at least some cases, to the extinctions and first appearances of biotic species that mark many of the geologic stage boundaries.

  12. 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.

  13. 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

  14. Impact Materials of Takamatsu Crater in Japan

    NASA Astrophysics Data System (ADS)

    Miura, Y.; Okamoto, M.; Fukuchi, T.

    1995-09-01

    Shocked quartz materials have been found in Japanese K.T boundary (Hokkaido) and mountains of middle main-islands of Japan, though there are few direct evidence of "natural circular structure" on the surface in Japan. However circular structure has been recently found as a buried crater(up to 150m deep) [1] which is ca. 4km in diameter with -10 mgal of Bouguer gravity anomaly from surrounding Rhyoke granitic region of the southern part of Takamatsu City, Kagawa Prefecture, northeast Shikoku, Japan [1,2,3]. Two boring cores of 300m deep near small mountains inside the crater could not reach the bottom of the crater so far. From model calculation of the negative gravity anomaly, the Takamatsu crater shows deep basin structure up to 1.4km. If the Takamatsu crater is considered to be only impact crater, it is difficult to discuss only surface materials on the crater. But anomalous minerals are found only around small volcanic intrusions inside the crater, which the mixed minerals are clearly different with those of other volcanic intrusions of the Yashima and Goshikidai outside the crater [1,2,3]. The small volcanic intrusions are not origin of large Takamatsu crater, because the small volcanic intrusions are found on whole areas of Kagawa Prefecture. Major different activity of the small intrusions inside the crater is to bring the brecciated materials of the interior (esp. crater sediments). The xenolith materials around only volcanic intrusion of andesite are divided into the following four major mineral materials:(a) round pebble fragments from the Rhyoke granitic basement (Sampling No.15), (b) rock fragments from intruded biotite andesites (Nos. 2,15), (c) impact-induced fragments of shocked Quartz grains (Nos. 2,3,6,15), diaplectic feldspars (Nos. 2,3,6,15), silica glasses (Nos. 2,15) and small Fe-Ni metallic grains (No.15), and (d) small sedimentary fragments of halite and mordenite, as listed in Table 1. Table I, showing the characterization of surface samples

  15. 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

  16. The Complicated Geologic Histories of Large Venusian Impact Craters

    NASA Astrophysics Data System (ADS)

    Rumpf, M. E.; Herrick, R.; Gregg, T. K.

    2005-12-01

    One of the more surprising discoveries from the Magellan imaging campaign was that the impact craters have a spatial distribution closely consistent with a random pattern. First impressions of most craters were that they are also well preserved. These observations led to an initial post-Magellan consensus that the planet is nearly geologically inactive and that activity rapidly ceased a few hundred million years ago. Early mapping efforts were mostly interpreted in terms of a rapid, linear, globally uniform stratigraphic evolution in the nature of volcanism and deformation. A number of challenges to this view have been made as detailed study of the Magellan data has progressed, and several researchers now advocate a more uniformitarian view of the planet. A valuable research tool has been topography derived from Magellan stereo imagery; it provides an order of magnitude improvement in horizontal resolution over the altimetry data (1 km vs. 10 km). Previous studies utilizing the stereo-derived topography have shown that impact craters with radar-dark floors (most of the population) are shallow and probably partially filled with post-impact lavas, and detailed mapping of Mead impact basin (the planet's largest impact structure) has revealed post-impact volcanic embayment. We have recently performed detailed photogeologic mapping, aided by stereo-derived topography, of several 50-100 km diameter impact craters. Most of these craters are not at the top of the stratigraphic column, and in some cases there is a complex, multi-event post-emplacement history. The combined histories of these craters are not consistent with a rapid cessation of geologic activity, and we are still synthesizing the individual histories to evaluate the hypothesis of a linear global stratigraphic evolution. Although the stereo-derived topography greatly aided interpretation, in many cases geologic contacts were ambiguous, individual volcanic flows could not be distinguished, source vents could

  17. 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

  18. Impact fragmentation of Lonar Crater, India: Implications for impact cratering processes in basalt

    NASA Astrophysics Data System (ADS)

    Senthil Kumar, P.; Prasanna Lakshmi, K. J.; Krishna, N.; Menon, R.; Sruthi, U.; Keerthi, V.; Senthil Kumar, A.; Mysaiah, D.; Seshunarayana, T.; Sen, M. K.

    2014-09-01

    Impact fragmentation is an energetic process that has affected all planetary bodies. To understand its effects in basalt, we studied Lonar Crater, which is a rare terrestrial simple impact crater in basalt and analogues to kilometer-scale simple craters on Mars. The Lonar ejecta consists of basaltic fragments with sizes ranging from silt to boulder. The cumulative size and mass frequency distributions of these fragments show variation of power index for different size ranges, suggesting simple and complex fragmentation. The general shape of the fragments is compact, platy, bladed, and elongated with an average edge angle of 100°. The size distribution of cobble- to boulder-sized fragments is similar to the fracture spacing distribution in the upper crater wall, indicating the provenance of those large fragments. Its consistency with a theoretical spallation model suggests that the large fragments were ejected from near surface of the target, whereas the small fragments from deeper level. The petrophysical properties of the ejecta fragments reflect the geophysical heterogeneity in the target basalt that significantly reduced the original size of spall fragments. The presence of Fe/Mg phyllosilicates (smectites) both in the ejecta and wall indicates the role of impact in excavating the phyllosilicates from the interior of basaltic target affected by aqueous alteration. The seismic images reveal a thickness variation in the ejecta blanket, segregation of boulders, fractures, and faults in the bedrock beneath the crater rim. The fracturing, fragmentation, and fluvial degradation of Lonar Crater have important implications for Mars.

  19. High-explosive cratering analogs for bowl-shaped, central uplift, and multiring impact craters

    NASA Technical Reports Server (NTRS)

    Roddy, D. J.

    1976-01-01

    The paper describes six experimental explosion craters in terms of their basic morphology, subsurface structural deformation, and surrounding ejecta blanket. These craters exhibit one or more of the following features: bowl shapes with underlying breccia lens, central uplifts, multirings, terraced walls, rim strata, zones of concentric rim deformation, inner continuous ground cover of ejecta blankets formed by overturned flaps, secondary cratering, and fused alluvium. These craters were formed by large shock wave energy transfers at or near zero heights-of-burst, and it is possible that impact craters with analogous morphologic and structural features may have formed under similar surface energy transfer conditions.

  20. On the scaling of crater dimensions. II - Impact processes

    NASA Technical Reports Server (NTRS)

    Holsapple, K. A.; Schmidt, R. M.

    1982-01-01

    Holsapple and Schmidt (1980) previously addressed the problem of the scaling of explosive cratering. Their analysis included results which show under which conditions the scaling can be bounded between quarter-root and cube-root rules. The present investigation is an extension of the earlier analysis and approaches the case of impact cratering. More restrictive bounds are found for impact cratering than for the explosive case. These stronger results come from considering the role of the impactor momentum as an independent variable for impact cratering. Attention is given to impact cratering variables, general scaling rules, the bounds on scaling rules, a generalization to more variables, and previous scaling rules and results.

  1. Topographical analysis of lunar impact craters using SELENE images

    NASA Astrophysics Data System (ADS)

    Vijayan, S.; Vani, K.; Sanjeevi, S.

    2013-10-01

    Lunar craters provide ample opportunities to study and understand crater morphology because of their vast numbers. This paper focuses on the topographical mapping of 33 Mare craters (Flat- and Round-floor) of ˜2 km diameter, using the SELENE DTM. Each crater was analyzed individually for its slope, regional topography and rim signature. The crater slope analysis revealed a small slope variation between the flat- and round-floor craters, in a similar diameter range, with some overlap between them. In the regional topographical analysis, the impact craters formed on the flat- and sloped-surface were analyzed in detail. The crater profile extracted through the rim crest was compared with its corresponding regional topographic profile (obtained over ˜3 crater radii). Four types of crater occurrences were observed: type i, ii and iv craters were formed on sloped surface, whereas type iii craters are formed on a flat surface with an equally raised rim. The occurrences of the rim crest on type i and ii craters are on the topographically elevated side of the terrain. But in type iv craters, the rim crest occurs on the topographically lower side of the terrain. The type iv craters uplifted the topographically lower terrain, which depicts the alteration that had taken place due to the impact. This topographical analysis suggests that the surrounding topography should also be considered for understanding the craters. Finally, from the crater rim signature analysis, it was evident that the prominent V-shaped incisions on the rim are caused due to landslide/slumping and by small impactors. This DTM based simple lunar crater analysis revealed information about the crater association with their surrounding topography and their morphological variations on flat- and sloped- surface.

  2. Venus - Impact Crater in Eastern Navka Region

    NASA Technical Reports Server (NTRS)

    1991-01-01

    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 crater, which is approximately 8 kilometers (5 miles) in diameter, displays a butterfly symmetry pattern. The ejecta pattern most likely results from an oblique impact, where the impactor came from the south and ejected material to the north.

  3. Meteoritic material at four Canadian impact craters

    NASA Technical Reports Server (NTRS)

    Wolf, R.; Woodrow, A. B.; Grieve, R. A. F.

    1980-01-01

    Eleven impact melt and six basement rock samples from four craters were analyzed by neutron activation for Au, Co, Cr, Fe, Ge, Ir, Ni, Os, Pd, Re and Se. Wanapitei Lake, Ontario: the impact melts show uniform enrichments corresponding to 1-2% C1-chondrite material. Interelement ratios (Co/Cr, Ni/Cr, Ni/Ir) suggest that the impacting body was a C1-, C2-, or LL-chondrite. Nicholson Lake, North West Territory: Ni, Cr and Co are distinctly more enriched than Ir and Au which tentatively suggests an olivine-rich achondrite (nakhlite or ureilite). Gow Lake, Saskatchewan and Mistastin, Labrador: small enrichments in Ir and Ni; both the low Ir/Ni ratios and low Cr content suggest iron meteorites, but the signals are too weak for conclusive identification. A tentative comparison of meteoritic signatures at 10 large, greater than or equal to 4 km craters and their presumed celestial counterparts (13 Apollo and Amor asteroids) shows more irons and achondrites among known projectile types, and a preponderance of S-type objects, having no known meteoritic equivalent, among asteroids. It is not yet clear that these differences are significant, in view of the tentative nature of the crater identifications and the limited statistics.

  4. Ejecta thickness and structural rim uplift measurements of Martian impact craters: Implications for the rim formation of complex impact craters

    NASA Astrophysics Data System (ADS)

    Sturm, Sebastian; Kenkmann, Thomas; Hergarten, Stefan

    2016-06-01

    The elevated rim in simple craters results from the structural uplift of preimpact target rocks and the deposition of a coherent proximal ejecta blanket at the outer edge of the transient cavity. Given the considerable, widening of the transient cavity during crater modification and ejecta thickness distributions, the cause of elevated crater rims in complex craters is less obvious. The thick, proximal ejecta in complex impact craters is deposited well inside the final crater rim and target thickening should rapidly diminish with increasing distance from the transient cavity rim. Our study of 10 complex Martian impact craters ranging from 8.2 to 53.0 km in diameter demonstrates that the mean structural rim uplift at the final crater rim makes 81% of the total rim elevation, while the mean ejecta thickness contributes 19%. Thus, the structural rim uplift seems to be the dominant factor to build up the total amount of the raised crater rim of complex craters. To measure the widening of the transient cavity during modification and the distance between the rim of the final crater and that of the transient cavity, we constructed balanced cross section restorations to estimate the transient cavity of nine complex Martian impact craters. The final crater radii are ~1.38-1.87 times the transient cavity radii. We propose that target uplift at the position of the final crater rim was established during the excavation stage.

  5. Impact cratering and spall failure of gabbro

    NASA Technical Reports Server (NTRS)

    Lange, M. A.; Ahrens, T. J.; Boslough, M. B.

    1984-01-01

    Both hypervelocity impact and dynamic spall experiments were carried out on a series of well-indurated samples of gabbro. The impact experiments carried out with 0.04 to 0.2 g, 5-6 km/sec projectiles produced deci-centimeter-sized craters and demonstrated crater efficiencies of 6/10 to the -9 g/erg, and order of magnitude greater than in metal and some two to three times that of previous experiments on less strong igneous rocks. Most of the crater volume (some 60 to 80 percent) is due to spall failure. Distribution of cumulative fragment number, as a function of mass of fragments with masses greater than 0.1 gram yield values of b = d(log10N sub f)dlog10(m) of -0.5 to -0.6, where N sub f is the cumulate number of fragments and m is the mass of fragments. These values are in agreement or slightly higher than those obtained for less strong rocks and indicate that a large fraction of the ejecta resides in a few large fragments.

  6. Impact cratering and spall failure at gabbro

    NASA Technical Reports Server (NTRS)

    Lange, M. A.; Ahrens, T. J.; Boslough, M. B.

    1983-01-01

    Both hypervelocity impact and dynamic spall experiments were carried out on a series of well-indurated samples of gabbro. The impact experiments carried out with 0.04 to 0.2g, 5-6 km/sec projectiles produced deci-centimeter-sized craters and demonstrated crater efficiencies of 6/10 to the - 9 g/erg, and order of magnitude greater than in metal and some two to three times that of previous experiments on less strong igneous rocks. Most of the crater volume (some 60 to 80%) is due to spall failure. Distribution of cumulative fragment number, as a function of mass of fragments with masses greater than 0.1 gram yield values of b = d(log10N sub f)dlog10(m)of -0.5 to -0.6, where N sub f is the cumulate number of fragments and m is the mass of fragments. These values are in agreement or slightly higher than those obtained for less strong rocks and indicate that a large fraction of the ejectra resides in a few large fragments.

  7. The Microstructure of Lunar Micrometeorite Impact Craters

    NASA Technical Reports Server (NTRS)

    Noble, S. K.; Keller, L. P.; Christoffersen, R.; Rahman, Z.

    2016-01-01

    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 impacts are still not fully understood. Much effort has focused on evaluating the physical and optical effects of micrometeorite impacts on lunar and meteoritic material using pulsed lasers to simulate the energy deposited into a substrate in a typical hypervelocity impact. Here we characterize the physical and chemical changes that accompany natural micrometeorite impacts 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 craters that revealed important micro-structural details of micrometeorite impact processes, including the creation of npFe (sup 0) in the melt, and extensive deformation around the impact site.

  8. Central ring structure identified in one of the world's best-preserved impact craters

    NASA Astrophysics Data System (ADS)

    Gebhardt, A. C.; Niessen, F.; Kopsch, C.

    2006-03-01

    Seismic refraction and reflection data were acquired in 2000 and 2003 to study the morphology and sedimentary fill of the remote El'gygytgyn crater (Chukotka, northeastern Siberia; diameter 18 km). These data allow a first insight into the deeper structure of this unique impact crater. Wide-angle data from sonobuoys reveal a five-layer model: a water layer, two lacustrine sedimentary units that fill a bowl-shaped apparent crater morphology consisting of an upper layer of fallback breccia with P-wave velocities of ˜3000 m/s, and a lower layer of brecciated bedrock (velocities >3600 m/s). The lowermost layer shows a distinct anticline structure that, by analogy with other terrestrial and lunar craters of similar size, can be interpreted as a central ring structure. The El'gygytgyn crater exhibits a well-expressed morphology that is typical of craters formed in crystalline target rocks.

  9. Crater annihilation on silver by cluster ion impacts

    NASA Astrophysics Data System (ADS)

    Henriksson, K. O. E.; Nordlund, K.; Keinonen, J.

    2007-02-01

    Using the MD/MC-CEM potential we have investigated the impacts of 20 keV Ag 13 cluster ions on (0 0 1) silver surfaces having one initial crater. This one was made in the zeroth ion impact. The degree of annihilation of the initial crater was investigated as a function of the lateral distance ri between the crater and the ion. The impact points were selected randomly inside a circular area with a radius of 75 Å centered on the crater. To reduce the total number of simulations, the circular area was divided into annuli. The initial and final atomic positions in the impact simulations were analyzed and the degree of annihilation of the initial crater was determined. The results indicate that for r ≲ 60 Å there is a net growth of the initial crater, and for distances r ∈ (60, 80) Å there is a small net filling of the crater.

  10. 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.

  11. Impact spallation processes on the Moon: A case study from the size and shape analysis of ejecta boulders and secondary craters of Censorinus crater

    NASA Astrophysics Data System (ADS)

    Krishna, N.; Kumar, P. Senthil

    2016-01-01

    have subdued ejecta (rayless craters), while some possess bright-rayed ejecta (bright-rayed craters). The CSFD of rayless craters show a steep power-law slope with a b-value of -4.0, similar to the secondary craters produced by the impact of ejecta from primary craters. We therefore interpret the rayless craters as the secondary craters of Censorinus. On the other hand, the CSFD of bright-rayed craters have smaller power-law slope (b value -2.7) which is a characteristic of primary craters, and thus provide 3 Ma age for Censorinus crater. When the characteristics of Censorinus boulders are compared with the theoretical spallation models that are sensitive to the petrophysical properties of the target (lunar highland), the models generally agree with the Censorinus boulders. However, the observed shape and size characteristics of the Censorinus boulders are found to be more complex than the theoretical spallation models. The ejecta boulders suffered more complex fragmentation and asymmetric distribution in response to the oblique impact. The spallation models accounting oblique impacts have not yet been developed. Therefore, our Censorinus boulder observations can be used to develop and validate the new theoretical spallation models for the effects of oblique impacts.

  12. The two Suvasvesi impact structures, Finland: Argon isotopic evidence for a "false" impact crater doublet

    NASA Astrophysics Data System (ADS)

    Schmieder, Martin; Schwarz, Winfried H.; Trieloff, Mario; Buchner, Elmar; Hopp, Jens; Tohver, Eric; Pesonen, Lauri J.; Lehtinen, Martti; Moilanen, Jarmo; Werner, Stephanie C.; Öhman, Teemu

    2016-05-01

    The two neighboring Suvasvesi North and South impact structures in central-east Finland have been discussed as a possible impact crater doublet produced by the impact of a binary asteroid. This study presents 40Ar/39Ar geochronologic data for impact melt rocks recovered from the drilling into the center of the Suvasvesi North impact structure and melt rock from glacially transported boulders linked to Suvasvesi South. 40Ar/39Ar step-heating analysis yielded two essentially flat age spectra indicating a Late Cretaceous age of ~85 Ma for the Suvasvesi North melt rock, whereas the Suvasvesi South melt sample gave a Neoproterozoic minimum (alteration) age of ~710 Ma. Although the statistical likelihood for two independent meteorite strikes in close proximity to each other is rather low, the remarkable difference in 40Ar/39Ar ages of >600 Myr for the two Suvasvesi impact melt samples is interpreted as evidence for two temporally separate, but geographically closely spaced, impacts into the Fennoscandian Shield. The Suvasvesi North and South impact structures are, thus, interpreted as a "false" crater doublet, similar to the larger East and West Clearwater Lake impact structures in Québec, Canada, recently shown to be unrelated. Our findings have implications for the reliable recognition of impact crater doublets and the apparent rate of binary asteroid impacts on Earth and other planetary bodies in the inner solar system.

  13. Crater morphology in sandstone targets: The MEMIN impact parameter study

    NASA Astrophysics Data System (ADS)

    Dufresne, Anja; Poelchau, Michael H.; Kenkmann, Thomas; Deutsch, Alex; Hoerth, Tobias; SchńFer, Frank; Thoma, Klaus

    2013-01-01

    Hypervelocity (2.5-7.8 km s-1) impact experiments into sandstone were carried out to investigate the influence of projectile velocity and mass, target pore space saturation, target-projectile density contrast, and target layer orientation on crater size and shape. Crater size increases with increasing projectile velocity and mass as well as with increasing target pore space saturation. Craters in water-saturated porous targets are generally shallower and larger in volume and in diameter than craters from equivalent impacts into dry porous sandstone. Morphometric analyses of the resultant craters, 5-40 cm in diameter, reveal features that are characteristic of all of our experimental craters regardless of impact conditions (I) a large central depression within a fragile, light-colored central part, and (II) an outer spallation zone with areas of incipient spallation. Two different mechanical processes, grain fragmentation and intergranular tensile fracturing, are recorded within these crater morphologies. Zone (I) approximates the shape of the transient crater formed by material compression, displacement, comminution, and excavation flow, whereas (II) is the result of intergranular tensile fracturing and spallation. The transient crater dimensions are reconstructed by fitting quadric parabolas to crater profiles from digital elevation models. The dimensions of this transient and of the final crater show the same trends: both increase in volume with increasing impact energy, and with increasing water saturation of the target pore space. The relative size of the transient crater (in percent of the final crater volume) decreases with increasing projectile mass and velocity, signifying a greater contribution of spallation on the final crater size when projectile mass and velocity are increased.

  14. Differential impact cratering of Saturn's satellites by heliocentric impactors

    NASA Astrophysics Data System (ADS)

    Hirata, Naoyuki

    2016-02-01

    Saturnian satellites are thought to have been struck by two different types of impactors: those with heliocentric origins and those with planetocentric origins. Many of the impacts are suggested to come from planetocentric debris, while many crater count studies assume an ecliptic comet origin when determining the ages of the surfaces. To assess the contribution of planetocentric impactors, this study examines the global distribution and apex-antapex asymmetry of impact craters on Rhea and Iapetus. The results demonstrate that the craters of Rhea (more than 20 km in diameter) and Iapetus (more than 30 km in diameter) show an apex-antapex asymmetry. This suggests that most of the large craters are formed from heliocentric impacts. In contrast, the craters less than 20 km in diameter seem to show no asymmetry. Possible explanations for this are either planetocentric impactor origins or saturation with impact craters.

  15. 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.

  16. 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

  17. Impact cratering and ejection of material on porous asteroids

    NASA Astrophysics Data System (ADS)

    Housen, K.; Sweet, W.

    2014-07-01

    The manner in which an impact crater and its ejecta blanket are created involves an interplay between gravity and the strength properties of the target material. Gravity is important because the overburden stress at depth in an asteroid determines the material shear strength, which affects the mechanics of crater and ejecta formation. This has important implications when attempting to use lab experiments to simulate large-crater formation on asteroids. The only way to perform small-scale experimental simulations of cratering events on asteroids is to adjust the ambient ''gravity'', g, such that the experiment has the same product of gL as the actual impact event being simulated, where L is an important length scale, such as the projectile or crater size [1]. In this way, the lab crater has the same overburden stress (and shear strength) and ejecta ballistics as a much larger cratering event on an asteroid. Even though asteroids have weak gravity fields, the overburden stress of a multiple-km crater is larger than can be reproduced in the lab at 1 G. Therefore, simulation of large impacts on asteroids requires that the ''gravity'' of the experiment is greater than 1 G. Here we report on a series of impact experiments conducted at elevated gravity on a geotechnical centrifuge. These experimental craters are subscale replicas of the much larger craters they simulate; larger G-levels simulate larger craters. Using the Boeing 600-G centrifuge, we directly simulate the formation of asteroid (g˜0.001 G) craters as large as several tens of km. The target materials are cohesionless with porosity ranging from 35 % to 95 %. Cratering experiments in soils with small or moderate porosity (<30 %) show a decrease in cratering efficiency (crater volume/impactor volume) with increasing size scale or, equivalently, increasing G in a centrifuge experiment. This well-known gravity-regime behavior is due to the fact that the shear strength of the target material goes up due to the

  18. 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

  19. The distribution and modes of occurrence of impact melt at lunar craters

    NASA Technical Reports Server (NTRS)

    Hawke, B. Ray; Head, J. W.

    1992-01-01

    Numerous studies of the returned lunar samples as well as geologic and remote-sensing investigations have emphasized the importance of impact melts on the surface of the Moon. Information concerning the distribution and relative volumes is important for (1) an improved understanding of cratering processes, (2) kinetic energy estimates and energy partitioning studies, (3) the proper interpretation of melt-bearing lunar samples, and (4) comparative planetology studies. The identification of major flows of fluidized material associated with impact craters on the surface of Venus has increased interest in impact melt flows on the other terrestrial planets. For a number of years, we have been investigating the distribution, modes of occurrence, and relative and absolute amounts of impact melt associated with lunar craters as well as the manner in which melt volumes vary as a function of crater size, morphology, and target characteristics. The results of this effort are presented.

  20. Mexican site for K/T impact crater?

    NASA Technical Reports Server (NTRS)

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

    1991-01-01

    Research throughout the Caribbean suggests that the geophysical anomalies in the Yucatan first noted by Penfield and Camargo (1981) and called the Chicxulub crater could be the site of the impact purported to have caused the K/T extinctions. A semicircular ring of sink holes, known locally as cenotes, which correlates with the geophysical anomalies has been identified, and it is argued that the origin of the cenote ring is related to postimpact subsidence of the Chicxulub crater rim. If there is indeed a crater, the region within the cenote ring corresponds to its floor and the crater rim diameter is probably larger than 200 km. If confirmed as a site of impact, the Chicxulub crater would be the largest terrestrial impact crater known, which is consistent with the uniqueness of the K/T global catastrophe.

  1. Mexican site for K/T impact crater?

    NASA Astrophysics Data System (ADS)

    Pope, K. O.; Ocampo, A. C.; Duller, C. E.

    1991-05-01

    Research throughout the Caribbean suggests that the geophysical anomalies in the Yucatan first noted by Penfield and Camargo (1981) and called the Chicxulub crater could be the site of the impact purported to have caused the K/T extinctions. A semicircular ring of sink holes, known locally as cenotes, which correlates with the geophysical anomalies has been identified, and it is argued that the origin of the cenote ring is related to postimpact subsidence of the Chicxulub crater rim. If there is indeed a crater, the region within the cenote ring corresponds to its floor and the crater rim diameter is probably larger than 200 km. If confirmed as a site of impact, the Chicxulub crater would be the largest terrestrial impact crater known, which is consistent with the uniqueness of the K/T global catastrophe.

  2. Impact Diamonds in the Craters of the Ukrainian Shield

    NASA Astrophysics Data System (ADS)

    Gurov, E. P.; Gurova, E. P.; Rakitskaya, R. B.

    1995-09-01

    The impact diamonds discovery and investigations in the rocks of the Popigay crater [1,2] stimulated the search of the carbon high pressure phases in the craters of the Ukrainian shield. Seven impact craters are located on the territory of the Ukrainian Shield and its North-Eastern slope. Impact diamonds were discovered in the rocks of the Ilyinets, Zapadnaya, Obolon craters and some other impact structures. The highest concentration of impact diamonds was determined in the Zapadnaya crater. The Zapadnaya impact crater, about 3 km in diameter, is located in the Western part of the Ukrainian shield. The target of the crater is presented by granites and gneisses of the Precambrian crystalline basement. The Zapadnaya crater is represented the intensively eroded astrobleme of a complex structure. The inner crater with the conelike central uplift preserves only at the recent erosional level [3,4]. The allochthonous rocks complex in the crater is presented by the suevites, breccia and impactites. The allochthonous breccia forms the lowermost layer in the crater. The suevites with the glass content from 10-15 to 40-50% compose the upper annular layer around the central uplift. The massive impactites form the dykelike veins in the brecciated rocks of the subcrater basement. The impact diamonds occur in suevites and massive impactites of the crater. The diamonds are represented with the tabular grains from tens of micron up to 0.4-0.5 mm in diameter. The colour of the diamond grains changes from colourless, white and yellowish to grey, dark grey and black. The diamonds are anisotropic, their birefringence is up to 0.015. The impact diamonds phase composition was investigated with X-ray methods. The diamond grains are represented by the submicroscopic aggregates of cubic and hexagonal phases. The cubic phase prevalents in all investigated diamonds; the hexagonal phase content in the diamonds from the Zapadnaya crater changes from 5-10 to 40-50%. The direct dependence of the

  3. Seismic interpretation of the sedimentation systems, structural geology and stratigraphic of the Chicxulub crater, carbonate platform of Yucatan, Mexico.

    NASA Astrophysics Data System (ADS)

    Iza, Canales-Garcia; Jaime, Urrutia-Fucugauchi; Joaquin Eduardo, Aguayo-Camargo; Angel, Alatorre-Mendieta Miguel

    2016-04-01

    In order to describe the structural and stratigraphic features of the Chicxulub crater, was performed the present work of seismic interpretation, seismic attributes and generation of 3D surfaces. Load data it was performed in SEG-Y format, to display a total of 19 seismic reflection profiles were worked at domain time; the corresponding interpretation was carried out by separating five packages with textural differences, for this separation were used five horizons with seismic response representing the base of these packages, the correlation of horizons was made for all lines, creating composed lines so that all profiles were interpret together at intersections for form a grid. Multiple fault zones, were interpreted with the help of seismic attributes, like RMS amplitude, complex trace analysis, gradient of the trace and cosine phase. Was obtained the structural and stratigraphic interpretation , 3D models of the surfaces interpreted with which it is possible to observe the morphology of the base of the basin, it is controlled by the effect of the impact that formed the crater, has the features as a multi-ring crater. Shallower horizons shows that the topography of the base of the crater continues to affect the upper relief, which tends to be horizontal as it approaches the surface but is modeled by themselves sedimentary processes of the carbonate platform of Yucatán; packages below the base of the crater show the characteristics that own carbonated breccia, product the rupture of the material at impact, the material was deposited in a chaotic way, at this level we found the faults and fractures zone.

  4. Ganymede - Ancient Impact Craters in Galileo Regio

    NASA Technical Reports Server (NTRS)

    1996-01-01

    Ancient impact craters shown in this image of Jupiter's moon Ganymede taken by NASA's Galileo spacecraft testify to the great age of the terrain, dating back several billion years. At the margin at the left, half of a 19-kilometer-diameter (12-mile) crater is visible. The dark and bright lines running from lower right to upper left and from top to bottom are deep furrows in the ancient crust of dirty water ice. The origin of the dark material is unknown, but it may be accumulated dark fragments from many meteorites that hit Ganymede. In this view, north is to the top, and the sun illuminates the surface from the lower left about 58 degrees above the horizon. The area shown is part of Ganymede's Galileo Regio region at latitude 18 degrees north, longitude 147 degrees west; it is about 46 by 64 kilometers (29 by 38 miles) in extent. Resolution is about 80 meters (262 feet) per pixel. The image was taken June 27 at a range of 7.563 kilometers (4,700 miles). The Jet Propulsion Laboratory manages the Galileo mission for NASA's Office of Space Science.

  5. 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.

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

    USGS Publications Warehouse

    Squyres, S. W.; Arvidson, R. E.; Bell, J.F., III; Calef, F.J., III; Clark, B. C.; Cohen, B. A.; Crumpler, L.A.; de Souza, P. A., Jr.; 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.

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

    PubMed

    Squyres, S W; Arvidson, R E; Bell, J F; Calef, F; Clark, B C; Cohen, B A; Crumpler, L A; de Souza, P A; Farrand, W H; Gellert, R; 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

    2012-05-01

    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. PMID:22556248

  8. Fresh lunar impact craters - Review of variations with size

    NASA Technical Reports Server (NTRS)

    Howard, K. A.

    1974-01-01

    Thirty-three morphologic characteristics are reviewed for fresh lunar impact craters wider than 1 km. Bar graphs express the way each characteristic varies with crater size. The features are grouped as crater structure, ejecta, and downhill flow features. Major structural transitions occur at diameters of about 15 and 200 km. Details of the ejecta blanket, which include several kinds of lineations, dunelike ridges, troughs, and lobes, reflect different transport regimes in the ejecta. Some materials at larger craters flowed downhill in lavalike fashion after the ejecta was deposited; the lavalike materials are probably impact melt.

  9. Mapping and interpretation of Sinlap crater on Titan using Cassini VIMS and RADAR data

    USGS Publications Warehouse

    Le, Mouelic S.; Paillou, P.; Janssen, M.A.; Barnes, J.W.; Rodriguez, S.; Sotin, C.; Brown, R.H.; Baines, K.H.; Buratti, B.J.; Clark, R.N.; Crapeau, M.; Encrenaz, P.J.; Jaumann, R.; Geudtner, D.; Paganelli, F.; Soderblom, L.; Tobie, G.; Wall, S.

    2008-01-01

    Only a few impact craters have been unambiguously detected on Titan by the Cassini-Huygens mission. Among these, Sinlap is the only one that has been observed both by the RADAR and VIMS instruments. This paper describes observations at centimeter and infrared wavelengths which provide complementary information about the composition, topography, and surface roughness. Several units appear in VIMS false color composites of band ratios in the Sinlap area, suggesting compositional heterogeneities. A bright pixel possibly related to a central peak does not show significant spectral variations, indicating either that the impact site was vertically homogeneous, or that this area has been recovered by homogeneous deposits. Both VIMS ratio images and dielectric constant measurements suggest the presence of an area enriched in water ice around the main ejecta blanket. Since the Ku-band SAR may see subsurface structures at the meter scale, the difference between infrared and SAR observations can be explained by the presence of a thin layer transparent to the radar. An analogy with terrestrial craters in Libya supports this interpretation. Finally, a tentative model describes the geological history of this area prior, during, and after the impact. It involves mainly the creation of ballistic ejecta and an expanding plume of vapor triggered by the impact, followed by the redeposition of icy spherules recondensed from this vapor plume blown downwind. Subsequent evolution is then driven by erosional processes and aeolian deposition. Copyright 2008 by the American Geophysical Union.

  10. Craters produced on metals by single ion impacts.

    SciTech Connect

    Birtcher, R. C.

    1998-12-23

    Single ion impacts have been observed using in-situ transmission electron microscopy during irradiation. In addition to internal defects, single-ion impacts create surface craters as large as 12 nm on In, Ag, Pb and Au. Crater formation rates have been determined from video recordings with a time-resolution of 33 milliseconds. The cratering rate for Xe ions increases linearly with increasing target mass density above a threshold density of approximately 7 gm/cm{sup 3}. The cratering rate increases as the ion mass is increased. These results suggest that cratering requires a high energy-density, near-surface displacement cascade. TRIM calculations have been made in an effort to establish a near-surface energy-density criterion for cratering.

  11. The depths of the largest impact craters on Venus

    NASA Technical Reports Server (NTRS)

    Ivanov, B. A.; Ford, P. G.

    1993-01-01

    The largest impact craters on Venus may be used as evidence of various geological processes within the Venusian crust. We are continuing to construct a data base for the further investigation of large craters on Venus (LCV). We hope to find evidence of crater relaxation that might constrain the thickness and thermal gradient of the crust, as was proposed in an earlier work. The current work concentrates on 27 impact craters with diameters (d) larger than 70 km, i.e., large enough that the footprint of the Magellan altimeter has a good chance of sampling the true crater bottom. All altimeter echoes from points located within (d/2)+70 km from the crater center have been inspected.

  12. Auto-Detection of Impact Crater Statistics and Crater Morphologies in Mars THEMIS Data

    NASA Astrophysics Data System (ADS)

    Plesko, C. S.; Brumby, S. P.; Asphaug, E.

    2003-12-01

    One of the challenges of planetary science is the development of tools adequate to provide automated crater statistics, for use in chronology, geomorphology and a variety of other investigations. We will present the current results of an ongoing effort to develop new tools for culling THEMIS imagery for crater statistics. Our eventual goal is to generate crater density and age maps of Mars. We are also developing tools to probe the morphologies and near-surface compositions of type-class craters. One crater type of particular significance is the rampart crater, which is unique to Mars. These are widely believed to be the result of impacts into volatile-rich surface materials. We will present the results of our examination of the spectral and morphological properties of several rampart craters in THEMIS IR images as a demonstration of image processing and automated feature extraction techniques. Using techniques developed at Los Alamos National Laboratory, we are able to obtain an automated count of craters in an image, their centroids and radii, extract spectra and compare them to spectral libraries of known reference minerals.

  13. Hypervelocity impact cratering - A catastrophic terrestrial geologic process

    NASA Astrophysics Data System (ADS)

    Grieve, Richard A. F.

    It is possible to infer a 5.4 x 10 to the 15th/sq km per year terrestrial impact cratering rate for hypervelocity impact structures with diameters greater than 20 km. These craters often contain such shock-metamorphic effects as shatter cones, tectosilicate microscopic planar features, diapleptic solid-state glasses, and impact melting. Impact melt rocks may contain siderophile anomalies indicative of siderophile material admixtures. Hypervelocity impacts have gained recognition as catastrophes with potentially severe biological effects; the cratering record is such as to suggest that the earth may be subjected to periodic cometary showers.

  14. Dimensional scaling for impact cratering and perforation

    NASA Technical Reports Server (NTRS)

    Watts, Alan J.; Atkinson, Dale

    1995-01-01

    POD Associates have revisited the issue of generic scaling laws able to adequately predict (within better than 20 percent) cratering 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 impacts 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.

  15. Scaling of liquid-drop impact craters in granular media

    NASA Astrophysics Data System (ADS)

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

    Granular impact cratering by liquid drops is a ubiquitous phenomenon, directly relevant to many important natural and industrial processes such as soil erosion, drip irrigation, and dispersion of micro-organisms in soil. Here, by combining the high-speed photography with high precision laser profilometry, we investigate the liquid-drop impact dynamics on granular surfaces and monitor the morphology of resulting craters. Our experiments reveal novel scaling relations between the size of granular impact craters and important control parameters including the impact energy, the size of impinging drops and the degree of liquid saturation in a granular bed. Interestingly, we find that the scaling for liquid-drop impact cratering in dry granular media can be quantitatively described by the Schmidt-Holsapple scaling originally proposed for asteroid impact cratering. On the other hand, the scaling for impact craters in wet granular media can be understood by balancing the inertia of impinging drops and the strength of impacted surface. Our study sheds light on the mechanism governing liquid-drop impacts on dry/wet granular surfaces and reveals a remarkable analogy between familiar phenomena of raining and catastrophic asteroid strikes. Scaling of liquid-drop impact craters in granular media.

  16. 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

  17. Grazing Impacts Upon Earth's Surface: Towards an Understanding of the Rio Cuarto Crater Field

    NASA Astrophysics Data System (ADS)

    Beech, Martin

    2014-10-01

    The origin of the Rio Cuarto crater field, Argentina has been widely debated since the early 1990s when it was first brought to public attention. In a binary on-off sense, however, the craters are either of a terrestrial origin or they formed via a large asteroid impact. While there are distinct arguments in favour of the former option being the correct interpretation, it is the latter possibility that is principally investigated here, and five distinct impact formation models are described. Of the impact scenarios it is found that the most workable model, although based upon a set of fine-tuned initial conditions, is that in which a large, 100-150-m initial diameter asteroid, entered Earth's atmosphere on a shallow angle path that resulted in temporary capture. In this specific situation a multiple-thousand kilometer long flight path enables the asteroid to survive atmospheric passage, without suffering significant fragmentation, and to impact the ground as a largely coherent mass. Although the odds against such an impact occurring are extremely small, the crater field may nonetheless be interpreted as having potentially formed via a very low-angle, smaller than 5° to the horizon, impact with a ground contact speed of order 5 km/s. Under this scenario, as originally suggested by Schultz and Lianza (Nature 355:234, 1992), the largest of the craters (crater A) in the Rio Cuarto structure was produced in the initial ground impact, and the additional, smaller craters are interpreted as being formed through the down-range transport of decapitated impactor material and crater A ejecta.

  18. Determining long-term regional erosion rates using impact craters

    NASA Astrophysics Data System (ADS)

    Hergarten, Stefan; Kenkmann, Thomas

    2015-04-01

    More than 300,000 impact craters have been found on Mars, while the surface of Moon's highlands is even saturated with craters. In contrast, only 184 impact craters have been confirmed on Earth so far with only 125 of them exposed at the surface. The spatial distribution of these impact craters is highly inhomogeneous. Beside the large variation in the age of the crust, consumption of craters by erosion and burial by sediments are the main actors being responsible for the quite small and inhomogeneous crater record. In this study we present a novel approach to infer long-term average erosion rates at regional scales from the terrestrial crater inventory. The basic idea behind this approach is a dynamic equilibrium between the production of new craters and their consumption by erosion. It is assumed that each crater remains detectable until the total erosion after the impact exceeds a characteristic depth depending on the crater's diameter. Combining this model with the terrestrial crater production rate, i.e., the number of craters per unit area and time as a function of their diameter, allows for a prediction of the expected number of craters in a given region as a function of the erosion rate. Using the real crater inventory, this relationship can be inverted to determine the regional long-term erosion rate and its statistical uncertainty. A limitation by the finite age of the crust can also be taken into account. Applying the method to the Colorado Plateau and the Deccan Traps, both being regions with a distinct geological history, yields erosion rates in excellent agreement with those obtained by other, more laborious methods. However, these rates are formally exposed to large statistical uncertainties due to the small number of impact craters. As higher crater densities are related to lower erosion rates, smaller statistical errors can be expected when large regions in old parts of the crust are considered. Very low long-term erosion rates of less than 4

  19. Large impact crater histories of Mars: The effect of different model crater age techniques

    NASA Astrophysics Data System (ADS)

    Robbins, Stuart J.; Hynek, Brian M.; Lillis, Robert J.; Bottke, William F.

    2013-07-01

    Impact events that produce large craters primarily occurred early in the Solar System's history because the largest bolides were remnants from planetary formation. Determining when large impacts occurred on a planetary surface such as Mars can yield clues to the flux of material in the early inner Solar System which, in turn, can constrain other planetary processes such as the timing and magnitude of resurfacing and the history of the martian core dynamo. We have used a large, global planetary database in conjunction with geomorphologic mapping to identify craters superposed on the rims of 78 larger craters with diameters D ⩾ 150 km on Mars, ≈78% of which have not been previously dated in this manner. The densities of superposed craters with diameters larger than 10, 16, 25, and 50 km, as well as isochron fits were used to derive model crater ages of these larger craters and basins from which we derived an impact flux. In discussing these ages, we point out several internal inconsistencies of crater-age modeling techniques and chronology systems and, all told, we explain why we think isochron-fitting is the most reliable indicator of an age. Our results point to a mostly obliterated crater record prior to ˜4.0 Ga with the oldest preserved mappable craters on Mars dating to ˜4.3-4.35 Ga. We have used our results to constrain the cessation time of the martian core dynamo which we found to have occurred between the formation of Ladon and Prometheus basins, approximately 4.06-4.09 Ga. We also show that, overall, surfaces on Mars older than ˜4.0-4.1 Ga have experienced >1 km of resurfacing, while those younger than ˜3.8-3.9 Ga have experienced significantly less.

  20. 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

  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. Liquid drop impact cratering on a granular layer

    NASA Astrophysics Data System (ADS)

    Katsuragi, H.

    2010-12-01

    Granular impact cratering has been studied both in terms of planetary science and fundamental granular physics. Recent studies have revealed morphological scaling and dynamics of the granular impact cratering phenomenon. In all these studies, solid impactors have been used. However, the actual geophysical scale impactors might be melt. To mimic what happens when the impactor is melt, we performed simple drop granular impact experiment. A small (millimeter scale) water drop was dropped onto a granular layer (abrasives of micrometer grain size) at low impact speed (about meter/second). Then, various kinds of novel crater shapes were discovered depending on the experimental conditions. For instance, "sink type", "flat type", "ring type", and "bump type" craters were observed. We measured the characteristic time scale and length scale of the cratering, using a high speed camera and a laser profilometry system. From the experimental data, a simple scaling of the crater radius is proposed. The obtained scaling exponent is same as that of usual solid impact cratering. In the solid impactor case, the scaling exponent is derived from energy balance between impactor and ejecta. However, we found that the liquid drop deformation determines the scaling exponent in this experiment. We have also used glycerol and ethanol and their aqueous solutions, in order to examine the effect of viscosity and capillary force of liquid drops. A picture of the impacting drop is shown below. A water drop impacting onto a layer of abrasive.

  3. Characterizing the geomorphology of fresh impact craters on Mercury

    NASA Astrophysics Data System (ADS)

    Barnouin, O. S.; Ernst, C. M.; Neumann, G. A.; Chabot, N. L.; Murchie, S. L.; Smith, D. E.; Zuber, M. T.; Solomon, S. C.

    2011-12-01

    Topographic data acquired by the Mercury Laser Altimeter (MLA) and images from the Mercury Dual Imaging System (MDIS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft are used to investigate the geomorphology of several fresh impact craters on Mercury. This analysis expands on previous efforts with Mariner 10 data to understand how craters on Mercury compare to similarly sized craters on other planets and moons. In particular, comparisons to craters on Mars, which has a surface gravitational acceleration nearly identical to that of Mercury, yield insights into the effects of surface properties, especially target strength, on crater morphology. Establishing the geomorphology of typical fresh craters on Mercury also will provide a baseline for assessing the modification of less well-preserved craters by volcanism, tectonics, and subsequent impacts. Hokusai crater, whose rays envelop much of the planet, is one of the freshest on the surface of Mercury. High-resolution MDIS images (~36 m/pixel) reveal few superposed craters on this 100-km-diameter crater, and several MLA profiles that pass through its center indicate that it is ~2 km deep from rim crest to crater floor, making it extremely deep for a crater of its diameter on Mercury. Impact melt fills the interior of Hokusai this crater, embaying a semi-circular central peak structure. The melt possesses small cracks that are likely due to cooling. Small variations in brightness seen in the melt deposit seem to be associated with small undulations in the topography as measured by MLA, possibly due to the underlying terrain. Some of the impact melt lies in local depressions within the terraces of the crater wall, and some in patches located throughout the crater ejecta. Hokusai crater also possesses intriguing topographic features in its near-rim ejecta field. The MLA data indicate that the thickness of ejecta beyond the crater rim is not well modeled by a power-law function

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

    SciTech Connect

    Morris, A. J. W.; Price, M. C.; Burchell, M. J.

    2013-09-01

    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 considered 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.

  5. 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.

  6. 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.

  7. Low-velocity impact cratering experiments in a wet sand target.

    PubMed

    Takita, Haruna; Sumita, Ikuro

    2013-08-01

    Low-velocity impact cratering experiments were conducted in a wet sand target. With the addition of interstitial water, the sand stiffens and the yield stress σ(y) increases by a factor of 10 and we observe a significant change in the resulting crater shape. A small water saturation (S~0.02) is sufficient to inhibit the crater wall collapse, which causes the crater diameter d to decrease and the crater depth to increase, and results in the steepening of the crater wall. With a further addition of water (S~0.04), the collapse is completely inhibited such that cylindrical craters form and the impactor penetration depth δ and ejecta dispersal are suppressed. However, for S>0.7, the wet sand becomes fluidized such that both d and δ increase thereafter. Comparing the relevant stresses, we find that cylindrical craters form when the yield stress is more than about three times larger than the gravitational stress such that it can withstand collapse. Experiments with different impactor sizes D and velocities indicate that for S≤0.02, gravity-regime scaling applies for d. However, the scaling gradually fails as S increases. In contrast, we find that δ/D can be scaled by the inertial stress normalized by the yield stress, for a wide range of S. This difference in the scaling is interpreted as arising from d being affected by whether or not the crater wall collapses, whereas δ is determined by the penetration process that occurs prior to collapse. The experimental parameter space in terms of dimensionless numbers indicates that our experiments may correspond to impact cratering in small asteroids. PMID:24032824

  8. Impact cratering and regolith dynamics. [on moon

    NASA Technical Reports Server (NTRS)

    Hoerz, F.

    1977-01-01

    The most recent models concerning mechanical aspects of lunar regolith dynamics related to impact cratering 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 impact processes can be modeled; it appears that catastrophic rupture dominates over single particle abrasion.

  9. Searching for impact craters using space shuttle photography

    NASA Technical Reports Server (NTRS)

    Wood, C. A.; Dailey, C.; Daley, W.; Wells, G.

    1984-01-01

    Extrapolation of impact cratering rates derived from Canada and Europe suggests that in the cratonic regions of Australia, India, Africa, and Brazil, 14-15 impact craters 20 km diameter should have formed during the last 120 my, and survived erosional erasure. In fact, in these areas, only 2 craters are known that approximately qualify: (1) Gosses Bluff, 22 km, 130 + or - 6 my old, and; Strangways, 24 km and 150 + or - 70 my old. It is therefore likely that about a dozen relatively large and preserved impact craters await discovery in these less explored cratons. A larger number of younger and smaller craters must also exist. An informal search is reported for impact craters using photographs obtained by Shuttle astronauts. Photographs taken with the 250 mm lens on Hassalblad cameras have a resolution of 25 m and cover a nominal area of 50x60 sq km. A larger format Linhof camera with similar resolution but 4 times larger area was flown March 1984, and will fly again in the future. Shuttle imagery has numerous advantages in looking for impact craters and for other types of Earth observations.

  10. 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.

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

    SciTech Connect

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

    1995-02-01

    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. The authors 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 they hope to derive an empirical relationship between crater shape and impactor velocity, direction and particle properties. Such a relationship can be applied to any surface exposed to space debris or micrometeoroid particles for which a detailed pointing history is available.

  12. 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.

  13. Martian impact cratering rate over the last 3 billions years derived from layered ejecta craters dating

    NASA Astrophysics Data System (ADS)

    Lagain, Anthony; Bouley, Sylvain; Costard, François; Baratoux, David

    2016-04-01

    All chronology models used in dating planetary surfaces are based on the lunar chronology system. The cratering density of the Moon has been calibrated with absolute ages from Apollo lunar samples. However, there are no lunar samples between 3 Gy and 800 My and only four samples have been dated between 800 My and present. Therefore, the evolution of the cratering rate after the LHB and before 3 Gy is well constrained. The cratering rate between 3 Gy and present has been assumed to be constant [1, 2]. Nevertheless, this assumption is challenged by the analysis of the geological record, such as the frequency of landslide on Mars as a function of time [3, 4]. It is therefore necessary to re-examine the validity of this assumption and place constraints on the cratering rate since the last 3 Gy. For this purpose, we study the rate of impact cratering using small craters on a set of 53 layered ejecta craters larger than 5 km in diameter in Acidalia Planitia, Mars. LECs larger than 5km have large enough surfaces to date their formation by counting craters larger than 100m present on their blankets. Furthermore, limits of their ejecta blankets are clearly defined by a terminal bead. In order to determine the crater emplacement ages, we have applied the methodology dating described in our previous study [6] on all ejecta layers. Errors on measured ages were calculated following [7]. The age of the study area is 2.8±0.2 Gy. Our crater counts on distal ejecta blankets reveal ages younger than the age of the surrounding surface, as expected. It is essential to take into account errors on measured ages. The statistical sample used to build this emplacement frequency distribution and our dating methodology are sufficiently reliable to deduce that a constant impact cratering rate over the last 3 Gy is not a correct approximation. The excessive number of craters emplaced 1Gy ago compared to the cratering rate used suggests a decreased impact cratering rate over the last 1Gy and

  14. The age of the Pretoria Saltpan impact crater, South Africa

    NASA Technical Reports Server (NTRS)

    Storzer, Dieter; Koeberl, Christian; Reimold, Wolf Uwe

    1993-01-01

    The Pretoria Saltpan impact crater, situated about 40 km NNW of Pretoria, South Africa, has a diameter of about 1.13 km. The structure was formed in 2.05 Ga Nebo granite of the Bushveld Complex. The impact origin of the crater was recently established by the discovery of characteristic shock-metamorphic features in breccias found in drill cores at depths greater than 90 m. Impact glass fragments were recovered by standard magnetic separation techniques and handpicking from the melt breccias. As no reliable crater age was known so far, several hundred sub-millimeter-sized glass fragments were studied for fission tracks. The results show that the Saltpan impact crater has an age of 220 +/- 52 ka. This is in agreement with field geological observations.

  15. Impact Craters on Comets from a Granular Material Perspective

    NASA Astrophysics Data System (ADS)

    de Niem, D.; Kührt, E.

    2015-02-01

    The contribution applies an algorithm for finite-deformation elasticity and plasticity to demonstrate new results for the behaviour of granular materials during impact crater formation in a low-gravity environment.

  16. Experimental Impact Cratering into Sandstone: A MEMIN-Progress Report

    NASA Astrophysics Data System (ADS)

    Poelchau, M. H.; Deutsch, A.; Kenkmann, T.; Hoerth, T.; Schäfer, F.; Thoma, K.; Memin Team

    2011-03-01

    The MEMIN Project is currently focused on impact experiments into sandstone. First results are presented here, including the evaluation of high-speed cameras, ejecta catchment devices, crater morphology, and chemical projectile-target interaction.

  17. Topography of the Martian Impact Crater Tooting

    NASA Technical Reports Server (NTRS)

    Mouginis-Mark, P. J.; Garbeil, H.; Boyce, J. M.

    2009-01-01

    Tooting crater is approx.29 km in diameter, is located at 23.4degN, 207.5degE, and is classified as a multi-layered ejecta crater [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 crater cavity, we have focused this year on creating digital elevation models (DEMs) for the crater 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

  18. Bilateral symmetry elements of the Zhamanshin impact crater

    NASA Technical Reports Server (NTRS)

    Masaytis, V. L.

    1988-01-01

    The internal structure of the Zhamanshin impact structure and the nature of rocks developed within it are studied to establish the impact structure parameters. It is found that the diameter of the visible crater is about 13 km. The small annular structures observed are found to not be secondary craters, and no correlation is found between the asymmetrical distribution of ejecta material and the arrangement of these annular forms.

  19. 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.

  20. Fluvial erosion of impact craters: Earth and Mars

    NASA Astrophysics Data System (ADS)

    Baker, V. R.

    1984-04-01

    Geomorphic studies of impact structures in central Australia are being used to understand the complexities of fluvial dissection in the heavily cratered terrains of Mars. At Henbury, Northern Territory, approximately 12 small meteorite craters have interacted with a semiarid drainage system. The detailed mapping of the geologic and structural features at Henbury allowed this study to concentrate on degradational landforms. The breaching of crater rims by gullies was facilitated by the northward movement of sheetwash along an extensive pediment surface extending from the Bacon Range. South-facing crater rims have been preferentially breached because gullies on those sides were able to tap the largest amounts of runoff. At crater 6 a probable rim-gully system has captured the headward reaches of a pre-impact stream channel. The interactive history of impacts and drainage development is critical to understanding the relationships in the heavily cratered uplands of Mars. Whereas Henbury craters are younger than 4700 yrs. B.P., the Gosses Bluff structure formed about 130 million years ago. The bluff is essentially an etched central peak composed of resistant sandstone units. Fluvial erosion of this structure is also discussed.

  1. Fluvial erosion of impact craters: Earth and Mars

    NASA Technical Reports Server (NTRS)

    Baker, V. R.

    1984-01-01

    Geomorphic studies of impact structures in central Australia are being used to understand the complexities of fluvial dissection in the heavily cratered terrains of Mars. At Henbury, Northern Territory, approximately 12 small meteorite craters have interacted with a semiarid drainage system. The detailed mapping of the geologic and structural features at Henbury allowed this study to concentrate on degradational landforms. The breaching of crater rims by gullies was facilitated by the northward movement of sheetwash along an extensive pediment surface extending from the Bacon Range. South-facing crater rims have been preferentially breached because gullies on those sides were able to tap the largest amounts of runoff. At crater 6 a probable rim-gully system has captured the headward reaches of a pre-impact stream channel. The interactive history of impacts and drainage development is critical to understanding the relationships in the heavily cratered uplands of Mars. Whereas Henbury craters are younger than 4700 yrs. B.P., the Gosses Bluff structure formed about 130 million years ago. The bluff is essentially an etched central peak composed of resistant sandstone units. Fluvial erosion of this structure is also discussed.

  2. A Method of Estimating Transient-Cavity Diameters for Impact Craters Formed in Dry Sand

    NASA Technical Reports Server (NTRS)

    Cintala, M. J.; Barnouin-Jha, O. S.; Hoerz, F.

    2003-01-01

    Analyses of impact craters formed in laboratory experiments historically have been the source of many fundamental observations and interpretations of the impact-cratering process itself. Due to its ready availability, ease of handling, and lack of strength, dry sand of various types has been the target material of choice in the majority of such experiments. A consequence of its lack of intrinsic strength, however, is dry sand's inability to maintain slopes above its angle of repose. Evidence from field observations of simple terrestrial craters and laboratory craters formed in more cohesive granular media suggests that transient cavities are similar to paraboloids in shape. Cross-sections of craters formed in dry sand, however, are nearly conical with the wall slopes at or near the angle of repose, indicating that the original crater form has been modified by one or more processes, among which is simple slope failure. Because the dimensions and shape of the transient cavity reflect the detailed conditions of a given impact event, its characterization has long been a desired goal in experimentation. A means of estimating the position of the transient cavity's rim is suggested below, relying on determination of velocities of material ejected from the growing cavity.

  3. Hydrothermal Processes and Mobile Element Transport in Martian Impact Craters - Evidence from Terrestrial Analogue Craters

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.; Nelson, M. J.; Shearer, C. K.; Dressler, B. L.

    2005-01-01

    Hydrothermal alteration and chemical transport involving impact craters probably occurred on Mars throughout its history. Our studies of alteration products and mobile element transport in ejecta blanket and drill core samples from impact craters show that these processes may have contributed to the surface composition of Mars. Recent work on the Chicxulub Yaxcopoil-1 drill core has provided important information on the relative mobility of many elements that may be relevant to Mars. The Chicxulub impact structure in the Yucatan Peninsula of Mexico and offshore in the Gulf of Mexico is one of the largest impact craters identified on the Earth, has a diameter of 180-200 km, and is associated with the mass extinctions at the K/T boundary. The Yax-1 hole was drilled in 2001 and 2002 on the Yaxcopoil hacienda near Merida on the Yucatan Peninsula. Yax-1 is located just outside of the transient cavity, which explains some of the unusual characteristics of the core stratigraphy. No typical impact melt sheet was encountered in the hole and most of the Yax-1 impactites are breccias. In particular, the impact melt and breccias are only 100 m thick which is surprising taking into account the considerably thicker breccia accumulations towards the center of the structure and farther outside the transient crater encountered by other drill holes.

  4. 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.

  5. 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

  6. Geophysical Signature of the Lake Bosumtwi Impact Crater from Pre-drilling Site Surveys

    NASA Astrophysics Data System (ADS)

    Banour, S.; Pohl, J.; Menyeh, A.; Milkereit, B.; Boadu, F.

    2006-12-01

    The Bosumtwi impact crater located near Kumasi, Ghana was formed by a meteorite impact about one million years ago and has a diameter of about 10.5 km. Geophysical investigations involving gravity and magnetic measurements were carried out at the Bosumtwi crater to determine the geophysical signature of the crater with the aim of understanding the impact process. Gravity data was acquired on land at 163 locations around the crater area, as well as on the shore of the lake. The separation between the gravity stations was 500 m for profiles which ran radially toward the lake, and 700 1000 m along roads and footpaths which ran parallel to the shore. In addition, marine gravity and magnetic surveys were carried out along 14 north-south and 15 east- west profiles on the lake with a line spacing of 800 m using a Garmin 235 Echo Sounder/GPS as a navigational tool. Results from gravity modelling showed that the gravity signature of the crater is characterized by a negative Bouguer anomaly with an amplitude roughly equal to 18 mgal. The results also indicated a central uplift at 250 m depth below the lake, thus confirming it as a complex impact crater. Magnetic modelling yielded a model for the causative body, which is located north of the central uplift. The model has a magnetic susceptibility of 0.03 SI and extends from 200 to 610 m depth below the lake surface. The causative body has been interpreted as magnetized bodies consisting of thin sheets of suevitic impact formations. These results serve as a contribution to the understanding of the impact process of this young crater.

  7. 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.

  8. A Sharper View of Impact Craters from Clementine Data

    NASA Astrophysics Data System (ADS)

    Pieters, C. M.; Staid, M. I.; Fischer, E. M.; Tompkins, S.; He, G.

    1994-12-01

    The ultraviolet-visible camera on the Clementine spacecraft obtained high-spatial resolution images of the moon in five spectral channels. Impact craters mapped with these multispectral images show a scale of lithologic diversity that varies with crater size and target stratigraphy. Prominent lithologic variations (feldspathic versus basaltic) occur within the south wall of Copernicus (93 kilometers in diameter) on the scale of 1 to 2 kilometers. Lithologic diversity at Tycho (85 kilometers in diameter) is less apparent at this scale, although the impact melt of these two large craters is remarkably similar in this spectral range. The lunar surface within and around the smaller crater Giordano Bruno (22 kilometers in diameter) is largely dominated by the mixing of freshly excavated material with surrounding older soils derived from a generally similar feldspathic lithology.

  9. Unified force law for granular impact cratering

    NASA Astrophysics Data System (ADS)

    Katsuragi, Hiroaki; Durian, Douglas J.

    2007-06-01

    Experiments on the low-speed impact of solid objects into granular media have been used both to mimic geophysical events and to probe the unusual nature of the granular state of matter. Observations have been interpreted in terms of conflicting stopping forces: product of powers of projectile depth and speed; linear in speed; constant, proportional to the initial impact speed; and proportional to depth. This is reminiscent of high-speed ballistics impact in the nineteenth and twentieth centuries, when a plethora of empirical rules were proposed. To make progress, we developed a means to measure projectile dynamics with 100nm and 20μs precision. For a 1-inch-diameter steel sphere dropped from a wide range of heights into non-cohesive glass beads, we reproduce previous observations either as reasonable approximations or as limiting behaviours. Furthermore, we demonstrate that the interaction between the projectile and the medium can be decomposed into the sum of velocity-dependent inertial drag plus depth-dependent friction. Thus, we achieve a unified description of low-speed impact phenomena and show that the complex response of granular materials to impact, although fundamentally different from that of liquids and solids, can be simply understood.

  10. 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.

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

    PubMed

    Pope, K O; Ocampo, A C; Duller, C 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. PMID:11539441

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

    NASA Astrophysics Data System (ADS)

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

    1993-11-01

    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.

  13. 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.

  14. 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).

  15. Kalkkop crater, Eastern Cape: A new impact crater in South Africa

    NASA Technical Reports Server (NTRS)

    Reimold, W. U.; Leroux, F. G.; Koeberl, C.; Shirey, S. B.

    1993-01-01

    Reimold et al. suggested that the 640 m diameter Kalkkop crater, at 32 deg 43 min S/24 deg 34 min E in the Eastern Cape Province (South Africa), could possibly be of impact origin. This idea was based on the circularity of this structure, its regional uniqueness, lack of recent igneous activity in the region, and descriptions of drillcore indicating that the crater is not underlain by a salt dome and is partially filled with a breccia layer of a thickness which would agree with the dimensions expected for an impact structure of this size. Unfortunately the old drillcore was no longer available for detailed study, and in the absence of sufficient surface exposure only drilling could provide the evidence needed to solve the problem of the origin of Kalkkop. For this reason and to study the crater fill from a paleoenvironmental point of view, the S. African Geological Survey decided to sponsor a new research drilling project at the Kalkkop site. First petrographic and isotopic results from Kalkkop drill core studies confirming, without doubt, that this crater is of impact origin are presented.

  16. A discussion of 'Anomalous quartz from the Roter Kamm impact crater, Namibia - Evidence for post-impact hydrothermal activity?'

    NASA Technical Reports Server (NTRS)

    Roedder, Edwin

    1990-01-01

    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 impact crater (Namibia) and the quartz of the pegmatites present in the basement rocks of this crater can be best interpreted as evidence that the pebbles were formed (or 'recrystallized') by a post-impact hydrothermal system. Arguments are presented that suggest that the three quartz pebbles are, most likely, fragments of a preimpact vein quartz of hydrothermal origin.

  17. A discussion of 'Anomalous quartz from the Roter Kamm impact crater, Namibia - Evidence for post-impact hydrothermal activity?'

    NASA Astrophysics Data System (ADS)

    Roedder, Edwin

    1990-11-01

    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 impact crater (Namibia) and the quartz of the pegmatites present in the basement rocks of this crater can be best interpreted as evidence that the pebbles were formed (or 'recrystallized') by a post-impact hydrothermal system. Arguments are presented that suggest that the three quartz pebbles are, most likely, fragments of a preimpact vein quartz of hydrothermal origin.

  18. 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.

  19. Impact craters of Venus - A continuation of the analysis of data from the Venera 15 and 16 Spacecraft

    NASA Astrophysics Data System (ADS)

    Bazilevskii, A. T.; Burba, G. A.; Chernaia, I. M.; Kriuchkov, V. P.; Ivanov, B. A.

    1987-11-01

    This paper describes and interprets data on about 150 impact craters on the northern quarter of the Venusian surface, approximately 115,000,000 sq km, which was surveyed by the Venera 15/16 spacecraft. The craters were found to display the size-dependent variations in morphology which are well known from other planets. Assuming a crater production rate based on estimates by Hartmann et al. (1981), their areal density indicates an age for the total population of approximately 1 billion yr. The analysis of areal and size frequency distribution of a number of circular features of unclear origin has indicated that some of them may be highly degraded impact craters corresponding to a population of about 3 billion years of age. A table listing the craters, their positions, diameters, class, and the terrain is presented.

  20. MGS Mars Orbiter Laser Altimeter Topographic Profile of Impact Crater

    NASA Technical Reports Server (NTRS)

    1997-01-01

    Among the myriad of interesting landforms sampled by MOLA on its first traverse across the Red Planet on 15 September 1997 is this 13-mile (21-kilometer) diameter impact crater located at 48oN. The figure shows the topography, the computed position of the spacecraft groundtrack (solid line) and the track adjusted to correct for image location error (dashed line). The topographic profile provides some of the first indications of how landscape modification has operated in Martian geologic history. The relief of the crater rim, in combination with the steepness (over 20o) of the inner crater wall, are intriguing in that most craters of this size are much more subdued. The shape of the outer ejecta blanket of the crater likely indicates impact into an H2O rich crust. Issues concerning how craters such as this can be used to understand the properties of the uppermost crust of Mars in regions where the role of water and other volatiles may be important can be addressed with the high spatial and vertical resolution topographic profiles that will be acquired by MOLA once it starts its detailed mapping of the Red Planet in March of 1998.

  1. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1979-01-01

    The paper reports on a series of low-velocity impact experiments performed in ice and ice-saturated sand. It is found that crater diameters in ice-saturated sand were about 2 times larger than in the same energy and velocity range in competent blocks of granite, basalt and cement, while craters in ice were 3 times larger. It is shown that if this dependence of crater size on strength persists to large hypervelocity impact craters, then surface of geologic units composed of ice or ice-saturated soil would have greater crater count ages than rocky surfaces with identical influx histories. Among the conclusions are that Martian impact crater energy versus diameter scaling may also be a function of latitude.

  3. 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

  4. Raindrop impact on sand: dynamic and crater formation

    NASA Astrophysics Data System (ADS)

    Zhao, Song-Chuan; de Jong, Rianne; van der Meer, Devaraj

    2015-03-01

    Droplet impact on a granular bed is very common in nature, industry, and agriculture and extends from raindrops falling on earth to wet granulation in the production process of many pharmaceuticals. In contrast to more traditionally studied impact phenomena, such as a droplet impact on solid substrate and solid object impact on fluid-like substrate, raindrop impact on sand induces more complicated interactions. First, both the intruder and the target deform during impact; second, the liquid composing the droplet may penetrate into the substrate during the impact and may, in the end, completely merge with the grains. These complex interactions between the droplet intruder and the granular target create the very diverse crater morphologies that has been described in the literature. An appealing and natural question is how the craters are formed. To gain insight in the mechanism of crater formation, we resolve the dynamics with high-speed laser profilometry and study the dependence of the dynamics on impact speed and packing fraction of the granular substrate. Finally, we establish a dynamical model to explain the various crater morphologies.

  5. An interpretation of volcanic and structural features of crater Aitken. [from Apollo 17 panoramic photography

    NASA Technical Reports Server (NTRS)

    Bryan, W. B.; Adams, M.-L.

    1974-01-01

    Detailed observations from the study of Apollo 17 panoramic photography of the Aitken crater are reported which suggest that there has been significant late-stage compressional deformation of the crater and its adjacent highlands. A speculative interpretation of eruptive activity and drain-back events within Aitken is presented, which leads to the conclusion that hummocky topography within certain cones represents collapsed lava rather than extrusive domes. That is, eruptive activity within Aitken probably commenced with an explosive cone-building stage, followed by lava eruptions from cones and fissures, and ended with drain-back restricted to the relatively deep lava ponded in the vents.

  6. Geophysical Signature of the Lake Bosumtwi Impact Crater, Ghana

    NASA Astrophysics Data System (ADS)

    Karp, T.; Milkereit, B.; Janle, P.; Danuor, S. K.; Berckhemer, H.; Pohl, J.; Scholz, C. A.

    2001-12-01

    The Bosumtwi impact structure in Ghana has an age of 1.07 Ma, a rim-to-rim diameter of 10.5 km, and is the youngest large impact crater on earth. It is the source crater of the Ivory Coast tectites (Koeberl et al., Geoch. Cosmoch. Acta 61, 1997). The central part of the structure is filled by Lake Bosumtwi. Marine seismic studies were conducted to investigate crater morphology (thickness of post-impact sediments, depth and shape of central uplift). Refraction seismic (OBH and PDAS seismometer) and multichannel reflection data were collected to image the complex subsurface crater structure. Results from integrated modelling reveal low P-wave velocities in the young post-impact sediments (less than 1.8 km/s) and a prominent central uplift structure about 120 m high. The total thickness of the sediments does not exceed 350 m. Gravity and magnetic surveys complement regional airborne geophysical data across the structure (Plado et al., Meteor. & Planet. Sc., 35, 2000). Gravity data from 160 stations on land around the lake show the expected minimum resulting from the sedimentary filling of the lake, low density impact formations, brecciated and fragmented basement. In the fall of 2001 additional gravity measurements will be carried out on the lake to better delineate prominent anomalies associated with the central structure. The magnetic anomalies are attributed to remanent magnetization of melt, breccias and footwall complex. Further integration of different data sets will help to develop a detailed lithological model of the crater's subsurface structure. The geophysical data confirm that the Lake Bosumtwi structure provides an ideal setting for drilling of a young and large impact crater.

  7. Fractal dimensions of rampart impact craters on Mars

    NASA Technical Reports Server (NTRS)

    Ching, Delwyn; Taylor, G. Jeffrey; Mouginis-Mark, Peter; Bruno, Barbara C.

    1993-01-01

    Ejecta blanket morphologies of Martian rampart craters may yield important clues to the atmospheric densities during impact, and the nature of target materials (e.g., hard rock, fine-grained sediments, presence of volatiles). In general, the morphologies of such craters suggest emplacement by a fluidized, ground hugging flow instead of ballistic emplacement by dry ejecta. We have quantitatively characterized the shape of the margins of the ejecta blankets of 15 rampart craters using fractal geometry. Our preliminary results suggest that the craters are fractals and are self-similar over scales of approximately 0.1 km to 30 km. Fractal dimensions (a measure of the extent to which a line fills a plane) range from 1.06 to 1.31. No correlations of fractal dimension with target type, elevation, or crater size were observed, though the data base is small. The range in fractal dimension and lack of correlation may be due to a complex interplay of target properties (grain size, volatile content), atmospheric pressure, and crater size. The mere fact that the ejecta margins are fractals, however, indicates that viscosity and yield strength of the ejecta were at least as low as those of basalts, because silicic lava flows are not generally fractals.

  8. Impact cratering and catastrophic disruption of porous targets through hypervelocity impact experiments

    NASA Astrophysics Data System (ADS)

    Ferri, F.; Giacomuzzo, C.; Pavarin, D.; Francesconi, A.; Bettella, A.; Flamini, E.; Angrilli, F.

    We present an experimental study of impact cratering and fragmentation processes onto low density materials by means of high velocity impact experiments using a two-stage light-gas gun, the impact facility of CISAS "G. Colombo" of the University of Padova (http://cisas.unipd.it/lgg/lgg.html). The goal of our experiments is to obtain a better comprehension of the impact processes on different materials in order to analyze the evolution of the surface of the solid bodies and the collisional evolution of the minor bodies of the Solar System. The results of this research are also aimed to contribute to the data interpretation of the ground- and space-based observations, in particular in view of space missions such as Smart1, MarsExpress, VenusExpress, BepiColombo, Cassini-Huygens, Rosetta, Dawn. Porosity is an important physical characteristic of the minor bodies, affecting their behaviour during cratering and greatly lengthening the collisional lifetimes of porous asteroids. Porous targets are likely to have average sound velocity lower than those of nonporous targets composed of same material; compaction of initially porous materials can produce rapid attenuation of the shock, thus affecting energy propagation during collisions. Therefore we focus on the study of impact processes on porous targets both by experimental and theoretical approach in order to complement and extend the available data to ranges of velocity and physical conditions not yet explored. In order to simulate porous asteroids, comets, icy satellites, we have manufactured and used targets of different material, e.g. glass ceramic foam, natural pumices, water ice, and different porosity (with density ranging from 0.35 to 1.07 g/cm3 ). Impact test campaign have been performed on the different samples varying the impact kinetic energy (by changing projectile mass and velocity) in order to study the craterization up to catastrophic disruption. The impact and shattering events are observed by high speed

  9. Genesis and fluid source in Arabia crater mounds: mapping, fractal analysis, and impact simulations

    NASA Astrophysics Data System (ADS)

    Pozzobon, R.; Mazzarini, F.; Rossi, A.; Lucchetti, A.; Pondrelli, M.; Marinangeli, L.; Martellato, E.; Cremonese, G.; Massironi, M.

    2013-12-01

    Arabia Terra is dominated by heavily cratered terrains, and some peculiar landforms can be found mostly in craters interior. With high-resolution images from HiRISE (25 cm/px) and CTX (6 m/px) cameras pitted cones, mounds and knobs can be easily recognized. Those mounds are interpreted to have worked as pathways for subsurface fluid. It is commonly hypothesized that Arabia Terra is an area of past fluid activity, being crater central bulges a place of sulfate precipitation. In this work we investigate the presence, origin and timing of their formation as well as the the depth of the mounds fluid source. The spatial distribution of monogenic eruptive structures within volcanic areas on Earth has been linked to fracture systems that allowed an efficient hydraulic connection between surface and crustal or subcrustal magma reservoirs. Self-similarity in vent distribution is described by a power law distribution with fractal exponent D and defined over a range of lengths comprised between a lower limit (lower cutoff, Lco) and an upper limit (upper cutoff, Uco). On Earth, volcanic vents as well as mud volcanoes have shown that the Uco of their fractal distribution scales with the depth of pressurized fluid reservoirs. The same approach has been this applied to mounds mapped at Firsoff and Crommelin craters. 431 mounds were mapped on Firsoff Crater's floor, and 160 on Crommelin Crater's floor. The reslulting Uco for both craters are similar giving a source depth of 2.3 ×0.3 km from Firsoff Crater's ground floor and 2.6 ×0.5 km from Crommelin's floor. Hence it is possible to hypothesize a common regional-scale pressurized fluid level at 2.5 km of depth from craters floor. Morphogic and stratigraphical analyses of the high-resolution imagery and topography of those mounds allowed us to discern from actual mud volcano candidates and stratigraphic erosional remnants. We also studied the craters formation by simulating the impact with the hydrocode. We used iSALE shock code

  10. 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.

  11. 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.

  12. Impact cratering and the surface age of Venus: The Pre-Magellan controversy

    NASA Technical Reports Server (NTRS)

    Schaber, Gerald G.; Shoemaker, E. M.; Shoemaker, C. S.; Kozak, Richard C.

    1989-01-01

    The average surface age of a planet is a major indicator of the level of its geologic activity and thus of the dynamics of its interior. Radar images obtained by Venera 15/16 from the northern quarter of the Venus (lat 30 to 90 degs) reveal about 150 features that resemble impact craters, and they were so interpreted by Soviet investigators B. A. Ivanov, A. T. Basilevsky, and their colleagues. These features range in diameter from about 10 to 145 km. Their areal density is remarkably similar to the density of impact structures found on the American and European continental shields. The basic difference between the Soviet and American estimates of the average surface age of Venus's northern quarter is due to which crater-production rate is used for the Venusian environment. Cratering rates based on the lunar and terrestrial cratering records, as well as statistical calculations based on observed and predicted Venus-crossing asteroids and comets, have been used in both the Soviet and American calculations. The single largest uncertainty in estimating the actual cratering rates near Venus involves the shielding effect of the atmosphere.

  13. Karakul: a young complex impact crater in the Pamir, Tajikistan

    NASA Astrophysics Data System (ADS)

    Bouley, S.; Baratoux, D.; Baratoux, L.; Colas, F.; Dauvergne, J.; Losiak, A.; Vaubaillon, J.; Bourdeille, C.; Jullien, A.; Ibadinov, K.

    2011-12-01

    A fascinating controversy has been recently renewed about the origin of the Karakul depression in the Pamir (Tajikistan, 39°1'N, 73°27'E), about 4000 m above sea level. Based on the work of E. Gurov reporting breccia and shock features in minerals, the circular depression was mentioned in the Earth Impact Database as one of the largest complex craters, about 50 km in diameter. However, recent studies have suggested that the basin is actually a NW-SE extensional rift. We report the preliminary results of a new expedition in the Karakul area that successfully took place in June 2011. Different types of rocks have been observed, including metamorphosed sediments, granite, limestone, and rare occurrence. The granite appears to be the youngest rock predating the crater, with an age of 230-190 My2. The most exciting preliminary result is the finding of shatter cones in metamorphosed sediments in the northern part of the peninsula. Breccias (not necessary impact-breccia) occur as floats on the central island, and were also found in the northern part of the rim. Thin sections are in preparation at the time of writing, and the report on the search for shock features in granite and breccias will be presented at the conference. The age of the crater is unknown, but is necessarily younger than the India-Asia collision, 55 - 60 My ago. On the basis of the oldest sediments filling the depression, the crater has been tentatively attributed to Neogene, or Pliocene, and would be then younger than 23 My. Consequences of the formation of a large complex crater in the recent geological history of the Pamir have yet to be explored. In a context of elevated convergence rate and rapid exhumation, the site offers the possibility to investigate the possible interactions between impact cratering and tectonic activity. The formation of a 50 km crater has considerable effects on the environment, at least at the regional scale, suggesting the search for such effects in the sediment record

  14. Z-model analysis of impact cratering - An overview

    NASA Technical Reports Server (NTRS)

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

    1981-01-01

    The Maxwell Z-Model has been applied to two continuum mechanics computer calculations: (1) a laboratory-scale impact of an aluminum projectile into plasticene clay, and (2) a planetary-scale impact of an iron meteor into gabbroic anorthosite. The material flow in the cratering flow field may be well approximated by incompressible flow for most of the excavation stage of crater growth. The center of the flow field is located beneath, not at, the surface. Soon after energy partitioning is complete, Z can assume values less than 2.0 associated with the initial directedness of the projectile's momentum. The Z-Model parameters are time dependent during a significant portion of the crater growth time, and Z increases steadily with time from about 2.0 or slightly less at the beginning of the excavation stage to level off at values in the neighborhood of about 3.0 before the excavation stage is half-over.

  15. Lessons from studies of impact crater hydrothermal processes in terrestrial analogs and their implications for impact craters on Mars

    NASA Astrophysics Data System (ADS)

    Newsom, H. E.

    2011-12-01

    Studying hydrothermal processes in terrestrial impact craters as martian analogs has sometimes been fraught with objections, including the Earth's greater abundance of water, the neutral instead of acidic aqueous environments and the composition of the targets. Although recent discoveries have dispelled many objections, some misconceptions remain. For example, the relevance of the Chicxulub crater as a martian analog is sometimes questioned because the target was covered with sediments, including carbonates and sulfates. However the impactites at the Yaxcopoil-1 drill site are derived from the underlying silicate basement. Comparisons can also be difficult because of scale issues, as many terrestrial craters with evidence of hydrothermal activity, e.g. Lonar, Haughton, Ries etc., are smaller than the Martian craters with phyllosilicate signatures (Ehlmann et al., 2010). Summarizing, the results of many studies of terrestrial craters show that: 1) Most terrestrial craters larger than 1.8 km diameter have at least some evidence of aqueous or hydrothermal processes in the form of alteration minerals (e.g., Naumov, 2005). 2) Impact melts in crater fill and ejecta blankets provide heat that can produce hydrothermal alteration if water is available (Newsom, 1980). 3) The uplifted geothermal gradient can be as important a heat source as shock effects. 4) Mineralogical evidence for high-temperature fluids (> 350 oC) is present in the central uplift of the Manson structure, and in the ejecta from the Chicxulub impact, where precipitation of phyllosilicates from hydrothermal fluids has also been described (Newsom et al., 2010). 5) Impact deposits begin hot, but have an extended cooling period during which alteration phases can back react to low temperature phases with corresponding stable isotope signatures. 5) Hydrothermal fluids can travel long distances from their sources (e.g., Chicxulub, Yaxcopoil site) and are often localized to faults or porous breccias (e.g. Sudbury

  16. The fractured Moon: Production and saturation of porosity in the lunar highlands from impact cratering

    NASA Astrophysics Data System (ADS)

    Soderblom, Jason M.; Evans, Alexander J.; Johnson, Brandon C.; Melosh, H. Jay; Miljković, Katarina; Phillips, Roger J.; Andrews-Hanna, Jeffrey C.; Bierson, Carver J.; Head, James W.; Milbury, Colleen; Neumann, Gregory A.; Nimmo, Francis; Smith, David E.; Solomon, Sean C.; Sori, Michael M.; Wieczorek, Mark A.; Zuber, Maria T.

    2015-09-01

    We have analyzed the Bouguer anomaly (BA) of ~1200 complex craters in the lunar highlands from Gravity Recovery and Interior Laboratory observations. The BA of these craters is generally negative, though positive BA values are observed, particularly for smaller craters. Crater BA values scale inversely with crater diameter, quantifying how larger impacts produce more extensive fracturing and dilatant bulking. The Bouguer anomaly of craters larger than 93-19+47 km in diameter is independent of crater size, indicating that there is a limiting depth to impact-generated porosity, presumably from pore collapse associated with either overburden pressure or viscous flow. Impact-generated porosity of the bulk lunar crust is likely in a state of equilibrium for craters smaller than ~30 km in diameter, consistent with an ~8 km thick lunar megaregolith, whereas the gravity signature of larger craters is still preserved and provides new insight into the cratering record of even the oldest lunar surfaces.

  17. Formation of complex impact craters - Evidence from Mars and other planets

    NASA Technical Reports Server (NTRS)

    Pike, R. J.

    1980-01-01

    An analysis of the depth vs diameter data of Arthur (1980), is given along with geomorphic data for 73 Martian craters. The implications for the formation of complex impact craters on solid planets is discussed. The analysis integrates detailed morphological observations on planetary craters with geologic data from terrestrial meteorite and explosion craters. The simple to complex transition for impact craters on Mars appears at diameters in the range of 3 to 8 km. Five features appear sequentially with increasing crater size, flat floors, central peaks and shallower depths, scalloped rims, and terraced walls. This order suggests that a shallow depth of excavation and a rebound mechanism have produced the central peaks, not centripetal collapse and deep sliding. Simple craters are relatively uniform in shape from planet to planet, but complex craters vary considerably. Both the average onset diameter for complex impact craters on Mars and the average depth of complex craters vary inversely with gravitational acceleration on four planets.

  18. Earth's Largest Meteorite Impact Craters discovered in South America?

    NASA Astrophysics Data System (ADS)

    Kellndorfer, J. M.; Schmidt-Falkenberg, H.

    2014-12-01

    Novel analysis of high resolution InSAR-based digital elevation data from the year 2001 Shuttle Radar Topography Mission combined with a recently produced dataset of pan-tropical vegetation height from ALOS-1 SAR and IceSAT/GLAS Lidar estimates led to the quasi-bald-Earth discovery of four sizable near-perfect circle arcs in South America under dense tropical forests ranging in length from 216 km to 441 km. Terrain elevation profiles of cross-sections across the arcs show a distinct vertical rising and falling in elevations of hundreds of meters over a horizontal distance of tens of kilometers. It is hypothesized that these sizable arcs and associated rim-like topographic terrain features are remnants of huge meteorite impact craters with diameters ranging from 770 km to 1,310 km, thus forming potentially the largest known impact carter structures discovered on Earth today. The potential impact crater rim structures are located north of the eastern Amazon River, in the coastal region of Recife and Natal, and in the Brazilian, Bolivian and Paraguayan border region encompassing the Pantanal. Elevation profiles, hillshades and gray-shaded elevation maps were produced to support the geomorphologic analysis. It is also speculated whether in three of the four potential impact craters, central uplift domes or peaks, which are typical for complex impact crater structures can be identified. The worlds largest iron ore mining area of Carajás in Para, Brazil, falls exactly in the center of the largest hypothesized circular impact crater showing topographic elevations similar to the rim structure discovered 655 km to the north-north-west. Based on the topographic/geomorphologic driven hypothesis, geologic exploration of these topographic features is needed to test whether indeed meteorite impact craters could be verified, what the more exact ellipsoidal shapes of the potential impact craters might be, and to determine when during geologic times the impacts would have taken

  19. Fourier analysis of planimetric lunar crater shape - Possible guide to impact history and lunar geology

    NASA Technical Reports Server (NTRS)

    Eppler, D. T.; Nummedal, D.; Ehrlich, R.

    1977-01-01

    If the lithology of lunar crust influences impact crater morphology, a method of analysis that is sensitive to small-scale changes in crater shape is required. In the present paper, it is shown that Fourier analysis in closed form can provide detailed information regarding planimetric crater shape. Preliminary analysis of the rim crest outline of 247 nearside lunar craters (larger than 18 km in diam) led to the following information: Imbrian and pre-Imbrian craters are more elongate than younger craters, possibly as a result of widespread crustal deformation early in the moon's history. Crater size does not affect the planimetric shape of craters. Highland craters are less circular than mare craters, probably due to the greater structural and lithologic complexity of the highland crust. Craters comprising each shape family of the eleventh harmonic typically are located in the same general geographic region of the moon.

  20. 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

  1. 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.

  2. 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,…

  3. Impact Cratering: Bridging the Gap Between Modeling and Observations

    NASA Technical Reports Server (NTRS)

    2003-01-01

    This volume contains abstracts that have been accepted for presentation at the workshop on Impact Cratering: 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.

  4. 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.

  5. Single impact crater functions for ion bombardment of silicon

    SciTech Connect

    Kalyanasundaram, N.; Ghazisaeidi, M.; Freund, J. B.; Johnson, H. T.

    2008-03-31

    The average effect of a single 500 eV incident argon ion on a silicon surface is studied using molecular dynamics simulations. More than 10{sup 3} ion impacts at random surface points are averaged for each of seven incidence angles, from 0 deg. to 28 deg. off normal, to determine a local surface height change function, or a crater function. The crater shapes are mostly determined by mass rearrangement; sputtering has a relatively small effect. Analytical fitting functions are provided for several cases, and may serve as input into kinetic Monte Carlo calculations or stability analyses for surfaces subjected to ion bombardment.

  6. Constraining geologic properties and processes through the use of impact craters

    NASA Astrophysics Data System (ADS)

    Barlow, Nadine G.

    2015-07-01

    Impact cratering is the one geologic process which is common to all solar system objects. Impact craters form by the resulting explosion between a solar system body and hypervelocity objects. Comparison with craters formed by chemical and nuclear explosions reveals that crater diameter is related to other morphometric characteristics of the crater, such as depth and rim height. These relationships allow scientists to use impact craters to probe the subsurface structure within the upper few kilometer of a planetary surface and to estimate the amounts and types of degradational processes which have affected the planet since crater formation. Crater size-frequency distribution analysis provides the primary mechanism for determining ages of planetary terrains and constraining the timing of resurfacing episodes. Thus, impact craters provide many important insights into the evolution of planetary surfaces.

  7. 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.

  8. Hypervelocity impact study: The effect of impact angle on crater morphology

    NASA Technical Reports Server (NTRS)

    Crawford, Gary; Hill, David; Rose, Frank E.; Zee, Ralph; Best, Steve; Crumpler, Mike

    1993-01-01

    The Space Power Institute (SPI) of Auburn University has conducted preliminary tests on the effects of impact angle on crater morphology for hypervelocity impacts. Copper target plates were set at angles of 30 deg and 60 deg from the particle flight path. For the 30 deg impact, the craters looked almost identical to earlier 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 impacts showed marked differences in crater symmetry, crater lip shape, and particle residue distribution. Further research on angle effects is planned, because the particle velocities for these shots were relatively slow (7 km/s or less).

  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. Chesapeake Bay Crater, Virginia: Confirmation of Impact Origin

    NASA Astrophysics Data System (ADS)

    Koeberl, C.; Reimold, W. U.; Brandt, D.; Poag, C. W.

    1995-09-01

    Poag et al. [1] identified a late Eocene boulder bed in drill cores from southeast Virginia, and interpreted it as an impact-generated tsunami deposit. Seismic studies and other geophysical evidence indicated the existence of a possible impact structure centered at Chesapeake Bay (37 degrees x 15' N and 76 degrees x 04' W), which may be 85-90 km in diameter [2]. Four drill cores have penetrated into the breccia, although none is available from the center of the structure, or reaches basement. A central peak-ring of crystalline rocks with about 25 km diameter is surrounded by a 30 km-wide annular trough and terrace terrane. The trough is filled with polymictic breccia composed mainly of autochthonous sedimentary clasts in a sandy matrix with some angular clasts of granitic and metasedimentary basement rocks [2]. The Chesapeake Bay crater is of special interest, because it is close to the region identified as the possible source region for the North American tektites, is of about the expected size, and has an age identical to that of the tektites [3]. While the source craters for the Central European and Ivory Coast tektite strewn fields are known, the source crater of the North American tektites has remained elusive. A variety of locations were suggested, including Popigai (Siberia), Wanapitei (Canada), Mistastin (Canada), and Bee Bluff (Texas), but all were later discounted. The distribution of the tektites and microtektites in the strewn field suggests that the North American tektite source crater is likely to be located at or near the eastern coast of the North American continent, maybe underwater [4,5]. The location of the Chesapeake Bay structure is in agreement with the area suggested before [4,5]. We have started a petrological and geochemical study of target rocks and breccias from the Chesapeake Bay structure. We analyzed the major and trace element composition of 17 mainly sedimentary samples, for comparison with North American tektite values. 14 of these

  11. Mars: New Determination of Impact Crater Production Function Size Distribution

    NASA Astrophysics Data System (ADS)

    Hartmann, William K.

    2006-12-01

    Several authors have questioned our knowledge of Martian impact crater production function size-frequency distribution (PFSFD), especially at small diameters D. Plescia (2005) questioned whether any area of Mars shows size distributions used for estimating crater retention ages on Mars. McEwen et al. (2005) and McEwen and Bierhaus (2006) suggested existing PFSFD’s are hopelessly confused by the presence of secondaries, and that my isochrons give primary crater densities off by factors of several thousand at small D. In 2005, I addressed some of these concerns, noting my curves do not estimate primary crater densities per se, but show total numbers of primaries + semi-randomly “distant secondaries” (negating many McEwen et al. critiques). In 2006 I have conducted new crater counts on a PFSFD test area suggested by Ken Tanaka. This area shows young lava flows of similar crater density, west of Olympus Mons (around 30 deg N, 100 deg W). Multiple crater counts were made on several adjacent Odyssey THEMIS images and MGS MOC images, giving the SFD over a range of 11mcrater retention model age (using the “2004” iteration), is 150 My, reaffirming Martian meteorite evidence for young volcanism. The uncertainty in fitting the counts to the isochron shape is probably <40% the uncertainty in absolute age is probably a factor 2-4 due mostly to uncertainties in the Mars/moon cratering rate and in the accumulation rate of globally scattered background secondaries (Hartmann 2005). References: Hartmann, W.K., 2005, Icarus 174, 294-320. McEwen, A.S., Bierhaus, E.B., 2006, Ann. Rev. Earth. Planet. Sci. 34, 535-567. McEwen, A.S., 2005, Icarus 176, 351-381. Plescia, J.B. 2005, LPSC 36, 2171.

  12. Geochemical aspect of impact cratering: Studies in Vernadsky Institute

    NASA Technical Reports Server (NTRS)

    Yakovlev, O. I.; Basilevsky, A. T.

    1992-01-01

    Studies of the geochemical effects of impact cratering at the Vernadsky Institute in collaboration with the Institute of Dynamics of Geospheres, Moscow State University, Leningrad State University, and some other institutions were fulfilled by several approaches. At the initial stage, three approaches were used: (1) experimental studies of high-temperature vaporization of geological materials (basalts, granites, and so on) in vacuum that was considered as a model of behavior of impact melt and vapor; (2) search of impact-induced geochemical effects in the rock from terrestrial impact craters; and (3) studies of samples of lunar regolith. The next stage of the studies included experiments on quasi-equilibrium vaporization of geological material in Knudsen cells. The results of this investigation are discussed.

  13. Fake Statistically Valid Isotopic Ages in Impact Crater Geochronology

    NASA Astrophysics Data System (ADS)

    Jourdan, F.; Schmieder, M.; McWilliams, M. M.; Buchner, E.

    2009-05-01

    Precise dating of impact structures is crucial in several fundamental aspects, such as correlating effects on the bio- and geosphere caused by these catastrophic processes. Among the 176 listed impact structures [1], only 25 have a stated age precision better than ± 2%. Statistical investigation of these 25 ages showed that 11 ages are accurate, 12 are at best ambiguous, and 2 are not well characterized [2]. In this study, we show that even with statistically valid isotope ages, the age of an impact can be "missed" by several hundred millions of years. We present a new 40Ar/39Ar plateau age of 444 ± 4 Ma for the Acraman structure (real age ˜590 Ma [3]) and four plateau ages ranging from 81.07 ± 0.76 Ma to 74.6 ± 1.5 Ma for the Brent structure (estimated real age ˜453 Ma [4]). In addition, we discuss a 40Ar/39Ar plateau age of 994 ± 11, recently obtained by [5] on the Dhala structure (real age ˜2.0 Ga [5]). Despite careful sample preparations (single grain handpicking and HF leaching, in order to remove alteration phases), these results are much younger than the impact ages. Petrographic observations show that Acraman and Dhala grain separates all have an orange color and show evidence of alteration. This suggests that these ages are the results of hydrothermal events that triggered intensive 40Ar* loss and crystallization of secondary phases. More intriguing are the Brent samples (glassy melt rocks obtained from a drill core) that appeared very fresh under the microscope. The Brent glass might be a Cretaceous pseudotachylite generated by a late adjustment of the structure and/or by a local earthquake. Because we know the approximate age of the craters with stratigraphic evidences, these outliers are easy to identify. However, this is a red flag for any uncritical interpretation of isotopic ages (including e.g., 40Ar/39Ar, U/Pb, or U-Th/He [6]). In this paper, we encourage a multi-technique approach (i.e., isotopic, stratigraphic, paleogeographic [7,8]) and

  14. 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

  15. Zumba crater, Daedalia Planum, Mars: Geologic investigation of a young, rayed impact crater and its secondary field

    NASA Astrophysics Data System (ADS)

    Chuang, Frank C.; Crown, David A.; Tornabene, Livio L.

    2016-05-01

    Zumba is a ∼2.9 km diameter rayed crater on Mars located on extensive lava plains in Daedalia Planum to the southwest of Arsia Mons. It is a well-preserved young crater with large ejecta rays that extend for hundreds of kilometers from the impact site. The rays are thermally distinct from the background lava flows in THEMIS daytime and nighttime thermal infrared data, a unique characteristic among martian rayed craters. Concentrated within the rays are solitary or dense clusters of secondary craters with associated diffuse dark-toned deposits along with fewer secondary craters lacking dark-toned deposits. Using CTX images, we have mapped secondary craters with dark-toned deposits, collectively termed "secondary fields", to investigate their distribution as a function of distance from the impact site. The mapped secondary field was then used to investigate various aspects of the crater-forming event such as the surface angle and direction of the projectile, the effect of secondary craters on surface age estimates, and the number of secondary craters produced by the impact event. From our mapping, a total of 13,064 secondary fields were documented out to a 200 km radial distance beyond a 15 km-wide non-secondary zone around Zumba crater. Results show that the highest areal coverage of secondary fields occurs within 100 km of Zumba and within its rays, decreasing radially with distance to a background scattering of small secondary fields that are <10 km2 in size (∼91.9% of the total population). The strong east-west asymmetry of crater rays and low areal coverage of fields to the south of Zumba correlate well with studies of Zumba impact melt deposits, indicating a moderately oblique impact projectile coming from the south. Using primary craters in a ∼101 km2 sample region and all craters (primaries and secondaries) from 43 select secondary fields in two map sectors in the study area, we obtain ages of ∼580 ± 100 Ma and ∼650 ± 70 Ma, respectively, for the

  16. The MEMIN research unit: First results from impact cratering experiments into quartzite and tuff

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

    The MEMIN research unit is focused on performing and evaluating impact cratering experiments into geological materials. As a research unit, MEMIN uses a multidisciplinary approach, with different subprojects analyzing various aspects of the same cratering experiments, including crater morphology, ejecta dynamics, subsurface deformation, etc., along with numerical simulations of the impact process. A series of impact cratering experiments into quartzite and tuff targets is planned for June 2012. We intend to have completed a preliminary evaluation of these experiments for the EPSC conference.

  17. Impact cratering as a major process in planet formation: Projectile identification of meteorite craters

    NASA Astrophysics Data System (ADS)

    Schmidt, G.; Kratz, K.

    2009-12-01

    Ancient surfaces of solid planets show that impact cratering is a major process in planet formation. Understanding origin and influence of impactors on the chemical composition of planets (core, mantle and crust) it is important to know the relative abundances of highly siderophile elements (Os, Ir, Ru, Pt, Rh, Pd) in the silicate mantle and crust of planets and meteorites. Refractory highly siderophile elements, such as Os and Ir, are abundant in most meteorites but depleted in crustal rocks (low target/meteorite ratios) and thus the most reliable elements for projectile identification. However, target/meteorite ratios are high if target rocks consist of mantle rocks. In such cases elements are enriched in impactites due to relatively high abundances (ng/g level) in target rocks to make the identification of projectile types difficult (e.g., Gardnos impact structure in Norway). The Ru/Ir ratio is the most reliable key ratio that rules out Earth primitive upper mantle (PUM) derived refractory highly siderophile element components in impactites. The well established Ru/Ir ratio of the Earth mantle of 2.0 ± 0.1 (e.g. Schmidt and Kratz 2004) is significantly above the chondritic ratios varying from 1.4 to 1.6. On Earth Rh/Ir, Ru/Ir, Pd/Ir, and Pt/Os derived from PUM match the ratios of group IV irons with fractionated trace element patterns. The question raise if HSE in mantle rocks are added to the accreting Earth by a late bombardment of pre-differentiated objects or the cores of these objects (magmatic iron meteorites as remnants of the first planetesimals, e.g. Kleine et al. 2009) or some unsampled inner solar system materials from the Mercury-Venus formation region, not sampled through meteorite collections (Schmidt 2009). The PGE and Ni systematics of the upper continental crust (UCC) closely resembles group IIIAB iron meteorites with highly fractionated refractory trace element patterns, pallasites, and the evolved suite of Martian meteorites (representing

  18. 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.

  19. Gale Crater: Formation and post-impact hydrous environments

    NASA Astrophysics Data System (ADS)

    Schwenzer, S. P.; Abramov, O.; Allen, C. C.; Bridges, J. C.; Clifford, S. M.; Filiberto, J.; Kring, D. A.; Lasue, J.; McGovern, P. J.; Newsom, H. E.; Treiman, A. H.; Vaniman, D. T.; Wiens, R. C.; Wittmann, A.

    2012-09-01

    Gale Crater, the landing site of the 2011 Mars Science Laboratory mission, formed in the Late Noachian. It is a 150 km diameter complex impact structure with a central mound (Mount Sharp), the original features of which may be transitional between a central peak and peak ring impact structure. The impact might have melted portions of the substrate to a maximum depth of ˜17 km and produced a minimum of 3600 km3 of impact melt, half of which likely remained within the crater. The bulk of this impact melt would have pooled in an annular depression surrounding the central uplift, creating an impact melt pool as thick as 0.5-1 km. The ejecta blanket surrounding Gale may have been as thick as ˜600 m, which has implications for the amount of erosion that has occurred since Gale Crater formed. After the impact, a hydrothermal system may have been active for several hundred thousand years and a crater lake with associated sediments is likely to have formed. The hydrothermal system, and associated lakes and springs, likely caused mineral alteration and precipitation. In the presence of S-rich host rocks, the alteration phases are modelled to contain sheet silicates, quartz, sulphates, and sulphides. Modelled alteration assemblages may be more complex if groundwater interaction persisted after initial alteration. The warm-water environment might have provided conditions supportive of life. Deep fractures would have allowed for hydraulic connectivity into the deep subsurface, where biotic chemistry (and possibly other evidence of life) may be preserved.

  20. 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

  1. 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

    , VDEQ, HRPDC and WM on the principles of geology, the formation of impact craters, the consequences of the impacting body on the atmosphere, ocean, surface and sub-surface, the geological, chemical and biological analyses of the core and the cataloguing and storage of the core segments, etc. After the briefings, the Girl Scouts visited the drilling site where they inspected the core drilling rig, examined the core samples and discussed the drilling procedures, cores and interpretation of the cores with scientists and educators from the organizations conducting the core drilling. Demonstrations at the drilling site included demonstrations of impacting objects hitting multi-colored layered mud targets at different angles of entry. The multi-colored layers of mud were instructive in mapping out the distribution of impact-ejected material around the impact crater. The presentation will include a series of photographs of the Girl Scout participating in activities at the Chesapeake Bay Impact Crater drill site, including retrieving cores from the drilling rig, inspecting the core samples and participating in the impact-crater formation demonstrations.

  2. Roter Kamm impact crater, Namibia: Geochemistry of basement rocks and breccias

    NASA Astrophysics Data System (ADS)

    Reimold, Wolf Uwe; Koeberl, Christian; Bishop, Janice

    1994-06-01

    The Roter Kamm crater in the southern Namib Desert has previously been identified as an impact structure on the basis of crater morphology and the presence of impact melt breccias which contain shock metamorphosed quartz and lithic clasts. To better define the variety of target rocks and breccias, we studied the petrography and chemical composition of a new suite of twenty-eight basement and breccia samples from the Roter Kamm crater. Based on chemical data for target lithologies and breccias we suggest that the crater was formed in a two-layer target region: an upper layer of Gariep metasediments (schist, marble, ± quartzite and sandstone) overlying the crystalline basement of the Namaqualand Metamorphic Complex. The basement was also heavily intruded by coarse-grained quartz veins and quartz- and quartz-feldspar pegmatites. The clast population in the melt breccias indicates that impact-induced melting involved mainly metasedimentary target rocks, with rarely detected contributions from pegmatite and granite/granodiorite. Three varieties of melt breccias can be defined: (1) "schistose," (2) quartzitic melt breccias, (3) "true" impact melt breccias. These melt breccia types are chemically heterogeneous, and even the impact melt breccias may have been produced in situ and not from a coherent melt body. The shapes of the schistose melt breccias, previously thought to be ejected impact breccias, are most likely caused by erosion, and these breccias are now interpreted to be locally derived. The crater basement as exposed at the rim was structurally severely affected and, at least locally, considerable thermal energy was generated during formation of large volumes of cataclastic, mylonitic, and pseudotachylitic breccias. Analyses of mylonite and pseudotachylites from the crater rim, as well as their respective host rocks, show that these breccias were mainly formed from local material. Analyses of pseudotachylite-like breccias indicate that these possible friction

  3. 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

  4. 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

  5. Calculation of Planetary Impact Cratering to Late Times

    NASA Astrophysics Data System (ADS)

    Ahrens, Thomas J.; OKeefe, John D.; Stewart, Sarah T.

    2003-01-01

    Simulation of impact cratering on planetary materials is crucially dependent on adequate description of shock processing of surface materials. Two recent examples of the importance of these processes is demonstrated by the simulation of impact induced flow from the impact of a ca. 10 km bolide at 20 km/sec onto the Earth. This has been inferred to have occurred along the Yucatan (Mexican) coast, 65 million years ago. This impact is inferred to have triggered global climatic change, induced by the impact devolatilization of the marine anhydrite (CaSiO4) and gypsum (CaSO42H2O) deposits of the target rocks. These calculations conducted with Sandia's CTH code de-pend crucially upon utilizing a rock damage model which reduced crustal rock strength from 100 MPa to 1 MPa over a volume some 102 times that of the bolide in about 1 minute and gives rise to a 100 km diameter central peak, flat-floored crater with overturned target flap some 8 minutes after impact. Comparison of calculated post-impact deformation compares favorably with seismic profiling and drill-core data. A second example is the formation of ejecta blankets giving rise to rampart Martian craters by fluidization with liquid water by a new impact cratering simulation and recent shock wave data on H2O ice. We demonstrate that ground ice is melted by the impact shock within a hemisphere of radius equal to the final crater radius, resulting in excavation of a mixture of liquid water and brecciated rock into the continuous ejecta blanket. Our shock wave experiments demonstrate that ice at Mars temperature, 150 to 275 K, will begin to melt when shocked above 2.2 to 0.6 GPa, respectively, lower than previously expected. Hence, the presence of liquid water near the pre-impacted surface is not required to form fluidized ejecta. The amount of ice melted and incorporated into the ejecta blanket debris flow is within a factor of two of the subsurface ice content; therefore, debris flow modeling of fluidized ejecta

  6. The Ries impact crater described as an analogue for a Martian double-layered ejecta crater on Earth

    NASA Astrophysics Data System (ADS)

    Sturm, Sebastian; Wulf, Gerwin; Jung, Dietmar; Kenkmann, Thomas

    2014-05-01

    The Ries impact crater (~26 km-diameter) is described as a relatively pristine, complex impact crater in southern Germany. The oblique impact occurred during the Miocene (14.9 Ma) and hit into a two-layered target material that consists of ~650 m partly water-saturated and subhorizontally layered sediments (limestones, sandstones, shales) of Triassic to Tertiary ages underlain by crystalline basement rocks (mainly gneisses, granites and amphibolites) [1, 2, 3, 4]. The continuous and well-preserved ejecta blanket reaches up to a distance of 45 km from the crater center. It is built up by so called Bunte Breccia material that is described as a polymict lithic breccia. Bunte Breccia mainly consists of unshocked to weakly shocked sedimentary target clasts including a minority of crystalline basement clasts and reworked surfical sediments (e.g., Upper Freshwater Molasses or Upper Seawater Molasses) [5, 6]. Here we present our final interpolation results of the morphology of the paleo-surface and the thickness variations of the continuous ejecta blanket (Bunte Breccia) with radial range outside of the Ries impact crater. Our results were then compared with ejecta distribution characteristics of Martian complex double-layered ejecta craters (DLE) [7]. We combined digital elevation data (ASTER DEM) and geologic information of the recent geologic map [8], in addition with nine NASA Drillings [6], and up to 40 Bavarian Environment Agency drillings in ArcGIS (ESRI) and RockWorks14 (RockWare) to interpolate the elevation of the lower contact plane ("paleo-surface") and the contact between the Bunte breccia and the overlain Suevite deposits to reconstruct the Bunte Breccia thickness variation outside of the Ries impact crater [7]. Our final interpolation results of the paleo-surface and Bunte Breccia top surface provide an increasing Bunte breccia thickness with increasing distance from the crater center. The ejecta thickness distribution clearly deviates from a steady decrease

  7. UNAM Scientific Drilling Program of Chicxulub Impact Structure-Evidence for a 300 kilometer crater diameter

    NASA Astrophysics Data System (ADS)

    Urrutia-Fucugauchi, J.; Marin, L.; Trejo-Garcia, A.

    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 crater's center. Core samples from both sites show a sequence of post-crater carbonates on top of a thick impact breccia pile covering the disturbed Mesozoic platform rocks. At UNAM-7, two impact 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 impact 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 impact craters. 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 crater 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 crater model.

  8. Fragment shapes in impact experiments ranging from cratering to catastrophic disruption

    NASA Astrophysics Data System (ADS)

    Michikami, Tatsuhiro; Hagermann, Axel; Kadokawa, Tokiyuki; Yoshida, Akifumi; Shimada, Akira; Hasegawa, Sunao; Tsuchiyama, Akira

    2016-01-01

    Laboratory impact experiments have found that impact fragments tend to be elongated. Their shapes, 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. This corresponds 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 created in catastrophic disruptions. Catastrophic disruption is, however, a process that is different from impact cratering. In order to systematically investigate the shapes of fragments in the range from impact cratering to catastrophic disruption, impact experiments for basalt targets 5-15 cm in size were performed. A total of 28 impact experiments were carried out by firing a spherical nylon projectile (diameter 7.14 mm) perpendicularly into the target surface at velocities of 1.60-7.13 km/s. More than 12,700 fragments with b ⩾ 4 mm generated in the impact experiments were measured. We found that the mean value of c/a in each impact decreases with decreasing impact energy per unit target mass. For instance, the mean value of c/a in an impact cratering event is nearly 0.2, which is considerably smaller than c/a in a catastrophic disruption (∼0.5). The data presented here can provide important evidence to interpret the shapes of asteroids and boulders on asteroid surfaces, and can constrain current interpretations of asteroid formation. As an example, by applying our experimental results to the boulder shapes on Asteroid Itokawa's surface, we can infer that Itokawa's parent body must have experienced a catastrophic disruption.

  9. Impact Cratering, Mantle Removal, and Catastrophic Disruption of Differentiated Asteroids

    NASA Astrophysics Data System (ADS)

    Asphaug, E.; Agnor, C.

    2005-08-01

    We present results from impact simulations, applying a version of the SPH hydrocode (Benz 1990) used in recent planetary collisional studies (e.g. Canup & Asphaug, Nature 2001; Agnor & Asphaug, Ap.J. 2004) to examine the impact evolution of differentiated asteroids. We use 4 Vesta as an archetype to connect this research to previous modeling (Asphaug M&PS 1997). We also extend our simulations to larger (1000 km) and smaller (200 km) targets, and span velocity regimes from subsonic (0.5 km/s) to hypervelocity (10 km/s), in order to complement previous impact studies by Benz & Asphaug (Icarus 1999), who focused on the catastrophic disruption threshold (Q*D) of non-differentiated spheres of rock and ice at fixed impact velocity. The ˜ 520 km diameter asteroid Vesta is the first Dawn mission target (Russell et al., P&SS 2004). It is a riddle not only for the unique survival of its basaltic crust, but also for the existence of a southern-hemispheric crater of diameter 450 km (Thomas et al., Icarus 1997) and its taxonomic and dynamical connection to the family of V-class asteroids (Binzel & Xu, Science 1993). It also represents an important end-member in the mechanics of complex cratering, given that its giant crater forms in a gravity field ˜ 1/30 that of Earth. Our focus on large differentiated asteroids addresses four questions: (1) How do the largest craters on such asteroids form; (2) under what conditions can high-velocity impacts remove a significant fraction of the mantle, possibly exposing core materials in the manner proposed for M-class asteroids like Psyche (Davis et al., Icarus 1999); (3) what mechanical and thermodynamical processing occurs in the shock acceleration of this escaping mantle material, in the context of meteorite petrogenesis, and (4) what processing occurs to the surviving target asteroid. This work is funded by NASA PG&G ``Small Bodies and Planetary Collisions".

  10. 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.

  11. Identification of buried lunar impact craters from GRAIL data and implications for the nearside maria

    NASA Astrophysics Data System (ADS)

    Evans, Alexander J.; Soderblom, Jason M.; Andrews-Hanna, Jeffrey C.; Solomon, Sean C.; Zuber, Maria T.

    2016-03-01

    Gravity observations from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have revealed more than 100 quasi-circular mass anomalies, 26-300 km in diameter, on the lunar nearside. These anomalies are interpreted to be impact craters filled primarily by mare deposits, and their characteristics are consistent with those of impact structures that formed prior to, and during, intervals of flooding of feldspathic terrane by mare basalt lavas. We determine that mare deposits have an average density contrast of 850-200+300 kg m-3 relative to the surrounding crust. The presence of a large population of volcanically buried craters with minimal topographic expression and diameters up to 300 km requires an average nearside mare thickness of at least 1.5 km and local lenses of mare basalt as thick as ~7 km.

  12. Ice-Associated Impact Craters on Mars: Implications from MOLA Observations

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

    Impact features adjacent to the permanent North Polar Cap on Mars provide a unique perspective on the crater formation and modification process. Little attention has been previously paid to the dozen's of ice-associated or 'frost-filled' craters north of 70N on Mars. We have examined Mars Orbiter Laser Altimeter (MOLA) cross-sections of 13 of these features between 7ON and 82N in an effort to understand cavity modification processes potentially associated with the advance and retreat of the North Polar ice cap. Here we treat the general geometric properties of these impact features and focus attention on one almost entirely filled example (i.e., 32 km diameter, located at 77N, 89E) for which high resolution Viking Orbiter images (50 m per pixel) provide key constraints for interpreting MOLA's meter-precision topographic measurements.

  13. Suevites from the Rochechouart Impact Crater, France, and the Lake Mien Impact Crater, Sweden: The Search for Robust Carbon Minerals

    NASA Astrophysics Data System (ADS)

    Hough, R. M.; Langenhorst, F.; Stoffler, D.; Pillinger, C. T.; Gilmour, I.

    1995-09-01

    Suevite from the 24km Ries crater in southern Germany has recently been shown to contain diamond, lonsdaleite and silicon carbide (1). These minerals are of impact, not meteoritic, origin and probably formed by a combination of shock and plasma processes with the contribution due to each mechanism yet to be resolved (1). Diamonds are increasingly becoming an accepted impact signature and have been reported for several Ukranian impact craters including Zapadnaya (2) and also for the Popigai impact crater in Siberia (3). We have also found diamonds associated with the K/T boundary event 65 Ma ago in North America (4) and Mexico (5). The genesis of suevite at the Ries is thought to be within a fireball at very high temperatures and travelling at high velocities. Shocked minerals are associated with the suevite as are the high pressure polymorphs of quartz namely coesite and stishovite (6). Such an extreme temperature and pressure history for the suevite make it an ideal rock type to search for impact diamonds, we are therefore endeavouring to study other suevites from further impact craters, including Rochechouart and Mien. The 165-200 Ma Rochechouart impact crater in the Massif Central, France, is thought to have originally been some 20 km across and therefore is very similar in size to the Ries (7). The basement material of gneisses and granites is also akin to the Ries and as such makes it an ideal candidate for diamond poltypes and possibly silicon carbide. Lake Mien in Sweden has no outcrops of suevite breccia but does have glacial erratic blocks of suevite. The impact crater is only some 7-9 km in size and has an age of 120 Ma (8). It affords a useful method of investigating the importance of size as a controlling factor in formation of carbon impact minerals. The samples were treated with an acid demineralization procedure first developed for the extraction of diamond from meteorites and modified for the particular needs of studying terrestrial samples

  14. EVIDENCE IN CRATER AGES FOR PERIODIC IMPACTS ON THE EARTH

    SciTech Connect

    Alvarez, W.; Muller, R.A.

    1984-01-01

    Recent evidence has indicated that the impact of a comet or asteroid may have been responsible for mass extinction at the ends of both the Cretaceous and the Eocene. Quantitative analysis by Raup and Sepkoski showed that mass extinctions occur with a 26-Myr period, similar to the period seen in qualitative pelagic records by Fischer and Arthur. To account for the possibility of periodic comet showers, Davis et al. proposed that such showers could be triggered by an unseen solar companion star as it passes through perihelion on a moderately eccentric orbit. To test a prediction implicit in this model we examined records of large impact craters on the Earth. We report here that most of the craters occur in a 28.4-Myr cycle. Within measurement errors, this period and its phase are the same as those found in the fossil mass extinctions. The probability that such agreement is accidental is 1 in 10.

  15. 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.

  16. Thermoluminescence dating of the Kamil impact crater (Egypt)

    NASA Astrophysics Data System (ADS)

    Sighinolfi, Gian Paolo; Sibilia, Emanuela; Contini, Gabriele; Martini, Marco

    2015-02-01

    Thermoluminescence (TL) dating has been used to determine the age of the meteorite impact crater at Gebel Kamil (Egyptian Sahara). Previous studies suggested that the 45 m diameter structure was produced by a fall in recent times (less than 5000 years ago) of an iron meteorite impactor into quartz-arenites and siltstones belonging to the Lower Cretaceous Gilf Kebir Formation. The impact caused the complete fragmentation of the impactor, and the formation of a variety of impactites (e.g., partially vitrified dark and light materials) present as ejecta within the crater and in the surrounding area. After a series of tests to evaluate the TL properties of different materials including shocked intra-crater target rocks and different types of ejecta, we selected a suite of light-colored ejecta that showed evidence of strong thermal shock effects (e.g., partial vitrification and the presence of high-temperature and -pressure silica phases). The abundance of quartz in the target rocks, including the vitrified impactites, allowed TL dating to be undertaken. The variability of radioactivity of the intracrateric target rocks and the lack of direct in situ dosimetric evaluations prevented precise dating; it was, however, possible to constrain the impact in the 2000 BC-500 AD range. If, as we believe, the radioactivity measured in the fallback deposits is a reliable estimate of the mean radioactivity of the site, the narrower range 1600-400 BC (at the 2σ confidence level) can be realistically proposed.

  17. 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.

  18. Impact cratering on granular beds: From the impact of raindrops to the strike of hailstones

    NASA Astrophysics Data System (ADS)

    Gordillo, Leonardo; Wang, Junping; Japardi, Fred; Teddy, Warren; Gao, Ming; Cheng, Xiang

    Impact craters generated by the impact of a spherical object onto a granular bed strongly depend on the material properties of impactors. As an example, impact cratering by liquid drops and by solid spheres exhibits qualitatively different power-law scalings for the size of resulting impact craters. While the basic energy conservation and dimensional analysis provide simple guiding rules, the detailed dynamics governing the relation between these power-law scalings is still far from clear. To analyze the transition between liquid-drop and solid-sphere impact cratering, we investigate impact cratering by liquid drops for a wide range of viscosities over 7 decades. Using high-speed photography and laser profilometry, we delineate the liquid-to-solid transition and show the emergence of the two asymptotic behaviors and their respective power laws. We find that granular avalanches triggered by impacts are crucial in understanding the energy partition between impacted surfaces and impactors, which directly determines the observed scaling relations. A simple model is constructed for the initial stage of the impact that explains the energy partition during crater formation. We ackowledge the support of NSF CAREER DMR-1452180. LG acknowledges fundings from CONICYT/BECAS CHILE 74160007.

  19. Spall velocity measurements from laboratory impact craters

    NASA Technical Reports Server (NTRS)

    Polanskey, Carol A.; Ahrens, Thomas J.

    1986-01-01

    Spall velocities were measured for a series of impacts into San Marcos gabbro. Impact velocities ranged from 1 to 6.5 km/sec. Projectiles varied in material and size with a maximum mass of 4g for a lead bullet to a minimum of 0.04 g for an aluminum sphere. The spall velocities were calculated both from measurements taken from films of the events and from estimates based on range measurements of the spall fragments. The maximum spall velocity observed was 27 m/sec, or 0.5 percent of the impact velocity. The measured spall velocities were within the range predicted by the Melosh (1984) spallation model for the given experimental parameters. The compatability between the Melosh model for large planetary impacts and the results of these small scale experiments is considered in detail. The targets were also bisected to observe the internal fractures. A series of fractures were observed whose location coincided with the boundary of the theoretical near surface zone predicted by Melosh. Above this boundary the target material should receive reduced levels of compressive stress as compared to the more highly shocked region below.

  20. Delineating Bukit Bunuh impact crater boundary by geophysical and geotechnical investigation

    SciTech Connect

    Azwin, I. N. Rosli, S.; Nordiana, M. M.; Ragu, R. R.; Mark, J.; Mokhtar, S.

    2015-03-30

    Evidences of crater 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 impact site, detailed studies are needed to verify the boundary of the crater 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 crater and rim respectively with diameter approximately 8km. There are also few spots of high elevated bedrock appear at the centre of the crater 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 crater, on the rim, as well as at the rebound area.

  1. Delineating Bukit Bunuh impact crater boundary by geophysical and geotechnical investigation

    NASA Astrophysics Data System (ADS)

    Azwin, I. N.; Rosli, S.; Mokhtar, S.; Nordiana, M. M.; Ragu, R. R.; Mark, J.

    2015-03-01

    Evidences of crater 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 impact site, detailed studies are needed to verify the boundary of the crater 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 crater and rim respectively with diameter approximately 8km. There are also few spots of high elevated bedrock appear at the centre of the crater 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 crater, on the rim, as well as at the rebound area.

  2. The MEMIN research unit: Scaling impact cratering experiments in porous sandstones

    NASA Astrophysics Data System (ADS)

    Poelchau, Michael H.; Kenkmann, Thomas; Thoma, Klaus; Hoerth, Tobias; Dufresne, Anja; SchńFer, Frank

    2013-01-01

    The MEMIN research unit (Multidisciplinary Experimental and Modeling Impact research Network) is focused on analyzing experimental impact craters and experimental cratering processes in geological materials. MEMIN is interested in understanding how porosity and pore space saturation influence the cratering process. Here, we present results of a series of impact experiments into porous wet and dry sandstone targets. Steel, iron meteorite, and aluminum projectiles ranging in size from 2.5 to 12 mm were accelerated to velocities of 2.5-7.8 km s-1, yielding craters with diameters between 3.9 and 40 cm. Results show that the target's porosity reduces crater volumes and cratering efficiency relative to nonporous rocks. Saturation of pore space with water to 50% and 90% increasingly counteracts the effects of porosity, leading to larger but flatter craters. Spallation becomes more dominant in larger-scale experiments and leads to an increase in cratering efficiency with increasing projectile size for constant impact velocities. The volume of spalled material is estimated using parabolic fits to the crater morphology, yielding approximations of the transient crater volume. For impacts at the same velocity these transient craters show a constant cratering efficiency that is not affected by projectile size.

  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. Liquefaction of sedimentary rocks during impact crater development

    NASA Astrophysics Data System (ADS)

    Hippertt, J. P.; Lana, C.; Weinberg, R. F.; Tohver, E.; Schmieder, M.; Scholz, R.; Gonçalves, L.; Hippertt, J. F.

    2014-12-01

    Impact crater development on every planetary body requires catastrophic movement of large volumes of crustal rocks. The process produces well-known features such as brecciation and frictional melting, but a mechanism that explains how rocks accommodate the strain during the cratering flow remains unclear. Here, we investigate target rocks from the Araguainha impact crater (central Brazil) that typify what happens to a consolidated, fluid-saturated sedimentary rock at ˜ 2 km below the surface prior to the impact event. Sandstone units record a pattern of chaotic large-scale folds and pervasive microscopic (grain-to-grain) brecciation that result from rock strength degradation triggered by the impact. Field mapping and extensive textural observations indicate that these sandstones experienced initial microstructural damage from the shock wave and that this process may have weakened grain-to-grain bonds and started the process of pervasive microbrecciation. Accompanying heating and decompression lead to vaporization and expansion of fluids in the sandstone pores, magnifying the process of brecciation by effectively liquefying the rock mass and allowing for chaotic folding (at a range of scales up to blocks 100 m in length) in the central uplift. This is a vaporization-assisted microbrecciation, and it may have inhibited the formation of pseudotachylites, because energy was dissipated by pervasive microcracking, vaporization of pore fluids, and large scale chaotic folding, rather than localized displacement on brittle faults and frictional heating. We suggest that impact liquefaction of sedimentary rocks depends on whether the presence of pore-fluids and related micro-brecciation are sufficient to dissipate most of the impact energy.

  5. Internal structure of the Chicxulub Impact crater imaged with magnetotelluric exploration

    NASA Astrophysics Data System (ADS)

    Campos, O.; Unsworth, M.; Bedrosian, P.; Belmonte, S.; Arzate, J.; Lazorek, M.; Zimmer, U.

    2001-12-01

    The magnetotelluric technique allows remote sensing of the Earth's subsurface structure using natural, low frequency radio waves. It measures the electrical resistivity, a parameter that contains information about the lithology and fluid content of subsurface rock units. In January 2001, magnetotelluric (MT) data were collected on two radial profiles across the Chicxulub impact crater in Yucatan, Mexico. Each profile extended from the centre of the crater near Puerto Chicxulub to beyond the cenote ring. The MT data were processed and then combined with data collected in previous years by UNAM. The combined data set was then inverted to give a two-dimensional image of the subsurface resistivity structure of the crater. The following features can be resolved in the subsurface resistivity model. The Tertiary sedimentary sequence that fills the crater has a resistivity of 1-3 ohm-m and is approximately 2 km deep. In the basement a zone of high resistivity is imaged from the centre of the impact structure to a radius of approximately 45 km. This high resistivity at shallow depth can be interpreted as uplifted basement rocks of the structural high in the centre of the crater. Between radial distances of 50 and 70 km is a zone of lower resistivities in the upper 5-10 km of the crust. This coincides with the observed low in the Bouguer gravity anomaly. The coincidence of these two anomalies suggests a common origin. This is most probably due to a region of breccia that exhibits both low electrical resistivity and density.

  6. The MEMIN Research Unit: New results from impact cratering experiments into geological materials

    NASA Astrophysics Data System (ADS)

    Poelchau, M. H.; Deutsch, A.; Thoma, K.; Kenkmann, T.

    2013-09-01

    The MEMIN research unit (Multidisciplinary Experimental and Modeling Impact research Network) is focused on performing hypervelocity impact experiments, analyzing experimental impact craters and modeling cratering rocesses in geological materials. The main goal of the MEMIN project is to comprehensively quantify impact processes by conducting stringently controlled experimental impact cratering campaigns on the mesoscale with a multidisciplinary analytical approach. As a unique feature we use two-stage light gas guns capable of producing impact craters in thedecimeter size-range in solid rocks that, in turn, allow detailed spatial analysis of petrophysical, structural, and geochemical changes in target rocks and ejecta.

  7. Tectonic-karstic origin of the alleged "impact crater" of Lake Isli (Imilchil district, High Atlas, Morocco)

    NASA Astrophysics Data System (ADS)

    Ibouh, Hassan; Michard, André; Charrière, André; Benkaddour, Abdelfattah; Rhoujjati, Ali

    2014-03-01

    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 impact crater" by a group of geoscientists. This was promptly denied by a group of meteorite specialists, but the first team reiterated their impact crater interpretation, now restricted to Lake Isli. This alleged 40-kyr-old impact crater 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.

  8. 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.

  9. Cleopatra crater on Venus - Venera 15/16 data and impact/volcanic origin controversy

    NASA Astrophysics Data System (ADS)

    Basilevsky, A. T.; Ivanov, B. A.

    1990-02-01

    The morphology and morphometry of the 100-km diameter, 2.4-km deep Cleopatra crater on Venus are examined using Venera 15/16 images. The Cleopatra crater is compared to circular structures on Venus, Mercury, Mars, the earth and the moon. Consideration is given to the possible causes for the genesis of the Cleopatra crater. It is concluded that Cleopatra has a clear impact basin morphology with an anomalous crater depth.

  10. 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, C.; 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.

  11. Deep Onshore Crustal Structure of Chicxulub Impact Crater Hinted From Mt Studies.

    NASA Astrophysics Data System (ADS)

    Arzate, J. A.; Campos-Enríquez, J. O.

    This detailed MT study provides information about the deep continental structure of the Chicxulub impact crater (Yucatan, Mexico). In particular MT images of the elec- trical resistivity distribution along three radial profiles confirm the presence of shallow high resistive material at the crater center. Over this resitive high the MT soundings are featured by a sharper rise in resistivity related to the basement. This uplifted base- ment material coincides with the central structural high inferred in previous gravity, magnetic and MT studies. The top to the uplifted material is about 5 km in agreement with a recent seismic study. Its diameter is about 40 km and according to our images the basement material has been uplifted from a depth of about 10 km. The cenotes ring mark the rim of a deep basin featured by low resistivities. These low resistivities are interpreted as due to the fluids filling and interconecting the fractures of this portion.

  12. Impact Crater of the Australasian Tektites, Southern Laos

    NASA Astrophysics Data System (ADS)

    Sieh, K.; Herrin, J. S.; Wiwegwin, W.; Charusiri, P.; Singer, B. S.; Singsomboun, K.; Jicha, B. R.

    2015-12-01

    The Australasian strewn field, a horizon of glassy clasts formed of molten ejecta from the impact of a bolide about 770,000 years ago, covers about a tenth of the Earth - from Indochina to Australia and from the Indian to western Pacific oceans. The distribution of chemical and physical characteristics of these tektites implies a very large impact somewhere in central Indochina. A half-century of unsuccessful searching for the impact crater implies obscuration by either erosion or burial. Geomorphological and stratigraphic evidence suggests that the crater lies buried beneath lavas and cinder cones of a 100-km wide volcanic shield centered atop the Bolaven Plateau of southern Laos. One critical test of this hypothesis, using precise 40Ar/39Ar dating, is now in progress - are these highly weathered basalts younger than the tektites? Although volcanic rocks cover most of the area proximal to our purported impact site, a thick, crudely bedded, bouldery to pebbly breccia that crops out southeast of the obscured crater rim appears to be part of an ejecta blanket. The basal unit of this fining-upward sequence comprises large boulders of late-Mesozoic sandstone bedrock that display in situ shattering. This implies emplacement ballistically rather than by debris-flow. Old surfaces in the surrounding region (as others have noted) and on the Plateau have a mantle of pebbly, detrital lateritic debris that in its upper 15 cm contains angular tektite fragments. We hypothesize that this debris is a proximal fall bed produced by shock-induced comminution and ejection of a lateritic soil that covered the Plateau bedrock. Deposition was nearly complete when sparse tektite fragments ejected from nearer the center of the impact began to land. At many sites this pebbly, lateritic bed is overlain by a thick silty bed that others have associated with aeolian erosion of a barren, incinerated tropical landscape. See Herrin et al (this meeting) for more on the volcanic rocks.

  13. Fractal Fragmentation triggered by meteor impact: The Ries Crater (Germany)

    NASA Astrophysics Data System (ADS)

    Paredes Marino, Joali; Perugini, Diego; Rossi, Stefano; Kueppers, Ulrich

    2015-04-01

    FRACTAL FRAGMENTATION TRIGGERED BY METEOR IMPACT: THE RIES CRATER (GERMANY) Joali Paredes (1), Stefano Rossi (1), Diego Perugini (1), Ulrich Kueppers (2) 1. Department of Physics and Geology, University of Perugia, Italy 2. Department of Earth and Environmental Sciences, University of Munich, Germany The Nördlinger Ries is a large circular depression in western Bavaria, Germany. The depression was caused by a meteor impact, which occurred about 14.3 million-14.5 million years ago. The original crater rim had an estimated diameter of 24 kilometers. Computer modeling of the impact event indicates that the impact or probably had diameters of about 1.5 kilometers and impacted the target area at an angle around 30 to 50 degrees from the surface in a west- southwest to east-northeast direction. The impact velocity is thought to have been about 20 km/s. The meteor impact generated extensive fragmentation of preexisting rocks. In addition, melting of these rocks also occurred. The impact melt was ejected at high speed provoking its extensive fragmentation. Quenched melt fragments are ubiquitous in the outcrops. Here we study melt fragment size distributions with the aim of understanding the style of melt fragmentation during ejection and to constrain the rheological properties of such melts. Digital images of suevite (i.e. the rock generated after deposition and diagenesis of ash and fragments produced by the meteor impact) were obtained using a high-resolution optical scanner. Successively, melt fragments were traced by image analysis and the images segmented in order to obtain binary images on which impact melt fragments are in black color, embedded on a white background. Hence, the size of fragments was determined by image analysis. Fractal fragmentation theory has been applied to fragment size distributions of melt fragments in the Ries crater. Results indicate that melt fragments follow fractal distributions indicating that fragmentation of melt generated by the

  14. The Impact Crater as a Habitat: Effects of Impact Processing of Target Materials

    NASA Astrophysics Data System (ADS)

    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.

  15. 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. PMID:12804371

  16. 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.

  17. The Sirente crater, Italy: Impact versus mud volcano origins

    NASA Astrophysics Data System (ADS)

    Stoppa, Francesco

    2006-03-01

    The Sirente crater is a circular structure with a diameter of ˜80 m. The rim deposit is an inverse-graded, matrix-supported breccia. Sedimentological features of the rim deposit suggest that the crater is not related to an explosion or violent mechanical displacement. The structure and texture of the deposit exhibit a primary sedimentary character. The rim deposits do not contain artifacts and do not show evidence of reworking. A multistage formation is reconstructed for the rim growth and associated deposits. The geometry and sedimentology of the deposits indicate that they were produced by the extrusion and accumulation of mudflow deposits. The dominant ejection mechanism was low mud fountains and the transport medium was water. Petrographic and geochemical evidence does not indicate any physical or cryptic trace of an extraterrestrial body. The most realistic agent that explains the observed effects is a rapid local emission of mud and/or water. Geological processes capable of producing these features include piping sinkholes or, more probably, "caldera"-type mud volcanoes, which may result from underground water-table perturbation and/or decompression of deep CO2/hydrocarbon gas reservoirs due to tectonic deformation or faulting activity during a seismic event. In both cases, the name "crater" for this geological form may be maintained, but there is no compelling evidence for an impact origin. In this paper, the scientific literature on the Sirente crater is reconsidered in the light of new morphological, sedimentological, geochemical, and archaeological data. A new mechanism is proposed involving mud-fountaining.

  18. WIRGO in TIC's? [What (on Earth) is Really Going On in Terrestrial Impact Craters?

    NASA Astrophysics Data System (ADS)

    Dence, Michael R.

    2003-02-01

    Canada is well endowed with impact craters formed in crystalline rocks with relatively homogeneous physical properties. They exhibit all the main morphological-structural variations with crater size seen in craters 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 craters, exemplified by Brent (D = 3.7 km) allow direct comparison with models and experimental data. Results of interest include: 1. The central pool of impact melt and underlying breccia at the base of the crater fill is interpreted as the remnant of the transient crater lining; 2. The overlying main mass of breccias filling the final apparent crater 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 crater 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 impact melt and the energy released on impact. In larger complex craters (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

  19. Fullerenes in an impact crater on the LDEF spacecraft

    NASA Technical Reports Server (NTRS)

    Radicati di Brozolo, F.; Bunch, T. E.; Fleming, R. H.; Macklin, J.

    1994-01-01

    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 impact residue in a crater on the Long Duration Exposure Facility (LDEF) spacecraft. Laser ionization mass spectrometry and Raman spectroscopy indicate the presence of fullerenes in the crater and in adjacent ejecta. Man-made fullerenes survive experimental hypervelocity (approximately 6.1 km s-1) impacts into aluminium targets, suggesting that space fullerenes contained in a carbonaceous micrometeorite could have survived the LDEF impact 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 impact produced the fullerenes in situ on LDEF, then this suggests a viable mechanism for fullerene production in space.

  20. The Manicouagan impact crater: Shallow and deep structure considerations

    NASA Astrophysics Data System (ADS)

    Spray, J. G.

    2011-12-01

    The Manicouagan impact structure of Canada was formed at 214 Ma. It has an apparent rim-to-rim diameter of 80-90 km, with two ring features developed beyond this at 100 km and 120 km diameter. The structure is well preserved, undeformed and well exposed. It has suffered some erosion (<500 m), mainly due to glacial activity. As part of the 10-year Manicouagan Impact Research Program (MIRP), students and research scientists are engaged in studies to characterize this important terrestrial crater. In addition, MIRP collaborates with colleagues from other institutions to complement expertise and to provide additional insights (e.g., Arizona State University, Ludwig Maximilians University). Results from the first 5 years of MIRP activities will be presented, with emphasis on shallow (< 1-2 km) versus deep (>2 km) structure of the crater, based on field, geophysical and drill core. Shallow structure reveals a well-exposed anorthositic central uplift, collapsed rim (terrace zone) and sub-melt-sheet breccias. Drill core shows that, in places, the impact-melt sheet-footwall contact exhibits considerable topography, which is attributed to high-angle faulting. Thicker sections (>1 km) of the impact-melt sheet exhibit differentiation via fractional crystallization. Deep structure requires considerable bulk hydrodynamic behavior.

  1. Geologic mapping and distribution of impact melt pools of the lunar crater Tycho

    NASA Astrophysics Data System (ADS)

    Krüger, Tim; Hiesinger, Harald; Howes van der Bogert, Carolyn

    2013-04-01

    ) = 6.16 x 10-5) [e.g.,4,5], thus being significantly older. The absolute model age for the crater floor is 25.7 ± 5.3 Ma (Ncum(D ≥ 1 km) = 2.15 x 10-5). However, the impact melt pools and ejecta blanket should have formed at about the same time [e.g., 7]. One interpretation of the different model ages of melt pools and the ejecta blanket is, that they have different target properties, i.e., the melt could be less porous and stronger [4,5], hence forming smaller craters for a given projectile size and impact velocity. Such an effect would result in younger ages of the melt pools compared to the ejecta blanket. Self-secondary cratering might also cause differences in CSFDs [8,9,10]. References [1] Schultz, P.H. (1976), Moon Morphology, p. 641. [2] Morris, A.R. et al. (2000), LPSC XXXI, #1828. [3] Hawke, B.R., & Head, J.W., (1977), Impact melt on lunar crater rims, pp. 815-841. [4] van der Bogert, C.H. et al. (2010), LPSC XLI, #2165. [5] Hiesinger, H. et al. (2012), JGR, doi:10.1029/2011JE003935. [6] Melosh, H. J. (1989), Impact cratering; a geologic process, Oxford Monographs on Geology and Geophysics, 11. [7] Osinski, G.R. (2004), EPSL, vol. 226, p. 529-543. [8] Shoemaker, E.M. et al. (1968), Surveyor 7 Mission Report. Part 2 - Science Results, Tech. Rep. 32-1264, pp. 9-76. [9] Plescia, J.B. et al. (2011), LPSC XLII, #1839. [10] Zanetti, M. et al. (2012), LPSC XLIII, #2131.

  2. Morphometry of small recent impact craters on Mars: Size and terrain dependence, short-term modification

    NASA Astrophysics Data System (ADS)

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

    2015-02-01

    Most recent studies of crater morphometry on Mars have addressed large craters (D>5 km) using elevation models derived from laser altimetry. In the present work, we examine a global population of small (25 m ≤D≤5 km), relatively well-preserved simple impact craters using HiRISE stereo-derived elevation models. We find that scaling laws from prior studies of large simple craters generally overestimate the depth and volume at small diameters. We show that crater rim curvature exhibits a strong diameter dependence that is well-described by scaling laws for D<1 km. Above this diameter, upper rim slopes begin to exceed typical repose angles and crater rims sharpen significantly. This transition is likely the result of gravity-driven collapse of the upper cavity walls during crater formation or short-term modification. In addition, we identify a tendency for small craters (D<500m) to be more conical than large craters, and we show that the average cavity cross section is well-described by a power law with exponent ˜1.75 (neither conical nor paraboloidal). We also conduct a statistical comparison of crater subpopulations to illuminate trends with increasing modification and target strength. These results have important implications for describing the "initial condition" of simple crater shape as a function of diameter and geological setting and for understanding how impact craters are modified on the Martian surface over time.

  3. Raindrop impact on sand: a dynamic explanation of crater morphologies.

    PubMed

    Zhao, Song-Chuan; de Jong, Rianne; van der Meer, Devaraj

    2015-09-01

    As a droplet impacts upon a granular substrate, both the intruder and the target undergo deformation, during which the liquid may penetrate into the substrate. These three aspects together distinguish it from other impact phenomena in the literature. We perform high-speed, double-laser profilometry measurements and disentangle the dynamics into three aspects: the deformation of the substrate during the impact, the maximum spreading diameter of the droplet, and the penetration of the liquid into the substrate. By systematically varying the impact speed and the packing fraction of the substrate, (i) the substrate deformation indicates a critical packing fraction ϕ* ≈ 0.585; (ii) the maximum droplet spreading diameter is found to scale with a Weber number corrected by the substrate deformation; and (iii) a model of the liquid penetration is established and is used to explain the observed crater morphology transition. PMID:26158484

  4. 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

  5. Wildfires Caused by Formation of Small Impact Craters: A Kaali Crater Case

    NASA Astrophysics Data System (ADS)

    Losiak, Anna; Belcher, Claire; Hudspith, Victoria; Zhu, Menghua; Bronikowska, Malgorzata; Jõeleht, Argo; Plado, Juri

    2016-04-01

    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 impacts smaller than Chicxulub is inconclusive. On one hand, no signs of fires are associated with the formation of 24-km Ries crater [6]. On the other hand, the Tunguska site was burned after the impact 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 crater (Estonia) within which we find pieces of charred organic material. Those pieces appear to have been produced during the impact, according to their stratigraphic location and following 14C analysis [19] as opposed to pre- or post-impact 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

  6. Evidence for Impact-induced Hydrothermal Alteration at the Lonar Crater, India, and Mistastin Lake, Canada

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.; Hagerty, J. J.

    2003-01-01

    The 50,000 year old, 1.8km diameter Lonar crater is located in Maharashtra, India. This relatively small crater is of particular interest because of its unique morphological and mineralogical properties, which make it a valid analogue for similar craters on the surface of Mars. We show that even in this relatively small crater, substantial hydrothermal alteration of shocked breccias in the floor of the crater has occurred, probably due to the thermal effects of the impact event. The 38 my old, 28 km diameter, Mistastin crater contains an 80 m thick impact melt sheet. We have also documented the presence of alteration phases in the material from this larger crater.

  7. Melt production in large-scale impact events: Calculations of impact-melt volumes and crater scaling

    NASA Technical Reports Server (NTRS)

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

    1992-01-01

    Along with an apparent convergence in estimates of impact-melt volumes produced during planetary impact events, intensive efforts at deriving scaling relationships for crater dimensions have also yielded results. It is now possible to examine a variety of phenomena associated with impact-melt production during large cratering events and apply them to planetary problems. This contribution describes a method of combining calculations of impact-melt production with crater scaling to investigate the relationship between the two.

  8. Lunar crater chains of non-impact origin

    NASA Technical Reports Server (NTRS)

    Eppler, D.; Heiken, G.

    1975-01-01

    Apollo 15, 16, and 17 photographs were scanned for lunar crater chains consisting of three or more aligned craters with similar states of degradation, and the origin of these chains is considered. The mode of origin for mare crater chains appears to be associated with either collapsed lava tubes or cinder cones, while the origin of highland crater chains generally seems to involve highland volcanoes. Crater chains from mare regions range from 20 to 40 km long and appear to have no preferred structural control of their orientation. Highland crater chains range from 1 to 113 km long and may be structurally controlled by the lunar grid system.

  9. The origin of polygonal impact craters - Evidence from Argyre region, Mars.

    NASA Astrophysics Data System (ADS)

    Ohman, T.; Aittola, M.; Kostama, V.-P.; Hyvarinen, M.; Raitala, J.

    2005-08-01

    Polygonal impact craters are a ubiquitous feature on the surfaces of various bodies throughout the Solar System (Ohman et al., 2005). We studied the polygonal craters in the Argyre region, Mars, with two goals in mind: a) to better constrain the origin of polygonality in impact craters, and thus, understand the effects of pre-existing structures of the target material during the formation of impact craters (this work), and b) to see how polygonal craters reflect the complex geotectonic history of Argyre impact basin's surroundings. Differential erosion is still often regarded as the cause for crater's polygonality, although already Eppler et al. (1983) showed that erosion actually increases the circularity, not the polygonality of impact craters. Our work reveals that both eroded (no rim wall), rimmed, and fresh (preserved ejecta blanket) craters all display the same amount of polygonality, as measured by the number of straight rim segments. Also the directions of the rim segments in all erosional stages are statistically generally the same. This suggests that the fracture systems these polygonal craters reflect have quite ancient origins. These observations are very difficult to understand by means of erosion, but instead are a natural outcome if, as we believe, the polygonal plan view stems already from the formation of the crater. The currently favoured acoustic fluidisation model of impact crater's modification (collapse) stage requires that the rim material is nearly strengthless during the collapse, and thus can not have a ``memory" of the pre-existing crustal structures (e.g. Melosh and Ivanov, 1999). In the view of polygonal crater data, this is not the case. Therefore, at least a slight adjustment is required to the current cratering models for them to correctly depict nature. Funding from the Vaisala Foundation is gratefully acknowledged.

  10. The phanerozoic impact cratering rate: Evidence from the farside of the Moon

    USGS Publications Warehouse

    McEwen, A.S.; Moore, Johnnie N.; Shoemaker, E.M.

    1997-01-01

    The relatively recent (< 1 b.y.) flux of asteroids and comets forming large craters on the Earth and Moon may be accurately recorded by craters with bright rays on the Moon's farside. Many previously unknown farside rayed craters are clearly distinguished in the low-phase-angle images returned by the Clementine spacecraft. Some large rayed craters 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 craters is similar to that measured for Eratosthenian craters (up to 3.2 b.y.) at diameters larger than 15 km. The areal density of farside rayed craters matches that of a corrected tabulation of nearside Copernican craters. Hence the presence of bright rays due to immature soils around large craters provides a consistent time-stratigraphic basis for defining the base of the Copernican System. The density of large craters less than ???3.2 b.y. old is ???3.2 times higher than that of large farside rayed craters alone. This observation can be interpreted in two ways: (1) the average cratering rate has been constant over the past 3.2 b.y. and the base of the Copernican is ???1 Ga, or (2) the cratering 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 cratering rate was ???35% higher than the average Eratosthenian rate. Other lines of evidence for an increase in the Phanerozoic (545 Ga) cratering rate are (1) the densities of small craters superimposed on Copernicus and Apollo landing sites, (2) the rates estimated from well-dated terrestrial craters (??? 120 m.y.) and from present-day astronomical

  11. The Phanerozoic Impact Cratering Rate: Evidence from the Farside of the Moon

    NASA Technical Reports Server (NTRS)

    McEwen, Alfred S.; Moore, Jeffrey M.; Shoemaker, Eugene M.

    1997-01-01

    The relatively recent (< 1 b.y.) flux of asteroids and comets forming large craters on the Earth and Moon may be accurately recorded by craters with bright rays on the Moon's farside. Many previously unknown farside rayed craters are clearly distinguished in the low-phase-angle images returned by the Clementine spacecraft. Some large rayed craters 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 craters is similar to that measured for Eratosthenian craters (up to 3.2 b.y.) at diameters larger than 15 km. The areal density of farside rayed craters matches that of a corrected tabulation of nearside Copernican craters. Hence the presence of bright rays due to immature soils around large craters provides a consistent time-stratigraphic basis for defining the base of the Copernican System. The density of large craters less than approximately 3.2 b.y. old is approximately 3.2 times higher than that of large farside rayed craters alone. This observation can be interpreted in two ways: (1) the average cratering rate has been constant over the past 3.2 b.y. and the base of the Copernican is approximately 1 Ga, or (2) the cratering 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 cratering rate was approximately 35% higher than the average Eratosthenian rate. Other lines of evidence for an increase in the Phanerozoic (545 Ga) cratering rate are (1) the densities of small craters superimposed on Copernicus and Apollo landing sites, (2) the rates estimated from well-dated terrestrial craters

  12. Mid-Latitude versus Polar-Latitude Transitional Impact Craters: Geometric Properties from Mars Orbiter Laser Altimeter (MOLA) Observations and Viking Images

    NASA Technical Reports Server (NTRS)

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

    1998-01-01

    One intriguing aspect of martian impact crater morphology is the change of crater 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 crater 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 crater 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 crater 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 craters; 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 crater located at 12.8degN 83.8degE on the Hesperian ridge plains unit (Hvr). Viking images, as well as MOLA data, show that this crater has well developed wall terraces and a central peak with 429 m of relative relief. Three MOLA passes have been acquired for a second impact crater, which is located at 69.5degN 41degE on the Vastitas Borealis Formation. This fresh rampart crater 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 craters. Eight main units were identified, four of which are common on both craters.

  13. Impact craters and landslide volume distribution in Valles Marineris, Mars

    NASA Astrophysics Data System (ADS)

    De Blasio, Fabio

    2014-05-01

    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 impact damage prior to the formation of Valles Marineris; studies of impact craters on Earth show that the volumes of damaged rock extends much deeper than the crater itself; iv) direct triggering of a landslide due to the seismic waves generated by a large meteoroid impact in the vicinity, and v) direct triggering of a landslide con-sequent to impact 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 impact 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. crater

  14. Potential for observing and discriminating impact craters and comparable volcanic landforms on Magellan radar images

    NASA Technical Reports Server (NTRS)

    Ford, J. P.

    1989-01-01

    Observations of small terrestrial craters by Seasat synthetic aperture radar (SAR) at high resolution (approx. 25 m) and of comparatively large Venusian craters by Venera 15/16 images at low resolution (1000 to 2000 m) and shorter wavelength show similarities in the radar responses to crater morphology. At low incidence angles, the responses are dominated by large scale slope effects on the order of meters; consequently it is difficult to locate the precise position of crater rims on the images. Abrupt contrasts in radar response to changing slope (hence incidence angle) across a crater produce sharp tonal boundaries normal to the illumination. Crater morphology that is radially symmetrical appears on images to have bilateral symmetry parallel to the illumination vector. Craters are compressed in the distal sector and drawn out in the proximal sector. At higher incidence angles obtained with the viewing geometry of SIR-A, crater morphology appears less compressed on the images. At any radar incidence angle, the distortion of a crater outline is minimal across the medial sector, in a direction normal to the illumination. Radar bright halos surround some craters imaged by SIR-A and Venera 15 and 16. The brightness probably denotes the radar response to small scale surface roughness of the surrounding ejecta blankets. Similarities in the radar responses of small terrestrial impact craters and volcanic craters of comparable dimensions emphasize the difficulties in discriminating an impact origin from a volcanic origin in the images. Similar difficulties will probably apply in discriminating the origin of small Venusian craters, if they exist. Because of orbital considerations, the nominal incidence angel of Magellan radar at the center of the imaging swath will vary from about 45 deg at 10 deg N latitude to about 16 deg at the north pole and at 70 deg S latitude. Impact craters and comparable volcanic landforms will show bilateral symmetry parallel to the illumination

  15. Potential for observing and discriminating impact craters and comparable volcanic landforms on Magellan radar images

    NASA Astrophysics Data System (ADS)

    Ford, J. P.

    Observations of small terrestrial craters by Seasat synthetic aperture radar (SAR) at high resolution (approx. 25 m) and of comparatively large Venusian craters by Venera 15/16 images at low resolution (1000 to 2000 m) and shorter wavelength show similarities in the radar responses to crater morphology. At low incidence angles, the responses are dominated by large scale slope effects on the order of meters; consequently it is difficult to locate the precise position of crater rims on the images. Abrupt contrasts in radar response to changing slope (hence incidence angle) across a crater produce sharp tonal boundaries normal to the illumination. Crater morphology that is radially symmetrical appears on images to have bilateral symmetry parallel to the illumination vector. Craters are compressed in the distal sector and drawn out in the proximal sector. At higher incidence angles obtained with the viewing geometry of SIR-A, crater morphology appears less compressed on the images. At any radar incidence angle, the distortion of a crater outline is minimal across the medial sector, in a direction normal to the illumination. Radar bright halos surround some craters imaged by SIR-A and Venera 15 and 16. The brightness probably denotes the radar response to small scale surface roughness of the surrounding ejecta blankets. Similarities in the radar responses of small terrestrial impact craters and volcanic craters of comparable dimensions emphasize the difficulties in discriminating an impact origin from a volcanic origin in the images. Similar difficulties will probably apply in discriminating the origin of small Venusian craters, if they exist. Because of orbital considerations, the nominal incidence angel of Magellan radar at the center of the imaging swath will vary from about 45 deg at 10 deg N latitude to about 16 deg at the north pole and at 70 deg S latitude. Impact craters and comparable volcanic landforms will show bilateral symmetry parallel to the illumination

  16. 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

  17. Cratering in glasses impacted by debris or micrometeorites

    NASA Technical Reports Server (NTRS)

    Wiedlocher, David E.; Kinser, Donald L.

    1993-01-01

    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 impacts 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 impact events on the sample were not detected in the mechanical strength measurements. The physical form and structure of the impact sites was carefully examined to determine the influence of those events upon stress concentration associated with the impact and the resulting mechanical strength. The size of the impact site, insofar as it determines flaw size for fracture purposes, was examined. Surface topography of the impacts reveals that six of the seven sites display impact melting. The classical melt crater 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 impact events are presented.

  18. Gradational evolution of young, simple impact craters on the Earth

    NASA Technical Reports Server (NTRS)

    Grant, J. A.; Schultz, P. H.

    1991-01-01

    From these three craters, a first order gradational evolutionary sequence can be proposed. As crater rims are reduced by backwasting and downwasting through fluvial and mass wasting processes, craters are enlarged by approx. 10 pct. Enlargement of drainages inside the crater 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 crater 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 craters appear to be mostly gradient dependent, they may not be unique to simple crater morphologies. Similar signatures may develop on portions of complex craters as well; however, important differences may also occur.

  19. The 1993 Zimbabwe impact crater and meteorite expedition

    NASA Astrophysics Data System (ADS)

    Reimold, W. U.; Master, S.; Koeberl, C.; Robertson, D.

    1994-07-01

    In September 1993 our expedition visited four strucutres in Zimbabwe that had been selected because of circular outlines or because of unusual aeromagnetic anomalies. The first one, the 1.1-km-diameter Thuli structure was identified as a well-preserved volcanic caldera formed by a series of basaltic, gabbroic, and dioritic instrusions. Preliminary results of magnetic traverses are consistent with the model of a volcanic pipe. The 600- and 800-m-wide Save craters near the Mozambican border closely resemble young, well-preserved impact craters such as the Pretoria Saltpan crater in South Africa. However, detailed geological traverses revealed only volcanic rocks intruded into sandstone forming the sharp rim crests. The Mucheka region is the site of the most prominent aeromagnetic anomaly in Zimbabwe. In the absence of any exposures other than Archean basement, the cause of this anomaly is still unknown. None of the basement rock specimens obtained yielded any evidence for shock metamorphism. In 1985 German geologists reportedly noted a circular structure in the Highbury area on Landsat images. An approximately 25-km-wide circular structure is visible on a SPOT satellite image as well. The regional geological map revealed the presence of a slight elevation near the center of this otherwise flat area. The flat floor of this structure is formed by fertile soils overlying locally exposed Deweras arkose and metadolomites, in turn surrounded by hills of Lomagundi sandstones and slates. Near the geographical center a small hill of sandstone and quartzite was indeed detected. Reconnaissance sampling in 'rim' and 'central uplift' provided several specimens with significant numbers of quartz grains with single or multiple sets of planar deformation features (PDFs). A strongly hematized sample from the 'central uplift' contains shocked quartz and relics of glass.

  20. Focused Ion Beam Recovery of Hypervelocity Impact Residue in Experimental Craters on Metallic Foils.

    SciTech Connect

    Graham, G A; Teslich, N; Dai, Z R; Bradley, J P; Kearsley, A T; Horz, F

    2005-11-04

    The Stardust sample return capsule will return to Earth in January 2006 with primitive debris collected from Comet 81P/Wild-2 during the fly-by encounter in 2004. In addition to the cometary particles embedded in low-density silica aerogel, there will be microcraters preserved in the Al foils (1100 series; 100 {micro}m thick) that are wrapped around the sample tray assembly. Soda lime spheres ({approx}49 {micro}m in diameter) have been accelerated with a Light Gas Gun into flight-grade Al foils at 6.35 km s{sup -1} to simulate the capture of cometary debris. The experimental craters have been analyzed using scanning electron microscopy (SEM) and x-ray energy dispersive spectroscopy (EDX) to locate and characterize remnants of the projectile material remaining within the craters. In addition, ion beam induced secondary electron imaging has proven particularly useful in identifying areas within the craters that contain residue material. Finally, high-precision focused ion beam (FIB) milling has been used to isolate and then extract an individual melt residue droplet from the interior wall of an impact. This enabled further detailed elemental characterization, free from the background contamination of the Al foil substrate. The ability to recover ''pure'' melt residues using FIB will significantly extend the interpretations of the residue chemistry preserved in the Al foils returned by Stardust.

  1. Focused Ion Beam Recovery of Hypervelocity Impact Residue in Experimental Craters on Metallic Foils

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

    The Stardust sample return capsule will return to Earth in January 2006 with primitive debris collected from Comet 81P/Wild-2 during the fly-by encounter in 2004. In addition to the cometary particles embedded in low-density silica aerogel, there will be microcraters preserved in the Al foils (1100 series; 100 micrometers thick) that are wrapped around the sample tray assembly. Soda lime spheres (approximately 49 m in diameter) have been accelerated with a light-gas-gun into flight-grade Al foils at 6.35 km s(sup -1) to simulate the potential capture of cometary debris. The preserved crater penetrations have been analyzed using scanning electron microscopy (SEM) and x-ray energy dispersive spectroscopy (EDX) to locate and characterize remnants of the projectile material remaining within the craters. In addition, ion beam induced secondary electron imaging has proven particularly useful in identifying areas within the craters that contain residue material. Finally, high-precision focused ion beam (FIB) milling has been used to isolate and then extract an individual melt residue droplet from the interior wall of an impact penetration. This enabled further detailed elemental characterization, free from the background contamination of the Al foil substrate. The ability to recover pure melt residues using FIB will significantly extend the interpretations of the residue chemistry preserved in the Al foils returned by Stardust.

  2. The cratering record at Uranus: Implications for satellite evolution and the origin of impacting objects

    NASA Technical Reports Server (NTRS)

    Strom, Robert G.

    1987-01-01

    The crater size/frequency distributions on the major Uranian satellites show two distinctly different crater populations of different ages. Any hypothesis on the origin of the objects responsible for the period of heavy bombardment must account for the occurrence of different crater populations (size/frequency distributions) in different parts of the solar system. A computerized simulation using short-period comet impact velocities and a modified Holsapple-Schmidt crater scaling law was used to recover the size distribution of cometary nuclei from the observed cratering record. The most likely explanation for the cratering record is that the period of heavy bombardment was caused by different families of accretional remnants indigenous to the system in which the different crater populations occurred.

  3. 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.

  4. Dating a Small Impact Crater: An Age of Kaali Crater (Estonia) Based on Charcoal Emplaced Within Proximal Ejecta

    NASA Astrophysics Data System (ADS)

    Losiak, A.; Wild, E. M.; Geppert, W. D.; Huber, M. S.; Jõeleht, A.; Kriiska, A.; Kulkov, A.; Paavel, K.; Pirkovic, I.; Plado, J.; Steier, P.; Välja, R.; Wilk, J.; Wisniowski, T.; Zanetti, M.

    2015-09-01

    The Kaali crater was formed shortly after (tpq) 1530-1455 BC (3237 ± 10 14C yr BP). This age is based on dating charcoal within the ejecta blanket that makes it directly related to the impact, and not susceptible to potential reservoir effects.

  5. 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

  6. Hydrothermal activity recorded in post Noachian-aged impact craters on Mars

    NASA Astrophysics Data System (ADS)

    Turner, Stuart M. R.; Bridges, John C.; Grebby, Stephen; Ehlmann, Bethany L.

    2016-04-01

    Hydrothermal systems have previously been reported in ancient Noachian and Hesperian-aged craters on Mars using CRISM but not in Amazonian-aged impact craters. However, the nakhlite meteorites do provide evidence of Amazonian hydrothermal activity. This study uses CRISM data of 144 impact craters of ≥7 km diameter and 14 smaller craters (3-7 km diameter) within terrain mapped as Amazonian to search for minerals that may have formed as a result of impact-induced hydrothermal alteration or show excavation of ancient altered crust. No evidence indicating the presence of hydrated minerals was found in the 3-7 km impact craters. Hydrated minerals were identified in three complex impact craters, located at 52.42°N, 39.86°E in the Ismenius Lacus quadrangle, at 8.93°N, 141.28°E in Elysium, and within the previously studied Stokes crater. These three craters have diameters 20 km, 62 km, and 51 km. The locations of the hydrated mineral outcrops and their associated morphology indicate that two of these three impact craters—the unnamed Ismenius Lacus Crater and Stokes Crater—possibly hosted impact-induced hydrothermal systems, as they contain alteration assemblages on their central uplifts that are not apparent in their ejecta. Chlorite and Fe serpentine are identified within alluvial fans in the central uplift and rim of the Ismenius Lacus crater, whereas Stokes crater contains a host of Fe/Mg/Al phyllosilicates. However, excavation origin cannot be precluded. Our work suggests that impact-induced hydrothermalism was rare in the Amazonian and/or that impact-induced hydrothermal alteration was not sufficiently pervasive or spatially widespread for detection by CRISM.

  7. Location and Sampling of Aqueous and Hydrothermal Deposits in Martian Impact Craters

    NASA Astrophysics Data System (ADS)

    Newsom, Horton E.; Hagerty, Justin J.; Thorsos, Ivan E.

    2001-03-01

    Do large craters on Mars represent sites that contain aqueous and hydrothermal deposits that provide clues to astrobiological processes? Are these materials available for sampling in large craters? Several lines of evidence strongly support the exploration of large impact craters to study deposits important for astrobiology. The great depth of impact craters, up to several kilometers relative to the surrounding terrain, can allow the breaching of local aquifers, providing a source of water for lakes and hydrothermal systems. Craters can also be filled with water from outflow channels and valley networks to form large lakes with accompanying sedimentation. Impact melt and uplifted basement heat sources in craters >50 km in diameter should be sufficient to drive substantial hydrothermal activity and keep crater lakes from freezing for thousands of years, even under cold climatic conditions. Fluid flow in hydrothermal systems is focused at the edges of large planar impact melt sheets, suggesting that the edge of the melt sheets will have experienced substantial hydrothermal alteration and mineral deposition. Hydrothermal deposits, fine-grained lacustrine sediments, and playa evaporite deposits may preserve evidence for biogeochemical processes that occurred in the aquifers and craters. Therefore, large craters may represent giant Petri dishes for culturing preexisting life on Mars and promoting biogeochemical processes. Landing sites must be identified in craters where access to the buried lacustrine sediments and impact melt deposits is provided by processes such as erosion from outflow channels, faulting, aeolian erosion, or excavation by later superimposed cratering events. Very recent gully formation and small impacts within craters may allow surface sampling of organic materials exposed only recently to the harsh oxidizing surface environment.

  8. Phobos grooves and impact craters: A stereographic analysis

    NASA Astrophysics Data System (ADS)

    Simioni, Emanuele; Pajola, Maurizio; Massironi, Matteo; Cremonese, Gabriele

    2015-08-01

    Phobos parallel grooves were first observed on Viking images 38 years ago and since then they have been greatly debated leading to several formation hypotheses. Nevertheless, none of them have been favoured and widely accepted. In this work, we provide a different approach, assuming that Phobos grooves can be the expression of fracture planes, and deriving their spatial distribution and orientation on 3D reconstructions, we point out that any origin related only to craters at Phobos surface should be ruled out, since the majority of the grooves is unrelated to any craters now present at its surface. This raises the intriguing possibility that such grooves, if expression of fracture planes, are remnant features of an ancient parent body from which Phobos could have originated. Such scenario has never been considered for Phobos, though this origin was already proposed for the formation of 433 Eros grooves (Buczkowski, D.L., Barnouin-Jha, O.S., Prockter, L.M. [2008]. Icarus 193, 39). If this idea holds true, the observed groove distribution could be explained as the result of possible major impacts on the larger parent body, which were inherited by the "Phobos shard".

  9. FIB-TEM Anatomy of a Sub-Micrometer Impact Crater on a Hayabusa Grain

    NASA Astrophysics Data System (ADS)

    Harries, D.; Yakame, S.; Uesugi, M.; Langenhorst, F.

    2015-07-01

    We investigated Hayabusa grain RA-QD02-0265, which was found to contain a cluster of sub-micrometer-sized crater-like features. The cluster of craters is most likely due to secondary impacts of particles generated by an nearby (micro-)impact event.

  10. Characterization of the Morphometry of Impact Craters Hosting Polar Deposits in Mercury's North Polar Region

    NASA Technical Reports Server (NTRS)

    Talpe Matthieu; Zuber, Maria T.; Yang, Di; Neumann, Gregory A.; Solomon, Sean C.; Mazarico, Erwan; Vilas, Faith

    2012-01-01

    Earth-based radar images of Mercury show radar-bright material inside impact craters near the planet s poles. A previous study indicated that the polar-deposit-hosting craters (PDCs) at Mercury s north pole are shallower than craters 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 craters at high northern latitudes on Mercury. We measured the depth and diameter of 537 craters located poleward of 45 N, evaluated the slopes of the northern and southern walls of 30 PDCs, and assessed the floor roughness of 94 craters, including nine PDCs. We find that the PDCs appear to have a fresher crater morphology than the non-PDCs and that the radar-bright material has no detectable influence on crater depths, wall slopes, or floor roughness. The statistical similarity of crater 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 crater 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 craters.

  11. The Araguainha impact crater at the Permo-Triassic boundary: implications for the carbon isotope excursion and the mass extinction.

    NASA Astrophysics Data System (ADS)

    Lana, C.; Tohver, E.; Siret, D.; Cawood, P.; Sherlock, S.; Marangoni, Y. R.; Trindade, R. I.; Souza, R.

    2007-12-01

    The Araguainha crater is a complex crater with a diameter of 40 km exposed on the northern margin of the Parana Basin of central Brazil. This intracontinental basin, correlated to the Karoo Basin of southern Africa, was the locus of marine sedimentation over an area of 5 million km2 throughout the late Paleozoic. Carbonate sedimentation in the early Permian was marked by large accumulations of organic carbon in pyrite-bearing oil shales such as the Irati Fm, considered to be the world's second largest oil shale. Regional borehole data from outside the crater reveals a thickness of 40m for the oil shale horizon, which is partly to completely absent within the crater. Our structural and stratigraphic survey of the Araguainha crater reveal the post-impact rebound of the crater has removed ca. 2-2.5 km of sediments from the ca. 10 km diameter central uplift, with minimal subsequent erosion (<250m). Vaporization of the colliding body and the approximate shadowed target region are assumed, with energy models for impact craters suggesting a body of 2-3 km diameter. Ongoing radiogenic isotope dating of the impact melts and breccias is being undertaken by U-Pb SHRIMP analysis of shocked zircons and 40Ar/39Ar analysis of glassy vein material interpreted as pseudotachylite. Preliminary U-Pb age data yield an impact age of 252.7 +/- 3.8 Ma (2 sigma error), essentially synchronous with the Permo-Triassic boundary. The minimum amount of isotopically light carbon (-17 to -25 per mill PDB) available in the target rocks for release by the impact is estimated at 10 Gigatons, considering only the area of the central uplift. Possible sources of additional, isotopically-light carbon include the remainder of the 20-25 km transient crater, as well as methane clathrates released by impact-induced slope destabilization. We propose that the Araguainha impact could have been responsible for observed shifts shift in global carbon isotopes at the Permo-Triassic boundary. The possible effect of

  12. Degradation of selected terrestrial and Martian impact craters

    NASA Astrophysics Data System (ADS)

    Grant, J. A.; Schultz, P. H.

    1993-06-01

    The history of degradation of 50,000-yr-old 1.2-km-diam Meteor Crater in Arizona is defined using field mapping, and the degradation states of the progressively more degraded 68,000-yr-old 1.8-km-diam Lonar Crater in Indiana and 0.5-3.0 Myr old 1.75-km-diam Talemzane Crater in Algeria are assessed using air photos. The results on these terrestrial craters are then compared with the gradational morphology associated with craters in southern Ismenius Lacus on Mars, in order to develop first-order constraints on gradational activity. Common degradation signatures associated with craters on both planets are described. These signatures are used to assemble a first-order degradational sequence for the terrestrial craters that is then compared with the Martian degradational signatures to infer past processes and climate.

  13. Degradation of selected terrestrial and Martian impact craters

    NASA Technical Reports Server (NTRS)

    Grant, John A.; Schultz, Peter H.

    1993-01-01

    The history of degradation of 50,000-yr-old 1.2-km-diam Meteor Crater in Arizona is defined using field mapping, and the degradation states of the progressively more degraded 68,000-yr-old 1.8-km-diam Lonar Crater in Indiana and 0.5-3.0 Myr old 1.75-km-diam Talemzane Crater in Algeria are assessed using air photos. The results on these terrestrial craters are then compared with the gradational morphology associated with craters in southern Ismenius Lacus on Mars, in order to develop first-order constraints on gradational activity. Common degradation signatures associated with craters on both planets are described. These signatures are used to assemble a first-order degradational sequence for the terrestrial craters that is then compared with the Martian degradational signatures to infer past processes and climate.

  14. Morphology of large impact craters and basins on Venus: Implications for ring formation

    NASA Astrophysics Data System (ADS)

    Alexopoulos, Jim S.; McKinnon, William B.

    1993-03-01

    A nearly complete examination of the Magellan radar data for the Venusian surface reveals 72 unequivocal peak-ring craters and 4 larger structures that we interpret to be multiringed. This report updates our earlier studies and that of the Magellan team. The general morphology of peak-ring craters, decreasing ring diameter ratio trends with increasing crater diameter, and the general size-morphology progression from complex central-peak crater to peak-ring crater on Venus and the terrestrial planets suggest similar processes of peak-ring formation. Observations are consistent with a model of dynamic collapse, downward and outward, of an unstable central peak to form a ring. We interpret the four larger ringed structures (Klenova, Lise Meitner, Mead, and Isabella) to be morphologically similar to the Orientale Basin on the Moon, and thus, true multiringed basins.

  15. Morphology of large impact craters and basins on Venus: Implications for ring formation

    NASA Technical Reports Server (NTRS)

    Alexopoulos, Jim S.; Mckinnon, William B.

    1993-01-01

    A nearly complete examination of the Magellan radar data for the Venusian surface reveals 72 unequivocal peak-ring craters and 4 larger structures that we interpret to be multiringed. This report updates our earlier studies and that of the Magellan team. The general morphology of peak-ring craters, decreasing ring diameter ratio trends with increasing crater diameter, and the general size-morphology progression from complex central-peak crater to peak-ring crater on Venus and the terrestrial planets suggest similar processes of peak-ring formation. Observations are consistent with a model of dynamic collapse, downward and outward, of an unstable central peak to form a ring. We interpret the four larger ringed structures (Klenova, Lise Meitner, Mead, and Isabella) to be morphologically similar to the Orientale Basin on the Moon, and thus, true multiringed basins.

  16. Application of a New Method for Lunar Crater Age Dating to Copernican Impact Flux

    NASA Astrophysics Data System (ADS)

    Mazrouei, S.; Ghent, R. R.

    2014-12-01

    The Moon's surface, without any substantial atmosphere, weather, or tectonic activity, is a genuine time capsule for events taking place in our region of the Solar System. Previously, geological maps and crater counting methods were used for age determination for terrains and individual features, such as large craters and basins; however, those methods are extremely time consuming, are limited by image quality and availability and the need to identify small craters over datable regions, and are subject to systematic errors derived from uncertainty in the cratering function and small number statistics. We have recently shown that the rockiness of large craters' ejecta, derived from the Lunar Reconnaissance Orbiter's Diviner thermal radiometer data, provides a new method for determining the ages of Copernican craters (younger than roughly one billion years old). This method is not subject to the constraints of traditional crater counting methods using visible images. Here, we apply this new method to search for variations in the impact flux over the Copernican period. We investigate the size-frequency distributions and ejecta rock abundances of rocky craters five kilometers and larger, and compare the results to canonical relationships for Copernican craters. Because the lunar impact cratering rate is directly related to interactions among near-Earth objects and main belt asteroids, our results will provide a new platform for testing various dynamical hypotheses about the evolution of the asteroid belt and interactions within it.

  17. 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.

  18. Geophysical signature of the Pretoria Saltpan impact structure and a possible satellite crater

    NASA Astrophysics Data System (ADS)

    Brandt, Dion; Reimold, Wolf Uwe; Durrheim, Raymond J.

    1994-05-01

    The genesis of the 1.13-km-diameter Pretoria Saltpan crater has long been the focus of a controversy. Its origin has been explained by either meteorite impact or 'crytoexplosive' volcanic activity, but it was recently confirmed, through detailed petrographic and chemical analysis of a breccia layer forming part of the crater fill, that the crater was formed by impact. As the limited previous geophysical work failed to support an impact origin, a more detailed gravity and magnetic study was conducted. A possible 400-m-diameter circular crater located 3 km to the southwest of the main crater was also investigated with geophysical methods, including resistivity, seismics and ground-probing radar. The gravity signature of the main crater is compatible with that of a simple impact crater and the magnetic signature (no magnetic anomaly could be detected) rules out the possibility of a central magnetic volcanic body below the crater-fill sediments. The results for the possible twin or satellite crater are inconclusive. As it is the only such feature in the entire region, it should not be overlooked. A drilling program may reveal interesting results.

  19. 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

  20. Geomorphic analysis of small rayed craters on Mars: Examining primary versus secondary impacts

    NASA Astrophysics Data System (ADS)

    Calef, Fred J.; Herrick, Robert R.; Sharpton, Virgil L.

    2009-10-01

    Twenty confirmed impacts over a 7-year time period on Mars were qualitatively and statistically compared to 287 secondary craters believed to originate from Zunil, an ˜500 ka, 10-km diameter, primary crater. Our goal was to establish criteria to distinguish secondaries from primaries in the general crater population on the basis of their horizontal planforms. Recent primary impacts have extensive “air blast” zones, distal ray systems (>100 crater radii, R), and ephemeral ejecta. Recent primaries formed clusters of craters from atmospheric fragmentation of the meteoroid body. Secondary craters have ejecta blankets with shorter rays that are consistent with emplacement by low-impact velocities (near 1 km/s). The mean extent of the continuous ejecta blankets was less distal for secondaries (5.38 ± 1.57R) versus primaries (18.07 ± 7.01R), though primary ejecta were less fractal (Fractal Dimension Index (FD I ) < 1.30) and more circular on average (Circularity Ratio (C R ) = 0.55 ± 0.25 versus 0.27 ± 0.13 for secondaries). Crater rims were remarkably circular (primaries C R = 0.97 ± 0.02, secondaries at 0.94 ± 0.05), though secondaries have the lowest values (C R < 0.9). Secondary crater rims were elongated toward or orthogonal to their primary of origin. Uprange source directions for most secondaries, determined by ejecta planform and crater rim ellipticity, point toward Zunil, although contamination from other primaries is considered in some areas. Ejecta blanket discrepancies between recent primaries and Zunil secondaries are attributable to differences in impact velocity and retention age. After removal of the ejecta blanket, crater rims are generally not diagnostic for determining crater origin. Fragmentation of primaries may play some role in steepening the size-frequency distribution of crater diameters in the 5 m < D < 30 m range.

  1. Investigations of Martian Impact Crater Morphologies and Morphometries

    NASA Technical Reports Server (NTRS)

    Barlow, Nadine G.

    2002-01-01

    We have made substantial progress towards completion of the original objectives and are continuing to include new data from the Mars Global Surveyor MOC and TES instruments as they become available (the MOLA instrument has ceased operation as of 2002). The project funding has been used to provide salary support to the PI and several undergraduate students, cover publication charges for two papers, reimburse travel expenses to conferences and workshops incurred by the PI and students, and cover a number of other expenses such as software upgrades and production costs of slides and color prints. This study is revising the PI's Catalog of Large Martian Impact Craters with information obtained from MGS and is utilizing data in the revised Catalog to investigate which planetary factors (such as location, elevation, terrain type, etc.) primarily affect the formation of specific ejecta morphologies and morphometries.

  2. 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

  3. 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

  4. Detrital shocked minerals: microstructural provenance indicators of impact craters

    NASA Astrophysics Data System (ADS)

    Cavosie, A. J.

    2014-12-01

    The study of detrital shocked minerals (DSMs) merges planetary science, sedimentology, mineralogy/crystallography, accessory mineral geochemistry, and geochronology, with the goal of identifying and determining provenance of shock metamorphosed sand grains. Diagnostic high-pressure impact-generated microstructures (planar fractures, planar deformation features) are readily identified on external grain surfaces using standard SEM imaging methods (BSE), and when found, unambiguously confirm an impact origin for a given sand grain. DSMs, including quartz, zircon, monazite, and apatite, have thus far been documented at the Vredefort Dome [1,2,3], Sudbury [4], Rock Elm [5], and Santa Fe [6,7] impact structures. DSMs have been identified in alluvium, colluvium, beach sand, and glacial deposits. Two main processes are recognized that imply the global siliciclastic record contains DSMs: they survive extreme distal transport, and they survive 'deep time' lithification. Distal transport: In South Africa, shocked minerals are preserved in alluvium from the Vaal River >750 km downstream from the Vredefort impact; SHRIMP U-Pb geochronology has confirmed the origin of detrital shocked zircon and monazite from shocked Vredefort bedrock [2]. Vredefort-derived shocked zircons have also been found at the mouth of the Orange River on the Atlantic coast, having travelled ~2000 km downriver from Vredefort [8]. Deep time preservation: Vredefort-derived shocked zircon and quartz has been documented in glacial diamictite from the 300 Myr-old Dwyka Group in South Africa. Shocked minerals were thus entrained and transported in Paleozoic ice sheets that passed over Vredefort [9]. An impact crater can thus be viewed as a unique 'point source', in some cases for billions of years [2,4]; DSMs thus have applications in studying eroded impact craters, sedimentary provenance, landscape evolution, and long-term sediment transport processes throughout the geologic record. This work was supported by

  5. 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.

  6. Impact cratering in sandstone: The MEMIN pilot study on the effect of pore water

    NASA Astrophysics Data System (ADS)

    Kenkmann, Thomas; Wünnemann, Kai; Deutsch, Alexander; Poelchau, Michael H.; Schäfer, Frank; Thoma, Klaus

    2011-06-01

    Planetary surfaces are subjected to meteorite bombardment and crater formation. Rocks forming these surfaces are often porous and contain fluids. To understand the role of both parameters on impact cratering, we conducted laboratory experiments with dry and wet sandstone blocks impacted by centimeter-sized steel spheres. We utilized a 40 m two-stage light-gas gun to achieve impact velocities of up to 5.4 km s-1. Cratering efficiency, ejection velocities, and spall volume are enhanced if the pore space of the sandstone is filled with water. In addition, the crater morphologies differ substantially from wet to dry targets, i.e., craters in wet targets are larger, but shallower. We report on the effects of pore water on the excavation flow field and the degree of target damage. We suggest that vaporization of water upon pressure release significantly contributes to the impact process.

  7. Systematic comparison of automated geological feature detection methods for impact craters

    NASA Astrophysics Data System (ADS)

    Vinogradova, T.; Mjolsness, E.

    2001-12-01

    Accurate, automated crater counts will be essential in extrapolating from existing Mars crater catalogs to much larger catalogs of impact craters in high-resolution orbital imagery for use in relative dating of surfaces in such imagery. Once validated, automatic methods for performing crater counts could be integrated into tools such as the Planetary Image Atlas, which is designed to be a convenient interface through which a user can search for, display, and download images and other ancillary data for planetary Missions, and the Diamond Eye image mining system. Here we report on preliminary computational experiments in using a trainable feature detection algorithm [Burl et al. 2001] to detect craters in real and simulated Mars orbital imagery, and to derive approximate impact crater counts for geological use. In these experiments, we consider two uses of the trainable feature detector: first, directly as a crater detector, and second, as two detectors for sunlit and shadowed inner walls of craters which can then be assembled into a single crater detection based on multiple pieces of evidence. For both of these methods, we consider two data sources: one consisting of real Viking Orbiter imagery of Mars with human expert-supplied ground truth labels, and the other consisting of computer generated renderings of simplified, synthetic cratered terrain with 100% accurate ground truth labels and known, controllable crater density. Each detector reports out a numeric detection ``likelihood'' for every candidate crater. This likelihood must then be thresholded to produce a detection decision. For each combination of two data sources (one natural and one synthetic) and two crater detection methods (whole-crater and parts-model), we vary image complexity and finally measure detection accuracy. Detection accuracy is measured by a Receiver Operator Characteristic (ROC) curve in which detection efficiency (the fraction of true craters detected) and purity (the fraction of

  8. Fluid outflows from Venus impact craters - Analysis from Magellan data

    NASA Technical Reports Server (NTRS)

    Asimow, Paul D.; Wood, John A.

    1992-01-01

    Many impact craters on Venus have unusual outflow features originating in or under the continuous ejecta blankets and continuing downhill into the surrounding terrain. These features clearly resulted from flow of low-viscosity fluids, but the identity of those fluids is not clear. In particular, it should not be assumed a priori that the fluid is an impact melt. A number of candidate processes by which impact events might generate the observed features are considered, and predictions are made concerning the rheological character of flows produce by each mechanism. A sample of outflows was analyzed using Magellan images and a model of unconstrained Bingham plastic flow on inclined planes, leading to estimates of viscosity and yield strength for the flow materials. It is argued that at least two different mechanisms have produced outflows on Venus: an erosive, channel-forming process and a depositional process. The erosive fluid is probably an impact melt, but the depositional fluid may consist of fluidized solid debris, vaporized material, and/or melt.

  9. 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.

  10. Gale crater and impact processes - Curiosity's first 364 Sols on Mars

    NASA Astrophysics Data System (ADS)

    Newsom, Horton E.; Mangold, Nicolas; Kah, Linda C.; Williams, Joshua M.; Arvidson, Ray E.; Stein, Nathan; Ollila, Ann M.; Bridges, John C.; Schwenzer, Susanne P.; King, Penelope L.; Grant, John A.; Pinet, Patrick; Bridges, Nathan T.; Calef, Fred; Wiens, Roger C.; Spray, John G.; Vaniman, David T.; Elston, Wolf E.; Berger, Jeff A.; Garvin, James B.; Palucis, Marisa C.

    2015-03-01

    Impact processes at all scales have been involved in the formation and subsequent evolution of Gale crater. Small impact craters in the vicinity of the Curiosity MSL landing site and rover traverse during the 364 Sols after landing have been studied both from orbit and the surface. Evidence for the effect of impacts on basement outcrops may include loose blocks of sandstone and conglomerate, and disrupted (fractured) sedimentary layers, which are not obviously displaced by erosion. Impact ejecta blankets are likely to be present, but in the absence of distinct glass or impact melt phases are difficult to distinguish from sedimentary/volcaniclastic breccia and conglomerate deposits. The occurrence of individual blocks with diverse petrological characteristics, including igneous textures, have been identified across the surface of Bradbury Rise, and some of these blocks may represent distal ejecta from larger craters in the vicinity of Gale. Distal ejecta may also occur in the form of impact spherules identified in the sediments and drift material. Possible examples of impactites in the form of shatter cones, shocked rocks, and ropy textured fragments of materials that may have been molten have been observed, but cannot be uniquely confirmed. Modification by aeolian processes of craters smaller than 40 m in diameter observed in this study, are indicated by erosion of crater rims, and infill of craters with aeolian and airfall dust deposits. Estimates for resurfacing suggest that craters less than 15 m in diameter may represent steady state between production and destruction. The smallest candidate impact crater observed is ∼0.6 m in diameter. The observed crater record and other data are consistent with a resurfacing rate of the order of 10 mm/Myr; considerably greater than the rate from impact cratering alone, but remarkably lower than terrestrial erosion rates.

  11. Mid-IR Reflectance (DRIFT) Spectral Variations in Basaltic Mineralogy with Direction of Impact at Lonar Crater, India

    NASA Astrophysics Data System (ADS)

    Basavaiah, N.; Chavan, R. S.; Arif, M.

    2012-12-01

    Identification of spectral changes with the direction of impact has important implications for understanding the impact cratering phenomenon occurring on both terrestrial and extraterrestrial planets and also for geology of the crater. Fortuitously, Lonar Impact Crater (India) is the only well-preserved terrestrial simple crater excavated on Deccan basalts and serves as an excellent analogue to craters on Mars and Moon. An ~570 ka old Lonar crater was suggested to be formed by an oblique impact of a chondritic impactor that struck the pre-impact target from the east into a sequence of six basaltic Deccan flows and created a 1.88 km diameter crater with two layers of ejecta blanket. Here we report preliminary laboratory studies of spectral results on fine-grained rock powers (<45 microns) using Mid-IR (4000-400 cm-1) Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy. The basalts were collected from two profiles in the east and south sections of the crater wall and the upper most crater rim, which later subdivided into sector-wise samples to carry out a systematic study of spectral properties of Lonar basalts, together with impact related samples of breccias and impact melts. For the first time, data of the shock metamorphism of Lonar basalt is examined using DRIFT spectroscopy. Infrared spectra of rock powders of relatively unshocked and shocked basalts are obtained to document the mineralogical variations and the distribution of primary (e.g. Plagioclase Feldspar, Pyroxene), and secondary Phyllosilicate minerals (e.g. Illite, Smectite, Montmorillonite, Saponite, Serpentine) with direction of impact. The spectral data between pre-impact unshocked and post-impact shocked basalts are interpreted to reflect the effect of shock pressure and alteration that rock have undergone. On western crater rim sector, typical silicate spectral features in 900-1200 cm-1 which attributed to Si-O stretching, are observed to change slightly in the width and shift in

  12. 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.

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

    PubMed

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

    2015-01-13

    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

  14. 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

  15. 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.

  16. The equivalent depth of burst for impact cratering

    NASA Technical Reports Server (NTRS)

    Holsapple, K. A.

    1980-01-01

    The concept of modeling an impact cratering 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 impact conditions. The results show a decrease in equivalent d.o.b. with increasing energy for fixed impact 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.

  17. 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.

  18. A Re-Examination of the Relative Ages of Mare-Filled Impact Basins on the Lunar Nearside from the Gravity Signatures of Buried Craters

    NASA Astrophysics Data System (ADS)

    Evans, A. J.; Soderblom, J. M.; Solomon, S. C.; Zuber, M. T.

    2015-05-01

    GRAIL gravity data have revealed more than 100 putative buried impact craters beneath the nearside maria. We use this population of buried craters to re-assess basin chronology and the impact crater density of the lunar nearside.

  19. A Topographic Image Map of the Sabrina Valles Region Including Information on Large Martian Impact Craters

    NASA Astrophysics Data System (ADS)

    Gehrke, S.; Köhring, R.; Barlow, N. G.; Gwinner, K.; Scholten, F.; Lehmann, H.; Albertz, J.

    2007-03-01

    The Catalog of Large Martian Impact Craters provides detailed information on 42,283 craters >5 km; it is planned to be integrated in the Topographic Image Map Mars 1:200,000 series. Such an update is shown in a special target map, based on HRSC data.

  20. 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.; Vaniman, D. T.; Wiens, R. C.; Wittmann, A.

    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.

  1. High Temperature Emplacement of Clastic Breccia Dikes and Implications for the Development and Magnetization of Impact Craters

    NASA Astrophysics Data System (ADS)

    Fairchild, L. M.; Swanson-Hysell, N.; Tikoo, S. M.

    2014-12-01

    Breccia dikes are a common feature of impact craters on Earth and should also be present within impact structures on other planetary bodies. Within the ~450 Ma, ~30 km diameter Slate Islands impact structure in Ontario, Canada, breccia dikes can be classified into two categories: 1) mm-scale irregular or anastomosing veins composed of a fine-grained to glassy matrix with variable clast content (type A of Lambert, 1981) and 2) thicker (2 cm to >15 m wide) polymict breccia bodies intruding parautochthonous host rock (type B of Lambert, 1981). We have targeted the clasts and matrix from 9 type B breccia dikes throughout the impact structure for paleomagnetic analysis. Preliminary results on one dike show that clasts fail a conglomerate test, indicating that they were completely remagnetized after the breccia dike was emplaced. We interpret this result to indicate that lithic breccia dikes can experience levels of frictional heating capable of fully thermally remagnetizing clasts. Furthermore, breccia bodies from different locales yield similar overprint directions minimally affected by tilting or rotation. This implies that these breccia dikes cooled to blocking temperatures at a rate slower than that of crater modification and obtained their magnetic remanence subsequent to the crater's final structural state. The magnetic directions of samples yield a virtual geomagnetic pole (VGP) that can serve as a reference direction for constraining the structural dynamics of crater formation/modification and evaluating the mechanism whereby impact-related overprints were imparted into the host rock. Breccia dikes have been interpreted to be present within impact craters on Mars (Head, 2006) and should be expected in other extraterrestrial impact structures where erosion levels have allowed exposure of the crater substructure. While breccia dike material would either be remagnetized or demagnetized by the impact (depending on the presence or absence of an ambient field), the

  2. 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

  3. The Manannan Impact Crater on Europa: Determination of Surface Compositions of Key Stratigraphic Units

    NASA Astrophysics Data System (ADS)

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

    2011-12-01

    Mannanan is a 22-km-diameter impact crater located at 3 N, 240 W on Europa's orbital trailing side. Detailed high resolution geologic mapping by Moore et al. (2001) revealed the likely presence of extensive deposits of impact melt materials largely filling the crater floor, together with surrounding continuous ejecta deposits that may have been excavated from Europa's interior. Terrains surrounding Mannanàn include some of Europa's visibly darkest surfaces, with extensive areas of chaos, traversed by the prominent structure of Belus Linea. The Mannannàn impact crater and its surrounding areas were imaged during the C3 orbital encounter of the Galileo Mission by the orbiter's Near-Infrared Mapping Spectrometer (NIMS). This NIMS observation (C3ENLINEA01A) has not been subjected to a detailed investigation until now, possibly due to the presence of moderate levels of radiation noise. A "despiked" version of this observation has been produced using methods described in Shirley et al. (2010). In addition, new geologic mapping precisely registered to the NIMS coverage of Manannàn and its surroundings allows the extraction of high-quality near-infrared spectra that are specific to individual geologic units and morphological features. We will present linear mixture modeling solutions for the compositions of several of Manannàn's key stratigraphic units, including the crater floor deposits and the adjacent chaos and linea materials. We will interpret these results in the context of ongoing investigations of the interplay of exogenic and endogenic influences on the surface composition of Europa. This work was performed at the Jet Propulsion Laboratory-California Institute of Technology, Johns Hopkins University-Applied Physics Laboratory, and the SETI Institute under a contract with NASA. Support by NASA's Outer Planets Research program is gratefully acknowledged. Moore, J. M. and 25 others 2001. Impact Features on Europa: Results of the Galileo Europa Mission (GEM

  4. Compositional analysis and classification of projectile residues in LDEF impact craters

    NASA Technical Reports Server (NTRS)

    Horz, Friedrich; Bernhard, Ronald P.

    1992-01-01

    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 impact craters greater than 20 micrometers in diameter. Some 30 percent of the craters 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 impact features on LDEF.

  5. Numerical Modeling of the Impact-Induced Hydrothermal System at Sudbury Crater

    NASA Astrophysics Data System (ADS)

    Abramov, O.; Kring, D. A.

    2003-12-01

    An understanding of impact-generated hydrothermal systems is crucial for deciphering the environment on early Earth and Mars, as well as predicting promising locations for finding evidence of past life on Mars. Impact events and early life may be tightly connected -- a sudden increase in the number of impact events which occurred at ˜3.9 Ga coincides remarkably well with the earliest isotopic evidence of life on Earth at ˜3.85 Ga, and hydrothermal systems generated by impact events can provide a habitable environment for thermophilic organisms. Several hydrothermal systems associated with terrestrial impact craters have been identified on the basis of mineralogical evidence. Examples of known systems include the 35 km Manson crater, the 80 km Puchezh-Katunki crater, and the 250 km Sudbury crater. In order to better constrain the expected lifetimes of these systems and further understand their mechanics, a finite-difference computer simulation is used to evaluate the effects of convective cooling by circulating water and steam. In this work we present modeling results of water and heat transport shortly after the formation of the Sudbury impact crater in present-day Ontario, Canada. Our model predicts that an impact-induced hydrothermal system associated with a Sudbury-sized impact crater can remain active for at least 105 - 106 years. While the location and volume of the habitable zone within the crater changes as the crater undergoes cooling, it is sufficiently long-lived for an ecosystem to develop. The insight into the mechanics of these systems gained from this model can help locate hydrothermal vents and hydrothermally altered minerals at Martian impact craters.

  6. Defrosting processes on the Russell crater megadune of Mars: quantitative analysis and interpretation

    NASA Astrophysics Data System (ADS)

    Douté, S.; Wu, C.; Guo, X.; Luo, B.

    2015-10-01

    The megadune located in the Russell Crater of Mars is the siege of a complex defrosting sequence imply- ing seasonal CO2 and a small amount of water ice in each spring [3]. Besides on its pole facing slope, the dune displays gullies thought to have been carved by liquid water although they could also be related to dry avalanches triggered by the defrosting activity. In order to improve our understanding of seasonal versus secular phenomena, we conducted a quantitative analysis of a time series of joint image pairs : hyperspectral(CRISM) and high-resolution panchromatic (HiRISE),both sensors operating on board MRO. Automatic extraction and characterization of sublimation structures(e.g. dark spots) in the HiRISE images is performed on the basis of their geometry or their texture with image processing methods. The different conditions of CO2 ice are mapped by applying unsupervised linear spec- tral unmixing methods on the CRISM images. Modeling the spectral signatures with a radiative transfer model reveals the structural organization of the ice and its level of dust contamination. Finally we propose a joint interpretation of all the resulting products for understanding the defrosting processes and their role in shaping the dune.

  7. Dating a small impact crater: An age of Kaali crater (Estonia) based on charcoal emplaced within proximal ejecta

    NASA Astrophysics Data System (ADS)

    Losiak, A.; Wild, E. M.; Geppert, W. D.; Huber, M. S.; Jõeleht, A.; Kriiska, A.; Kulkov, A.; Paavel, K.; Pirkovic, I.; Plado, J.; Steier, P.; VäLja, R.; Wilk, J.; Wisniowski, T.; Zanetti, M.

    2016-04-01

    The estimates of the age of the Kaali impact structure (Saaremaa Island, Estonia) provided by different authors vary by as much as 6000 years, ranging from ~6400 to ~400 before current era (BCE). In this study, a new age is obtained based on 14C dating charred plant material within the proximal ejecta blanket, which makes it directly related to the impact structure, and not susceptible to potential reservoir effects. Our results show that the Kaali crater was most probably formed shortly after 1530-1450 BCE (3237 ± 10 14C yr BP). Saaremaa was already inhabited when the bolide hit the Earth, thus, the crater-forming event was probably witnessed by humans. There is, however, no evidence that this event caused significant change in the material culture (e.g., known archeological artifacts) or patterns of human habitation on Saaremaa.

  8. 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

  9. Cracking associated with micrometeoroid impact craters in anodized aluminum alloy clamps on LDEF

    NASA Technical Reports Server (NTRS)

    Murr, Lawrence E.; Niou, Chorng S.; Quinones, Stella; Murr, Kyle S.

    1992-01-01

    The Long Duration Exposure Facility (LDEF) is a reusable hollow-cylindrical satellite sustaining a total of 57 different experiments. The 130 sq m of spacecraft surface area included anodized 6061-T6 Al alloy bay frames and clamps for holding experiment trays in the bay areas. Attention is presently given to the micrometeoroid impact crater features observed on two tray clamps recovered from the LDEF leading-edge locations. It is found that even very subtle surface modifications in structural alloy anodizing can influence micrometeoroid impact crater cracking, notable radial cracking due to the ejecta-rim of the impact craters.

  10. Small craters on the meteoroid and space debris impact experiment

    NASA Technical Reports Server (NTRS)

    Humes, Donald H.

    1995-01-01

    Examination of 9.34 m(exp 2) of thick aluminum plates from the Long Duration Exposure Facility (LDEF) using a 25X microscope revealed 4341 craters 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 crater diameter measured was the diameter at the top of the raised lips. There was a large variation in the number density of craters 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 crater size distribution on the space end of the LDEF. An argument is made that nearly all the craters 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 craters between 10 micron and 100 micron in diameter and 3 craters 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 crater dimensions to meteoroid size. The equations suggest that meteoroids must have a density near 2.5 g/cm(exp 3) to produce craters 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 craters 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.

  11. Martian Polar Region Impact Craters: Geometric Properties From Mars Orbiter Laser Altimeter (MOLA) Observations

    NASA Technical Reports Server (NTRS)

    Garvin, J. B.; Sakimoto, S. E. H.; Frawley, J. J.; Matias, A.

    1998-01-01

    The Mars Orbiter Laser Altimeter (MOLA) instrument onboard the Mars Global Surveyor (MGS) spacecraft has so far observed approximately 100 impact landforms in the north polar latitudes (>60 degrees N) of Mars. Correlation of the topography with Viking Orbiter images indicate that many of these are near-center profiles, and for some of the most northern craters, multiple data passes have been acquired. The northern high latitudes of Mars may contain substantial ground ice and be topped with seasonal frost (largely CO2 with some water), forming each winter. We have analyzed various diagnostic crater topologic parameters for this high-latitude crater population with the objective of characterizing impact features in north polar terrains, and we explore whether there is evidence of interaction with ground ice, frost, dune movement, or other polar processes. We find that there are substantial topographic variations from the characteristics of midlatitude craters in the polar craters that are not readily apparent from prior images. The transition from small simple craters to large complex craters is not well defined, as was observed in the midlatitude MOLA data (transition at 7-8 km). Additionally, there appear to be additional topographic complexities such as anomalously large central structures in many polar latitude impact features. It is not yet clear if these are due to target-induced differences in the formation of the crater or post-formation modifications from polar processes.

  12. Impact melting on Venus: Some considerations for the nature of the cratering record.

    NASA Astrophysics Data System (ADS)

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

    1995-03-01

    Modeling the volume of impact melt and its variation with the size of the impact event indicates that, for similar-sized final craters, venusian impacts create about 25% more impact melt than terrestrial impacts. More significantly, venusian impacts result in approximately a factor of three more impact melt than lunar events producing equivalent-sized craters. This difference is due to the higher average impact velocity and higher ambient temperatures on Venus, which enhance impact-melt production, combined with higher planetary gravity, which inhibits crater growth for a given impact event. The initial, higher intrinsic temperature of incorporated clastic debris also contributes to impact melts with higher initial temperatures, lower viscosities, and longer cooling times on Venus with respect to lunar impact melts. The enhanced production of relatively hot, low-viscosity impact melts under venusian impact conditions may account for the long exterior runout flows and also for the radar-smooth interior floors of some venusian craters. We also argue that the anomalously deep character of Cleopatra may be attributed to drainage of its interior impact-melt pool to form the smooth deposits in the adjacent Fortuna Tessera. Increasing depth of melting with increasing cavity size, resulting in the progressive weakening of transient-cavity floor material, is offered as a possible explanation for the replacement of uplifted central peaks by rings with increasing crater diameter. A consequence of this process is that interior rings will increase in diameter relative to the diameter of the final crater's rim crest with increasing crater size, a trend observed on Venus and other terrestrial planets. This weakening of the target due to relatively enhanced impact-melt production in the venusian environment makes it unlikely that Orientale-style impact basins ever formed on Venus.

  13. Geophysical signature of the Pretoria saltpan impact structure and a possible satellite crater

    NASA Technical Reports Server (NTRS)

    Brandt, D.; Durrheim, R. J.; Reimold, W. U.

    1993-01-01

    The Pretoria Saltpan Crater is located in the southern portion of the Bushveld Igneous Complex, some 40 km NNW of Pretoria, South Africa, at 25 deg 24 min 30 sec S/28 deg 4 min 59 sec E. An origin by impact for this crater structure was recently confirmed. The results of the only gravity reconnaissance carried out over the crater to date failed to support an impact origin. With the aid of recent results obtained from a central drill-core, it was necessary to carry out more geophysical work which would include a gravity profile of higher resolution. A second, smaller, circular depression (about 400 m in diameter) to the SW of the crater is suggestive of a twin crater. This site had never been investigated, and thus various geophysical surveys were conducted.

  14. Scaling of liquid-drop impact craters in wet granular media

    NASA Astrophysics Data System (ADS)

    Zhang, Qianyun; Gao, Ming; Zhao, Runchen; Cheng, Xiang

    2015-10-01

    Combining high-speed photography with laser profilometry, we study the dynamics and the morphology of liquid-drop impact cratering in wet granular media—a ubiquitous phenomenon relevant to many important geological, agricultural, and industrial processes. By systematically investigating important variables such as impact energy, the size of impinging drops, and the degree of liquid saturation in granular beds, we uncover a scaling law for the size of impact craters. We show that this scaling can be explained by considering the balance between the inertia of impinging drops and the strength of impacted surface. Such a theoretical understanding confirms that the unique energy partition originally proposed for liquid-drop impact cratering in dry granular media also applies for impact cratering in wet granular media. Moreover, we demonstrate that compressive stresses, instead of shear stresses, control the process of granular impact cratering. Our study enriches the picture of generic granular impact cratering and sheds light on the familiar phenomena of raindrop impacts in granular media.

  15. Scaling of liquid-drop impact craters in wet granular media.

    PubMed

    Zhang, Qianyun; Gao, Ming; Zhao, Runchen; Cheng, Xiang

    2015-10-01

    Combining high-speed photography with laser profilometry, we study the dynamics and the morphology of liquid-drop impact cratering in wet granular media-a ubiquitous phenomenon relevant to many important geological, agricultural, and industrial processes. By systematically investigating important variables such as impact energy, the size of impinging drops, and the degree of liquid saturation in granular beds, we uncover a scaling law for the size of impact craters. We show that this scaling can be explained by considering the balance between the inertia of impinging drops and the strength of impacted surface. Such a theoretical understanding confirms that the unique energy partition originally proposed for liquid-drop impact cratering in dry granular media also applies for impact cratering in wet granular media. Moreover, we demonstrate that compressive stresses, instead of shear stresses, control the process of granular impact cratering. Our study enriches the picture of generic granular impact cratering and sheds light on the familiar phenomena of raindrop impacts in granular media. PMID:26565233

  16. Periodic impact cratering and extinction events over the last 260 million years

    NASA Astrophysics Data System (ADS)

    Rampino, Michael R.; Caldeira, Ken

    2015-12-01

    The claims of periodicity in impact cratering and biological extinction events are controversial. A newly 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.

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

    SciTech Connect

    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 gross 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.

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

    SciTech Connect

    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 gross 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.

  19. 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.

  20. The number of impact craters on Earth: Any room for further discoveries?

    NASA Astrophysics Data System (ADS)

    Hergarten, S.; Kenkmann, T.

    2015-09-01

    Only 128 impact craters exposed at Earth's surface have been found so far, while new craters are discovered occasionally. Taking into account the permanent consumption of craters by erosion we present the first estimate on the number of impact craters that should be present at Earth's surface. Our study yields no evidence for any systematic incompleteness in the available inventory of the craters larger than about 6 km in diameter exposed at the surface. In contrast, more than 90 craters in the diameter range from 1 km to 6 km should still be waiting to be discovered, and even more than 250 between 0.25 km and 1 km diameter. The transition from a probably complete inventory above 6 km to a strongly incomplete record at smaller sizes may be related to the difference between simple and complex craters. Beyond these results on the terrestrial crater record, our findings tentatively suggest that erosion rates on the 10 to 100 million year scale may be closer to present-day erosion rates than previously assumed.

  1. LDEF impact craters formed by carbon-rich impactors: A preliminary report

    NASA Technical Reports Server (NTRS)

    Bunch, T. E.; Dibrozolo, F. Radicati; Fleming, Ronald H.; Harris, David W.; Brownlee, Don; Reilly, Terrence W.

    1992-01-01

    Two impact craters found in Al from the Long Duration Exposure Facility (LDEF) experiment tray have residues concentrated in the bottoms, along the walls, and on top of overturned rims. Analyses indicate a 'chondritic' compositional signature (Si, S, Ca, Fe, Mg, and Ni) for the bulk residue. In one crater (number 74), round to irregular silicate grains are overlain by carbon. In addition, carbon also partially covers the crater walls, the top of the raised overturned rim, and extends outward from the crater. The second crater (number 31) also contains carbon with similar distribution in and about the crater, although the silicate residue appears to be glassy. Silver, I, K, and F (possibly some of the Ca, S, and Cl) appear to be contaminants as well as analyzed aromatic carbonaceous species associated with the raised rim and the area surrounding the crater. The origin of the impactors is assumed to be extraterrestrial. The existence of impactor residue in two craters implies impact velocities less than or equal to 6 km, based on experimental hypervelocity studies.

  2. Venus - Mead Crater

    NASA Technical Reports Server (NTRS)

    1991-01-01

    This Magellan image mosaic shows the largest (275 kilometers in diameter [170 miles]) impact crater known to exist on Venus at this point in the Magellan mission. The crater is located north of Aphrodite Terra and east of Eistla Regio at latitude 12.5 degrees north and longitude 57.4 degrees east, and was imaged during Magellan orbit 804 on November 12, 1990. The Magellan science team has proposed to name this crater Mead, after Margaret Mead, the American Anthropologist (1901- 1978). All Magellan-based names of features on Venus are, of course, only proposed until final approval is given by the International Astronomical Union-Commission on Planetary Nomenclature. Mead is classified as a multi-ring crater with its innermost, concentric scarp being interpreted as the rim of the original crater cavity. No inner peak-ring of mountain massifs is observed on Mead. The presence of hummocky, radar-bright crater ejecta crossing the radar-dark floor terrace and adjacent outer rim scarp suggests that the floor terrace is probably a giant rotated block that is concentric to, but lies outside of, the original crater cavity. The flat, somewhat brighter inner floor of Mead is interpreted to result from considerable infilling of the original crater cavity by impact melt and/or by volcanic lavas. To the southeast of the crater rim, emplacement of hummocky ejecta appears to have been impeded by the topography of preexisting ridges, thus suggesting a very low ground-hugging mode of deposition for this material. Radar illumination on this and all other Magellan image products is from the left to the right in the scene.

  3. Classification and analysis of candidate impact crater-hosted closed-basin lakes on Mars

    NASA Astrophysics Data System (ADS)

    Goudge, Timothy A.; Aureli, Kelsey L.; Head, James W.; Fassett, Caleb I.; Mustard, John F.

    2015-11-01

    We present a new catalog of 205 candidate closed-basin lakes contained within impact craters across the surface of Mars. These basins have an inlet valley that incises the crater rim and flows into the basin but no visible outlet valley, and are considered candidate closed-basin lakes; the presence of a valley flowing into a basin does not necessitate the formation of a standing body of water. The major geomorphic distinction within our catalog of candidate paleolakes is the length of the inlet valley(s), with two major classes - basins with long (>20 km) inlet valleys (30 basins), and basins with short (<20 km) inlet valleys (175 basins). We identify 55 basins that contain sedimentary fan deposits at the mouths of their inlet valleys, of which nine are fed by long inlet valleys and 46 are fed by short inlet valleys. Analysis of the mineralogy of these fan deposits suggests that they are primarily composed of detrital material. Additionally, we find no evidence for widespread evaporite deposit formation within our catalog of candidate closed-basin lakes, which we conclude is indicative of a general transience for any lakes that did form within these basins. Morphometric characteristics for our catalog indicate that as an upper limit, these basins represent a volume of water equivalent to a ∼1.2 m global equivalent layer (GEL) of water spread evenly across the martian surface; this is a small fraction of the modern water ice reservoir on Mars. Our catalog offers a broader context within which results from the Mars Science Laboratory Curiosity rover can be interpreted, as Gale crater is a candidate closed-basin lake contained within our catalog. Gale is also one of 12 closed-basin lakes fed by both long and short inlet valleys, and so in␣situ analyses by Curiosity can shed light on the relative importance of these two types of inlets for any lacustrine activity within the basin.

  4. Comparing Radar and Optical Data Sets of Lunar Impact Crater Ejecta

    NASA Astrophysics Data System (ADS)

    Stickle, A. M.; Patterson, G.; Cahill, J.; Grier, J.

    2015-12-01

    Impact cratering is a primary weathering process of airless bodies and is the dominant method of redistributing material across the lunar surface. Crater ejecta blankets are a window into the impact cratering process and can provide important information on the properties of subsurface materials as well as surface evolution. Radar scattering information, in particular the circular polarization ratio (CPR), provides a useful means of investigating these properties. Using data returned from the Mini-RF instrument onboard NASA's LRO, we observe significant diversity in the CPR around young mare craters as a function of distance from the crater rim, regardless of crater size or relative age. Some commonalities in the scattering profiles are observed for all crater diameters: higher CPR values occur near the crater rim that decay with radial distance outward, larger craters have a higher CPR than smaller craters, and the overall shapes of the profiles are similar such that the main scattering characteristics of the studied craters can generally be grouped into three main categories. Comparing CPR profiles with data at other wavelengths provides additional insights and suggests two interesting results. The first is that comparisons of radar and optical data imply relationships between mare subsurface stratigraphy and structure and the relative size of the material found within the ejecta blanket. Of the examined craters, twelve have shelves of approximately constant CPR as well as discrete layers outcropping in the subsurface, and nine fall along a trend line when comparing shelf-width with thickness of subsurface layers. The second is that comparisons of radar data with other wavelengths may provide insights into the maturity of the surface. For example, some examined craters have laterally extensive, optically bright ejecta blankets suggesting that a region of rough, high-CPR material should be present near the crater rim, though this is not observed. Radar data is

  5. The Deep Impact crater on 9P/Tempel-1 from Stardust-NExT

    NASA Astrophysics Data System (ADS)

    Schultz, Peter H.; Hermalyn, Brendan; Veverka, Joe

    2013-02-01

    The Stardust-NExT (SdN) mission returned to Comet 9P/Tempel-1 and viewed the site of the Deep Impact (DI) collision just over one comet year later. Comparisons between pre-impact images from the ITS camera on the DI probe and SdN images reveal a 50 m-diameter crater surrounded by a low rim about 180 m in diameter. The removal of a small mound uprange (but offset from the trajectory) from the impact site can be related to changes in the evolution of ejecta. A narrow (6°) gap in the ejecta curtain downrange indicates that a ridge extending from the impact-facing scarp downrange interrupted the final stages of cratering in one small region. Together, these observations indicate that the DI excavation crater diameter was about 200 m (±20 m), a value consistent with the ejected mass derived from Earth- and space-based observations with the assumption that this mass represents only 10-20% of the total ejected mass. As a result, the DI crater visible today is consistent with either a larger transient crater, which collapsed, or a central crater of a nested crater resembling an inverted sombrero. The latter alternative would be expected from a layered target: a loose particulate surface about 1-2 m deep over a slightly more competent substrate.

  6. Anomalous quartz from the Roter Kamm impact crater, Namibia: Evidence for post-impact hydrothermal activity

    SciTech Connect

    Koeberl, C. Univ. of Vienna ); Fredriksson, K. ); Goetzinger, M. ); Reimold, W.U. )

    1989-08-01

    Centimeter-sized quartz pebbles have been found on the rim of the Roter Kamm impact crater. The Roter Kamm crater has a diameter of about 2.5 km and is situated in the Namib Desert, SWA/Namibia. Because of the sand coverage, impact products are exposed exclusively in the form of ejecta on the crater rim. The quartz pebbles were found close to the main deposits of the impact breccias and show signs of wind abrasion. Thin sections revealed that the pebbles consist of individual quartz domains that are up to 1 mm in size. Under crossed nicols (polarized light), all individual domains show extinction almost simultaneously within {plus minus}2{degree}, which is a rare phenomenon. Microprobe studies, neutron activation analyses, and X-ray diffractometry confirmed that the material consists of pure quartz. The quartz contains three different types of fluid inclusions: primary inclusions that record the formation conditions of the quartz, very small (<1 {mu}m) secondary inclusions associated with the grain boundaries, and late inclusions of irregular size. Freezing point depression measurements of the primary inclusions indicate fluid salinities between 18.3 and 19.6 wt% NaCl. Homogenization temperatures (T{sub h}) for the primary inclusions range from 165 to 250{degree}C. The quartz and the primary inclusions may provide evidence for a post-impact phase of extensive hydrothermal activity, generated by the residual heat from the kinetic energy of the impact.

  7. Impact Cratering Experiment for a Course in Lunar and Planetary Geology.

    ERIC Educational Resources Information Center

    Smith, Eugene; And Others

    1980-01-01

    Described is an inexpensive and safe laboratory experiment that accurately duplicates the shapes and structures of simple impact craters using fireplace ash, finely ground charcoal, and an air gun. (Author/DS)

  8. Ice-associated Impact Craters on Mars: Implications from MOLA Observations

    NASA Astrophysics Data System (ADS)

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

    1999-03-01

    Impact craters adjacent to the North Polar Cap on Mars are observed to display anomalously large amounts of infill, with 10-20 m scale layering in some cases. This suggests dynamic modification of these features.

  9. Understanding Spatial Statistics for Purposes of Identifying Non-Primary and Saturated Impact Crater Populations

    NASA Astrophysics Data System (ADS)

    Riggs, J. D.; Robbins, S. J.; Kirchoff, M. R.; Bierhaus, E. B.; Weaver, B. P.

    2015-05-01

    We discuss some traditional unidimensional summarization statistics and some newer spatial point statistical methods for understanding and identifying non-primary and saturated impact crater populations observed on a variety of solar system bodies.

  10. Carbonate Melts and Sedimentary Impactite Variation at Crooked Creek and Decaturville Impact Craters, Missouri, USA

    NASA Astrophysics Data System (ADS)

    Beauford, R. E.

    2012-03-01

    The Crooked Creek and Decaturville, Missouri, impact craters offer an opportunity to understand variation in impactite lithologies in carbonate and mixed sedimentary environments. Impactites involve mixes of carbonates, sandstone, chert, and shale.

  11. Cleopatra crater on Venus: Venera 15/16 data and impact/volcanic origin controversy

    SciTech Connect

    Basilevsky, A.T. ); Ivanov, B.A. )

    1990-02-01

    Cleopatra structure is a 100-km diameter feature having a morphology similar to that of double-ring basins of the Moon and Mercury and dissimilar to that of volcanic calderas on Mars, Earth, and Venus. The 2.4-km depth of Cleopatra is anomalously large compared to venusian and terrestrial impact craters of equivalent diameters. An impartial summary of the situation is as follows: if Cleopatra is a volcanic caldera, it is a strange caldera, if Cleopatra is an impact crater, it is a strange crater.

  12. Impact Crater Geometries Provide Evidence for Ice-rich Layers at Low Latitudes on Mars

    NASA Technical Reports Server (NTRS)

    Black, B. A.; Stewart, S. T.

    2005-01-01

    The impact cratering record documents the history of resurfacing events on Mars. The morphology and distribution of layered (rampart) ejecta blankets provide insights into the presence of volatiles in the upper crust [1-4]. The physical properties of the crust and history of water have been revealed through recent quantitative studies of the geometry of Martian craters [5-91. Here, we present the results from a study focused on impact craters in Utopia Planitia and the Elysium Mons province to infer the history and properties of resurfacing episodes.

  13. Analyses of radar images of small craters

    NASA Astrophysics Data System (ADS)

    Greeley, R.; Christensen, P. R.; McHone, J. F.

    1985-04-01

    Clouds hide the surface of Venus from all but radar imaging systems, supplemented by limited views from land spacecraft. Among the surfaces features likely to be observed by radar are craters that have formed by a variety of processes. In order to assess the radar characteristics of craters, volcanic craters and impact structures on Earth are described as imaged by the Shuttle Imaging Radar (SIR-A) experiment. Although most of the craters are small, this analysis provides insight into the ability to discriminate craters of various origins and provides some basis for interpreting radar images returned from Venus.

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

    NASA Technical Reports Server (NTRS)

    Humes, Donald H.

    1992-01-01

    Examination of 29.37 sq m of thick aluminum plates from the LDEF, which were exposed to the meteoroid and man-made orbital debris environments for 5.8 years, revealed 606 craters that were 0.5 mm in diameter or larger. Most were nearly hemispherical. There was a large variation in the number density of craters around the three axis gravity gradient stabilized spacecraft. A new model of the near-Earth meteoroid environment gives good agreement with the crater fluxes measured on the fourteen faces of the LDEF. The man-made orbital debris model of Kessler, which predicts that 16 pct. of the craters would be caused by man-made debris, is plausible. No chemical analyses of impactor residue that will distinguish between meteoroids and man-made debris is yet available.

  15. Measured and Modeled Morphometry of Simple Impact Craters

    NASA Astrophysics Data System (ADS)

    Watters, W. A.; Collins, G. S.

    2015-09-01

    We discuss the measured diameter dependence of well-preserved simple crater morphometry on Mars and compare with iSALE simulations. We also describe future work to fully characterize the dependence on impactor velocity and mass, and target properties.

  16. 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.

  17. 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.

  18. The gravity signature of mantle uplift from impact modeling craters on the Moon

    NASA Astrophysics Data System (ADS)

    Milbury, Colleen; Johnson, Brandon C.; Melosh, H. Jay; Collins, Gareth S.; Blair, David M.; Soderblom, Jason M.; Zuber, Maria T.

    2014-11-01

    NASA’s dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have globally mapped the lunar gravity field at unprecedented resolution; this has enabled the study of lunar impact craters of all sizes and ages. Soderblom et al. [2014, LPSC abstract #1777] calculated the residual Bouguer anomalies for ~2700 craters 27-184 km in diameter (D). They found that the residual central Bouguer anomaly of craters smaller than 100 km is essentially zero, that there is a transition for 100-150 km, and that craters larger than 184 km have a positive residual Bouguer anomaly that increases with increasing crater size. We use the iSALE shock physics hydrocode to model crater formation, including the effects of porosity and dilatancy (shear bulking). We use strength parameters of gabbroic anorthosite for a 35-km-thick crust, and dunite for the mantle. Our dunite impactors range in size from 6-30 km, which produce craters 86-450 km in diameter. We calculate the Bouguer gravity anomaly due solely to mantle uplift. We eliminate the effects of pressure and temperature on density by setting the output densities from the simulations to 2550 kg/m^3 if they are below the cutoff value of 3000 kg/m^3, and 3220 kg/m^3 if they are above. We compare our modeling results to gravity data from GRAIL. We find that the crater size at which mantle uplift dominates the crater gravity occurs at a crater diameter that is close to the complex crater to peak-ring basin transition. This is in agreement with the observed trend reported by Soderblom et al. [2014, LPSC abstract #1777].

  19. 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

  20. Control of impact crater fracture systems on subsurface hydrology, ground subsidence, and collapse, Mars

    USGS Publications Warehouse

    Rodriguez, J.A.P.; Sasaki, S.; Dohm, J.M.; Tanaka, K.L.; Strom, B.; Kargel, J.; Kuzmin, R.; Miyamoto, H.; Spray, J.G.; Fairen, A.G.; Komatsu, G.; Kurita, K.; Baker, V.

    2005-01-01

    Noachian layered materials are pervasively exposed throughout the highlands of Mars. The layered deposits, in places many kilometers thick, exhibit impact craters of diverse morphologic characteristics, ranging from highly degraded to pristine, most of which formed during the period of heavy bombardment. In addition, exhumed impact craters, ancient channels, and fluvial and alluvial fans are visible in the layered deposits through MOC imagery. These features are more abundant in Noachian terrains, which indicates relatively high erosion rates during ancient Mars that competed with heavy meteoritic bombardment. The Noachian layered materials are thus expected to contain numerous buried impact craters in various states of preservation. Here, we propose that impact craters (buried and exposed) and associated fracture systems dominate the basement structural fabric of the ancient highlands and that they have significantly influenced the hydrogeology. Diversity in the occurrence of high and low densities of impact craters and associated fracture systems controls the magnitude of the local effects of magmatic-driven hydrothermal activity. In and surrounding the Tharsis region, for example, the formation of chaotic terrains (the source regions of the circum-Chryse outflow channel system) and a large diversity of collapse structures, including impact crater moats and pit chains, appear to be the result of enhanced hydrothermal activity. Copyright 2005 by the American Geophysical Union.

  1. 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

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

    USGS Publications Warehouse

    Self-Trail J.M.

    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.

  3. Production of impact melt in craters on Venus, Earth, and the moon

    NASA Technical Reports Server (NTRS)

    Vickery, A. M.; Melosh, H. J.

    1991-01-01

    Impact craters imaged by Magellan clearly show large amounts of flow-like ejecta whose morphology suggests that the flows comprise low-viscosity material. It was suggested that this material may be either turbidity flows or very fine-grained ejecta, flows of ejecta plus magma, or impact melts. The last of these hypotheses is considered. If these flows are composed of impact melts, there is much more melt relative to the crater volume than is observed on the moon. The ANEOS equation of state program was used for dunite to estimate the shock pressures required for melting, with initial conditions appropriate for Venus, Earth, and the moon. A simple model was then developed, based on the Z-model for excavation flow and on crater scaling relations that allow to estimate the ratio of melt ejecta to total ejecta as a function of crater size on the three bodies.

  4. Large-Scale Impact Cratering and Early Earth Evolution

    NASA Technical Reports Server (NTRS)

    Grieve, R. A. F.; Cintala, M. J.

    1997-01-01

    The surface of the Moon attests to the importance of large-scale impact in its early crustal evolution. Previous models of the effects of a massive bombardment on terrestrial crustal evolution have relied on analogies with the Moon, with allowances for the presence of water and a thinner lithosphere. It is now apparent that strict lunar-terrestrial analogies are incorrect because of the "differential scaling" of crater dimensions and melt volumes with event size and planetary gravity. Impact melt volumes and "ancient cavity dimensions for specific impacts were modeled according to previous procedures. In the terrestrial case, the melt volume (V(sub m)) exceeds that of the transient cavity (V(sub tc)) at diameters > or = 400 km. This condition is reached on the Moon only with transient cavity diameters > or = 3000 km, equivalent to whole Moon melting. The melt volumes in these large impact events are minimum estimates, since, at these sizes, the higher temperature of the target rocks at depth will increase melt production. Using the modification-scaling relation of Croft, a transient cavity diameter of about 400 km in the terrestrial environment corresponds to an expected final impact "basin" diameter of about 900 km. Such a "basin" would be comparable in dimensions to the lunar basin Orientale. This 900-km "basin" on the early Earth, however, would not have had the appearance of Orientale. It would have been essentially a melt pool, and, morphologically, would have had more in common with the palimpsests structures on Callisto and Ganymede. With the terrestrial equivalents to the large multiring basins of the Moon being manifested as muted palimpsest-like structures filled with impact melt, it is unlikely they played a role in establishing the freeboard on the early Earth. The composition of the massive impact melt sheets (> 10 (exp 7) cu km) produced in "basin-forming" events on the early Earth would have most likely ranged from basaltic to more mafic for the

  5. Towards a Unified Theory of Impacts and Crater Populations on Icy Satellites

    NASA Astrophysics Data System (ADS)

    Bierhaus, Edward B.; Robbins, Stuart; Dones, Luke

    2014-11-01

    We present our recent work to derive a unified, self-consistent model for the divergent crater populations seen on the Saturnian (and Galilean) satellites. We attack this problem from multiple fronts: modeling the flux of impactors, the resulting primary craters on the satellites' surfaces, modeling the production of ejecta fragments and their corresponding secondary craters, and correlation between the modeling and measured crater populations on the satellites.Our recent work includes (i) quantifying the expected secondary populations, and (ii) extensive crater measurements against which to compare our models. For (i), we find that the interplay between v_min (the min speed to make a crater), v_esc, surface gravity, and the inverse relationship between ejection speed and fragment size, result in different secondary crater populations on satellites. For (ii), we found that the escape speed on Mimas is so small that secondaries may not form on that satellite, or if they do, they are too small to be seen at currently available image resolution. We are expanding our measurements on Rhea, on which we predict a measurable and significant secondary crater population. We will continue our measurements to include Tethys, Dione, Iapetus, and Hyperion, and will compare those with existing measurements of the icy Galilean satellites.We find that the different combinations of impact speeds and surface gravities across the satellites, in conjunction with minimum (v_min) and maximum (v_esc) speeds, produce a diverse set of outcomes between primary crater sizes and secondary crater production and distribution; the net effect is that a single impacting population (e.g. comets) can generate different crater populations. These predictions have been borne out by the crater measurements made to date. Thus it may not be necessary to appeal to multiple or time-dependent impacting populations to explain differences observed in the crater populations on the mid-sized Saturnian satellites

  6. Spectral changes with the direction of asteroid impact at Lonar crater, India: Findings from Mid-IR DRIFT analysis

    NASA Astrophysics Data System (ADS)

    Basavaiah, Nathani; Shriram Chavan, Rajesh

    2013-04-01

    thus serves as measure of the crystallinity and mineralogy of the rock. All these distinctive spectral changes are inferred as caused by pressure-induced structural distortions in bending and stretching motions of Si and Al tetrahedra dominantly within plagioclase feldspars rich basalts [2,3].The IR patterns in this relatively high pressure western sector are interpreted as a mixture of decreasing amounts of Tectosilicates, Ionosilicates and increasing amounts of Phyllosilicates. Thus, in shocked samples, crystalline and amorphous phases are likely coexist as intimate mixtures with the proportion of primary mineralogy decreases with increasing shock pressure resulting in the gradual disappearance of small absorption bands below 500 cm-1. Additionally, Omnic-present mineral distribution maps reveal abundance of primary and secondary minerals around the crater. These abundance maps are interpreted to reflect the effect of shock pressure distribution at Lonar. Future multi-technique spectroscopic studies (Emission, µ-FTIR, ATR, XRD and XRF) are targeted to reflect overall impact-, alteration- and weathering-processes occurring at Lonar crater and Mars. References: [1] Fredriksson, K. et al (1973), Science, 180,862-864 [2] R.Ostertag (1983), JGR,88, B364-B376 [3] J.R.Johnson et al. (2007), American Mineralogist, 92,1148-1157.

  7. Chicxulub Impact Crater and Yucatan Carbonate Platform - PEMEX Oil Exploratory Wells Revisited

    NASA Astrophysics Data System (ADS)

    Pérez-Drago, G.; Gutierrez-Cirlos, A. G.; Pérez-Cruz, L.; Urrutia-Fucugauchi, J.

    2008-12-01

    Geophysical oil exploration surveys carried out by PEMEX in the 1940's revealed occurrence of an anomalous pattern of semi-circular concentric gravity anomalies. The Bouguer gravity anomalies covered an extensive area over the flat carbonate platform in the northwestern Yucatan Peninsula; strong density contrasts were suggestive of a buried igneous complex or basement uplift beneath the carbonates, which was referred as the Chicxulub structure. The exploration program carried out afterwards included a drilling program, starting with Chicxulub-1 well in 1952 and comprising eight deep boreholes through the 1970s. An aeromagnetic survey in late 1970's showed high amplitude anomalies in the gravity anomaly central sector. Thus, research showing Chicxulub as a large complex impact crater formed at the K/T boundary was built on the PEMEX decades-long exploration program. Despite frequent reference to PEMEX information and samples, original data and cores have not been openly available for detailed evaluation and integration with results from recent investigations. Core samples largely remain to be analyzed and interpreted in the context of recent marine, aerial and terrestrial geophysical surveys and the drilling/coring projects of UNAM and ICDP. In this presentation we report on the stratigraphy and paleontological data for PEMEX wells: Chicxulub- 1 (1582m), Sacapuc-1 (1530m), Yucatan-6 (1631m), Ticul-1 (3575m) Yucatan-4 (2398m), Yucatan-2 (3474m), Yucatan-5A (3003m) and Yucatan-1 (3221m). These wells remain the deepest drilled in Chicxulub, providing samples of impact lithologies, carbonate sequences and basement, which give information on post- and pre-impact stratigraphy and crystalline basement. We concentrate on stratigraphic columns, lateral correlations and integration with UNAM and ICDP borehole data. Current plans for deep drilling in Chicxulub crater target the peak ring and central sector, with offshore and onshore boreholes proposed to the IODP and ICDP

  8. Siderophile element fractionation in meteor crater impact glasses and metallic spherules

    NASA Technical Reports Server (NTRS)

    Mittlefehldt, David W.; See, T. H.; Scott, E. R. D.

    1993-01-01

    Meteor Crater, Arizona provides an opportunity to study, in detail, elemental fractionation processes occurring during impacts through the study of target rocks, meteorite projectile and several types of impact products. We have performed EMPA and INAA on target rocks, two types of impact glass and metallic spherules from Meteor Crater. Using literature data for the well studied Canyon Diablo iron we can show that different siderophite element fractionations affected the impact glasses than affected the metallic spherules. The impact glasses primarily lost Au, while the metallic spherules lost Fe relative to other siderophile elements.

  9. 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

  10. Pre-impact crustal porosity and its effect on the gravity signature of lunar craters

    NASA Astrophysics Data System (ADS)

    Milbury, Colleen; Johnson, Brandon C.; Melosh, H. Jay; Collins, Gareth C.; Blair, David M.; Soderblom, Jason M.; Zuber, Maria T.

    2015-04-01

    NASA's dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft have globally mapped the lunar gravity field at unprecedented resolution. Soderblom et al. [2015] made a comprehensive analysis of the residual and central uplift Bouguer gravity anomalies associated with more than 5200 lunar craters. There were two main observations that are related to the work presented here: 1) craters less than ~150 km in diameter (D) have a residual Bouguer anomaly (BA) that is near zero on average (although a negative trend is observed), but have both positive and negative anomalies that vary by approximately ±25 mGal about the mean, and, 2) there is a transition at which the central uplift BA becomes positive and increases with D. Craters that are located in the maria and South Pole-Aitken (SPA) basin were excluded from the analysis because they tend to have more negative signatures than highlands craters. These gravitational signatures contrast with the invariably negative gravity anomalies associated with terrestrial craters. In this study, we investigate pre-impact porosity by modeling crater formation using the iSALE hydrocode, including a new approach to include dilatancy, to determine their effects on the gravity signature of craters. We calculated the BA for the simulations, but due to mantle uplift alone. We find that the magnitude of the BA increases with increasing porosity, and that variable initial porosity of the lunar crust can explain why craters on the Moon exhibit both positive and negative Bouguer anomalies. This can also explain the observed negative residual BA associated with craters formed in the lunar maria and SPA (and associated melt sheet) because they are typically less porous than the highlands crust. Gravity anomalies due to mantle uplift reproduce the observed transition from zero to a positive central uplift BA, which coincides with the morphological transition from complex craters to peak-ring basins.

  11. Laboratory investigations of marine impact events: Factors influencing crater formation and projectile survivability

    NASA Astrophysics Data System (ADS)

    Milner, D. J.; Baldwin, E. C.; Burchell, M. J.

    2008-12-01

    Given that the Earth’s surface is covered in around two-thirds water, the majority of impact events should have occurred in marine environments. However, with the presence of a water layer, crater formation may be prohibited. Indeed, formation is greatly controlled by the water depth to projectile diameter ratio, as discussed in this paper. Previous work has shown that the underlying target material also influences crater formation (e.g., Gault and Sonett 1982; Baldwin et al. 2007). In addition to the above parameters we also show the influence of impact angle, impact velocity and projectile density for a variety of water depths on crater formation and projectile survivability. The limiting ratio of water depth to projectile diameter on cratering represents the point at which the projectile is significantly slowed by transit through the water layer to reduce the impact energy to that which prohibits cratering. We therefore study the velocity decay produced by a water layer using laboratory, analytical and numerical modelling techniques, and determine the peak pressures endured by the projectile. For an impact into a water depth five times the projectile diameter, the velocity of the projectile is found to be reduced to 26-32% its original value. For deep water impacts we find that up to 60% of the original mass of the projectile survives in an oblique impact, where survivability is defined as the solid or melted mass fraction of the projectile that could be collected after impact.

  12. Basalt depths in lunar basins using impact craters as stratigraphic probes: Evaluation of a method using orbital geochemical data

    NASA Technical Reports Server (NTRS)

    Andre, C. G.

    1986-01-01

    A rare look at the chemical composition of subsurface stratigraphy in lunar basins filled with mare basalt is possible at fresh impact craters. Mg/Al maps from orbital X-ray flourescence measurements of mare areas indicate chemical anomalies associated with materials ejected by large post-mare impacts. A method of constraining the wide-ranging estimates of mare basalt depths using the orbital MG/Al data is evaluated and the results are compared to those of investigators using different indirect methods. Chemical anomalies at impact craters within the maria indicate five locations where higher Mg/Al basalt compositions may have been excavated from beneath the surface layer. At eight other locations, low Mg/Al anomalies suggest that basin-floor material was ejected. In these two cases, the stratigraphic layers are interpreted to occur at depths less than the calculated maximum depth of excavation. In five other cases, there is no apparent chemical change between the crater and the surrounding mare surface. This suggests homogeneous basalt compositions that extend down to the depths sampled, i.e., no anorthositic material that might represent the basin floor was exposed.

  13. Microwave scattering and emission properties of large impact craters on the surface of Venus

    NASA Technical Reports Server (NTRS)

    Stacy, N. J. S.; Campbell, D. B.; Devries, C.

    1992-01-01

    Many of the impact craters on Venus imaged by the Magellan synthetic aperture radar (SAR) have interior floors with oblique incidence angle backscatter cross sections 2 to 16 times (3 dB to 12 dB) greater than the average scattering properties of the planet's surface. Such high backscatter cross sections are indicative of a high degree of wavelength-scale surface roughness and/or a high intrinsic reflectivity of the material forming the crater floors. Fifty-three of these (radar) bright floored craters are associated with 93 percent of the parabolic-shaped radar-dark features found in the Magellan SAR and emissivity data, features that are thought to be among the youngest on the surface of Venus. It was suggested by Campbell et al. that either the bright floors of the parabolic feature parent craters are indicative of a young impact and the floor properties are modified with time to a lower backscatter cross section or that they result from some property of the surface or subsurface material at the point of impact or from the properties of the impacting object. As a continuation of earlier work we have examined all craters with diameters greater than 30 km (except 6 that were outside the available data) so both the backscatter cross section and emissivity of the crater floors could be estimated from the Magellan data.

  14. Shocking H2O Ice: The Role of Phase Changes during Impact Crater Formation

    NASA Astrophysics Data System (ADS)

    Stewart, S. T.; Senft, L. E.; Seifter, A.; Obst, A. W.

    2008-12-01

    New experimental data and cratering calculations illustrate the complex response of H2O ice to shock compression. We present peak and post-shock temperature measurements from shocked H2O ice. In experiments with shock pressures between 8 and 14 GPa, initially ~150 K ice is compressed to a supercritical state. In the time frame of the experiment, the supercritical H2O releases to the saturation vapor curve and does not achieve full decompression. Further decompression requires a significant volume expansion. In general, the time scale of expansion will depend on the internal energy and the surrounding conditions (e.g., confined or unconfined). The temperature data validate a new 5-Phase hydrocode equation of state model for H2O, which includes ice Ih, VI, VII, liquid, and vapor. Using the 5-Phase EOS, we model impact cratering onto icy satellites. After passage of the impact-generated shock wave, material beneath the growing transient crater has a layered composition: vapor, liquid, high- pressure phases (ices VII and VI), and ice Ih. The high pressure phases cannot fully decompress without a large volume increase. Thus, these phases initially unload to the pressure along the phase boundary; this pressurized region affects the excavation flow field. The changes in crater excavation lead to differences in crater size and amount of ejecta compared to excavation in a homogeneous target. The differences are significant for large craters (e.g., complex craters on Ganymede and Callisto). The modified excavation flow field also concentrates highly shocked material in the crater floor. In cases where a large, hot plug is buried during crater collapse, explosions occur as the material cools by transforming to vapor, producing features similar to central pits observed on Ganymede, Callisto, and Mars. The behavior of shocked H2O ice during decompression should lead to a variety of features that depend on the ambient conditions specific to each icy planetary body.

  15. 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

  16. The enigmatic Zerelia twin-lakes (Thessaly, Central Greece): two potential meteorite impact Craters

    NASA Astrophysics Data System (ADS)

    Dietrich, V. J.; Lagios, E.; Reusser, E.; Sakkas, V.; Gartzos, E.; Kyriakopoulos, K.

    2013-09-01

    Two circular permanent lakes of 150 and 250 m diameter and 6-8 m depth to an unconsolidated muddy bottom occur 250 m apart from each other in the agricultural fields SW of the town of Almiros (Thessaly, central Greece). The age of the lakes is assumed to be Late Pliocene to Early Holocene with a minimum age of approx. 7000 yr BP. The abundant polymict, quartz-rich carbonate breccia and clasts with a clay rich matrix in the shallow embankments of the lakes show weak stratification but no volcanic structures. The carbonate clasts and particles often display spheroidal shapes and consist of calcite aggregates with feathery, arborescent, variolitic to micro-sparitic textures and spheroidal fabrics, recrystallized and deformed glass-shaped fragments, calcite globules in quartz; thus indications of possible carbonate melting, quenching and devitrification. The carbonatic matrix includes small xenomorphic phases, such as chromspinel, zircon with blurred granular and skeletal textures, skeletal rutile and ilmenite, which are interpreted as relicts of partial melting and quenching under high temperatures of 1240-1800 °C. Only a few quartz fragments exhibit indistinct planar fractures. In several cases they include exotic Al-Si- and sulfur bearing Fe-phases, < 1-10 μm as globules. The modeled "Residual Gravity" profiles through the lakes indicate negative gravity anomalies of bowl-type structures down to 150 m for the eastern lake and down to 250 m for the larger western lake. Several hypotheses can be drawn upon to explain the origin of these enigmatic twin-lakes: (a) Maar-type volcanic craters; (b) hydrothermal or CO2/hydrocarbon gas explosion craters; (c) and (d) doline holes due to karstification; or (e) small meteorite impact craters, the latter being a plausible explanation due to geologic, petrologic, and geophysical evidence. The morphology and dimensions of the lakes as well as the density contrast tomography of the bedrock favor a meteorite impact hypothesis of a

  17. The Highway Flow in the Craters of the Moon Lava Field; A New Interpretation of Eruption History

    NASA Astrophysics Data System (ADS)

    Caress, M. E.; Owen, D. E.

    2005-12-01

    The Highway flow is a trachyandesitic lava flow that lies west of Sunset Cone in the Craters of the Moon lava field, and is part of a complex series of eruptive events that took place in the vicinity of North Crater during the most recent eruptive episode of the field (2,500-2,000 years ago). The trachyandesitic Devil's Orchard and Serrate flows originated from the same vicinity during this period, and carried large masses of rafted cinder cone blocks and disaggregated cinder cone material up to 12 km to the east. The rafted blocks have long been thought to be the remnants of a disintegrating North Crater cinder cone. However, recent work has established that the flows carry a cumulative volume of rafted blocks too large to have come from the existing breach in North Crater. Previous studies had postulated the Highway flow vent to be on the north side of North Crater, and suggested the lava had flowed north, and later drained back to the south when the Highway fault downdropped the vent area. This study examined lava flow characteristics and flow direction indicators based on flow fold patterns interpreted from aerial photographs and field mapping to provide new insight into the complicated history of the Highway flow. We found two vents on the northern side of the flow, and evidence that the lava flowed to the south and ponded against a formerly present cinder cone, which we have named "South Highway Cone". The following sequence of events for eruption of the Highway flow is hypothesized: 1) eruption from two linear vent systems in the northern part of the present day flow 2) flow from the second vent southward, down the valley between Sunset and Grassy Cones 3) ponding of the lava flow at the base of the South Highway Cone and 4) downdrop to the south along the Highway fault due to collapse into a lava chamber beneath South Highway Cone. The rafted blocks in the Devil's Orchard and Serrate flows represent pieces of North Crater and the now hypothesized South

  18. Afekan Crater, Titan: Estimation of Impact Conditions.

    NASA Astrophysics Data System (ADS)

    Echaurren, J. C.

    2011-12-01

    Introduction: Titan has very few impact craters. With more than 30% of the surface now imaged by Cassini Radar through data take T44 there are only seven certain impact structures known. The certain craters have two distinct morphologies, and the probable craters appear to mostly be more degraded version of these two types [1]. In relation to Afekan crater, with a diameter of~115 km, its ejecta blanket is largely covered by surrounding surface materials, its rim is extensively cut by chutes, and the broad flat floor carries a small central peak [1]. In this work are estimated the possible impact conditions, that could have given origin to this crater [2]. The models used here, are based on: some equations postulated by Holsapple (crater depth) [4]; scaling; polynomial analysis; and adaptation of quantum formalism for the mathematical representation of the energy pulse generated in the impact point, in where besides, is used one solution (soliton type) of the Korteweg-De Vries's equation [3]. The development of this crater is realized in 4 stages [5], in which are specified the variables of impact more common [5], as follows: a). Contact/Compression Stage: Diameter of impactor~28.6 km, velocity of impact~6.2 km/s,i.e., between 3 km/s and 15 km/s according [6], impact angle~82.8°, density of impactor~1.1 gm/cm3, volume of melt~1,449.4 km3, total energy of impact~1.6×1030 Erg, pressure to 1 km of the impact point~11,974.4 Gpa, the seismic shock-wave magnitude is>10.0 according the Richter Scale. b). Modification/Excavation Stage: Diameter of transient crater~76.6 km, number of ejected fragments~4.4×1010, the average size of fragments~11.9 m, average density of fragments~1.5 gm/cm3, distance of ejection of fragments~245.7 km, velocity of ejection~902.6 m/s, minimal angle of ejection~12.1°, maximum height of ejection~13.1 km. c). Collapse/Modification Stage: In this stage the pressure toward the final crater rim decrease to~3.6 Gpa. d

  19. 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

  20. Asteroid Impacts, Crater Scaling Laws, and a Proposed Younger Age for Venus's Surface

    NASA Astrophysics Data System (ADS)

    Bottke, William; Ghent, Rebecca; Mazrouei, Sara; Robbins, Stuart; Vokrouhlicky, David

    2015-11-01

    A fascinating on-going debate concerns the asteroid sizes needed to form certain large craters. For example, numerical hydrocode models predict that ~12-14 km and ~8 km diameter asteroids are needed to produce craters like Chicxulub (~180 km) and Popigai (~100 km), respectively. The abundance of extraterrestrial Ir/Os measured at well-characterized impact boundaries on land and in oceanic cores, however, predict far smaller projectiles, 4-6 km and 2.5-4 km, respectively (e.g., Paquay et al. 2014; F. Kyte, pers. comm). To test who might be right by proxy, we transformed the near-Earth object (NEO) size distribution (Harris & D'Abramo 2015), where > 90% of the D > 1 km asteroids are known, into a model crater size distribution and compared it to the distribution of D > 20 km craters formed on the Moon, Mars, and Venus over the last ~1-3 Gyr. Here we kept things simple and assumed that f described the ratio between all crater and asteroid diameters of interest (i.e., f = D_crater / D_proj).To our surprise, we found f ~ 23-26 produced excellent matches for the crater size distributions on the Moon, Mars, and Venus, despite their differences in gravity, surface properties, impact velocities, etc. These same values work well for the Earth as well. Consider that terrestrial crater production rates derived by Shoemaker (1998) indicate 340 +/- 170 D > 20 km craters formed over the last 120 Myr. Using f = 25, we get the same value; a D > 0.8 km asteroid makes a D > 20 km crater, and they hit Earth every 0.35 Myr on average (e.g., Bottke et al. 2002), for a total of ~340 over 120 Myr. Accordingly, we predict Chicxulub and Popigai were made by D ~ 7 and D ~ 4 km asteroids, respectively, values close to their predicted sizes from Ir/Os measurements. This result also potentially explains why Chicxulub formed ~65 Myr ago; the interval between D ~ 7 km impacts on Earth is close to this rate.The NEO model by Bottke et al. (2002) also suggests asteroids hit Venus at roughly the same

  1. 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

  2. Crustal structure of the Chicxulub Impact crater imaged with magnetotelluric exploration

    NASA Astrophysics Data System (ADS)

    Unsworth, Martyn; Enriquez, Oscar Campos; Belmonte, Salvador; Arzate, Jorge; Bedrosian, Paul

    2002-08-01

    The electrical resistivity structure of the Chicxulub Impact crater has been imaged using broadband magnetotelluric exploration. A 1-2 km thick sequence of conductive Tertiary sedimentary rocks was imaged within the crater. The shallow resistivity of this layer increases across the cenote ring. This is primarily due to a decrease in porosity, although the groundwater composition may have some effect. While this layer reduces the sensitivity of MT, several features can be discerned beneath it. In the center of the crater the structural high is imaged as a region of high resistivity. In the outer part of the crater, lower resistivities in the upper crust may be due to mineralization or hydrothermal alteration.

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

    NASA Astrophysics Data System (ADS)

    Neish, C. D.; 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.

    2015-05-01

    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.

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

    SciTech Connect

    Bunch, T.E.; Paque, J.M.; Zolensky, M. |

    1995-02-01

    A 5.2 mm crater in Al-metal represents the largest found on LDEF. The authors 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 is hypothesized that the crater may be the result of impact with space debris.

  5. Martian Polar Region Impact Craters: Topographical Perspectives from the Mars Orbiter Laser Altimeter

    NASA Technical Reports Server (NTRS)

    Garvin, J. B.; Sakimoto, S. E. H.; Frawley, J. J.; Matias, A.

    1998-01-01

    The Mars Orbiter Laser Altimeter (MOLA) has acquired over 100 topographic cross-sections of impact landforms in the polar regions of Mars as part of Mars Global Surveyor (MGS) Science Phasing Orbit observations during the period from April to July, 1998. These MOLA topographic profiles offer the first three-dimensional perspectives of high latitude craters on Mars yet available, and provide evidence of landform geometries not previously recognized. Indeed, the relatively poor quality of Viking Orbiter images of many high northern latitude regions has allowed the MOLA data to provide insights into the cavities and ejecta topologies of non-degraded impact landforms that have clearly experienced interactions with condensates, either as part of their formation, or as a post-modification stage effect. Here we report a preliminary summary of the results associated with topographic measurements for a statistically significant population of impact features all of which lie north of 60N latitude. MOLA sampled four impact features with frost-related interior deposits, including the 81 km (diameter) Korolev feature. In several cases, there is evidence from near-centerline MOLA cross-sections of crater interior features (i.e., central peak or ice-dust deposits) that are anomalously large relative to the crater cavity. Central structures that make up more than 50% of the volume of a crater cavity are observed, suggesting that either substantial accumulation of mantling materials has occurred, or that crater excavation triggered production of volume-enhancing materials (ice?). Pedestal craters sampled by MOLA also attest to enhanced production of ejecta materials in high latitude terrains. For example, many of the pedestal craters suggest a volume of ejecta (Ve) to volume of cavity (Vc) ratio far in excess of 1.0 (i.e., over 3.0), even in cases where the floor of the cavity appears unfilled. Finally, the well-defined transitions between simple and complex craters observed in

  6. How Small Can Impact Craters Be Detected at Large Scale by Automated Algorithms?

    NASA Astrophysics Data System (ADS)

    Bandeira, L.; Machado, M.; Pina, P.; Marques, J. S.

    2013-12-01

    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 crater dimension and image or surface type, permitting to realize that automated detections in large crater datasets in HiRISE imagery datasets with 25cm/pixel resolution can be successfully done (high correct and low false positive detections) until a crater dimension of about 8-10 m or 32-40 pixels. [1] Martins L, Pina P. Marques JS, Silveira M, 2009, Crater 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 impact craters and advanced evaluation of crater 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 craters in high resolution planetary images using shape and texture features. Advances in Space Research 49: 64-74.

  7. Planar deformation features in quartz from impact-produced polymict breccia of the Xiuyan crater, China

    NASA Astrophysics Data System (ADS)

    Chen, Ming; Koeberl, Christian; Xiao, Wansheng; Xie, Xiande; Tan, Dayong

    2011-05-01

    The 1.8 km-diameter Xiuyan crater is an impact structure in northeastern China, exposed in a Proterozoic metamorphic rock complex. The major rocks of the crater are composed of granulite, hornblendite, gneiss, tremolite marble, and marble. The bottom at the center of the crater covers about 100 m thick lacustrine sediments underlain by 188 m thick crater-fill breccia. A layer of polymict breccia composed of clasts of granulite, gneiss, hornblendite, and fragments of glass as well as clastic matrix, occurs near the base, in the depth interval from 260 to 295 m. An investigation in quartz from the polymict breccia in the crater-fill units reveals abundant planar deformation features (PDFs). Quartz with multiple sets of PDFs is found in clasts of granulite that consist of mainly quartz and feldspar, and in fine-grained matrix of the impact-produced polymict breccia. A universal stage was used to measure the orientation of PDFs in 70 grains of quartz from five thin sections made from the clasts of granulite of polymict breccia recovered at the depth of 290 m. Forty-four percent of the quartz grains contain three sets of PDFs, and another 40% contain two sets of PDFs. The most abundant PDFs are rhombohedron forms of ?, ?, and ? with frequency of 33.5, 22.3, and 9.6%, respectively. A predominant PDF form of ? in quartz suggests a shock pressure >20 GPa. The occurrence of PDFs in quartz from the polymict breccia provides crucial evidence for shock metamorphism of target rocks and confirms the impact origin of this crater, which thus appears to be the first confirmed impact crater in China.

  8. 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°.

  9. 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.

  10. 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

  11. Corrigendum to "Impact and Cratering Rates onto Pluto" [Icarus 258 (2015) 267-288

    NASA Astrophysics Data System (ADS)

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

    2016-08-01

    The authors regret that an error was found in the code used to compute Charon primary crater densities by mistakenly using Pluto's diameter instead of Charon's diameter, causing the Charon cumulative crater density plots and R-plots (Figure 12) to have values that were too low by a factor of ≈12002/6002 ≈ 4. The corrected figure presented here implies younger surface ages (by roughly a factor of four) for Charon and should be used for interpretation of the New Horizons data.

  12. Availability of Heat to Drive Hydrothermal Systems in Large Martian Impact Craters

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

    The central uplift in large craters on Mars can provide a substantial source of heat, equivalent to heat produced by the impact melt sheet. The heat generated in large impacts could play a significant role in hydrothermal systems on Mars. Additional information is contained in the original extended abstract.

  13. Discovery of a probable meteorite impact crater off the W coast of South Africa

    NASA Astrophysics Data System (ADS)

    Shaw-Kahle, B.; Smith, G.; Mhlambi, S.; Kahle, R. L.

    2015-12-01

    We describe a probable submarine meteorite impact crater, discovered offshore the west coast of South Africa, using industry 3D seismic data. The feature is roughly circular, with a diameter of about 10 km; it has some depth extent and disrupts underlying strata. Two major possibilities exist for its origin: that it is an igneous diatreme or that it is a meteorite impact crater. We assess both possibilities through a detailed description of its morphology and seismic characteristics. Although a line of known alkaline volcanic pipes does project towards the coast, comparison of this feature with similar structures worldwide leads us to suggest that the crater is more likely to have formed through the impact of a meteorite. Using simple scaling relationships, we estimate the likely size of the impactor and attempt to arrive at an age limit by extrapolating the ages of mapped horizons from a borehole, located at a distance of approximately 5.5 km.

  14. 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.

  15. 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.

  16. 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

  17. 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

  18. Secondary submicrometer impact cratering on the surface of asteroid 25143 Itokawa

    NASA Astrophysics Data System (ADS)

    Harries, Dennis; Yakame, Shogo; Karouji, Yuzuru; Uesugi, Masayuki; Langenhorst, Falko

    2016-09-01

    Particle RA-QD02-0265 returned by the Hayabusa spacecraft from near-Earth asteroid 25143 Itokawa displayed a unique abundance of submicrometer-sized (≤500 nm) impact craters, which are rarely observed among the Hayabusa samples. The particle consists of intensely twinned diopside that was subjected to a large-scale shock event before exposure to the space environment on the surface of 25143 Itokawa. Intense (sub-)micrometer-scale impact cratering may suggest a long surface exposure and, hence, a long residence time of regolith material on the surface of small asteroids, bearing implications for the dynamical evolution of these bodies. However, our combined FE-SEM and FIB/TEM study shows that the degree of solar wind-induced space weathering and the accumulation of solar flare tracks are not exceptionally different from other Hayabusa particles with surface exposure ages estimated to be less than 1 ka. A 500 nm wide crater on the surface of RA-QD02-0265 exhibits microstructural damage to a depth of 400 nm below its floor and contains residues of Fe-Ni metal, excluding a formation by space craft exhausts or curatorial handling. The geometrical clustering among the 15 craters is unlikely random, and we conclude that the craters have formed through the impacts of secondary projectiles (at least partially Fe-Ni metal) created in a nearby (micro-)impact event. Besides structural damage by the solar wind and deposition of impact-generated melts and vapors, secondary impact cratering on the submicrometer-scale is another potential mechanism to modify the spectral properties of individual regolith grains. The lack of extensively exposed regolith grains supports a dynamic regolith on the surface of 25143 Itokawa.

  19. 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

  20. Large rock slides in impact craters on the Moon and Mercury

    NASA Astrophysics Data System (ADS)

    Brunetti, Maria Teresa; Xiao, Zhiyong; Komatsu, Goro; Peruccacci, Silvia; Guzzetti, Fausto

    2015-11-01

    Impact craters are the most common surface features on the Moon and Mercury. On these two bodies, we recognized and mapped large landslides on the walls of impact craters. Through visual inspection of high-resolution imagery, we compiled an inventory of 60 landslides on the Moon and a second inventory of 58 landslides on Mercury. Adopting categories used to catalog terrestrial mass movements, we classified the landslides on the Moon and Mercury as rock slides. We determined the probability density distribution of their planimetric area, and we compared the distributions with similar distributions for terrestrial and martian landslides using data from the literature. We found that rock slides mapped in impact craters on the Moon are, on average, larger than analogous rock slides on Mercury. The relationship between the area of the individual rock slides and the area of the hosting crater suggests that rock slides on Mercury initiate in smaller craters. We hypothesize that the above findings are an effect of the weaker surface gravity of the Moon compared to that of Mercury and/or an effect of the rock material properties.

  1. Meteorite impact craters and possibly impact-related structures in Estonia

    NASA Astrophysics Data System (ADS)

    Plado, Jüri

    2012-10-01

    Three structures (Neugrund, Kärdla, and Kaali) of proven impact origin make Estonia the most cratered country in the world by area. In addition, several candidate impact structures exist, waiting for future studies to determine their origin. This article is an overview of these proven and possible impact structures, including some breccia layers. It summarizes the information and descriptions of the morphology; geological characteristics; and mineralogical, chemical, and geophysical data available in the literature. The overview was prepared to make information in many earlier publications in local journals (many of which had been published in Estonian or Russian) accessible to the international community. This review summarizes the facts and observations in a historical fashion, summarizing the current state of knowledge with some additional comments, and providing the references.

  2. Anomalous quartz from the Roter Kamm impact crater, Namibia - Evidence for post-impact hydrothermal activity?

    NASA Technical Reports Server (NTRS)

    Koeberl, Christian; Fredriksson, Kurt; Goetzinger, Michael; Reimold, Wolf Uwe

    1989-01-01

    Quartz pebbles from the Roter Kamm impact crater (the Namib Desert, SWA/Namibia) were examined for evidence of impact-induced hydrothermal activity, using results from microprobe analyses, neutron activation analyses, transmission IR spectroscopy, and X-ray diffractometry. It was found that the pebbles consisted of pure quartz, which contains three different types of fluid inclusions. These were identified as primary inclusions (5-10 microns) that record the formation conditions of the quartz, very small (less than 1 micron) secondary inclusions associated with the grain boundaries, and late inclusions of irregular size. It is concluded that the quartz and the primary inclusions may provide evidence for a postimpact phase of extensive hydrothermal activity, generated by the residual heat from the kinetic energy of the impact.

  3. Scoria Cone and Tuff Ring Stratigraphy Interpreted from Ground Penetrating Radar, Rattlesnake Crater, Arizona

    NASA Astrophysics Data System (ADS)

    Kruse, S. E.; McNiff, C. M.; Marshall, A. M.; Courtland, L. M.; Connor, C.; Charbonnier, S. J.; Abdollahzadeh, M.; Connor, L.; Farrell, A. K.; Harburger, A.; Kiflu, H. G.; Malservisi, R.; Njoroge, M.; Nushart, N.; Richardson, J. A.; Rookey, K.

    2013-12-01

    Numerous recent studies have demonstrated that detailed investigation of scoria cone and maar morphology can reveal rich details the eruptive and erosion histories of these volcanoes. A suite of geophysical surveys were conducted to images Rattlesnake Crater in the San Francisco Volcanic Field, AZ, US. We report here the results of ~3.4 km of ground penetrating radar (GPR) surveys that target the processes of deposition and erosion on the pair of cinder cones that overprint the southeast edge of Rattlesnake crater and on the tuff ring that forms the crater rim. Data were collected with 500, 250, 100, and 50 MHz antennas. The profiles were run in a radial direction down the northeast flanks of the cones (~1 km diameter, ~120 meters height) , and on the inner and outer margins of the oblong maar rim (~20-80 meters height). A maximum depth of penetration of GPR signal of ~15m was achieved high on the flanks of scoria cones. A minimum depth of essentially zero penetration occurred in the central crater. We speculate that maximum penetration occurs near the peaks of the cones and crater rim because ongoing erosion limits new soil formation. Soil formation would tend to increase surface conductivity and hence decrease GPR penetration. Soil is probably better developed within the crater, precluding significant radar penetration there. On the northeast side of the gently flattened rim of the easternmost scoria cone, the GPR profile shows internal layering that dips ~20 degrees northeast relative to the current ground surface. This clearly indicates that the current gently dipping surface is not a stratigraphic horizon, but reflects instead an erosive surface into cone strata that formed close to the angle of repose. Along much of the cone flanks GPR profiles show strata dipping ~4-5 degrees more steeply than the current surface, suggesting erosion has occurred over most of the height of the cone. An abrupt change in strata attitude is observed at the gradual slope

  4. 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

  5. High Temperature and High Pressure Mixtures of Iron Oxides from the Impact Event at the Bee Bluff Crypto-Meteorite Impact Crater of South Texas

    NASA Astrophysics Data System (ADS)

    Graham, R. A.

    2012-10-01

    Disturbed geology within a several km diameter surface area of sedimentary Carrizo Sandstone near Uvalde, Texas, indicates the presence of a partially buried meteorite impact crater. Identification of its impact origin is supported by detailed studies but quartz grains recovered from distances of about100 km from the structure also show planar deformation features (PDFs). While PDFs are recognized as uniquely from impact processes, quantitative interpretation requires extension of Hugoniot materials models to more realistic grain-level, mixture models. Carrizo sandstone is a porous mixture of fine quartz and goethite. At impact pressures of tens of GPa, goethite separates into hematite and water vapor upon release of impact pressure. Samples from six different locations up to 50 km from the impact site preserve characteristic features resulting from mixtures of goethite, its water vapor, hematite and quartz. Spheroids resulting from local radial acceleration of mixed density, hot products are common at various sites. Local hydrodynamic instabilities cause similar effects.

  6. Discovery of the largest impact crater field on Earth in the Gilf Kebir region, Egypt

    NASA Astrophysics Data System (ADS)

    Paillou, Philippe; El Barkooky, Ahmed; Barakat, Aly; Malezieux, Jean-Marie; Reynard, Bruno; Dejax, Jean; Heggy, Essam

    2004-12-01

    Using orbital imaging radar, we have detected a large number of circular structures in the southwestern Egyptian desert, covering more than 4500 km 2 close to the Gilf Kebir plateau in sandstones of Upper Cretaceous. Fieldwork confirmed that it is a new impact crater field: 13 craters from 20 m to 1 km in diameter were studied. The impact origin is confirmed by the observation of shock-related structures, such as shatter cones and planar fractures in quartz grains of breccia. Considering the extension of the crater field, it was possibly created by several meteorites that broke up when entering the atmosphere. To cite this article: P. Paillou et al., C. R. Geoscience 336 (2004).

  7. Experimental Results Investigating Impact Velocity Effects on Crater Growth and the Transient Depth-to-Diameter Ratio

    NASA Technical Reports Server (NTRS)

    Barnouin, O. S.; Ernst, C. M.; Heinick, J. T.; Cintala, M. J.; Crawford, D. A.; Matsui, T.

    2011-01-01

    We performed vertical hypervelocity impacts (0.5-6 km/s) at the NASA Ames Vertical Gun Range to evaluate if increasing impact velocity, which alters the coupling time between the projectile and target, might change the rates of crater growth and transient crater shape.

  8. 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

  9. 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. ?? 2005 Geological Society of America.

  10. 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.

  11. Geology of Lofn Crater, Callisto

    NASA Technical Reports Server (NTRS)

    Greeley, Ronald; Heiner, Sarah; Klemaszewski, James E.

    2001-01-01

    Lofn crater is a 180-km-diameter impact structure in the southern cratered 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 crater suggests that (1) it is a class of impact structure intermediate between complex craters and palimpsests or (2) it formed by the impact of a projectile which fragmented before reaching the surface, resulting in a shallow crater (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 impact. The "target" for the Lofn impact is inferred to have included layered materials associated with the Adlinda multiring structure northwest of Loh and ejecta deposits from the Heimdall crater area to the southeast. The Lofn impact 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.

  12. Derivation of particulate directional information from analysis of elliptical impact craters on LDEF

    NASA Technical Reports Server (NTRS)

    Newman, P. J.; Mackay, N.; Deshpande, S. P.; Green, S. F.; Mcdonnell, J. A. M.

    1993-01-01

    The Long Duration Exposure Facility provided a gravity gradient stabilized platform which allowed limited directional information to be derived from particle impact experiments. The morphology of impact craters on semi-infinite materials contains information which may be used to determine the direction of impact 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.

  13. 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.

  14. Computer modeling of large asteroid impacts into continental and oceanic sites: Atmospheric, cratering, and ejecta dynamics

    NASA Technical Reports Server (NTRS)

    Roddy, D. J.; Schuster, S. H.; Rosenblatt, M.; Grant, L. B.; Hassig, P. J.; Kreyenhagen, K. N.

    1988-01-01

    Numerous impact cratering events have occurred on the Earth during the last several billion years that have seriously affected our planet and its atmosphere. The largest cratering 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 impact 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 cratering and ejecta dynamics associated with impact of the asteroid into two different targets, i.e., an oceanic site and a continental site. The calcuations were designed to broadly represent giant impact events that have occurred on the Earth since its formation and specifically represent an impact cratering 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 impact area. Calculations of the cratering events in both the continental and oceanic targets were carried to 120 s. Despite geologic differences, impacts in both targets developed comparable dynamic flow fields, and by approx. 29 s similar-sized transient craters approx. 39 km deep and approx. 62 km across had formed. For all practical purposes, the atmosphere was nearly completely removed from the impact 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

  15. Tenoumer impact crater, Mauritania: Impact melt genesis from a lithologically diverse target

    NASA Astrophysics Data System (ADS)

    Schultze, Dina Simona; Jourdan, Fred; Hecht, Lutz; Reimold, Wolf Uwe; Schmitt, Ralf-Thomas

    2016-02-01

    Impact melt rocks from the 1.9 km diameter, simple bowl-shaped Tenoumer impact crater in Mauritania have been analyzed chemically and petrologically. They are heterogeneous and can be subdivided into three types based on melt matrix color, occurrence of lithic clast components, amount of vesiculation (melt degassing), different proportions of carbonate melt mingled into silicate melt, and bulk rock chemical composition. These heterogeneities have two main causes (1) due to the small size of the impact crater, there was probably no coherent melt pool where a homogeneous mixture of melts, derived from different target lithologies, could be created; and (2) melt rock heterogeneity occurring at the thin section scale is due to fast cooling during and after the dynamic ejection and emplacement process. The overall period of crystal growth from these diverse melts was extremely short, which provides a further indication that complete chemical equilibration of the phases could not be achieved in such short time. Melt mixing processes involved in the generation of impact melts are, thus, recorded in nonequilibrium growth features. Variable mixing processes between chemically different melt phases and the formation of hybrid melts can be observed even at millimeter scales. Due to extreme cooling rates, different mixing and mingling stages are preserved in the varied parageneses of matrix minerals and in the mineral chemistry of microlites. 40Ar39Ar step-heating chronology on specimens from three melt rock samples yielded five concordant inverse isochron ages. The inverse isochron plots show that minute amounts of inherited 40Ar* are present in the system. We calculated a weighted mean age of 1.57 ± 0.14 Ma for these new results. This preferred age represents a refinement from the previous range of 21 ka to 2.5 Ma ages based on K/Ar and fission track dating.

  16. Workshop on The Role of Volatile and Atmospheres on Martian Impact Craters

    NASA Technical Reports Server (NTRS)

    2005-01-01

    This volume contains abstracts that have been accepted for presentation at the Workshop on the Role of Volatiles and Atmospheres on Martian Impact Craters, 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.

  17. Impacts and Cratering on Pluto: Implications for the Source of Pluto's Nitrogen (N2)

    NASA Astrophysics Data System (ADS)

    Singer, K. N.; Stern, S. A.

    2015-05-01

    Craters on Pluto and Charon will provide key information, including clues to the source of Pluto's surface and atmospheric N2. With current estimates of impactor flux on Pluto, comets could not deliver enough N2, but impacts might excavate it.

  18. Evidence for Amazonian mid-latitude glaciation on Mars from impact crater asymmetry

    NASA Astrophysics Data System (ADS)

    Conway, Susan J.; Mangold, Nicolas

    2013-07-01

    We find that crater slopes in the mid-latitudes of Mars have a marked north-south asymmetry, with the pole-facing slopes being shallower. We mapped impact craters in two southern hemisphere sites (Terra Cimmeria and Noachis Terra) and one northern hemisphere site (Acidalia Planitia) and used elevation data from the High Resolution Stereo Camera (HRSC) onboard Mars Express to find the maximum slope of impact crater walls in the four cardinal directions. Kreslavsky and Head (Kreslavsky, M.A., Head, J.W. [2003]. Geophys. Res. Lett. 30), using Mars Orbiter Laser Altimeter (MOLA) track data, also found that, in general, conjugate slopes are shallower in the pole-facing direction, but over a narrower (˜10°) and more constrained latitude band. They linked the asymmetry to active-layer formation (thaw) at high obliquity. However, Parsons and Nimmo (Parsons, R.A., Nimmo, F. [2009]. J. Geophys. Res. 114) studied crater asymmetry using MOLA gridded data and found no evidence of a relationship between crater asymmetry and latitude. Our work supports the observations of Kreslavsky and Head (Kreslavsky, M.A., Head, J.W. [2003]. Geophys. Res. Lett. 30), and shows that asymmetry is also found on conjugate crater slopes below the resolution of MOLA, over a wider latitude band than found in their work. We do not systematically find a sudden transition to asymmetric craters with latitude as expected for thaw-related processes, such as solifluction, gelifluction, or gully formation. The formation of gullies should produce the opposite sense of asymmetry to our observations, so cannot explain them despite the mid-latitude location and pole-facing preferences of gullies. We instead link this asymmetry to the deposition of ice-rich crater deposits, where the base of pole-facing slopes receive ten to hundreds of meters of additional net deposition, compared to equator-facing ones over the mid-latitudes. In support of this hypothesis we found that craters in Terra Cimmeria that have

  19. Thermal Emission Spectrometer Mosaics of Impact Craters: Progress on Shocked Plagioclase Detections

    NASA Technical Reports Server (NTRS)

    Johnson, J. R.; Staid, M. I.; Titus, T. N.; Gaddis, L.

    2003-01-01

    High shock pressures disorder the mineral lattice of plagioclase feldspars and cause weakening and shifts in thermal infrared absorption bands related to an increase in diaplectic glass content, particularly at shock pressures above 20-25 GPa [1- 9]. We are continuing our investigation of spectral deconvolutions of TES mosaics and mosaics using standard TES orbits for eight impact crater areas. Using a combination of mineral laboratory spectra and spectra of experimentally shocked bytownite feldspars [5] to deconvolve the TES spectra, we find that locations of shocked feldspar detections are not restricted to ejecta near large craters.

  20. 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

  1. Dawn Framing Camera: Morphology and morphometry of impact craters on Ceres

    NASA Astrophysics Data System (ADS)

    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.

    2015-10-01

    In the first approach images of Ceres we tried to discern the simple-to-complex transition diameter of impact craters. Limited by spatial resolution we found the smallest complex crater 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

  2. Copernicus (Crater)

    NASA Astrophysics Data System (ADS)

    Murdin, P.

    2000-11-01

    One of the Moon's most conspicuous craters, with a diameter of 93 km, centered at 9.7 °N, 20.1°W. It is named after the Polish astronomer Nicholas Copernicus. It is one of the Moon's younger features, the impact that produced it having taken place an estimated 1 billion years ago. Like other young craters it is surrounded by a system of bright rays formed by ejecta from the impact; the rays from ...

  3. Impact melt- and projectile-bearing ejecta at Barringer Crater, Arizona

    NASA Astrophysics Data System (ADS)

    Osinski, Gordon R.; Bunch, Ted E.; Flemming, Roberta L.; Buitenhuis, Eric; Wittke, James H.

    2015-12-01

    Our understanding of the impact cratering process continues to evolve and, even at well-known and well-studied structures, there is still much to be learned. Here, we present the results of a study on impact-generated melt phases within ejecta at Barringer Crater, Arizona, one of the first impact craters on Earth to be recognized and arguably the most famous. We report on previously unknown impact melt-bearing breccias that contain dispersed fragments of the projectile as well as impact glasses that contain a high proportion of projectile material - higher than any other glasses previously reported from this site. These glasses are distinctly different from so-called "melt beads" that are found as a lag deposit on the present-day erosion surface and that we also study. It is proposed that the melts in these impact breccias were derived from a more constrained sub-region of the melt zone that was very shallow and that also had a larger projectile contribution. In addition to low- and high-Fe melt beads documented previously, we document Ca-Mg-rich glasses and calcite globules within silicate glass that provide definitive evidence that carbonates underwent melting during the formation of Barringer Crater. We propose that the melting of dolomite produces Ca-Mg-rich melts from which calcite is the dominant liquidus phase. This explains the perhaps surprising finding that despite dolomite being the dominant rock type at many impact sites, including Barringer Crater, calcite is the dominant melt product. When taken together with our estimate for the amount of impact melt products dispersed on, and just below, the present-day erosional surface, it is clear that the amount of melt produced at Barringer Crater is higher than previously estimated and is more consistent with recent numerical modeling studies. This work adds to the growing recognition that sedimentary rocks melt during hypervelocity impact and do not just decompose and/or devolatilize as was previously thought

  4. Shock Metamorphic Evolution on the Moon and Impact Craters Applied by Shock Impact Experiment

    NASA Astrophysics Data System (ADS)

    Miura, Y.; Kato, T.; Imai, M.

    1992-07-01

    It has been considered that quartz minerals can be formed by magmatic crystallization of the Earth or Earth-type planets under high-temperature condition of the magma. However, if similar high temperature can be obtained at impact processes, silica minerals will be formed even under impact condition (1,2,3,4). Impact experiments. The following various silica and feldspar minerals can be obtained in the artificial impact crater experiments of various type target rocks. a) Fine-grained shocked quartz aggregates crystallized from vaporization of feldspar compositions are shown by the increased abundance of shocked quartz (SQ) and feldspar(F) at the "fine ejecta"; that is, SQ/F=3.0 and 5.6 in the granite and gabbroic anorthosite, respectively (cf. Table 1). Chemical compositions of large fragments broken by impact processes reveal partly anomalous diaplectic feldspar grains with irregularly wavy extinction and nonstoichiometric composition. b) Impact effects of density change and shocked quartz formation (SQ/F) show larger in fine-grained gabbroic anorthosite than hard coarse-grained granite. c) Stishovite and coesite could not be observed in small laboratory experiments. d) The highest density of shocked quartz crystal (SQ) in fine-grained ejecta can be obtained in quartz-rich target-rock of sandstone, which is the same implication to the Barringer impact crater with sandstone (1,3). Shock metamorphism of lunar and planetary materials. By using the experimental impact results of shock metamorphism (4), major plagioclase minerals of anorthosite formed by magmatic ocean processes on the primordial planetary and lunar surfaces, can be changed to diaplectic plagioclases and shocked silica minerals by impact shock effects, resulting in the formation of shocked quartz (SQ) by rapid crystallization. The SU phases formed by impact can be changed to normal quartz (Q) by magmatic evolution process under high temperature. The present results of shock metamorphic evolution will

  5. Mean age of rifting and volcanism on Venus deduced from impact crater densities

    NASA Astrophysics Data System (ADS)

    Price, Maribeth; Suppe, John

    1994-12-01

    UNLIKE the extensively cratered highlands of the Moon and Mars, the surface of Venus does not preserve a record of heavy bombard-ment from the early history of the Solar System1-3. Those craters that are found on Venus appear to be statistically indistinguishable from a random spatial population and rarely show modification by folds, faults and lava flows1-3. Although the volcanic and tec-tonic history of Venus is still much debated2-5, there is mounting evidence for near-global resurfacing ˜300-500 Myr ago1,2,6. Moreover, it has recently been noted that the density of impact craters on large volcanic structures is less than the average crater density of the planet, suggestive of significant activity after the resurfacing event7. It is not clear, however, whether these features represent late remnants of the global event or continuing volcanism and tectonism of a still active planet. To address this question, we have used the regional variations in crater density to date volcan-oes, rifts and coronae which, based on stratigraphic evidence, clearly post-date the main resurfacing event8-11. The calculated mean ages of 70-125 Myr exclude the possibility that the majority of these features represent the final stages of the global event.

  6. Numerical modelling of impact crater formation associated with isolated lunar skylight candidates on lava tubes

    NASA Astrophysics Data System (ADS)

    Martellato, E.; Foing, B. H.; Benkhoff, J.

    2013-09-01

    Skylights are openings on subsurface voids as lava tubes and caves. Recently deep hole structures, possibly skylights, were discovered on lunar photo images by the JAXA SELenological and ENgineering Explorer (SELENE)-Kaguya mission, and successively confirmed by the NASA Lunar Reconnaissance Orbiter (LRO) mission. Vertical hole structures and possibly underlying subsurface voids have high potential as resources for scientific study, and future unmanned and manned activities on the Moon. One mechanism proposed for their formation is impact cratering. The collapse of craters is due to the back spallation phenomena on the rear surface of the lava tube roofs. Previous analysis in this topic was based on small-scales laboratory experiments. These have pointed out that (i) the target thickness-to-crater diameter ratio is 0.7, and (ii) the projectile diameter-to-target thickness ratio is 0.16, at the ballistic limit once extrapolated to planetary conditions.

  7. Twelve-year trail of clues leads to impact crater from the K-T boundary

    SciTech Connect

    Levi, B.G.

    1992-12-01

    In 1980, scientists at the University of California, Berkeley proposed that a massive comet or asteroid might have struck the earth about 65 million years ago, changing the earth's climate so drastically that dinosaurs and other creatures could no longer survive. This article describes the evidence for the elusive crater required to support this theory. The structure in question is 180 km in diameter and is submeged beneath the Yucatan peninsula and centered on the Mexican village of Chicxulub. Material drilled from this crater has been linked chemically and geologically to pellets found in Northeast Mexico and Haiti. The link between this ejecta material and the crater was confirmed by a report that the Chicxulub melt rock and pellets are coeval, all having ages consistent with 65 million years. This puts the possible impact at the K-T boundary -- the dividing line between the Cretaceous period of the dinosaurs and the Tertiary period of the mammals. 13 refs.

  8. 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.; Bridges, John; Brownlee, Donald E.; Burchell, Mark; Burghammer, Manfred; Butterworth, Anna L.; Changela, Hitesh; Cloetens, Peter; Davis, Andrew M.; Doll, Ryan; Floss, Christine; Flynn, George; Fougeray, Patrick; Frank, David; Sandford, Scott A.; Zolensky, Michael E.

    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

  9. 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.

  10. Terrace Zone Structure in the Chicxulub Impact Crater Based on 2-D Seismic Reflection Profiles: Preliminary Results From EW#0501

    NASA Astrophysics Data System (ADS)

    McDonald, M. A.; Gulick, S. P.; Gorney, D. L.; Christeson, G. L.; Barton, P. J.; Morgan, J. V.; Warner, M. R.; Urrutia-Fucugauchi, J.; Melosh, H. J.; Vermeesch, P. M.; Surendra, A. T.; Goldin, T.; Mendoza, K.

    2005-05-01

    Terrace zones, central peaks, and flat floors characterize complex craters like the Chicxulub impact crater located near the northeast coast of the Yucatan Peninsula. The subsurface crater structure was studied using seismic reflection surveying in Jan/Feb 2005 by the R/V Maurice Ewing. We present 2-D seismic profiles including constant radius, regional, and grid profiles encompassing the 195 km width of the crater. These diversely oriented lines clearly show the terrace zones and aid in the search for crater ejecta as we investigate the formation of the crater including the incidence angle and direction of the extraterrestrial object that struck the Yucatan Peninsula 65 million years ago (K-T boundary). Terrace zones form in complex craters after the modification stage as a result of the gravitational collapse of overextended sediment back into the crater cavity. The terrace zone is clearly imaged on seismic profiles confirming the complex structure of the Chixculub crater. Recent work on reprocessed 1996 profiles found different sizes and spacing of the terraces and concluded that the variations in radial structure are a result of an oblique impact. A SW-NE profile from this study was the only line to show a concentration of deformation near the crater rim hinting that the northeast was the downrange direction of impact. We confirm this narrowing in terrace spacing using a profile with a similar orientation in the 2005 images. Through integration of the new dense grid of profiles and radial lines from the 1996 and 2005 surveys we map the 3-D variability of the terrace zones to further constrain impact direction and examine the formative processes of the Chixculub and other large impact craters.

  11. Hypervelocity dust impact craters on photovoltaic devices imaged by ion beam induced charge

    NASA Astrophysics Data System (ADS)

    Yang, Changyi; Wu, Yiyong; Lv, Gang; Rubanov, Sergey; Jamieson, David N.

    2015-04-01

    Hypervelocity dust has a speed of greater than 5 km/s and is a significant problem for equipment deployed in space such as satellites because of impacts that damage vulnerable components. Photovoltaic (PV) arrays are especially vulnerable because of their large surface area and the performance can be degraded owing to the disruption of the structure of the junction in the cells making up the array. Satellite PV arrays returned to Earth after service in orbit reveal a large number of craters larger than 5 μm in diameter arising from hypervelocity dust impacts. Extensive prior work has been done on the analysis of the morphology of craters in PV cells to understand the origin of the micrometeoroid that caused the crater and to study the corresponding mechanical damage to the structure of the cell. Generally, about half the craters arise from natural micrometeoroids, about one third from artificial Al-rich debris, probably from solid rocket exhausts, and the remainder from miscellaneous sources both known and unknown. However to date there has not been a microscopic study of the degradation of the electrical characteristics of PV cells exposed to hypervelocity dust impacts. Here we present an ion beam induced charge (IBIC) pilot study by a 2 MeV He microbeam of craters induced on a Hamamatsu PIN diode exposed to artificial hypervelocity Al dust from a dust accelerator. Numerous 5-30 μm diameter craters were identified and the charge collection efficiency of the crater and surrounds mapped with IBIC with bias voltages between 0 and 20 V. At highest bias, it was found the efficiency of the crater had been degraded by about 20% compared to the surrounding material. The speed distribution achieved in the Al dust accelerator was peaked at about 4 km/s compared to 11-68 km/s for dust encountered in low Earth orbit. We are able to extrapolate the charge collection efficiency degradation rate of unbiased cells in space based on our current measurements and the differences

  12. 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.

  13. Height-depth ratios of lunar and terrestrial craters.

    NASA Technical Reports Server (NTRS)

    Pike, R. J.

    1971-01-01

    Quantitative analysis of Gilbert's (1893) observation regarding the surface geometry of lunar craters and terrestrial calderas. Topographic measurements were made using the ratio of exterior rim height to interior crater depth, and then extended to other types of crater. The morphometric data obtained as well as those presented elsewhere (Murray et al., 1970; Guest and Murray, 1969) verify Gilbert's contention that terrestrial calderas and most rimmed lunar craters are entirely unrelated phenomena. Auxiliary characteristics previously interpreted in terms of primary volcanic cratering on the moon are either of nonendogenic origin or are secondary endogenic features superposed on initial impact landforms (Pike, 1967).

  14. 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

  15. Formation and geomorphologic history of the Lonar impact crater deduced from in situ cosmogenic 10Be and 26Al

    NASA Astrophysics Data System (ADS)

    Nakamura, Atsunori; Yokoyama, Yusuke; Sekine, Yasuhito; Goto, Kazuhisa; Komatsu, Goro; Kumar, P. Senthil; Matsuzaki, Hiroyuki; Kaneoka, Ichiro; Matsui, Takafumi

    2014-08-01

    Lonar impact crater is one of a few craters on Earth formed directly in basalt, providing a unique opportunity to study an analog for crater degradation processes on Mars. Here we present surface 10Be and 26Al exposure dates in order to determine the age and geomorphic evolution of Lonar crater. Together with a 14C age of preimpact soil, we obtain a crater age of 37.5 ± 5.0 ka, which contrasts with a recently reported and apparently older 40Ar/39Ar age (570 ± 47 ka). This suggests that the 40Ar/39Ar age may have been affected by inherited radiogenic 40Ar (40Ar*inherited) in the impact glass. The spatial distribution of surface exposure ages of Lonar crater differs from that for Barringer crater, indicating Lonar crater rim is actively eroding. Our new chronology provides a unique opportunity to compare the geomorphological history of the two craters, which have similar ages and diameters, but are located in different climate and geologic settings.

  16. 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

  17. Three-D crater analysis of LDEF impact features from stereo imagery

    NASA Technical Reports Server (NTRS)

    Sapp, Clyde A.; See, Thomas H.; Zolensky, Michael E.

    1993-01-01

    The preliminary results from attempts to derive depth and diameter information from digitized stereo images of impact features on the LDEF are reported. Contrary to our prior assumption, we find that impact craters in the T6 A1 alloy are not paraboloid in cross section, but rather are better described by a 6th-order polynomial curve. We explore the implications of this discovery.

  18. LU60645GT and MA132843GT Catalogues of Lunar and Martian Impact Craters Developed Using a Crater Shape-based Interpolation Crater Detection Algorithm for Topography Data

    NASA Technical Reports Server (NTRS)

    Salamuniccar, Goran; Loncaric, Sven; Mazarico, Erwan Matias

    2012-01-01

    For Mars, 57,633 craters from the manually assembled catalogues and 72,668 additional craters identified using several crater detection algorithms (CDAs) have been merged into the MA130301GT catalogue. By contrast, for the Moon the most complete previous catalogue contains only 14,923 craters. 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 Crater 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 craters; and (3) it provides more accurate automated measurements of craters' properties. The results are: (1) LU60645GT, which is currently the most complete (up to D>=8 km) catalogue of Lunar craters; and (2) MA132843GT catalogue of Martian craters 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 craters, 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 craters that are very close to poles; and (3) the extension of the

  19. Evidence from Impact Crater Observations for Few Large Impacts on the Moon 0.8-1.7 Ga

    NASA Astrophysics Data System (ADS)

    Kirchoff, M. R.; Bottke, W. F.; Marchi, S.; Chapman, C. R.; Enke, B.

    2012-12-01

    Our Moon is a keystone for understanding the inner solar system impact flux through time, because it is the only body for which we have crater size-frequency distributions (SFDs) through most of bombardment history and radiometric ages of probable associated terrains. Even so, the bombardment rate over the last 3.5 Gyr is poorly understood. According to the spatial density of sub-km craters on dated lunar terrains, the lunar impact flux has been roughly constant over this interval [e.g., 1 and references therein]. If so, one may expect that craters with diameter (D) > 50 km should also be equally dispersed in time over the last 3.5 Gyr. Surprisingly, our new work indicates this may not be so. We have compiled SFDs for small, superposed craters with D~0.6-15 km on the original floors of several previously designated Copernican and Eratothenian craters (USGS Geological Atlas of the Moon and [2]) with D > 50 km using JMARS. Using these data we compute the large craters' formation model ages with the Model Production Function chronology developed by Marchi et al. [3]. Many of these craters, especially on the farside (e.g., Sharnov, Birkeland), can now be suitably examined only because of the excellent LROC imaging (we use the Wide Angle Camera mosaic). As a test of our methods, we calculated the model age of the 55 km crater Aristillus (34°N, 1°E), a relatively young crater thought to have showered the Apollo 15 landing site with ejecta. Interestingly, our model age of 2.2 ± 0.6 Ga is surprisingly consistent with a 2.1 Ga-old impact-derived clast (radiometric age) returned by the Apollo 15 astronauts [4]. We find that nearly all of our computed ages for the large craters are older than indicated by previous work, with very few having ages younger than 3 Ga. Reasons for these discrepancies include (i) use of poor resolution Lunar Orbiter images (especially away from the near side) and (ii) application of the unreliable "DL" method, which involves simplified

  20. Characterization and Petrologic Interpretation of Olivine-Rich Basalts at Gusev Crater, Mars

    NASA Technical Reports Server (NTRS)

    McSween, H. Y.; Wyatt, M. B.; Gellert, R.; Bell, J. F., III; Morris, R. V.; Herkenhoff, K. E.; Crumpler, L. S.; Milam, K. A.; Stockstill, K. R.; Tornabene, L. L.; Arvidson, R. E.; Bartlett, P.; Blaney, D.; Cabrol, N. A.; Christensen, P. R.; Clark, B. C.; Crisp, A.; DesMarais, D. J.; Economou, T.; Farmer, J. D.; Farrand, W.; Ghosh, A.; Golombek, M.; Gorevan, S.; Greeley, R.

    2006-01-01

    Rocks on the floor of Gusev crater are basalts of uniform composition and mineralogy. Olivine, the only mineral to have been identified or inferred from data by all instruments on the Spirit rover, is especially abundant in these rocks. These picritic basalts are similar in many respects to certain Martian meteorites (olivine-phyric shergottites). The olivine megacrysts in both have intermediate compositions, with modal abundances ranging up to 20-30%. Associated minerals in both include low-calcium and high-calcium pyroxenes, plagioclase of intermediate composition, iron-titanium-chromium oxides, and phosphate. These rocks also share minor element trends, reflected in their nickel-magnesium and chromium-magnesium ratios. Gusev basalts and shergottites appear to have formed from primitive magmas produced by melting an undepleted mantle at depth and erupted without significant fractionation. However, apparent differences between Gusev rocks and shergottites in their ages, plagioclase abundances, and volatile contents preclude direct correlation. Orbital determinations of global olivine distribution and compositions by thermal emission spectroscopy suggest that olivine-rich rocks may be widespread. Because weathering under acidic conditions preferentially attacks olivine and disguises such rocks beneath alteration rinds, picritic basalts formed from primitive magmas may even be a common component of the Martian crust formed during ancient and recent times.

  1. Characterization and petrologic interpretation of olivine-rich basalts at Gusev Crater, Mars

    USGS Publications Warehouse

    McSween, H.Y.; Wyatt, M.B.; Gellert, Ralf; Bell, J.F.; Morris, R.V.; Herkenhoff, K. E.; Crumpler, L.S.; Milam, K.A.; Stockstill, K.R.; Tornabene, L.L.; Arvidson, R. E.; Bartlett, P.; Blaney, D.; Cabrol, N.A.; Christensen, P.R.; Clark, B. C.; Crisp, J.A.; Des Marais, D.J.; Economou, T.; Farmer, J.D.; Farrand, W.; Ghosh, A.; Golombek, M.; Gorevan, S.; Greeley, R.; Hamilton, V.E.; Johnson, J. R.; Joliff, B.L.; Klingelhofer, G.; Knudson, A.T.; McLennan, S.; Ming, D.; Moersch, J.E.; Rieder, R.; Ruff, S.W.; Schrorder, C.; de Souza, P.A.; Squyres, S. W.; Wanke, H.; Wang, A.; Yen, A.; Zipfel, J.

    2006-01-01

    Rocks on the floor of Gusev crater are basalts of uniform composition and mineralogy. Olivine, the only mineral to have been identified or inferred from data by all instruments on the Spirit rover, is especially abundant in these rocks. These picritic basalts are similar in many respects to certain Martian meteorites (olivine-phyric shergottites). The olivine megacrysts in both have intermediate compositions, with modal abundances ranging up to 20-30%. Associated minerals in both include low-calcium and high-calcium pyroxenes, plagioclase of intermediate composition, iron-titanium-chromium oxides, and phosphate. These rocks also share minor element trends, reflected in their nickel-magnesium and chromium-magnesium ratios. Gusev basalts and shergottites appear to have formed from primitive magmas produced by melting an undepleted mantle at depth and erupted without significant fractionation. However, apparent differences between Gusev rocks and shergottites in their ages, plagioclase abundances, and volatile contents preclude direct correlation. Orbital determinations of global olivine distribution and compositions by thermal emission spectroscopy suggest that olivine-rich rocks may be widespread. Because weathering under acidic conditions preferentially attacks olivine and disguises such rocks beneath alteration rinds, picritic basalts formed from primitive magmas may even be a common component of the Martian crust formed during ancient and recent times. Copyright 2006 by the American Geophysical Union.

  2. 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.

  3. Geometric properties of Martian impact craters: Preliminary results from the Mars Orbiter Laser Altimeter

    NASA Astrophysics Data System (ADS)

    Garvin, James B.; Frawley, James J.

    1998-12-01

    The Mars Orbiter Laser Altimeter (MOLA) acquired high spatial and vertical resolution topographic data for 18 tracks across the northern hemisphere of Mars during the Fall of 1997. It sampled 98 minimally degraded impact craters between the latitudes of 80°N and 12°S The best fitting depth (d) versus diameter (D) power-law relationship for these craters is: d = 0.14 D0.90 for simple varieties, and d = 0.25 D0.49 for complex structures. The simple-to-complex transition diameter is 8 km (+/-0.5 km). The cross-sectional “shape” of the crater cavities was determined by fitting a power-function to each profile. Variation in the exponent (n) suggest the craters flatten with increasing diameter and impact energy. The ejecta thickness is skewed suggesting that use of existing empirical expressions for the expected radial decay of ejecta thickness is inappropriate for Mars in most cases.

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

    NASA Astrophysics Data System (ADS)

    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-latitudes 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 micrometers, 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.

  5. Mapping Buried Impact Craters in the Chryse Basin to Understand the Distribution of Outflow Channel Sediment

    NASA Astrophysics Data System (ADS)

    Miller, Moira; Frey, Herbert V.

    2016-01-01

    The Chryse Basin's location in the northern hemisphere of Mars allowed it to collect water from a number of major outflow channels. These outflows likely deposited significant amounts of sediment within the Basin. This project's goal was to see if mapping buried impact craters, revealed as Quasi-Circular Depressions (QCDs) in Mars Orbiter Laser Altimeter (MOLA) data, could be used to determine the distribution and variation of sediment thickness within the Basin. QCDs, including likely buried impact craters, were mapped to test the hypothesis that further into the basin there would be fewer smaller craters because thicker sediments would have preferentially covered them. Mapping was done using Gridview, an interactive graphics program that manipulates data, in this case topographic data from MOLA. It should be possible to estimate the thickness of the sediment from the smallest buried craters found in a given area, and therefore map out the change in sediment thickness across the basin. The smallest QCDs beginning to be completely covered by sediment were just below 30 km in diameter. The minimum sediment needed to cover a QCD of this size was calculated to be between 1-2km. Therefore, the absence of QCDs below 30 km in the NE corner of Chryse could be explained by sediment at least that thick. Lower thickness is expected elsewhere in the basin, especially in the SW, where more QCDs with smaller diameters were found. The method of mapping buried impact craters provides a way to determine variations in sediment thickness within the Chryse Basin. This method could be used on other sediment-covered areas to learn about past water flow.

  6. Identification of Impact Craters in Foils from the Stardust Interstellar Dust Collector

    NASA Technical Reports Server (NTRS)

    Stroud, R. M.; 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.; Floss, C.; Flynn, G. J.; Frank, D.; Gainsforth, Z.; Gruen, E.; Heck, P. R.; Hillier, J. K.; Hoppe, P.; Howard, L.; Sandford, S. A.; Tsou, P.; Zolensky, M. E.

    2011-01-01

    The Stardust Interstellar Dust Collection tray provides the first opportunity for the direct laboratory-based measurement of contemporary interstellar dust. The total exposed surface of the tray was approximately 0.1 square meters, including 153 square centimeters of Al foil in addition to the silica aerogel tiles that are the primary collection medium. Preliminary examination of aerogel tiles has already revealed 16 tracks from particle impacts with an orientation consistent with an interstellar origin, and to date four of the particles associated with these tracks have a composition consistent with an extraterrestrial origin. Tentative identification of impact craters on three foil samples was also reported previously. Here we present the definitive identification of 20 impact craters on five foils.

  7. The variability of crater identification among expert and community crater analysts

    NASA Astrophysics Data System (ADS)

    Robbins, Stuart J.; Antonenko, Irene; Kirchoff, Michelle R.; Chapman, Clark R.; Fassett, Caleb I.; Herrick, Robert R.; Singer, Kelsi; Zanetti, Michael; Lehan, Cory; Huang, Di; Gay, Pamela L.

    2014-05-01

    The identification of impact craters on planetary surfaces provides important information about their geological history. Most studies have relied on individual analysts who map and identify craters and interpret crater statistics. However, little work has been done to determine how the counts vary as a function of technique, terrain, or between researchers. Furthermore, several novel internet-based projects ask volunteers with little to no training to identify craters, and it was unclear how their results compare against the typical professional researcher. To better understand the variation among experts and to compare with volunteers, eight professional researchers have identified impact features in two separate regions of the Moon. Small craters (diameters ranging from 10 m to 500 m) were measured on a lunar mare region and larger craters (100s m to a few km in diameter) were measured on both lunar highlands and maria. Volunteer data were collected for the small craters on the mare. Our comparison shows that the level of agreement among experts depends on crater diameter, number of craters per diameter bin, and terrain type, with differences of up to ∼±45%. We also found artifacts near the minimum crater diameter that was studied. These results indicate that caution must be used in most cases when interpreting small variations in crater size-frequency distributions and for craters ≲10 pixels across. Because of the natural variability found, projects that emphasize many people identifying craters on the same area and using a consensus result are likely to yield the most consistent and robust information.

  8. Impact Crater Size-Frequency Distributions (SFD) on Saturnian Satellites in Comparison with Possible Impactor Populations

    NASA Astrophysics Data System (ADS)

    Schmedemann, Nico; Neukum, Gerhard; Denk, Tilmann; Wagner, Roland; Hartmann, Oliver

    2010-05-01

    One of the major goals of the Cassini imaging experiment (ISS) is the examination of the geologic history of the saturnian satellites [1]. The understanding of the impact crater SFD of the saturnian satellites allows insights of the bombardment history of the early outer solar system. Thus it provides not only information of the geologic development of the target bodies but is also key for the determination of the impactor sources as well. The impact-crater SFD of the mid-sized saturnian satellites has been measured as described by [2]. There are high similarities in the shapes of the asteroid-body SFD around the 3:1 mean motion resonance (MMR) gap with Jupiter and the measured impact crater SFD on the saturnian satellites. This allows for an estimation of the impact-crater scaling. The observationally derived scale factor between the impactor diameter and the respective impact-crater diameter is about three to four in case of Iapetus's larger craters and doesn't change much on other mid-sized saturnian satellites like Rhea or Dione. Hence, by shifting the impact-crater SFD curve of Iapetus to smaller sizes by the amount of the scaling factor of three to four, we get the impactor-body SFD for Iapetus. Thus we can compare the impactor-body SFD of Iapetus with body SFD of possible populations of impacting bodies like Kuiper- Belt objects (KBO), asteroids or the irregular satellites of Saturn. As stated by [3], intensive analyses of the impact crater diameter SFDs of the surfaces of the inner solar system bodies have revealed a characteristic W-shaped curve in the R-plot. The measurements of the crater-diameter SFD on the saturnian satellites Mimas, Tethys, Dione, Rhea, and Iapetus also show high similarities to those W-shaped curves of the inner solar system bodies. The derived body SFD of the asteroid belt (method of abs. magnitude to size conversion by [4]) around the 3:1 MMR with Jupiter gives a very good match to the lunar SFD and thus to the jovian and saturnian

  9. Crater chains on Mercury

    NASA Astrophysics Data System (ADS)

    Shevchenko, V.; Skobeleva, T.

    After discovery of disruption comet Shoemaker-Levy 9 into fragment train before it's collision with Jupiter there was proposed that linear crater chains on the large satellites of Jupiter and on the Moon are impact scars of past tidally disrupted comets.It's known that radar images have revealed the possible presence of water ice deposits in polar regions of Mercury. Impacts by a few large comets seem to provide the best explanation for both the amount and cleanliness of the ice deposits on Mercury because they have a larger volatile content that others external sources, for example, asteroid. A number of crater chains on the surface of Mercury are most likely the impact tracks of "fragment trains" of comets tidally disrupted by Sun or by Mercury and are not secondary craters. Mariner 10 image set (the three Mariner 10 flybys in 1974-1975) was used to recognize the crater chains these did not associate with secondary crater ejecta from observed impact structures. As example, it can be shown such crater chain located near crater Imhotep and crater Ibsen (The Kuiper Quadrangle of Mercury). Resolution of the Mariner 10 image is about 0.54 km/pixel. The crater chain is about 50 km long. It was found a similar crater chain inside large crater Sophocles (The Tolstoj Quadrangle of Mercury). The image resolution is about 1.46 km/pixel. The chain about 50 km long is located in northen part of the crater. Image resolution limits possibility to examine the form of craters strongly. It seems the craters in chains have roughly flat floor and smooth form. Most chain craters are approximately circular. It was examined many images from the Mariner 10 set and there were identified a total 15 crater chains and were unable to link any of these directly to any specific large crater associated with ejecta deposits. Chain craters are remarkably aligned. All distinguished crater chains are superposed on preexisting formations. A total of 127 craters were identified in the 15 recognized

  10. Origin of complex impact craters on native oxide coated silicon surfaces

    SciTech Connect

    Samela, Juha; Nordlund, Kai; Popok, Vladimir N.; Campbell, Eleanor E. B.

    2008-02-15

    Crater structures induced by impact of keV-energy Ar{sub n}{sup +} cluster ions on silicon surfaces are measured with atomic force microscopy. Complex crater structures consisting of a central hillock and outer rim are observed more often on targets covered with a native silicon oxide layer than on targets without the oxide layer. To explain the formation of these complex crater structures, classical molecular dynamics simulations of Ar cluster impacts on oxide coated silicon surfaces, as well as on bulk amorphous silica, amorphous Si, and crystalline Si substrates, are carried out. The diameter of the simulated hillock structures in the silicon oxide layer is in agreement with the experimental results, but the simulations cannot directly explain the height of hillocks and the outer rim