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Sample records for impact crater drill

  1. 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

  2. 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

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

    NASA Technical Reports Server (NTRS)

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

    1977-01-01

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

  4. 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

  5. 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

  6. Structural deformation at the Flynn Creek impact crater, Tennessee - A preliminary report on deep drilling

    NASA Technical Reports Server (NTRS)

    Roddy, D. J.

    1979-01-01

    The geologic and core drilling studies described in the present paper show that the Flynn Creek crater has such distinctive morphological features as a broad flat hummocky floor; large central peak; locally terraced crater walls; uplifted, as well as flat-lying rim segments; and a surrounding ejecta blanket. The major structural features include a shallow depth of total brecciation and excavation as compared with apparent crater diameter; a thin breccia lens underlain by a thin zone of disrupted strata; concentric ring fault zones in inner rim, beneath crater wall, and outer crater floor regions; a large central uplift underlain by a narrow dipping zone of deeply disrupted strata; faulted, folded, brecciated, and fractured rim strata; and uplifted rim strata, which dip away from the crater, and flat-lying rim strata, which terminate as inward dipping rocks.

  7. An international and multidisciplinary drilling project into a young complex impact structure: The 2004 ICDP Bosumtwi Crater Drilling Project—An overview

    NASA Astrophysics Data System (ADS)

    Koeberl, Christian; Milkereit, Bernd; Overpeck, Jonathan T.; Scholz, Christopher A.; Amoako, Philip Y. O.; Boamah, Daniel; Danuor, Sylvester; Karp, Tobias; Kueck, Jochem; Hecky, Robert E.; King, John W.; Peck, John A.

    The Bosumtwi impact crater in Ghana, arguably the best-preserved complex young impact structure known on Earth, displays a pronounced rim and is almost completely filled by Lake Bosumtwi, a hydrologically closed basin. It is the source crater of the Ivory Coast tektites. The structure was excavated in 2.1-2.2 Gyr old metasediments and metavolcanics of the Birimian Supergroup. A drilling project was conceived that would combine two major scientific interests in this crater: 1) to obtain a complete paleoenvironmental record from the time of crater formation about one million years ago, at a near-equatorial location in Africa for which very few data are available so far, and 2) to obtain a complete record of impactites at the central uplift and in the crater moat, for ground truthing and comparison with other structures. Within the framework of an international and multidisciplinary drilling project led by the International Continental Scientific Drilling Program (ICDP), 16 drill cores were obtained from June to October 2004 at six locations within Lake Bosumtwi, which is 8.5 km in diameter. The 14 sediment cores are currently being investigated for paleoenvironmental indicators. The two impactite cores LB-07A and LB-08A were drilled into the deepest section of the annular moat (540 m) and the flank of the central uplift (450 m), respectively. They are the main subject of this special issue of Meteoritics & Planetary Science, which represents the first detailed presentations of results from the deep drilling into the Bosumtwi impactite sequence. Drilling progressed in both cases through the impact breccia layer into fractured bedrock. LB-07A comprises lithic (in the uppermost part) and suevitic impact breccias with appreciable amounts of impact melt fragments. The lithic clast content is dominated by graywacke, besides various metapelites, quartzite, and a carbonate target component. Shock deformation in the form of quartz grains with planar microdeformations is

  8. 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

  9. 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.

  10. The Chicxulub Multiring Impact Crater and the Cretaceous/Paleogene Boundary: Results From Geophysical Surveys and Drilling

    NASA Astrophysics Data System (ADS)

    Urrutia-Fucugauchi, J.; Perez-Cruz, Ligia

    2010-03-01

    The Chicxulub crater has attracted considerable attention as one of the three largest terrestrial impact structures and its association with the Cretaceous/Paleogene boundary (K/Pg). Chicxulub is a 200 km-diameter multi-ring structure formed 65.5 Ma ago in the Yucatan carbonate platform in the southern Gulf of Mexico and which has since been buried by Paleogene and Neogene carbonates. Chicxulub is one of few large craters with preserved ejecta deposits, which include the world-wide K/Pg boundary clay layer. The impact has been related to the global major environmental and climatic effects and the organism mass extinction that mark the K/Pg boundary, which affected more than 70 % of organisms, including the dinosaurs, marine and flying reptiles, ammonites and a large part of the marine microorganisms. The impact and crater formation occur instantaneously, with excavation of the crust down to 25 km depths in fractions of second and lower crust uplift and crater formation in a few hundreds of seconds. Energy released by impact and crustal deformation generates seismic waves traveling the whole Earth, and resulting in intense fracturing and deformation at the target site. Understanding of the physics of impacts on planetary surfaces and modeling of processes of crustal deformation, rheological behavior of materials at high temperatures and pressures remain a major challenge in geosciences. Study of the Chicxulub crater and the global effects and mass extinction requires inter- and multidisciplinary approaches, with researchers from many diverse fields beyond the geosciences. With no surface exposures, geophysical surveys and drilling are required to study the crater. Differential compaction between the impact breccias and the surrounding carbonate rocks has produced a ring-fracture structure that at the surface reflects in a small topographic depression and the karstic cenote ring. The crater structure, located half offshore and half on-land, has been imaged by

  11. 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.

  12. Impact Crater

    NASA Technical Reports Server (NTRS)

    2002-01-01

    [figure removed for brevity, see original site]

    The irregularly shaped rim of this bowl shaped impact crater is most likely due to erosion and the subsequent infilling of sediment.

    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.

  13. The Chicxulub Multiring Impact Crater and the Cretaceous/Paleogene Boundary: Results From Geophysical Surveys and Drilling

    NASA Astrophysics Data System (ADS)

    Urrutia-Fucugauchi, J.; Perez-Cruz, Ligia

    2010-03-01

    The Chicxulub crater has attracted considerable attention as one of the three largest terrestrial impact structures and its association with the Cretaceous/Paleogene boundary (K/Pg). Chicxulub is a 200 km-diameter multi-ring structure formed 65.5 Ma ago in the Yucatan carbonate platform in the southern Gulf of Mexico and which has since been buried by Paleogene and Neogene carbonates. Chicxulub is one of few large craters with preserved ejecta deposits, which include the world-wide K/Pg boundary clay layer. The impact has been related to the global major environmental and climatic effects and the organism mass extinction that mark the K/Pg boundary, which affected more than 70 % of organisms, including the dinosaurs, marine and flying reptiles, ammonites and a large part of the marine microorganisms. The impact and crater formation occur instantaneously, with excavation of the crust down to 25 km depths in fractions of second and lower crust uplift and crater formation in a few hundreds of seconds. Energy released by impact and crustal deformation generates seismic waves traveling the whole Earth, and resulting in intense fracturing and deformation at the target site. Understanding of the physics of impacts on planetary surfaces and modeling of processes of crustal deformation, rheological behavior of materials at high temperatures and pressures remain a major challenge in geosciences. Study of the Chicxulub crater and the global effects and mass extinction requires inter- and multidisciplinary approaches, with researchers from many diverse fields beyond the geosciences. With no surface exposures, geophysical surveys and drilling are required to study the crater. Differential compaction between the impact breccias and the surrounding carbonate rocks has produced a ring-fracture structure that at the surface reflects in a small topographic depression and the karstic cenote ring. The crater structure, located half offshore and half on-land, has been imaged by

  14. A Fresh Crater Drills to Tharsis Bedrock

    NASA Technical Reports Server (NTRS)

    2007-01-01

    The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) took this image of a newly formed impact crater in the Tharsis region of Mars at 1316 UTC (8:16 a.m. EST) on Jan. 13, 2007, near 17.0 degrees north latitude, 246.4 degrees east longitude. CRISM's image was taken in 544 colors covering 0.36-3.92 micrometers, and shows features as small as 20 meters (66 feet) across. The region covered by the image is just over 10 kilometers (6 miles) wide at its narrowest point.

    The Tharsis region is a high volcanic plateau that stands about 5 kilometers (3 miles) above the surrounding plains. The rocks forming Tharsis are younger than in most parts of mars, as evidenced by their low density of craters. The best estimate of their age is comparable to the age of Shergotty-class meteorites thought to originate from Mars. However, Tharsis is covered by a nearly unbroken, meters-thick layer of dust that has frustrated all attempts to measure its bedrock composition remotely, and to determine if it matches the composition of Shergotty-class meteorites.

    The recent discovery of dark, newly formed impact craters on Mars has provided the CRISM team a chance, finally, to measure the rocks that make up Tharsis. Over the lifetime of the Mars Global Surveyor mission, its high-resolution Mars Orbiter Camera monitored the surface and documented the very recent formation of some two dozen small impact craters. Several of them are in Tharsis and pierce the plateau's dust blanket to expose bedrock. MRO's instruments have been trained on these 'drill holes' into Mars' volcanic crust, including the crater shown here.

    The top image was constructed from three infrared wavelengths that usually highlight compositional variations. This image shows the impact crater, a ring of dark, excavated rock (inset), and a surrounding system of rays. Crater rays are common around young impact craters, and they form when ejected boulders reimpact the surface and stir up the local rock

  15. 10Be content in clasts from fallout suevitic breccia in drill cores from the Bosumtwi impact crater, Ghana: Clues to preimpact target distribution

    NASA Astrophysics Data System (ADS)

    Losiak, Anna; Wild, Eva Maria; Michlmayr, Leonard; Koeberl, Christian

    2014-03-01

    Rocks from drill cores LB-07A (crater fill) and LB-08A (central uplift) into the Bosumtwi impact crater, Ghana, were analyzed for the presence of the cosmogenic radionuclide 10Be. The aim of the study was to determine the extent to which target rocks of various depths were mixed during the formation of the crater-filling breccia, and also to detect meteoric water infiltration within the impactite layer. 10Be abundances above background were found in two (out of 24) samples from the LB-07A core, and in none of five samples from the LB-08A core. After excluding other possible explanations for an elevated 10Be signal, we conclude that it is most probably due to a preimpact origin of those clasts from target rocks close to the surface. Our results suggest that in-crater breccias were well mixed during the impact cratering process. In addition, the lack of a 10Be signal within the rocks located very close to the lake sediment-impactite boundary suggests that infiltration of meteoric water below the postimpact crater floor was limited. This may suggest that the infiltration of the meteoric water within the crater takes place not through the aerial pore-space, but rather through a localized system of fractures.

  16. Diaplectic transformation of minerals: Vorotilov drill core, Puchezh-Katunki impact crater, Russia

    NASA Technical Reports Server (NTRS)

    Feldman, V. I.

    1992-01-01

    The Vorotilov core was drilled in the central uplift of the Puchezh-Katunki astrobleme to a depth of 5.1 km. Impactites are revealed in the rocks of the core beginning from a depth of 366 m: suevites (66 m), allogenic breccias (112 m), and autogenic breccias (deeper than 544 m). These rocks are represented by shocked-metamorphic gneisses, schists, amphibolites of Archean age, and magmatic rocks (dolerites, olivines, and peridotites) that lie between them.

  17. 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.

  18. Impact craters on Titan

    USGS Publications Warehouse

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

    2010-01-01

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

  19. 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.

  20. 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.

  1. 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

  2. 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.

  3. 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

  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. Cratering reservoir potential by impact cratering

    SciTech Connect

    Schultz, P.H.

    1996-12-31

    Impact craters are gaining increasing acceptance and value as sites for potential hydrocarbon reservoirs. Nevertheless, such structures are often difficult to interpret and assess because their physical expressions from physical data have few exposed terrestrial analogs for comparison. Observational, theoretical, and experimental studies directed - toward understanding the nature of well-preserved craters on other planets, however, establish a two-dimensional template for understanding and interpreting the three-dimensional view, critical or assessing hydrocarbon potentials. But terminology often used in describing an impact structure needs to be placed in a process context. Impact craters are not produced instantaneously but evolve through time. The process occurs in three different stages of formation corresponding to the transfer of kinetic energy: compression, excavation, and modification. The compression stage roughly corresponds to the time required for transfer of energy from impactor to target and is reflected in the formation of a central penetration zone in smaller craters and the central uplift in larger craters often called the {open_quotes}central plug, diapir, brecciated core, or distributed zone{close_quotes}. The excavation stage occurs as the cratering flow field draws material downward near the center and outward from the cavity. Traps are created stratigraphically inside (shock-disrupted rock and depositional capping) or outside (inverted stratigraphy, fractured/fault target, porous ejecta) as well as structurally inside (uplift, wall terraces) or outside (concentric listric faults or seismically triggered failure). Larger complex craters create greater potential traps. Consequently, potential reserve can be created during each stage but the most important criteria remains the realtors motto: location, location, location!

  7. Cratering reservoir potential by impact cratering

    SciTech Connect

    Schultz, P.H. )

    1996-01-01

    Impact craters are gaining increasing acceptance and value as sites for potential hydrocarbon reservoirs. Nevertheless, such structures are often difficult to interpret and assess because their physical expressions from physical data have few exposed terrestrial analogs for comparison. Observational, theoretical, and experimental studies directed - toward understanding the nature of well-preserved craters on other planets, however, establish a two-dimensional template for understanding and interpreting the three-dimensional view, critical or assessing hydrocarbon potentials. But terminology often used in describing an impact structure needs to be placed in a process context. Impact craters are not produced instantaneously but evolve through time. The process occurs in three different stages of formation corresponding to the transfer of kinetic energy: compression, excavation, and modification. The compression stage roughly corresponds to the time required for transfer of energy from impactor to target and is reflected in the formation of a central penetration zone in smaller craters and the central uplift in larger craters often called the [open quotes]central plug, diapir, brecciated core, or distributed zone[close quotes]. The excavation stage occurs as the cratering flow field draws material downward near the center and outward from the cavity. Traps are created stratigraphically inside (shock-disrupted rock and depositional capping) or outside (inverted stratigraphy, fractured/fault target, porous ejecta) as well as structurally inside (uplift, wall terraces) or outside (concentric listric faults or seismically triggered failure). Larger complex craters create greater potential traps. Consequently, potential reserve can be created during each stage but the most important criteria remains the realtors motto: location, location, location

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

    USGS Publications Warehouse

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

    1973-01-01

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

  9. Lonar lake, India: an impact crater in basalt.

    PubMed

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

    1973-05-25

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

  10. Shock-metamorphic petrography and microRaman spectroscopy of quartz in upper impactite interval, ICDP drill core LB-07A, Bosumtwi impact crater, Ghana

    NASA Astrophysics Data System (ADS)

    Morrow, Jared R.

    Standard and universal stage optical microscope and microRaman spectroscopic examination of quartz from the upper impactite interval of the International Continental Scientific Drilling Program (ICDP) Lake Bosumtwi crater drill core LB-07A demonstrates widespread but heterogeneous evidence of shock metamorphism. In the upper impactite, which comprises interbedded polymict lithic breccia and suevite from a drilling depth of 333.4-415.7 m, quartz occurs as a major component within metasedimentary lithic clasts and as abundant, isolated, single-crystal grains within matrix. The noted quartz shock-metamorphic features include phenomena related to a) deformation, such as abundant planar microstructures, grain mosaicism, and reduced birefringence; b) phase transformations, such as rare diaplectic quartz glass and very rare coesite; c) melting, such as isolated, colorless to dark, glassy and devitrified vesicular melt grains; and d) secondary, post-shock features such as abundant, variable decoration of planar microstructures and patchy grain toasting. Common to abundant planar deformation features (PDFs) in quartz are dominated by -equivalent crystallographic planes, although significant percentages of and other higher index orientations also occur; notably, c(0001) planes are rare. Significantly, the quartz PDF orientations match most closely those reported elsewhere from strongly shocked, crystalline-target impactites. Barometry estimates based on quartz alteration in the upper impactite indicate that shock pressures in excess of 20 GPa were widely reached; pressures exceeding 40-45 GPa were more rare. The relatively high abundances of decorated planar microstructures and grain toasting in shocked quartz, together with the nature and distribution of melt within suevite, suggest a water- or volatile-rich target for the Bosumtwi impact event.

  11. Impact Cratering Calculations

    NASA Technical Reports Server (NTRS)

    Ahrens, Thomas J.

    2001-01-01

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

  12. 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.

  13. Description of Tessaracoccus profundi sp.nov., a deep-subsurface actinobacterium isolated from a Chesapeake impact crater drill core (940 m depth)

    USGS Publications Warehouse

    Finster, K.W.; Cockell, C.S.; Voytek, M.A.; Gronstal, A.L.; Kjeldsen, K.U.

    2009-01-01

    A novel actinobacterium, designated CB31T, was isolated from a 940 m depth sample of a drilling core obtained from the Chesapeake meteor impact crater. The strain was isolated aerobically on R2A medium agar plates supplemented with NaCl (20 g l-1) and MgCl2???6H 2O (3 g l-1). The colonies were circular, convex, smooth and orange. Cells were slightly curved, rod-shaped in young cultures and often appeared in pairs. In older cultures cells were coccoid. Cells stained Gram-positive, were non-motile and did not form endospores. The diagnostic diamino acid of the peptidoglycan was ll-diaminopimelic acid. The polar lipids included phosphatidylglycerol, diphosphatidglycerol, four different glycolipids, two further phospholipids and one unidentified lipid. The dominant menaquinone was MK-9(H4) (70%). The major cellular fatty acid was anteiso C15:0 (83%). The DNA G + C content was 68 mol%. The strain grew anaerobically by reducing nitrate to nitrite or by fermenting glucose. It was catalase positive and oxidase negative. It grew between 10 and 45??C, with an optimum between 35 and 40??C. The pH range for growth was 5.7-9.3, with an optimum at pH 7.5. The closest phylogenetic neighbors based on 16S rRNA gene sequence identity were members of the genus Tessaracoccus (95-96% identity). On the basis of phenotypic and phylogenetic distinctiveness, strain CB31T is considered to represent a novel species of the genus Tessaracoccus, for which we propose the name Tessaracoccus profundi sp. nov.. It is the first member of this genus that has been isolated from a deep subsurface environment. The type strain is CB31T (=NCIMB 14440T = DSM 21240T). ?? 2009 Springer Science+Business Media B.V.

  14. 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.

  15. 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…

  16. 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.

  17. 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).

  18. 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.

  19. 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.

  20. 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.

  1. Seismic investigation of the Lake Bosumtwi impact crater: preliminary results

    NASA Astrophysics Data System (ADS)

    Karp, Tobias; Milkereit, Bernd; Janle, Peter; Danuor, Sylvester K.; Pohl, Jean; Berckhemer, Hans; Scholz, Christopher A.

    2002-06-01

    The Lake Bosumtwi impact crater in Ghana, West Africa, has a diameter of 10.5 km and is one of the youngest ( 1.07 Ma) well-preserved large craters on Earth. It has a total dynamic range of topography of more than 400 m, and it is the source crater of tektites and microtektites of the Ivory Coast strewn field. The crater was excavated in early Proterozoic rocks. According to its size, the Bosumtwi impact crater should be a complex impact structure, with a central peak. Multichannel seismic (MCS) reflection and wide angle data, using Ocean-Bottom-Hydrophones (OBHs), were acquired in order to investigate the structure's subsurface, image the presumed central uplift and determine the thickness of impact-related formations and the post-impact sediments. An integrated interpretation of the seismic data sets, and modelling and inversion of the OBH data yield an initial 2D velocity-depth model, which shows indications for a central peak feature. Due to the relatively low seismic velocity ( 3.0 km s -1) of the corresponding layer, the top of the uplifted structure is interpreted to consist of allochthonous breccia. The central peak has a width of ˜1.8 km and a maximum height of 120 m above the top of the breccia away from the center. Fracturing may be responsible for the relatively low velocity of 3.8 km s -1 in the crater floor. The post-impact sediments covering the crater structure are 180- 300 m thick. The apparent crater depth, defined as the difference between the original target surface and the top of the breccia layer, is ˜550 m and thereby slightly deeper than some other larger complex impact structures on Earth. The results indicate that the Lake Bosumtwi impact structure provides an interesting setting for scientific drilling of a young large impact crater and will be supplemented by complimentary recent geophysical (potential field) and possibly future drilling studies.

  2. 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.

  3. 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.

  4. 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

  5. Locating the K/T boundary impact crater(s)

    NASA Astrophysics Data System (ADS)

    Bush, Susan M.

    Stratigraphic, mineralogical, chemical and isotopic evidence have led to the large (˜10-km) asteroid or comet impact theory as the cause of the Cretaceous period coming to an end. However, a suitable crater has not yet been found. Although the crater may have been destroyed because half of what was then the ocean floor has since been subducted, researchers are still hot on the trail of the impact site(s).A. R. Hildebrand and W. V. Boynton, Department of Planetary Sciences, University of Arizona, Tucson, believe that locating the original crater(s) would resolve the volcanism versus impact debate over what ended the Cretaceous period. Based on a large concentration of shocked mineral grains and the largest grains occurring in North America, and impact-wave deposits at the K/T boundary only from the Caribbean and southern North America, they suggest that the K/T boundary impact occurred between North and South America. They suggest the 300-km-diameter buried basement structure in the Columbia Basin as a possible K/T impact crater. The location of impact-wave deposits and possibly seismically triggered slumps also helped the two decide that impact(s) musthave occurred in the Caribbean region.

  6. 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

  7. 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.

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

    NASA Technical Reports Server (NTRS)

    Ivanov, B. A.

    1992-01-01

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

  9. 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

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

    NASA Astrophysics Data System (ADS)

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

    1995-09-01

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

  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. The impact cratering record on Triton

    NASA Astrophysics Data System (ADS)

    Strom, Robert G.; Croft, Steven K.; Boyce, Joseph M.

    1990-10-01

    Impact craters on Triton are scarce owing to the relatively recent resurfacing by icy melts. The most heavily cratered surface has a crater density about the same as the lunar maria. The transition diameter from simple to complex craters occurs at a diameter of about 11 kilometers, and the depth-diameter relationship is similar to that of other icy satellites when gravity is taken into account. The crater size-frequency distribution has a differential -3 slope (cumulative -2 slope) and is the same as that for the fresh crater population on Miranda. The most heavily cratered region is on the leading hemisphere in Triton's orbit. Triton may have a leading-trailing asymmetry in its crater population. Based primarily on the similarity of size distributions on Triton and Miranda and the relatively young surface on Triton, the source of Triton's craters is probably comets. The very peculiar size distribution of sharp craters on the 'cantaloupe' terrain and other evidence suggests thay are volcanic explosion craters.

  13. 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.

  14. A Buried Precambrian Impact Crater in Scotland

    NASA Astrophysics Data System (ADS)

    Simms, M. J.

    2016-08-01

    Field evidence indicates that the source of the Stac Fada impact deposit (Mesoproterozoic) in NW Scotland was to the east, and that the now buried crater is represented by the 40+ km diameter Lairg Gravity Low.

  15. 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).

  16. 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.

  17. 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.

  18. 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

  19. 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

  20. 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.

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

    PubMed

    Lindsay, John; Brasier, Martin

    2006-04-01

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

  2. Impact Craters as Biospheric Microenvironments, Lawn Hill Structure, Northern Australia

    NASA Astrophysics Data System (ADS)

    Lindsay, John; Brasier, Martin

    2006-04-01

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

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

    PubMed

    Lindsay, John; Brasier, Martin

    2006-04-01

    Impact craters on Mars act as traps for eolian sediment and in the past may have provided suitable microenvironments that could have supported and preserved a stressed biosphere. If this is so, terrestrial impact structures such as the 18-km-diameter Lawn Hill Structure, in northern Australia, may prove useful as martian analogs. We sampled outcrop and drill core from the carbonate fill of the Lawn Hill Structure and recorded its gamma-log signature. Facies data along with whole rock geochemistry and stable isotope signatures show that the crater fill is an outlier of the Georgina Basin and was formed by impact at, or shortly before, approximately 509-506 million years ago. Subsequently, it was rapidly engulfed by the Middle Cambrian marine transgression, which filled it with shallow marine carbonates and evaporites. The crater formed a protected but restricted microenvironment in which sediments four times the thickness of the nearby basinal succession accumulated. Similar structures, common on the martian surface, may well have acted as biospheric refuges as the planet's water resources declined. Low-pH aqueous environments on Earth similar to those on Mars, while extreme, support diverse ecologies. The architecture of the eolian crater fill would have been defined by long-term ground water cycles resulting from intermittent precipitation in an extremely arid climate. Nutrient recycling, critical to a closed lacustrine sub-ice biosphere, could be provided by eolian transport onto the frozen water surface. PMID:16689651

  4. 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.

  5. Titan's Impact Craters and Associated Fluvial Features

    NASA Astrophysics Data System (ADS)

    Gilliam, A.; Jurdy, D. M.

    2012-12-01

    The Cassini spacecraft has detected remarkably few impact craters on the surface of Titan. By early 2010, with surface radar coverage reaching 33%, seven certain impact craters were discovered, with another 52 nearly certain and probable ones. The paucity of craters implies that the surface of Titan is very dynamic and relatively young. Dynamical models of the internal structure of Titan suggest the possibility of a subsurface ocean of ammonia-water liquid beneath its icy shell. If a large subsurface ocean does exist, it should have measurable effects on Titan's surface and the morphology of its craters. Using a combination of available Cassini radar-SAR, ISS, and VIMS data, we construct geomorphologic maps of Titan's "certain" impact craters with associated features we interpret as fluvial in origin. The best example, Menrva, a 445 km wide double-ring impact basin, hosts a complex network of channels. On the western, more degraded side of the crater, channels cut through the outer rim. To the east of Menrva, a curious network of channels start near the rim crest and appear to have flowed away into a large catchment basin; the complex is termed Elivagar Flumina. Channels surrounding Menrva display a low order - a classification of stream segments based on the number of tributaries upstream - measuring one or two, occasionally up to three. This matches observations of two other confirmed impact craters with associated fluvial features. A halo of low-order channels encircles Selk, an 80 km diameter crater with a small central peak. Also, Ksa, a 30 km diameter crater with a bright central peak and radial ejecta, has a feature that appears to be a first order channel. These differ radically from the tree-shaped dendritic channels common on Titan, which are generally attributed to heavy rainfall. For example, the Xanadu region, as observed on the T13 swath, exhibits a very complex and dendritic network of channels, where the order of channels reaches six to seven. The

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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.

  12. Major and Trace Element Variations in Impact Crater Clay from Chicxulub, Lonar, and Mistastin, Implications for the Martian Soil

    NASA Technical Reports Server (NTRS)

    Newsom, H. E.; Nelson, M. J.; Shearer, C. K.; Rietmeijer, F. J. M.; Gakin, R.; Lee, K.

    2004-01-01

    The catastrophic Chicxulub event should have generated a large hydrothermal system with volatile element mobilization, producing interesting alteration materials and clays. The Yaxcopoil-1 (YAX) drill hole is located in the annular trough, about 70 km southwest of the crater center, in an area where the impactite layers are relatively thin (approx. 100 m thick). We have analyzed samples from the YAX drill core and from other impact craters including Mistastin and Lonar to determine the nature of alteration and trace element mobilization.

  13. 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

  14. 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

  15. 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

  16. 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.

  17. The Characteristics of Polygonal Impact Craters on Venus

    NASA Astrophysics Data System (ADS)

    Aittola, Marko; Öhman, Teemu; Leitner, Johannes J.; Raitala, Jouko

    2007-10-01

    Polygonal impact craters (PICs) are craters whose shape in plan view is more or less angular instead of being circular or ellipsoidal. This type of craters are present and often common on the Moon, Mercury, Mars and several asteroids and icy moons and after the careful analysis we found on Venus 131 impact craters, which show at least two straight rim segments. This survey proves that there are polygonal impact craters on Venus and they may provide a good tool to analyse the properties of the planet’s surface/crust/lithosphere as well as the impact process itself. This study also collaborates our previous results, that PICs are not an anomaly among craters, but an integral part of all impact craters regardless of their size or environment. We compared the polygonal impact craters to “normal”-shaped craters by using different characteristics (diameter, altitude, geologic setting, morphologic class, floor reflectance, degradation stage, and wall terracing). It turned out that the smaller crater sizes favor the formation of straight rim segments, but otherwise these craters show similar characteristics to other craters. Our study also shows that there are regions where the straight segments of the crater rims most clearly follow the orientations of the dominant tectonic features of the area. Thus, the orientations of crater walls reflect-at least in some places-the local tectonics and zones of weakness also on Venus and could thus tell us about the directions and distributions of fractures or other zones of weakness in the crust.

  18. 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.

  19. Paleomagnetism of Lonar Crater Impact Glass

    NASA Astrophysics Data System (ADS)

    Garrick-Bethell, I.; Weiss, B. P.; Maloof, A. C.; Stewart, S. T.; Louzada, K. L.; Soule, S. A.; Swanson-Hysell, N.

    2006-12-01

    The source of magnetic fields on extraterrestrial bodies is largely unknown. There is particularly little information about magnetic fields on asteroids and the Moon for the last 3 billion years because most samples from these bodies predate this time. An exception is the small amount of impact-melt which has been continuously created by hypervelocity impactors over most of solar system history. Impact melt can be used to test the controversial hypothesis that magnetic fields on extraterrestrial bodies were predominantly the product of impact-produced plasmas rather than of core dynamos. However, to date only a small amount of impact melt has been analyzed paleomagnetically. To assess the quality of impact melts as recorders of magnetic fields, in January 2004 and January 2005 we collected thousands of samples of basaltic glass from the perimeter of Lonar Crater, a 1.8 km diameter impact crater which formed approximately 50,000 years ago in the Deccan Traps in Maharashtra, India. Lonar crater is a unique extraterrestrial analog because it is the only fresh impact crater on the Earth in a basaltic target. Most glass samples have rounded features and are between 0.01 and 1 cm in size, indicating that they are fladen and impact spherules (microtektites) formed from molten ejecta that cooled in mid-air while subject to rotational and aerodynamic forces. We have found that both types of glasses are strongly magnetic (saturation remanence of ~2 A m-1), contain ferromagnetic crystals that are predominantly single domain in size, and have no significant remanence anisotropy. The glasses also carry a natural remanent magnetization (NRM) presumably acquired just after the impact. However, alternating field demagnetization results in large directional changes of the magnetic moment, with little decrease in moment intensity. We interpret this unusual behavior as progressive removal of different coercivity components that cooled while the orientation of the spinning glasses

  20. Density of impact craters on tessera, Venus

    NASA Technical Reports Server (NTRS)

    Ivanov, M. A.; Basilevsky, A. T.

    1993-01-01

    After the plains, tessera is the most abundant terrain on Venus. It occupies about 10 percent of the Venusian surface, forming the continent-like blocks and small islands above the adjacent plains. Tessera is a result of tectonic deformations of some precursor terrain. However, the nature of that precursor, as well as the causes and mechanisms of its formations, are under debate. Any models considering tessera terrain involve estimation of tessera age, either relative or absolute. It is well known that the important information on the age of a planetary surface comes from impact crater statistics. The Magellan global overview of Venus with improved resolution provides an opportunity to gather data on impact craters in amounts large enough for statistically reliable estimations of crater density for different terrains. Our study of impact crater density on tesserae compared to the surrounding terrains has a goal to determine whether it is higher, lower, or the same and to interpret it in terms of the tessera age and processes involved.

  1. 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.

  2. 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.

  3. Exploring Impact Crater Paleolakes in 2003

    NASA Astrophysics Data System (ADS)

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

    2001-01-01

    Paleolakes in impact craters have been surveyed for the past 20 years and have raised considerable interest because of their potential to document many of the questions that are at the heart of the Mars exploration program, especially Astrobiology and search for life. Recent high-resolution Mars Orbiter Camera (MOC) images seem to provide another support to their existence and are giving new data to explore these past lakes that Viking had helped us unravel. They also show the importance of a continuing exploration program at increasing resolution. It is now possible to fully investigate the broad spectrum of martian Crater lakes from Noachian to Amazonian, up to very recent times, since fresh gullies have been also observed in impact craters. Before the confirmation by MOC, several studies on the subject had pointed out the importance of martian limnology as a method to understand the past climate, hydrogeology, and possibly biology of Mars. Considering the questions raised both by the Viking and MGS mission about these crater lakes and their extraordinary potential for astrobiological investigations, the next logical step is to explore them in situ, and it is possible with MER-A and MER-B in 2003.

  4. 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

  5. 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

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

    NASA Technical Reports Server (NTRS)

    Levine, Arlene S.

    2008-01-01

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

  7. Dependence of Secondary Crater Shape on Impact Velocity

    NASA Astrophysics Data System (ADS)

    Watters, W. A.; Collins, G. S.; Hundal, C.; Radford, A.; Tornabene, L. L.

    2016-08-01

    We have characterized the transition in crater shape from "splash" to hypervelocity impacts as a function of impactor speed using the morphometry of small martian secondary craters in HiRISE stereo-derived DEMs, as well as computer simulations.

  8. 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

  9. Potential Cement Phases in Sedimentary Rocks Drilled by Curiosity at Gale Crater, Mars

    NASA Technical Reports Server (NTRS)

    Rampe, E. B.; Morris, R. V.; Bish, D. L.; Chipera, S. J.; Ming, D. W.; Blake, D. F.; Vaniman, D. T.; Bristow, T. F.; Cavanagh, P.; Farmer, J. D.; Morrison, S. M.; Siebach, K.; Treiman, A. H.; Achilles, C. N.; Blaney, D.; Crisp, J. A.; Des Marais, D. J.; Downs, R. T.; Fendrich, K.; Martin-Torres, J.; Morookian, J. M.; Zorzano, M.-P.; Sarrazin, P.; Spanovich, N.; Yen, A. S.

    2015-01-01

    The Mars Science Laboratory rover Curiosity has encountered a variety of sedimentary rocks in Gale crater with different grain sizes, diagenetic features, sedimentary structures, and varying degrees of resistance to erosion. Curiosity has drilled three rocks to date and has analyzed the mineralogy, chemical composition, and textures of the samples with the science payload. The drilled rocks are the Sheepbed mudstone at Yellowknife Bay on the plains of Gale crater (John Klein and Cumberland targets), the Dillinger sandstone at the Kimberley on the plains of Gale crater (Windjana target), and a sedimentary unit in the Pahrump Hills in the lowermost rocks at the base of Mt. Sharp (Confidence Hills target). CheMin is the Xray diffractometer on Curiosity, and its data are used to identify and determine the abundance of mineral phases. Secondary phases can tell us about aqueous alteration processes and, thus, can help to elucidate past aqueous environments. Here, we present the secondary mineralogy of the rocks drilled to date as seen by CheMin and discuss past aqueous environments in Gale crater, the potential cementing agents in each rock, and how amorphous materials may play a role in cementing the sediments.

  10. Deep drilling into the Chesapeake Bay impact structure

    USGS Publications Warehouse

    Gohn, G.S.; Koeberl, C.; Miller, K.G.; Reimold, W.U.; Browning, J.V.; Cockell, C.S.; Horton, J.W.; Kenkmann, T.; Kulpecz, A.A.; Powars, D.S.; Sanford, W.E.; Voytek, M.A.

    2008-01-01

    Samples from a 1.76-kilometer-deep corehole drilled near the center of the late Eocene Chesapeake Bay impact structure (Virginia, USA) reveal its geologic, hydrologic, and biologic history. We conducted stratigraphic and petrologic analyses of the cores to elucidate the timing and results of impact-melt creation and distribution, transient-cavity collapse, and ocean-water resurge. Comparison of post-impact sedimentary sequences inside and outside the structure indicates that compaction of the crater fill influenced long-term sedimentation patterns in the mid-Atlantic region. Salty connate water of the target remains in the crater fill today, where it poses a potential threat to the regional groundwater resource. Observed depth variations in microbial abundance indicate a complex history of impact-related thermal sterilization and habitat modification, and subsequent post-impact repopulation.

  11. Deep drilling into the Chesapeake Bay impact structure.

    PubMed

    Gohn, G S; Koeberl, C; Miller, K G; Reimold, W U; Browning, J V; Cockell, C S; Horton, J W; Kenkmann, T; Kulpecz, A A; Powars, D S; Sanford, W E; Voytek, M A

    2008-06-27

    Samples from a 1.76-kilometer-deep corehole drilled near the center of the late Eocene Chesapeake Bay impact structure (Virginia, USA) reveal its geologic, hydrologic, and biologic history. We conducted stratigraphic and petrologic analyses of the cores to elucidate the timing and results of impact-melt creation and distribution, transient-cavity collapse, and ocean-water resurge. Comparison of post-impact sedimentary sequences inside and outside the structure indicates that compaction of the crater fill influenced long-term sedimentation patterns in the mid-Atlantic region. Salty connate water of the target remains in the crater fill today, where it poses a potential threat to the regional groundwater resource. Observed depth variations in microbial abundance indicate a complex history of impact-related thermal sterilization and habitat modification, and subsequent post-impact repopulation. PMID:18583604

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. Impact melt flows at Lowell crater

    NASA Astrophysics Data System (ADS)

    Plescia, Jeffrey B.; Spudis, Paul D.

    2014-11-01

    A deposit of low-albedo lobate material occurs on the southeastern wall and floor of Lowell on the western Outer Montes Rook ring of the lunar Orientale basin. Lowell is an Upper Imbrian, 66-km diameter crater located at 13° S, 257° E (103° W). The lobate material begins at the lowest part of the rim of Lowell H, a 9-km diameter crater superposed on the southeast rim and inner wall of Lowell, and the material extends ~14-15 km down the slope and across Lowell's eastern floor. This lobate material resembles lava flows with a linear form, lobate margins, central channels, and embayment relations with older higher terrain. Srivastava et al. (2013a) interpret it to be of volcanic origin, with a vent on the floor of Lowell H. We suggest instead that the lobate material is impact melt derived from Lowell H. In this context, the material splashed out and flowed over the low northwestern rim of Lowell H and continued to flow down to and across the floor of the larger crater Lowell. The morphology and composition of this material resembles that of other impact melt deposits on the Moon.

  19. Impact Crater Deposits in the Martian Highlands

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  20. 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.

  1. 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.

  2. Roter Kamm Impact Crater in Namibia

    NASA Technical Reports Server (NTRS)

    1995-01-01

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

  3. Relative Age of Polygonal Impact Craters on Venus

    NASA Astrophysics Data System (ADS)

    Weihs, G. T.; Leitner, J. J.; Firneis, M. G.

    2014-04-01

    Impact craters form typical landforms on the inner planets of our Solar System, and their number, distribution and conservation status reflect the geological history of the planet. Polygon Impact Craters (PICs) are different from other impact craters by a more or less angular shape [1]. Criterion is that the crater rims are made up of at least two straight adjacent segments. Previous studies (e.g. [5]) have proven that the PICs were found on the Moon, on Mercury, Venus, Mars and several asteroids and icy moons. These papers showed that there are regions where the straight edge of the crater segments seem to align with the local tectonics near the crater, especially at points of lower density, so-called "zones of weakness". With this technique the physical properties of the target material, as well as details of the mechanics of crater formation could be examined.

  4. The Impact Cratering Record of Fennoscandia

    NASA Astrophysics Data System (ADS)

    Pesonen, L. J.

    1996-02-01

    The current database of craterform structures in Fennoscandia contains 22 structures of impact origin and about fifty other structures which lack sufficient evidence for impact. The discovery rate of new structures has been one or two per year during the past ten years. The proven impact structures are located in southern Fennoscandia and the majority have been found in Proterozoic target rocks. The age of the structures varies from prehistoric to ≤ 1000 Ma and their diameters (D) from 0.04 km to 55 km. Nine of the structures contain impact melt. A characteristic feature of the Fennoscandian impact record is a relatively large number of small (≤ 5 km) but old (> 200 Ma) structures: this is a result of success of geophysical methods to discover small but old impact structures in an eroded shield covered with relatively thin overburden. Some of the large circular structures in satellite images and/or in geophysical maps may represent deeply eroded scars of very old impacts, but due to the lack of shock metamorphic features, impact-generated rocks or identified ejecta layers, they cannot yet be classified as impact sites. Two huge structures are proposed here as possible impact sites on the basis of circular satellite images and distinct geophysical anomalies: the Lycksele structure in northern Sweden (D ~ 120 km, see also Witschard, 1984) and the Valga structure in Latvia/Estonia (D ~ 180 km). However, endogeneous explanations, like buried granites, basement domings, or fault-bounded blocks are also possible for these structures. Hints, such as distal ejecta layers or impact produced breccia dykes, of an Archaean or Early Proterozoic impact structure have not been found in Fennoscandia so far. New ways of searching for these structures are proposed with particular emphasis on high-resolution integrated geophysical methods. The impact cratering rate in Fennoscandia is ~ 2.0 · 10-14 km-2 a-1 (for craters with D > 3 km) corresponding to about two events per every

  5. 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

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

    NASA Astrophysics Data System (ADS)

    Mouginis-Mark, P. J.; Hayashi, J. N.

    1993-04-01

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

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2012-04-01

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

  9. 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.

  10. Craters and coronae - the influence of volcano-tectonic features on impact crater formation on Venus

    NASA Astrophysics Data System (ADS)

    Kukkonen, S.; Aittola, M.; Öhman, T.

    2015-10-01

    This study takesa more detailed look on the types of Venusian tectonic structures affecting polygonal impact crater formation and shows that the surroundings of the Venusian volcano-tectonic features do not actually favour the formation of polygonal impact craters compared to the circular craters. However, the preexisting structures in the target, caused by volcano-tectonic features,clearly control the orientation of PIC rims when PICs form near these features. As PICs reveal older tectonic features below the surface, this study provide further insight into the tectonic history of Venus and PIC formation.

  11. Deep drilling in the Chesapeake Bay impact structure - An overview

    USGS Publications Warehouse

    Gohn, G.S.; Koeberl, C.; Miller, K.G.; Reimold, W.U.

    2009-01-01

    The late Eocene Chesapeake Bay impact structure lies buried at moderate depths below Chesapeake Bay and surrounding landmasses in southeastern Virginia, USA. Numerous characteristics made this impact structure an inviting target for scientific drilling, including the location of the impact on the Eocene continental shelf, its threelayer target structure, its large size (??85 km diameter), its status as the source of the North American tektite strewn field, its temporal association with other late Eocene terrestrial impacts, its documented effects on the regional groundwater system, and its previously unstudied effects on the deep microbial biosphere. The Chesapeake Bay Impact Structure Deep Drilling Project was designed to drill a deep, continuously cored test hole into the central part of the structure. A project workshop, funding proposals, and the acceptance of those proposals occurred during 2003-2005. Initial drilling funds were provided by the International Continental Scientific Drilling Program (ICDP) and the U.S. Geological Survey (USGS). Supplementary funds were provided by the National Aeronautics and Space Administration (NASA) Science Mission Directorate, ICDP, and USGS. Field operations were conducted at Eyreville Farm, Northampton County, Virginia, by Drilling, Observation, and Sampling of the Earth's Continental Crust (DOSECC) and the project staff during September-December 2005, resulting in two continuously cored, deep holes. The USGS and Rutgers University cored a shallow hole to 140 m in April-May 2006 to complete the recovered section from land surface to 1766 m depth. The recovered section consists of 1322 m of crater materials and 444 m of overlying postimpact Eocene to Pleistocene sediments. The crater section consists of, from base to top: basement-derived blocks of crystalline rocks (215 m); a section of suevite, impact melt rock, lithic impact breccia, and cataclasites (154 m); a thin interval of quartz sand and lithic blocks (26 m); a

  12. 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.

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

    USGS Publications Warehouse

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

    2012-01-01

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

  14. 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.

  15. 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

  16. Projectile Remnants in Central Peaks of Lunar Impact Craters

    NASA Astrophysics Data System (ADS)

    Johnson, B.; Yue, Z.; Minton, D.; Melosh, H. J.; Di, K.; Hu, W.; Liu, Y.

    2012-12-01

    It is generally assumed that during the formation of a large impact crater the projectile is largely melted or vaporized and that only traces remain in the final crater. However, using the finite difference hydrocode iSALE, we show that at impact velocities below about 12 km/sec the projectile, while crushed and strongly deformed, may largely survive the impact. In small craters the projectile is nevertheless widely dispersed across the crater floor. But in complex craters much of the projectile debris is swept back into the central peak area by the collapse flow. Furthermore, on the Moon approximately 30% of asteroid impacts occur at velocities less than 12 km/sec, so that the central peaks of many lunar craters should retain a recognizable signature of the projectile. This observation may explain recent observations of exotic Mg-rich spinels and olivine in the central peaks of craters too small to have excavated the deep crust or mantle of the Moon. Similar conclusions apply to central peaks of complex craters on Mars and Rheasilvia crater on Vesta.

  17. 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.

  18. 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.

  19. Shock metamorphism of Bosumtwi impact crater rocks, shock attenuation, and uplift formation.

    PubMed

    Ferrière, Ludovic; Koeberl, Christian; Ivanov, Boris A; Reimold, Wolf Uwe

    2008-12-12

    Shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures. The distribution of shock metamorphism in drilled basement rocks from the 10.5-kilometer-diameter Bosumtwi crater, and results of numerical modeling of inelastic rock deformation and modification processes during uplift, constrained with petrographic data, allowed reconstruction of the pre-impact position of the drilled rocks and revealed a shock attenuation by approximately 5 gigapascals in the uppermost 200 meters of the central uplift. The proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure. The results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure. PMID:19074347

  20. Shock metamorphism of Bosumtwi impact crater rocks, shock attenuation, and uplift formation.

    PubMed

    Ferrière, Ludovic; Koeberl, Christian; Ivanov, Boris A; Reimold, Wolf Uwe

    2008-12-12

    Shock wave attenuation rate and formation of central uplifts are not precisely constrained for moderately sized complex impact structures. The distribution of shock metamorphism in drilled basement rocks from the 10.5-kilometer-diameter Bosumtwi crater, and results of numerical modeling of inelastic rock deformation and modification processes during uplift, constrained with petrographic data, allowed reconstruction of the pre-impact position of the drilled rocks and revealed a shock attenuation by approximately 5 gigapascals in the uppermost 200 meters of the central uplift. The proportion of shocked quartz grains and the average number of planar deformation feature sets per grain provide a sensitive indication of minor changes in shock pressure. The results further imply that for moderately sized craters the rise of the central uplift is dominated by brittle failure.

  1. 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.

  2. 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.

  3. 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

  4. 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

  5. Late Eocene Star Wars: The Toms Canyon and Chesapeake Bay Impact Craters, U.S. East Coast

    NASA Astrophysics Data System (ADS)

    Poag, C. W.

    1995-09-01

    Two coeval(?) impacts produced craters on the middle late Eocene continental shelf of the United States at ~35 Ma. The smaller crater (1 5-20-km diameter) is buried beneath the New Jersey continental shelf, near Toms Canyon [1]; the larger crater (90-km diameter) lies beneath the floor of Chesapeake Bay, Virginia [2]. Both features are documented by seismic reflection profiles, bore-hole stratigraphy, and shock metamorphism. The Chesapeake Bay crater also is expressed by a distinctive bull's-eye gravity signature. The Toms Canyon crater exhibits atypical features attributable to an oblique impact into a water column 500-1000 m deep. Tektite-bearing sediment gravity flows, generated by the impact, have been cored 30 km southeast of the crater at Deep Sea Drilling Project Site 612 and Ocean Drilling Project Site 904 [3]. The Chesapeake Bay crater appears to be a typical peak-ring crater, as expressed on seismic profiles, but its gravity signature may indicate the presence of an irregular central peak, as well. Seismic profiles document the fault-bounded outer rim of the crater at four locations in the bay and two locations on the adjacent continental shelf, which constrains the position and geometry of two-thirds of the crater perimeter. Two seismic profiles show the presence of six secondary craters (1-5-km diameter) outside the crater rim. Depsite the large size of the Chesapeake Bay crater, there is no signal of global environmental distress or mass extinction associated with the impact. The postimpact strata immediately overlying the breccia lens, however, contain a record of local paleoenvironmental damage. A distinctive postimpact assemblage of agglutinated foraminifera is associated with a low-diversity, infaunal group of calcareous benthic foraminifera, plus abundant planktoninc foraminifera and radiolarians. This taphofacies reflects highly productive late Eocene surface waters (200-500 m deep), resulting in abundant organic matter and oxygen-poor conditions

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

    PubMed

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

    2010-07-01

    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.

  8. 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

  9. 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

  10. Target rock mechanisms influence the impact crater morphology.

    NASA Astrophysics Data System (ADS)

    Öhman, T.; Aittola, M.; Kostama, V. P.; Korteniemi, J.; Raitala, J.

    2008-09-01

    Abstract Polygonal impact craters (PICs) can be used to decipher tectonics of a cratered surface [1-4]. Studies of PICs on Mars and Venus [5-7] have provided information of their importance in revealing ancient structures. Some observations are not fully explained with the current ideas. Thus, new ideas for the PIC formation type and preferred PIC size are proposed.

  11. Results of pre-drilling potential field measurements at the Bosumtwi crater

    NASA Astrophysics Data System (ADS)

    Danuor, S. K.; Menyeh, A.

    Gravity and magnetic measurements were carried out at the Bosumtwi crater to determine the geophysical signature of the crater. Land gravity data was acquired at 163 locations around the structure and on the shore of the lake. The separation between the gravity stations was 500 m for radial profiles, but 700-1000 m along roads and footpaths that ran parallel to the lake's shore. Additionally, a marine gravity survey was carried out along 14 north-south and 15 east-west profiles on the lake. Magnetic data was also acquired along 14 north-south profiles on the lake. In all marine surveys, the line spacing was 800 m, and navigation was provided by a Garmin 235 Echo Sounder/GPS. The gravity signature of the crater is characterized by a negative Bouguer anomaly with an amplitude of about -18 mgal. Using the seismic results as constraints, the gravity model obtained indicates the central uplift at a depth of 250 m. The negative anomaly is the contribution of the gravity deficiencies due to fractured and brecciated rocks in the rim area and below the crater floor, the impact breccias within the crater, and the sedimentary and water infilling of the lake. Magnetic modeling yielded a model for the causative body, which is located north of the central uplift: the model has a magnetic susceptibility of 0.03 S.I. and extends from a depth of 250 to 610 m. The causative bodies have been interpreted as impactites.

  12. Research core drilling in the Manson impact structure, Iowa

    NASA Technical Reports Server (NTRS)

    Anderson, R. R.; Hartung, J. B.; Roddy, D. J.; Shoemaker, E. M.

    1992-01-01

    The Manson impact structure (MIS) has a diameter of 35 km and is the largest confirmed impact structure in the United States. The MIS has yielded a Ar-40/Ar-39 age of 65.7 Ma on microcline from its central peak, an age that is indistinguishable from the age of the Cretaceous-Tertiary boundary. In the summer of 1991 the Iowa Geological Survey Bureau and U.S. Geological Survey initiated a research core drilling project on the MIS. The first core was beneath 55 m of glacial drift. The core penetrated a 6-m layered sequence of shale and siltstone and 42 m of Cretaceous shale-dominated sedimentary clast breccia. Below this breccia, the core encountered two crystalline rock clast breccia units. The upper unit is 53 m thick, with a glassy matrix displaying various degrees of devitrification. The upper half of this unit is dominated by the glassy matrix, with shock-deformed mineral grains (especially quartz) the most common clast. The glassy-matrix unit grades downward into the basal unit in the core, a crystalline rock breccia with a sandy matrix, the matrix dominated by igneous and metamorphic rock fragments or disaggregated grains from those rocks. The unit is about 45 m thick, and grains display abundant shock deformation features. Preliminary interpretations suggest that the crystalline rock breccias are the transient crater floor, lifted up with the central peak. The sedimentary clast breccia probably represents a postimpact debris flow from the crater rim, and the uppermost layered unit probably represents a large block associated with the flow. The second core (M-2) was drilled near the center of the crater moat in an area where an early crater model suggested the presence of postimpact lake sediments. The core encountered 39 m of sedimentary clast breccia, similar to that in the M-1 core. Beneath the breccia, 120 m of poorly consolidated, mildly deformed, and sheared siltstone, shale, and sandstone was encountered. The basal unit in the core was another sequence

  13. 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.

  14. Is the Large Crater on the Asteroid (2867) Steins Really an Impact Crater?

    NASA Astrophysics Data System (ADS)

    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.

  15. 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.

  16. A Chronology Of Mars Climatic Evolution From Impact Crater Degradation

    NASA Astrophysics Data System (ADS)

    Mangold, N.; Adeli, S.; Conway, S.; Ansan, V.; Langlais, B.

    2012-04-01

    Impact crater degradation provides a powerful tool to analyze past Martian hydrological evolution. Degraded craters are one of the main lines of evidence for a warmer climate on early Mars. Global altimetry and recent high resolution imagery enable us to revisit previous studies. In particular it allowed us to identify preserved impact ejecta, which is strong evidence for limited degradation, and fluvial landforms on rims. These details were particularly pertinent in the case of the craters with alluvial fans. We distinguished only three classes, using two main parameters: the presence of preserved ejecta and of fluvial activity: Type I: Craters with fluvial erosion on walls and rim but lacking an ejecta blanket. Type II: Craters with fluvial erosion on walls and rim and a preserved ejecta blanket. Type III: Fresh craters lacking any fluvial erosion on rim with a preserved ejecta blanket. Type II craters are those containing alluvial fans. A total of 283 craters in two main regions were able to be classified according to our scheme. We have extracted parameters such as diameter, depth, slope and concavity. Type III, which are the youngest craters have the deepest depths for a given diameter, and type I, the shallowest depths. Type II craters lay in-between these two other types. The fact that type II craters lay between types I and III, shows that this crater type is intermediate in the degradation series and therefore implies that this crater type is inter-mediate in age. The chronology of all the craters in this region can be performed using classical isochrons. All the craters together gives an isochron at 4.00±0.03 Gy, which corresponds to the age of the basement. The transition between type I and type II craters occurs at 3.70±0.06 Gy, an age corresponding to the middle of the Early Hesperian period in this model age system. This age pinpoints the period during which the strong fluvial degradation of Early Mars stopped. The transition between type II and

  17. 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.

  18. 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.

  19. 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

  20. Impact craters on venus: initial analysis from magellan.

    PubMed

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

    1991-04-12

    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.

  1. 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.

  2. On the Role of Shock Wave Reflections in Impact Cratering

    NASA Astrophysics Data System (ADS)

    Bertoglio, O.

    2015-07-01

    When the downward impact shockwave meets a rock discontinuity, an upward reflected pressure wave is created. When travelling through the crater fill deposits, this wave projects upwards the shattered rocks which so may contribute to the rim creation.

  3. Planetary science: Meteor Crater formed by low-velocity impact.

    PubMed

    Melosh, H J; Collins, G S

    2005-03-10

    Meteor Crater in Arizona was the first terrestrial structure to be widely recognized as a meteorite impact scar and has probably been more intensively studied than any other impact crater on Earth. We have discovered something surprising about its mode of formation--namely that the surface-impact velocity of the iron meteorite that created Meteor Crater was only about 12 km s(-1). This is close to the 9.4 km s(-1) minimum originally proposed but far short of the 15-20 km s(-1) that has been widely assumed--a realization that clears up a long-standing puzzle about why the crater does not contain large volumes of rock melted by the impact.

  4. The Geology of Impact Fragmentation and Crater Controlled Fracture Networks

    NASA Astrophysics Data System (ADS)

    Asphaug, E.

    2007-12-01

    Overall, the study of planetary impact crater physics has made significant advances in the past two decades, thanks to modeling and observation. However, our understanding of the fragmentation network beyond a crater wall remains poorly understood. At the fundamental level, we do not yet understand where the transition takes place, and over what scale, between the so-called "strength regime" (where strength and other rheological properties dominate) and the "gravity regime" of impact crater scaling. The issue is muddled by the fact that numerical shock-hydrodynamical models (hydrocodes) have difficulty accurately evolving a stress tensor in a solid undergoing shock and hydrodynamic motion. Furthermore, the evolution of the stress tensor during the production of gravity-scaled craters is a subject of much debate, for if strength were truly negligible, there would be no final craters. Further still, and of subject here, only a few published efforts have made inroads into the topic of what damage occurs beyond the crater walls in a planetary impact. The latter subject is one of some importance, for it is speculated that large, deep-seated craters on Mars may dominate the subsequent regional hydrologic evolution. If so, then the same may be true, to a more limited extent given its other activity, of Earth's lithosphere. Radial fissures in crater systems, resulting primarily from hoop stresses and listric faults towards the crater interior, may set the stage for post-impact volatile evolution. On Europa, there is evidence that small secondary impact craters create fracture networks in an ice lithosphere a few km thick, and that these fractures accommodate the far-field stresses of impact rebound by connecting into long faults. One Enceladus, Dione, Ganymede and other icy bodies, the effect of impact cratering beyond the rim is observed in fault patterns. Here I present evidence for crater controlled fracture networks in planetary lithospheres, and provide an fundamental

  5. 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

  6. The Toms Canyon structure, New Jersey outer continental shelf: A possible late Eocene impact crater

    USGS Publications Warehouse

    Poag, C.W.; Poppe, L.J.

    1998-01-01

    The Toms Canyon structure [~20-22 km wide] is located on the New Jersey outer continental shelf beneath 80-100 m of water, and is buried by ~1 km of upper Eocene to Holocene sedimentary strata. The structure displays several characteristics typical of terrestrial impact craters (flat floor; upraised faulted rim: brecciated sedimentary fill), but several other characteristics are atypical (an unusually thin ejecta blanket; lack of an inner basin, peak ring, or central peak; bearing nearly completely filled with breccia). Seismostratigraphic and biostratigraphic analyses show that the structure formed during planktonic foraminiferal biochron P15 of the early to middle late Eocene. The fill unit is stratigraphically correlating with impact ejecta cored nearby at Deep Sea Drilling Project (DSDP) Site 612 and at Ocean Drilling Program (ODP) Sites 903 and 904 (22-35 km southeast of the Toms Canyon structure). The Toms Canyon fill unit also correlates with the Exmore breccia, which fills the much larger Chesapeake Bay impact crater (90-km diameter; 335 km to the southwest). On the basis of our analyses, we postulate that the Toms Canyon structure is an impact crater, formed when a cluster of relatively small meteorites approached the target site bearing ~N 50 E, and struck the sea floor obliquely.

  7. 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.

  8. 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

  9. 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.

  10. 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.

  11. 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

  12. Polygonal impact craters on Venus: Association with surrounding tectonic features

    NASA Astrophysics Data System (ADS)

    Aittola, M.; Öhman, T.; Leitner, J. J.; Raitala, J.; Kostama, V.-P.; Törmänen, T.

    2007-08-01

    It has been proved that the polygonal impact craters (PICs) are found on the Moon, Mercury, Mars and several asteroids and icy moons. Latest studies have shown that they exist also on Venus, even though the polygonal shape is not as well developed as it is on the Moon or Mars. On Mars, the polygonal impact craters - and especially their straight rim segment orientations - are not randomly distributed, but follow the large-scale tectonic trends formed by e.g. Hellas and Isidis basins. To study if this is the case also on Venus is more problematic because, unlike on Mars, there is not a large population of impact craters on Venus. Thus, we don't have statistically reliable population of PICs on Venus to analyze their correlation with the local tectonism. The preliminary studies, however, showed that there are regions where the orientations of straight rim segments seem to align with tectonic features close to the craters. To find out if there are some real correlations between the local tectonics and the straight walls of the Venusian impact craters, we measured and analyzed the orientations of the straight crater walls as well as all the surrounding tectonic features. The preliminary results show that clear correlations can be found and they seem to depend on the distance between the tectonic features and the craters as well as the type of tectonism. This indicates that the orientations of the straight rim of the craters reflect - in many cases - the local tectonics and zones of weaknesses as they do also on Mars and, therefore, they might be good tools to determine the tectonism beneath the young surface. However, this is still ongoing study and to find out the reason for these correlations and uncorrelations, every polygonal crater and their surroundings have to be analyzed in detail.

  13. Polygonal impact craters in Argyre region, Mars: Implications for geology and cratering mechanics

    NASA Astrophysics Data System (ADS)

    Öhman, T.; Aittola, M.; Kostama, V.-P.; Raitala, J.; Korteniemi, J.

    2008-10-01

    Impact craters are not always circular; sometimes their rims are composed of several straight segments. Such polygonal impact craters (PICs) are controlled by pre-existing target structures, mainly faults or other similar planes of weakness. In the Argyre region, Mars, PICs comprise ˜17% of the total impact crater population (>7 km in diameter), and PICs are relatively more common in older geologic units. Their formation is mainly controlled by radial fractures induced by the Argyre and Ladon impact basins, and to a lesser extent by the basin-concentric fractures. Also basin-induced conjugate shear fractures may play a role. Unlike the PICs, ridges and graben in the Argyre region are mostly controlled by Tharsis-induced tectonism, with the ridges being concentric and graben radial to Tharsis. Therefore, the PICs primarily reflect an old impact basin-centered tectonic pattern, whereas Tharsis-centered tectonism responsible for the graben and the ridges has only minor influence on the PIC rim orientations. According to current models of PIC formation, complex PICs should form through a different mechanism than simple PICs, leading to different orientations of straight rim segments. However, when simple and complex PICs from same areas are studied, no statistically significant difference can be observed. Hence, in addition to enhanced excavation parallel to the strike of fractures (simple craters) and slumping along the fracture planes (complex craters), we propose a third mechanism involving thrusting along the fracture planes. This model is applicable to both simple and small complex craters in targets with some dominating orientations of structural weakness.

  14. The Lake Bosumtwi impact crater, Ghana

    USGS Publications Warehouse

    Jones, William B.; Bacon, Michael; Hastings, David A.

    1981-01-01

    Analogy with better-known craters suggests that Bosumtwi has a central uplift rising to 200 m beneath the lake floor. An aeromagnetic anomaly of amplitude 50 nanotesla (nT) over the northern half of the lake is interpreted as due to a layer of magnetized fallback breccia beneath the lake sediments. The normal polarity of the breccia shows that the crater was formed during the normal Jaramillo event of 0.97 to 0.85 m.y. ago, which agrees with the magnetic stratigraphy of the related Ivory Coast microtektites. A regional gravity survey indicates a negative Bouguer anomaly over the crater. There is some geochemical evidence that the meteorite was an iron, and its mass and energy are suggested as about 108 tons and 3 × 1019 joules or 7.3 × 103 megatons.

  15. A sharper view of impact craters from clementine data.

    PubMed

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

    1994-12-16

    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.

  16. Detailed structural analysis of the rim of a large, complex impact crater: Bosumtwi Crater, Ghana

    NASA Astrophysics Data System (ADS)

    Reimold, Wolf U.; Brandt, Dion; Koeberl, Christian

    1998-06-01

    The 1 Ma Bosumtwi Crater in Ghana is an 11-km-diameter, presumably complex, well-preserved impact structure that is associated with the Ivory Coast tektite strewnfield. Detailed structural geologic studies along a complete traverse through the northwestern rim section indicated four zones characterized by distinct deformation styles from just outside of the crater rim to near the crater floor. Zone 1 is dominated by thick deposits of lithic impact breccia, intercalated in places with products of local mass wasting. Zone 2 contains inward-dipping thrust planes, conjugate radial fractures, isoclinal folding, and overturned stratigraphic sequences. Zone 3 represents a megabreccia zone, in which block size decreases upward and outward toward the rim crest. The innermost zone 4 is dominated by intense thrust faulting of multiple orientations, resulting in complex duplex- and lens-shaped bodies. These deformation styles generally correspond to those previously reported from the rims of simple bowl-shaped meteorite-impact craters and appear to be characteristic of impact structures in general.

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

    NASA Technical Reports Server (NTRS)

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

    2005-01-01

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

  18. 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.

  19. 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.

  20. 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.

  1. Impact Craters on Jupiter's Icy Moons as Astrobiological Targets

    NASA Astrophysics Data System (ADS)

    Bierhaus, E. B.; Lipps, J. H.

    2004-12-01

    Impact craters are prime astrobiological targets on icy moons with possible subsurface oceans. Craters are natural probes to subsurface materials; hence may sequester biologic signatures such as whole organisms, fossils, biochemicals, biomarkers, and biotextures. Craters expose a stratigraphic record. The closer to the crater center, the more deep-seated is the excavated material. All craters provide samples of the crust in the walls, overturned ice, and ejecta. Larger craters excavate deep interior ice in the central peaks, which may arise at the interface between solid ice and liquid water. The largest craters possess concentric rings, and flat floors that may be frozen water from under the icy shell that might expose information about the water column. Craters immediately deliver sub-surface materials to the surface, in contrast to endogenic processes (e.g. Europa) that likely operate over days to thousands or more years. The slower endogenic processes allow any extant life proactively to migrate from their habitats to other marginal regions or to die and degrade. Craters also offer unique habitats. A sub-surface "lens" of melt remains beneath the crater floor for up to thousands of years after impact. Life could rapidly exploit and abandon these habitats as they form and disappear, so these sub-surface melt-lenses may serve as rich - albeit temporary - locales of biological activity or repositories for fossils as they freeze. Although Europa displays the best evidence for a global ocean of the three icy Galilean satellites, Ganymede and Callisto also may have liquid water beneath their icy crusts. Ganymede, at least, bears evidence of an extensive geological history, which may have provided energy and habitats for biological processes. Though briny oceans (if they exist) are deeper beneath the icy crusts on Ganymede and Callisto than on Europa, the investigative principle largely remains the same. However, excavation to the deeply buried water requires larger

  2. 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.

  3. 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.

  4. 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.

  5. Investigation of impact crater processes using experimental and numerical techniques

    NASA Astrophysics Data System (ADS)

    Baldwin, Emily Clare

    2008-12-01

    Impact events throughout the history of the Solar System have occurred at all scales, from craters produced by the hypervelocity impact of cosmic dust observed on lunar return samples, to the giant planet-sculpting impacts that have shaped the solid bodies of the Solar System. Investigating the impact process in the laboratory allows us to understand crater formation at a small scale where strength effects dominate however, it is difficult to scale directly to planetary sized impacts because gravity governs the cratering process at this large scale. Through computer modeling, it is possible to bridge the gap from small to large scale impact events. The influence of target porosity, saturation and an overlying water layer on crater morphology is investigated in the laboratory using a two-stage light gas gun to fire 1 mm diameter stainless steel projectiles at 5 km s"1 into sandstone targets. Larger craters were formed in the higher porosity targets and saturated targets. A critical water depth of 11.6 0.5 times the projectile diameter was required to prevent cratering in an unsaturated target, compared with 12.7 0.6 for saturated targets. The sensitivity of this critical water depth to impact velocity, projectile diameter and density is examined through use of the AUTODYN numerical code, for both laboratory and planetary scale impact events. Projectile survivability into water and sand targets is investigated in the lab for stainless steel and shale projectiles impacting at 2-5 km s"1 up to 30% of the projectile is found to survive. AUTODYN simulations show that basalt or sandstone meteorites impacting a simulated lunar surface survive the impact at velocities < 5 km s"1 and at a range of angles, which has positive implications for detecting terrestrial meteorites on the Moon. Groundwork has also been laid for the modelling of the deliberate collision of the SMART-1 spacecraft into the Moon. Finally, lunar and terrestrial impact events are simulated in order to

  6. Small impact craters in the lunar regolith - Their morphologies, relative ages, and rates of formation

    NASA Technical Reports Server (NTRS)

    Moore, H. J.; Boyce, J. M.; Hahn, D. A.

    1980-01-01

    The size frequency distributions, relative ages, and absolute age determination of lunar impact craters ranging in diameter from 1 to 100 m are discussed in relation to present-day and past impact rates. The size frequency distributions of craters produced by impacts on the lunar surface and of craters remaining after degradation with time and later impacts are examined, together with the steady state frequency curves for various crater morphologies. Relations between the relative ages of craters, their morphologies and their diameters are discussed, and the calibration of this kind of relationship with absolute crater ages by the location of individual craters with known absolute ages, diameters and frequency distribution statistics is considered. Estimates of present and past cratering rates based on crater size-frequency distributions are presented which suggest that the rate of impacting objects producing small lunar craters could have been constant over the last 100 million years.

  7. 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

  8. 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.

  9. Impact Crater Environments as Potential Sources of Hadean Detrital Zircons

    NASA Astrophysics Data System (ADS)

    Kenny, G. G.; Whitehouse, M. J.; Kamber, B. S.

    2016-08-01

    Here we show that contrary to previous suggestions, there is no reason to rule out impact melt sheets as major sources of Hadean detrital zircons. We then explore the potential of other impact crater-related environments in which zircons crystallise.

  10. 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.

  11. Impact Lithologies and Post-Impact Hydrothermal Alteration Exposed by the Chicxulub Scientific Drilling Project, Yaxcopoil, Mexico

    NASA Technical Reports Server (NTRS)

    Kring, David A.; Zurcher, Lukas; Horz, Friedrich

    2003-01-01

    The Chicxulub Scientific Drilling Project recovered a continuous core from the Yaxcopoil-1 (YAX-1) borehole, which is approx.60-65 km from the center of the Chicxulub structure, approx.15 km beyond the limit of the estimated approx.50 km radius transient crater (excavation cavity), but within the rim of the estimated approx.90 km radius final crater. Approximately approx.100 m of melt-bearing impactites were recoverd from a depth of 794 to 895 m, above approx.600 m of underlying megablocks of Cretaceous target sediments, before bottoming at 1511 m. Compared to lithologies at impact craters like the Ries, the YAX-1 impactite sequence is incredibly rich in impact melts of unusual textural variety and complexity. The impactite sequence has also been altered by hydrothermal activity that may have largely been produced by the impact event.

  12. 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.

  13. Volcanotectonic history of Crater Flat, southwestern Nevada, as suggested by new evidence from drill hole USW-VH-1 and vicinity

    USGS Publications Warehouse

    Carr, W.J.

    1982-01-01

    New evidence for a possible resurgent dome in the caldera related to eruption of the Bullfrog Member of the Crater Flat Tuff has been provided by recent drilling of a 762-meter (2,501-foot) hole in central Crater Flat. Although no new volcanic units were penetrated by the drill hole (USW-VH-1), the positive aeromagnetic anomaly in the vicinity of the drill hole appears to result in part from the unusually thick, densely welded tuff of the Bullfrog. Major units penetrated include alluvium, basalt of Crater Flat, Tiva Canyon and Topopah Spring Members of the Paintbrush Tuff, and Prow Pass and Bullfrog Members of the Crater Flat Tuff. In addition, the drill hole provided the first subsurface hydrologic information for the area. The water table in the hole is at about 180 meters (600 feet), and the temperature gradient appears slightly higher than normal for the region.

  14. 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.

  15. 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.

  16. 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.

  17. Crater-ray formation by impact-induced ejecta particles

    NASA Astrophysics Data System (ADS)

    Kadono, T.; Suzuki, A. I.; Wada, K.; Mitani, N. K.; Yamamoto, S.; Arakawa, M.; Sugita, S.; Haruyama, J.; Nakamura, A. M.

    2015-04-01

    We performed impact experiments with granular targets to reveal the formation process of crater "rays", the non-uniform ejecta distributions around some fresh craters on the Moon and planets. We found mesh patterns, loosely woven with spaces like a net, as ejecta. A characteristic length of spaces between meshes was evaluated, and an angle, defined as the ratio of the characteristic length to the distance from the ejection point, was obtained as ∼a few degrees. These features are similar to the results of the analyses of the ray patterns around two lunar craters, Glushko and Kepler. Numerical simulations of granular material showed that clear mesh pattern appeared at lower coefficients of restitution between particles but was less clear at larger one, suggesting that the inelastic collisions between particles cause the clear mesh-pattern formation of impact ejecta.

  18. 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.

  19. Mercurian Impact Craters: Implications for Polar Ground Ice

    NASA Astrophysics Data System (ADS)

    Barlow, Nadine G.; Allen, Ruth A.; Vilas, Faith

    1999-10-01

    Recent radar observations of Mercury have detected strong depolarized echoes from the north and south polar regions which have been interpreted by some as ice deposits in the floors of permanently shadowed impact craters. We have used the experience from Mars, where subsurface ice lowers the depth-to-diameter ratio ( d/ D) of impact craters, to test for subsurface ice deposits on Mercury. This analysis determines the d/ D ratios for 170 impact craters in the Borealis (north polar), Tolstoj (equatorial), Kuiper (equatorial), and Bach (south polar) quadrangles of the planet. Possible effects from sun angle and terrain were eliminated. To test whether d/ D differences could be detected at Mariner 10 resolutions (˜1 km/pixel), we perform a similar analysis using Mariner 9 images of Mars which have similar resolutions. We demonstrate that d/ D differences due to terrain softening can be detected between craters in the martian polar regions and the equatorial regions at the Mariner 9 resolutions. Although our initial results indicate that the south polar Bach Quadrangle has a statistically lower d/ D than the north polar (Borealis) or two equatorial (Tolstoj and Kuiper) quadrangles, further investigation reveals that this finding is most likely the result of the filtering which was applied to the images of the Bach quadrangle by JPL. Thus, no unequivocal evidence exists that the possible ice deposits in craters at Mercury's north and south poles are the exposed portions of more extensive subsurface ice caps. Combined with the temporal constraint imposed by the fact that the proposed ice deposits are found only in USGS Class 4 craters, this suggests a large, rapidly emplaced exogenic source of water to Mercury during the Mansurian period. We suggest that the source was multiple impacts from a fragmented comet or a comet shower.

  20. Spurious periods in the terrestrial impact crater record

    NASA Astrophysics Data System (ADS)

    Jetsu, L.; Pelt, J.

    2000-01-01

    We present a simple solution to the controversy over periodicity in the ages of terrestrial impact craters and the epochs of mass extinctions of species. The first evidence for a 28.4 million year cycle in catastrophic impacts on Earth was presented in 1984. Our re-examination of this earlier Fourier power spectrum analysis reveals that the rounding of the impact crater data distorted the Monte Carlo significance estimates obtained for this cycle. This conclusion is confirmed by theoretical significance estimates with the Fourier analysis, as well as by both theoretical and Monte Carlo significance estimates with the Rayleigh method. We also apply other time series analysis methods to six subsamples of the currently available more extensive impact crater record and one sample of mass extinction epochs. This analysis reveals the spurious ``human-signal'' induced by rounding. We demonstrate how the data rounding interferes with periodicity analysis and enhances artificial periodicities between 10 and 100 million years. Only integer periodicities connected to irregular multimodal phase distributions reach a significance of 0.001 or 0.01. We detect no real periodicity in the ages of terrestrial impact craters, nor in the epochs of mass extinctions of species.

  1. 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

  2. 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.

  3. 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

  4. 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,…

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. Structural effects of meteorite impact on basalt: Evidence from Lonar crater, India

    NASA Astrophysics Data System (ADS)

    Kumar, P. Senthil

    2005-12-01

    Lonar crater is a simple, bowl-shaped, near-circular impact crater in the ˜65 Myr old Deccan Volcanic Province in India. As Lonar crater is a rare terrestrial crater formed entirely in basalt, it provides an excellent opportunity to study the impact deformation in target basalt, which is common on the surfaces of other terrestrial planets and their satellites. The present study aims at documenting the impact deformational structures in the massive basalt well exposed on the upper crater wall, where the basalt shows upward turning of the flow sequence, resulting in a circular deformation pattern. Three fracture systems (radial, concentric, and conical fractures) are exposed on the inner crater wall. On the fracture planes, plumose structures are common. Uplift and tilting of the basalt sequence and formation of the fractures inside the crater are clearly related to the impact event and are different from the preimpact structures such as cooling-related columnar joints and fractures of possible tectonic origin, which are observed outside the crater. Slumping is common throughout the inner wall, and listric faulting displaces the flows in the northeastern inner wall. The impact structures of Lonar crater are broadly similar to those at other simple terrestrial craters in granites and clastic sedimentary rocks and even small-scale experimental craters formed in gabbro targets. As Lonar crater is similar to the strength-controlled laboratory craters, impact parameters could be modeled for this crater, provided maximum depth of fracture formation would be known.

  12. 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).

  13. Impact and Cratering History of the Pluto System

    NASA Astrophysics Data System (ADS)

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

    2014-11-01

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

  14. 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

  15. 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.

  16. 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

  17. 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

  18. Distribution, Classification, and Ages of Martian Impact Crater Lakes

    NASA Astrophysics Data System (ADS)

    Cabrol, Nathalie A.; Grin, Edmond A.

    1999-11-01

    Paleolakes in impact craters on Mars are characterized at global scale using the Viking Orbiter data. We identified 179 paleolakes in impact structures formed by the influx of water and sediment derived from valley networks and channels that can be classified into three different fluviolacustrine systems: closed, open, and lake-chain systems. We show the hydrogeologic implications for each of the three systems and their significance in terms of duration of fluviolacustrine activity. This study provides a catalog of areographic, physical, and physiographic data for each of the studied impact crater lakes, associated with the description of the sedimentary structures observed. It also identifies environments where life and/or precursors to life could have found favorable conditions to evolve.

  19. Properties of Ejecta Blanket Deposits Surrounding Morasko Meteorite Impact Craters (Poland)

    NASA Astrophysics Data System (ADS)

    Szokaluk, M.; Muszyński, A.; Jagodziński, R.; Szczuciński, W.

    2016-08-01

    Morasko impact craters are a record of the fall of a meteorite into the soft sediments. The presented results illustrate the geological structure of the area around the crater as well as providing evidence of the occurrence of ejecta blanket.

  20. 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.

  1. New modeling results of the Bunte breccia ejecta morphology and thickness variations outside the Ries impact crater, southern Germany

    NASA Astrophysics Data System (ADS)

    Sturm, S.; Wulf, G.; Jung, D.; Kenkmann, T.

    2012-04-01

    The Ries impact crater with a diameter of ~25 km represents a relatively pristine, complex impact crater in southern Germany that was formed during the Miocene (14.34+-0.08 Ma) [1, 2]. The impact occurred into a two-layered target 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) [3, 4]. The continuous ejecta blanket of the crater ejected up to a distance of 45 km from the crater center is built up by so called Bunte breccias, a polymict lithic breccia. The ejected breccia material mainly consists of unshocked to weakly shocked sedimentary target clasts in addition to a minority of crystalline basement clasts and reworked surfical sediments (e.g., Upper Freshwater Molasses or Upper Seawater Molasses) [5, 6]. Here we present new results of the morphology of the (i) paleo-relief and (ii) the thickness variations of the continuous ejecta blanket with radial range. For this study we combined digital elevation data and geologic information of the recent geologic map [7] in ArcGIS (ESRI) and RockWorks14 (RockWare) to extract the elevation of the lower contact plane ("paleo-surface") and the contact between the Bunte breccia and the overlain Suevite deposits. In detail, we extracted the mapping information of the autochthonous-allochthonous ("Bunte breccia base") and allochthonous-suevite ("Bunte breccia top") intersections from the geologic map [7], descriptions of nine NASA drilling sites [6], and included up to 40 drillings carried out by the Bavarian Environment Agency to interpolate the morphology and thickness variation of the Bunte breccia ejecta outside the Ries impact crater. Due to the highest data density and the widespread occurrence of Bunte breccia deposits as well as Suevite, the southwestern part of the ejecta blanket was selected for the study and delivered a more or less

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

    USGS Publications Warehouse

    ,; 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

  3. 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

  4. Importance of pre-impact crustal structure for the asymmetry of the Chicxulub impact crater

    NASA Astrophysics Data System (ADS)

    Gulick, Sean P. S.; Barton, Penny J.; Christeson, Gail L.; Morgan, Joanna V.; McDonald, Matthew; Mendoza-Cervantes, Keren; Pearson, Zulmacristina F.; Surendra, Anusha; Urrutia-Fucugauchi, Jaime; Vermeesch, Peggy M.; Warner, Mike R.

    2008-02-01

    Impact craters are observed on the surfaces of all rocky planets and satellites in our Solar System; some impacts on Earth, such as the Cretaceous/Tertiary one that formed the Chicxulub impact crater, have been implicated in mass extinctions. The direction and angle of the impact-or its trajectory-is an important determinant of the severity of the consequent environmental damage, both in the downrange direction (direction bolide travels) and in the amount of material that enters the plume of material vaporized on impact. The trajectory of the Chicxulub impact has previously been inferred largely from asymmetries in the gravity anomalies over the crater. Here, we use seismic data to image the Chicxulub crater in three dimensions and demonstrate that the strong asymmetry of its subsurface correlates with significant pre-existing undulations on the end-Cretaceous continental shelf that was the site of this impact. These results suggest that for rocky planets, geological and geomorphological heterogeneities at the target site may play an important role in determining impact crater structure, in addition to impact trajectories. In those cases where heterogeneous targets are inferred, deciphering impact trajectories from final crater geometries alone may be difficult and require further data such as the distribution of ejecta.

  5. Exploring Martian impact craters: what they can reveal about the subsurface and why they are important for the search for life

    SciTech Connect

    Wiens, Roger C; Vaniman, David T; Schwenzer, Susanne P; Abramov, O.; Allen, C. C.; Clifford, S.; Filiberto, J.; Kring, J.; Lasue, D. A.; Mcgovern, P. J.; Newsom, H. E.; Treiman, A. H.; Wittmann, A.

    2009-01-01

    Impact craters are important targets for Mars exploration, especially craters of Noachian age, which record conditions on Early Mars. Smaller craters can also be used during missions to the planet as natural 'drill holes' or excavation pits into the subsurface, and so can provide information and samples that would otherwise be inaccessible. During the Noachian period impact cratering was the dominant geological process on Early Mars and on the contemporary Earth and Moon; investigation of craters will inform our understanding of this geologic process and its effects on the water-bearing Martian crust at the time. Impact craters disturbed and heated this water-bearing crust, and likely initiated long-lived hydrothermal systems, which may have created some clement environments for life and formed secondary minerals. Also, impact-heat generated lakes may have formed. Thus, Noachian impact craters are particularly important exploration targets, providing subsurface access, data on crucial geological processes, and warm, water-rich environments possibly conducive to life.

  6. 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.

  7. 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.

  8. Impacts of gas drilling on human and animal health.

    PubMed

    Bamberger, Michelle; Oswald, Robert E

    2012-01-01

    Environmental concerns surrounding drilling for gas are intense due to expansion of shale gas drilling operations. Controversy surrounding the impact of drilling on air and water quality has pitted industry and lease-holders against individuals and groups concerned with environmental protection and public health. Because animals often are exposed continually to air, soil, and groundwater and have more frequent reproductive cycles, animals can be used as sentinels to monitor impacts to human health. This study involved interviews with animal owners who live near gas drilling operations. The findings illustrate which aspects of the drilling process may lead to health problems and suggest modifications that would lessen but not eliminate impacts. Complete evidence regarding health impacts of gas drilling cannot be obtained due to incomplete testing and disclosure of chemicals, and nondisclosure agreements. Without rigorous scientific studies, the gas drilling boom sweeping the world will remain an uncontrolled health experiment on an enormous scale. PMID:22446060

  9. 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.

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

    USGS Publications Warehouse

    Horton, J.W.; 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.

  11. 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

  12. A paleomagnetic and rock magnetic study of the Manicouagan impact structure: Implications for crater formation and geodynamo effects

    NASA Astrophysics Data System (ADS)

    Eitel, Michael; Gilder, Stuart A.; Spray, John; Thompson, Lucy; Pohl, Jean

    2016-02-01

    We report rock magnetic and paleomagnetic data from the ~214 Ma Manicouagan (Canada) impact crater based on 25 widely distributed sites of impact melt and basement rocks collected at the surface as well as from boreholes drilled to depths ≤1.5 km. Titanomagnetite and titanohematite carry the magnetic remanence in impact melts above 320 m elevation and in most basement rocks. Impact melts below 320 m contain solely titanomagnetite. Magnetic susceptibility and saturation magnetization, proxies for titanomagnetite concentration, increase more than tenfold toward the base of the thickest impact melt that underwent fractional crystallization. The titanomagnetite-enriched zone partially contributes to a 2000 nT magnetic anomaly in the crater's center. Stepwise demagnetization reveals a single, normal polarity magnetization component in all samples regardless of the magnetic phases present. Coeval lock-in remanence times for titanomagnetite and titanohematite indicate that the titanohematite formed >570°C during oxi-exsolution. The average paleomagnetic direction and intensity coincide well with 214 Ma reference values. We find no evidence for an aberration of the geomagnetic field over the several thousands of years it took to cool a 481 m thick portion of the impact melt body. Hence, the energy released by the Manicouagan impact that created one of the 10 largest known craters on Earth provoked no measurable disturbance of the geodynamo. Magnetic anisotropy of clast-free impact melts define magnetic lineation directions that are, in places, radially oriented with respect to the crater's center. Centrifugal flow of the melt within the evolving transient crater probably generated the fabric.

  13. 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.

  14. 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.

  15. Comparison of Polygonal Impact Craters on Mercury and on other Terrestrial Planets

    NASA Astrophysics Data System (ADS)

    Weihs, G. T.; Leitner, J. J.; Firneis, M. G.

    2012-04-01

    The rims of a polygonal impact crater partly are composed of several straight segments. Analyzing the images transmitted back to Earth by the spacecrafts Mariner 10 and MESSENGER, polygonal impact craters with at least two straight rim segments, were detected on Mercury. The search for polygonal impact craters on Mercury was carried out, using the IAU/NASA/USGS-Planetary-Database: each of the 15 quadrangle-maps was scanned for impact craters with at least two straight rims. In a second step the data preparation was resulting in a set of two images per PIC, one with marked straight rims and an original one for the purpose of comparison. The polygonal impact craters found were documented: a total number of 33 polygonal impact craters out of 291 by IAU approved craters, is according to our expectation of 10 to 15 % polygonal impact craters out of all impact craters on Mercury. The polygonal impact craters' diameters reach from 65 km to 240 km, the mean diameter is about 120 km, the same value as for all Mercury's impact craters. Angles between the straight rims are found in a range between 98° and 132°. The specific morphology of polygonal impact craters on Mercury in general is of the type of complex craters with terraced rims, which often are found on other terrestrial planets like Mars. An assumed connection between the structure of polygonal impact craters and the structure of the geologic environment on the surface was not found at first sight. Several problems detecting the polygonal shape occurred, because many of the craters are heavily degraded. Though the quality of some of the images taken by Mariner 10 and MESSENGER is partly limited, it was possible to detect the polygonal shapes. The study proves the existence of polygonal impact craters on Mercury. Furthermore the assumption was confirmed, that polygonal impact craters are an integral part of impact craters and common on the Moon, all terrestrial planets and several asteroids and icy moons like Europa.

  16. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2003-01-01

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

  18. The 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

  19. 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.

  20. Fullerenes in an impact crater on the LDEF spacecraft.

    PubMed

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

    1994-05-01

    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.

  1. 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.

  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.

  4. Cratering Impacts into Finite Targets: Comparing Experiments, Code Simulations, and Scaling Laws

    NASA Astrophysics Data System (ADS)

    Ryan, E. V.

    1996-03-01

    Recent studies have indicated that cratering on small bodies in the solar system may be very different from craters formed on planar surfaces. The curvature of the cratering surface has been shown to affect final crater diameter. As collisional evolution work progresses, e.g., analyses of asteroids Gaspra, Ida, and Ida's moon Dactyl, as well as the Stickney crater on Phobos, reliable predictions for crater diameters formed by impacting projectiles are required. We compare Holsapple and Schmidt crater scaling laws (strength regime), derived primarily from impacts into semi-infinite targets, to results from high-velocity laboratory cratering experiments using spherical, strong cement mortar targets. We find that strength scaling underestimates crater size by about a factor of 2. We also use our 2D numerical code to model cratering impacts (under the same initial conditions) into both a sphere and the planar surface of a cylinder (axial symmetry). The crater diameter calculated by the code was larger for the curved-surface case (by 40%), in agreement with experimental results.

  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. 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.

  7. The Cretaceous-Tertiary impact crater and the cosmic projectile that produced it.

    PubMed

    Sharpton, V L; Marin, L E

    1997-05-30

    Evidence gathered to date from topographic data, geophysical data, well logs, and drill-core samples indicates that the buried Chicxulub basin, the source crater for the approximately 65 Ma Cretaceous-Tertiary (K/T) boundary deposits, is approximately 300 km in diameter. A prominent topographic ridge and a ring of gravity anomalies mark the position of the basin rim at approximately 150 km from the center. Wells in this region recovered thick sequences of impact-generated breccias at 200-300 m below present sea level. Inside the rim, which has been severely modified by erosion following impact, the subsurface basin continues to deepen until near the center it is approximately 1 km deep. The best planetary analog for this crater appears to be the 270 km-diameter Mead basin on Venus. Seismic reflection data indicate that the central zone of downward displacement and excavation (the transient crater is approximately 130 km in diameter, consistent with previous studies of gravity anomaly data). Our analysis of projectile characteristics utilizes this information, coupled with conventional scaling relationships, and geochemical constraints on the mass of extraterrestrial material deposited within the K/T boundary layer. Results indicate that the Chicxulub crater would most likely be formed by a long-period comet composed primarily of nonsilicate materials (ice, hydrocarbons, etc.) and subordinate amounts (< or = 50%) primitive chondritic material. This collision would have released the energy equivalent to between 4 x 10(8) and 4 x 10(9) megatons of TNT. Studies of terrestrial impact rates suggest that such an event would have a mean production rate of approximately 1.25 x 10(-9) y-1. This rate is considerably lower than that of the major mass extinctions over the last 250 million years (approximately 5 x 10(-7) y-1). Consequently, while there is substantial circumstantial evidence establishing the cause-effect link between the Chicxulub basin forming event and the K

  8. The Cretaceous-Tertiary Impact Crater and the Cosmic Projectile that Produced it

    NASA Technical Reports Server (NTRS)

    Sharpton, Virgil L.; Marin, Luis E.

    1997-01-01

    Evidence gathered to date from topographic data, geophysical data, well logs, and drill-core samples indicates that the buried Chicxulub basin, the source crater for the approximately 65 Ma Cretaceous-Tertiary (K/T) boundary deposits, is approximately 300 km in diameter. A prominent topographic ridge and a ring of gravity anomalies mark the position of the basin rim at approximately 150 km from the center. Wells in this region recovered thick sequences of impact-generated breccias at 200-300 m below present sea level. Inside the rim, which has been severely modified by erosion following impact, the subsurface basin continues to deepen until near the center it is approximately 1 km deep. The best planetary analog for this crater appears to be the 270 km-diameter Mead basin on Venus. Seismic reflection data indicate that the central zone of downward displacement and excavation (the transient crater is approximately 130 km in diameter, consistent with previous studies of gravity anomaly data). Our analysis of projectile characteristics utilizes this information, coupled with conventional scaling relationships, and geochemical constraints on the mass of extraterrestrial material deposited within the K/T boundary layer. Results indicate that the Chicxulub crater would most likely be formed by a long-period comet composed primarily of nonsilicate materials (ice, hydrocarbons, etc.) and subordinate amounts (less than or equal to 50 percent) primitive chondritic material. This collision would have released the energy equivalent to between 4 x 10(exp 8) and 4 x 10(exp 9) megatons of TNT. Studies of terrestrial impact rates suggest that such an event would have a mean production rate of approximately 1.25 x 10(exp -9) y(exp -1). This rate is considerably lower than that of the major mass extinctions over the last 250 million years (approximately 5 x 10(exp -7) y(exp -1). Consequently, while there is substantial circumstantial evidence establishing the cause-effect link

  9. Initial Assessment of the Excavation and Deposition of Impact Lithologies Exposed by the Chicxulub Scientific Drilling Project, Yaxcopoil, Mexico

    NASA Technical Reports Server (NTRS)

    Kring, David A.; Horz, Friedrich; Zurcher, Lukas

    2003-01-01

    The Chicxulub Scientific Drilling Project (www.icdp-online.de) recovered a continuous core from a depth of 404 m (in Tertiary cover) to 1511 m (in a megablock of Cretaceous target sediments), penetrating approx. 100 m of melt-bearing impactites between 794 and 895 m. The Yaxcopoil-1 (YAX-1) borehole is approx. 60-65 km from the center of the Chicxulub structure, which is approx. 15 km beyond the limit of the estimated approx. 50 km radius transient crater (excavation cavity), but within the rim of the estimated approx. 90 km radius final crater. In general, the impactite sequence is incredibly rich in impact melts of unusual textural variety and complexity, quite unlike melt-bearing impact formations from other terrestrial craters.

  10. Effect of impact angle on central-peak/peak-ring formation and crater collapse on Venus

    NASA Technical Reports Server (NTRS)

    Schultz, Peter H.

    1992-01-01

    Although asymmetry in ejecta patterns and craters shape-in-plan are commonly cited as diagnostic features of impact angle, the early-time transfer of energy from impactor to target also creates distinctive asymmetries in crater profile with the greatest depth uprange. In order to simulate gravity-controlled crater-growth, laboratory experiments use loose particulate targets as analogs for low-strength material properties following passage of the shock. As a result, impact crater diameter D in laboratory experiments generally is many times greater than the impactor diameter 2r (factor of 40), and early-time asymmetries in energy transfer from oblique impacts are consumed by subsequent symmetrical crater growth, except at the lowest angles (less than 25 deg). Such asymmetry is evident for oblique (less than 60 deg from horizontal) impacts into aluminum where D/2r is only 2 to 4. Because cratering efficiency decreases with increasing crater size and decreasing impact angle, large scale planetary craters (4080 km) should have transient excavation diameters only 6-10 times larger than the impactor. At basin scales, D/2r is predicted to be only 3-5, i.e., approaching values for impacts into aluminum in laboratory experiments. As a result, evidence for early-time asymmetry in impactor energy transfer should become evident on planetary surfaces, yet craters generally retain a circular outline for all but the lowest impact angles.

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. Manganese-oxide minerals in fractures of the Crater Flat Tuff in drill core USW G-4, Yucca Mountain, Nevada

    SciTech Connect

    Carlos, B.A.; Bish, D.L.; Chipera, S.J.

    1990-07-01

    The Crater Flat Tuff is almost entirely below the water table in drill hole USW G-4 at Yucca Mountain, Nevada. Manganese-oxide minerals from the Crater Flat Tuff in USW G-4 were studied using optical, scanning electron microscopic, electron microprobe, and x-ray powder diffraction methods to determine their distribution, mineralogy, and chemistry. Manganese-oxide minerals coat fractures in all three members of the Crater Flat Tuff (Prow Pass, Bullfrog, and Tram), but they are most abundant in fractures in the densely welded devitrified intervals of these members. The coatings are mostly of the cryptomelane/hollandite mineral group, but the chemistry of these coatings varies considerably. Some of the chemical variations, particularly the presence of calcium, sodium, and strontium, can be explained by admixture with todorokite, seen in some x-ray powder diffraction patterns. Other chemical variations, particularly between Ba and Pb, demonstrate that considerable substitution of Pb for Ba occurs in hollandite. Manganese-oxide coatings are common in the 10-m interval that produced 75% of the water pumped from USW G-4 in a flow survey in 1983. Their presence in water-producing zones suggests that manganese oxides may exert a significant chemical effect on groundwater beneath Yucca Mountain. In particular, the ability of the manganese oxides found at Yucca Mountain to be easily reduced suggests that they may affect the redox conditions of the groundwater and may oxidize dissolved or suspended species. Although the Mn oxides at Yucca Mountain have low exchange capacities, these minerals may retard the migration of some radionuclides, particularly the actinides, through scavenging and coprecipitation. 23 refs., 21 figs., 2 tabs.

  16. Tomography Study of Shock-Induced Damage Beneath Craters by Normal and Oblique Impacts

    NASA Astrophysics Data System (ADS)

    Ai, H.; Ahrens, T.

    2004-12-01

    Comparisons of laboratory impact craters produced in rock and planetary-scale impact structures, indicate that the observed reductions in elastic wave velocities by shock-induced damage of rock beneath impact craters can be used to constrain the impact history. A series of small-scale normal and oblique impact experiments were conducted on 20x20x15 cm samples of San Marcos granite by a 1.2 km/s, 2 kJ impactor. The resulting largely circular (8 cm in diameter) crater dimensions agrees closely with previous data. By conducting a multiple source-receiver ultrasonic survey of the shocked rock beneath laboratory craters (sampled by 290 ray paths beneath the crater) we have tomographically mapped the in-situ P-wave velocity beneath craters and find measurable damage, as defined by > 0.1 km/s velocity reduction, are induced to depths of 7 cm beneath the crater for normal impacts. However, oblique impacts produce shallower damage zone ( ˜ 3 cm deep) that are asymmetric along the plane containing the impact trajectory. The downrange shows more damage than the uprange. Since the extent of the shock-damage region depends on impact velocity and impact energy, the extent of damage in our laboratory impact structures , and we presume also planetary scale impact structures, carries both impact velocity and direction of impact information not previously recognized or sought. Hence damage zone dimensions are expected to constrain planetary impacts parameters. Oblique impacts, where the tracjectory is ≥ 15° relative to the impacted surface, yields approximately circular craters, can in principle, provide information on impactor trajectory. For planetary impacts, the damage profile, as measured by seismic velocity deficit, beneath craters allow some statistical constraint on impacts produced by low-inclination orbit objects (asteroids and Jupiter-family comets), versus, high-inclination orbit objects (long-period and new comets).

  17. 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.

  18. 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.

  19. 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.

  20. 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.

  1. 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

  2. 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".

  3. 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.

  4. Geology and geochemistry of shallow drill cores from the Bosumtwi impact struture, Ghana

    NASA Astrophysics Data System (ADS)

    Boamah, D.; Koeberl, C.

    2003-08-01

    The 1.07 Ma well-preserved Bosumtwi impact structure in Ghana (10.5 km in diameter) formed in 2 Ga-old metamorphosed and crystalline rocks of the Birimian system. The interior of the structure is largely filled by the 8 km diameter Lake Bosumtwi, and the crater rim and region in the environs of the crater is covered by tropical rainforest, making geological studies rather difficult and restricted to road cuts and streams. In early 1999, we undertook a shallow drilling program to the north of the crater rim to determine the extent of the ejecta blanket around the crater and to obtain subsurface core samples for mineralogical, petrological, and geochemical studies of ejecta of the Bosumtwi impact structure. A variety of impactite lithologies are present, consisting of impact glass- rich suevite and several types of breccia: lithic breccia of single rock type, often grading into unbrecciated rock, with the rocks being shattered more or less in situ without much relative displacement (autochthonous?), and lithic polymict breccia that apparently do not contain any glassy material (allochtonous?). The suevite cores show that melt inclusions are present throughout the whole length of the cores in the form of vesicular glasses with no significant change of abundance with depth. Twenty samples from the 7 drill cores and 4 samples from recent road cuts in the structure were studied for their geochemical characteristics to accumulate a database for impact lithologies and their erosion products present at the Bosumtwi crater. Major and trace element analyses yielded compositions similar to those of the target rocks in the area (graywacke-phyllite, shale, and granite). Graywacke-phyllite and granite dikes seem to be important contributors to the compositions of the suevite and the road cut samples (fragmentary matrix), with a minor contribution of Pepiakese granite. The results also provide information about the thickness of the fallout suevite in the northern part of the

  5. 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.

  6. 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

    Impact spallation is a fundamental process responsible for formation of ejecta boulders from impact craters. Although theoretical spallation models were developed about three decades ago, only limited geological observations have been made so far to test these models. The 3.8 km Censorinus crater on the Moon provides an excellent opportunity for studying the impact spallation processes associated with a fresh simple crater formed by oblique impact. Using the Lunar Reconnaissance Orbiter Narrow Angle Camera images, we prepared the ejecta boulder distribution map of Censorinus crater and measured the boulder sizes and shapes. Mapping of about 242,000 ejecta boulders enabled us to document the size distribution of boulders both radial and concentric to the impact crater. Larger size boulders dominate the crater rim areas, while they become smaller away from the crater. The boulder distribution exhibits a radial asymmetry suggesting Censorinus is a oblique impact, in which the uprange ejecta have smaller ranges with larger concentration of boulders near the southwestern crater rim, while the downrange ejecta are in general characterized by smaller boulders with high spatial dispersion. The cumulative size-frequency distribution (CSFD) of boulders shows a highly variable fragmentation history in which the uprange boulders suffered more complex fragmentation. The ejecta boulders also exhibit a variety of shapes that are gleaned from their axial ratios and edge angle characteristics. There is a general decrease of axial ratios away from the crater rim. Rectangular boulders dominate the crater rim and they become more equant away from the crater. In addition to the boulder sizes, the boulder shape distribution also exhibits a mild asymmetry in response to the oblique impact. Small size fresh impact craters (84,000 craters) are abundant on the Censorinus ejecta and post-date Censorinus. These craters are found in two morphologic types in which a large majority of craters

  7. 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.

  8. 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.

  9. 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.

  10. Melting of Permafrost on Mars in the Formation of Large Impact Craters (Invited)

    NASA Astrophysics Data System (ADS)

    Pierazzo, E.; Ivanov, B. A.

    2010-12-01

    The idea that on Mars impact craters larger than about 50 km in diameter would release enough heat to drive substantial hydrothermal activity underneath the crater for thousands of years, and craters larger than about 200 km in diameter keeping warm for periods as long as 1--10 Myr, is at least a decade old. Numerical efforts to predict the extent and time scale of hydrothermal activity in Martian impact craters have mostly relied on numerical simulations of impact cratering into uniform dry targets or, at most, layered ice-rock targets. We present a case modeling study of impact melting of permafrost on Mars to investigate the general thermal state of the rock layers modified in the formation of hyper-velocity impact craters. We modeled the formation of a mid-size crater, about 30 km in diameter, formed on a target with an ice/water content varying with depth, where water and rock form either a macroscopic mixture (something like ice lenses in rock fractures) or a microscopic mixture (where ice and rock are fully equilibrated in temperature). Our model results of dry and mixed rock-ice targets indicate that for craters larger than about 30 km in diameter the onset of post-impact hydrothermal circulation is characterized by two stages: first, the formation of a mostly dry, hot central uplift, followed by water beginning to flow in and circulate through the initially dry and hot uplifted crustal rocks. The post-impact thermal field in the periphery of the crater is dependent on crater size: in mid-size craters, 30--50 km in diameter, crater walls are not strongly heated in the impact event, and even though ice present in the rock may initially be heated enough to melt, overall temperatures in the rock remain below melting, undermining the development of a crater-wide hydrothermal circulation. We speculate that salt deposition from supercritical water may occur immediately after impact in some locations even before the beginning of hydrothermal circulation. In large

  11. 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.

  12. 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.

  13. 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

  14. Preparing the 2017 Drilling Campaign at Rochechouart Impact Structure

    NASA Astrophysics Data System (ADS)

    Lambert, P.; Goderis, S.; Hodges, K. V.; Kelley, S.; Lee, M. R.; Jourdan, G. R.; Osinski, G. R.; Sapers, H. M.; Schmieder, M.; Schwenzer, S.; Trumel, H.; Wittmann, A.

    2016-08-01

    Presenting the programme and objective of 2017 drilling campaign towards a better understanding of 1- Rochechouart, and 2- large impacts and collateral effects (habitability of early Earth and planets/emergence and evolution of life).

  15. Shock Melting, Crater Formation, and Ejecta Distribution in the 17th March 2013 Lunar Impact Event

    NASA Astrophysics Data System (ADS)

    Luther, R.; Prieur, N. C.; Tasdelen, E.; Wünnemann, K.; Werner, S. C.

    2016-08-01

    We measure crater characteristics by LRO-NAC images. By these constraints, we model the impact using the iSALE shock physics code. We determine melt volumes and ejecta distribution for various impact scenarios.

  16. Impact cratering on the H chondrite parent asteroid

    NASA Astrophysics Data System (ADS)

    Wittmann, Axel; Swindle, Timothy D.; Cheek, Leah C.; Frank, Elizabeth A.; Kring, David A.

    2010-07-01

    This paper reports petrological data for LaPaz Icefield 02240, 03922, 031125, 031173, 031308, 04462, and 04751, which are meteoritic samples of clast-rich impact melt rocks from the H chondrite parent asteroid. The size distribution and metallographic characteristics of Fe-Ni metal in the melts indicate very rapid 1 to 40°C/s cooling in the temperature range between >1500 and ˜950°C when the clast-melt mixtures were thermally equilibrating. Cooling slowed to values between 10-3 and 10-2°C/s in the temperature range between 700 and 400°C when the melt rocks were cooling to their surroundings. These data suggest that the rocks cooled near the surface of the H chondrite asteroid within suevitic impact deposits. Integrating these data with the petrologic characteristics of other H chondrite melt rocks and their radioisotopic ages indicates that the H chondrite asteroid suffered at least one large impact event while still cooling from endogenous metamorphism at ˜4500 Ma; this impact must have degraded the asteroid's integrity but did not cause shattering. Impact events in the era between ˜4100 and ˜3600 Ma produced melt volumes large enough to allow segregation of metal and troilite from silicate melts, possibly within continuous impact melt sheets contained in craters. The impact record after 3600 Ma does not display such assemblages, which suggests a decrease in the rate of large impact events or a catastrophic size reduction of the H chondrite parent asteroid at around this time.

  17. Origin of small pits in martian impact craters

    NASA Astrophysics Data System (ADS)

    Boyce, Joseph M.; Wilson, Lionel; Mouginis-Mark, Peter J.; Hamilton, Christopher W.; Tornabene, Livio L.

    2012-09-01

    We propose a numerical model for the formation of the closely-spaced pits found in the thin, ejecta-related deposits superposed on the floors, interior terrace blocks, and near-rim ejecta blankets of well-preserved martian impact craters. Our model predicts the explosive degassing of water from this pitted material, which is assumed to originally be water-bearing, impact melt-rich breccia at the time of deposition. This process is analogous to what occurred in the fall-out suevite deposits at the Ries impact structure in Germany. At Ries, impact heating of water-bearing target material resulted in the rapid degassing of its water and other volatiles. The martian environment plays an important role in enhancing the effects of this degassing by increasing the flow-speed of the escaping gas. The high flow-rate of gas through particulate materials, such as suevite, tends to quickly form segregation channels or vent pipes, similar to those found in the Ries deposits. These pipes act as conduits for the efficient high-speed escape of the gas and small clasts that it entrains. Escaping gas and entrained clasts abraded and eroded the conduit walls, flaring them to form pits above a network of pipes.

  18. Lithostratigraphic and petrographic analysis of ICDP drill core LB-07A, Bosumtwi impact structure, Ghana

    NASA Astrophysics Data System (ADS)

    Coney, Louise; Gibson, Roger L.; Reimold, Wolf Uwe; Koeberl, Christian

    Lithostratigraphic and petrographic studies of drill core samples from the 545.08 m deep International Continental Scientific Drilling Program (ICDP) borehole LB-07A in the Bosumtwi impact structure revealed two sequences of impactites below the post-impact crater sediments and above coherent basement rock. The upper impactites (333.38-415.67 m depth) comprise an alternating sequence of suevite and lithic impact breccias. The lower impactite sequence (415.67-470.55 m depth) consists essentially of monomict impact breccia formed from meta-graywacke with minor shale, as well as two narrow injections of suevite, which differ from the suevites of the upper impactites in color and intensity of shock metamorphism of the clasts. The basement rock (470.55-545.08 m depth) is composed of lower greenschist-facies metapelites (shale, schist and minor phyllite), meta-graywacke, and minor meta-sandstone, as well as interlaminated quartzite and calcite layers. The basement also contains a number of suevite dikelets that are interpreted as injection veins, as well as a single occurrence of granophyric-textured rock, tentatively interpreted as a hydrothermally altered granitic intrusion likely related to the regional pre-impact granitoid complexes. Impact melt fragments are not as prevalent in LB-07A suevite as in the fallout suevite facies around the northern crater rim; on average, 3.6 vol% of melt fragments is seen in the upper suevites and up to 18 vol% in the lower suevite occurrences. Shock deformation features observed in the suevites and polymict lithic breccias include planar deformation features in quartz (1 to 3 sets), rare diaplectic quartz glass, and very rare diaplectic feldspar glass. Notably, no ballen quartz, which is abundant in the fallout suevites, has been found in the within-crater impact breccias. An overall slight increase in the degree of shock metamorphism occurs with depth in the impactites, but considerably lower shock degrees are seen in the suevites of

  19. 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.

  20. Impact Craters on Pluto and Charon Indicate a Deficit of Small Kuiper Belt Objects

    NASA Astrophysics Data System (ADS)

    Singer, Kelsi N.; McKinnon, William B.; Greenstreet, Sarah; Gladman, Brett; Parker, Alex Harrison; Robbins, Stuart J.; Schenk, Paul M.; Stern, S. Alan; Bray, Veronica; Spencer, John R.; Weaver, Harold A.; Beyer, Ross A.; Young, Leslie; Moore, Jeffrey M.; Olkin, Catherine B.; Ennico, Kimberly; Binzel, Richard; Grundy, William M.; New Horizons Geology Geophysics and Imaging Science Theme Team, The New Horizons MVIC and LORRI Teams

    2016-10-01

    The impact craters observed during the New Horizons flyby of the Pluto system currently provide the most extensive empirical constraints on the size-frequency distribution of smaller impactors in the Kuiper belt. These craters also help us understand the surface ages and geologic evolution of the Pluto system bodies. Pluto's terrains display a diversity of crater retention ages and terrain types, indicating ongoing geologic activity and a variety of resurfacing styles including both exogenic and endogenic processes. Charon's informally named Vulcan Planum did experience early resurfacing, but crater densities suggest this is also a relatively ancient surface. We will present and compare the craters mapped across all of the relevant New Horizons LOng Range Reconnaissance Imager (LORRI) and Multispectral Visible Imaging Camera (MVIC) datasets of Pluto and Charon. We observe a paucity of small craters on all terrains (there is a break to a shallower slope for craters below 10 km in diameter), despite adequate resolution to observe them. This lack of small craters cannot be explained by geological resurfacing alone. In particular, the main area of Charon's Vulcan Planum displays no obviously embayed or breached crater rims, and may be the best representation of a production population since the emplacement of the plain. The craters on Pluto and Charon are more consistent with Kuiper belt and solar system evolution models producing fewer small objects.This work was supported by NASA's New Horizons project.

  1. 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.

  2. 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

  3. 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

  4. 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.

  5. 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.

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

    PubMed

    Namiki, N; Solomon, S C

    1994-08-12

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

  7. Intra-crater sedimentary deposits at the Haughton impact structure, Devon Island, Canadian High Arctic

    NASA Astrophysics Data System (ADS)

    Osinski, Gordon R.; Lee, Pascal

    2005-12-01

    Detailed field mapping has revealed the presence of a series of intra-crater sedimentary deposits within the interior of the Haughton impact structure, Devon Island, Canadian High Arctic. Coarse-grained, well-sorted, pale gray lithic sandstones (reworked impact melt breccias) unconformably overlie pristine impact melt breccias and attest to an episode of erosion, during which time significant quantities of impact melt breccias were removed. The reworked impact melt breccias are, in turn, unconformably overlain by paleolacustrine sediments of the Miocene Haughton Formation. Sediments of the Haughton Formation were clearly derived from pre-impact lower Paleozoic target rocks of the Allen Bay Formation, which form the crater rim in the northern, western, and southern regions of the Haughton structure. Collectively, these field relationships indicate that the Haughton Formation was deposited up to several million years after the formation of the Haughton crater and that they do not, therefore, represent an immediate, post-impact crater lake deposit. This is consistent with new isotopic dating of impactites from Haughton that indicate an Eocene age for the impact event (Sherlock et al. 2005). In addition, isolated deposits of post-Miocene intra-crater glacigenic and fluvioglacial sediments were found lying unconformably over remnants of the Haughton Formation, impact melt breccias, and other pre-impact target rock formations. These deposits provide clear evidence for glaciation at the Haughton crater. The wealth and complexity of geological and climatological information preserved as intra-crater deposits at Haughton suggests that craters on Mars with intra-crater sedimentary records might present us with similar opportunities, but also possibly significant challenges.

  8. 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.

  9. 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.

  10. Geophysical survey of the Målingen structure, a proposed marine-target impact crater.

    NASA Astrophysics Data System (ADS)

    Melero-Asensio, I.; Ormö, J.; Sturkell, E.

    2013-09-01

    Målingen is a 700m wide circular structure situated about 15km to SW of Lockne impact crater (central Sweden). Its circular shape and exposed sedimentary breccias resembling the resurge deposits at Lockne of the same age, strongly points towards a formation in relation to Lockne. The existence of shocked quartz grains in the lower parts of the about 149m long MAL-1 drill core retrieved from the center of the structure provides evidence for an impact origin[1]. The core showed a breccia-and sediment-filled depression of about 115 m depth. The basement in the Lockne/Målingen area is mainly constituted by Precambrian granitoids (Revsund Granite and a slightly foliated rock that we refer to as "older granite"), but sporadic occurrences of mafic rocks are also of interest for this study. The basement is covered by about 30m of Cambrian dark shale and about 50m of Ordovician limestones. The aim of this study is to develop a mutually constrained gravity and magnetic model to determine the dimensions and shape of the Målingen structure and evaluate its impact origin.

  11. 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.

  12. Seismic Profiles Across The Chesapeake Bay Impact Crater

    NASA Astrophysics Data System (ADS)

    Goldman, M. R.; Catchings, R. D.; Powars, D. S.; Gohn, G. S.

    2005-12-01

    In September and October 2004, the U.S. Geological Survey and Virginia Tech acquired a series of seismic reflection and refraction profiles along the southern Delmarva Peninsula, Virginia. Our objective was to determine the overall geometry and structure of the 35-million-year-old Chesapeake Bay Impact Crater (CBIC). One of the profiles, an approximately 7-km-long east-west-trending seismic refraction and low-fold reflection profile was acquired about 6 km north of the town of Cape Charles. Seismic sources (5 to 45 kg) for the main east-west profile consisted of explosions in approximately 20-m-deep boreholes, spaced at about 1 km intervals; data were recorded with 146 PASSCAL "Texan" seismographs, spaced at 50-m intervals across land surfaces and water bodies. We also acquired an approximately 2-km-long, high-resolution (5 m shot and geophone spacing) seismic profile along a section of the main east-west profile using a combination of small (0.5 kg) explosive and seisgun sources. These profiles were located across part of the crater moat, north of the central uplift. We developed tomographic velocity images and stacked CDP images for both the main east-west profile and the high-resolution profile. Tomographic velocity images suggest that coherent basement rocks (greater than 5.5 km/s) are relatively shallow (about 1.6 km) beneath the eastern end of the main east-west seismic profile, but these higher velocities deepen (to about 2.1 km) near the western end of the profile. The overlying rocks and sediments also dip to the west along the profile. Post-impact sediments (less than 2.5 km/s) are approximately 0.7 km thick and are underlain by 0.7 km of brecciated rocks (about 2.5 to 4.0 km/s) and the top of fractured basement (about 4.0 to 5.5 km/s) at 1.4 km depth. The reflection and tomographic images suggest similar subsurface structures, including westward dips of higher-velocity layers near the western end of the profile. High-resolution CDP images suggest

  13. Impact Velocity as a Source of Variations in Crater Depth on Mercury

    NASA Astrophysics Data System (ADS)

    Barnouin, O. S.; Susorney, H. C.; Ernst, C. M.; Neumann, G. A.; Johnson, C. L.; Balcerski, J.; Hauck, S. A.

    2012-12-01

    High-resolution images and altimetry of 115 craters obtained by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) mission have been analyzed to further the understanding of the formation and subsequent modification on impact craters on Mercury. Measurements derived from altimetry include crater depth (d), rim height, central peak/ring height, and crater wall/terrace width. Images have been used to derive crater diameter (D) and to assess crater degradation state as well as the nature of any observed impact melt. Analyses of the measurements tie these geometrical parameters to the crater characteristics seen in images. An important first observation is that the freshest craters on Mercury are not necessarily the deepest, as is typically inferred in most studies of d/D ratios. Frequently, the heights of the central peak are also smaller. A good example is provided by a comparison of two peak-ring craters of similar size on Mercury: Atget (D = 102 km) and Hokusai (D = 93 km). Hokusai is extremely fresh and has few superposed craters, broadly extensive craters rays, and distal secondaries. Hokusai also possesses substantial amounts of visible impact melt and evidence for a rampart-like structure reminiscent of ejecta observed on Mars. Although not markedly altered by subsequent impacts, Atget crater is slightly older and more degraded. Atget ejecta show no obvious evidence for melt ponds in the ejecta as seen at Hokusai. The younger Hokusai has a smaller d/D value of 0.022 (d = 2.1 km) than Atget's ratio of 0.032 (d = 3.3 km). In other examples, shallower fresh craters also display a central structure with less relief than comparable but less fresh craters of similar size. The Hokusai-Atget comparison suggests that a shallower depth may be associated with a greater volume of impact melt, but calculations indicate that this increased melt volume is probably not directly responsible for the lesser depth. The observed variation in impact melt

  14. 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.

  15. High-resolution seismic-reflection images across the ICDP-USGS Eyreville deep drilling site, Chesapeake Bay impact structure

    USGS Publications Warehouse

    Powars, D.S.; Catchings, R.D.; Goldman, M.R.; Gohn, G.S.; Horton, J.W.; Edwards, L.E.; Rymer, M.J.; Gandhok, G.

    2009-01-01

    The U.S. Geological Survey (USGS) acquired two 1.4-km-long, high-resolution (??5 m vertical resolution) seismic-reflection lines in 2006 that cross near the International Continental Scientifi c Drilling Program (ICDP)-USGS Eyreville deep drilling site located above the late Eocene Chesapeake Bay impact structure in Virginia, USA. Five-meter spacing of seismic sources and geophones produced high-resolution images of the subsurface adjacent to the 1766-m-depth Eyreville core holes. Analysis of these lines, in the context of the core hole stratigraphy, shows that moderateamplitude, discontinuous, dipping reflections below ??527 m correlate with a variety of Chesapeake Bay impact structure sediment and rock breccias recovered in the cores. High-amplitude, continuous, subhorizontal reflections above ??527 m depth correlate with the uppermost part of the Chesapeake Bay impact structure crater-fi ll sediments and postimpact Eocene to Pleistocene sediments. Refl ections with ??20-30 m of relief in the uppermost part of the crater-fi ll and lowermost part of the postimpact section suggest differential compaction of the crater-fi ll materials during early postimpact time. The top of the crater-fi ll section also shows ??20 m of relief that appears to represent an original synimpact surface. Truncation surfaces, locally dipping reflections, and depth variations in reflection amplitudes generally correlate with the lithostratigraphic and sequence-stratigraphic units and contacts in the core. Seismic images show apparent postimpact paleochannels that include the fi rst possible Miocene paleochannels in the Mid-Atlantic Coastal Plain. Broad downwarping in the postimpact section unrelated to structures in the crater fi ll indicates postimpact sediment compaction. ?? 2009 The Geological Society of America.

  16. High-resolution seismic-reflection images across the ICDP-USGS Eyreville deep drilling site, Chesapeake Bay impact structure

    USGS Publications Warehouse

    Powars, David S.; Catchings, Rufus D.; Goldman, Mark R.; Gohn, Gregory S.; Horton, J. Wright; Edwards, Lucy E.; Rymer, Michael J.; Gandhok, Gini

    2009-01-01

    The U.S. Geological Survey (USGS) acquired two 1.4-km-long, high-resolution (~5 m vertical resolution) seismic-reflection lines in 2006 that cross near the International Continental Scientific Drilling Program (ICDP)-USGS Eyreville deep drilling site located above the late Eocene Chesapeake Bay impact structure in Virginia, USA. Five-meter spacing of seismic sources and geophones produced high-resolution images of the subsurface adjacent to the 1766-m-depth Eyreville core holes. Analysis of these lines, in the context of the core hole stratigraphy, shows that moderate-amplitude, discontinuous, dipping reflections below ~527 m correlate with a variety of Chesapeake Bay impact structure sediment and rock breccias recovered in the cores. High-amplitude, continuous, subhorizontal reflections above ~527 m depth correlate with the uppermost part of the Chesapeake Bay impact structure crater-fill sediments and postimpact Eocene to Pleistocene sediments. Reflections with ~20-30 m of relief in the uppermost part of the crater-fill and lowermost part of the postimpact section suggest differential compaction of the crater-fill materials during early postimpact time. The top of the crater-fill section also shows ~20 m of relief that appears to represent an original synimpact surface. Truncation surfaces, locally dipping reflections, and depth variations in reflection amplitudes generally correlate with the lithostrati-graphic and sequence-stratigraphic units and contacts in the core. Seismic images show apparent postimpact paleochannels that include the first possible Miocene paleochannels in the Mid-Atlantic Coastal Plain. Broad downwarping in the postim-pact section unrelated to structures in the crater fill indicates postimpact sediment compaction.

  17. 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.

  18. 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.

  19. The XRD Amorphous Component in John Klein Drill Fines at Yellowknife Bay, Gale Crater, Mars

    NASA Technical Reports Server (NTRS)

    Morris, Richard V.; Ming,, Douglas W.; Blake, David; Vaniman, David; Bish, David L; Chipera, Steve; Downs, Robert; Morrison, Shaunna; Gellert, Ralf; Campbell, Iain; Treiman, Alan H.; Achilles, Cherie; Bristow, Thomas; Crisp, Joy A.; McAdam, Amy; Archer, Paul Douglas; Sutter, Brad; Rampe, Elizabeth B.

    2013-01-01

    Drill fines of mudstone (targets John Klein and Cumberland) from the Sheepbed unit at Yel-lowknife Bay were analyzed by MSL payload elements including the Chemistry and Mineralogy (CheMin), APXS (Alpha Particle X-Ray Spectrometer), and Sample Analysis at Mars (SAM) instruments. CheMin XRD results show a variety of crystalline phases including feldspar, pyroxene, olivine, oxides, oxyhydroxides, sulfates, sulfides, a tri-octahedral smectite, and XRD amorphous material. The drill fines are distinctly different from corresponding analyses of the global soil (target Rocknest) in that the mudstone samples contained detectable phyllosilicate. Here we focus on John Klein and combine CheMin and APXS data to calculate the chemical composition and concentration of the amorphous component. The chemical composition of the amorphous plus smectite component for John Klein was calculated by subtracting the abundance-weighted chemical composition of the individual XRD crystalline components from the bulk composition of John Kline as measured by APXS. The chemical composition of individual crystalline components was determined either by stoichiometry (e.g., hematite and magnetite) or from their unit cell parameters (e.g., feldspar, olivine, and pyroxene). The chemical composition of the amorphous + smectite component (approx 71 wt.% of bulk sample) and bulk chemical composition are similar. In order to calculate the chemical composition of the amorphous component, a chemical composition for the tri-octahedral smectite must be assumed. We selected two tri-octahedral smectites with very different MgO/(FeO + Fe2O3) ratios (34 and 1.3 for SapCa1 and Griffithite, respectively). Relative to bulk sample, the concentration of amorphous and smectite components are 40 and 29 wt.% for SapCa1 and 33 and 36 wt.% for Griffithite. The amount of smectite was calculated by requiring the MgO concentration to be approx 0 wt.% in the amorphous component. Griffithite is the preferred smectite because

  20. The XRD Amorphous Component in John Klein Drill Fines at Yellowknife Bay, Gale Crater, Mars

    NASA Astrophysics Data System (ADS)

    Morris, R. V.; Ming, D. W.; Blake, D.; Vaniman, D.; Bish, D. L.; Chipera, S.; Downs, R.; Morrison, S.; Gellert, R.; Campbell, I.; Treiman, A. H.; Achilles, C.; Bristow, T.; Crisp, J. A.; McAdam, A.; Archer, P. D.; Sutter, B.; Rampe, E. B.; Team, M.

    2013-12-01

    Drill fines of mudstone (targets John Klein and Cumberland) from the Sheepbed unit at Yel-lowknife Bay were analyzed by MSL payload elements including the Chemistry and Mineralogy (CheMin), APXS (Alpha Particle X-Ray Spectrometer), and Sample Analysis at Mars (SAM) instruments. CheMin XRD results show a variety of crystalline phases including feldspar, pyrox-ene, olivine, oxides, oxyhydroxides, sulfates, sulfides, a tri-octahedral smectite, and XRD amorphous material. The drill fines are distinctly different from corresponding analyses of the global soil (target Rocknest) in that the mudstone samples contained detectable phyllosilicate. Here we focus on John Klein and combine CheMin and APXS data to calculate the chemical composition and concentration of the amorphous component. The chemical composition of the amorphous plus smectite component for John Klein was cal-culated by subtracting the abundance-weighted chemical composition of the individual XRD crystalline components from the bulk composition of John Kline as measured by APXS. The chemical composition of individual crystalline components was determined either by stoichiome-try (e.g., hematite and magnetite) or from their unit cell parameters (e.g., feldspar, olivine, and pyroxene). The chemical composition of the amorphous + smectite component (~71 wt.% of bulk sample) and bulk chemical compositon are similar. In order to calculate the chemical composition of the amorphous component, a chemical composition for the tri-octahedral smectite must be assumed. We selected two tri-octahedral smectites with very different MgO/(FeO + Fe2O3) ratios (34 and 1.3 for SapCa1 and Griffithite, respectively). Relative to bulk sample, the concentration of amorphous and smectite components are 40 and 29 wt.% for SapCa1 and 33 and 36 wt.% for Griffithite. The amount of smectite was calculated by requiring the MgO concentration to be~0 wt.% in the amporphous component. Griffithite is the preferred smectite because the position

  1. 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.

  2. Assessment of the Preservation of Impact Residues in Stardust Analogue Craters Using Advanced EDX Imagery with an Annular SDD

    NASA Astrophysics Data System (ADS)

    Salge, T.; Kearsley, A. T.; Price, M. C.; Burchell, M. J.; Cole, M. J.

    2016-08-01

    Low voltage SEM/EDX analysis with an annular SDD can show relationships between even tiny impact residues throughout complex crater shapes. The technique should be used as a preliminary reconnaissance method on all Stardust cometary dust craters.

  3. 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.

  4. 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.

  5. 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.

  6. Shock metamorphism of quartz at the submarine Mjølnir impact crater, Barents Sea

    NASA Astrophysics Data System (ADS)

    Sandbakken, PâL. T.; Langenhorst, Falko; Dypvik, Henning

    2005-10-01

    Shock metamorphosed quartz grains have been discovered in a drill core from the central peak of the Late Jurassic, marine Mjølnir structure; this finding further corroborates the impact origin of Mjølnir. The intersected strata represent the Upper Jurassic Hekkingen Formation and underlying Jurassic and Upper Triassic formations. The appearance, orientation, and origin of shock features in quartz grains and their stratigraphic distribution within the core units have been studied by optical and transmission electron microscopy. The quartz grains contain planar fractures (PFs), planar deformation features (PDFs), and mechanical Brazil twins. The formation of PFs is the predominant shock effect and is attributed to the large impedance differences between the water-rich pores and constituent minerals in target sediments. This situation may have strengthened tensional/extensional and shear movements during shock compression and decompression. The combination of various shock effects indicates possible shock pressures between 5 and at least 20 GPa for three core units with a total thickness of 86 m (from 74.00 m to 171.09 m core depth). Crater-fill material from the lower part of the core typically shows the least pressures, whereas the uppermost part of the allochthonous crater deposits displays the highest pressures. The orientations of PFs in studied quartz grains seem to become more diverse as the pressure rises from predominantly (0001) PFs to a combination of (0001), ?, and ? orientations. However, the lack of experimental data on porous sedimentary rocks does not allow us to further constrain the shock conditions on the basis of PF orientations.

  7. 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.

  8. Crater evolution after the impact of a drop onto a semi-infinite liquid target.

    PubMed

    Bisighini, Alfio; Cossali, Gianpietro E; Tropea, Cameron; Roisman, Ilia V

    2010-09-01

    This paper is devoted to an experimental and theoretical investigation of the crater formed by the impact of a single drop onto a semi-infinite target of the same liquid. The shape of the crater at various time instances after impact has been observed using a high-speed video system and then accurately characterized. A theoretical model for the crater expansion has been developed, which is able to predict the temporal variation of the crater depth for sufficiently high Weber, Froude, and Reynolds numbers. The flow around the crater is approximated by an irrotational velocity field past a moving and expanding sphere. The equations describing the propagation of the surface of the crater have been obtained from the balance of stresses at the crater interface, accounting for inertia, gravity, and surface tension. The temporal evolution of the crater depth has been calculated by numerical solution of the equations of motion. The agreement between the theoretical predictions and experimental data are rather good.

  9. 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

  10. 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.

  11. Morphology of Morasko Crater Field: An Interaction of Glacial and Impact Landforms

    NASA Astrophysics Data System (ADS)

    Włodarski, W.; Papis, J.; Szczuciński, W.

    2016-08-01

    Regarding the small sizes of impact craters, their potential superimposition on primary landforms may be complex. This study reveals this superimposition in the area of the Morasko Hill push moraine based on digital terrain modelling.

  12. 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.

  13. 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)

  14. Exploratory hydrocarbon drilling impacts to Arctic lake ecosystems.

    PubMed

    Thienpont, Joshua R; Kokelj, Steven V; Korosi, Jennifer B; Cheng, Elisa S; Desjardins, Cyndy; Kimpe, Linda E; Blais, Jules M; Pisaric, Michael F J; Smol, John P

    2013-01-01

    Recent attention regarding the impacts of oil and gas development and exploitation has focused on the unintentional release of hydrocarbons into the environment, whilst the potential negative effects of other possible avenues of environmental contamination are less well documented. In the hydrocarbon-rich and ecologically sensitive Mackenzie Delta region (NT, Canada), saline wastes associated with hydrocarbon exploration have typically been disposed of in drilling sumps (i.e., large pits excavated into the permafrost) that were believed to be a permanent containment solution. However, failure of permafrost as a waste containment medium may cause impacts to lakes in this sensitive environment. Here, we examine the effects of degrading drilling sumps on water quality by combining paleolimnological approaches with the analysis of an extensive present-day water chemistry dataset. This dataset includes lakes believed to have been impacted by saline drilling fluids leaching from drilling sumps, lakes with no visible disturbances, and lakes impacted by significant, naturally occurring permafrost thaw in the form of retrogressive thaw slumps. We show that lakes impacted by compromised drilling sumps have significantly elevated lakewater conductivity levels compared to control sites. Chloride levels are particularly elevated in sump-impacted lakes relative to all other lakes included in the survey. Paleolimnological analyses showed that invertebrate assemblages appear to have responded to the leaching of drilling wastes by a discernible increase in a taxon known to be tolerant of elevated conductivity coincident with the timing of sump construction. This suggests construction and abandonment techniques at, or soon after, sump establishment may result in impacts to downstream aquatic ecosystems. With hydrocarbon development in the north predicted to expand in the coming decades, the use of sumps must be examined in light of the threat of accelerated permafrost thaw, and the

  15. Exploratory hydrocarbon drilling impacts to Arctic lake ecosystems.

    PubMed

    Thienpont, Joshua R; Kokelj, Steven V; Korosi, Jennifer B; Cheng, Elisa S; Desjardins, Cyndy; Kimpe, Linda E; Blais, Jules M; Pisaric, Michael F J; Smol, John P

    2013-01-01

    Recent attention regarding the impacts of oil and gas development and exploitation has focused on the unintentional release of hydrocarbons into the environment, whilst the potential negative effects of other possible avenues of environmental contamination are less well documented. In the hydrocarbon-rich and ecologically sensitive Mackenzie Delta region (NT, Canada), saline wastes associated with hydrocarbon exploration have typically been disposed of in drilling sumps (i.e., large pits excavated into the permafrost) that were believed to be a permanent containment solution. However, failure of permafrost as a waste containment medium may cause impacts to lakes in this sensitive environment. Here, we examine the effects of degrading drilling sumps on water quality by combining paleolimnological approaches with the analysis of an extensive present-day water chemistry dataset. This dataset includes lakes believed to have been impacted by saline drilling fluids leaching from drilling sumps, lakes with no visible disturbances, and lakes impacted by significant, naturally occurring permafrost thaw in the form of retrogressive thaw slumps. We show that lakes impacted by compromised drilling sumps have significantly elevated lakewater conductivity levels compared to control sites. Chloride levels are particularly elevated in sump-impacted lakes relative to all other lakes included in the survey. Paleolimnological analyses showed that invertebrate assemblages appear to have responded to the leaching of drilling wastes by a discernible increase in a taxon known to be tolerant of elevated conductivity coincident with the timing of sump construction. This suggests construction and abandonment techniques at, or soon after, sump establishment may result in impacts to downstream aquatic ecosystems. With hydrocarbon development in the north predicted to expand in the coming decades, the use of sumps must be examined in light of the threat of accelerated permafrost thaw, and the

  16. Exploratory Hydrocarbon Drilling Impacts to Arctic Lake Ecosystems

    PubMed Central

    Thienpont, Joshua R.; Kokelj, Steven V.; Korosi, Jennifer B.; Cheng, Elisa S.; Desjardins, Cyndy; Kimpe, Linda E.; Blais, Jules M.; Pisaric, Michael FJ.; Smol, John P.

    2013-01-01

    Recent attention regarding the impacts of oil and gas development and exploitation has focused on the unintentional release of hydrocarbons into the environment, whilst the potential negative effects of other possible avenues of environmental contamination are less well documented. In the hydrocarbon-rich and ecologically sensitive Mackenzie Delta region (NT, Canada), saline wastes associated with hydrocarbon exploration have typically been disposed of in drilling sumps (i.e., large pits excavated into the permafrost) that were believed to be a permanent containment solution. However, failure of permafrost as a waste containment medium may cause impacts to lakes in this sensitive environment. Here, we examine the effects of degrading drilling sumps on water quality by combining paleolimnological approaches with the analysis of an extensive present-day water chemistry dataset. This dataset includes lakes believed to have been impacted by saline drilling fluids leaching from drilling sumps, lakes with no visible disturbances, and lakes impacted by significant, naturally occurring permafrost thaw in the form of retrogressive thaw slumps. We show that lakes impacted by compromised drilling sumps have significantly elevated lakewater conductivity levels compared to control sites. Chloride levels are particularly elevated in sump-impacted lakes relative to all other lakes included in the survey. Paleolimnological analyses showed that invertebrate assemblages appear to have responded to the leaching of drilling wastes by a discernible increase in a taxon known to be tolerant of elevated conductivity coincident with the timing of sump construction. This suggests construction and abandonment techniques at, or soon after, sump establishment may result in impacts to downstream aquatic ecosystems. With hydrocarbon development in the north predicted to expand in the coming decades, the use of sumps must be examined in light of the threat of accelerated permafrost thaw, and the

  17. Drill core LB-08A, Bosumtwi impact structure, Ghana: Petrographic and shock metamorphic studies of material from the central uplift

    NASA Astrophysics Data System (ADS)

    Ferrière, Ludovic; Koeberl, Christian; Reimold, Wolf Uwe

    During a recent drilling project sponsored by the International Continental Scientific Drilling Progam (ICDP), two boreholes (LB-07A and LB-08A) were drilled into the crater fill of the Bosumtwi impact structure and the underlying basement, into the deep crater moat and the outer flank of the central uplift, respectively. The Bosumtwi impact structure in Ghana (West Africa), which is 10.5 km in diameter and 1.07 Myr old, is largely filled by Lake Bosumtwi. Here we present the lithostratigraphy of drill core LB-08A (recovered between 235.6 and 451.33 m depth below lake level) as well as the first mineralogical and petrographic observations of samples from this core. This drill core consists of approximately 25 m of polymict, clast-supported lithic breccia intercalated with suevite, which overlies fractured/brecciated metasediment that displays a large variation in lithology and grain size. The lithologies present in the central uplift are metasediments composed dominantly of fine-grained to gritty meta-graywacke, phyllite, and slate, as well as suevite and polymict lithic impact breccia. The suevites, principally present between 235.6 and 240.5 m and between 257.6 and 262.2 m, display a fine-grained fragmental matrix (about 39 to 45 vol%) and a variety of lithic and mineral clasts that include meta-graywacke, phyllite, slate, quartzite, carbon-rich organic shale, and calcite, as well as melt particles, fractured quartz, unshocked quartz, unshocked feldspar, quartz with planar deformation features (PDFs), diaplectic quartz glass, mica, epidote, sphene, and opaque minerals). The crater-fill suevite contains calcite clasts but no granite clasts, in contrast to suevite from outside the northern crater rim. The presence of melt particles in suevite samples from the uppermost 25 meters of the core and in suevite dikelets in the basement is an indicator of shock pressures exceeding 45 GPa. Quartz grains present in suevite and polymict lithic impact breccia abundantly

  18. 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.

  19. 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.

  20. 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.

  1. 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.

  2. Impact Metamorphism of Sandstones at Amguid Crater, Algeria

    NASA Astrophysics Data System (ADS)

    Sahoui, R.; Belhai, D.

    2016-08-01

    Amguid is a 450 m diameter sample crater; it is emplaced in Lower Devonian sandstones.We have carried out a petrographic study in order to investigate shock effects recorded in these sandstones and define shock stages in Amguid.

  3. Impact Breccia Clast from the Corossol Crater, Canada

    NASA Astrophysics Data System (ADS)

    Higgins, M. D.; Lajeunesse, P.; St-Onge, G.; Sanfaçon, R.; Duchesne, M. J.

    2013-09-01

    A breccia clast was dredged from the 4-km diameter underwater Corossol Crater near Sept Iles, Canada. It contains fragmented glassy droplets with a composition similar to fluorapatite, and a quartz crystal showing planar deformation features.

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

    NASA Astrophysics Data System (ADS)

    Rodríguez, Jose Alexis Palmero; Sasaki, Sho; Dohm, James M.; Tanaka, Ken L.; Strom, Bob; Kargel, Jeff; Kuzmin, Ruslan; Miyamoto, Hideaki; Spray, John G.; Fairén, Alberto G.; Komatsu, Goro; Kurita, Kei; Baker, Victor

    2005-06-01

    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.

  5. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2001-12-01

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

  7. Neugrund structure — the newly discovered submarine early Cambrian impact crater

    NASA Astrophysics Data System (ADS)

    Suuroja, Kalle; Suuroja, Sten

    The Neugrund Bank is situated on the southern side of the entrance of the Gulf of Finland (59°20N; 23°31E) between Osmussaar and Krass islands. It is a shoal of a very peculiar multi-ring shape. In the coastal and offshore area of North-Western Estonia, numerous erratic boulders, consisting of rocks resembling impact breccias, have been found. The investigations proved that under Neugrund Bank and in its surrounding is located a classic buried and partially newly exposed impact crater. The studies revealed the general morphology of the structure. In the summer of 1998, during three expeditions, the submarine impact structure was investigated in detail by diving and sidescan sonar profiling. As a result, the hypothesis, which had been indirectly indicated by remote sensing, was finally verified. The Neugrund impact crater formed ca. 540 My ago in a shallow epicontinental sea as the result of the impact of an extraterrestrial body with a diameter of ca. 400 m. As a consequence of the impact a crater with the rim-to-rim diameter of 7 km was formed. The depth of the ca. 5 km-diameter crater has not yet been determined, but is assumed to range over 500 m. At the distance of about 10 km around the crater, the target rocks are strongly disturbed. After the impact the crater deep was filled with clastic deposits and was buried within a rather short time (some millions of years). The sedimentation conditions in the crater differed from those of the surrounding area until the Middle Ordovician. Since then, and up to the Tertiary, the crater remained buried and was partially uncovered during the Neogene.

  8. 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

  9. 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

  10. 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.

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

    USGS Publications Warehouse

    ,

    2003-01-01

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

  12. 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

  13. 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

  14. Morphology of craters generated by hypervelocity impacts of micron-sized polypyrrole-coated olivine particles

    NASA Astrophysics Data System (ADS)

    Li, Y. W.; Bugiel, S.; Trieloff, M.; Hillier, Jon K.; Postberg, F.; Price, M. C.; Shu, A.; Fiege, K.; Fielding, L. A.; Armes, S. P.; Wu, Y. Y.; Grün, E.; Srama, R.

    2014-08-01

    To understand the process of cosmic dust particle impacts and translate crater morphology on smoothed metallic surfaces to dust properties, correct calibration of the experimental impact data is needed. This article presents the results of studies of crater morphology generated by impacts using micron-sized polypyrrole (PPy)-coated olivine particles. The particles were accelerated by an electrostatic dust accelerator to high speeds before they impacted onto polished aluminum targets. The projectile diameter and velocity ranges were 0.3-1.2 μm and 3-7 km s-1. After impact, stereopair images of the craters were taken using scanning electron microscope and 3-D reconstructions made to provide diameter and depth measurements. In this study, not just the dimensions of crater diameters and depths, but also the shape and dimensions of crater lips were analyzed. The craters created by the coated olivine projectiles are shown to have complicated shapes believed to be due to the nonspherical shape of the projectiles.

  15. Introducing and discussing a novel diagrammatic representation of impact crater dimensions

    NASA Astrophysics Data System (ADS)

    Caprarelli, Graziella

    2014-07-01

    Impact craters on the surface of Mars are degraded by erosion and infilling due to combinations of geological processes. These result in modifications of relative crater dimensions, including diameter increase and reduction of rim-floor depths. In principle, the longer a crater is exposed to geological processes, the more pronounced the modifications. Visualization and analysis of these effects are achieved by plotting the measured depths (M) of impact craters vs the corresponding theoretical depths (predicted: P) calculated from the crater diameters using depth/Diameter power laws. This type of diagram is referred to as MPD (measured depth vs predicted depth diagram). The advantage of using the MPD representation consists in the fact that the data plot along linear regressions, more easily interpreted than standard depth vs diameter diagrams. As an example of application of the method, the MPD was used to discriminate different generations of impact craters in Terra Sabaea into four groups: T0 (fresh craters), T1, T2 and T3 (from younger to older), all located on the most ancient geological unit in the area (Npld). Other units in the area are Hpl3 and Hr, impacted only by craters belonging to group T0, suggesting that these units are stratigraphically correlated. The data of 5 craters in superposition relationships with the eastern reaches of Evros Vallis, one of the major valley networks in the area, were plotted in the diagram and assigned each to a regression depending on the location of their data points in relation to the prediction bands of the regressions. The craters superposed to the valley all belonged to T0, indicating that Evros Vallis has the same relative age of units Hpl3 and Hr. A conceptual discussion of the results demonstrates that MPD statistics (a) are unaffected by the procedures used to acquire depths and diameters of impact craters and by the power laws used, and (b) can be interpreted irrespective of the sequence or combination of

  16. Nature of the Yucatan Block Basement as Derived From Study of Granitic Clasts in the Impact Breccias of Chicxulub Crater

    NASA Astrophysics Data System (ADS)

    Vera-Sanchez, P.; Rebolledo-Vieyra, M.; Perez-Cruz, L.; Urrutia-Fucugauchi, J.

    2008-05-01

    The tectonic and petrologic nature of the basement of the Yucatan Block is studied from analyses of basement clasts present in the impact suevitic breccias of Chicxulub crater. The impact breccias have been sampled as part of the drilling projects conducted in the Yucatan peninsula by Petroleos Mexicanos, the National University of Mexico and the Chicxulub Scientific Drilling Project. Samples analyzed come mainly from the Yaxcopoil-1, Tekax, and Santa Elena boreholes, and partly from Pemex boreholes. In this study we concentrate on clasts of the granites, granodiorites and quartzmonzonites in the impact breccias. We report major and trace element geochemical and petrological data, which are compared with data from the granitic and volcanic rocks from the Maya Mountains in Belize and from the Swannee terrane in Florida. Basement granitic clasts analyzed present intermediate to acidic sub-alkaline compositions. Plots of major oxides (e.g., Al2O3, Fe2O3, TiO2 and CaO) and trace elements (e.g., Th, Y, Hf, Nb and Zr) versus silica allow separation of samples into two major groups, which can be compared to units in the Maya Mountains and in Florida basement. The impact suevitic breccia samples have been affected by alteration likely related to the hydrothermal processes associated with the crater melt sheet. Cloritization, seritization and fenitization alterations are recognized, due to the long term hydrothermalism. Krogh et al. (1993) reported U-Pb dates on zircons from the suevitic breccias, which gave dates of 545 +/- 5 Ma and 418 +/- 6 Ma, which were interpreted in terms of the deep granitic metamorphic Yucatan basement. The younger date correlates with the age for the Osceola Granite and the St. Lucie metamorphic complex of the Swannee terrane in the Florida peninsula. The intrusive rocks in the Yucatan basement may be related to approx. 418 Ma ago collisional event in the Late Silurian.

  17. 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

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1993-03-01

    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.

  20. 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

  1. Lightning remagnetization of the Vredefort impact crater: No evidence for impact-generated magnetic fields

    NASA Astrophysics Data System (ADS)

    Carporzen, Laurent; Weiss, Benjamin P.; Gilder, Stuart A.; Pommier, Anne; Hart, Rodger J.

    2012-01-01

    The Vredefort impact crater in South Africa is one of the oldest and largest craters on Earth, making it a unique analog for planetary basins. Intense and randomly oriented remanent magnetization observed in surface samples at Vredefort has been attributed to impact-generated magnetic fields. This possibility has major implications for extraterrestrial paleomagnetism since impact-generated fields have been proposed as a key alternative to the dynamo hypothesis for magnetization on the Moon and asteroids. Furthermore, the presence of single-domain magnetite found along shock-generated planar deformation features in Vredefort granites has been widely attributed to the 2.02 Ga impact event. An alternative hypothesis is that the unusual magnetization and/or rock magnetic properties of Vredefort rocks are the products of recent lightning strikes. Lightning and impact-generated fields can be distinguished by measuring samples collected from below the present surface. Here we present a paleomagnetic and rock magnetic study of samples from two 10 m deep vertical boreholes. We show that the magnetization at depth is consistent with a thermoremanent magnetization acquired in the local geomagnetic field following the impact, while random, intense magnetization and some of the unusual rock magnetic properties observed in surface rocks are superficial phenomena produced by lightning. Because Vredefort is the only terrestrial crater that has been proposed to contain records of impact-generated fields, this removes a key piece of evidence in support of the hypothesis that paleomagnetism of the Moon and other extraterrestrial bodies is the product of impacts rather than past core dynamos.

  2. 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.

  3. 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.

  4. A hydrogeophysical conceptual model of Mount Toondina impact crater, South Australia

    NASA Astrophysics Data System (ADS)

    Dressler, Andrew Kelly

    Mount Toondina, South Australia is an impact crater that currently has groundwater discharging through evapotranspiration, but formerly had eight springs or more flowing around the crater ring. Using field geophysical and geochemical data, a hydrogeophysical conceptual model was developed that suggests that advection of groundwater to the surface through a sandstone layer is the dominant flow mechanism for the system, creating a ring of vegetation at the surface, although faults provide controls over some spring locations. The data also suggest that sufficient fluid density contrast combined with a vertical permeability structure may allow free convection to occur in the impact crater. The conceptual model was tested by developing numerical models to evaluate the permeability structure and the potential for mixed convection in the Mount Toondina system. The FEFLOW models suggest that the Mount Toondina impact crater spring system is controlled by mixed convective flow from the subsurface to the ring of vegetation around the springs which maintains brackish conditions relative to adjacent saline conditions. The models indicated that convective processes result throughout the crater although the character of convection is controlled by the relative permeability of the formations. The results can be applied to better manage flora and fauna in the Mount Toondina area and help to interpret potential for groundwater flow in and around other impact craters.

  5. Present-day impact cratering rate and contemporary gully activity on Mars.

    PubMed

    Malin, Michael C; Edgett, Kenneth S; Posiolova, Liliya V; McColley, Shawn M; Dobrea, Eldar Z Noe

    2006-12-01

    The Mars Global Surveyor Mars Orbiter Camera has acquired data that establish the present-day impact cratering rate and document new deposits formed by downslope movement of material in mid-latitude gullies on Mars. Twenty impacts created craters 2 to 150 meters in diameter within an area of 21.5 x 10(6) square kilometers between May 1999 and March 2006. The values predicted by models that scale the lunar cratering rate to Mars are close to the observed rate, implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating. The new gully deposits, formed since August 1999, are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water: relatively long, extended, digitate distal and marginal branches, diversion around obstacles, and low relief. The observations suggest that liquid water flowed on the surface of Mars during the past decade.

  6. Present-day impact cratering rate and contemporary gully activity on Mars.

    PubMed

    Malin, Michael C; Edgett, Kenneth S; Posiolova, Liliya V; McColley, Shawn M; Dobrea, Eldar Z Noe

    2006-12-01

    The Mars Global Surveyor Mars Orbiter Camera has acquired data that establish the present-day impact cratering rate and document new deposits formed by downslope movement of material in mid-latitude gullies on Mars. Twenty impacts created craters 2 to 150 meters in diameter within an area of 21.5 x 10(6) square kilometers between May 1999 and March 2006. The values predicted by models that scale the lunar cratering rate to Mars are close to the observed rate, implying that surfaces devoid of craters are truly young and that as yet unrecognized processes of denudation must be operating. The new gully deposits, formed since August 1999, are light toned and exhibit attributes expected from emplacement aided by a fluid with the properties of liquid water: relatively long, extended, digitate distal and marginal branches, diversion around obstacles, and low relief. The observations suggest that liquid water flowed on the surface of Mars during the past decade. PMID:17158321

  7. Suevite breccia of the Ries impact crater, Germany: Petrography, chemistry and shock metamorphism of crystalline rock clasts

    NASA Astrophysics Data System (ADS)

    von Engelhardt, Wolf

    1997-07-01

    Clasts of deep seated crystalline basement rocks in suevites of the Ries crater, Germany, were catalogued lithologically and classified with regard to their degree of shock metamorphism. The sample suite consisted of eight hundred and six clasts from ten outcrops in fall out suevites and four hundred and forty seven clasts from drill cores in the crater interior encountering crater suevite. These clasts can be grouped into seven types of metamorphic and nine types of igneous rocks. One hundred and forty three clasts, representing these lithologies, were analyzed for major element bulk-composition. The fall out suevite contains on the average 4 vol % of crystalline basement clasts, 0.4 vol % of sedimentary rocks, 16 vol % of glass bodies, some of them aerodynamically shaped, and 79 vol % of grundmass. On the average, 52 % of all crystalline clasts are from metamorphic sources and 42 % of igneous origin. Using the shock classification of Stoffler (1974), 8 % of all crystalline clasts appear unshocked (< 10 GPa), 34, 30 and 27 %, respectively, are shocked to stages I (10-35 Gpa), II (35-45 GPa) and III (45-60 GPa). The bulk composition of suevite glasses is consistent with the modal proportions of crystalline rock types, observed in the clast populations. This indicates that the glasses originate by shock-fusion of a similarly composed basement. The crater suevite contains the same crystalline rock types which occur in the fall out suevites. The bore hole "Nordlingen 1973" yields an average of 62 vol % metamorphic and 38 vol% igneous rocks. The crater suevite differs from fall out suevites by a higher clast/glass ratio, by preponderance (65-95 %) of clasts shocked to stage I only, and by the absence of aerodynamically shaped glass bodies. The source of crystalline clasts and melt particles of suevites is a volume of rocks, located deep in the crystalline basement, to which the projectile transmitted most of its energy, so that only rocks of the basement were shocked

  8. Magnetic Susceptibility and Geochemistry Records in the Yax-1 Borehole in the Chicxulub Impact Crater: A paleoclimatic approach in the K/Pg and P/E Boundaries.

    NASA Astrophysics Data System (ADS)

    Marca-Castillo, M.; Perez-Cruz, L. L.; Fucugauchi, J. U.; Buitrón Sánchez, B. E.

    2015-12-01

    Chicxulub impact crater is located in the northwestern sector of Yucatan Peninsula, Mexico. It is the best-preserved multi-ring impact crater on Earth. Several studies have been focused in this crater structure due its association with the Cretaceous/Paleogenous boundary events. The aim of this study is document the abrupt climate changes during the K/Pg and P/E boundaries based on the stratigraphy, magnetic properties (magnetic susceptibility) and geochemical (major elements) records in the Yaxcopoil-1 (Yax-1) borehole in the Chicxulub impact crater. The Yax 1 was drilled at 20° 44' 38.45'' N, 89° 43' 6.70'' W. Two intervals from 830 to 750 and between 750 and 700 m depth were selected for this study. Magnetic susceptibility logs and X-Ray Fluorescence (XRF) measures were taken every 10 cm using a Bartington magnetic susceptibility meter and a Thermo Scientific Niton XL3tGOLDD XRF analyzer. Results show variations in magnetic susceptibility logs and major elements (Ca, Si, Fe, Ti and Si) content in the K/Pg boundary at ca. 794 m depth. Magnetic susceptibility decrease abruptly, Ca values increase, and the other elements show low values. Geochemical results, manly the Ca-record, suggest that the P/E boundary might have happened around 745 m depth. These values are compared with 13C isotopes and they coincide with the Carbon Isotope Excursion (CIE), suggesting their relationship with the abrupt climate change and with the ocean acidification.

  9. 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

  10. Uppermost impact fallback layer in the Bosumtwi crater (Ghana): Mineralogy, geochemistry, and comparison with Ivory Coast tektites

    NASA Astrophysics Data System (ADS)

    Koeberl, Christian; Brandstätter, Franz; Glass, Billy P.; Hecht, Lutz; Mader, Dieter; Reimold, Wolf Uwe

    In 2004, an International Continental Scientific Drilling Program (ICDP) drilling project at the Bosumtwi impact crater, Ghana (10.5 km in diameter, 1.07 Myr old), was performed to study the sediments that fill the lake as well as the underlying impactites. In one (LB-05) of 16 cores drilled into the lake sediments, the zone between the impact breccias and the post-impact sediments was penetrated, preserving the final, fine-grained impact fallback layer. This ~30 cm thick layer contains in the top 10 cm “accretionary” lapilli, microtektite-like glass spherules, and shocked quartz grains. Glass particles -- mostly of splash form less than 1 mm size -- make up the bulk of the grains (~70-78% by number) in the coarser size fraction (>125 μm) of the top of the fallback layer. About one-third of all quartz grains in the uppermost part of the layer are shocked, with planar deformation features (PDFs); almost half of these grains are highly shocked, with 3 or more sets of PDFs. K-feldspar grains also occur and some show shock deformation. The abundance of shocked quartz grains and the average shock level as indicated by the number of sets of PDFs, for both quartz and K-feldspar, decrease with depth into the layer. The well-preserved glass spherules and fragments are chemically rather homogeneous within each particle, and also show relatively small variations between the various particles. On average, the composition of the fallback spherules from core LB-5B is very similar to the composition of Ivory Coast tektites and microtektites, with the exception of CaO contents, which are about 1.5 to 2 times higher in the fallback spherules. This is a rare case in which the uppermost fallback layer and the transition to the post-impact sediments has been preserved in an impact structure; its presence indicates that the impactite sequence at Bosumtwi is complete and that Bosumtwi is a very well-preserved impact crater.

  11. 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.

  12. Petrophysical and paleomagnetic data of drill cores from the Bosumtwi impact structure, Ghana

    NASA Astrophysics Data System (ADS)

    Elbra, T.; Kontny, A.; Pesonen, L. J.; Schleifer, N.; Schell, C.

    Physical properties from rocks of the Bosumtwi impact structure, Ghana, Central Africa, are essential to understand the formation of the relatively young (1.07 Ma) and small (10.5 km) impact crater and to improve its geophysical modeling. Results of our petrophysical studies of deep drill cores LB-07A and LB-08A reveal distinct lithological patterns but no depth dependence. The most conspicuous difference between impactites and target lithologies are the lower bulk densities and significantly higher porosities of the suevite and lithic breccia units compared to meta-graywacke and metapelites of target lithologies. Magnetic susceptibility shows mostly paramagnetic values (200-500 × 10-6 SI) throughout the core, with an exception of a few metasediment samples, and correlates positively with natural remanent magnetization (NRM) and Q values. These data indicate that magnetic parameters are related to inhomogeneously distributed ferrimagnetic pyrrhotite. The paleomagnetic data reveals that the characteristic direction of NRM has shallow normal (in a few cases shallow reversed) polarity, which is in agreement with the Lower Jaramillo N-polarity chron direction, and is carried by ferrimagnetic pyrrhotite. However, our study has not revealed the expected high magnetization body required from previous magnetic modeling. Furthermore, the LB-07A and LB08-A drill cores did not show the predicted high content of melt in the rocks, requiring a new interpretation model for magnetic data.

  13. 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

  14. 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

  15. 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

  16. 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.

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

    PubMed Central

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

    2015-01-01

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

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

    PubMed Central

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

    2015-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Lefticariu, L.

    2005-05-01

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

  20. Determination of impact crater size-frequency distributions in GIS environments

    NASA Astrophysics Data System (ADS)

    Kneissl, Thomas; van Gasselt, Stephan; Neukum, Gerhard

    2010-05-01

    Analysis of crater size-frequency distributions (CSFD) of impact craters on planetary surfaces is a well-established method to derive absolute ages on the basis of remotelysensed image data. Although modelling approaches and the derivation of absolute ages from a given CSFD have been described in considerable depth since the late 1960s, there is no standardized methodology and guideline for measuring impact-crater diameters and area sizes that are both needed in order to determine absolute ages in a correct way. Distortions of distances (i.e., diameters) and areas within different map projections are considerable error sources within this measurement phase. In order to address that problem and to minimize such errors, a software extension for ESRI's ArcMap (ArcGIS) has been developed where CSFDs on planetary surfaces can be measured independently of image and data frame map projections and which can be theoretically transferred to every GI system capable of working with different map projections. Using this new approach each digitized impact crater is internally projected to a stereographic map projection with the crater's central-point set as the projection center. In this projection the circle is defined without any distortion of its shape (i.e., conformality). Using a sinusoidal map projection with a center longitude set to the crater's centralpoint, the diameter of the impact crater is measured along this central meridian which is true-scale and does not show any distortion. The crater is re-projected to the map projection of the current data frame and stored as vector geometry with attributes (shapefile). Output of this workflow comprises correct impact-crater diameters and area sizes in sinusoidal map projections and can be used for further processing, e.g., absolute age determinations. For GIS-based measurements we strongly recommend our procedure to be the standardised methodology to determine CSFD on planetary surfaces in order to minimize map distortion

  1. 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

  2. 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.

  3. 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

  4. Puchezh-Katunki Impact Crater: Preliminary Model of Hydrothermal Circulation System

    NASA Astrophysics Data System (ADS)

    Masaitis, V. L.; Naumov, M. V.

    1993-07-01

    Research (using the results of deep drilling) of hydrothermal alteration in the Puchezh-Katunki Crater [1,2] enables us to construct a preliminary model of a hot-water circulation system in this giant astrobleme. Unlike previous reconstructions [3] that consider a circulation system originated in connection with the mass of impact melt in an ideal astrobleme, we examine this process in the impact crater as a whole. Considerable hydrothermal alteration of rocks is restricted by central uplift of the Puchezh-Katunki Crater. The preimpact temperature of the uplift's crystalline rocks (those that occur at 5-6 km in depth before impact) could be more than 100 degrees C. The principal factors that caused the creation of the circulation system are (1) the thermal field of the massif of brecciated and heated rocks and (2) crater lake formation. Shock- and friction-enhanced heating coupled with the influence of injecting impact melt masses generated an ellipsoidal-shaped thermal anomaly for 5-6 km in depth and near 600 km in volume. The heated massif was characterized by temperature values after equilibration from 500 degrees-600 degrees C in the center to 100 degrees-200 degrees C at the edges. The porosity of rocks decreased at depth and outward from the center as well. Hydrothermal convection took place when water from a ring trough lake infiltrated the lens of hot and porous impact breccia and basement rocks, reaching the surface at the uplift's margins and in the bottom of the central pit. A meteoric origin of circulated water is corroborated by isotopic values of fracture-filling calcite (delta ^18O = 21-24 per mil SMOW; delta ^13C = -20-3 per mil PDB) and anhydrite (delta ^18O = 8-10 per mil SMOW). There is no reliable information about addition of any juvenile substance in the circulation system. These facts support the subsurface origin of hydrothermal circulation. The united regressive hydrothermal process may be subdivided into three successive stages (Fig. 1): 1

  5. 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.

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

    NASA Astrophysics Data System (ADS)

    Isac, Anca; Mandea, Mioara; Purucker, Michael

    2013-04-01

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

  7. 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°.

  8. Seismic Investigation and Numerical Modeling of the Lake Bosumtwi Impact Crater

    NASA Astrophysics Data System (ADS)

    Karp, T.; Artemieva, N. A.; Milkereit, B.

    2003-02-01

    The Lake Bosumtwi impact crater, Ghana, (age 1.07 Ma, diameter 10.5 km) is one of the youngest and best-preserved complex terrestrial impact structures. It was excavated from hard crystalline target rock and is the source of the Ivory Coast tektite strewn field. It is almost entirely filled by the Lake Bosumtwi.

  9. Venus: further evidence of impact cratering and tectonic activity from radar observations.

    PubMed

    Campbell, D B; Burns, B A; Boriakoff, V

    1979-06-29

    Earth-based radar images at a resolution of 10 kilometers show a diverse surface terrain on Venus, probably produced by both impact events and tectonic activity. Only a small number of craters of apparent impact origin are seen. Large-scale features show lineaments and parallel ridges suggesting tectonic origins.

  10. 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.

  11. 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

  12. 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

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

    NASA Astrophysics Data System (ADS)

    Bartali, R.; Fucugauchi, J. U.

    2011-12-01

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

  14. Young viscous flows in the Lowell crater of Orientale basin, Moon: Impact melts or volcanic eruptions?

    NASA Astrophysics Data System (ADS)

    Srivastava, N.; Kumar, D.; Gupta, R. P.

    2013-10-01

    Topographical, morphological and spectral reflectance studies have been carried out for a distinct resurface event inside Copernican aged Lowell crater (13.00°S 103.40°W), Orientale basin, using high resolution TC, MI-VIS, LROC-NAC, and M3 data from Kaguya, Lunar Reconnaissance Orbiter (LRO) and Chandrayaan-1 missions. The resurfacing is predominantly gabbroic/basaltic in composition and is confined to nearly a linear ~17 km long, a 3-6 km wide and a ~100 m deep channel, possibly a graben. It is characterised with distinct surface features such as small uplift with melt pond, several lava-like flows, cracks going up to decimetre size, 20-80 m pits/craters with small central uplifts or depressions and ~100 m craters that emanate liquid. A minimum of three generations of flows have been identified within the unit, the oldest one being less viscous and the subsequent younger ones showing well developed lobes due to the high viscosity. There is a conspicuous absence of unambiguously identified primary impact craters on these flows suggesting their fresh nature. On the basis of these integrated observations we hypothesise that at least the younger portions of this amazingly carved resurfaced unit might be composed of volcanic flows erupted from single or multiple sources subsequent to the emplacement of impact melts from a ~9 km diameter crater on the edge of Lowell crater. Gabbroic/basaltic signatures have also been identified at several other locations inside Lowell crater indicating that it would have impacted on a pre-existing basaltic surface or on a gabbroic pluton. These findings have implications to lunar magmatism and understanding of the genesis of young flows on the lunar surface.

  15. 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.

  16. Impact cratering of the terrestrial planets and the Moon during the giant planet instability

    NASA Astrophysics Data System (ADS)

    Roig, Fernando Virgilio; Nesvorny, David; Bottke, William

    2016-10-01

    The dynamical instability of the giant planets and the planetesimal driven migration both have major implications for the crater record of the terrestrial planets and the Moon. The crater record can thus provide contraints to the behavior of the planets in the early Solar System. Here we determine the impact fluxes and the crater production rates on the terrestrial planets and the Moon from impactors originating in the primordial asteroid main belt (2.1 to 3.2 au) and the E-belt (1.5 to 2.1 au - Bottke et al. 2012). We determine the impact flux over the age of the Solar System, with particular focus on the instability of the giant planets in the jumping Jupiter model. We start with a population of asteroids uniformly distributed in the orbital parameters space, and numerically evolve them as test particles under the gravitational perturbations of the giant and terrestrial planets. We test the effects on this population due to different jumping Jupiter evolutions (the idealized jump as in Bottke et al. 2012 or models taken from Nesvorny & Morbidelli 2012). The number of impacts is determined by applying Opik's theory. We compute the impact rates on different targets (Mercury, Venus, Earth, Moon, and Mars) and from different source regions in the asteroid belt (E-belt, inner belt, outer belt). By properly calibrating the impact rates, and using crater scaling laws, we estimate the number and size distribution of craters. We show how the impact flux and crater production rates depend on the different parameters of the model such as the initial orbital distribution of the asteroids, time of the instability, different evolution of the planets, initial size distribution of the impactors, etc.

  17. 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.

  18. ChemCam investigation of the John Klein and Cumberland drill holes and tailings, Gale crater, Mars

    NASA Astrophysics Data System (ADS)

    Jackson, R. S.; Wiens, R. C.; Vaniman, D. T.; Beegle, L.; Gasnault, O.; Newsom, H. E.; Maurice, S.; Meslin, P.-Y.; Clegg, S.; Cousin, A.; Schröder, S.; Williams, J. M.

    2016-10-01

    The ChemCam instrument on the Mars Science Laboratory rover analyzed the rock surface, drill hole walls, tailings, and unprocessed and sieved dump piles to investigate chemical variations with depth in the first two martian drill holes and possible fractionation or segregation effects of the drilling and sample processing. The drill sites are both in Sheepbed Mudstone, the lowest exposed member of the Yellowknife Bay formation. Yellowknife Bay is composed of detrital basaltic materials in addition to clay minerals and an amorphous component. The drill tailings are a mixture of basaltic sediments and diagenetic material like calcium sulfate veins, while the shots on the drill site surface and walls of the drill holes are closer to those pure end members. The sediment dumped from the sample acquisition, processing, and handling subsystem is of similar composition to the tailings; however, due to the specifics of the drilling process the tailings and dump piles come from different depths within the hole. This allows the ChemCam instrument to analyze samples representing the bulk composition from different depths. On the pre-drill surfaces, the Cumberland site has a greater amount of CaO and evidence for calcium sulfate veins, than the John Klein site. However, John Klein has a greater amount of calcium sulfate veins below the surface, as seen in mapping, drill hole wall analysis, and observations in the drill tailings and dump pile. In addition, the Cumberland site does not have any evidence of variations in bulk composition with depth down the drill hole, while the John Klein site has evidence for a greater amount of CaO (calcium sulfates) in the top portion of the hole compared to the middle section of the hole, where the drill sample was collected.

  19. Numerical modeling of an impact-induced hydrothermal system at the Sudbury crater

    NASA Astrophysics Data System (ADS)

    Abramov, Oleg; Kring, David A.

    2004-10-01

    Large impact events, like the one that formed the Sudbury crater in Ontario, Canada, at 1.85 Ga, significantly increase the temperature of target rocks. The heat sources generated by such an impact event can drive the circulation of groundwater, establishing a hydrothermal system. We report on the results of numerical modeling of postimpact cooling with and without the presence of water at the Sudbury crater. A hydrothermal system is initiated in the annular trough between the peak ring and final crater rim, perhaps venting through faults that bound blocks of the crust in the modification zone of the crater. Although circulation through the overlying breccias may occur in the center of the crater, the central melt sheet is initially impermeable to circulating fluids. By ~105 years the central melt sheet crystallizes and partially cools, allowing fluids to flow through it. Host rock permeability is the main factor affecting fluid circulation and lifetimes of hydrothermal systems. High permeabilities lead to a rapid system cooling, while lower permeabilities allow a steady transport of hot fluids to the surface, resulting in high surface temperatures for longer periods of time than cooling by conduction alone. The simulations presented in this paper show that a hydrothermal system at a Sudbury-sized impact crater can remain active for several hundred thousand to several million years, depending on assumed permeability. These results suggest that a hydrothermal system induced by an impact event can remain active for sufficiently long periods of time to be biologically significant, supporting the idea that impact events may have played an important biological role, especially early in Earth's history.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2004-05-01

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

  6. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2008-02-01

    Crater structures induced by impact of keV-energy Arn+ 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 structures when the oxide coated silicon substrate is free of defects. However, in simulations of 5keV /atom Ar12 cluster impacts, transient displacements of the amorphous silicon or silicon oxide substrate surfaces are induced in an approximately 50nm wide area surrounding the impact point. In silicon oxide, the transient displacements induce small topographical changes on the surface in the vicinity of the central hillock. The comparison of cluster stopping mechanisms in the various silicon oxide and silicon structures shows that the largest lateral momentum is induced in the silicon oxide layer during the impact; thus, the transient displacements on the surface are stronger than in the other substrates. This can be a reason for the higher frequency of occurrence of the complex craters on oxide coated silicon.

  8. Characterization of impact craters in 3D meshes using a feature lines approach

    NASA Astrophysics Data System (ADS)

    Jorda, L.; Mari, J.; Viseur, S.; Bouley, S.

    2013-12-01

    Impact craters are observed at the surface of most solar system bodies: terrestrial planets, satellites and asteroids.The measurement of their size-frequency distribution (SFD) is the only method available to estimate the age of the observed geological units, assuming a rate and velocity distributions of impactors and a crater scaling law. The age of the geological units is fundamental to establish a chronology of events explaining the global evolution of the surface. In addition, the detailed characterization of the crater properties (depth-to-diameter ratio and radial profile) yields a better understanding of the geological processes which altered the observed surfaces. Crater detection is usually performed manually directly from the acquired images. However, this method can become prohibitive when dealing with small craters extracted from very large data sets. A large number of solar system objects is being mapped at a very high spatial resolution by space probes since a few decades, emphasizing the need for new automatic methods of crater detection. Powerful computers are now available to produce and analyze huge 3D models of the surface in the form of 3D meshes containing tens to hundreds of billions of facets. This motivates the development of a new family of automatic crater detection algorithms (CDAs). The automatic CDAs developed so far were mainly based on morphological analyses and pattern recognition techniques on 2D images. Since a few years, new CDAs based on 3D models are being developed. Our objective is to develop and test against existing methods an automatic CDA using a new approach based on the discrete differential properties of 3D meshes. The method produces the feature lines (the crest and the ravine lines) lying on the surface. It is based on a double step algorithm: first, the regions of interest are flagged according to curvature properties, and then an original skeletonization approach is applied to extract the feature lines. This new

  9. 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.

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

    NASA Technical Reports Server (NTRS)

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

    2012-01-01

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

  11. 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

  12. Three dimensional gravity field modelling of the Chicxulub impact crater

    NASA Astrophysics Data System (ADS)

    Hildebrand, A.; Millar, J.; Pilkington, M.; Lawton, D.

    2003-04-01

    Three dimensional gravity field modeling of the Chicxulub crater’s gravity field has refined our working structural model [e.g. 1, 2], and differs somewhat from the results of [3]. The 3D gravity model establishes that the central uplift is within reach of scientific drilling. The 3D gravity modeling method employed is that of [4]. Modelling results particularly reveal the crater’s central structures. The central uplift is a twin peaked structural high with vergence towards the southwest as previously indicated by 2D models [1] and consistent with seismic refraction results [5]. An arm extends towards the northeast, in contrast to the steep gradients that bound the central uplift to the southwest. The width of the uplift at 4 km depth is ~45 km broadening to ~60 km at 5 km depth consistent with 2D modeling. The central uplift rises into the melt sheet to ~2 km depth in contrast to the results of [4] where a top of ~4 km was obtained. However, as refraction results [5] independently constrain the central uplift width and the central uplift density contrast is limited (+0.11gcm-3 here), this is probably a realistic result. The shape of the modeled central uplift is radically different from that advocated by [6] who, based on seismic refraction results, proposed a cup-shaped central uplift (concave top) with a top at ~3 km depth, but of similar width. This interpretation requires substantial departure from density velocity proportionality, and we doubt that the central uplift has an annular top. The filling of the CDC, which we interpret as melt, is revealed as a body slightly elongated in a NE-SW sense with a size consistent with previous 2D model results. With the density contrast measured from the top of the melt sheet, its base lies near ~4 km is obtained consistent with the result of [4]. This depth is dependent upon the density contrast used (-0.15 g/cc), however, and all the mass deficiency need not be melt. The derived melt volume is 1.5 X 104 km3

  13. Integrated method for crater detection from topography and optical images and the new PH9224GT catalogue of Phobos impact craters

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    In a large majority of lunar and planetary surface images, impact craters are the most abundant geological features. Therefore, it is not surprising that crater detection algorithms (CDAs) are one of the most studied subjects of image processing and analysis in lunar and planetary science. In this work we are proposing an Integrated CDA, consisting of: (1) utilization of DEM (digital elevation map)-based CDA; (2) utilization of an optical-based CDA; (3) re-projection of used datasets and crater coordinates from normal to rotated view and back; (4) correction of the brightness and contrast of a used optical image; and (5) tile generation for the optical-based CDA and an assembling of results with an elimination of multiple detections, in combination with a pyramid approach down to the resolution of the available DEM image; and (6) a final integration of the results of DEM-based and optical-based CDAs, including a removal of duplicates. The proposed CDA is applied to one specific asteroid-like body, the small Martian moon Phobos. The experimental evaluation of the proposed CDA is done by a manual verification of crater-candidates and a search for uncatalogued craters. The evaluation has shown that the proposed CDA was used successfully for cataloging Phobos craters. The major result of this paper is the PH9224GT - currently the most complete global catalogue of the 9224 Phobos craters. The possible applications of the new catalogue are: (1) age estimations for any selected location; and (2) comparison/evaluation of the different chronology and production functions for Phobos. This confirms the practical applicability of the new Integrated CDA - an additional result of this paper, which can be used in order to considerably extend the current crater catalogues.

  14. A Simple Method Enabling Students to Model Impact Cratering from 0° to 90°.

    NASA Astrophysics Data System (ADS)

    Burgener, J. A.

    2016-08-01

    A simple, inexpensive method to produce craters with impact angles ranging from 0° to 90° is presented. It utilizes low speed pellet guns and soft clay. Varying the hardness of the clay and speed of the pellets allows a wide range of experiments.

  15. Experimental Study on Impact Craters Formed on Basalt Target Covered with Weak Mortar Layer

    NASA Astrophysics Data System (ADS)

    Arakawa, M.; Dohi, K.; Okamoto, C.; Hasegawa, S.

    2011-03-01

    High-velocity impact experiments on layered targets were conducted to investigate the formation mechanism of tiny complex crates with the size less than 1 km found on the Moon. Then the crater morphology was found to change with the upper layer thickness.

  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. Screening Earth — A Student (Re)search Project to Improve the Terrestrial Impact Crater Record

    NASA Astrophysics Data System (ADS)

    Kenkmann, T.; Foster, C.; Biermanns, P.

    2013-09-01

    A master-level module at the University of Freiburg is devoted to improve the impact crater record on Earth. The awarded project consists of a systematic survey based on remote sensing data and includes field work at the most promising structures.

  18. 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.

  19. Search for a meteoritic component in drill cores from the Bosumtwi impact structure, Ghana: Platinum group element contents and osmium isotopic characteristics

    NASA Astrophysics Data System (ADS)

    McDonald, Iain; Peucker-Ehrenbrink, Bernhard; Coney, Louise; Ferrière, Ludovic; Reimold, Wolf Uwe; Koeberl, Christian

    An attempt was made to detect a meteoritic component in both crater-fill (fallback) impact breccias and fallout suevites (outside the crater rim) at the Bosumtwi impact structure in Ghana. Thus far, the only clear indication for an extraterrestrial component related to this structure has been the discovery of a meteoritic signature in Ivory Coast tektites, which formed during the Bosumtwi impact event. Earlier work at Bosumtwi indicated unusually high levels of elements that are commonly used for the identification of meteoritic contamination (i.e., siderophile elements, including the platinum group elements [PGE]) in both target rocks and impact breccias from surface exposures around the crater structure, which does not allow unambiguous verification of an extraterrestrial signature. The present work, involving PGE abundance determinations and Os isotope measurements on drill core samples from inside and outside the crater rim, arrives at the same conclusion. Despite the potential of the Os isotope system to detect even small amounts of extraterrestrial contribution, the wide range in PGE concentrations and Os isotope composition observed in the target rocks makes the interpretation of unradiogenic, high-concentration samples as an impact signature ambiguous.

  20. Viscous relaxation of impact crater relief on Venus - Constraints on crustal thickness and thermal gradient

    NASA Technical Reports Server (NTRS)

    Grimm, Robert E.; Solomon, Sean C.

    1988-01-01

    Models for the viscous relaxation of impact crater topography are used to constrain the crustal thickness (H) and the mean lithospheric thermal gradient beneath the craters on Venus. A general formulation for gravity-driven flow in a linearly viscous fluid has been obtained which incorporates the densities and temperature-dependent effective viscosities of distinct crust and mantle layers. An upper limit to the crustal volume of Venus of 10 to the 10th cu km is obtained which implies either that the average rate of crustal generation has been much smaller on Venus than on earth or that some form of crustal recycling has occurred on Venus.

  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. Early Fracturing and Impact Residue Emplacement: Can Modeling Help to Predict Their Location in Major Craters?

    NASA Astrophysics Data System (ADS)

    Kearsley, A. T.; Graham, G. A.; McDonnell, J. A. M.; Bland, P. A.; Hough, R. M.; Helps, P. A.

    2003-01-01

    The nature of the extraterrestrial bodies that created some terrestrial impact craters has been determined by collection of disrupted and shocked impactor fragments (e.g. the well-known iron meteorite Canyon Diablo from the vicinity of Barringer Crater, Arizona). In other cases, finding sufficient chemical residue from the bolide for diagnostic analysis has proven more difficult, yet modern trace-element and particularly isotopic analyses have been successfully employed, e.g. The big question is often: "In a limited field investigation, where should we look?"

  3. The mechanics of ringed basin formation. [lunar impact craters

    NASA Technical Reports Server (NTRS)

    Melosh, H. J.; Mckinnon, W. B.

    1978-01-01

    The study investigates the mechanics of ring formation in lunar basins by collapse or slumping. Two classes of models are presented in order to broaden the range of plausible mechanisms involved. Extrusion flow models which assume a weak layer underlying a strong layer as well as plastic flow models which assume a continuous decrease of cohesion strength with depth are considered. In both classes, strength or resistance to deformation decreases with depth. If this decrease is rapid enough, in either set of models, at least one concentric fault scarp forms. The ratio between the scarp radius and the crater radius varies between 1.2 and about 2.7 depending on the model, and is thus in the range of observed radius ratios.

  4. 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

  5. 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

  6. 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

  7. 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.

  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. 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

  10. The effect of a thin weak layer covering a basalt block on the impact cratering process

    NASA Astrophysics Data System (ADS)

    Dohi, Koji; Arakawa, Masahiko; Okamoto, Chisato; Hasegawa, Sunao; Yasui, Minami

    2012-04-01

    To clarify the effect of a surface regolith layer on the formation of craters in bedrock, we conducted impact-cratering experiments on two-layered targets composed of a basalt block covered with a mortar layer. A nylon projectile was impacted on the targets at velocities of 2 and 4 km s-1, and we investigated the crater size formed on the basalt. The crater size decreased with increased mortar thickness and decreased projectile mass and impact velocity. The normalized crater volume, πV, of all the data was successfully scaled by the following exponential equation with a reduction length λ0: π=b0πY-b1exp(-λ/λ0), where λ is the normalized thickness T/Lp, T and Lp are the mortar thickness and the projectile length, respectively, b0 and b1 are fitted parameters obtained for a homogeneous basalt target, 10-2.7±0.7 and -1.4 ± 0.3, respectively, and λ0 is obtained to be 0.38 ± 0.03. This empirical equation showing the effect of the mortar layer was physically explained by an improved non-dimensional scaling parameter, πY∗, defined by πY∗=Y/(ρup2), where up was the particle velocity of the mortar layer at the boundary between the mortar and the basalt. We performed the impact experiments to obtain the attenuation rate of the particle velocity in the mortar layer and derived the empirical equation of {u}/{v}=0.50exp-{λ}/{1.03}, where vi is the impact velocity of the projectile. We propose a simple model for the crater formation on the basalt block that the surface mortar layer with the impact velocity of up collides on the surface of the basalt block, and we confirmed that this model could reproduce our empirical equation showing the effect of the surface layer on the crater volume of basalt.

  11. 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.

  12. 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

  13. 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.

  14. 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.

  15. 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

  16. The geology of Darwin Crater, western Tasmania, Australia

    NASA Astrophysics Data System (ADS)

    Howard, Kieren T.; Haines, Peter W.

    2007-08-01

    Darwin glass is a siliceous impact glass found in a 400 km 2 strewn field near Mt Darwin, western Tasmania, Australia. It has been dated by Ar-Ar methods at 816 ± 7 ka. A 1.2 km diameter circular depression, named Darwin Crater (42°18.39'S, 145°39.41'E), is the assumed source crater for the glass. Darwin Crater is situated in a remote rain forested valley developed within Siluro-Devonian quartzite and slate (Eldon Group). Earlier geophysical investigations demonstrated that the structure is an almost circular bowl-shaped sediment-filled basin. This paper provides the first detailed description of the geology of Darwin Crater. The centre of the crater has been penetrated by two drill cores, the deeper to a maximum depth of ˜ 230 m. The drill cores intersected fine-grained lacustrine sediments (˜ 60 m thick) overlying poorly sorted coarser crater-fill deposits. The pre-lacustrine crater-fill stratigraphy comprises an uppermost polymict breccia (˜ 40 m thick) of angular quartz and country rock, which contains very rare (≪ 1%) fresh glass fragments (Crater-fill Facies A). Beneath the polymict breccia facies, the drill core intersected monomict sandy breccias of angular quartz (Crater-fill Facies B), and a complicated package of deformed slate clasts (Crater-fill Facies C). Quartz grains in the crater-fill samples contain abundant irregular fractures. In some of the most deformed quartz grains, sub-planar fractures define zones of alternating extinction that superficially resemble twinning. Kinked micas are also present. While the deformation observed in clasts of the crater-fill facies is far greater than in rocks cropping out around the crater, no diagnostic shock indicators, such as planar deformation features (PDF's) in quartz, were observed. If the crater is of impact origin, as seems likely due to the close association with Darwin glass, this is another example of a simple crater where diagnostic shock indicators appear to be absent, preventing

  17. Lake evolution during the Early Danian Dan-C2 hyperthermal, Boltysh impact crater, Ukraine

    NASA Astrophysics Data System (ADS)

    Ebinghaus, Alena; Jolley, David W.

    2016-04-01

    Lacustrine facies record complex relationships between lake evolution and environmental conditions and provide proxies for climate changes. However, lacustrine successions formed during past hyperthermals as recorded from negative carbon isotope excursions (CIEs) are of limited availability and thus less well understood. Here, we present a complete lacustrine record of the Early Danian Dan-C2 hyperthermal at c. 65.2 Ma from a core drilled in the K-Pg Boltysh impact crater, Ukraine. This borehole allows a detailed facies analysis and reconstruction of lake evolution and associated plant ecosystem in correspondence with rapid climate change. The Boltysh borehole reveals a c. 400 m thick siliciclastic and organic-rich succession overlying impact melt-breccia dated at 65.17 ± 0.64 Ma. Based on detailed core logging, 8 distinctive facies associations are identified, including 1) littoral mudstones, 2) siliciclastic shoreline deposits, 3) siliciclastic littoral to sublittoral deposits, 4) mudstone laminites, 5) organic-rich mudstones, and deposits of 6) coarse-grained, 7) fine-grained density currents, and 8) debris flows. Based on the occurrence of these facies associations 3 major phases of lake evolution are distinguished: 1) an initial pre-CIE rising clastic-dominated lake phase characterised by the presence of coarse-grained density and debris flow deposits, 2) an organic-rich fluctuating shallow lake phase during the main phase of the CIE, characterised by alternating packages of the mudstone laminites and organic-rich mudstones; and 3) a rising clastic-dominated lake during and post-CIE recovery phase, which shows a high presence of siliciclastic shoreline and littoral to sublittoral deposits. This study provides a full record of lacustrine response to climate change during the Dan-C2 hyperthermal, and subsequently allows us to infer lake formation and environmental conditions at different stages during climate warming. The high resolution sedimentary record

  18. 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

  19. 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

  20. 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

  1. Evidence for coeval Late Triassic terrestrial impacts from the Rochechouart (France) meteorite crater

    NASA Astrophysics Data System (ADS)

    Gilder, S. A.; Carporzen, L.

    2006-12-01

    High temperature impact melt breccias from the Rochechouart (France) meteorite crater record a magnetization component with antipodal, normal and reverse polarities. The corresponding paleomagnetic pole for this component lies between the 220 Ma and 210 Ma reference poles on the Eurasian apparent polar wander path, consistent with the 214 ± 8 Ma ^{40} Ar/ ^{39} Ar age of the crater [Kelley and Spray, 1997]. Late Triassic tectonic reconstructions of the Eurasian and North American plates place this pole within 95 % confidence limits of the paleomagnetic pole from the Manicouagan (Canada) meteorite impact crater, which is dated at 214 ± 1 Ma [Hodych and Dunning, 1992]. Together, these observations reinforce the hypothesis of Spray et al. [1998] for a Late Triassic, multiple meteorite impact event on Earth. References: Hodych, J. P., and G. R. Dunning (1992), Did the Manicouagan impact trigger end-of-Triassic mass extinction?, Geology, 20, 51-54. Kelley, S. P., and J. G. Spray (1997), A late Triassic age for the Rochechouart impact structure, France, Meteor., 32, 629-636. Spray, J. G., S. P. Kelley, and D. B. Rowley (1998), Evidence for a late Triassic multiple impact event on Earth, Nature, 392, 171-173.

  2. Cratering on Titan: impact melt, ejecta, and the fate of surface organics

    NASA Astrophysics Data System (ADS)

    Artemieva, Natalia; Lunine, Jonathan

    2003-08-01

    We conduct three-dimensional hydrodynamical simulations of hypervelocity impacts into the crust of Titan to determine the fraction of liquid water generated, under the reasonable assumption that the crust is largely water ice, and to track the fate of the organic-rich layer that is thought to overlie the ice over much of the surface. Impactors larger than a kilometer in diameter are only slightly affected by the atmosphere, while those well under that size are strongly decelerated and broken up before reaching the surface. Impact of a 2 km diameter icy projectile into the crust at velocities of 7 km per second or higher, and angles of impact between 30° and 45°, generate about 2-5% melt by volume within the crater. Our results for the amount of aqueous melt generated in impacts on Titan are broadly consistent with the analytic model developed by Thompson and Sagan (1992) although our numerical model allows us to more precisely quantify the fraction of melt, and fate of the organics, as a function of the impact parameters. While much of the organic surface layer is heavily shocked and ejected from the immediate region of the crater, a significant fraction located behind the oblique impact trajectory is only lightly shocked and is deposited in the liquid water at the crater base. Simple calculations suggest that the resulting aqueous organic phase may remain liquid for hundreds of years or longer, enough time for the synthesis of simple precursor molecules to the origin of life.

  3. Insights into the stratigraphy of Mars' northern plains from impact crater mineralogy

    NASA Astrophysics Data System (ADS)

    Pan, Lu; Ehlmann, Bethany; Carter, John; Ernst, Carolyn; CRISM Team

    2016-10-01

    The northern lowland of Mars has an ancient basement, buried underneath widespread Hesperian lavas and outflow channel sediments, and may have recorded geologic and aqueous activity related to global climate, e.g., the existence of a northern ocean. To better understand the geologic record of this depositional basin, we conducted a comprehensive survey of the mineralogy of northern plains impact craters, using 1905 images covering 689 impact craters, acquired by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onboard the Mars Reconnaissance Orbiter (MRO). Mafic minerals are detected in 33% of all the craters, and hydrated minerals in 10% of the craters. Thus, though the northern plains surface is relatively spectrally homogeneous, the subsurface is spectrally diverse and includes a set of mafic (olivine and pyroxene) and hydrated minerals (Fe/Mg phyllosilicate, chlorite/prehnite, hydrated silica etc.) similar to the southern highlands. The distribution of hydrated minerals, especially Fe/Mg phyllosilicates, is more concentrated in large craters, while mafic minerals are relatively insensitive to crater size. This is consistent with a deeper origin for hydrated minerals compared to mafic minerals, or alternatively the post-impact formation of hydrated minerals due to impact-induced hydrothermal alteration only in the largest craters. Under the assumption of excavation from depth, we calculate the possible origin of these hydrated minerals to be -5000 ~ -6000 m relative to the global Mars Orbital Laser Altimeter (MOLA) datum, possibly representing the ancient basement buried by 1-2 km layer with mafic minerals. In contrast, the mafic materials are derived from only ~200 m deep. We also delineate several distinct topographic and geographic provinces. The large number of mafic mineral detections in Chryse Planitia probably indicates the influence of a local volcanic source; and Arcadia and Amazonis Planitiae probably have been resurfaced more recently

  4. 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.

  5. 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.

  6. Gamma (γ)-Ray Activity as a Tool for Identification of Hidden Ejecta Deposits Around Impact Crater on Basaltic Target: Example from Lonar Crater, India

    NASA Astrophysics Data System (ADS)

    Bose, T.; Misra, S.; Chakraborty, S.; Reddy, K.

    2013-11-01

    Geophysical techniques based on radioactivity measurements are not generally used for exploration of asteroid impact craters. Our studies on the field and laboratory measurements of radioactivity on samples from the Lonar crater, India, show that this technique could be an important method for mapping the distribution of ejecta around the deeply excavated impact craters particularly when these structures are formed on relatively old target rocks/palaeosol. The Lonar ejecta shows ~1.3 times higher γ-ray count rates in the field on average compared to the underlying palaeosol and ~1.9 times higher values over the target basalt while measured by a portable Geiger-Müller pulse counter. The absorbed γ-dose rate (D) of the Lonar samples, computed from 232Th, 238U, and 40K abundances in these samples, also show that the ejecta has distinct bulk dose rates (average ~8.42 nGy h-1) as compared to those of the palaeosol (~18.34 nGy h-1), target basalt (~11.97 nGy h-1), and the impact-melts and spherules (~14 nGy h-1). Therefore, radioactivity mapping of the terrestrial and planetary impact craters by direct methods has importance in mapping ejecta distributions around these structures.

  7. Drill core LB-08A, Bosumtwi impact structure, Ghana: Geochemistry of fallback breccia and basement samples from the central uplift

    NASA Astrophysics Data System (ADS)

    Ferrière, Ludovic; Koeberl, Christian; Reimold, Wolf Uwe; Mader, Dieter

    The 1.07 Myr old Bosumtwi impact structure in Ghana (West Africa), which measures 10.5 km in diameter and is largely filled by Lake Bosumtwi, is associated with one of four currently known tektite strewn fields. Two boreholes were drilled to acquire hard-rock samples of the deep crater moat and from the flank of the central uplift (LB-07A and LB-08A, respectively) during a recent ICDP-sponsored drilling project. Here we present results of major and trace element analysis of 112 samples from drill core LB-08A. This core, which was recovered between 235.6 and 451.33 m depth below lake level, contains polymict lithic breccia intercalated with suevite, which overlies fractured/brecciated metasediment. The basement is dominated by meta-graywacke (from fine-grained to gritty), but also includes some phyllite and slate, as well as suevite dikelets and a few units of a distinct light greenish gray, medium-grained meta-graywacke. Most of the variations of the major and trace element abundances in the different lithologies result from the initial compositional variations of the various target rock types, as well as from aqueous alteration processes, which have undeniably affected the different rocks. Suevite from core LB-08A (fallback suevite) and fallout suevite samples (from outside the northern crater rim) display some differences in major (mainly in MgO, CaO, and Na2O contents) and minor (mainly Cr and Ni) element abundances that could be related to the higher degree of alteration of fallback suevites, but also result from differences in the clast populations of the two suevite populations. For example, granite clasts are present in fallout suevite but not in fallback breccia, and calcite clasts are present in fallback breccia and not in fallout suevite. Chondrite-normalized rare earth element abundance patterns for polymict impact breccia and basement samples are very similar to each other. Siderophile element contents in the impact breccias are not significantly

  8. 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

  9. 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

    We will present a new, detailed geological map of the lunar crater Tycho, as well as a map of all melt pools within our study area. Tycho crater is ~ 83 km in diameter and is located in the southern highlands on the nearside of the Moon. The distribution of melt pools and the new topographical analysis show evidence for an oblique impact from the southwest [1,2]. Our melt pool map also indicates that pre-existing topography affected the spatial distribution of melt pools [3].Crater size-frequency distribution (CSFD) model ages show discrepancies between absolute model ages of the ejecta blanket and the melt pools [4,5]. The apparent absolute model ages measured for melt pools at Tycho crater are younger than the ages of the ejecta blanket. The geological map shows that Tycho is a typical complex crater with a central peak, terraced crater walls and a continuous ejecta blanket [6]. The emplacement of melt pools has two major controlling factors: (1) the direction of the impact and (2) the pre-existing topography. Impact melt pools at Tycho are mostly located outside of the crater rim and are more or less evenly distributed around the crater, with the exception of the zone of avoidance related to the impactor path from the SW [1,2]. With increasing distance from the crater center, the melt pools tend to get smaller in size and less frequent. Melt pools with larger overall surface areas are clustered in the ENE and ESE of Tycho crater, likely influenced by preexisting topography. Oblique impacts often show, the most extensive melt deposits in the inferred downrange direction. Therefore, the distribution of the impact melt pools around Tycho is consistent with an oblique impact from the southwest. Absolute model ages derived from CSFD measurements of different melt pools give ages between 14.1 ± 1.4 Ma (Ncum(D ≥ 1 km) = 1.18 x 10-5) and 56.9 ± 5.1 Ma (Ncum(D ≥ 1 km) = 4.77 x 10-5), whereas our model age for the ejecta blanket is 73.5 ± 0.89 Ma (Ncum(D ≥ 1 km

  10. A model for the formation of the extended paraboloidal halos around some impact craters on Venus

    NASA Technical Reports Server (NTRS)

    Newman, W. I.; Jones, E. M.; Campbell, D. B.; Stacy, N. J. S.

    1992-01-01

    Many parabolic-shaped extended impact crater-related features have been found in Magellan synthetic aperture radar and emissivity data covering much of the surface of Venus. They are oriented east-west with the apex to the east and the impact crater located just west of the apex. A model for the formation of the parabolic features is developed based on the injection of small particles into the upper atmosphere at the time of impact, and their subsequent transport to the west by the east-west zonal winds. Fallout times from 50 km in the Venus atmosphere for particles of this size are about two hours, allowing westerly drifts of several hundred kilometers for zonal winds of 50 to 100 m s(exp -1).

  11. 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.

  12. The effect of target rheology on impact cratering : case for a wet sand

    NASA Astrophysics Data System (ADS)

    Takita, H.; Sumita, I.

    2011-12-01

    Rheology of the target material is one of the important factors which controls the crater morphology. There have been several experiments using dry granular materials, one of which showed the importance of particle size which in turn affects the rheology (Walsh et al., PRL, 2003). Wet granular material which is partially saturated with liquid, has a yield stress and therefore its rheology differs from a dry granular material. Here we report the results of impact cratering experiments using a wet sand target with volumetric liquid saturation (S) as the changeable parameter. Experiments were performed by releasing a steel ball from a holder so that it fell vertically into a cylindrical container filled with beach sand (grain size 0.2mm). We use a high-speed camera to record the crater formation process and laser displacement meter to measure crater profiles, diameter and depth. We change water saturation (S=0 - 80%), projectile size (diameter 10 - 22.2 mm) and release height (h = 200-1700mm) and study how the crater size and morphology change with these parameters. For S=0-3%, a cone-shaped crater forms. For S=4.1-5.5% it changes to a cylindrical crater with an outer ring, which forms as the ejecta settles. For S > 5.8% the outer ring disappears because of less ejecta volume. For S > 57%, it becomes accompanied by a depression surrounding the crater. When cylindrical craters form, ejection occurs only from the surface and the ejecta volume decreases with S. However its volume increases again for S > 72% when the target becomes a slurry. Similarly, the crater diameter and depth becomes smaller with S, and then it increases again from about S = 60%. We studied how the depth and the diameter scales with the impactor energy. For dry sand, we confirmed that the power-law exponent becomes close to 1/4, consistent with previous works. However for wet sand (S = 5-20%), we find that it cannot be scaled with energy. We find that the crater diameter is approximately equal to

  13. Petrographic observations on the Exmore breccia, ICDP-USGS drilling at Eyreville, Chesapeake Bay impact structure, USA

    USGS Publications Warehouse

    Reimold, W.U.; Bartosova, K.; Schmitt, R.T.; Hansen, B.; Crasselt, C.; Koeberl, C.; Wittmann, A.; Powars, D.S.

    2009-01-01

    The International Continental Scientific Drilling Program (ICDP)-U.S. Geological Survey (USGS) Eyreville A and B drill cores sampled crater fill in the region of the crater moat, ??9 km to the NE of the center of the Chesapeake Bay impact structure, Virginia, USA. They provide a 953 m section (444-1397 m depth) of sedimentary clast breccia and intercalated sedimentary and crystalline megablocks knownas Exmore beds, deposited on top of the impactite sequence between 1397 and 1551 m depth. We petrographically investigated the sandy-clayey groundmass-dominated breccia, which resembles a diamictite ("Exmore breccia"), and which, in its lower parts, carries sedimentary and crystalline blocks. The entire breccia interval is characterizedby the presence of glauconite and bioclastic carbonate, which distinguishes the Exmore breccia from other sandy facies above and below in the stratigraphy. The sediment-clast breccia exhibits strong heterogeneity from sample to sample with respect to groundmass nature, e.g., clay versus sand content, as well as clast content, in general, and shocked clast content, in particular. There is a consistently signifi cantly larger macroscopic sedimentary to crystalline clast content. On the microscopic scale, the intersample sediment to crystalline clast ratios are quite variable. A very small component of shocked material, in the form of shock-deformed quartz, and to an even lesser degree feldspar, and somewhat more abundant but still relatively scarce shardshaped,altered melt particles, is present throughout the section. However, between ??458 and 469 m, and between 514 and 527 m depths, the abundance of such melt particlesis notably enhanced. These sections are also chemically distinct and relatively more mafic than the other parts of the Exmore breccia. It appears that from the time of deposition of the 527 m material, calming of the ocean occurred over the crater area as a result of abatement of resurge activity, so that ejecta from the

  14. 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 structures when the oxide coated silicon substrate is free of defects. However, in simulations of 5 keV/atom Ar{sub 12} cluster impacts, transient displacements of the amorphous silicon or silicon oxide substrate surfaces are induced in an approximately 50 nm wide area surrounding the impact point. In silicon oxide, the transient displacements induce small topographical changes on the surface in the vicinity of the central hillock. The comparison of cluster stopping mechanisms in the various silicon oxide and silicon structures shows that the largest lateral momentum is induced in the silicon oxide layer during the impact; thus, the transient displacements on the surface are stronger than in the other substrates. This can be a reason for the higher frequency of occurrence of the complex craters on oxide coated silicon.

  15. Results of the Workshop on Impact Cratering: Bridging the Gap Between Modeling and Observations

    NASA Technical Reports Server (NTRS)

    Herrick, Robert (Editor); Pierazzo, Elisabetta (Editor)

    2003-01-01

    On February 7-9,2003, approximately 60 scientists gathered at the Lunar and Planetary Institute in Houston, Texas, for a workshop devoted to improving knowledge of the impact cratering process. We (co-conveners Elisabetta Pierazzo and Robert Herrick) both focus research efforts on studying the impact cratering process, but the former specializes in numerical modeling while the latter draws inferences from observations of planetary craters. Significant work has been done in several key areas of impact studies over the past several years, but in many respects there seem to be a disconnect between the groups employing different approaches, in particular modeling versus observations. The goal in convening this workshop was to bring together these disparate groups to have an open dialogue for the purposes of answering outstanding questions about the impact process and setting future research directions. We were successful in getting participation from most of the major research groups studying the impact process. Participants gathered from five continents with research specialties ranging from numerical modeling to field geology, and from small-scale experimentation and geochemical sample analysis to seismology and remote sensing.With the assistance of the scientific advisory committee (Bevan French, Kevin Housen, Bill McKinnon, Jay Melosh, and Mike Zolensky), the workshop was divided into a series of sessions devoted to different aspects of the cratering process. Each session was opened by two invited t a b , one given by a specialist in numerical or experimental modeling approaches, and the other by a specialist in geological, geophysical, or geochemical observations. Shorter invited and contributed talks filled out the sessions, which were then concluded with an open discussion time. All modelers were requested to address the question of what observations would better constrain their models, and all observationists were requested to discuss how their observations can

  16. Fossil Meteorite Unearthed From Crater

    NASA Astrophysics Data System (ADS)

    Martel, L. M. V.

    2006-06-01

    A team of scientists lead by Wolf Maier (University of Quebec, Canada and University of Pretoria, South Africa and soon at University of Western Australia, Perth) and Marco Andreoli (University of the Witwatersrand and South African Nuclear Energy Corp.) and colleagues who also hail from Canada, South Africa, the United Kingdom, and the United States, have announced the discovery of a 25-centimeter-wide chondritic meteorite unearthed from the 145-million-year-old Morokweng impact crater in South Africa. Found within the crater's impact melt sheet about 770 meters (half a mile) down a drilling borehole, the hefty meteorite's existence would seem improbable given its low chance of surviving the high shock pressures and temperatures normally associated with large impact events. Its unusual composition could mean it is a sample from a previously unknown part of the LL chondrite parent body or maybe it is from an entirely different asteroid population than other known meteorites.

  17. Impact craters: their importance in geologic record and implications for natural resource development

    SciTech Connect

    Levie, D. Jr.

    1986-05-01

    Impacting bodies of sufficient size traveling at hypervelocities carry tremendous potential energy. This relatively infrequent process results in the instantaneous formation of unique structures that are characterized by extensive fracturing and brecciation of the target material. Impacts onto continental shield areas can create rich ore deposits, such as the Sudbury mining district in Canada. Impacts into the sedimentary column can instantaneously create hydrocarbon reservoirs out of initially nonporous rocks, such as at Red Wing Creek and Viewfield in the Williston basin. Associated reservoirs are usually limited to a highly deformed central uplift in larger craters, or to the fractured rim facies in smaller craters. The presence of reservoirs and trapping mechanisms is largely dependent, however, upon the preservation state of the crater in the subsurface. A catastrophic extraterrestrial event (a large asteroid impact) has also been suggested as the cause for the extinction of the dinosaurs, but the latest theory proposes a companion star with a 26 m.y. periodicity as the cause for numerous lifeform extinctions over a similar time interval. Regardless of their magnitude and distribution over the earth, it is clear that catastrophic extraterrestrial events have been responsible for altering the geologic column locally, regionally, and quite possibly on a global scale.

  18. A Hydrogeophysical Conceptual Model of Mount Toondina Impact Crater, South Australia

    NASA Astrophysics Data System (ADS)

    Dressler, D. K.; Halihan, T.; Love, A.; Xie, Y.; Simmons, C.

    2011-12-01

    Mount Toondina, located on the Great Artesian Basin (GAB), South Australia, is a meteorite impact crater and a ground water discharge feature with a water hole, a tufa salt flat and several former mapped springs. Aerial photographs and field survey data indicate that water was flowing from springs as recent as twenty years ago. Geophysical site surveys including electrical resistivity imaging (ERI), gravity and seismic data were utilized to constrain a hydrogeologic model for the site. Regional magnetic and gravity surveys were also utilized to evaluate the site boundaries using Oasis Montaj. Fluid chemistry and electrical conductivity from the site was used along with the geophysical data to constrain FEFLOW models to test hydrogeological conceptual models of the permeability structure of Mount Toondina. It is hypothesized that the spring system is controlled by advective flow from the subsurface artesian aquifer to the ring of vegetation around the perimeter of the impact structure. Additionally, it is hypothesized that the central salt flat portion of the impact crater is influenced by free convective processes. The field data and FEFLOW model results will be used to better manage flora and fauna in the Mount Toondina area and to better predict groundwater flow on other impact craters.

  19. Craters on Pluto and Charon: The Influence of Low Gravities, Low Impact Speeds, and Unique Ices

    NASA Astrophysics Data System (ADS)

    Singer, K. N.; Schenk, P.; McKinnon, W. B.; Robbins, S. J.; Moore, J. M.; Bray, V. J.; Spencer, J. R.; Stern, S. A.; Grundy, W. M.; Beyer, R. A.; Howett, C.; Dalle Ore, C.; White, O. L.; Parker, A. H.; Porter, S.; Zangari, A. M.; Young, L. A.; Olkin, C.; Ennico Smith, K.; Weaver, H. A., Jr.

    2015-12-01

    The surfaces of Pluto and Charon display a wide variety of crater landforms. Pluto and Charon present a unique regime to investigate cratering physics due to a combination of circumstances: 1) their relatively low gravities—Pluto's gravity (~0.66 m s-2) falls between those of the large icy satellites of Jupiter and their mid-sized saturnian cousins, while Charon's gravity (0.28 m s-2) is more similar to the latter, 2) the low primary impact velocities onto Pluto and Charon's surfaces (average ~2 km s-1), and 3) the mix of surface ices likely present (e.g., N2, CO, CH4, H2O). We use available images from both the Long Range Reconnaissance Imager (LORRI; Cheng et al., 2008, SSR 140, 189-215) and data from the Ralph (Reuter et al., 2008, SSR 140, 129-154) color/composition instruments to characterize crater morphologies and ejecta characteristics. This presentation will focus on understanding formation of craters on Pluto and Charon (with reference to deformation/degradation processes described in other presentations) and will include comparison to icy satellites. We will also discuss what inferences can be drawn about impactor characteristics.

  20. 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.

  1. Update on the Chemical Composition Of Crystalline, Smectite, and Amorphous Components for Rocknest Soil and John Klein and Cumberland Mudstone Drill Fines at Gale Crater, Mars

    NASA Technical Reports Server (NTRS)

    Morris, R. V.; Ming, D. W.; Gellert, R.; Vaniman, D. T.; Bish, D. L.; Blake, D. F.; Chipera, S. J.; Morrison, S. M.; Downs, R. T.; Rampe, E. B.; Treiman, A. H.; Yen, A. S.; Achilles, C. N.; Archer, P. D.; Bristow, T. F.; Cavanaugh, P.; Fenrdrich, K.; Crisp, J. A.; Des Marais, D. J.; Farmer, J. D.; Grotzinger, J. P.; Mahaffy, P. R.; McAdam, A. C.; Morookian, J. M.

    2015-01-01

    We have previously calculated the chemical compositions of the X-ray-diffraction (XRD) amorphous component of three solid samples (Rocknest (RN) soil, John Klein (JK) drill fines, and Cumberland (CB) drill fines) using major-element chemistry (APXS), volatile-element chemistry (SAM), and crystalline- phase mineralogy (CheMin) obtained by the Curiosity rover as a part of the ongoing Mars Science Laboratory mission in Gale Crater. According to CheMin analysis, the RN and the JK and CB samples are mineralogically distinct in that RN has no detectable clay minerals and both JK and CB have significant concentrations of high-Fe saponite. The chemical composition of the XRD amorphous component is the composition remaining after mathematical removal of the compositions of crystalline components, including phyllosilicates if present. Subsequent to, we have improved the unit cell parameters for Fe-forsterite, augite, and pigeonite, resulting in revised chemical compositions for the XRD-derived crystalline component (excluding clay minerals). We update here the calculated compositions of amorphous components using these revised mineral compositions.

  2. 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.

  3. The XLLGG — A Hypervelocity Launcher for Impact Cratering Research

    NASA Astrophysics Data System (ADS)

    Lexow, B.; Bückle, A.; Wickert, M.; Hiermaier, S.

    2015-09-01

    Hypervelocity launchers are used to accelerate projectiles that simulate impacting meteoroids or asteroids. The XLLGG (eXtra Large Light Gas Gun) at the EMI (Ernst-Mach-Institute) was used within the MEMIN program.

  4. Global Geometric Properties of Martian Impact Craters: An Assessment from Mars Orbiter Laser Altimeter (MOLA) Digital Elevation Models

    NASA Technical Reports Server (NTRS)

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

    2000-01-01

    Global geometric characteristics of topographically fresh impact craters have been assessed, for the first time, from gridded MOLA topography. Global trends of properties such as depth/diameter differ from previous estimates. Regional differences are observed.

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

    NASA Technical Reports Server (NTRS)

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

    2014-01-01

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

  6. Integrated Remote Sensing of the Spider Impact Structure, Australia -- Potential Effects of the Morphostructural Setting on Cratering

    NASA Astrophysics Data System (ADS)

    Abels, A.

    2001-03-01

    The Spider impact structure has been investigated by means of integrated remote sensing. It is concluded that cratering was influenced by the original morphostructural setting leading to the present, highly asymmetric properties of the deeply eroded site.

  7. Reconstruction of the Morasko Meteorite Impact: From Atmospheric Entry to Individual Crater Formation - Insight from Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Bronikowska, M.; Artemieva, N. A.; Wünnemann, K.; Szczuciński, W.

    2016-08-01

    Here we present modeling results of the atmospheric break-up of the meteoroid, the distribution of fragments and the formation of craters during the Morasko event. Our goal is to reconstruct the most probable impact scenario.

  8. Automated Crater Delineation

    NASA Astrophysics Data System (ADS)

    Marques, J. S.; Pina, P.

    2015-05-01

    An algorithm to delineate impact craters based on Edge Maps and Dynamic Programming is presented. The global performance obtained on 1045 craters from Mars (5 m to about 200 km in diameter), achieved 96% of correct contour delineations.

  9. Biospheric effects of a large extraterrestrial impact: Case study of the Cretaceous/Tertiary boundary crater

    NASA Technical Reports Server (NTRS)

    Pope, Kevin O.

    1994-01-01

    The Chicxulub Crater in Yucatan, Mexico, is the primary candidate for the impact that caused mass extinctions at the Cretaceous/Tertiary boundary. The target rocks at Chicxulub contain 750 to 1500 m of anhydrite (CaSO4), which was vaporized upon impact, creating a large sulfuric acid aerosol cloud. In this study we apply a hydrocode model of asteroid impact to calculate the amount of sulfuric acid produced. We then apply a radiative transfer model to determine the atmospheric effects. Results include 6 to 9 month period of darkness followed by 12 to 26 years of cooling.

  10. Molecular dynamics study of crater formation by core-shell structured cluster impact

    NASA Astrophysics Data System (ADS)

    Aoki, Takaaki; Seki, Toshio; Matsuo, Jiro

    2012-07-01

    Crater formation processes by the impacts of large clusters with binary atomic species were studied using molecular dynamics (MD) simulations. Argon and xenon atoms are artificially organized in core-shell cluster structures with various component ratios and irradiated on a Si(1 0 0) target surface. When the cluster has Xe1000 core covered with 1000 Ar atoms, and impacts at a total of 20 keV, the core Xe cluster penetrates into the deep area, and a crater with a conical shape is left on the target. On the other hand, in the case of a cluster with the opposite structure, Ar1000 core covered with 1000 Xe atoms, the cluster stops at a shallow area of the target. The incident cluster atoms are mixed and tend to spread in a lateral direction, which results in a square shaped crater with a shallower hole and wider opening. The MD simulations suggest that large cluster impacts cause different irradiation effects by changing the structure, even if the component ratio is the same.

  11. 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.

  12. 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.

  13. Polygonal impact craters on Dione: Evidence for tectonic structures outside the wispy terrain

    NASA Astrophysics Data System (ADS)

    Beddingfield, Chloe B.; Burr, Devon M.; Tran, Liem T.

    2016-08-01

    Plan-view impact crater geometries can be indicative of pre-impact structures within the target material. Impact events that occur on a pre-fractured surface generate craters exhibiting one or more straight rim segments, termed polygonal impact craters (PICs). Impact craters that appear to be PICs are abundant on the surface of Saturn's icy satellite, Dione, both within the wispy terrain, a region with large visible fractures, and also outside the wispy terrain (the 'non-wispy terrain'), where less evidence for fracturing has been observed. In the non-wispy terrain, subtle lineaments are hypothesized to be NE-SW, NW-SE, and E-W trending fractures, suggesting that tectonism may have been an important process in this terrain. Results of previous studies have shown that PIC straight rim segment azimuths ('PIC azimuths') commonly parallel pre-impact fracture azimuths, although disagreements about this relationship exist in the literature. We investigated the hypothesis that fractures, either subtle or nonvisible with available spacecraft images, are present within Dione's non-wispy terrain. Our first step was to assess the relationship between PICs and pre-existing fracture azimuths in the wispy terrain. Our results from this initial assessment show a parallel relationship between PIC azimuths and fracture azimuths. Based on this correlation in the wispy terrain, we find it likely that this relationship would hold true in the non-wispy terrain if PICs are present. We tested for PICs using crater rim azimuth data collected from randomly distributed study locations throughout the non-wispy terrain. From these data, we identified widespread PICs in this terrain, which supports the hypothesis that subtle fractures are also present. Analysis of the PIC azimuth data yield a pattern for these inferred fractures across Dione's surface that is consistent with the hypothesized global deformation that would result from a combination of satellite despinning and volume expansion

  14. Numerical Modeling of Shatter Cones Development in Impact Craters

    NASA Technical Reports Server (NTRS)

    Baratoux, D.; Melosh, H. J.

    2003-01-01

    Shatter cones are the characteristic forms of rock fractures in impact structures. They have been used for decades as unequivocal fingerprints of meteoritic impacts on Earth. The abundant data about shapes, apical angles, sizes and distributions of shatter cones for many terrestrial impact structures should provide insights for the determination of impact conditions and characteristics of shock waves produced by high-velocity projectiles in geologic media. However, previously proposed models for the formation of shatter cones do not agree with observations. For example, the widely accepted Johnson-Talbot mechanism requires that the longitudinal stress drops to zero between the arrival of the elastic precursor and the main plastic wave. Unfortunately, observations do not support such a drop. A model has been also proposed to explain the striated features on the surface of shatter cones but can not invoked for their conical shape. The mechanism by which shatter cones form thus remains enigmatic to date. In this paper we present a new model for the formation of shatter cones. Our model has been tested by means of numerical simulations using the hydrocodes SALE 2D enhanced with the Grady-Kipp-Melosh fragmentation model.

  15. A Model of the Chicxulub Impact Basin Based on Evaluation of Geophysical Data, Well Logs, and Drill Core Samples

    NASA Technical Reports Server (NTRS)

    Sharpton, Virgil L.; Marin, Luis E.; Carney, John D.; Lee, Scott; Ryder, Graham; Schuraytz, Benjamin C.; Sikora, Paul; Spudis, Paul D.

    1996-01-01

    Abundant evidence now shows that the buried Chicxulub structure in northern Yucatan, Mexico, is indeed the intensely sought-after source of the ejecta found world-wide at the Cretaceous-Tertiary (K/T) boundary. In addition to large-scale concentric patterns in gravity and magnetic data over the structure, recent analyses of drill-core samples reveal a lithological assemblage similar to that observed at other terrestrial craters. This assemblage comprises suevite breccias, ejecta deposit breccias (Bunte Breccia equivalents), fine-grained impact melt rocks, and melt-matrix breccias. All these impact-produced lithologies contain diagnostic evidence of shock metamorphism, including planar deformation features in quartz, feldspar, and zircons; diaplectic glasses of quartz and feldspar; and fused mineral melts and whole-rock melts. In addition, elevated concentrations of Ir, Re, and Os, in meteoritic relative proportions, have been detected in some melt-rock samples from the center of the structure. Isotopic analyses, magnetization of melt-rock samples, and local stratigraphic constraints identify this crater as the source of K/T boundary deposits.

  16. Shallow crustal composition of Mercury as revealed by spectral properties and geological units of two impact craters

    NASA Astrophysics Data System (ADS)

    D'Incecco, Piero; Helbert, Jörn; D'Amore, Mario; Maturilli, Alessandro; Head, James W.; Klima, Rachel L.; Izenberg, Noam R.; McClintock, William E.; Hiesinger, Harald; Ferrari, Sabrina

    2015-12-01

    We have performed a combined geological and spectral analysis of two impact craters on Mercury: the 15 km diameter Waters crater (106°W; 9°S) and the 62.3 km diameter Kuiper crater (30°W; 11°S). Using the Mercury Dual Imaging System (MDIS) Narrow Angle Camera (NAC) dataset we defined and mapped several units for each crater and for an external reference area far from any impact related deposits. For each of these units we extracted all spectra from the MESSENGER Atmosphere and Surface Composition Spectrometer (MASCS) Visible-InfraRed Spectrograph (VIRS) applying a first order photometric correction. For all the mapped units, we analyzed the spectral slope in two wavelength ranges, 350-450 nm and 450-650 nm, and the absolute reflectance in the 700-750 nm range. Normalized spectra of Waters crater display a generally bluer spectral slope than the external reference area over both wavelength windows. Normalized spectra of Kuiper crater generally display a redder slope than the external reference area in the 350-450 nm window, while they display a bluer slope than the external reference area in the 450-650 nm wavelength range. The combined use of geological and spectral analyses enables reconstruction of the local scale stratigraphy beneath the two craters, providing insight into the properties of the shallower crust of Mercury. Kuiper crater, being ~4 times larger than Waters crater, exposes deeper layers with distinctive composition, while the result for Waters crater might indicate substantial compositional homogeneity with the surrounding intercrater plains, though we cannot exclude the occurrence of horizontal compositional heterogeneities in the shallow sub-surface.

  17. Breccia Formation at a Complex Impact Crater: Slate Islands, Lake Superior, Ontario, Canada

    NASA Technical Reports Server (NTRS)

    Dressler, B. O.; Sharpton, V. L.

    1997-01-01

    The Slate Islands impact structure is the eroded remnant of a approximately 30-32 km-diameter complex impact structure located in northern Lake Superior, Ontario, Canada. Target rocks are Archean supracrustal and igneous rocks and Proterozoic metavolcanics, metasediments, and diabase. A wide variety of breccias occurs on the islands, many of which contain fragments exhibiting shock metamorphic features. Aphanitic, narrow and inclusion-poor pseudotachylite veins, commonly with more or less parallel boundaries and apophyses branching off them, represent the earliest breccias formed during the compression stage of the impact process. Coarse-grained, polymictic elastic matrix breccias form small to very large, inclusion-rich dikes and irregularly shaped bodies that may contain altered glass fragments. These breccias have sharp contacts with their host rocks and include a wide range of fragment types some of which were transported over minimum distances of approximately 2 km away from the center of the structure. They cut across pseudotachylite veins and contain inclusions of them. Field and petrographic evidence indicate that these polymictic breccias formed predominantly during the excavation and central uplift stages of the impact process. Monomictic breccias, characterized by angular fragments and transitional contacts with their host rocks, occur in parautochthonous target rocks, mainly on the outlying islands of the Slate Islands archipelago. A few contain fragmented and disrupted, coarse-grained, polymictic clastic matrix breccia dikes. This is an indication that at least some of these monomictic breccias formed late in the impact process and that they are probably related to a late crater modification stage. A small number of relatively large occurrences of glass-poor, suevitic breccias occur at the flanks of the central uplift and along the inner flank of the outer ring of the Slate Islands complex crater. A coarse, glass-free, allogenic breccia, containing

  18. IMPACT CRATERING ON MERCURY: CONSEQUENCES FOR THE SPIN EVOLUTION

    SciTech Connect

    Correia, Alexandre C. M.; Laskar, Jacques

    2012-06-01

    Impact basins identified by Mariner 10 and Messenger flyby images provide us with a fossilized record of the impactor flux of asteroids on Mercury during the last stages of the early solar system. The distribution of these basins is not uniform across the surface and is consistent with a primordial synchronous rotation. By analyzing the size of the impacts, we derive a simple collisional model coherent with the observations. When combining it with the secular evolution of the spin of Mercury, we are able to reproduce the present 3/2 spin-orbit resonance ({approx}50% of chances), as well as a primordial synchronous rotation. This result is robust with respect to variations in the dissipation and collisional models, or in the initial spin state of the planet.

  19. 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

  20. Henry Crater

    NASA Technical Reports Server (NTRS)

    2002-01-01

    [figure removed for brevity, see original site]

    Located in Arabia Terra, the crater shown here is known as Henry Crater. Like many other craters on Mars, the interior of Henry Crater is filled with a layered deposit. These materials were brought into the crater sometime after the impact formed the crater. The fine scale of layering can be seen in the right- center portion of the image.

    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.

  1. Lunar dark-haloed impact craters - Origin and implications for early mare volcanism

    NASA Technical Reports Server (NTRS)

    Bell, J. F.; Hawke, B. R.

    1984-01-01

    Spectral, thermal, radar, and photogeologic data were used to determine the composition and origin of lunar dark-haloed craters. Analyses of reflectance spectra (near-infrared) of dark-haloed craters on light plains indicate that in every instance these craters exposed mare basalts which had previously been covered by varying thicknesses of highlands debris. In the Schiller-Schickard region a relatively thick highlands unit was emplaced as a result of the Orientale impact event. The results of recent remote sensing photogeologic and lunar samples studies indicate that mare volcanism was a significant process during much of the pre-Imbrian epoch and may have been initiated as early as 4.2-4.3 Ga. The very early volcanic episodes contributed materials to the lunar surface which were later incorporated into the upper portion of the highlands crust by subsequent impact mixing. On the basis of the data it is concluded that current models of the extent and duration of mare volcanisms, as well as those involving the composition of thermal evolution of the lunar interior will have to be revised.

  2. Ganymede - Mixture of Terrains and Large Impact Crater in Uruk Sulcus Region

    NASA Technical Reports Server (NTRS)

    1996-01-01

    A mixture of terrains studded with a large impact crater is shown in this view of the Uruk Sulcus region of Jupiter's moon Ganymede taken by NASA's Galileo spacecraft during its first flyby of the planet-sized moon on June 27, 1996. The image shows fine details of bright areas that make up about half of the surface of Ganymede. Pock-marked, ancient, heavily cratered terrain is seen at the top; it is cut by younger, line-like structures in the lower left of the image. The bright, circular feature in the lower middle is an impact crater with some dark ejecta superimposed on the linear ridges. These types of relationships revealed by Galileo allow scientists to work out the complex geologic history of Ganymede. In this view, north is to the top and the sun illuminates the surface from the lower left nearly overhead. The area shown, at latitude 10 degrees north, longitude 168 degrees west, is about 59 by 40 kilometers (36 by 25 miles), and the resolution is 74 meters (80 yards) per picture element. The image was taken on June 27 at a range of 7,448 kilometers (4.628 miles). The Jet Propulsion Laboratory manages the Galileo mission for NASA's Office of Space Science.

  3. A seismic refraction technique used for subsurface investigations at Meteor Crater, Arizona

    NASA Technical Reports Server (NTRS)

    Ackermann, H. D.; Godson, R. H.; Watkins, J. S.

    1975-01-01

    A seismic refraction technique for interpreting the subsurface shape and velocity distribution of an anomalous surface feature such as an impact crater is described. The method requires the existence of a relatively deep refracting horizon and combines data obtained from both standard shallow refraction spreads and distant offset shots by using the deep refractor as a source of initial arrivals. Results obtained from applying the technique to Meteor crater generally agree with the known structure of the crater deduced by other investigators and provide new data on an extensive fractured zone surrounding the crater. The breccia lens is computed to extend roughly 190 m below the crater floor, about 30 m less than the value deduced from early drilling data. Rocks around the crater are fractured as distant as 900 m from the rim crest and to a depth of at least 800 m beneath the crater floor.

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

    NASA Astrophysics Data System (ADS)

    Nakamura, A.; Yokoyama, Y.; Sekine, Y.; Goto, K.; Komatsu, G.; Kumar, P.; Matsuzaki, H.; Matsui, T.

    2013-12-01

    Impact cratering is a dominant surface modification process on planetary surfaces. In the inner solar system, the large majority of impacts occur on bodies covered by primitive igneous rocks. However, most of the impacts remaining on Earth surface are on different rock types than that of the inner planet and hence geologic knowledge derived from Earth's surface cannot be translated readily. The Lonar crater is a 1.88-km-diameter crater located on the Deccan basaltic traps in India (ca. 65 Ma), and is one of a few craters on Earth bombarded directly on basaltic lava flows. Thus, the Lonar crater provides a rare opportunity to study impact structures on the basaltic surfaces of other terrestrial planets and the Moon. Since the ages of terrestrial impact structures is a key to understand geomorphological processes after the impact, various dating methods have been applied to the Lonar Crater such as fission track (Storzer and Koeberl, 2004), radiocarbon (Maloof, 2010), thermoluminescence (Sengupta et al., 1997), and 40Ar/39Ar (Jourdan et al., 2011). Yet, a large discrepancy between these methods ranging from ca. 1.79 to 570 ka has been resulted. Here we report surface exposure ages based on in-situ cosmogenic 10Be and 26Al in order to obtain a precise age of the Lonar crater formation as well as to study the geomorphologic evolution. The samples are collected from the topographic highs on the rim of the crater and from the ejecta blanket. Exposure ages together with newly obtained radiocarbon age of pre-impact soil indicate much younger ages than that of obtained from 40Ar/39Ar method. This suggests the potential bias because of inherited 40Ar in impact glass. Systematically young exposure age from the rim samples compared to the samples from the ejecta blanket indicate that the rim of the Lonar crater is being actively eroded. Spatial distributions of geomorphic ages observed from the Lonar creator is not the same as the pattern reported from the well

  5. 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.

  6. Sampling and Analysis of Impact Crater Residues Found on the Wide Field Planetary Camera-2 Radiator

    NASA Technical Reports Server (NTRS)

    Kearsley, A. T.; Grime, G. W.; Colaux, J. L.; Jeynes, C.; Palitsin, V. V.; Webb, R, P.; Griffin, T. J.; Reed, B. B.; Anz-Meador, P. D.; Kou, J.-C.; Robinson, G. A.; Opiela, J. N.; Gerlach, L.

    2013-01-01

    After nearly 16 years in low Earth orbit (LEO), the Wide Field Planetary Camera-2 (WFPC2) was recovered from the Hubble Space Telescope (HST) in May 2009, during the 12 day shuttle mission designated STS-125. The WFPC-2 radiator had been struck by approximately 700 impactors producing crater features 300 microns and larger in size. Following optical inspection in 2009, agreement was reached for joint NASA-ESA study of crater residues, in 2011. Over 480 impact features were extracted at NASA Johnson Space Center's (JSC) Space Exposed Hardware clean-room and curation facility during 2012, and were shared between NASA and ESA. We describe analyses conducted using scanning electron microscopy (SEM) - energy dispersive X-ray spectrometry (EDX): by NASA at JSC's Astromaterials Research and Exploration Science (ARES) Division; and for ESA at the Natural History Museum (NHM), with Ion beam analysis (IBA) using a scanned proton microbeam at the University of Surrey Ion Beam Centre (IBC).

  7. Distribution of mid-latitude ground ice on Mars from new impact craters.

    PubMed

    Byrne, Shane; Dundas, Colin M; Kennedy, Megan R; Mellon, Michael T; McEwen, Alfred S; Cull, Selby C; Daubar, Ingrid J; Shean, David E; Seelos, Kimberly D; Murchie, Scott L; Cantor, Bruce A; Arvidson, Raymond E; Edgett, Kenneth S; Reufer, Andreas; Thomas, Nicolas; Harrison, Tanya N; Posiolova, Liliya V; Seelos, Frank P

    2009-09-25

    New impact craters at five sites in the martian mid-latitudes excavated material from depths of decimeters that has a brightness and color indicative of water ice. Near-infrared spectra of the largest example confirm this composition, and repeated imaging showed fading over several months, as expected for sublimating ice. Thermal models of one site show that millimeters of sublimation occurred during this fading period, indicating clean ice rather than ice in soil pores. Our derived ice-table depths are consistent with models using higher long-term average atmospheric water vapor content than present values. Craters at most of these sites may have excavated completely through this clean ice, probing the ice table to previously unsampled depths of meters and revealing substantial heterogeneity in the vertical distribution of the ice itself. PMID:19779195

  8. Remote sensing studies of lunar dark-halo impact craters - Preliminary results and implications for early volcanism

    NASA Technical Reports Server (NTRS)

    Hawke, B. R.; Bell, J. F.

    1982-01-01

    A summary of the nature and origin of lunar dark-halo craters is presented. New remote sensing data for dark-haloed impact craters were obtained and interpreted. A variety of spectral, thermal, radar, and photogeologic data are presented which confirm the hypothesis that Copernicus H crater excavated mare basalt from beneath lighter deposits emplaced by the Copernicus impact event. Multispectral imagery suggests that analogous impact re-exposure of basaltic material on the ejecta blankets of other large Copernican and Eratosthenian craters resulted in the formation of other dark-halo craters. Preliminary analyses of near-infrared spectra of dark-haloed impact craters in the Schickard-Schiller region are consistent with the hypothesis that basaltic material was excavated from beneath light plains. These light plains may have been emplaced as a result of the Orientale impact event. Additional evidence is presented which suggests that both pre- and post-Orientale volcanic activity was more prevalent in this region than has previously been recognized.

  9. A new look at lunar impact craters provides insights into ejecta and melt emplacement on the terrestrial planets

    NASA Astrophysics Data System (ADS)

    Osinski, G. R.; Grieve, R. A.; Tornabene, L. L.

    2011-12-01

    Impact cratering is one of the most fundamental processes responsible for shaping the surfaces of solid planetary bodies. Even on Earth, where the impact record is sparse, it is now apparent that impact events also have played an important role throughout Earth's history, shaping the geological landscape, affecting the evolution of life and producing economic benefits. It is widely acknowledged that the Moon provides a unique natural laboratory for studying the impact processes on planetary scales. One of the most important, but least understood aspects of impact cratering is the generation and emplacement of impact ejecta. In this contribution, we utilize new high-resolution imagery of lunar craters in addition to observations of terrestrial impact structures. Current models of ejecta emplacement do not account for several important observations of ejecta deposits on the terrestrial planets, in particular, the presence of more than one layer of ejecta. On the Moon, this addional ejecta layer takes the form of impact melt ponds on the rim terraces of complex lunar craters and overlying parts of the continuous e