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NASA NTRS1992

Martian parent craters for the SNC meteorites

Information on the petrology and ages of the SNC meteorites, together with geological data derived from Viking Orbiter images, are used to identify 25 candidate impact craters in the Tharsis region of Mars that could possibly be the source craters for these meteorites. The craters chosen as candidate source craters had diameters greater than 10 km, morphologies indicative of young craters, and satisfied both the petrological criteria of the SNCs and the proposed 1.3 Ga crystallization ages. On the basis of the constraints implied by the identification of the candidate source craters, interpretations of the absolute chronology of Mars are proposed.

Mouginis-Mark, P. J.↗
NASA NTRS2012

Sampling South Pole-Aitken Basin: The Moonrise Approach

The South Pole-Aitken basin (SPA) is the largest of the giant impact basins in the inner Solar System, and its location on Earth s Moon makes it the most accessible. Exploration of SPA through direct collection and analysis of representative materials addresses issues as fundamental as the characteristics of the chemical reservoir from which the Moon originated, early differentiation and production of crust and development of global asymmetry, relationships between magmatic activity and internal thermal evolution, and effects of giant impact events on the terrestrial planets. Owing to its great size and superposition relationships with other lunar impact basins, SPA is the oldest and as such anchors the lunar chronology. Moreover, numerous large impact craters and basins are contained within it such that materials (rocks) of the SPA basin contain a record of the early impact chronology, one less likely to have been affected by the large, late nearside basins (e.g., Imbrium). Understanding the early basin chronology is key to deciphering the sequence and effects of early giant impact bombardment of the inner Solar System. That record exists on the Moon, and materials of the SPA basin will allow us to read that record. Knowledge of the early bombardment history will test - and may reshape - a key paradigm relating to early Solar System evolution. Did the planets form with the alignment of today, or was there a major reorientation of the giant planets that led to destabilization of asteroid orbits, and a cataclysmic bombardment of the inner Solar System hundreds of millions of years after accretion of the planets? Implications include understanding environments for early life-supporting habitats on Earth and Mars, and relationships to new observations of extra-solar planetary systems.

Jolliff, B. L.↗
NASA NTRS2022

Global geologic map of asteroid (101955) Bennu indicates heterogeneous resurfacing in the past 500,000 years

Global geologic maps are useful tools for efficient interpretation of a planetary body, and they provide global context for the diversity and evolution of the surface. We used data acquired by the OSIRIS-REx spacecraft to create the first global geologic map of the near-Earth asteroid (101955) Bennu. As this is the first geologic map of a small, non-spherical, rubble-pile asteroid, we discuss the distinctive mapping challenges and best practices that may be useful for future exploration of similar asteroids, such as those to be visited with the Hera and Janus missions. By mapping on two centimeter-scale global image mosaics (2D projected space) and a centimeter-scale global shape model (3D space), we generated three input maps respectively describing Bennu’s shape features, geologic features, and surface texture. Based on these input maps, we defined two geologic units: the Smooth Unit and the Rugged Unit. The units are differentiated primarily on the basis of surface texture, concentrations of boulders, and the distributions of lineaments, mass movement features, and craters. They are bounded by several scarps. The Rugged Unit contains abundant boulders and signs of recent mass movement. It also has fewer small(<20 m), putatively fresh craters than the Smooth Unit, suggesting that such craters have been erased in the former. Based on these geologic indicators, we infer that the Rugged Unit has the younger surface of the two. Differential crater size-frequency distributions and the distribution of the freshest craters suggest that both unit surfaces formed ~10–65 million years ago, when Bennu was located in the Main Asteroid Belt, and the Smooth Unit has not been significantly resurfaced in the past 2 million years. Meanwhile, the Rugged Unit has experienced resurfacing within the past ~500,000years during Bennu’s lifetime as a near-Earth asteroid. The geologic units are consistent with global diversity in slope, surface roughness, normal albedo, and thermal emission spectral characteristics. The site on Bennu where the OSIRIS-REx mission collected a regolith sample is located in the Smooth Unit, in a small crater nested within a larger one. So although the Smooth Unit is an older surface than the Rugged Unit, the impact-crater settingindicates that the material sampled was recently exposed. Several similarities are apparent between Bennu and asteroid (162173) Ryugu from a global geologic perspective, including two geologic units distinguishable by variations in the number density of boulders, as well as in other datasets such as brightness.

E R Jawin↗
NASA NTRS1998

Lunar Basins: New Evidence from Gravity for Impact-Formed Mascons

The prominent gravity highs (mascons) associated with uncompensated mass anomalies in lunar mare basins are a dramatic expression of the present-day rigidity of the lunar lithosphere. First discovered in Lunar Orbiter tracking data, these about 350-mGal gravity highs have been redetermined from the analysis of Clementine and historical tracking. These highs coincide with topographic lows, indicating nonisostatic support. One of the rediscoveries of this analysis is the encirclement of the highs by substantial negative anomalies over topographic highs. Recent gravity fields are providing the increased resolution necessary to determine the causes of this unique mascon signature. The compensation of the basin anomalies remains controversial. The mascon highs have long been interpreted as the result of mare loading, subsequent to the decay of residual stresses resulting from the impact. Substantially more mare fill is required to produce mascon highs than has been inferred on geological grounds, and the amount of near-surface mass deficit required to produce a gravity most exceeds bounds inferred from terrestrial examples. This problem is most acute for the youngest basin, Orientale. Recent gravity fields from Lunar Prospector have suggested mascon highs associated with nonmare basins such as Mendel-Rydberg, or minimally filled basins like Humboldtianum, further calling this explanation into question. We suggest that the mascon gravity signal is produced by a combination of crustal thickness changes, manifested by central mantle uplift, outward displacement of crust, and downward flexure of the lithosphere under mare loading. The mantle uplift is superisostatic, maintained by residual stresses resulting from the process of impact cratering and modification. In particular, the process of crater collapse and mantle rebound terminates abruptly, leaving the mantle plug in a non-equilibrium state, surrounded by a ring of thickened crust. Viscous relaxation over geological timescales has erased some but not all of the signature of the impact process. Mantle uplift inferred from gravity modeling is inversely correlated with age. While the oldest basins such as South Pole Aitken are mainly compensated isotatically, the younger basins appear to have been in a state of superisostatic loading prior to mare emplacement. If this is true, this places an important constraint on the impact process at basin scales. The idea that rebound of the transient crater via acoustic fluidization may freeze substantial stresses imcomplete to this day, may be tested by examining the gravity signatures of major basins on terrestrial bodies. The moon provides the clearest resolved examples to date, but uncertainty in gravity knowledge remains problematic.

Neumann, Gregory A.↗
NASA NTRS1990

Meteorite impact, cryptoexplosion, and shock metamorphism - A perspective on the evidence at the K/T boundary

A perspective on the evidence of a major impact event at the K/T boundary is proposed using field and laboratory studies of terrestrial impact craters. Recent assertions that diagnostic indications of shock metamorphism are also produced in volcanic environments are challenged. A general geological framework of impact structures is developed and the issue of volcanically induced shock metamorphism is examined. Cryptoexplosion is addressed by assessing the geology of two structures: the Slate Islands and Manson, which are often cited by advocates of an internal origin for shock metamorphism as volcanic structures. It is concluded that the link between shock metamorphism and meteorite impact is now established beyond reasonable doubt. The occurrence and worldwide distribution of shocked minerals at the K/T boundary is considered to be the conclusive evidence for a major impact event.

Sharpton, V. L.↗
NASA NTRS1993

Assumptions about the presence of natural glasses on Mars

Natural glasses occur not only on Earth but also in lunar rocks and in some meteorites. On geological grounds, natural glasses could be expected on the surface of Mars and their presence would have important implications for the weathering and alteration of the near-surface layer. Ultramafic and mafic magmatism rich in iron and some volatiles appears to have been important on Mars as has been impact cratering, volcanism, and possibly hydrothermal alteration. Available data indicate that we can presume the past or present existence of volcanic basaltic glasses, impact glasses formed by thermal fusion of meteorite-impact targets, and diaplectic (mainly maskelynite) glasses. Conditions appear unsuitable for the formation of tektites on the Martian surface, and the production of measurable amounts of fulgurite or combustion glass seems improbable. Prospects for the remote and in-situ identification of Martian glasses and their subsequent weathering products are discussed and include orbital reflectance and thermal emission spectroscopic measurements and Mossbauer spectroscopy from a surface lander.

Bouska, Vladimir↗
NASA NTRS1993

Assumptions About the Presence of Natural Glasses on Mars

Natural glasses occur not only on Earth but also in lunar rocks and in some meteorites. On geological grounds, natural glasses could be expected on the surface of Mars and their presence would have important implications for the weathering and alteration of the near-surface layer. Ultramafic and mafic magmatism rich in iron and some volatiles appears to have been important on Mars as has been impact cratering, volcanism, and possibly hydrothennal alteration. Available data indicate that we can presume the past or present existence of volcanic basaltic glasses, impact glasses formed by thermal fusion of meteorite-impact targets, and diaplectic (mainly maskelynite) glasses. Conditions appear unsuitable for the formation of tektites on the Martian surface, and the production of measurable amounts of fulgurite or combustion glass seems improbable. Prospects for the remote and in situ identification of Martian glasses and their subsequent weathering products are discussed and include orbital reflectance and thermal emission spectroscopic measurements and Mossbauer spectroscopy from a surface lander.

Bouska, Vladimir↗
NASA NTRS1993

Assumption About the Presence of Natural Glasses on Mars

Natural glasses occur not only on Earth but also in lunar rocks and in some meteorites. On geological grounds, natural glasses could be expected on the surface of Mars and their presence would have important implications for the weathering and alteraton of the near-surface layer. Ultramafic and mafic magmatism rich in iron and some volatiles appears to have been important on Mars as has been impact cratering, volcanism, and possibly hydrothertnal alteration, Available data indicate that we can presume the past or present existence of volcanic basaltic glasses, impact glasses formed by thermal fusion of meteorite-impact targets, and diaplectic (mainly maskelynite) glasses. Conditions appear unsuitable for the formation of tektites on the Martian surface, and the production of measurable amounts of fulgurite or combustion glass seems improbable. Prospects for the remote and in situ identificaton of Martian glasses and their subsequent weathering products are discussed and include orbital reflectance and thermal emission spectroscopic measurements and Mossbauer spectroscopy from a surface lander.

Bouska, Vladimir↗
NASA NTRS2012

Depth and Differentiation of the Orientale Melt Lake

Impact melt emplacement and evolution in lunar multi-ring basins is poorly understood since impact melt deposits in basins are generally buried by mare basalt fill and obscured by subsequent impact cratering. The relatively young Orientale basin, which is only partially flooded with mare basalt, opens a rare window into basin-scale impact melts. We describe the geology of impact melt-related facies in Orientale and suggest that the central depression of Orientale may represent a solidified impact melt lake that vertically subsided shortly after basin formation due to solidification and cooling. We use Lunar Orbiter Laser Altimeter (LOLA) data to measure the depth (approx. 1.75 km) and diameter (approx 350 km) of this central depression. If all the observed subsidence of the central depression is due to solidification and cooling, the melt lake should be approx 12.5-16 km deep, far more voluminous (approx 106 km3) than the largest known differentiated igneous intrusions on Earth. We investigate the possibility that the Orientale melt lake has differentiated and model 1) the bulk composition of the melt lake, 2) the operation of melt mixing in the melt lake, and 3) the chemical evolution of the resulting liquids on the An-Fo-Qz ternary in order to predict the lithologies that might be present in the solidified Orientale melt lake. Finally, we consider the possible significance of these lithologies.

Vaughan, W. M.↗
NASA NTRS2015

Using the Shuttle In Situ Window and Radiator Data for Meteoroid Measurements

Every time NASA's Space Shuttle flew in orbit, it was exposed to the natural meteoroid and artificial debris environment. NASA Johnson Space Center maintains a database of impact cratering data of 60 Shuttle missions flown since the mid‐1990's that were inspected after flight. These represent a total net exposure time to the space environment of 2 years. Impact damage was recorded on the windows and radiators, and in many cases information on the impactor material was determined by later analysis of the crater residue. This information was used to segregate damage caused by natural meteoroids and artificial space debris. The windows represent a total area of 3.565 sq m, and were capable of resolving craters down to about 10 micrometers in size. The radiators represent a total area of 119.26 sq m, and saw damage from objects up to approximately 1 mm in diameter. These data were used extensively in the development of NASA's ORDEM 3.0 Orbital Debris Environment Model, and gives a continuous picture of the orbital debris environment in material type and size ranging from about 10 micrometers to 1 mm. However, the meteoroid data from the Shuttles have never been fully analyzed. For the orbital debris work, special "as flown" files were created that tracked the pointing of the surface elements and their shadowing by structure (such as the ISS during docking). Unfortunately, such files for the meteoroid environment have not yet been created. This talk will introduce these unique impact data and describe how they were used for orbital debris measurements. We will then discuss some simple first‐order analyses of the meteoroid data, and point the way for future analyses.

Matney, Mark↗
NASA NTRS2012

The Violent Early Solar System, as Told by Lunar Sample Geochronology

One of the legacies of the samples collected by the Apollo and Luna missions is the link forged between radiometric ages of rocks and relative ages according to stratigraphic relationships and impact crater size-frequency distributions. Our current understanding of the history of the inner solar system is based on the relative chronology of individual planets, tied to the absolute geochronology of the Moon via these important samples. Samples from these nearside locations reveal a preponderance of impact-disturbed or recrystallized ages between 3.75 and 3.95 billion years. Argon and lead loss (and correlated disturbances in the Rb-Sr system) have been attributed to metamorphism of the lunar crust by an enormous number of impacts in a brief pulse of time, called the Lunar Cataclysm or Late Heavy Bombardment. Subsequent high-precision geochronometric analyses of Apollo samples and lunar highlands meteorites show a wider range of ages, but very few older than 4 Ga. The paucity of ancient impact melt rocks has been interpreted to mean that either that most impact basins formed at this time, or that ejecta from the large, near-side, young basins dominates the Apollo samples. Selenochronology is getting more complicated: new results question meaning of sample ages, crater counts, crater production functions, and the solar system itself. Improved geological mapping of lunar geologic units and boundaries using multiple remote sensing datasets. High-resolution image-based crater counting of discrete geologic units and relating them to location. Improved understanding of the regolith thickness and its global variation (GRAIL). Tying the sampling of impact-melt rocks to the lunar impact flux. Using improved techniques (magnetic fields, diffusion studies, isotopic analysis) on existing samples. New sample return from benchmark craters, particularly SPA, which appears in 2013 Decadal Survey.

Cohen, Barbara↗
NASA NTRS1982

Experimental shock lithification of water-bearing rock powders

The geology and morphology of the terrestrial planets and their moons have been profoundly affected by impact cratering. Some of these bodies contain substantial quantities of water or ice in their regoliths. It is pointed out that the effects of impacts into water-bearing target rocks are not well understood, and may be significantly different from those produced by identical impacts on a desiccated surface. The present investigation has the objective to determine the effects of water on targets of powdered rock and to seek evidence of impact-induced hydration or clay formation. Samples of andesitic basalt were crushed and sieved, and experiments were conducted on the material smaller than 150 micrometers. These experiments show that the water content of a powdered rock target can strongly affect its physical condition following an impact. A relatively small component (5-15 wt %) of water or ice in planetary surface material could inhibit or prevent lithification throughout much of the shocked volume at an impact site.

Allen, C. C.↗
NASA NTRS2004

Ancient Giant Basin/Aquifer System in the Arabia Region, Mars

Ancient geologic/hydrologic phenomena on Mars observed through the magnetic data [1,2] provide windows to the ancient past through the younger Argyre and Hellas impacts [e.g., 3,4], the northern plains basement [5], and the Tharsis and Elysium magmatic complexes (recently referred to as superplumes [6,7]). These signatures, coupled with highly degraded macrostructures (tectonic features that are tens to thousands of km-long [8]), reflect an energetic planet during its embryonic development (.5 Ga or so of activity) with an active dynamo and magnetosphere [1,2,6]. One such window into the ancient past occurs northwest of the Hellas impact basin in Arabia Terra. Arabia Terra is one of the few water-rich equatorial regions of Mars, as indicated through impact crater [9] and elemental [10,11] information. This region records many unique traits, including stratigraphy, topography, cratering record, structural character, geomorphology, and geophysical, elemental, albedo, and thermal inertia signatures. We interpret these to collectively indicate a possible ancient giant impact basin that later became an important aquifer, as it provided yet another source of water for the formation of putative water bodies that occupied the northern plains [12,13] and addresses possible water-related characteristics that may be observed at the Opportunity landing site. This basin is antipodal to Tharsis and estimated to be at least 3,000 km in diameter.

Dohm, James M.↗
NASA NTRS1974

A comparison of infrared, radar, and geologic mapping of lunar craters

Between 1000 and 2000 infrared (eclipse) and radar anomalies have been mapped on the nearside hemisphere of the moon. A study of 52 of these anomalies indicates that most are related to impact craters and that the nature of the infrared and radar responses is compatible with a previously developed geologic model of crater aging processes. The youngest craters are pronounced thermal and radar anomalies; that is, they have enhanced eclipse temperatures and are strong radar scatterers. With increasing crater age, the associated thermal and radar responses become progressively less noticeable until they assume values for the average lunar surface. The last type of anomaly to disappear is radar enhancement at longer wavelengths. A few craters, however, have infrared and radar behaviors not predicted by the aging model. One previously unknown feature - a field strewn with centimeter-sized rock fragments - has been identified by this technique of comparing maps at the infrared, radar, and visual wavelengths.

Thompson, T. W.↗
NASA NTRS1993

Projectile compositions and modal frequencies on the chemistry of micrometeoroids LDEF experiment

The Chemistry of Micrometeoroids Experiment (LDEF instrument A0187-1) exposed witness plates of high-purity gold (greater than 99.99 percent Au) and commercial aluminum (greater than 99 percent Al) with the objective of analyzing the residues of cosmic-dust and orbital-debris particles associated with hypervelocity impact craters. The gold substrates were located approximately 8 deg off LDEF's trailing edge (Bay A03), while the aluminum surfaces resided in Bay A11, approximately 52 deg from LDEF's leading edge. SEM-EDX techniques were employed to analyze the residues associated with 199 impacts on the gold and 415 impacts on the aluminum surfaces. The residues that could be analyzed represent natural or man-made materials. The natural particles dominate at all particle sizes less than 5 micron. It is possible to subdivide both particle populations into subclasses. Chondritic compositions dominate the natural impactors (71 percent), followed by monomineralic, mafic-silicate compositions (26 percent), and by Fe-Ni rich sulfides (approximately 3 percent). Approximately 30 percent of all craters on the gold collectors were caused by man-made debris such as aluminum, paint flakes, and other disintegrated, structural and electronic components. Equations-of-state and associated calculations of shock stresses for typical LDEF impacts into the gold and aluminum substrates suggest that substantial vaporization may have occurred during many of the impacts and is the reason why approximately 50 percent of all craters did not contain sufficient residue to permit analysis by the SEM-EDX technique. After converting the crater diameters into projectile sizes using encounter speeds typical for the trailing-edge and forward-facing (Row 11) directions, and accounting for normalized exposure conditions of the CME collectors, we derived the absolute and relative fluxes of specific projectile classes. The natural impactors encounter all LDEF pointing directions with comparable, modal frequencies suggesting compositional (and dynamic) homogeneity of the interplanetary-dust environment in near-Earth orbit.

Bernhard, Ronald P.↗
NASA NTRS1971

Martian cratering. II - Asteroid impact history.

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

Hartmann, W. K.↗
NASA NTRS2004

Spirit at Gusev Crater: Preliminary Observations, Potential Processes and Hypotheses

Spirit landed in a flat plain in Gusev crater with local undulations at meters scales generated by ridges covered with blocks, some of them looking rounded. Several, flat-topped, mesas are visible in the far field in direction of Ma adim Vallis. A set of north/south oriented hills reaches approximately 150 m elevation to the east of the landing site (LS). A dipping brighter unit with possibly some scarps is associated with it. This setting could be consistent with layering observed on the MOC images of the hills, local exposure of material with variable dust cover, or deflated or allochtonous material. Numerous small depressions are visible from LS referred to as "Columbia Memorial Station"* (CMS). Floors are partially filled with finer-grained, high albedo material. At least one of them, nicknamed "Sleepy Hollow"* (approximately 30 m diameter) may be an eroded secondary impact crater. It is unclear if they can all be related to small impact structures. Some of them are elongated and aligned with the ridges. The morphology of rocks and soil at this Gusev Crater is presented. Evidence of dynamic aeolian action along this Crater is also discussed.

Cabrol, N. A.↗