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  • 1
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    Recent grazing impacts on the earth recorded in the Rio Cuarto crater field, Argentina (1992)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: An anomalous alignment of oblong rimmed depressions has been observed on the otherwise featureless farmland of the Argentine Pampas. It is argued here, from sample analysis and by analogy with laboratory experiments, that the structure resulted from a low-angle impact and ricochet of a chondritic body originally 150-300 m in diameter.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Nature (ISSN 0028-0836); 355; 234-237
    Format: text
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  • 2
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    Atmospheric effects on crater growth on Venus (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Laboratory experiments allow examining the consequences of complex processes operating over a wide range of scales (both temporal and spatial) and frequently reveal effects that are obvious only in hindsight. Even though all processes may not scale directly, isolation of the controlling variables allows assessing first-order effects through analytical approximations. This approach can be illustrated by the systematic sequence of ballistic ejection, the response of an atmosphere to a strong energy source, the scaling of ejecta thickness, and the role of secondary cratering. Here it is proposed that the effects of atmospheric pressure and density on crater growth (hence, scaling) observed in laboratory experiments has particular relevance for craters on Venus.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Papers Presented to the International Colloquium on Venus; p 101-103
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  • 3
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    Effect of impact angle on central-peak/peak-ring formation and crater collapse on Venus (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: 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.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Lunar and Planetary Inst., Papers Presented to the International Colloquium on Venus; p 103-104
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  • 4
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    Impacts of free-floating objects: Unique Space Station experiments (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The transfer of momentum and kinetic energy between planetary bodies forms the basis for wide-ranging problems in planetary science ranging from the collective long-term effects of minor perturbations to the catastrophic singular effect of a major collision. In the former case, the evolution of asteroid spin rates and orientations and planetary rotation rates are cited. In the latter case, the catastrophic angular momenta and the near-global disruption of partially molten planets are included. Although the collisional transfer of momentum and energy were discussed over the last two decades, major issues remain that largely reflect current limitations in earth-based experimental conditions and 3-D numerical codes. Two examples with potential applications in a Space Station laboratory are presented.
    Keywords: ASTROPHYSICS
    Type: NASA, Lyndon B. Johnson Space Center, Experiments in Planetary and Related Sciences and the Space Station; 2 p
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  • 5
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    Debris-cloud collisions: Accretion studies in the Space Station (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The growth of planetesimals in the Solar System reflects the success of collisional aggregation over disruption. It is widely assumed that aggregation must represent relatively low encounter velocities between two particles in order to avoid both disruption and high-ejecta velocities. Such an assumption is supported by impact experiments and theory. Experiments involving particle-particle impacts, however, may be pertinent to only one type of collisional process in the early Solar System. Most models envision a complex protoplanetary nebular setting involving gas and dust. Consequently, collisions between clouds of dust or solids and dust may be a more relistic picture of protoplanetary accretion. Recent experiments performed at the NASA-Ames Vertical Gun Range have produced debris clouds impacting particulate targets with velocities ranging from 100 m/s to 6 km/s. The experiments produced several intriguing results that not only warrant further study but also may encourage experiments with the impact conditions permitted in a microgravity environment. Possible Space Station experiments are briefly discussed.
    Keywords: ASTROPHYSICS
    Type: NASA, Lyndon B. Johnson Space Center, Experiments in Planetary and Related Sciences and the Space Station; 2 p
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  • 6
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    Planetary impact experimentation (1987)
    In:  CASI
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    Publication Date: 2013-08-31
    Description: An understanding of impact processes in low- and microgravity environments would be advanced significantly by the construction and use of an impact facility on the Space Station. It is proposed that initial studies begin as soon as possible in ground-based impact laboratories, on the NASA KC-135 Reduced-Gravity Aircraft, and in existing drop towers. The resulting experience and information base could then be applied toward an experiment package designed for use on Shuttle orbiters to support pilot studies in orbital environments. These experiments, as well as the first efforts made on the IOC Space Station, should involve the impact of various free-floating targets; such studies would yield a substantial scientific return while providing valuable experience and engineering information for use in refining the design of the dedicated Space Station Impact Facility. The dedicated facility should be designed to support impact experimentation, including but not limited to cratering, asteroid and ring-particle dynamics, and accretional processes.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Experiments in Planetary and Related Sciences and the Space Station; 16 p
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  • 7
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    Recognizing impactor signatures in the planetary record (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Crater size reflects the target response to the combined effects of impactor size, density, and velocity. Isolating the effects of each variable in the cratering record is generally considered masked, if not lost, during late stages of crater modification (e.g., floor uplift and rim collapse). Important clues, however, come from the distinctive signatures of the impactor created by oblique impacts. In summary, oblique impacts allow for the identification of distinctive signatures of the impactor created during early penetration. Such signatures may further allow first-order testing of scaling relations for late crater excavation from the planetary surface record. Other aspects of this study are discussed.
    Keywords: GEOPHYSICS
    Type: Lunar and Planetary Inst., International Conference on Large Meteorite Impacts and Planetary Evolution; p 64-65
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  • 8
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    Timing of ancient extensional tectonic features on Mars (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Although numerous studies have delineated the Tharsis and post-Tharsis volcanic/tectonic history on Mars, only a few attempts have examined the earlier epochs. This is not an easy task since unambiguous crater ages for pre-Tharsis and early Tharsis units are difficult to determine owing to a variety of active surface processes. Ancient tectonic features, however, have a sufficiently large superposed crater population that should permit relative dating. A technique for crater counting along linear features analagous to areal crater density is proposed. A modification of this approach has been tested and applied to a variety of ancient tectonic features.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 474-475
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  • 9
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    Crater ejecta morphology and the presence of water on Mars (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The purpose of this contribution is to review the possible effects of projectile, target, and environment on the cratering process. The discussion presented suggests that contradictions in interpreting Martian crater ejecta morphologies reflect oversimplifying the process as a singular consequence of buried water. It seem entirely possible that most ejecta facies could be produced without the presence of liquid water. However, the combination of extraordinary ejecta fluidity, absence of secondaries, and high ejection angles all would point to the combined effects of atmosphere and fluid rich substrates. Moreover, recent experiments revealing the broad scour zone associated with rapid vapor expansion may account for numerous craters in the circum-polar regions with subtle radial grooving extending 10 crater radii away with faint distal ramparts. Thus certain crater ejecta morphologies may yet provide fundamental clues for the presence of unbound water.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 423-425
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  • 10
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    Early changes in gradation styles and rates on Mars (1987)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The wide annulus of massifs and knobs of Isidis and Argyre provided sufficiently large areas for meaningful crater statistics of large craters. Counts were made over adjacent and nested areas in order to test consistency and to derive relative age of each basin. Within the Isidis annulus, charateristic terrains provided counting areas for dating contrasting surface process: channeled hummocky terrain, etched terrains, and intermassif channeled plains. The channeled hummocky terrain contains a high channel density of narrow valley networks cutting both primary Isidis features and old craters. The etched terrains represent a broad region outside the inner high relief massifs of southwestern Isidis where numerous irregular plateaus, mesas, and relict craters indicate a different style of erosion. The intermassif channeled plains occur along the inner mountainous ring. Shallow meandering channels form a large integrated drainage system that is linked to numerous smaller intermountainous basins. These ponds and interconnected tributaries extend beyond the primary inner massif ring through broad canyons.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1986; p 416-417
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