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  • 1
    Publication Date: 2011-08-24
    Description: Recent mapping studies west of Elysium Mons, Mars, have pinpointed subice features that suggest the existence of a frozen paleolake in Utopia Planitia as recently as 1.8 billion years ago. The subice features are interpreted to be hyaloclastic ridges and hills, table moutains, associated joekulhalaup deposits, and fluvial channels. Photoclinometric studies of these features and of a basal scarp around the northwest flank of Elysium Mons interpreted to have been an ice-sheet boundary indicate that the maximum thickness of ice within the basin may have been about 180 m. This thickness of ice during a relatively late stage of Martian geologic history would have important implications concerning the atmospheric, the climatic, and possibly the exobiologic history of the planet.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus (ISSN 0019-1035); 109; 2; p. 393-406
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  • 2
    Publication Date: 2011-08-24
    Description: Multispectral images of the lunar western limb and far side obtained from Galileo reveal the compositional nature of several prominent lunar features and provide new information on lunar evolution. The data reveal that the ejecta from the Orientale impact basin (900 kilometers in diameter) lying outside the Cordillera Mountains was excavated from the crust, not the mantle, and covers pre-Orientale terrain that consisted of both highland materials and relatively large expanses of ancient mare basalts. The inside of the far side South Pole-Aitken basin (greater than 2000 kilometers in diameter) has low albedo, red color, and a relatively high abundance of iron- and magnesium-rich materials. These features suggest that the impact may have penetrated into the deep crust or lunar mantle or that the basin contains ancient mare basalts that were later covered by highlands ejecta.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Science (ISSN 0036-8075); 255; 570-576
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  • 3
    Publication Date: 2011-08-24
    Description: Three images of Venus have been returned so far by the Galileo spacecraft following an encounter with the planet on UT February 10, 1990. The images, taken at effective wavelengths of 4200 and 9900 A, characterize the global motions and distribution of haze near the Venus cloud tops and, at the latter wavelength, deep within the main cloud. Previously undetected markings are clearly seen in the near-infrared image. The global distribution of these features, which have maximum contrasts of 3 percent, is different from that recorded at short wavelengths. In particular, the 'polar collar', which is omnipresent in short wavelength images, is absent at 9900 A. The maximum contrast in the features at 4200 A is about 20 percent. The optical performance of the camera is described and is judged to be nominal.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Advances in Space Research (ISSN 0273-1177); 12; 9, Se; 91-103
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  • 4
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: Recent findings concerning craters and cratering populations on the satellites of Jupiter and Saturn are discussed. Current understanding of cratering mechanics is reviewed with emphasis placed on scaling and ejecta and the differences between cratering in rock and ice. Evidence from crater statistics regarding cratering histories on various planetary satellites is discussed and connections are made with what is known about the cratering record on the terrestrial bodies. Consideration is given to the source populations and an attempt is made to summarize and critique the various scenarios that have been proposed for linking the cratering records on the various planets and satellites. It is noted that early Voyager Uranus results seem compatible with the present summary.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 5
    Publication Date: 2011-08-24
    Description: Available crater counts and their interpretations are reviewed, with emphasis on essential scaling considerations and comparisons with hypotheses developed for interpreting the cratering records on other planets and satellites. New approaches are employed to scaling based on new measurements of crater depths and morphology, which show craters in ice to be unexpectedly different from those in rock. It is found that the published crater counts on the Uranian satellites, despite mutual inconsistencies, can be interpreted as compatible with cratering by the heliocentric population of cometary bodies that was responsible for much of the cratering of the satellites of Jupiter and Saturn. Scaling arguments are applied to the catastrophic breakup of icy satellites and ring particles. The importance of large-scale collisions in disrupting the inner Uranian satellites is found to depend on the shape of the size distribution of cometary bodies at large sizes.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 6
    Publication Date: 2011-08-16
    Description: It is pointed out that Mars is especially well adapted to statistical studies of crater morphologies for deciphering its geological history. A framework for understanding planetary geomorphological histories from the diameter-frequency relations of different morphological classes of craters described by Chapmam et al. (1970) is extended in order to understand Martian cratering, erosional, and depositional history. The cratering-obliteration history derived is compared with global interpretations considered by Hartman (1973) and Soderblom et al. (1974). An idealized dust-filling model is employed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Icarus; 22; July 197
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  • 7
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    Publication Date: 2011-08-17
    Description: The paper deals with the physical and chemical nature of the asteroids and with their physical and orbital distributions and interrelationships. Existing hypotheses about the formation and evolution of asteroids are examined. A thematic synopsis of these topics is presented, and accepted interpretations are discussed.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 8
    Publication Date: 2011-08-17
    Description: Early descriptions of regoliths on small bodies were devised to account for observations of asteroids (Chapman 1971, 1976) and the gas-rich meteorites (Anders 1975). Lack of agreement between these approaches prompted Housen et al. (1978, 1979) to examine the problem in detail. The resulting model predicted that moderate-sized (100-300 km) asteroids should evolve regoliths up to a few kilometers deep which could be source regions of gas-rich meteorites. Smaller objects should have regoliths ranging from dust coatings to meters-thick layers depending on the strength of the object. The earlier model could not treat asteroids larger than 300 km in diameter. The model, now modified to treat larger-sized objects, predicts regolith depths, on asteroids larger than 300 km, which decrease with increasing size. A regolith depth of 7 m is predicted for the lunar maria in reasonable agreement with the observed depths of 5 m.
    Keywords: LUNAR AND PLANETARY EXPLORATION
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  • 9
    Publication Date: 2011-08-17
    Description: Contrary to popular belief, very large meteorites can be sufficiently slowed by aerodynamic drag to survive impact with the earth's surface provided that they enter the atmosphere at very low angles. This is a stringent requirement and survival probabilities for large, unguided objects are low; but they are not zero. Based on high-velocity impact experiments and published tabulations of the parameters of shallow angle entry trajectories, we estimate the probability of survival for an iron meteorite approximately the size and shape of the legendary Chinguetti meteorite (100 x 40 x 20-40 m) to be between 0.1 and 1 percent. Together with a limiting estimate of the flux of such bodies encountering the earth, this leads to an expected survival rate of one per (0.1-1.0) billion years on the earth's land surface.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: Smithsonian Contributions to the Earth Sciences; 14, 1; 1975
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  • 10
    Publication Date: 2013-08-31
    Description: The geologic mapping compiled at 1:500,000 scale of the northern Kasei Valles area of Mars (MTMs 25062 and 25067) indicates (1) at least three periods of Kasei Valles channeling, (2) the development of Sacra Fossae (linear depressions on Tempe Terra and Lunae Planum) in relation to Kasei channeling episodes, and (3) the nature of ridged plains material dissected by Kasei Valles on northern Lunae Planum. (The three channeling periods consists of two flood events and a later, sapping related event). These findings suggest hydrologic conditions and processes that formed Kasei Valles and associated features and terrains. It is concluded that an early period of flooding, whose source is perhaps buried beneath lava flows of Tharsis Montes, may have eroded streamlined features in northern Lunae Planum. Also, later floods originating from Echus Chasma formed after the initial flooding and the mesas adjacent to the plateau. The Sacra Fossae formed after the initial flooding and during the second flooding by sapping, outbreak, scarp retreat, and collapse along joints and fractures in ridged plains materials.
    Keywords: LUNAR AND PLANETARY EXPLORATION
    Type: NASA, Washington, Reports of Planetary Geology and Geophysics Program, 1990; p 138-139
    Format: application/pdf
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