Mathematics – Logic
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p51f..01m&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P51F-01
Mathematics
Logic
[1027] Geochemistry / Composition Of The Planets, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6225] Planetary Sciences: Solar System Objects / Mars, [6250] Planetary Sciences: Solar System Objects / Moon
Scientific paper
Planetary soils constitute micron to meter sized debris blankets covering all or parts of the surfaces of many planetary bodies. Recent results from the Martian surface, by the MER rovers and Phoenix lander, the Huygens probe at Titan and perhaps even the NEAR mission to asteroid 433 Eros suggest a continuum between classic planetary soils, such as those on the Moon, and conventional sediments, such as those on Earth. Controls on this variation are governed by complex interactions related to (1) impact and volcanic history, (2) presence and nature of atmospheres (and thus climate), (3) occurrence, composition and physical state of near-surface volatiles (e.g., water, methane), and (4) presence and nature of crustal tectonics, crustal evolution, and so forth. The Moon represents one extreme where surficial deposits result almost exclusively from impact processes. Absence of water and air restrict further reworking or transport on a significant scale after initial deposition. Disruption and mixing of lunar soils takes place but is related to impact gardening operating on relatively local scales and largely in a vertical sense; alteration is restricted to space weathering. The effect is that lunar soils are compositionally variable and match the composition of the crust in the vicinity of where they form. Thus lunar soils in the highlands are fundamentally different in composition than those on maria. Earth provides the other extreme where the highly dynamic geochemical and geophysical nature of the surface precludes preservation of classic planetary soils, although analogs may exist in ejecta blankets and eolian loess. Instead, a complex suite of sedimentary deposits form in response to chemical and physical weathering, erosion, transport and deposition by a variety of mechanisms involving water, wind, ice and biology. Although there is substantial sedimentary lithological differentiation (e.g., shales, sands, carbonates, evaporites), greatly influenced by the presence of large bodies of water, the composition of terrestrial sediments has long been used to estimate the average composition of exposed crust and to trace the evolution of continental crust. Martian surficial deposits fall between the lunar and terrestrial extremes. Martian surficial deposits formed by a much wider variety of geological processes than did lunar soils, including impact, volcanic, glacial, eolian and subaqueous processes. On the other hand, the nature of Martian tectonics and climate change resulted in many surfical deposits being very ancient, similar to the Moon. Martian soils exhibit variation in textural and mineralogical makeup and contain both clastic and chemical mineralogical components. On the other hand, there appears to be more limited sedimentary lithological differentiation than seen on Earth and Martian soils are of broadly similar chemical composition, although an influence from local geology is commonly observed. These compositions reflect the average composition of the Martian upper crust. Accordingly, subsequent mixing of surficial debris on the Martian surface, by highly variable combinations of eolian, glacial and impact gardening processes is of sufficient scale to minimize the variation in soil compositions.
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