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Early Mars Environments Revealed Through Near-Infrared Spectroscopy of Alteration Minerals


While unstable on present-day Mars, liquid water was an important geologic agent in Mars' past. This work investigates the nature and timing of aqueous processes on ancient Mars, focusing on the earliest epoch of Mars history, the Noachian (>3.7 Gyr), and strata bearing alteration minerals. This work seeks: (1) a refined understanding of what is knowable about past aqueous conditions based on remote visible/near-infrared (VNIR) analyses of altered surfaces; (2) a greater understanding of the changing habitability potential of Mars through time and, more broadly, (3) an increased understanding of aqueous environments during the first billion years of the evolution of a terrestrial planet. Orbital data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) VNIR imaging spectrometer were used to identify key minerals and characteristic mineral assemblages, including hydrated silicates and carbonates. Coupling mineral identifications with high resolution morphology to assess stratigraphic relationships allows constraining past environmental conditions. The findings herein point to temporally and spatially variable settings of aqueous alteration on ancient Mars, including lacustrine, near-surface leaching, and subsurface hydrothermal environments. This diversity indicates multiple potentially habitable environments early in Mars history. Terrestrial field and laboratory investigations of mineralogic determinations derived from VNIR spectroscopy versus other techniques show that (1) infrared spectroscopy correctly characterizes the mineralogy of rocks from Mars-analogue weathering and hydrothermal systems in Iceland and (2) quantitative abundances for simple mixtures of smectite clays with mafic minerals can be successfully estimated with Hapke and Shkuratov radiative transfer models in well-controlled laboratory settings. Presently employed VNIR quantitative analyses techniques are, however, challenged by multi-component mixtures with complex textures or multiple grain sizes. Qualitative remote VNIR mineralogic analyses can be used synergistically with ground-based analytical techniques such as microscopic imaging, x-ray diffraction and geochemical analyses to elucidate further details of alteration mineral formation conditions. The multiple environments of aqueous alteration revealed through VNIR study of Mars' ancient rocks represent key targets for future exploration.
Thesis (Ph.D. -- Brown University (2010)

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Ehlmann, Bethany, "Early Mars Environments Revealed Through Near-Infrared Spectroscopy of Alteration Minerals" (2010). Earth, Environmental and Planetary Sciences Theses and Dissertations. Brown Digital Repository. Brown University Library.