Soil mineralogy and chemistry on Mars - Possible clues from salts and clays in SNC meteorites

摘要: Abstract All subgroups of the shergottite, nakhlite, and chassignite (SNC) meteorites contain traces water-precipitated minerals that include various combinations carbonates, sulfates, halides, ferric oxides, aluminosilicate clays preterrestrial origin. Traces sulfur- chlorine-bearing aluminosilicates, which suggest possible affinities with scapolite minerals, occur in one shergottite but might be products shock-metamorphic reactions rather than aqueous precipitation; even so, they are subordinate to discrete sulfate carbonate clearly If SNC parent planet is Mars, as previously inferred from independent evidence, precipitates indicate oxidizing, water-based solutions probably have been chemically active on Mars for at least time interval represented by radiometric ages meteorites, namely, past 200–1300 million years (myr). Those included chemical elements H, C, O, P, S (N has not yet found among salts), although inorganic apparently predominated over organic products. The 13C/12C ratios carbonates satisfactorily explained without requiring oxidation 12C-rich matter. Further detailed mineralogical stable-isotopic studies secondary help establish limits biological activity Martian chemistry 1300 myr. A mixture SNCs, comprising smectite, illite, and, gypsum (with minor halite ± calcite hematite), provides a self-consistent, though unique, model bulk elemental composition surface sediments Viking Lander sites. Among other implications, smectite-illite lends support previous hypothesis catalytic action clay was responsible surprising reactivity discovered biology experiments. smectite-ellite-salt also compatible visible infrared spectrophotometry dust while neither nor excluding components.