Spectral evidence for the mineralogy of high-albedo soils and dust on Mars

摘要: Because of the lack direct mineralogic data available for Mars, spectral remote sensing techniques and, in particular, earth-based reflectance spectroscopy remain primary source this information. Presented here are laboratory observations which further constrain mineralogy and origin high-albedo soils dust. Earth-based show spectra classical bright regions to be fairly uniform, with a strong Fe3+ → O2− charge transfer absorption edge extending from near UV through visible. This is relatively smooth, unlike those observed crystalline ferric oxides have superimposed crystal field bands. Dilution oxide spectrally more neutral medium (montmorillonite) weakens absorptions together does not serve make spectrum Mars-like (smoother). Nontronite (ferric-iron-bearing smectite clay) was also investigated agreement telescopic observations. Pure nontronite has analogous but different oxides. As previous case, very distinct inappropriate Mars. Admixture neither montmorillonite nor serves improve spectrum. The conclusion that major component martian soils, although presence other iron-poor clays cannot totally excluded based on currently observational data. best analogs known soil dust specific type palagonite Hawaii: X-ray amorphous weathering products mafic volcanic glass. indication therefore iron Mars likely occur poorly defined crystallo-graphic sites such as found these materials. These materials form slowly under semiarid conditions at ambient temperature. Even low-temperature hydrothermal alteration glass might provide enough ion mobility favor some formation over gels may mechanism responsible Hawaiian exist metastably thousands years Earth. Similar would expected survive considerably longer present cold dry climatic conditions.