The dominance of cold and dry alteration processes on recent Mars, as revealed through pan-spectral orbital analyses

Classic low-albedo regions of the martian surface are investigated using combined reflectance and emission ("pan-spectral") data to constrain the types of alteration mineral phases that are present at spectrally significant abundances (>10-15%). The lack of hydrated mineral species observed using near-infrared data suggests that anhydrous chemical alteration dominates at the regional scale. Spectral characteristics in the VNIR and TIR are consistent with those associated with weathering processes identified in the hyper-arid, hypo-thermal, and geologically stable McMurdo Dry Valleys of Antarctica, where oxidative weathering processes dominate and significant aqueous alteration does not occur. In addition, the spectral trends associated with oxidative weathering processes are similar to regional trends in VNIR spectral characteristics observed on Mars and potentially complicate the spectral interpretation of basaltic terrains. Collectively, these relationships suggest that the martian surface has been dominated by cold, dry, and stable conditions since the formation of these low-albedo regions. While significant at regional scales early in martian history, aqueous alteration appears to be predominantly absent from large-scale basaltic regions on Mars.