Volcanism or aqueous alteration on Mars?

摘要

The Mars Global Surveyor's Thermal Emission Spectrometer has identified two global spectral surface types in martian dark regions, which were initially interpreted as being of basaltic (type 1) and intermediate (type 2, basaltic andesite to andesite) volcanic composition. Wyatt and McSween suggest that northern-hemisphere occurrences of the type-2 spectrum are instead representative of weathered basalt, on the basis of ambiguity in the spectral interpretation and overlap between the distribution of this material and the outline of a putative ancient ocean. Although the spectral data may be open to interpretation within the limits of current understanding, creating weathered basalt and explaining its distribution is problematic. These competing hypotheses have significantly different implications for the igneous and aqueous history of Mars, and it is important to continue edbating the merits of each.