Author name: Harry Y. McSween Jr.

The Martian surface is dominated by primary igneous minerals common in basaltic rocks. Limited chemical alteration exists in fine-grained dust, and is likely in sands and rocks at high latitudes and in the northern lowland plains where materials have interacted with ice and snow. Evidence for extensive production of secondary phases is revealed at higher spatial resolutions, where alteration effects of unique, and perhaps time-limited, aqueous environments are observed. The distribution of ice on Mars thus appears to have a global influence on the production of alteration materials, whereas the effects of water are discovered in unique and locally diverse geological settings.

Water on Mars exists at the poles and in the subsurface. It has interacted with crustal rocks, providing geomorphological, geochemical, and mineralogical insights into Mars’ geological history and inferences about its biological potential. The roles of water are revealed through studies of altered materials using orbiting-spacecraft imagery and spectroscopy, instruments mounted on rovers, and laboratory measurements on Martian meteorites.