SPECTRAL ANALYSES OF MARS FROM ORBIT USING CRISM AND OMEGA

Visible to short-wave infrared (0.4–5.0 microns) reflectance spectroscopy has been a powerful tool to identify and map mineral groups on the Martian surface that reveal the planet's geologic evolution. The OMEGA instrument on Mars Express and then the CRISM instrument on the Mars Reconnaissance Orbiter have identified and mapped more than thirty mineral groups, revolutionizing previous understanding of Martian crustal composition and the role of water in altering it. From these data, and their analysis in the context of stereo and high-resolution imaging, the primary structure of the crust is revealed to be dominated by basalt, over a deep layer of segregated pyroxene- and olivine-rich plutons, with sparse feldspar-rich, differentiated intrusions. Martian volatile-bearing environments are revealed to have evolved through four phases: the pre-Noachian to early Noachian period when alteration by liquid water occurred near the surface and deep in the subsurface, in chemically neutral to alkaline environments that formed hydrated silicates and carbonates; the middle to late Noachian period when liquid water was widely present at the surface forming valley networks, lacustrine deposits, and clay-rich pedogenic horizons; the early Hesperian to early Amazonian period during which water became increasingly acidic and saline, forming deposits rich in sulfate salts, chlorides, and hydrated silica; and the Amazonian period when surface water has existed predominantly as ice, with only localized reaction with regolith and briny flow on the surface.