VISIBLE TO SHORT-WAVE INFRARED SPECTRAL ANALYSES OF MARS FROM ORBIT USING CRISM (Invited Presentation)

Visible to short-wave infrared hyperspectral observations from the Mars Reconnaissance Orbiter by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) have revolutionized knowledge of the primary and secondary mineralogic compositions of the Martian surface and the history of aqueous environments recorded by its secondary mineralogy. The data reveal the crust primarily to be igneous in composition as had previously been thought. Composition of volcanic materials transitioned from a lower- to higher-calcium composition in the early Hesperian period. The deepest exposed crust consists of differentiated plutonic materials. Ground truth from rovers complements the orbital data in understanding aqueous alteration and the environments recorded by secondary minerals. The crust was altered lightly but pervasively – almost certainly in the subsurface – to smectite clays mostly of Fe/Mg-rich composition, and locally to an Al-rich composition where soluble ions have been removed. Higher-temperature alteration occurred regionally, in association with impact basins and tectonic deformation. Carbonates formed in a variety of environments; the total inventory of sequestered carbon is an area of active research. Aqueous alteration at the surface was most pronounced during the late Noachian period when regionally extensive pedogenic layers formed, and clastic sediments and evaporites (including sulfates and chlorides) were deposited in lacustrine environments. Surface waters became progressively more acidic over time, and the youngest large evaporite-containing deposits are rich in sulfates that formed in lacustrine, groundwater, and/or subglacial environments.