CRISM Findings after One Mars Year in Orbit

CRISM has operated for one Mars year in orbit, and has returned over 8000 high-resolution (20-40 m/pixel) targeted observations, mapped nearly 60% of the planet at reduced spatial resolution (200 m/pixel), and monitored spatial and temporal variations in atmospheric trace gases and aerosols. The major discoveries regarding surface composition are that aqueous alteration was more widespread and diverse than previously thought. (1) Phyllosilicates occur as thousands of outcrops distributed throughout Noachian crustal units. There are different classes of phyllosilicate-containing deposits: massive exposures in crater walls and central peaks and the walls of Valles Marineris, compositionally stratified deposits in Nili Fossae and Mawrth Vallis, and intracrater fans. A wide variety of mineralogies is observed, suggesting a variety of environments and intensities of alteration of the early crust by liquid water. (2) Sulfate-containing layered materials in Valles Marineris exhibit unexpectedly fine compositional stratification. Interbedded sulfates in differing hydration states occur as layers as thin as tens of meters, sometimes in a repeating sequence. In some locations the sulfate-rich beds exhibit enhanced signatures of crystalline ferric minerals, and ferric minerals are concentrated by mass wasting processes to form the hematite concentrations observed by TES. These observations suggest variations in the depositional environment on geologically short time scales, and significant effects of subsequent erosion and redeposition. (3) A third major type of aqueous mineralogy, hydrated silica, has been found in widespread thin, light-toned, Hesperian-age layers on the plateau surrounding Valles Marineris. Some layers exhibit hydrated sulfates suggesting formation of the silica in an acidic environment. (4) Restricted thin layers of carbonate have been located in and around the Nili Fossae region, stratigraphically above the phyllosilicates and in close spatial association. The deposits are too limited to hold a massive ancient atmosphere, but their preservation indicates that subsequent sulfate- forming acidic aqueous environments were not sufficiently widespread to destroy all pre-existing carbonates. (5) Most recently a number of closed basins in the highlands, in both craters and intercrater plains, have been found to contain phyllosilicates or silica interbedded with or in close association with evaporites including sulfates and material interpreted from THEMIS data as chlorides. These may represent a variety of alluvial or lacustrine deposits.