NEW PERSPECTIVES ON MARS SURFACE MINERALOGY FROM THE INFRARED IMAGING

The OMEGA imaging spectrometer on the Mars Express (MEX) spacecraft has been gathering data relevant to the mineralogy of the martian surface since January, 2004. OMEGA has a wavelength range of 0.35 to 5.1 µm in 352 spectral bands and a spatial resolution between 0.3 and 4.8 km/pixel as a function of the elliptical orbit of MEX. The visible through near-infrared wavelength region is sensitive to a range of minerals including iron-bearing and hydrated silicates, carbonates, and sulfates. Here we report on the first results of the OMEGA observations. Relative abundances of mafic silicates (olivine, pyroxene) show spatial variation. High-calcium pyroxene-bearing materials, typically with a component of low-calcium pyroxene (LCP), are commonly observed in low albedo volcanic regions of Hesperian age. Regions of high concentrations of LCP are typically restricted to small outcrops in older, Noachian terrains. High olivine abundances have been found in crater floors in Lunae Planum, in crater rims in the southern highlands, and associated with volcanic rocks in and around Syrtis Major. Deposits with hydrated silicates have been identified on the basis of hydration bands at 1.4 and 1.9 µm, and sharp metal-OH bands in the 2-2.5 µm region. Nontronite is clearly identified by a distinct 2.28 µm band, while other clays and phyllosilicates are suggested by weak or non-unique absorptions. Sulfates have been identified on the basis of a number of distinct vibrational overtones in the 1-2.5 µm region. Kieserite is characterized by distinct 1.5, 1.9, and 2.4 µm bands. Gypsum has also been identified on the basis of its unique spectral properties. Sulfates typically occur in two types of deposits: associated with small deposits of light-toned layered materials such as in Valles Marineris, or as massive regional layered deposits in Aram Chaos, Arabia, and Meridiani Terra. However, not all light-toned layered deposits show evidence for sulfate. Hydrated silicates are commonly associated with both regional and local sulfate deposits. These first results show that visible-near infrared spectroscopy will significantly advance our understanding of surface mineralogy, complementing existing databases and providing a rich resource for furthering our understanding of Mars and its evolution.