VNIR SPECTRAL CLASSES OF ROCKS IN THE COLUMBIA HILLS, GUSEV CRATER, MARS AS OBSERVED BY THE MARS EXPLORATION ROVER SPIRIT

In its extended mission, the Mars Exploration Rover (MER) Spirit has been conducting a detailed examination of the Noachian-aged Columbia Hills. These hills represent a geologic province distinct from the younger basalt-dominated plains that the rover traversed for the first 158 sols of its mission. Among the instruments in its Athena science payload is the Pancam, a multispectral stereo camera that covers the VNIR (430 to 1010 nm) spectral range. The Pancam has 11 unique channels for multispectral analysis. Multispectral analyses have been conducted of scenes collected from the Gusev crater plains and in the Columbia Hills. The results of these analyses indicate distinct spectral classes of rocks. These spectral classes largely correspond with classes that have been determined from in situ chemical analyses with Spirit's APXS and Mössbauer spectrometers as well as from its thermal emission spectrometer (Mini-TES). The rocks that compose the West Spur of Husband Hill have VNIR spectral features consistent with basaltic tuffs collected from terrestrial tuff cones. Rocks on Husband Hill, including in situ outcrops, have spectral features consistent with a higher fraction of crystalline phases- in some instances highly altered. Evidence for alteration includes the detection of higher fractions of Fe³⁺ - bearing minerals by both the Mössbauer spectrometer and by detection of increased 535 nm band depth by the Pancam. Implications and possible causes of this aqueous alteration will be discussed. The rover has also observed a number of erratic basaltic rocks and there is spectral and lithologic variability among this population of rocks as well.