Rock spectral classes observed by the Spirit Rover’s Pancam on the Gusev Crater Plains and in the Columbia Hills

Abstract

This paper examines the ferrous and ferric iron mineralogy of rocks inferred from 246 visible/near-infrared (430–1010 nm) multispectral observations made by the Mars Exploration Rover Spirit’s Pancam on its traverse from its landing site to its second Winter Haven location. Principal component, correspondence analyses, and a sequential maximum angle convex cone technique were used to identify 14 candidate classes. Spectra from the West Spur of Husband Hill and the Watchtower area had the highest 535 and 601 nm band depths indicating that these areas were more oxidized. Differences in the depth and band center of a near infrared (NIR) absorption feature were observed using 904 nm band depth and 803:904 nm ratio and parameters gauging the 754–864 and 754–1009 nm slopes. Spectra of rocks from the southern flank of Husband Hill had negative 754–1009 nm slopes and a broad NIR absorption consistent with high olivine abundances. Rocks observed on the lower West Spur, at the Cumberland Ridge locale, at the Husband Hill summit, and at the Haskin Ridge locale had deep 904 nm band depths and steep 754–864 nm slopes consistent with greater pyroxene abundances. These observations are consistent with results on iron-bearing mineralogy from Spirit’s Mo¨ssbauer spectrometer. Comparisons of these rock spectral classes with a set of terrestrial analog samples found similarities between the West Spur and Watchtower classes and red hematite-bearing impact melts. Fewer similarities were found in comparisons of the Columbia Hills classes with basaltic hydrovolcanic tephras.