USING VISIBLE AND NEAR INFRARED MULTISPECTRAL IMAGERY FROM ROVER-BASED PLATFORMS TO DISTINGUISH ALTERED VOLCANIC TEPHRAS AND OXIDIZED MATERIALS

On sol 746 of its mission, the Mars Exploration Rover Spirit arrived at the approximately 80 m diameter low mesa known as Home Plate. Examination of the northwestern exposures of the layers making up Home Plate revealed a coarsely bedded lower unit and more finely bedded upper unit. A single bed sag feature was observed in the lower unit indicating plastic deformation generally associated with wet tephras produced by hydrovolcanic eruptions. A primary alteration pathway of hydrovolcanic tephras is palagonitization; however, examination of the Home Plate strata, both with Spirit's Mössbauer spectrometer and with the multispectral imaging of its Pancam indicated that the beds were poorly oxidized- inconsistent with any noticeable level of palagonitization. A plot of red-to-blue slope vs. reflectance peak position shows a correspondence of measurements of Rock Abrasion Tool (RAT) spots on the western Home Plate Barnhill unit with poorly oxidized (unpalagonitized) gray tuffs present at terrestrial hydrovolcanic features (tuff rings, tuff cones and sub-ice volcanic features). RAT spots measured on the eastern Home Plate Pesapallo unit have higher red-to-blue slopes than those types of terrestrial gray tuffs. The Pesapallo measurements are more consistent with minimally oxidized basaltic sands as observed elsewhere by both Spirit and Opportunity

Pancam measurements of 535 nm band depth are correlated with Mössbauer spectrometer measurements of Fe³⁺ / Fe_Total – a measure of the oxidation of the materials. Thus Pancam imagery has proven useful for determining the relative level of alteration of rocks encountered by Spirit, both at Home Plate and on Husband Hill. We will show how this capability will also be useful for the detection of oxidized, possibly phyllosilicate-bearing, materials encountered by Opportunity on the rim of Endeavor crater and also, through the use of its Mastcam, by MSL at its landing site.