Mineralogy of the Light-Toned Outcrop Rock at Meridiani Planum as seen by Mini-TES

Introduction: The Opportunity rover landed in Eagle Crater in Meridiani Planum on January 24, 2004. Among the first images acquired included a light-toned rock that was the first outcrop observed from the surface of Mars. As seen in Pancam and Microscopic Imager images [1,2], the outcrop rock is layered, and portions exhibit fine-scale morphology similar to terrestrial ripple marks [3]. The outcrop rock is also the source of the nearly ubiquitous hematite-rich spherules, which can be seen eroding out of the outcrop [2,4]. Initial in-situ analyses of the rock by the Alpha Particle X-ray Spectrometer (APXS) showed high levels of sulfur correlated with magnesium, suggesting the presence of magnesium sulfates [5]. This result was confirmed by the Miniature Thermal Emission Spectrometer (Mini-TES), which has also seen evidence for calcium sulfates [6]. Additionally, measurements by the Mössbauer spectrometer have indicated that the outcrop is composed of ~10% jarosite, a ferric iron sulfate [7]. In this work, we expand on the initial Mini-TES analyses of the light-toned outcrop rock [6,8], using the results of the APXS and Möss-bauer instruments to constrain mineral deconvolution models. We also examine Mini-TES spectra of fines derived from the outcrop rock by application of the Rock Abrasion Tool (RAT) [9,10] and compare these spectra to that of the globally homogenous fines (GHF). Methods: [8] used factor analysis and target transformation techniques to determine the independently varying components in the scene viewed by Mini-TES at Meridiani Planum. Seven spectral shapes were derived including hematite, surface dust, basaltic sand, outcrop rock, two atmospheric shapes, and blackbody. A spectral library consisting of silicate, sulfate, and oxide endmembers was used to decon-volve the outcrop spectral shape. The deconvolution model was constrained by the results of previous analyses of APXS [5,11,12] and Mössbauer [7] data as well as Mini-TES observations of outcrop-derived fines. Specifically, three constraints were placed on the deconvolution model: (1) the natrojarosite end-member was forced to be ~10% of the total rock, based on estimates from the Mössbauer and APXS instruments [5,7,11], (2) the spectral contrast of Mg-and Ca-bearing sulfates were adjusted to take into account the Mg/Ca ratio available for placement in sulfates [11,12], (3) carbonates are not included in the library based on Mini-TES observations of outcrop-derived