Mineralogy of basaltic sands at Meridiani Planum from the Miniature Thermal Emission Spectrometer and comparison to orbital observations

Introduction: The Miniature Thermal Emission Spectrometer (Mini-TES) instrument aboard the Mars Exploration Rover Opportunity has been used to acquire thousands of spectra from the surface of Merid-iani Planum [1]. The Mini-TES measures thermal in-frared energy at a similar spectral resolution and range to that of the Thermal Emission Spectrometer (TES) aboard the Mars Global Surveyor orbiting spacecraft. This similarity between the two instruments provides a unique opportunity for detailed surface-to-orbit comparisons. In addition, complementary compositional information from the APXS and Mössbauer instruments are also available. This new combination of datasets will be used to refine the modal mineralogy of Meridiani basaltic sands and to evaluate the accuracy of mineral abundance determination from orbit. From orbit, basaltic sands dominate the spectral signature measured by TES both inside and outside of the hematite region in Meridiani Planum [2-4]. Globally , low-albedo regions are dominated by basaltic lithologies. Therefore, this work focuses on the basal-tic sands component of the landing site, and compares the emissivity and derived mineralogy of basaltic sands from Mini-TES to derived surface emissivity and mineralogy of the Opportunity landing site and surrounding low-albedo surfaces with TES data. The Mini-TES data used in this work is a single basaltic sand endmember that was previously derived by [5]. Glotch et al. [5] applied factor analysis and target transformation techniques to the Mini-TES dataset acquired between Sols 1-350, and found that seven independently-varying endmember components are present in that dataset. These are: hematite, sil-ica/sulfate-rich outcrop, basaltic sand, fine-grained dust, two atmospheric dust opacity shapes, and black-body. The derived basaltic shape should be free of influence from dust, outcrop, and hematite components , unlike previous studies of basaltic sands using Mini-TES [1,6]. Methods: To estimate the modal mineralogy from TES spectra measured from orbit, and from the basal-tic endmember derived by [5], we employ linear least squares fitting techniques similar to that of Ramsey and Christensen [7] with a spectral library composed of common igneous and secondary minerals. Least squares fitting is performed in three different ways: (1) iterative removal of negative percentages until only positive percentages remain in the solution [7-8], (2) same as (1), except that small (<2%) negative percentages are allowed to remain in the solution until the last