Mastcam Multispectral Results from Vera Rubin Ridge and Laboratory Studies to Support and Enhance the Interpretation of Multispectral Data from the Curiosity rover

Abstract:

Mastcam multispectral observations have been instrumental in understanding mineralogical variations throughout the traverse of the Mars Science Laboratory mission’s Curiosity rover in Gale crater, especially during exploration around Vera Rubin ridge (VRR), a light-toned resistant unit interpreted from orbital remote sensing to have a strong hematite spectral signature. To help interpret trends found between Mastcam multispectral data and CheMin derived mineralogic compositions of drilled targets below and on VRR, we acquired new laboratory spectral data on powdered mineral mixtures. These mixtures had various abundances of phyllosilicate (nontronite), plagioclase, and pyroxene (augite), and also had a constant 5 wt.% red hematite, consistent with the range of CheMin-measured mineral abundances in this region. Both the new lab mixtures and the Mastcam multispectral data showed a strong positive correlation between the abundance of phyllosilicates and the depth of the ~860 nm spectral absorption feature. Further, modeling of these mixtures confirmed that the depth of the ~860 nm absorption can increase without changing the abundance or grain size of red hematite. We also made mixtures where all mineral abundances were constant, but the hematite grain size was varied. Results showed that the ~860 nm band depth increased with decreasing grain size. However, the mixture with the largest hematite grain size (90-150 µm) did not have an 860 nm absorption feature, but instead exhibited a band minimum at ~920 nm. It was not until the hematite grain size was <45 microns that the band minimum shifted to ~860 nm. Understanding potential mineralogical and grain size constraints on observed Mastcam absorption features is critical for understanding the possible mineralogy of rocks in areas where we do not have CheMin measurements.