Compositional Variations in Sands of the Bagnold Dunes, Gale Crater, Mars, from Visible-Shortwave Infrared Spectroscopy and Comparison with Ground Truth from the Curiosity Rover

1M. G. A. Lapotre,1,2B. L. Ehlmann,3S. E. Minson,4R. E. Arvidson,1F. Ayoub,1A. A. Fraeman,5R. C. Ewing,6N. T. Bridges
Journal of Geophysical Research Planets (in Press) Link to Article [DOI: 10.1002/2016JE005133]
1Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
2Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
3USGS, Menlo Park, CA, USA
4Washington University in St. Louis, St. Louis, MO, USA
5Texas A&M University, College Station, TX, USA
6Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, USA
Published by arrangement with John Wiley & Sons

During its ascent up Mount Sharp, the Mars Science Laboratory Curiosity rover traversed the Bagnold Dune Field. We model sand modal mineralogy and grain size at four locations near the rover traverse, using orbital shortwave infrared single scattering albedo spectra and a Markov-Chain Monte Carlo implementation of Hapke’s radiative transfer theory to fully constrain uncertainties and permitted solutions. These predictions, evaluated against in situ measurements at one site from the Curiosity rover, show that XRD-measured mineralogy of the basaltic sands is within the 95% confidence interval of model predictions. However, predictions are relatively insensitive to grain size and are non-unique, especially when modeling the composition of minerals with solid solutions. We find an overall basaltic mineralogy and show subtle spatial variations in composition in and around the Bagnold dunes, consistent with a mafic enrichment of sands with cumulative transport distance by sorting of olivine, pyroxene, and plagioclase grains during aeolian saltation. Furthermore, the large variations in Fe and Mg abundances (~20 wt%) at the Bagnold Dunes suggest that compositional variability induced by wind sorting may be enhanced by local mixing with proximal sand sources. Our estimates demonstrate a method for orbital quantification of composition with rigorous uncertainty determination and provide key constraints for interpreting in situ measurements of compositional variability within martian aeolian sandstones.

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