Paper No. 140-12
Presentation Time: 4:50 PM
COMPOSITIONAL VARIATIONS IN SANDS OF THE BAGNOLD DUNES AT GALE CRATER, MARS, FROM VISIBLE-SHORTWAVE INFRARED SPECTROSCOPY AND COMPARISON TO GROUND-TRUTH FROM THE CURIOSITY ROVER
During its ascent to higher stratigraphic positions of Mount Sharp in Gale crater on Mars, the Mars Science Laboratory (MSL) Curiosity rover traversed the informally named “Bagnold Dune Field”. We report spatial variations in spectral properties and quantitative composition of sands, detected using Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) images, and investigate their spatial correlation with dust cover and sand transport flux, inferred from High Resolution Imaging Experiment (HiRISE) images. 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 novel 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 modeling the composition of minerals with solid solutions remains complex. We find an overall basaltic mineralogy but predict subtle spatial variations in composition due to size sorting of olivine, pyroxene, and plagioclase. Our model results also suggest that the most mature sands, which have experienced the largest cumulative transport distance, become preferentially enriched in mafic minerals. We find that large variations in sand Fe and Mg abundances (>~25 wt%) can occur over short distances, possibly through mixing with more proximal sand sources. Altogether, our estimates demonstrate a method for orbital quantification of compositional variability in active dune fields and provide key constraints for interpreting in situ measurements of the composition of Martian aeolian sandstones [Lapotre et al., JGR, submitted].