Orbital and In Situ Investigation of the Bagnold Dunes and Sands of Forvie, Gale Crater, Mars

Abstract

The Bagnold linear dune field investigated by Curiosity at Mount Desert Island (MDI) is north of the ∼5.5 km high Aeolis Mons mound in Gale crater. False-color images (RGB: 2.496, 1.802, and 1.237 μm, respectively) generated from Mars Reconnaissance Orbiter Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data show the dune field has a reddish-brown color. The Sands of Forvie (SoF), located ∼2.5 km to the southeast of MDI, is darker and lacks the reddish-brown color. Single scattering albedo (SSA) spectra retrieved at 12 m/pixel using along-track oversampled CRISM observation FRT00021C92 show a long wavelength (1.7–2.5 μm) increase in albedo for MDI dunes. For the same wavelength interval, SoF is characterized by a broad ∼2.2 μm absorption feature, consistent with color differences between the two deposits. Checkerboard un-mixing of the SSA image cube was used to isolate spectral endmembers within the MDI and SoF deposits. Radiative modeling of these CRISM spectral endmembers using Hapke (2012, https://doi.org/10.1017/CBO9781139025683) theory implies finer grain sizes, more pigeonite, plagioclase, and olivine, and less basaltic glass and augite for MDI as compared to the SoF deposit. These results are consistent with Curiosity-based observations that MDI contains smaller ripples with overall finer grains, whereas SoF has large ripples with coarser grains on the crests. Although these sand deposits are only located ∼2.5 km away from one another, wind and local topographic controls are interpreted to have modulated grain sizes and mineralogy.