Assessing Martian bedrock mineralogy through “windows” in the dust using near-infrared and thermal infrared remote sensing

1Jason C.Lai,2Briony Horgan,1James F.Bell III,1Danika F.Wellington
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2019.01.019]
1School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
2Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN, USA
Copyright Elsevier

Much of Mars’ surface is mantled by bright dust, which masks the spectral features used to interpret the mineralogy of the underlying bedrock. Despite the wealth of near-infrared (NIR) and thermal infrared (TIR) data returned from orbiting spacecraft in recent decades, the detailed bedrock composition of approximately half of the Martian surface remains relatively unknown due to dust cover. To address this issue, and to help gain a better understanding of the bedrock mineralogy in dusty regions, Dust Cover Index results from the Mars Global Surveyor Thermal Emission Spectrometer (TES) and analysis of images from the Mars Reconnaissance Orbiter Mars Color Imager (MARCI) were used to identify 63 small localized areas within the classical bright dusty regions of Arabia Terra, Elysium Planitia, and Tharsis Montes as potential “windows” through the dust; that is, areas where the dust cover is thin enough to permit infrared remote sensing of the underlying materials. The mineralogy of each candidate window was inferred using spectra from the Mars Express Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activité (OMEGA) NIR spectrometer and, where possible, TES. Twelve areas of interest returned spectra that are consistent with mineral species expected to be present at the regional scale, such as high- and low-calcium pyroxene, olivine, and iron-bearing glass. Distribution maps were created using previously defined index parameters for each species present within an area. High-quality TES spectra, if present within an area of interest, were deconvolved to estimate modal mineralogy and to support NIR interpretations. OMEGA data from Arabia Terra and Elysium Planitia are largely similar and indicate the presence of high-calcium pyroxene with significant contributions of glass and olivine, while TES data suggest an intermediate between the established compositions of the southern highlands and Syrtis Major. Limited data from Tharsis are consistent with low-calcium pyroxene mixed with lesser amounts of glass and high-calcium pyroxene. TES data from southern Tharsis correlate well with the previously inferred compositions of the Aonium and Mare Sirenum highlands immediately to the south. Of particular note is the detection of iron-bearing glass as a significant component of all three analyzed regions, especially in Tharsis. Overall, the underlying compositions of the classically dust-covered regions of Mars appear consistent with the compositions of adjacent and other low-albedo (not dust covered) regions of the planet identified in previous studies, with the noted contribution from iron-bearing glass.

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