Mineralogical Assessment of Volcanic Edifices on Mars Using Near- and Thermal Infrared Remote Sensing

Introduction: Many of the largest volcanoes on Mars are located in high-albedo regions. These regions are spectrally bright due to mantling by surface dust, which masks the absorption features used to infer mineralogy in both the nearand thermal infrared [1-3]. As a result, the classical martian bright regions of Arabia Terra, Elysium Planitia, and Tharsis remain uncharacterized in detail with respect to mineralogy [4]. However, there are localized areas within these dusty regions where the dust cover is removed at varying time scales to expose the dark underlying substrate. These areas can serve as “windows” through the dust, allowing us to obtain higher quality mineralogical information via nearand thermal infrared spectroscopy. Here we present examples of near-infrared mineralogical analyses of dust-free “windows” that are associated with volcanic edifices. Some of Mars’ largest volcanoes are located within very bright regions, including Alba Patera, Elysium Mons, Olympus Mons, and Tharsis Montes. Their capacity for erupting large amounts of material onto the martian surface as volcanic ash [5] or glass [6] in addition to lava flows makes understanding the composition of the crust at and near these locations critical for reconstructing the planet’s volcanic history. Methods: Dust-free surfaces were identified using two methods. The Dust Cover Index (DCI) derived from Thermal Emission Spectrometer (TES) data uses emissivity in the 1350 to 1400 cm -1 wavenumber region to determine the amount of dust present on Mars’ surface [7]. Because the atmosphere is transparent in this region, emissivity can be solely attributed to the particle size of the silicate minerals at the surface. TES pixels appearing in large dusty regions that also match the parameter constraints defined by the DCI were mapped and targeted for further analysis. The DCI is a static map, so an alternative method is needed to search for dust-free surfaces that are shorterlived. The Mars Color Imager (MARCI) takes repeated visible-wavelength images of most of the surface every Mars day, allowing us to make small regional mosaics that identify areas with time-variable albedo during short time intervals. Previously mosaicked and sequenced MARCI quadrangles were used to distinguish areas that undergo significant darkening due to dustclearing events [8].