Chloride salt-bearing deposits are widely distributed across the southern highlands of Mars. Because chloride salts are highly water-soluble, these deposits may be representative of the last significant period of stable liquid water at the Martian surface. Therefore, these deposits are key to understanding the fate and evolution of surface waters on Mars. Yet, little consensus exists about the formation conditions of these deposits, and their origins remain enigmatic. This is due in part because remote spectroscopic detection and quantification of many chlorides is hampered by a lack of easily discernible diagnostic absorption features. To address this issue, we present a novel Hapke radiative transfer model (RTM)-based method to estimate hydration states and salt abundances of Martian chloride salt-bearing deposits using visible/near-infrared (VNIR) reflectance spectra. VNIR laboratory spectra are used to derive water abundances of analog chloride-bearing materials, establishing an experimental basis for application of these methods to Mars. These methods are then applied to orbital Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data to create maps of hydration state and modeled salt abundance of chloride-bearing deposits. When overlain onto high resolution 3D digital terrain models (DTMs), these methods produce the highest resolution, site-specific salt abundance maps currently available, enabling new discoveries and understanding of geologic context. As an example, deposits in the Terra Sirenum region are observed to have higher estimated salt abundances than previously recognized, exhibiting spatial variations in both abundance and surface morphology.

Constraining the volatile budget of the lunar interior has important ramifications for models of Moon formation. While many early and previous measurements of samples acquired from the Luna and Apollo missions suggested the lunar interior is depleted in highly volatile elements like H, a number of high-precision analytical studies over the past decade have argued that it may be more enriched in water than previously thought. Here, we integrate recent remotely sensed near-infrared reflectance measurements of several Dark-Mantle-Deposits (DMDs), interpreted to represent pyroclastic deposits, and physics-based eruption models to better constrain the pre-eruptive water content of lunar volcanic glasses. We model the trajectory and water loss of pyroclasts from eruption to deposition, coupling eruption dynamics with a volatile diffusion model for each pyroclast. Modeled pyroclast sizes and final water contents are then used to predict spectral reflectance properties for comparison with the observed orbital near-infrared data. We develop an inversion scheme based on the Markov-Chain Monte-Carlo (MCMC) method to retrieve constraints between governing parameters such as the initial volatile content of the melt and the pyroclast size distribution (which influences the remotely measured water absorption strengths). The MCMC inversion allows us to estimate the primordial (pre-eruption) water content for different DMDs and test whether their source is volatile-rich. Our results suggest that the parts of the lunar interior sampled by the source material of the DMDs investigated in this study range in water content from 400 to 800 ppm.

Previous studies have shown that Mt. Sharp has stratigraphic variation in mineralogy that may record a global transition from a climate more conducive to clay mineral formation to one marked by increased sulfate production. To better understand how small-scale observations along the traverse path of NASA’s Curiosity rover might be linked to such large-scale processes, it is necessary to understand the extent to which mineral signatures observed from orbit vary laterally and vertically. This study uses newly processed visible-near infrared CRISM data and corresponding visible images to re-examine the mineralogy of lower Mt. Sharp, map mineral distribution, and evaluate stratigraphic relationships. We demonstrate the presence of darker-toned strata that appears to be throughgoing with spectral signatures of monohydrated sulfate. Strata above and below this zone are lighter-toned and contain polyhydrated sulfate and variable distribution of Fe/Mg clay minerals. Clay minerals are observed at multiple stratigraphic positions; unlike the kieserite zone these units cannot be traced laterally across Mt. Sharp. The kieserite zone appears to be stratigraphically confined, but in most locations the orbital data do not provide sufficient detail to determine whether mineral signatures conform to or cut across stratigraphic boundaries, leaving open the question as to whether the clays and sulfates occur as detrital, primary chemical precipitates, and/or diagenetic phases. Future observations along Curiosity’s traverse will help distinguish between these possibilities. Rover observations of clay-bearing strata in northwest Mt. Sharp may be more reflective of local conditions that could be distinct from those associated with other clay-bearing strata.