The Nature of Hydrated Minerals on Mars: Linking Orbital and Rover Observations to Constrain the Climatic Evolution of Mars

Background: Orbital remote sensing observations over the past decade have shown Mars to host a great diversity of hydrous minerals, including clays, sulfates, zeolites, and opaline silica [1-3]. Though certain regions of Mars contain vast exposures of these minerals (e.g., clay minerals in Mawrth Vallis and Nili Fossae and sul-fates in the interior layered deposits of Valles Mari-neris), many of these mineral detections occur at much smaller spatial scales and are only observable at resolutions of tens to hundreds of meters. High-resolution imagery of these locations, such as that provided by the HiRISE, CTX, and MOC instruments, allows unprecedented analysis of the geomorphic setting of these minerals. The widespread occurrence of these hydrated minerals and the diversity of settings in which they occur [1] is profound, and it is now clear that Mars records a rich and complex history of water-rock interaction that spans billions of years. Perhaps most importantly, hydrous minerals and chemical precipitates can record information about pH, salinity, and redox conditions, which in turn can provide important constraints on aqueous geochemistry and atmospheric properties. However, it is important to understand if observed mineral assemblages reflect contemporaneous heterogeneity in local conditions or if they instead record global changes through time [e.g., 4]. Though in many ways we are in a golden era of Mars exploration, important questions remain as to how orbital information can be used to understand the geo-logic and climatic evolution of Mars as a whole. Our geologic knowledge of Earth was (and continues to be) built piece by piece through detailed field measurements at locations across the globe, supported by laboratory analyses and modeling. Our expectations for how we will unravel the mysteries of Mars should be no different. Detailed measurements and field campaigns at select locations are necessary to place orbital-scale observations in their proper geologic context, and in this regard the Spirit, Opportunity, and Curiosity rovers have been highly successful. Orbital assessments of mineralogy and morphologly were the driving factors in the selection of the MER and MSL landing sites, and these missions provide critical in situ observations that allow us to test hypotheses based on orbital remote sensing data. Hematite was observed in orbital TES data for Meridiani [5] and in CRISM data for Gale Crater [6], and both have been confirmed by independent in situ measurement techniques. However, the specific depositional environments in which these minerals occur could not be de-teremined …