Evidence for Amorphous Sulfates as the Main Carrier of Soil Hydration in Gale Crater, Mars

Abstract

Understanding the genesis of Martian soils is important to constrain the hydrogeologic history of the planet. Soils have the potential to record paleoenvironmental conditions, through the nature of secondary minerals formed during weathering. In situ X-ray diffraction analyses in Gale crater have revealed that about one third of each soil sample is composed of amorphous materials containing hydrated phases. Here, we use the geochemical data from the ChemCam instrument to investigate the nature and origin of the hydrated amorphous phases. We report for the first time with ChemCam clues for the presence of sulfates within the amorphous component of soils. We show that sulfates are the main carrier of the soil hydration and possibly explain the nature of hydrogen and sulfur measured from orbit. These sulfates and the apparent lack of significant Al-bearing weathering products are consistent with a model of soil formation including weathering of olivine in water-limited acidic conditions.