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

• Published in: Geophysical research letters Vol. 49; no. 21
• Main Authors: David, G., Dehouck, E., Meslin, P.‐Y., Rapin, W., Cousin, A., Forni, O., Gasnault, O., Lasue, J., Mangold, N., Beck, P., Maurice, S., Wiens, R. C., Berger, G., Fabre, S., Pinet, P., Clark, B. C., Smith, J. R., Lanza, N. L.
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.11.2022; American Geophysical Union
• Subjects: Acidic soils; Aluminium; Aluminum; amorphous hydrated sulfates; Amorphous materials; Astrophysics; ChemCam; Chemical analysis; Earth and Planetary Astrophysics; Hydration; Hydrogen; Hydrogeology; laser‐induced breakdown spectroscopy; Mars; Mars craters; Mars soil; Martian soils; Minerals; Moisture content; Olivine; Phases; Planets; Sciences of the Universe; Soil; Soil formation; Soil water; Sulfates; Sulfur; Sulphates; Sulphur; Water content; Weathering
• DOI: 10.1029/2022GL098755
• ISSN: 0094-8276

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. Plain Language Summary The study of Martian soils is of considerable interest as the nature of the mineral phases they contain, formed by the action of water for some of them, can give information on the past environments of the planet. Mineralogical analyses in Gale crater have shown that about one third of soils are composed of poorly crystalline materials whose nature remains unclear, and that soil hydration could be associated with these phases. Here, we use the chemical analyses from the ChemCam instrument to investigate the composition of the hydrogen‐bearing products, and we report for the first time the presence of sulfates in soils with this instrument. We demonstrate that sulfates are the main contributor to the water content of soils and are probably the source of the hydrogen and sulfur measured from orbit. The presence of sulfates and the lack of significant other secondary materials, especially enriched in aluminum, suggest that soils have probably undergone an acidic aqueous alteration with a low quantity of water, favoring the dissolution of olivine as the precursor to sulfates. Key Points The amorphous component of Gale crater soils contains hydrated sulfates The Eolian dust deposits are not the carrier of the identified hydrated sulfates Water‐limited acidic conditions may have led to the formation of these phases