JAROSITE AND FERRIHYDRITE TRANSFORMATION PRODUCTS IN NEAR-SATURATED MARTIAN BRINES

Recent data from Mars Exploratory Rovers and Mars Science Laboratory missions strongly supports the presence of near-saturated brines on the Martian surface, and past and current aqueous activity may be dominated by brines. Jarosite and ferrihydrite have also been detected alongside sulfate deposits in Meridiani Planum and Gale Crater. Ferrihydrite persistence on Mars is of particular interest as it is among the most abundant Fe-oxide phases in terrestrial environments but typically transforms to more thermodynamically stable dehydrated Fe-oxides. Previous studies of jarosite dissolution in near-saturated brines reveal that brines anion chemistry affects dissolution rate and prevents transformation of jarosite to more stable iron oxides. Similarly, we hypothesize that near-saturated brines may hinder the ferrihydrite dissolution and transformation to more thermodynamically favorable Fe-oxide phases such as goethite and/or hematite, preserving ferrihydrite on the surface of Mars. To determine the effect of anionic salt groups on ferrihydrite stability, we placed 2-line ferrihydrite in near-saturated solutions of varying chloride, sulfate, nitrate, carbonate, chlorate, and perchlorate concentrations, including near-saturated brines and mixed for a period of 30 days. Here we report the resulting XRD and Raman analyses of the transformation products from these mixtures, which serve as a simulation of ferrihydrite crystallinity and behavior in hypersaline, extraterrestrial environments such as those expected on Mars.