Organic Adsorption onto Iron Hydroxide and Sulfide Minerals: Implications for Ceres Sample Return Analysis

Characterizing the past and present habitability potential of Ceres is an important goal of a future NASA mission to the dwarf planet. Signs of organic molecules (potentially amino acid, carboxylic acids, etc.) on the surface of Ceres may be present and potentially interacting with surrounding minerals. To understand the potential environmental conditions of Ceres, we have developed an experimental matrix to investigate if potential organic acids are able to adsorb onto minerals commonly found on similar systems (carbonaceous chondrites). The focus of this work is to understand the interaction between five organics (alanine, glycine, acetate, malic acid, and aspartic acid) on two minerals systems (iron sulfides and iron (hydr)oxides) in a Ceres-like environment. Our experiments revealed little to no adsorption of amino acids onto each of the Fe-mineral (Fe (oxy)hydroxides and Fe sulfides). Our results also revealed that the redox state of our Fe2+ and Fe3+ minerals precipitated with NaOH remained stable throughout the experiment, however Fe2+ and Fe3+ minerals precipitated with Na2S experiment reduction or were maintained as reduced Fe2+ species. This work shows that organic acids remain mobile and may be used for further reactivity towards other complex molecules with astrobiological relevance.