Clay Minerals Investigation along the Martian Crustal Dichotomy to Assess Aqueous Conditions on Early Mars

On Mars, the crustal dichotomy marks the boundary between the old cratered highlands and the lowlands. Infrared datasets reveal several sites with extensive clay-bearing deposits therein, indicating widespread aqueous conditions on early Mars 1. Here we examine hyperspectral data to better characterize the near-infrared signatures of clay deposits, and verify an eventual mixture with carbonates. We investigate outcrops located in key regions located along this boundary, and compare them with carefully selected terrestrial analogs to follow-up and complement recent studies e.g., 25. Such outcrops are valuable targets to seek traces of past or present life on the planet, as clay minerals are known to store organic compounds 6. Knowing the exact positions of absorption band centers in the near-infrared spectra is crucial to ascertain possible species present in these outcrops, and search for changes in clay mineralogies. Variations observed between the targeted clay deposits suggest subtle changes in the iron and magnesium content, or even the oxidation state of iron 7. Mineralogical similarities observed in most regions suggest that clay deposits (i.e., ferrosaponites, vermiculites) may share a common weathering history. Conversely, nontronites extensively detected near Mawrth Vallis and its surroundings indicate different formation and alteration conditions. Nonetheless, the region may have shared a common aqueous history with other deposits found elsewhere on the planet, and then diverged to form more leached or oxidized clays with Al,Fe-rich compositions 8. Additionaly, the coprecipitation of clays and carbonates throughout the outcrops further strengthens the exobiological potential of the selected regions, where biosignatures might still be preserved. This work is in context with the ExoMars rover mission, planned to deploy the Rosalind Franklin rover to explore Oxia Planum. ExoMars rover will investigate clay deposits in surface and subsurface to search for signs of life on the planet, as biosignatures might still be preserved therein 6. This work is funded by the Italian Space Agency (ASI) Grant ASI-INAF n. 20233HH.0. References 1 Carter et al. (2013) JGR Planets, 2 Brossier et al. (2022) Icarus, 3 Brossier et al. (2023) PSJ, 4 Brossier et al. (under review) PSS, 5 Mandon et al. (2021) Astrobiology, 6 Vago et al. (2017) Astrobiology, 7 Michalski et al. (2015) EPSL, 8 Carter et al. (2015) LPSC Abstracts.