The habitability of water from distinct martian environments

Macey, Michael; Ramkissoon, Nisha; Baharier, Bea; Steele, Andrew; Kucukkilic-Stephens, Ezgi; Stephens, Ben; Schwenzer, Susanne; Pearson, Victoria and Olsson-Francis, Karen (2023). The habitability of water from distinct martian environments. In: ASB9: Celebrating 20 Years of the Astrobiology Society of Britain, 7-8 Sep 2023, Clore Management Centre, Birkbeck, University of London.



The habitability of fluids in martian aqueous environments would have been partially determined by the chemistry arising from interactions with the local geology. Therefore, the varied lithologies detected across Mars could have significant consequences for their proposed habitability and the resultant potential for biosignature formation. In this study, habitability and associated biosignature formation was investigated for simulated martian fluid chemistries. These fluid chemistries were derived from three distinct martian lithologies, 1) Rocknest (basaltic), 2) Paso Robles (SO4+-enriched) and 3) Haematite Slope (Fe3+-enriched). A consortium of microbes, enriched from a terrestrial Mars analogue environment and shown to grow under simulated martian chemical conditions, was used to inoculate these fluid chemistries. Abiotic experiments were simultaneously conducted for comparison. The influence of the fluid chemistries on the microbial community was assessed by cell counts and sequencing of 16S rRNA gene profiles. Associated changes to the fluid and precipitate chemistries were examined using ICP-OES, IC, Raman spectroscopy, and SEM-EDS. Changes in chemistry over geological timescales were modelled using CHIM-XPT. All three fluid chemistries were able to support microbial growth, and significant differences were observed in cell growth and abundance between the distinct chemistries; however, the same bacterial genera dominated (Acetobacterium, Desulfovibrio and Desulfosporomusa) regardless of the initial fluid chemistry. Differences were observed between the biotic fluid and precipitate chemistries compared to the abiotic test groups, with microbes eliminating sulfate in solution and enhancing the concentration of aluminium and sulfidic minerals in the formed precipitate. However, modelled extrapolation of the fluid chemistries under abiotic conditions over geological timescales identified shifts in chemistry that were shared by the biotic test groups in the experimental work. This result indicates that whilst metabolic activity may enhance the rate at which specific changes occur, they are not exclusively biological. This exemplifies the difficulty of identifying unambiguous geochemical biosignatures and highlights the importance of combining experimental and modelling approaches.

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