The habitability of 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 distinct martian environments. In: European Astrobiology Network Association EANA 2023, 19-22 Sep 2023, Madrid.

URL: http://www.eana-net.eu/index.php?page=Conferences/...

Abstract

The habitability of martian waters would have been partially determined by the chemistry arising from interactions with the local geology. Therefore, the varied lithologies detected by landers and rovers across Mars could have significant consequences for their proposed habitability and the resultant potential formation of biosignatures. In this study, the habitability of fluid chemistries from three distinct martian lithologies was investigated (basaltic, iron- and sulfur-enriched). A consortium of microbes, enriched from a terrestrial Mars analogue environment and previously shown to grow under simulated martian conditions, was used to inoculate the three fluid chemistries. Abiotic experiments were also simultaneously conducted for comparison. The impact 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 habitable and supported microbial growth, with significant differences in cell abundance between the distinct chemistries; however, the same genera dominated (Acetobacterium, Desulfovibrio and Desulfosporomusa) regardless of initial fluid. Significant differences were universally observed between the fluid and precipitate chemistries of the biotic test groups relative to the abiotic test groups, with the presence of microbes enhancing the concentration of aluminium and sulfidic minerals and eliminating sulfate in solution. However, extrapolation of the experimental fluid chemistries under abiotic conditions over geological timescales identified shifts in chemistry that were shared by the biotic test groups – indicating that whilst metabolic activity may enhance the rate at which specific changes occur, they are not exclusively biological in origin. This exemplifies the difficulty identifying unambiguous biosignatures and highlights the importance of combining experimental and modelling approaches when doing so.