Salty Environments: The importance of evaporites and brine environments as habitats and preservers of biosignatures

Abstract

The habitability of ancient Mars is directly related to the presence of late Noachian surface waters and their stability over geologic time. Evaporite minerals can capture and entomb organic matter, biological compounds, and intact cells within their intercrystalline and intracrystalline structure because they precipitate relatively quickly (Schopf et al. 2012). Additionally, evaporites can form macroscopic sedimentary structures understood to form in association with biological processes (e.g. stromatolites and other microbialites; Babel 2004, Braissant et al., 2008; Allwood et al. 2013). Thus, evaporite minerals constitute a target for biosignature investigation on Mars where evaporitic deposits have been observed by orbital CRISM spectroscopy (Viviano‐Beck et al. 2014). Such environments may be found in ice interfaces on Europa as well, where NaCl and Mg- rich sulfate salt minerals are thought to exist (Trumbo et al. 2019), and other ocean worlds. The purpose of this National Academy of Sciences white paper for the 2023-2032 Planetary Science and Astrobiology Decadal Survey is to highlight the strategic importance of evaporite minerals and brine settings on Mars and Europa as astrobiological targets of interest that would be able to contribute to future mission objectives. These are: A) Evaporite minerals can preserve intact fluids over geologic time, thereby recording ancient aqueous environments within the mineral matrices. B) Extant life can utilize preserved mineral fluids within micron-scale inclusion environments. C) Biosignatures from extinct life can also be preserved within fluid inclusions of evaporite minerals. D) Brine environments can support extant cellular life via depression of the freezing point of liquid water and by lowering eutectic temperatures. E) Both evaporites and brines offer radiation protection and long-term desiccation prevention allowing for extant life to potentially be maintained in modern Mars and Europa environments. F) Evaporite minerals are widespread globally across Mars and can benefit future Mars Sample Return mission objectives.