Salt Constructs in Paleo-Lake Basins as High-Priority Astrobiology Targets

Abstract

In extreme environments, microbial organisms reside in pockets with locally habitable conditions. Micro-climates conducive to the persistence of life in an otherwise inhospitable environment—“refugia”—are spatially restricted and can be micro- to centimeters in extent. If martian microbes are preserved in fossil refugia, this presents a double-edged sword for biosignature exploration: these locations will be specific and targetable but small and difficult to find. To better understand what types of features could be refugia in martian salt-encrusted basins, we explore a case study of two terrestrial habitats in salt-encrusted paleo-lake basins (salars): Salar Grande (SG) in the Atacama Desert and Salar de Pajonales (SdP) in the Altiplano Puna plateau of Chile. We review the formation of salt constructs within SG and SdP, which are the features that serve as refugia in those salars, and we explore the connection between the formation of salt constructs at the local scale with the larger-scale geologic phenomena that enable their formation. Our evaluation of terrestrial salars informs an assessment of which chloride basins on Mars might have had a high potential to form life-hosting salt constructs and may preserve biosignatures, or even host extant life. Our survey of martian salars identifies 102 salars in regions with a geographic context conducive to the formation of salt constructs, of which 17 have HiRISE coverage. We investigate these 17 martian salars with HiRISE coverage and locate the presence of possible salt constructs in 16 of them. Salt constructs are features that have may have been continuously habitable for the past ~3.8 Byr, have exceptional preservation potential, and are accessible by robotic exploration. Future work could explore in detail the mechanisms involved in the formation of the topographic features we identified in salt-encrusted basins on Mars to test the hypothesis that they are salt constructs.

Geomicrobiological characterization of the evaporitic ecosystem in the hypersaline lake Laguna Verde (Andean Puna, Northwestern Argentina)

“…Gypsum domes in Central Andes have been classified as either microbialites or endoevaporites (e.g. Farías et al., 2014 ; Herrero, 2019 ; Phillips et al., 2023 ). However, to date, no comprehensive studies have been conducted to identify if the gypsum formation is microbiologically influenced or is a purely chemical process.…”

“…At present, limited information is known about the role of microorganisms in gypsum precipitation (Farías et al., 2014 ; Fernandez et al., 2016 ; Herrero, 2019 ). Nevertheless, in recent years, microorganism ecosystems associated with gypsum deposits have gained great importance in relation to studies linked with the origin of life and astrobiology, due to their high potential to preserve biosignatures (Allwood et al., 2013 ; Phillips et al., 2023 ; Stivaletta et al., 2010 ).…”

“…GEMEs have been reported in shores of high‐salinity lakes in the Central Andes region, listed as (i) biofilms attached to the surface of minerals, where microorganisms extract water from them (Vignale et al., 2021 ); (ii) endolithic communities (endoevaporites), where minerals provide protection against desiccation and UV‐B radiation but allow photosynthetically active radiation (Vignale et al., 2021 ); or (iii) organo‐sedimentary structures (microbialites), formed by the dynamic interaction between microorganisms and the environment (Herrero, 2019 ; Phillips et al., 2023 ). Given its expanse and distinctive dome‐shaped structures that inhabit the lake, Laguna Verde stands out as a notable ‘endoevaporitic’ deposit in the Central Andes (see Vignale et al., 2021 ).…”

Translation as a Biosignature

“…Salinity exerts a major effect on the ability of an organism or a biomolecule to persist in a system: microbial activity can be detected throughout wide ranges of salinity levels and salt compositions, and biological structures such as intact cells and biomolecules can be preserved even beyond the saline limits for active life (Klempay et al, 2021;Oren, 2008). Thus, many have postulated that saline environments should be a major target for astrobiological exploration, given their biological relevance and presence throughout the solar system (Davila and Schulze-Makuch, 2016;Neveu et al, 2020;Pappalardo et al, 2013;Phillips et al, 2023). Although saline environments are biologically relevant, they can also pose challenges for conducting science in such environments.…”