Iceland and Mars-analogue hydrothermal environments

Previously, we talked about hydrothermal environments and settled the effective similarity between these systems and the Mars environment (Mars-analogue environments).

Mars-analogue environments — *Fig. 1 – Kerlingarfjöll and Kverkfjöll mountains in Iceland*;

According to this emergent research (dated 22 May 2021), the authors have analyzed geothermal pools in Iceland to expand their knowledge about potential Mars-analogue environments.

Vulcanoes in Iceland

Hydrothermal systems are one of the main environments on the Earth with the potential as “analogue” systems on Mars. These systems are able to support chemolithotrophic life; for this reason, they are a key target for astrobiological studies. This study is based on the analysis of water and sediment sampled in six geothermal pools from the rhyolitic Kerlingarfjöll and basaltic Kverkfjöll volcanoes in Iceland, to investigate hypothetical microbial communities.

The results show that the geochemistry of microbial communities is primarily controlled by deep volcanic processes, pool water pH, redox conditions and the external input derived by the melting of surrounding glaciers (regulating pools temperature). There is robust evidence about the existence of Mars-analogue hydrothermal systems, with similar volcanic processes that can be studied as possible transient environments for life on Mars. This study is an interesting starting point for the field of astrobiology.

Kerlingarfjöll pools was characterized by:

reductive conditions;
CO₂-rich waters;
authigenic calcite-, pyrite- and kaolinite-bearing sediments;
Dominant metabolisms: methanogenesis, respiration of sulphate and sulphur (S) oxidation;

Kverkfjöll pools was characterized by:

oxidate conditions;
acid water (pH < 3);
high concentrations of SO₄^2-;
high argillic alteration: Al-phyllosilicate-rich sediments;
Dominant metabolisms: iron oxidation, sulphur oxidation and nitrification;

Martian hydrothermal environments

In Kerlingarfjöll and Kverkfjöll pool chemistries, the major differences in pH and temperature can be explained by acid supply and the ratio of geothermal steam to snowmelt; most importantly, hot springs provide a useful example of how hydrothermal systems are a localized source of metabolic redox pairs for chemolithotrophic microorganisms; these conditions are fundamental of microbial life and metabolism as potentially prebiotic chemistry. On Mars, the presence of S and Fe on the surface suggests S and Fe-driven metabolisms that can characterize Martian hydrothermal systems. Above all, the results from these studies will be used for the detection of microbial biosignatures that are also measurable at the Martian surface (using rover-based instruments). In conclusion, the study has demonstrated how hydrothermal pools are relevant for understanding past Martian hydrothermal environments.

Sources: Moreras-Marti A, Fox-Powell M, Zerkle AL, et al. Volcanic controls on the microbial habitability of Mars-analogue hydrothermal environments. Geobiology. 2021;19:489–509. https://doi.org/10.1111/gbi.12459

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