Potential habitability of present-day Mars subsurface for terrestrial-like methanogens (2411.15064v2)

Abstract: The intense debate about the presence of methane in the Martian atmosphere has stimulated the study of methanogens adapted to terrestrial habitats that mimic Martian environments. We examinate the environmental conditions, energy sources and ecology of terrestrial methanogens thriving in deep crystalline fractures, sub-sea hypersaline lakes and subglacial water bodies considered as analogs of a hypothetical habitable Martian subsurface. We combine this information with recent data on the distribution of buried water or ice and radiogenic elements on Mars and with models of the subsurface thermal regime of this planet to identify a 4.3-8.8 km-deep regolith habitat at the mid-latitude location of Acidalia Planitia, that might fit the requirements for hosting putative Martian methanogens analogous to the methanogenic families Methanosarcinaceae and Methanomicrobiaceae.

• The paper investigates the potential habitability of the Mars subsurface for terrestrial-like methanogens, utilizing terrestrial analog studies and Martian geophysical data analysis to identify promising regions.
• The study highlights that terrestrial methanogens, specifically Methanosarcinaceae and Methanomicrobiaceae, show adaptability to extreme conditions relevant to Mars, including subzero temperatures and high salinities.
• The southern Acidalia Planitia is identified as a candidate region for future exploration, theorized to possess conditions suitable for methanogenic ecosystems, such as subsurface water-ice and favorable radiogenic heat flow.

An Exploration into the Habitability Potential of Mars' Subsurface for Terrestrial-Like Methanogens

The paper investigates the viability of Mars' subsurface as a habitable environment for terrestrial-like methanogens, such as those from the Methanosarcinaceae and Methanomicrobiaceae families. Through an interplay of terrestrial analog studies and Martian geophysical data, the authors present a multi-faceted analysis aiming to identify potential habitats on Mars that could support these life forms. The inquiry is centered around the availability of essential conditions such as liquid water, suitable energy sources, and sufficiently stable thermal environments within Mars' regolith.

Methane, a primary focus of astrobiological research, serves as a significant biosignature due to its close association with microbial life on Earth, particularly methanogens. Despite persistent curiosity regarding Martian methane detections and its origins (Webster et al., 2015; Korablev et al., 2019), the search for analogous methanogenic life forms on Mars has intensified. Terrestrial methanogens, which thrive in extreme environments such as deep crystalline fractures, sub-sea hypersaline lakes, and subglacial water bodies, offer critical insights into the potential survival and metabolic pathways of microorganisms on Mars.

The authors amalgamate data from 79 terrestrial sites with characterizations of the Martian subsurface to scrutinize methanogen viability under specific environmental conditions. The paper delineates three critical habitat analogs: fractures within crystalline bedrock (CBCS), subglacial lentic waters and brines (SGL), and deep-sea hypersaline anoxic basins (DHAB). Through this comparison, reconnaissance of methanogen presence, coexistence with other organisms, and the variety of energy sources available is advanced.

In terms of environmental tolerances, the research highlights that methanogens—particularly from Methanosarcinaceae and Methanomicrobiaceae—demonstrate adaptability to various extreme conditions akin to those expected on Mars. These organisms can survive subzero temperatures, high salinities, and engage in methanogenic pathways that leverage available energy sources such as CO2 and H2. While hydrogenotrophic and methylotrophic pathways predominate in certain conditions, the potential interactions with sulfur-based metabolisms in Mars' sulfate-rich milieu pose compelling questions regarding interspecies competition and ecological balance.

A significant implication of the paper is the potential identification of the southern Acidalia Planitia as a candidate region for further exploration. It is theorized to possess the conditions necessary for methanogenic ecological systems, including subsurface water-ice abundance combined with a notable radiogenic heat flow. This prospective habitat’s advantageous geothermal gradients could support temperature regimes conducive to sustaining terrestrial-like methanogenesis beyond the physical and geochemical impediments observed.

This intricate examination sets the groundwork for future astrobiological endeavors, suggesting that the Mars subsurface may include multispecies ecosystems similar to those in Earth's extreme environments. While the research underscores the complex nature of subsurface microbial ecosystems and their reliance on both environmental and biotic factors, it also calls for further exploration into the dynamic interactions and adaptability traits of potential Martian life forms.

The paper’s methodological rigor in comparing Earth's subsurface microbiomes with a hypothetical Martian habitat enriches our understanding of possible extraterrestrial life. It establishes a pathway for future exploratory missions and the continued development of bio-signature detection protocols tailored to uncovering life within Mars' challenging subsurface environments. The findings are notably significant in refining mission target areas for extant life detection while underscoring the need for enhanced understanding of Martian geophysical, chemical, and thermal conditions.