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It has been shown that ultraviolet (UV) irradiation is responsible for the destruction of organic compounds on the surface of Mars. When combined with the photochemically-driven production of oxychlorines (ClO x ) it can generate highly reactive species that can alter or destroy organic compounds. However, it has been assumed that since UV only penetrates the top few millimeters of the martian regolith, reactive ClO x oxidants are only produced on the surface. Of all the oxychlorine intermediates produced, gaseous chlorine dioxide [ClO 2 (g)] is of particular interest, being a highly reactive gas with the ability to oxidize organic compounds. Here we report on a set of experiments under Mars ambient conditions showing the production and permeation of ClO 2 (g) and its reaction with alanine as a test compound. Contrary to the accepted paradigm that UV irradiation on Mars only interacts with a thin layer of surface regolith, our results show that photochemically-generated ClO 2 (g) can permeate below the surface, depositing ClO x species (mainly Cl - and ClO 3 - ) and destroying organic compounds. With varying levels of humidity and abundant chloride and oxychlorines on Mars, our findings show that permeation of ClO 2 (g) must be considered as a significant contributing factor in altering, fragmenting, or potentially destroying buried organic compounds on Mars., (© 2024. The Author(s).)

Studies to understand the growth of organisms on Mars are hampered by the use of simulants to duplicate martian mineralogy and chemistry. Even though such materials are improving, no terrestrial simulant can replace a real martian sample. Here we report the use of actual martian regolith, in the form of Mars meteorite EETA79001 sawdust, to demonstrate its ability to support the growth of four microorganisms, E. coli .  Eucapsis sp., Chr20-20201027-1 , and P. halocryophilus , for up to 23 days under terrestrial conditions using regolith:water ratios from 4:1 to 1:10. If the EETA79001 sawdust is widely representative of regolith on the martian surface, our results imply that microbial life under appropriate conditions could have been present on Mars in the past and/or today in the subsurface, and that the regolith does not contain any bactericidal agents. The results of our study have implications not only for putative martian microbial life but also for building bio-sustainable human habitats on Mars., Competing Interests: Competing interestsThe authors declare no competing interests., (© The Author(s) 2023.)

The current understanding of the Martian surface indicates that briny environments at the near-surface are temporarily possible, e.g. in the case of the presumably deliquescence-driven Recurring Slope Lineae (RSL). However, whether such dynamic environments are habitable for terrestrial organisms remains poorly understood. This hypothesis was tested by developing a Closed Deliquescence System (CDS) consisting of a mixture of desiccated Martian Regolith Analog (MRA) substrate, salts, and microbial cells, which over the course of days became wetted through deliquescence. The methane produced via metabolic activity for three methanogenic archaea: Methanosarcina mazei, M. barkeri and M. soligelidi, was measured after exposing them to three different MRA substrates using either NaCl or NaClO 4 as a hygroscopic salt. Our experiments showed that (1) M. soligelidi rapidly produced methane at 4 °C, (2) M. barkeri produced methane at 28 °C though not at 4 °C, (3) M. mazei was not metabolically reactivated through deliquescence, (4) none of the species produced methane in the presence of perchlorate, and (5) all species were metabolically most active in the phyllosilicate-containing MRA. These results emphasize the importance of the substrate, microbial species, salt, and temperature used in the experiments. Furthermore, we show here for the first time that water provided by deliquescence alone is sufficient to rehydrate methanogenic archaea and to reactivate their metabolism under conditions roughly analogous to the near-subsurface Martian environment.