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Fe-rich smectite clays such as nontronite are widespread on Mars and serve as mineralogical archives of early aqueous processes and potential habitats. Their layered structures, high surface areas, and redox-active Fe sites make them promising candidates for adsorption, preservation, and catalytic transformation of organics. While clay–organic interactions have been extensively studied for Al-rich smectites, the role of Fe-rich clays in preserving nucleobases remains poorly constrained under Mars-like geochemical conditions. Here, we investigated adenine adsorption on nontronite across pH 1.8–13 and temperatures from −100 to 20 °C using Raman, UV–vis, dynamic light scattering (DLS), and scanning electron microscopy (SEM). Raman analyses revealed diagnostic adenine bands in nontronite, including the purine ring-breathing mode at 723 cm–1 and a doublet near 1310–1345 cm–1, persisting under acidic and cryogenic conditions. UV–vis and DLS showed enhanced adenine uptake and aggregation at low pH, declining toward neutral and moderately alkaline conditions. Adsorption remained minimal above pH 11, and the observed spectral changes were primarily attributed to pH-induced modifications of the nontronite surface and possible adenine self-association. SEM confirmed compact, sheet-like morphologies at acidic pH, contrasting with disaggregated, amorphous textures under alkaline conditions, consistent with adenine desorption and partial clay destabilization. Our results demonstrate that adenine adsorption on nontronite is strongly pH- and temperature-dependent, with acidic and cryogenic environments enhancing preservation and spectral detectability. These findings establish the first experimental framework for adenine–nontronite interactions under Mars-like temperatures, while also providing reference Raman fingerprints and mechanistic insights relevant to both planetary exploration and clay–organic processes in terrestrial environments.

Iron-rich minerals, such as hematite (α-Fe2O3), are prominent constituents of the Martian surface; they are considered to be potential indicators of past aqueous activity and habitability. This study investigated the interaction between the extremophilic black fungus Rhinocladiella similis LaBioMMi 1217 and hematite under simulated laboratory conditions on Mars, focusing on redox-mediated dissolution processes, metabolic adaptations, and biosignature formation. The fungus was cultivated with powdered and polished hematite substrates, and mineral alteration was monitored through physicochemical measurements and scanning electron microscopy (SEM). Genome mining was performed to identify and map genes involved in iron metabolism. The metabolic profile of the fungus under hematite treatment was assessed via untargeted metabolomics. Over 15 days, the cultures exhibited marked acidification (pH decreased from 7.0 to 4.7) and a 10-fold increase in the dissolved Fe2+ ion concentration (26–270 mg/L), indicating metabolically driven iron reduction. SEM revealed surface etching and localized roughening consistent with microbially induced weathering, whereas these changes were absent in the abiotic controls. Genes linked to siderophore biosynthesis (sidA, sidC, sidD, sidF, sidH, sidI, and sidL) and reductive iron assimilation (FET3, FTR1, and FRE1) were identified. Untargeted metabolomics confirmed the secretion of organic acids, iron-chelating siderophores (e.g., ferrichrome C), and redox-active aromatic compounds in the presence of hematite, supporting a multifaceted strategy that combines acidification, chelation, and redox mediation. Collectively, these results show that the fungus actively promotes hematite dissolution through organic molecule-mediated mechanisms. Such interactions hold astrobiological relevance, as fungal modification of hematite might lead to the production of diagnostic chemical and mineralogical biosignatures, informing future life-detection strategies on Mars.

Sulfate minerals are significant components of the martian surface and provide clues about the martian geochemical environment. One unusual Fe-sulfate phase has been intriguing Mars scientists for over a decade due to its unique spectral bands that are distinct from any known minerals and its occurrence in layered sedimentary rocks. We describe here detection of ferric hydroxysulfate (Fe3+SO4OH) and its implications for the geochemical history of Mars. Crystalline ferric hydroxysulfate is formed by heating hydrous Fe2+ sulfates to 100 °C or above and has a strong spectral band at 2.236 µm, similar to the spectral feature observed on Mars at Aram Chaos and on the plateau above Juventae Chasma. Hydrated sulfates at these locations likely formed through evaporative processes or low-temperature alteration. In contrast, Fe3+SO4OH is more consistent with heating and oxidation of hydrated ferrous sulfates, potentially through deposition of lava, ash, or through hydrothermal processes.

Calcium sulfate minerals are found in multiple environments on Earth and Mars, with chloride (Cl) salts widely distributed on both planets. Low-temperature studies have explored geochemical processes, including the formation of transient liquid water and ion migration on Mars. Some Cl-salts (e.g., NaCl and CaCl₂) can dissolve gypsum (CaSO₄·2H₂O) in certain environments, making gypsum-Cl salt interactions significant. Additionally, gypsum’s geochemical transformation at high temperatures reveals dehydration pathways crucial for understanding Mars’ aqueous history and potential for life. This study examines gypsum dehydration through (i) thermal analyses and (ii) interactions with Cl-salts over a temperature range of −90 to 400 °C. We applied three spectroscopic techniques (Raman, visible/near-infrared, and mid-IR) plus X-ray diffraction (XRD) to analyze these samples under variable conditions. This study also provides a low-temperature spectral data set for gypsum and gypsum-Cl salt mixtures, beneficial for orbital analyses. Our findings reveal that experimental (i) heating rates, (ii) temperature ranges, (iii) relative masses of gypsum and Cl-salts, and (iv) dehydration environments (e.g., in situ and in vacuo) influence Ca-sulfate phase formation. Although we find different results in some cases, this study demonstrates that changing experimental conditions affects the detectability and transformation of gypsum. Further, these results indicate that the geochemical environmental conditions on Mars play a role in gypsum’s geochemical transformation to dehydrated components. This study also provides structural and chemical data for Ca sulfate assemblages from vibrational spectroscopy and XRD, which extends our knowledge of gypsum and related materials under variable conditions, thus aiding orbital and surface planetary analyses that may help to advance our understanding of planetary geochemistry on Mars.

Detection of organic biosignatures by (cryo-)Raman spectroscopy in hydromagnesite-rich samples from Lake Salda, an analogue site for the Mg-carbonate deposits in Jezero Crater.

Liquid water is not stable on Mars surfaces due to low temperature and pressure conditions, but it may potentially be formed and stabilized through deliquescence of salts in the subsurface [1, 2]. Our preliminary findings suggest that the presence of hygroscopic divalent salts (e.g., CaCl2, MgCl2) enhances thewater sorption of nontronite, even at low water vapor pressures at 25 °C. Additionally, our Raman results revealed that nontronite in CaCl2 solution retained briny water better than other nontronite-salt mixtures (e.g.,NaCl, MgCl2) at -100 °C. This study revealed the complex roles of nontronite and various salts ability to form and retain briny water in an extended temperature range (-100 to 25 °C). It also offers essential insights to the aqueous (geo)chemical history of Mars and the search for potential water resources for future human explorations to Mars.

FeSO4OH is formed by heating hydrous Fe sulfates to 100°C or above and has a strong spectral band at 2.236 µm, also observed on Mars.

In this study, we compare new spectra of szomolnokite (FeSO4•H2O) acquired at low temperatures with the spectra of varied abundance of Fe/Mg-Monohydrated sulfates (MHS) samples.

The Raman/VNIR/XRD measurements of gypsum from low to high temperatures in our study may enable coordinating orbit and rover analyses in Mars.

On Mars, seasonal martian flow features known as recurring slope lineae (RSL) are prevalent on sun-facing slopes and are associated with salts. On Earth, subsurface interactions of gypsum with chlorides and oxychlorine salts wreak havoc: instigating sinkholes, cave collapse, debris flows, and upheave. Here, we illustrate (i) the disruptive potential of sulfate-chloride reactions in laboratory soil crust experiments, (ii) the formation of thin films of mixed ice-liquid water “slush” at −40° to −20°C on salty Mars analog grains, (iii) how mixtures of sulfates and chlorine salts affect their solubilities in low-temperature environments, and (iv) how these salt brines could be contributing to RSL formation on Mars. Our results demonstrate that interactions of sulfates and chlorine salts in fine-grained soils on Mars could absorb water, expand, deliquesce, cause subsidence, form crusts, disrupt surfaces, and ultimately produce landslides after dust loading on these unstable surfaces.