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The overwhelming presence of jarosite (KFe3(SO4)2(OH)6) on the Martian surface makes its chemical and isotopic signatures important because they carry a lot of information about the planet's past. In this study, using first principles density functional theory we have calculated: (i) the relative thermodynamic stability of jarosite in the presence of relevant dopants; and (ii) explored the possibility of suitably exploiting the thermal decomposition products of jarosite to deduce past Martian temperature conditions. Previous studies report that pure jarosite undergoes thermal decomposition under Martian conditions at 18 °C, which is well above the present-day average surface temperature of Mars. However, the presence of other elements in the jarosite matrix, namely, Na and Al is expected to influence this stability. Moreover, the planet has been known to have undergone several episodes of intense heating in the past, whereby the temperatures may have soared past the present day temperature conditions, potentially threatening jarosite stability. Previous estimates of the past temperatures on the Martian surface are found to be quite broad. To fine-tune this estimate and provide more precise temperature constraints, we have devised a thermometer based on the temperature-dependent distribution of Fe isotopes between the Fe-bearing decomposition products of jarosite. Our proposed thermometer has the potential to record past (post jarosite formation) temperature peaks on the Martian surface. Additionally, we propose that the time elapsed since then can be deduced using a relevant well-established chronometer, i.e., the 40Ar/39Ar dating method on the K-bearing end-product of jarosite.

Current understanding of Martian regolith has advanced due to various rover explorations. Due to this, there are now several variants of Martian regolith that are chemically known and commercially available. These simulants are vital for panspermia models that suggest a transfer of simple life throughout the solar system via ejecta containing life from Mars when its surface was more favourable to host life. Bacteria that produce endospores are suitable candidates for these models as they have adequate protection from the harsh conditions of space. To assess this, the simple endospore former, Bacillus subtilis, was assessed for growth on several Martian regolith that represented different locations and epochs of Mars. This consisted of a conventional Martian regolith, a sulphur rich regolith, and a simulant of the Jezero crater which was thought to have once been flooded with water. We found that the sulphur rich regolith inhibited endospore formation, while the other two variants favoured endospore production. Interestingly, we also identified that pulsing of UVC in a simulation of endospores on rotational ejecta show that endospores break down faster with lower rotational frequency despite receiving the same UVC dose. Moreover, and most strikingly is that viable endospores after surviving UVC dosage displayed elevated expression of the DNA damage SOS response gene, RecA. Importantly, this study suggests that astrobiological approaches that utilise endospore viability as a benchmark for survival require reassessment as genomic integrity may be compromised.

The MMX InfraRed Spectrometer (MIRS) is a spectro-imager on board the Japan Aerospace Exploration Agency Martian Moons eXploration mission, set to launch in 2026, to investigate the origin of the Martian moons, Phobos and Deimos, as well as the Martian atmosphere and surface. MIRS, operating in the 0.9-3.6 μm wavelength range, is designed to identify and map minerals, ices, and organic compounds on the Martian moons, while also monitoring water vapor and dust in Mars's atmosphere. This paper details the ground calibration and performance evaluation of the MIRS Flight Model, conducted at the Laboratory for Instrumentation and Research in Astrophysics at the Paris Observatory during the thermal-vacuum test campaign at the end of 2023. A detailed description of the apparatus and the procedures used during the campaign is provided. The calibration campaign tested the instrument's thermal response and radiometric performance, ensuring compliance with stringent mission requirements. The tests demonstrated MIRS's capability to deliver high-resolution spectral data, fulfilling critical scientific and technical objectives. The preliminary results indicate MIRS's readiness for in-flight operations and its potential to contribute significantly to the understanding of the Mars system.

Planetary protection hinges on understanding microbial survival following reduction procedures, the stressors of space travel, and exposure to extraterrestrial environmental conditions. This study identified 23 fungal strains isolated from NASA spacecraft assembly cleanrooms, capable of surviving ultraviolet radiation exposure. Using experimental simulation facilities, we conducted a comprehensive assessment of microbial survivability and morphology on the most resilient spacecraft-associated microorganisms. Aspergillus calidoustus demonstrated remarkable survival under simulated Martian conditions, withstanding up to 1,440 min of Martian solar irradiation, Mars atmospheric pressure and composition, and the presence of Martian regolith. Lethality only occurred under combined irradiation and cooling to -60°C (the mean Mars surface temperature), emphasizing the synergistic effect of these conditions. Furthermore, A. calidoustus survived long-duration neutron radiation exposure (replicating ionizing space radiation doses) and dry-heat microbial reduction technique (typically used for spacecraft components). This is the first study to perform an end-to-end evaluation of eukaryotic microbial survival across conditions that occur during preparation for, travel to, and robotic exploration of Mars. The experimental facilities and chronic exposure methods utilized offer a biologically meaningful model for understanding microbial risks during long-duration space missions. The capacity for fungal conidia to survive multiple space-relevant conditions suggests their potential as forward contaminants, capable of being transported to and persisting on Mars. As current spacecraft microbial reduction protocols prioritize bacterial spores, this research highlights a critical gap in planetary protection strategies. In addition to offering novel insights into microbial survival, these findings have broader implications for biocontamination within the food, pharmaceutical, and medical sectors.IMPORTANCEThis study reveals that conidia of the fungus Aspergillus calidoustus, which was isolated from spacecraft assembly cleanrooms, can survive simulated space-relevant stressors like ultraviolet irradiation, Martian cold atmospheric pressure, regolith exposure, ionizing radiation, and specific doses of recommended dry-heat microbial reduction method for spacecraft. Such fungal resistance demonstrates that the species can survive certain space and Mars conditions previously thought to be sterilizing, highlighting a need to revise current spacecraft decontamination standards that focus mainly on bacterial spores. This study also emphasizes the need for continued microbial monitoring of spacecraft during transit from Earth to other planets, not only to achieve goals of planetary protection but also to maintain healthy closed systems for human missions. Moreover, fungal species are highlighted as biocontamination risks for food, medical, and pharmaceutical industries, which may require the need for new standards of sterilization approaches transferable to space exploration.

We present a dataset of utilities developed to address the study of transient phenomena on the Martian surface through a seasonal approach. To this aim we selected high resolution HiRISE/MRO images. For each of these images (catalogue updated as of December 2024), we have compiled data records that are partly extracted from the archive itself but are supplemented with many other, associated or computed, new parameters. Further processing of this primary dataset has yielded two lists of image clusters related to a selection of Martian sites. Based on the spatio-temporal distribution of HiRISE images, these sites are ideal for studying: (i) seasonal surface variations through a 'virtual sampling' of the Martian year, and (ii) transient or seasonal changes through non-conventional stereoscopic pairing.

Detection of organic molecules on Mars is challenging due to a variety of degradation processes occurring at the Martian surface, including UV irradiation. Nevertheless, the NASA's Curiosity rover found evidence of organic molecules in clays, suggesting that these minerals might be particularly suitable to preserve organics on Mars. In this work, the photostability of L-histidine adsorbed at different pHs on nontronite under Martian-like UV irradiation was investigated in order to assess the preservation potential of this clay in the Martian environment. The interactions between L-histidine and nontronite were investigated via Infrared spectroscopy and X-Ray Diffraction, in order to understand the possible preservation mechanisms. Results indicate that L-histidine intercalates into the mineral interlayer at acidic pH, and undergoes minor degradation after UV exposure compared to the pure molecule. At basic pH, polymolecular layers are formed and no degradation is observed. These results show that nontronite acts as a photoprotective mineral for L-histidine both at acidic and basic pH, making it a suitable mineral target for organic detection on Mars.

Planet-wide interpretations of shorelines suggest that Mars once hosted an early ocean covering one-third of its surface1-9. However, the elevations of these shorelines deviate from an equipotential surface by several kilometres, challenging that interpretation3,7,10-12. Here we investigate whether a planet that once hosted an ocean should be expected to leave discernible shorelines. We show that on Earth, the most prominent topographic signature of a global ocean is not a shoreline. Rather, it is a band of low slope and curvature values that comprises coastal plains and the continental shelf, with an elevation range of -410 m to -15 m. When applying a similar analysis to the Martian surface, we observe a comparably flat zone between approximately -1,800 m and -3,800 m elevation, potentially marking a partially preserved Martian coastal shelf. Although other processes, such as lava flows13, might explain flat regions locally, a coastal shelf best explains the circumglobal band of flat topography, in addition to river delta deposits4,14-17, coastal deposits18, thick sequences of layered rock19,20 and aqueously altered minerals20,21, all observed within the putative coastal shelf zone. Our results support the presence of an ancient ocean on Mars and indicate that topographic shelves rather than shorelines may be better indicators of long-lived oceans.

Understanding how crops adapt to extraterrestrial environments is essential for sustainable space agriculture. Sweet potato (Ipomoea batatas), a nutritionally rich and stress-resilient crop, is a promising candidate for cultivation under Martian-like conditions, characterized by high salinity, heavy metal contamination, and poor water retention. This study aimed to elucidate the molecular mechanisms underlying sweet potato adaptation to Martian soil analog conditions using Mars Global Simulant-1 (MGS-1). Leaf, shoot, and storage root tissues of sweet potato grown in MGS-1 were subjected to RNA sequencing. Differentially expressed mRNAs and long non-coding RNAs (lncRNAs) were identified, and functional enrichment analyses were performed. Predicted trans-acting candidate lncRNAs were validated via virus-induced gene silencing (VIGS), with transcript levels confirmed by RT-qPCR. Transcriptome profiling revealed 2,344 differentially expressed mRNAs and 172 lncRNAs, enriched in abiotic stress-related pathways including secondary metabolite biosynthesis, ROS detoxification, zeatin biosynthesis, cell wall remodeling, and membrane transport. Several lncRNAs were predicted to regulate stress-responsive genes, including Kunitz trypsin inhibitors, myo-inositol oxygenase, cytochrome P450s, and WRKY transcription factors. Notably, MSTRG.1111.1 and MSTRG.5653.1 were identified as trans-acting regulators of myo-inositol oxygenase and Kunitz trypsin inhibitor genes, respectively. VIGS and RT-qPCR confirmed their regulatory roles, with transcript downregulation ranging from 0.5- to 2.8-fold. This study provides the first comprehensive mRNA and lncRNA expression atlas of sweet potato under Martian soil analog conditions. The findings reveal key molecular pathways and lncRNA-mediated regulatory mechanisms for abiotic stress adaptation, highlighting sweet potato's potential as a resilient crop for future space agriculture.

This study examines the tribological performance of dry-running mechanical face seals composed of a graphite rotating ring and a silicon carbide stationary ring under varying contact pressure conditions from 0.23 to 0.83&#xa0;MPa), both in clean operation and in the presence of a Martian regolith simulant (MGS-1, PR&#x2009;<&#x2009;80&#xa0;&#x3bc;m). Three preload levels were applied: zero preload (SP0), nominal preload (SP1), and double preload (SP2), based on a calibrated spring characteristic and contact area analysis. Under clean conditions, increasing preload elevated frictional torque from ~&#x2009;0.017 Nm (SP0) to ~&#x2009;0.030 Nm (SP1) and ~&#x2009;0.070 Nm (SP2), indicating a direct correlation between contact pressure and interfacial shear. When MGS-1 regolith simulant was introduced, torque increased significantly in all configurations, reaching&#x2009;~&#x2009;0.064 Nm (SP0MGS-1), ~&#x2009;0.082 Nm (SP1MGS-1), and ~&#x2009;0.095 Nm (SP2MGS-1). Real-time monitoring of torque and axial force enabled the calculation of dynamic friction forces and coefficients of friction, which revealed that contact pressure strongly influenced wear mechanisms: higher contact pressure enhanced interface conformity but accelerated abrasive degradation, while lower contact pressure reduced wear at the expense of sealing pressure. Scanning electron microscopy (SEM) confirmed the presence of abrasive grooves and embedded particles exclusively on the graphite ring, with no perceivable damage on the SiC counterface. The results demonstrate that nominal contact pressure (SP1) provides the most favorable balance between friction stability, wear resistance, and sealing reliability, offering valuable insights for the design of mechanical seals in particulate-laden environments such as Martian surface operations.

The thickness and volume of the stratigraphic sequence in Mars' northern lowlands remain poorly constrained, despite their key role in recording the planet's geological and paleoclimatic evolution. Reliable thickness estimates are essential because they directly control calculations of volcanic effusion, surface flooding, and associated climate forcing. Here we present a revised volumetric assessment of the lowland stratigraphy - dominated by volcanic infill - based on integrated geological mapping and crater-statistical modeling. Our approach combines crater size-frequency distributions with volumetric reconstructions of buried craters and intercrater plains across both lowland and Noachian highland reference terrains. The results indicate that the minimum cumulative stratigraphic volume is at least three times greater than previous estimates, implying a proportional increase in volcanic outgassing of CO2, H2O, and SO2. These new quantitative conservative bounds provide improved constraints on early Martian volatile budgets and on mid- to late-Noachian atmospheric evolution, with implications for transient climate warming and late-stage lowland flooding.

Deuterium is unevenly distributed in natural waters, while the same applies to the content of deuterium in ice on Mars. Moreover, changes in the deuterium content of drinking water are known to affect the bodies of mammals. Thus, since plans are in place to send people to Mars in the coming years, understanding the effects of water with a Martian isotopic composition is necessary. Therefore, this study aimed to evaluate the impact of water with an increased deuterium content of 1200 ppm on the dynamics of indicators in the body of mammals. The study was conducted on Wistar rats. The metabolic profile of blood and the content of deuterium in it were studied in dynamics by days using nuclear magnetic resonance (NMR) spectroscopy. Additionally, the isotopic composition of brain tissue was studied in dynamics by days using isotope mass spectrometry. A further study was conducted on the functioning of the antioxidant system in blood plasma and brain tissue using PCR analysis, chemiluminescence, and biochemical analysis methods; the intestinal microbiome was also studied. The durations of the animal experiments were 31 (blood and brain study) and 38 (stress-protective activity study) days. On day 23, the deuterium content in the blood plasma increased to 856 parts per million (ppm), and to 260 ppm in the brain on day 31. This increase led to an imbalance in the antioxidant/prooxidant processes. This effect was accompanied by shifts in the intensity of oxidative processes, alongside changes in enzyme activity and the expression of genes responsible for their synthesis, shifts in amino acid composition, and changes in the concentration of metabolites and microbiome molecules in the blood plasma. By the fifth and eighth days, the number of Bacteroides in the intestines had decreased by 14% and 21.8%, respectively, compared to the values measured on day zero of the experiment. Meanwhile, the population of Firmicutes-type bacteria increased by 12% and 16% on the fifth and eighth days, respectively, compared to the indicators measured on day zero of the experiment. An increase in the concentration of deuterium in the body promotes the development of a stress reaction and the activation of compensatory mechanisms aimed at adaptation.

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On Mars, a relatively pure water ice layer lies beneath several centimeters of dry-soil at midlatitudes. Its widespread presence poleward of 60&#xb0; latitude was detected by remote neutron spectroscopy. Recent observations of exposed ice indicate that the near-surface ice layer extends to 35&#xb0; latitude and exhibits pronounced spatial structure. However, previous models did not capture the observed spatial structure of the midlatitude ice layer. Here, using improved calculations using the Mars Planetary Climate Model, we show that mid-latitude buried ice could be the remnant of an ice layer deposited on the surface when the obliquity was higher than today. Assuming that the ice subsequently sublimated and became buried beneath a sublimation lag, we estimate that surface ice emplaced 630 thousand years (4.18 million years) ago at 35&#xb0; obliquity (40&#xb0;), at latitudes of 40-55&#xb0; North, would today reside at depths of 25-150 (41-255) centimeters, depending on regolith and ice properties. For ice emplaced 630 thousand years ago, the modeled burial depths align with observations and capture the observed longitudinal depth variations, in contrast to ice emplaced 4.18 million years ago. We therefore infer that the mid-latitude subsurface ice is younger than 4 million years.

Volcanic eruptions and glacial ice have occurred at virtually all latitudes and altitudes throughout Mars history. To assess the astrobiological potential of processes and microenvironments associated with lava flows onto glacial ice, we explore: (1) the influence of lava flow loading on the flow behavior of underlying ice, (2) whether, and for how long, wet-based conditions might occur and be sustained in otherwise cold-based glacial environments, and (3) the immediate fate of the meltwater generated, whether moulins can be generated, and whether and for how long wet-based conditions are generated by such processes. We employ a 1D time-dependent solution of the heat-flow equation to solve for the transient temperature field within a column of ice subjected to instantaneous deposition of a hot lava layer, exploring the parameter space by examining six different initial surface temperatures and three potential geothermal fluxes to characterize a range of past climates/geological regimes. We observe an initial pulse of accelerated flow due to the increased loading by the lava and consequent increase in the driving stress. A secondary pulse of acceleration occurs as the temperature wave from the lava penetrates the ice and reaches the bed, where the bulk of the deformation occurs in response to the warmer, softer ice. We observe basal melting as the bed briefly reaches the melting point and characterize the amounts of water produced during such brief basal melting intervals. Examination of the meltwater generated below, and in moats adjacent to the superposed lava, shows that completely full moats can propagate cracks through km-thick ice, and such crevasses can remain open (moulins) if they are at least 90% full. The greatest volume of drained water is produced by thin lava over thick ice, but the longest duration draining events occur for moderate lava thicknesses over thinner ice. Locally wet-based glacial conditions could persist below the superposed lava flow for durations well over &#x223c;103 years. We explore the detailed consequences of lava flow/ice interaction, highlighting those most important for the formation and dispersal of potential cryophilic microbiota on Mars, opening new windows of Mars history for astrobiological research and exploration.

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Following the Viking experiments in 1976, many of the original inferences of biological metabolism have been replicated via abiotic mechanisms we now know are plausible on Mars' surface. While in many cases subsequent experiments have cast doubt on whether Viking truly detected life, numerous other studies since Viking have greatly expanded our knowledge of life's limits and microbial metabolism. In particular, increased characterization of Earth's subsurface has revealed the astounding complexity and adaptability of life, highlighting chemically based metabolisms as potentially strong targets for future life detection missions. Over the same time frame, we have gained knowledge of putatively more habitable regions in Mars' subsurface, relative to the original Viking lander surface sites, that could host similar organisms. In this review, we discuss the wealth of knowledge concerning the habitability of zones across Mars' surface/subsurface, and we suggest specific microbial metabolisms that should be targeted in future life detection missions based on laboratory and field studies under analogous conditions on Earth and with consideration of recommendations from the larger Astrobiology community. The ability to leverage these advancements in subsurface research toward the incorporation of increased specificity in future life detection efforts is additionally discussed in the context of current Mars subsurface mission progress and planetary protection and defense concerns.

Oxidation processes in cold and freezing environments remain poorly constrained, despite their importance for redox evolution in both terrestrial cryospheric systems and planetary surfaces. Mars provides a natural laboratory: sedimentary Mn oxides indicate sustained surface oxidation, although early Mars likely remained frozen, limiting the effectiveness of atmospheric O2 oxidation. Here we demonstrate that bromate (BrO3-) rapidly oxidizes Mn(II) in acidic brines under freezing conditions. In laboratory simulations from -80 to 25 &#xb0;C, Mn(II) oxidation proceeds readily despite ice formation. Bromate is not quantitatively reduced to Br-; instead, a substantial fraction is inferred to be converted to reactive and volatile bromine intermediates (e.g., BrO, BrO-, Br2), based on the observed bromine mass balance and comparison with previously reported bromate-involved redox systems, enabling potential atmospheric release and redistribution. These species can be efficiently reoxidized to BrO3- via photochemical and atmospheric processes, suggesting the operation of an active bromine redox cycle. Our results identify bromate-driven oxidation as an efficient, oxygen-independent redox pathway operating under freezing conditions, capable of maintaining long-term oxidizing environments. This mechanism provides a plausible explanation for sustained oxidation on Mars throughout its climatic evolution and highlights the broader relevance of halogen-mediated redox cycling in frozen aquatic systems. These findings advance our understanding of low-temperature environmental oxidation processes and their implications for planetary surface chemistry and potential habitability.