Mars, one of the most Earth-like celestial bodies in the Solar System, is a key focus in the search for extraterrestrial life. However, pure liquid water – essential for life as we know it – is unstable on its surface today due to low pressure and frigid conditions. Concentrated salt solutions (brines) may form through the deliquescence of hygroscopic salts like chlorates and perchlorates detected on Mars, offering a potential water source for hypothetical halotolerant organisms due to the brines’ lower freezing point and reduced vapour pressure. This study simulates brine formation on Mars using a methodical setup. Martian global regolith simulant MGS-1 was either supplemented with hygroscopic salts such as sodium chloride (NaCl), sodium chlorate (NaClO3), sodium perchlorate (NaClO4) or used without the addition of salts as a control. Samples were inoculated with the halotolerant yeast Debaryomyces hansenii, chosen for its high (per)chlorate tolerance. Desiccated samples were transferred to an environment with constant relative humidity (98%), allowing the salts to absorb water from the atmosphere through deliquescence. The study examined the survival of D. hansenii after desiccation and its ability to grow using water absorbed through deliquescence. The results revealed that D. hansenii survived the desiccation in samples containing NaClO3, NaCl or no additional salt and grew in the control samples as well as in the deliquescent-driven NaClO3 and NaCl brines. No survival was observed in samples containing NaClO4 after the desiccation step. These findings suggest that Mars could potentially harbour life in specific niches where deliquescent brines form, specifically in NaCl or NaClO3 rich areas. NaClO4, at least for the yeast tested in this study, is too toxic to support survival or growth in deliquescene-driven habitats.

Dry permafrost underlain by ice-cemented permafrost has been reported in several locations in Antarctica. Initially thought to be relic ice, it is now understood that this subsurface ice is in equilibrium with the surface conditions, although it is not in equilibrium with the atmosphere. We use year-round data from University Valley in the Dry Valleys and Elephant Head in the Ellsworth Mountains to investigate the seasonal variations in water vapour flux that control the depth to the ice table under dry permafrost. Our analysis shows that the mean annual water vapour density of the soil surface exceeds the atmospheric value by a factor of up to ~2 due to summer snow. The attenuation and phase shift of the annual temperature cycle with depth result in colder temperatures at the ice table than at the surface of the soil in summer. We conclude that this temperature gradient, combined with the summer snow, provides the flux of water to the ice table necessary to maintain the ice. In University Valley, reducing the snow days by 40% moves the stability depth of the ice table from 42 to 66 cm. Increasing the snow days by 60% shifts the ice table to 17 cm. These variations can explain the observed gradient in the depth to the ice table in University Valley.

The search for biosignatures of past microbial life has promoted the interest in halophilic archaea trapped inside fluid inclusions of salt crystals. These hypersaline environments are promising targets for the preservation of microbial cell envelope biomolecules. In this study, we focused on the preservation of bacterioruberin, a carotenoid pigment found in the cell envelope of Halobacterium salinarum, within fluid inclusions of salt crystals mimicking early Mars environments and modern Earth. Halite (NaCl) and sylvite (KCl) crystals were subjected to Mars-like proton irradiation, and the preservation of carotenoids was assessed using in situ and ex situ Raman spectroscopy. Our findings demonstrate that Raman spectroscopy efficiently detected carotenoids within fluid inclusions in non-irradiated crystals. However, post-irradiation analyses posed great challenges due to fluorescence induced by the formation of colour centres in the crystal lattice, which suppressed the carotenoid signal. Cleavage of irradiated crystals revealed preserved carotenoid pigments beyond the radiation penetration depth, suggesting potential preservation of biomolecules in deeper inclusions within larger crystals. Furthermore, in some cases, carotenoids were detected even within fluorescent zones, suggesting extensive preservation. This study underscores the potential of Raman spectroscopy for the detection of carotenoids as biosignatures in planetary exploration contexts, particularly as a preliminary screening tool. However, it also highlights the need for optimized protocols to overcome fluorescence-related limitations. These findings contribute to the methodologies for detecting and interpreting biosignatures in salt deposits, advancing the search for possible traces of past microbial life beyond Earth.

Ionizing radiation is known to have a destructive effect on biology by causing damage to DNA, cells and the production of reactive oxygen species, among other things. While direct exposure to high-radiation dose is indeed not favorable for biological activity, ionizing radiation can and, in some cases, is known to produce a number of biologically useful products. One such mechanism is the production of biologically useful products via charged particle-induced radiolysis. Energetic charged particles interact with the surfaces of planetary objects such as Mars, Europa and Enceladus without much shielding from their rarefied atmospheres. Depending on the energy of said particles, they can penetrate several meters deep below the surface and initiate a number of chemical reactions along the way. Some of the byproducts are impossible to produce with lower-energy radiation (such as sunlight), opening up new avenues for life to utilize them. The main objective of the manuscript is to explore the concept of a Radiolytic Habitable Zone (RHZ), where the chemistry of galactic cosmic ray-induced radiolysis can be potentially utilized for metabolic activity. We first calculate the energy deposition and the electron production rate using the GEANT4 numerical model, then estimate the current production and possible chemical pathways which could be useful for supporting biological activity on Mars, Europa and Enceladus. The concept of RHZ provides a novel framework for understanding the potential for life in high-radiation environments. By combining energy deposition calculations with the energy requirements of microbial cells, we have defined the RHZ for Mars, Europa and Enceladus. These zones represent the regions where radiolysis-driven energy production is sufficient to sustain microbial metabolism. We find that bacterial cell density is highest in Enceladus, followed by Mars and Europa. We discuss the implications of these mechanisms for the habitability of such objects in the solar system and beyond.

Characterizing the structure and composition of clay minerals on the surface of Mars is important for reconstructing past aqueous processes and environments. Data from the CheMin X-ray diffraction (XRD) instrument on the Mars Science Laboratory Curiosity rover demonstrate a ubiquitous presence of collapsed smectite (basal spacing of 10 Å) in ~3.6-billion-year-old lacustrine mudstone in Gale crater, except for expanded smectite (basal spacing of 13.5 Å) at the base of the stratigraphic section in a location called Yellowknife Bay. Hypotheses to explain expanded smectite include partial chloritization by Mg(OH)2 or solvation-shell H2O molecules associated with interlayer Mg2+. The objective of this work is to test these hypotheses by measuring partially chloritized and Mg-saturated smectite using laboratory instruments that are analogous to those on Mars rovers and orbiters. This work presents Mars-analog XRD, evolved gas analysis (EGA), and visible/shortwave-infrared (VSWIR) data from three smectite standards that were Mg-saturated and partially and fully chloritized with Mg(OH)2. Laboratory data are compared with XRD and EGA data collected from Yellowknife Bay by the Curiosity rover to examine whether the expanded smectite can be explained by partial chloritization and what this implies about the diagenetic history of Gale crater. Spectral signatures of partial chloritization by hydroxy-Mg are investigated that may allow the identification of partially chloritized smectite in Martian VSWIR reflectance spectra collected from orbit or in situ by the SuperCam instrument suite on the Mars 2020 Perseverance rover. Laboratory XRD and EGA data of partially chloritized saponite are consistent with data collected from Curiosity. The presence of partially chloritized (with Mg(OH)2) saponite in Gale crater suggests brief interactions between diagenetic alkaline Mg2+-bearing fluids and some of the mudstone exposed at Yellowknife Bay, but not in other parts of the stratigraphic section. The location of Yellowknife Bay at the base of the stratigraphic section may explain the presence of alkaline Mg2+-bearing fluids here but not in other areas of Gale crater investigated by Curiosity. Early diagenetic fluids may have had a sufficiently long residence time in a closed system to equilibrate with basaltic minerals, creating an elevated pH, whereas diagenetic environments higher in the section may have been in an open system, therefore preventing fluid pH from becoming alkaline.

Determining a reliable method to detect life on another planet is an essential first step in the pursuit of discovering extraterrestrial life. Polyhydroxyalkanoates (PHAs), bioplastic polymers created by microorganisms, are strong candidates for defining the presence of extraterrestrial life due to their water insolubility, strong ultraviolet resistance, high melting points and high crystallinity, amongst other qualities. PHAs are abundant on Earth, and their chemical properties can easily be distinguished from non-biological matter. Their widespread distribution and conferred resistance to astrobiologically relevant extreme environments render PHAs highly favourable candidates for astrobiological detection. Integrating detection of PHA biosignatures into current and future life-detection instruments would be useful for the planetary search for life. PHAs are analysed and characterized in laboratories by gas chromatography-mass spectrometry, infrared spectroscopy, Raman spectroscopy and immunoassay analysis in addition to other methods. We outline a path forward to integrate PHA detection in astrobiology missions to aid the search for extraterrestrial life.

Martian meteorites are currently our only existing samples from Mars. They are divided into two primary types, the shergottites and the nakhlite-chassignite types. The shergottites are by far the most abundant of the Martian meteorites. Apatite in particular is the only volatile bearing phase in these and thus is crucial for understanding volatile cycles on Mars. The primary goal of the study is to understand the effects of shock metamorphism on the volatile content of apatite. In particular, looking at intergrown apatite-merrillite grains to observe the Cl variation within apatite and to determine if the merrillite is in fact merrillite or if its tuite. Here we used various chemical analyses to accurately map the mineralogy of shergottite NWA 7397 to learn more about volatile content and shock effects to constrain its petrogenesis.

For NWA 7397, what we focused on was the phosphates. Mainly on the calcium phosphates, apatite (Ca5[PO4]3[F, CL, OH]) and merrillite (Ca9Na(Fe, Mg)(PO4)7). We can identify apatite based on its volatile components (F and Cl) as part of its crystal structure which merrillite lacks. Apatite is, however, the only volatile bearing phase in shergottites, making it our only was to constrain water and Cl content of martian magmas and by extension martian mantle reservoirs. However, the volatile contents can be effected by shock ejection when the rock was blasted off the martian surface. This means we need to understand the effects of shock before using apatite to estimate magma volatile content. From our research so far we have been able to identify apatite and merrillite, but no tuite. This will require further analysis to identify tuite, if any is present.

Models of cation exchange mechanisms and driving forces have proven effective predictors of clay behavior and chemistry, but are largely theoretical, particularly in complex systems involving high ionic strength brines or systems where hydration is controlled by relative humidity. In arid and cold environments, such as Mars, cyclical relative humidity variations may play a role in chemical alteration, particularly if clay minerals such as smectite are in the presence of salts. This study examines the effects of relative humidity on smectite-salt mixtures using environmental scanning electron microscopy (ESEM) to observe the physiochemical effects of salt deliquescence and desiccation on smectite textures and elemental distributions. Results demonstrate that even reaction periods as short as a few minutes allow ample time for relative humidity to affect the smectite-salt mixtures. In addition to smectite swelling and salt deliquescence, we also observed rapid changes in element distributions within the smectite and new crystal growth in the presence of high relative humidity. Even in the absence of bulk liquid water, exchangeable cations migrated out of the smectite and formed new crystals at the smectite-salt interface. The observed microscopic changes in elemental distributions indicate that the migration of cations driven by cation exchange led to secondary mineral precipitation, likely a CaSO4 mineral, within a sub-micrometer-thick layer of water on the smectite grains. The results of this study demonstrate that during periods of elevated relative humidity, active smectite mineral alteration and secondary mineral precipitation may be possible on present-day Mars where salts and smectites are in direct physical contact.

An altar to Mars dedicated by a soldier of legio XI Claudia is shown to have been removed from the fabric of Marton church during restoration work and, along with much of the other stone for the Romanesque tower, nave and chancel probably derived from the Roman small town of Segelocum, Littleborough on Trent. The name of the dedicator, G. IVLIVS ANTONINUS, is discussed in the context of legio XI Claudia deployment on the Lower Danube.

In situ elemental imaging of planetary surface regolith at a spatial resolution of 100s to 1000s of microns can provide evidence of the provenance of rocks or sediments and their habitability, and can identify post-depositional diagenetic alteration affecting preservation. We use high-resolution elemental maps and XRF spectra from MapX, a flight prototype in situ X-ray imaging instrument, to demonstrate this technology in rock types relevant to astrobiology. Examples are given for various petrologies and depositional/diagenetic environments, including ultramafic/mafic rocks, serpentinites, hydrothermal carbonates, evaporites, stromatolitic cherts and diagenetic concretions.