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Water present on early Mars is often assumed to have been habitable. In this study, experiments were performed to investigate the habitability of well-defined putative martian fluids and to identify the accompanying potential formation of biosignatures. Simulated martian environments were developed by combining martian fluid and regolith simulants based on the chemistry of the Rocknest sand shadow at Gale Crater. The simulated chemical environment was inoculated with terrestrial anoxic sediment from the Pyefleet mudflats (United Kingdom). These enrichments were cultured for 28 days and subsequently subcultured seven times to ensure that the microbial community was solely grown on the defined, simulated chemistry. The impact of the simulated chemistries on the microbial community was assessed by cell counts and sequencing of 16S rRNA gene profiles. Associated changes to the fluid and precipitate chemistries were established by using ICP-OES, IC, FTIR, and NIR. The fluids were confirmed as habitable, with the enriched microbial community showing a reduction in abundance and diversity over multiple subcultures relating to the selection of specific metabolic groups. The final community comprised sulfate-reducing, acetogenic, and other anaerobic and fermentative bacteria. Geochemical characterization and modeling of the simulant and fluid chemistries identified clear differences between the biotic and abiotic experiments. These differences included the elimination of sulfur owing to the presence of sulfate-reducing bacteria and more general changes in pH associated with actively respiring cells that impacted the mineral assemblages formed. This study confirmed that a system simulating the fluid chemistry of Gale Crater could support a microbial community and that variation in chemistries under biotic and abiotic conditions can be used to inform future life-detection missions.

Northwest Africa 6963 (NWA 6963) is a coarse-grained, gabbroic Martian meteorite that further extends our Martian sample collection, both compositionally and texturally. Gabbroic shergottite NWA 6963 provides direct petrologic evidence of intrusive igneous conditions within the Martian crust. Here, we analyzed geochemical zoning profiles and microstructural-crystallographic information from electron backscattered diffraction of augite and pigeonite to constrain the crystallization history of NWA 6963. Compositional zoning profiles reveal pyroxenes with augite or pigeonite cores mantled by Fe-rich pigeonite rims. Our results suggest complex pyroxene textures and zoning profiles observed in pyroxenes in NWA 6963 are due to pyroxene accumulation from a crystallizing magma in a large intrusive environment (sill or magma chamber); however, without geologic context or companion samples, it is currently impossible to rule out accumulation at the base of a very large (>>100 m) differentiated flow.

This work describes a new high-altitude Mars analogue site and the stratification of microbial communities with depth within lake sediments. Understanding how microbial communities at this site change with depth may give insights into the type of metabolism that may have dominated paleolake environments on early Mars and the resulting biosignatures. Introduction: High-Altitude Andean lakes (HAALs) are poly-extreme environments which mimic many of the physiochemical conditions present on Mars during the Noachian (4.1 – 3.7 Gya) and Hesperian Mars (3.7 – 3.0 Gya)1,2. This combination of physiochemical conditions has led to HAALs being identified as natural laboratories for studying life under conditions analogous to early Earth and early Mars1,3. Present-day Mars is a cold, hyper-arid planet with surface conditions incapable of supporting liquid water in most locations. However, orbiter, rover, and lander missions have uncovered extensive hydrated mineral deposits and widespread geomorphological evidence of long-lasting fluvial and lacustrine environments, which dried up in the Hesperian4. Following the collapse of the martian magnetosphere, conditions on the surface would have become increasingly inclement. However, lake sediments may have offered refuge against desiccation, intense ultra-violet radiation (UV), large diurnal temperature fluctuations, and reduced atmospheric pressures with biosignatures potentially being preserved following lithificaytion5. For this reason, the study of analogue environments and the nascent microbiome is crucial in informing targets for biosignature detection. Despite their relevance to early Hesperian Mars, the lakes of the Argentinian Puna (a plateau between 3000 – 6000 m) remain understudied6. Here we present the geochemistry and microbial communities associated with the lake water and sediments from the previously undescribed Laguna de Antofagasta (LDA; Catamarca, Argentina, -26.111148, -67.407338) were analysed. We demonstrated that these communities change with depth, which will aid in identifying relevant metabolisms and biosignatures to inform current and future life-detection missions. Methods: Lake water and cores (5 x 30 cm) were collected from five sample points located around the perimeter of LDA in April 2022 (Figure 1). For each microbial core, a sister core was collected for geochemical analyses (pH, temperature, and dissolved oxygen (DO) readings) to avoid contamination of microbial cores. Each core was divided evenly into an upper, middle, and bottom section before being stored under anaerobic conditions. The lake water samples were collected and filtered using 0.22 µm Sterivex filters, and all samples were transported to The Open University, UK at 4˚C. Pore and lake water were analysed using ICP-OES and IC analysis to collect bulk chemical and ionic concentrations. DNA was extracted using the XS buffer method7, and 16S rRNA gene sequencing was performed to characterise the microbial communities. In addition, Postgate B media was used during culture-dependent analysis to isolate sulphate-reducing bacteria (SRB). Figure 1: Laguna de Antofagasta (LDA) is situated in the Argentinian Puna in the Andes (A). LDA sits at the base of the Volcán La Alumbrera lava field, Antofagasta volcanic field, Catamarca, Argentina (Image B). Image credit: Gerardo Antonio Stoppiello. Results: There were clear differences in physicochemical conditions as well as microbial communities between the sites. Depth correlated with temperature stability, e.g., the upper sections 0-10 cm (n=5) ranged from 2.5 – 13.0 and the bottom 20-30 cm (n=5) fluctuated between 6. 7 and 8.3˚C. pH ranged from 6.8 to 8.3 but appeared to be stable across the depth profiles (Figure 2). Microbial communities also shifted with depth; genera associated with sulfate-reduction became dominant in the bottom sections. Subsequent culture-independent analysis successfully enriched for sulfate-reducing microorganisms. Canonical Correspondence Analysis (CCA) indicated that dissolved oxygen levels, location, and pH had the greatest impact on microbial community composition. Figure 2: Cores were separated into sections before and data were collected on temperature, pH and DO. Implications: In line with previous works6,8,9, the results from this study highlight sulfate reduction as a key metabolism within HAALs and Mars analogue environments. This is significant as biosignatures, and their preservation may be influenced by depth. This work also highlights that physical conditions in the shallow subsurface remain stable, avoiding many of the challenges presented to life by extreme UV, desiccation, and diurnal temperature fluctuation. Future work: To identify how microbial communities may have stratified in martian paleolakes, simulation experiments will be performed. To replicate geochemical conditions, a novel simulant will be used in a column and microbial community structure will be monitored across depth and time. References [1] Cabrol et al. Geophys Res Biogeosciences. 2009;114(4):1–20. [2] Farías et al. J Geophys Res Biogeosciences. 2009;114(G2):0–04. [3] Mlewski et al. Front Microbiol. 2018;9(MAY):996. [4] Carr & Head JW. Earth Planet Sci Lett. 2010;294(3–4):185–203. [5] Grotzinger et al. Science (80- ). 2014;343(6169). [6] Gomez et al. PALAIOS. 2014;29(5):233–49. [7] Tillett & Neilan. J Phycol. 2000;36(1):251–8. [8] Nixon et al. Astron Geophys. 2013;54(1):13–6. [9] Westall et al. Astrobiology. 2015;15(11):998–1029.

Enceladus, an icy moon of Saturn, is a potentially habitable environment. Its South Polar Region hosts active plumes that eject material from the subsurface into space. Plume material was analysed by the Cassini spacecraft, which confirmed the presence of a global subsurface ocean, active hydrothermal activity, and the presence of bio-essential elements (carbon, nitrogen, and hydrogen) [1-4]. Data from the plumes provided a snapshot of the subsurface chemical environment, however, it could not fully constrain the composition of the silicate interior or specific ocean chemistry. We present work constraining a modern-day Enceladus ocean composition utilising theoretical compositions for the icy exterior (and subsurface ocean) and silicate interior of an early Enceladus and studying the evolution of the ocean chemistry over time. The modern-day ocean composition was determined by thermochemical modelling using CHIM-XPT [5], where hypothetical starting compositions for the ocean interact with the silicate interior. A CI carbonaceous chondrite was used as an analogue to represent the silicate interior of Enceladus [6] and a fluid of cometary ice composition was used as an analogue for the moon’s early ocean [7]. The water-rock interactions of these two analogues were modelled and used to investigate the evolution of the ocean chemistry of Enceladus over time. The models were run over a range of temperature and pressure conditions representative of the ocean floor conditions of Enceladus. For example, it has been determined [2] that a minimum temperature of 90 ℃ is required to form the SiO2 particles that have been measured in the stream believed to originate from Enceladus and the pressure hypothesized for the water-rock interface is 80 bar, based upon the combined depth of the subsurface ocean and ice crust, along with gravitational data measurements [2], so these conditions were modelled. Further modelling was carried out at higher temperatures (up to 250 ℃) and higher pressures (up to 150 bar), to explore reactions that may occur deeper within the porous silicate interior. The resultant modern-day ocean fluid was then both cooled and depressurized (using CHIM-XPT) to study changes in the chemical composition as water ascends from the water-rock interface to the ice-water interface on Enceladus. Finally, the ocean composition at the ice-ocean interface was frozen using FREZCHEM to replicate the freezing process in the plumes of Enceladus. The ice grain composition generated through thermochemical modelling was then critically compared to Cassini’s plume data. The ice grains generated through this study were dominated by water ice, with NaCl, NaHCO3, Na2CO3, KCl and a low concentration of Na2SO4, all of which have been detected in the plumes or E-ring, with the exception of Na2SO4, where the concentration may have been below the limit of detection of the instruments onboard Cassini [3]. These results suggests that a CI chondrite and a cometary ice composition may be suitable analogues for the silicate interior and the icy exterior of a proto-Enceladus. A complex modern-day ocean composition has been generated that is more complex that has been indicated by analysed ice grains. Additionally, this work may be able to constrain potential concentrations of aqueous species that have not been observed by Cassini, in particular trace species such as sulfates, transition metals and phosphates, that could be used to define the detection limits required to identify target chemical species on instruments onboard future missions. We will present the outcomes from this modelling, which includes a modern-day ocean composition and our findings from modelling of the cooling and freezing of ocean fluids as they are transported from the ocean floor to outer space. [1] Thomas P. C. et al., (2016), Icarus, 264, 37-47 [2] Hsu H. W. et al., (2015), Nature, 519, 207-210 [3] Waite, J. H., et al., Nature, 460, 487-490, 2009 [4] Postberg F. et al., (2018) Nature, 558, 564-568 [5] Reed, M. H., Spycher, N. F., Palandri, J., (2010) User guide for CHIM-XPT, University of Oregon, Oregon [6] Hamp R. E. et al., (2019), 50th LPSC 2019, Abstract 1091 [7] Hamp R.E et al., (2021), 52nd LPSC 2021, Abstract 2548

International audience; Aeolian processes have shaped and contributed to the geological record in Gale crater, Mars, long after the fluviolacustrine system existed ∼3 Ga ago. Understanding these aeolian deposits, particularly those which have been lithified and show evidence for aqueous alteration, can help to constrain the environment at their time of deposition and the role of liquid water later in Mars' history. The NASA Curiosity rover investigated a prominent outcrop of aeolian sandstone within the Stimson formation at the Greenheugh pediment as part of its investigation of the Glen Torridon area. In this study, we use geochemical data from ChemCam to constrain the effects of aeolian sedimentary processes, sediment provenance, and diagenesis of the sandstone at the Greenheugh pediment, comparing the Greenheugh data to the results from previous Stimson localities situated 2.5 km north and >200 m lower in elevation. Our results, supported by mineralogical data from CheMin, show that the Stimson formation at the Greenheugh pediment was predominately sourced from an olivine-rich unit that may be present farther up the slopes of Gale crater's central mound. Our results also suggest that the Greenheugh pediment Stimson formation was cemented by surface water runoff such as that which may have formed Gediz Vallis. The lack of alteration features in the Stimson formation at the Greenheugh pediment relative to those of the Emerson and Naukluft plateaus suggests that groundwater was not as available at this locality compared to the others. However, all sites share diagenesis at the unconformity

The abundance and distribution of water within Mars through time plays a fundamental role in constraining its geological evolution and habitability. The isotopic composition of martian hydrogen provides insights into the interplay between different water reservoirs on Mars. However, D/H (deuterium/hydrogen) ratios of martian rocks and of the martian atmosphere span a wide range of values. This has complicated identification of distinct water reservoirs in and on Mars within the confines of existing models that assume an isotopically homogenous mantle. Here we present D/H data collected by secondary ion mass spectrometry for two martian meteorites. These data indicate that the martian crust has been characterized by a constant D/H ratio over the last 3.9 billion years. The crust represents a reservoir with a D/H ratio that is intermediate between at least two isotopically distinct primordial water reservoirs within the martian mantle, sampled by partial melts from geochemically depleted and enriched mantle sources. From mixing calculations, we find that a subset of depleted martian basalts are consistent with isotopically light hydrogen (low D/H) in their mantle source, whereas enriched shergottites sampled a mantle source containing heavy hydrogen (high D/H). We propose that the martian mantle is chemically heterogeneous with multiple water reservoirs, indicating poor mixing within the mantle after accretion, differentiation, and its subsequent thermochemical evolution.

International audience; The clay-rich Glen Torridon region of Gale crater, Mars, was explored between sols 2300 and 3007. Here, we analyzed the diagenetic features observed by Curiosity, including veins, cements, nodules, and nodular bedrock, using the ChemCam, Mastcam, and Mars Hand Lens Imager instruments. We discovered many diagenetic features in Glen Torridon, including dark-toned iron- and manganese-rich veins, magnesium- and fluorine-rich linear features, Ca-sulfate cemented bedrock, manganese-rich nodules, and iron-rich strata. We have characterized the chemistry and morphology of these features, which are most widespread in the higher stratigraphic members in Glen Torridon, and exhibit a wide range of chemistries. These discoveries are strong evidence for multiple generations of fluids from multiple chemical endmembers that likely underwent redox reactions to form some of these features. In a few cases, we may be able to use mineralogy and chemistry to constrain formation conditions of the diagenetic features. For example, the dark-toned veins likely formed in warmer, highly alkaline, and highly reducing conditions, while manganese-rich nodules likely formed in oxidizing and circumneutral conditions. We also hypothesize that an initial enrichment of soluble elements, including fluorine, occurred during hydrothermal alteration early in Gale crater history to account for elemental enrichment in nodules and veins. The presence of redox-active elements, including Fe and Mn, and elements required for life, including P and S, in these fluids is strong evidence for habitability of Gale crater groundwater. Hydrothermal alteration also has interesting implications for prebiotic chemistry during the earliest stages of the crater’s evolution and early Mars.

Nitrate-dependent Fe

International audience; Data returned by NASA’s Mars Science Laboratory Curiosity rover showed evidence for abundant secondary materials, including Fe-oxides, phyllosilicates, and an amorphous component on and below Vera Rubin ridge in the Murray formation. We have used equilibrium thermochemical modeling to test the hypothesis that these altered sediments were deposited predominantly as detrital igneous grains and subsequently underwent diagenetic alteration. Chemical compositions of the altered components were calculated using data returned by the Chemistry and Mineralogy X-ray diffraction instrument and the Alpha Particle X-ray Spectrometer on board Curiosity. Reaction of these alteration compositions with a CO2-poor and oxidizing dilute aqueous solution was modeled at 25 – 100 °C, with varying amounts of Fe3+/Fetot of the host rock. The modeled alteration assemblages contained abundant phyllosilicates and Fe-oxides at >100 water to rock ratios, and were directly comparable to the abundances of hematite and clay minerals observed by Curiosity at 10,000 water to rock at 50 – 100 °C with pH ranging from 7.9 to 9.3. Our modeling results suggest that the hematite-clay mineral assemblage is primarily the result of enhanced groundwater flow compared to the Sheepbed mudstone in the Bradbury Group observed at Yellowknife Bay, and underwent further, localized alteration to produce the mineralogy observed by Curiosity.

Volcanic features and impact craters are ubiquitous features on Mars, and hydrothermal systems associated with the production of these features should have been abundant in Mars’s early history. These hydrothermal systems represent potentially habitable environments and are therefore a high priority for continued investigations of the Martian crust. Here we present a Mars analog study where basaltic magma intruded water-bearing sediments to produce a high-temperature (as high as ∼700°C) hydrothermal system, which we use to constrain the potential habitability of similar systems on Mars via mineralogy and geochemistry including S, C, and O isotopic systematics. Our analog site suggests evidence for a habitable environment once the system cooled below 120°C and the potential presence of microbial activity based on the combination of dolomite and C-isotopic systems in the same sample. These findings highlight the importance of future missions to investigate the interface of sediments with magmas and/or late-stage impact melts where microbial life may have taken hold when temperature conditions allowed.

Hydrothermal systems that formed as a result of impact events possess all the key requirements for life: liquid water, a supply of bio‐essential elements, and potential energy sources. Therefore, they are prime locations in the search for life on other planets. Here, we apply thermochemical modeling to determine secondary mineral formation within an impact‐generated hydrothermal system, using geochemical data returned for two soils on Mars found in regions that have previously experienced alteration. The computed mineral reaction pathways provide a basis for Gibbs energy calculations that enable both the identification of available geochemical energy, obtained from Fe‐based redox reactions, that could be utilized by potential microbial life within these environments, and an estimate of potential cell numbers. Our results suggest that water–rock interactions occurring within impact‐generated hydrothermal systems could support a range of Fe‐based redox reactions. The geochemical energy produced from these reactions would be substantial and indicates that crater environments have the potential to support microbial cell numbers similar to what has been identified in terrestrial environments.

In August 2015, the Curiosity Mars rover discovered tridymite, a high‐temperature silica polymorph, in Gale crater. The existing model for its occurrence suggests erosion and detrital sedimentation from silicic volcanic rocks in the crater rim or central peak. The chemistry and mineralogy of the tridymite‐bearing rocks, however, are not consistent with silicic volcanic material. Using data from Curiosity, including chemical composition from the Alpha Particle X‐ray Spectrometer, mineralogy from the CheMin instrument, and evolved gas and isotopic analyses from the Sample Analysis at Mars instrument, we show that the tridymite‐bearing rocks exhibit similar chemical patterns with silica‐rich alteration halos which crosscut the stratigraphy. We infer that the tridymite formed in‐place through hydrothermal processes and show additional chemical and mineralogical results from Gale crater consistent with hydrothermal activity occurring after sediment deposition and lithification.

Low‐grade metamorphic hydrous minerals and carbonates occur in various settings on Mars and in Martian meteorites. We present constraints on the stability of prehnite, zeolites, serpentine, and carbonates by modeling the influence of H2O‐CO2 fluids during low‐grade metamorphism in the Martian crust using compositions of a Martian basalt and an ultramafic cumulate. In basaltic compositions with 5 wt% fluid, our models predict prehnite in less oxidized, CO2‐poor conditions (≤0.44 mol kg−1 CO2) on warmer geotherms of 20 °C km−1. At fluid‐saturated conditions, epidote and laumontite are replaced by quartz, calcite, chlorite, and muscovite. In ultramafic compositions with 5 wt% fluid, antigorite (serpentine) is stable at CO2‐poor conditions of ≤0.33 mol kg−1, while talc forms at 0.05–0.56 mol kg−1 CO2. At fluid‐saturated conditions, antigorite is replaced by talc and chlorite, and at higher X(CO2) by magnesite and quartz. Our models therefore suggest that prehnite, zeolites, and serpentine have formed in a CO2‐poor environment on Mars implying that fluids during their formation either did not contain high amounts of CO2 or had degassed CO2. Carbonates and potentially talc would have formed in the presence of a CO2‐bearing fluid and therefore at different alteration stages than for prehnite, zeolites, and serpentine either in the same hydrothermal event during which the fluid composition changed gradually due to cooling and precipitation or by separate and successive alteration events with fluids of different compositions.

NASA’s search for habitable environments has focused on alteration mineralogy of the Martian crust and the formation of hydrous minerals, because they reveal information about the fluid and environmental conditions from which they precipitated. Extensive work has focused on the formation of alteration minerals at low temperatures, with limited work investigating metamorphic or high-temperature alteration. We have investigated such a site as an analog for Mars: a mafic dike on the Colorado Plateau that was hydrothermally altered from contact with groundwater as it was emplaced in the porous and permeable Jurassic Entrada sandstone. Our results show evidence for fluid mobility removing Si and K but adding S, Fe, Ca, and possibly Mg to the system as alteration progresses. Mineralogically, all samples contain calcite, hematite, and kaolinite; with most samples containing minor anatase, barite, halite, and dolomite. The number of alteration minerals increase with alteration. The hydrothermal system that formed during interaction of the magma (heat source) and groundwater would have been a habitable environment once the system cooled below ∼120 °C. The mineral assemblage is similar to alteration minerals seen within the Martian crust from orbit, including those at Gusev and Jezero Craters. Therefore, based on our findings, and extrapolating them to the Martian crust, these sites may represent habitable environments which would call for further exploration and sample return of such hydrothermally altered igneous materials.

Introduction The subsurface environment of Enceladus is potentially habitable: there is a global subsurface ocean [1], energy from hydrothermal activity [2] and bioessential elements [3]. Carbon, as a fundamental bioessential element, is critical for life, so understanding how it is processed within the Enceladus environment is crucial in assessing this moon’s potential habitability. Evidence from the south polar plumes suggests that carbon is likely to be bound within the silicate interior [4] and liberated through water-rock (silicate-ocean) interactions. Methods We have undertaken thermochemical modelling (CHIM-XPT) [5] of these interactions and tested different hypotheses for the formation of Enceladus. Both models reacted the silicate interior (with a CI chondrite composition [6]) with a fluid representative of the subsurface ocean: model 1) a dilute sodium chloride solution, based upon the assumption that the subsurface ocean originated as almost pure water [7]; model 2) a solution with a cometary composition (using data collected from 67P [8]), based upon the assumption that the ocean originated from melted cometary ice [9]. We have explored the full temperature and pressure ranges anticipated at the rock-water interface [2]. We have modelled the rock-water interactions: at the rock-water interface in the areas of hydrothermal activity; within the silicate interior, and in cooler areas of the ocean floor. In addition, we have run thermochemical models to cool the subsurface ocean fluid as it ascends from the ocean floor to the water-ice boundary; these results should be more comparable to the Cassini observations, as the plume material emanates from the ocean surface. Figure 1 - A cross section of the subsurface of Enceladus' South Polar Region, highlighting the area of study. The stars represent the different regions of study for the water-rock interaction models; each location represents different temperatures and pressure regimes. The arrows represent cooling and change in the chemical composition of the fluid as it moves from the ocean floor to the ice/ocean interface. Image Credit: R. E. Hamp Results/ Discussion With regards to the plausible chemistry of the Enceladus ocean, the model output agrees with the observations from the Cassini data; the dominant chemical species are sodium chloride, potassium chloride and sodium carbonates. The model has also revealed a possible formation mechanism for the silica nanoparticles within the subsurface ocean that could account for the detection of such particles in the Enceladus plumes [2]. This, in turn, validates our model and the simulant chemistry inputted. The cooling model results show that the pH of the ocean at the water/rock interface was significantly lower than that at the ocean/ice interface (8 compared with 10.5). Furthermore, the concentration of carbonates and sulfates decrease as they ascend though the water column, but the concentration of silica particles increases. The output from this work provides results very closely aligned to the concentrations of the chemical species detected by the Cassini Spacecraft. This work has also determined that a carbon cycle may operate at the rock-water interface, which could include a carbonate pump system and the formation of hydrocarbons up to C4. The availability of these chemical species and the potential for further ongoing reactions supports the evidence that the subsurface environment of Enceladus may be habitable. Summary We will present the outcomes from this modelling, which includes a theoretical composition for a modern day subsurface ocean, potential carbon cycling pathways and the effect of carbon species on the pH of the subsurface ocean fluid. We will also present the initial findings from modelling of the cooling of ocean fluids as they are transported from the ocean floor to the ocean/ice interface surface. [1] Thomas P. C. et al., (2016), Icarus, 264, 37-47 [2] Hsu H. W. et al., (2015), Nature, 519, 207-210 [3] McKay, C. P. et al., (2014) Astro-biology, 14, 352-355 [4] Glein C. R. & Waite J. H., (2020), Geophys Res Let, 47 [5] Reed, M. H., Spycher, N. F., Palandri, J., (2010) User guide for CHIM-XPT, University of Oregon, Oregon [6] Hamp R. E. et al., (2019), 50th LPSC 2019, Abstract 1091 [7] Brown R. H. et al, (2006) Science, 311, 1425-1428 [8] Hertier K. H., et al., (2017) RAS monthly notices, 469 [9] Neveu, M., et al., (2017) Geochim et Cosmochim, 212, 324-371

The environmental conditions on present-day Mars are detrimental for life as we know it; however cumulative evidence suggests that early Noachian Mars (~ 4 billion Ga) had a warmer climate with a denser atmosphere1 capable of supporting surficial liquid water, and providing protection from UV and cosmic radiation. It is possible, therefore, that early Mars could have been hospitable for microorganisms. While cellular degeneration is a rapid process following cell death, microorganisms do leave behind molecular clues as to their existence, or biosignatures, such as the lipid molecules that previously comprised their cell membranes. Each group of microorganisms leaves behind a distinct lipid “fingerprint” that is relatively resistant to harsh environmental conditions and can be preserved over geological timescales2. Various robotic and remote-sensing missions have confirmed the presence of salt deposits (e.g., chlorides, sulfates) at the late Noachian to late Hesperian (~ 4 to 3.5 Ga) boundaries of present-day Martian deposits. In particular, bulk enrichments of calcium and magnesium sulfates have been reported in the Hesperian (~ 3.3–3.7 Ga) sedimentary rocks of Gale crater3, which indicate the previous presence of widespread liquid water on Mars. On Earth, such salts have been found to harbour and protect microbial life for a prolonged period, possibly over millions of years4, thus evaporite sequences provide a compelling target for life detection, as putative biosignatures could be preserved5. Currently, the beneficial or deleterious effects of sulfate chemistry on the preservation of organic matter, especially under biologically destructive modern Martian conditions is not well constrained. Given the prominent presence of sulfates on the surface of Mars, this work explores whether sulfate minerals can act as viable substrates for the long-term preservation of lipids, when exposed to Mars-like radiative and atmospheric conditions, and aims to determine whether those signs of life can be explicitly detected. To carry out this work, we use a combination of analogue fieldwork and laboratory-based simulation studies. Microorganisms isolated from a magnesium sulfate-rich analogue site (Basque Lake) and other terrestrial early Mars analogues, will be entombed within artificial sulfate crystals by evaporating an experimental brine under low atmospheric pressure and UV radiation similar to that encountered on the surface of Mars using The Open University’s Mars chamber facility. The lipids within the samples will be extracted and derivatized to make them amenable to by pyrolysis-gas chromatography-mass spectrometry (py-GC-MS); py-GC-MS is an important component of the Sample Analysis at Mars (SAM) instrument suite onboard NASA’s Mars Science Laboratory (MSL) and of the Mars Organic Molecular Organizer (MOMA) on the ESA’s Rosalind Franklin (ExoMars) rover. This work will aid in characterizing the impacts of the simulated Martian environment and Martian mineralogy on the preservation and detection of lipid biomarkers within sulfitic evaporite deposits and will inform the robotic missions targeting the search for ancient signatures of life on Mars. References: [1] Carr MH, Head JW (2010) Earth and Planetary Science Letters 294: 185-203 [2] Luo G et al., (2019) Earth-Science Reviews 189: 99-124 [3] Rapin, W et al., (2019) Nature Geosciences 12:889–895 [4] Fendrihan S et al., (2006) Reviews in Environmental Science and Biotechnology 5: 203-218 [5] Johnson SS et al., (2020) Astrobiology 2020 20:167-178

International audience; The NASA Curiosity rover's ChemCam instrument suite has detected boron in calcium‐sulfate‐filled fractures throughout the sedimentary strata of Gale crater including Vera Rubin ridge. The presence of elevated B concentration provides insights into Martian subsurface aqueous processes. In this study we extend the data set of B in Ca‐sulfate veins across Gale crater, comparing the detection frequency and relative abundances with Li. We report 33 new detections of B within veins analyzed between Sols 1548 and 2311 where detections increase in Pettegrove Point and Jura members, which form Vera Rubin ridge. The presence of B and Li in the Ca‐sulfate veins is possibly due to dissolution of preexisting B in clays of the bedrock by acids or neutral water and redistribution of the elements into the veins. Elevated frequency of B detection in veins of Gale crater correlates with presence of dehydration features such as desiccation cracks, altered clay minerals and detections of evaporites such as Mg‐sulfates and chloride salts in the host rocks. The increased observations of B also coincide with decreased Li concentration in the veins (average Li concentration of veins drops by ~15 ppm). Boron and Li have varying solubilities, and Li does not form salts as readily upon dehydration as B, causing it to remain in the solution. So the weak negative correlation between B and Li may reflect the crystallization sequence during dehydration on Vera Rubin ridge.

This paper provides an overview of the Curiosity rover's exploration at Vera Rubin ridge and summarizes the science results. Vera Rubin ridge (VRR) is a distinct geomorphic feature on lower Aeolis Mons (informally known as Mt. Sharp) that was identified in orbital data based on its distinct texture, topographic expression, and association with a hematite spectral signature. Curiosity conducted extensive remote sensing observations, acquired data on dozens of contact science targets, and drilled three outcrop samples from the ridge, as well as one outcrop sample immediately below the ridge. Our observations indicate that strata composing VRR were deposited in a predominantly lacustrine setting and are part of the Murray formation. The rocks within the ridge are chemically in family with underlying Murray formation strata. Red hematite is dispersed throughout much of the VRR bedrock, and this is the source of the orbital spectral detection. Gray hematite is also present in isolated, gray‐colored patches concentrated towards the upper elevations of VRR, and these gray patches also contain small, dark Fe‐rich nodules. We propose that VRR formed when diagenetic event(s) preferentially hardened rocks, which were subsequently eroded into a ridge by wind. Diagenesis also led to enhanced crystallization and/or cementation that deepened the ferric‐related spectral absorptions on the ridge, which helped make them readily distinguishable from orbit. Results add to existing evidence of protracted aqueous environments at Gale crater and give new insight into how diagenesis shaped Mars’ rock record.

Authors acknowledge funding from the Science and Technology Facilities Council from the Grant ST/P000657/1. We would also like to acknowledge funding from a Leverhulme Trust Research Project Grant (RPG-2016-153) and thank the Polar Continental Shelf Program (Natural Resources Canada) for logistical field support in Nunavut. The transition of the martian climate from the wet Noachian era to the dry Hesperian (4.1–3.0 Gya) likely resulted in saline surface waters that were rich in sulfur species. Terrestrial analogue environments that possess a similar chemistry to these proposed waters can be used to develop an understanding of the diversity of microorganisms that could have persisted on Mars under such conditions. Here, we report on the chemistry and microbial community of the highly reducing sediment of Colour Peak springs, a sulfidic and saline spring system located within the Canadian High Arctic. DNA and cDNA 16S rRNA gene profiling demonstrated that the microbial community was dominated by sulfur oxidising bacteria, suggesting that primary production in the sediment was driven by chemolithoautotrophic sulfur oxidation. It is possible that the sulfur oxidising bacteria also supported the persistence of the additional taxa. Gibbs energy values calculated for the brines, based on the chemistry of Gale crater, suggested that the oxidation of reduced sulfur species was an energetically viable metabolism for life on early Mars. Publisher PDF

MURFI was financially supported in part by the UK Space Agency, and by the following grants: Balme: UK SA grants ST/L00643X/1 and ST/R001413/1; Bridges: UK SA grant ST/R00143X/1; Butcher and Wright: STFC studentship grant ST/N50421X/1; Coates and Griffiths: UK SA grant ST/R002223/1; Cousins: Royal Society of Edinburgh Research Fellowship and UK SA grant ST/P001297/1; Davis: UK STFC grant ST/K502388/1; Grindrod: UK SA and STFC grants ST/J005215/1, ST/L006456/1, ST/N000528/1; Gunn: UK SA grants ST/P001408/1, ST/P001394/1, ST/N006410/1; Muller: UK SA grant ST/P002145/1; Preston: UK SA grant ST/P001254/1; Stabbins: UK SA studentship grant ST/N002377/1. We thank the UK Harwell Campus Satellite Applications Catapult for providing access to the control room that became the MOC, and the STFC Rutherford Appleton Laboratory for other ROC support. The 2016 Mars Utah Rover Field Investigation (MURFI) was a Mars rover field trial run by the UK Space Agency in association with the Canadian Space Agency's 2015/2016 Mars Sample Return Analogue Deployment mission. MURFI had over 50 participants from 15 different institutions around the UK and abroad. The objectives of MURFI were to develop experience and leadership within the UK in running future rover field trials; to prepare the UK planetary community for involvement in the European Space Agency/Roscosmos ExoMars 2020 rover mission; and to assess how ExoMars operations may differ from previous rover missions. Hence, the wider MURFI trial included a ten-day (or ten-‘sol’) ExoMars rover-like simulation. This comprised an operations team and control centre in the UK, and a rover platform in Utah, equipped with instruments to emulate the ExoMars rovers remote sensing and analytical suite. The operations team operated in ‘blind mode’, where the only available data came from the rover instruments, and daily tactical planning was performed under strict time constraints to simulate real communications windows. The designated science goal of the MURFI ExoMars rover-like simulation was to locate in-situ bedrock, at a site suitable for sub-surface core-sampling, in order to detect signs of ancient life. Prior to “landing”, the only information available to the operations team was Mars-equivalent satellite remote sensing data, which were used for both geologic and hazard (e.g., slopes, loose soil) characterisation of the area. During each sol of the mission, the operations team sent driving instructions and imaging/analysis targeting commands, which were then enacted by the field team and rover-controllers in Utah. During the ten-sol mission, the rover drove over 100 m and obtained hundreds of images and supporting observations, allowing the operations team to build up geologic hypotheses for the local area and select possible drilling locations. On sol 9, the team obtained a subsurface core sample that was then analyzed by the Raman spectrometer. Following the conclusion of the ExoMars-like component of MURFI, the operations and field team came together to evaluate the successes and failures of the mission, and discuss lessons learnt for ExoMars rover and future field trials. Key outcomes relevant to ExoMars rover included a key recognition of the importance of field trials for (i) understanding how to operate the ExoMars rover instruments as a suite, (ii) building an operations planning team that can work well together under strict time-limited pressure, (iii) developing new processes and workflows relevant to the ExoMars rover, (iv) understanding the limits and benefits of satellite mapping and (v) practicing efficient geological interpretation of outcrops and landscapes from rover-based data, by comparing the outcomes of the simulated mission with post-trial, in-situ field observations. In addition, MURFI was perceived by all who participated as a vital learning experience, especially for early and mid-career members of the team, and also demonstrated the UK capability of implementing a large rover field trial. The lessons learnt from MURFI are therefore relevant both to ExoMars rover, and to future rover field trials. Postprint

We present results of an ongoing petrologic and modelling study of a new Martian analogue rock: The Frankenstein Gabbro (Odenwald, Germany). Our aim is to predict mineral reaction paths and fluid properties during hydrothermal alteration of basaltic host rocks on Mars – thought to be a common by-product of impact cratering – in order to assess the habitability of the fluids for the potential of Martian life, and establish a link between habitable fluid conditions and secondary mineral assemblages.Primary minerals of the analogue are mostly plagioclase (~70 vol.%) and clinopyroxene (~20 vol.%) with lesser percentages of amphiboles and Fe-oxides. We focus on a chloritic-propylitic alteration event associated with hairline fault planes and mineral veinlets. The secondary mineralisation shows strong small-scale variability, depending on host mineral and type of fluid pathway: For plagioclase hosts, fault planes are dominated by chlorite with additional epidote and prehnite, while mineral veinlets consist of albite ± calcite ± chlorite ± epidote ± K-feldspar ± mica. For clinopyroxene hosts, fault planes consist of actinolite with additional chlorite or vermiculite, while mineral veinlets consist of prehnite and vermiculite.We use the software CHIM-XPT to model mineral reaction paths, with published XRF bulk rock data, EMP analyses of single minerals, and a starting fluid enriched in Na, K, Mg and Si for input, the latter based on calculated element budgets of mineral replacement reactions. Our models reproduce secondary assemblages related to plagioclase-hosted fault planes (chlorite–epidote–prehnite) and veinlets (albite–chlorite–epidote–K-feldspar–mica), as well as alteration rims around clinopyroxene related to fault planes (actinolite–chlorite). Corresponding fluid conditions are ~200–250 °C, pH ~6.5–8.0, at water/rock ratios >3000, in agreement with pre-model constraints by mineralogy. The breakdown of clinopyroxene and plagioclase releases large amounts of Ca, with calcite inferred to be a late-stage product of cooling. Fluid redox state is shown to be largely controlled by host minerals, and in turn exerts strong influence on secondary mineral formation: clinopyroxene releases Fe2+ during alteration, which is taken up by chlorite; in contrast, plagioclase contains up to 0.5 wt.% Fe3+ substituting for Al, which is taken up by epidote. Prehnite, of the same elemental composition except for Fe, is inversely correlated with epidote. Thus, the relative percentages of chlorite, epidote and prehnite can serve as indicators of redox state in similar types of rock.Our models match key petrological observations and provide information about the alteration process beyond what may be directly observed. They illustrate the need to account for small-scale variability, and to adjust models on a case-by-case basis. This has important implications for models of Martian habitability, where similar features may be expected. Next, we will apply these reaction pathways to Martian rocks (shergottitic basalts), focusing especially on small-scale distribution of dissolved iron species, a suggested energy source for hypothetical microbial Martian life.

Following K-Ar dating of a mudstone and a sandstone, a third sample has been dated by the Curiosity rover exploring Gale Crater. The Mojave 2 mudstone, which contains relatively abundant jarosite, yielded a young K-Ar bulk age of 2.57 ± 0.39 Ga (1σ precision). A two-step heating experiment was implemented in an effort to resolve the K-Ar ages of primary and secondary mineralogical components within the sample. This technique involves measurement of 40Ar released in low-temperature (500°C) and high-temperature (930°C) steps, and a model of the potassium distribution within the mineralogical components of the sample. Using this method, the high-temperature step yields a K-Ar model age of 4.07 ± 0.63 Ga associated with detrital plagioclase, compatible with the age obtained on the Cumberland mudstone by Curiosity. The low-temperature step, associated with jarosite mixed with K-bearing evaporites and/or phyllosilicates, gave a youthful K-Ar model age of 2.12 ± 0.36 Ga. The interpretation of this result is complicated by the potential for argon loss after mineral formation. Comparison with the results on Cumberland and previously published constraints on argon retentivity of the individual phases likely to be present suggests that the formation age of the secondary materials, correcting for plausible extents of argon loss, is still less than 3 Ga, suggesting post-3 Ga aqueous processes occurred in the sediments in Gale Crater. Such a result is inconsistent with K-bearing mineral formation in Gale Lake and instead suggests postdepositional fluid flow at a time after surface fluvial activity on Mars is thought to have largely ceased.

We report the first in situ detection of boron on Mars. Boron has been detected in Gale crater at levels

Diagenetic silica enrichment in fracture-associated halos that crosscut lacustrine and unconformably overlying aeolian sedimentary bedrock is observed on the lower north slope of Aeolis Mons in Gale crater, Mars. The diagenetic silica enrichment is colocated with detrital silica enrichment observed in the lacustrine bedrock yet extends into a considerably younger, unconformably draping aeolian sandstone, implying that diagenetic silica enrichment postdates the detrital silica enrichment. A causal connection between the detrital and diagenetic silica enrichment implies that water was present in the subsurface of Gale crater long after deposition of the lacustrine sediments and that it mobilized detrital amorphous silica and precipitated it along fractures in the overlying bedrock. Although absolute timing is uncertain, the observed diagenesis likely represents some of the most recent groundwater activity in Gale crater and suggests that the timescale of potential habitability extended considerably beyond the time that the lacustrine sediments of Aeolis Mons were deposited.

Finding evidence of life elsewhere in the Solar System is dependent on understanding biotic processes that could occur within potentially habitable environments. Here, we describe a suite of high-pressure flow-through reactors that have been developed to investigate biotic and abiotic processes within simulated sub-surface martian and icy moon environments.

The UK Open University (UKOU) operates a distance-learning model supporting students who are geographically dispersed and studying part-time. Development of team-working skills is particularly challenging within such a model, but is considered a necessary partof the higher education experience of space scientists and astronomers. We report on three team-working projects in space science and astronomy that we run at the UKOU at advanced undergraduate and taught postgraduate levels. The projects are: (i) an investigation of quasar spectra using data from the Sloan Digital Sky Survey (SDSS), (ii) characterisation of variable star light curves using observations from a robotic telescope, and (iii) a Mars rover mission simulation. The robotic telescope and the Mars rover simulation are part of The Open University’s award-winning OpenSTEM Labs. All three projects involve teams of students working remotely from each other and communicating through asynchronous and synchronous (shared audio and whiteboard) methods. The projects are somewhat open-ended and require teams to make collective decisions about their actions.We describe how these projects are being studied in order to better understand the student experience of on-line team-working.

Existing martian simulants are predominantly based on the chemistry of the average ‘global’ martian regolith as defined by data on chemical and mineralogical variability detected by orbiting spacecraft, surface rovers and landers. We have therefore developed new martian simulants based on the known composition of regolith from four different martian surface environments: an early basaltic terrain, a sulfur-rich regolith, a haematite-rich regolith and a contemporary Mars regolith. Simulants have been developed so that the Fe2+/Fe3+ ratios can be adjusted, if necessary, leading to the development of four standard simulants and four Fe-modified simulants. Characterisation of the simulants confirm that all but two (both sulfur-rich) are within 5 wt% of the martian chemistries that they were based on and, unlike previous simulants, they have Fe2+/Fe3+ ratios comparable to those found on Mars. Here we outline the design, production and characterisation of these new martian regolith simulants. These are to be used initially in experiments to study the potential habitability of martian environments in which Fe may be a key energy source.

Although nucleation of magnetite and/or hematite along dislocations upon oxidation of olivine has been observed by many workers, the effect of oxidation on the magnetic properties of the sample with specific mineralogical alterations has not been studied. Therefore, we investigate this problem using a set of time series 1 bar oxidation experiments at 600 and 900 °C. Results show rapid olivine oxidation and alteration at both 600 and 900 °C, forming magnetite and hematite associated with a change from paramagnetic to ferromagnetic behavior after oxidation. Magnetite and hematite nucleate along dislocations and impurities in the crystal structure, along with surface coatings and within cracks in the crystals.\ud \ud Fresh, unaltered mantle xenoliths containing magnetite have been interpreted as having formed in cold tectonic regimes in the mantle, rather than through oxidation during or after ascent. Mantle xenoliths rapidly ascend through the mantle with estimates of the ascent of up to 90 km/h (3 GPa/h) based on the diffusion profile of water in mantle olivine. The rates correspond to xenoliths ascending through the mantle over hours and not days or weeks. Our results show that olivine oxidation and alteration can occur in days to weeks at 600 °C and within minutes at 900 °C. Therefore, if the xenolithic material is transported to the surface in a cold magma (at temperatures ≤600 °C), then the timescale of ascent is likely not long enough for oxidation to cause magnetite formation or a ferromagnetic signature to occur. However, if the material is transported in a hot oxidized basaltic magma (with temperatures ≥900 °C), then oxidation can cause magnetite formation and a ferromagnetic signature.

Currently, the surface of Mars cannot sustain liquid water, but there is evidence suggesting that water was present in the Noachian. Although water might exist in the subsurface of Mars, it could not sustain in the present day unless it was highly saline. Thus, saline springs in polar desert environments are analogues with which to investigate martian conditions. An example of this is Axel Heiberg Island, located in a region of continuous permafrost in the Canadian High Arctic, which hosts sulfidic and highly saline springs. In this study, cultivation-dependant and independent techniques were used to investigate the microbial diversity of a sediment sample collected from a saline cold (3–8 °C) pool at Colour Peak Springs on Axel Heiberg. Both DNA and RNA were extracted from the samples, and the microbial community was characterised using the 16S rRNA gene from the extracted nucleic acids. The metabolic profile was characterised by screening DNA and cDNA for functional genes relating to the cycling of carbon (coxL, xoxF, cbbL), nitrogen (nifH, nosZ, nod) and sulfur (dsrB, soxB). The community profiles were used to inform enrichment strategies, allowing for the isolation and characterisation of several halophilic isolates including strains of Marinobacter, Halomonas, Halanaerobium and Loktanella. Through this work we have been able to develop an in-depth characterisation of the metabolic and phylogenetic diversity that is present and viable within this analogue site. This allows us to start building an understanding of the underlying mechanisms and strategies that enable organisms to persist in these environments.

Mars Science Laboratory's Sample Analysis at Mars (SAM) investigation has measured all of the stable isotopes of the heavy noble gases krypton and xenon in the martian atmosphere, in situ, from the Curiosity Rover at Gale Crater, Mars. Previous knowledge of martian atmospheric krypton and xenon isotope ratios has been based upon a combination of the Viking mission's krypton and xenon detections and measurements of noble gas isotope ratios in martian meteorites. However, the meteorite measurements reveal an impure mixture of atmospheric, mantle, and spallation contributions. The xenon and krypton isotopic measurements reported here include the complete set of stable isotopes, unmeasured by Viking. The new results generally agree with Mars meteorite measurements but also provide a unique opportunity to identify various non-atmospheric heavy noble gas components in the meteorites. Kr isotopic measurements define a solar-like atmospheric composition, but deviating from the solar wind pattern at 80Kr and 82Kr in a manner consistent with contributions originating from neutron capture in Br. The Xe measurements suggest an intriguing possibility that isotopes lighter than 132Xe have been enriched to varying degrees by spallation and neutron capture products degassed to the atmosphere from the regolith, and a model is constructed to explore this possibility. Such a spallation component, however, is not apparent in atmospheric Xe trapped in the glassy phases of martian meteorites.

Clay minerals, although ubiquitous on the ancient terrains of Mars, have not been observed in Martian meteorite Allan Hills (ALH) 84001, which is an orthopyroxenite sample of the early Martian crust with a secondary carbonate assemblage. We used a low-temperature (20 °C) one-dimensional (1-D) transport thermochemical model to investigate the possible aqueous alteration processes that produced the carbonate assemblage of ALH 84001 while avoiding the coprecipitation of clay minerals. We found that the carbonate in ALH 84001 could have been produced in a process, whereby a low-temperature (~20 °C) fluid, initially equilibrated with the early Martian atmosphere, moved through surficial clay mineral and silica-rich layers, percolated through the parent rock of the meteorite, and precipitated carbonates (thereby decreasing the partial pressure of CO2) as it evaporated. This finding requires that before encountering the unweathered orthopyroxenite host of ALH 84001, the fluid permeated rock that became weathered during the process. We were able to predict the composition of the clay minerals formed during weathering, which included the dioctahedral smectite nontronite, kaolinite, and chlorite, all of which have been previously detected on Mars. We also calculated host rock replacement in local equilibrium conditions by the hydrated silicate talc, which is typically considered to be a higher temperature hydrothermal phase on Earth, but may have been a common constituent in the formation of Martian soils through pervasive aqueous alteration. Finally, goethite and magnetite were also found to precipitate in the secondary alteration assemblage, the latter associated with the generation of H2. Apparently, despite the limited water–rock interaction that must have led to the formation of the carbonates ~ 3.9 Ga ago, in the vicinity of the ALH 84001 source rocks, clay formation would have been widespread.

The Mars Science Laboratory's Chemistry and Camera (ChemCam) instrument suite on-board the Curiosity rover has analysed ∼1200 sedimentary targets during the mission up to sol 1482. These targets have included sedimentary rock, diagenetic features (e.g., fracture-associated alteration halos, mineral veins, nodules, and erosion resistant raised ridges), active aeolian fines, soils and float. We have isolated ChemCam geochemical trends relating to diagenetic features and alteration products from those of the sedimentary rock in order to identify the compositional characteristics of Gale crater's sediment source regions. The effects of grain size variation on sedimentary unit geochemistry have been taken into account by grouping and analysing geological units according to grain size. With obvious diagenetic features removed from the database, and predominately isochemical aqueous alteration inferred for the Mt Sharp Group samples, we propose that source region composition is a stronger source of geochemical change between the Bradbury and Mt Sharp Groups than open-system alteration. Additionally, a lack of correlation between the Chemical Index of Alteration (CIA) values and SiO 2 , MgO or FeO T indicates that the slight increase in chemical weathering of the Mt Sharp Group sediments was insufficient to overprint sediment source compositional signatures. This has led to the identification of five unique igneous endmember compositions which we hypothesise to have contributed to Gale crater's stratigraphic record. These endmembers are: (1) a subalkaline basalt, compositionally similar to the tholeiitic Adirondack Class basalts of Gusev crater, and dominant within the finer grained units up to the base of Mt Sharp; (2) a trachybasalt, mostly identified within conglomerate units from the Darwin waypoint to the base of Mt Sharp; (3) a potassium-rich volcanic source, determined from strong potassium enrichment and a high abundance of sanidine that is most dominant in the fluvial sandstones and conglomerates of the Kimberley formation; (4) a highly evolved, silica-rich igneous source that correlates with the presence of tridymite, and is recorded in the lacustrine mudstone of Mt Sharp's Marias Pass locality; and, (5) a fractionated, relatively SiO 2 -rich subalkaline basalt, seen to have influenced the composition of mudstone deposited in the lower part of the Mt Sharp Group. Endmembers (1), (2), (3), and (4) have previously been identified at specific waypoints along the rover's traverse, but we show that their influence extends throughout Gale's stratigraphic record. The occurrence of detected endmembers is also strongly correlated with stratigraphic position, which suggests changing sediment source regions with time. We conclude that Gale sediment provenances were much more varied than suggested by the largely homogenous, globally-distributed Martian basalt inferred from orbit, showing that complex magmatic assemblages exist within the ancient highland crust surrounding Gale.

Martian meteorite Northwest Africa (NWA) 8114 – a paired stone to NWA 7034 – provides an opportunity to examine the thermal history of a martian regolith and study near-surface processes and ancient environmental conditions near an impact crater on Mars. Our study reports petrographic and alteration textures and focuses on pyroxene and iron oxide grains. Some of the pyroxene clasts show exsolution lamellae, indicating a high temperature magmatic origin and slow cooling. However, transmission electron microscopy reveals that other predominantly pyroxene clasts are porous and have partially re-crystallised to form magnetite and a K-bearing feldspathic glassy material, together with relict pyroxene. This breakdown event was associated with oxidation, with up to 25% Fe3+/ΣFe in the relict pyroxene measured using Fe-K XANES. By comparison with previous studies, this breakdown and oxidation of pyroxene is most likely to be a result of impact shock heating, being held at a temperature above 700 °C for at least 7 days in an oxidising regolith environment.We report an approximate 40Ar39Ar maximum age of 1.13 Ga to 1.25 Ga for an individual, separated, augite clast. The disturbed nature of the spectra precludes precise age determination. In section, this clast is porous and contains iron oxide grains. This shows that it has undergone the high temperature partial breakdown seen in other relict pyroxene clasts, and has up to 25% Fe3+/ΣFe. We infer that the age corresponds to the impact shock heating event that led to the high temperature breakdown of many of the pyroxenes, after consolidation of the impact ejecta blanket.High temperatures, above 700 °C, may have been maintained for long enough to remobilise and congruently partially melt some of the alkali feldspar clasts to produce the feldspar veins and aureoles that crosscut, and in some cases surround, the oxidised pyroxene. However, the veins could alternatively be the result of a hydrothermal event in the impact regolith. A simple Fourier cooling model suggests that a regolith of at least five metres depth would be sufficient to maintain temperatures associated with the pyroxene breakdown for over seven days. Low temperature hydrous alteration took place forming goethite, identified via XRD, XANES and FTIR. Comparing with previous studies, the goethite is likely to be terrestrial alteration pseudomorphing martian pyrite.

The Mars Science Laboratory Curiosity rover has encountered both ancient lithified and modern active aeolian dune deposits within Gale crater, providing an opportunity to study how aeolian processes have changed during Gale crater's geological history. This study uses data from the Chemistry and Camera (ChemCam) and Chemistry and Mineralogy (CheMin) instrument suites onboard Curiosity to; (1) constrain the diagenetic processes that lithified and altered the ancient aeolian Stimson formation, (2) investigate whether the geochemical signature in the Stimson formation is consistent with the aeolian mafic-felsic mineral sorting trend identified in the modern Bagnold dune fields in Gale crater, and (3) discuss the provenance of the Stimson sediments, comparing it to those identified in the modern dune and ancient river and lake deposits also analyzed along Curiosity's traverse.\ud \ud The ancient Stimson dune deposits that stratigraphically overlie the Gale fluvio-lacustrine units were analyzed in two locations; the Emerson and the Naukluft plateaus. ChemCam data show that the Stimson formation has subtle variations in MgO, Al2O3, Na2O, and K2O between the two localities. An agglomerative cluster analysis of the constrained Stimson dataset reveals five clusters, four of which relate to different proportions of mafic and felsic minerals analyzed by ChemCam. In general, the cluster analysis shows that the Emerson plateau has a greater proportion of mafic minerals and fewer coarse, felsic grains relative to the Naukluft plateau. This variation in mafic and felsic minerals between localities suggests a southwest to northeast net sediment transport direction due to aeolian mineral sorting dynamics preferentially transporting mafic minerals that are easier to saltate than the elongate, often coarser, felsic minerals. This derived transport direction for the Stimson formation supports that determined by sedimentological evidence and is opposite to that previously determined for the active Bagnold dunes inferring a change in the wind regime with time. An opposite sediment transport direction between the ancient and modern dunes in Gale crater further supports geochemical and mineralogical evidence that suggests different basaltic source regions. Compositionally, the bulk Stimson formation is most similar to the subalkaline basalt source region that is inferred to be the dominant sediment source of the fluvio-lacustrine Bradbury group. This is likely the result of the Stimson formation and basaltic Bradbury group sediments sharing a similar local basaltic source region such as the rim and walls of Gale crater.

Society has long looked up at the sky to wonder if we are alone in the Solar System or the universe. Of the planetary bodies near the Earth, Mars has always inspired humankind’s imagination, and owing to its close proximity to Earth attracted scientific investigations. Centuries of observation have seen enthusiasm for the planet wax and wane as evidence seemed to prove or disprove habitable conditions on the planet. As telescopes became better, observers captured their views of the planet on maps and drawings. One of the famous and far reaching maps was drawn during the Mars opposition of 1877 by Giovanni Virginio Schiaparelli (18351910). It sparked a wide interest and discussion among contemporary scholars, finally leading to Lowell’s interpretation and book, “Mars, the Abode of Life.” Many other observers drew similar features at similar places on Mars, making it likely for them to be actual Martian features (see, e.g., Sagan and Pollack, 1966; Jones, 2008 for reviews). However, their linear nature was not confirmed by many, a controversy that led Sagan and Pollack (1966, p. 117) to conclude that those interpretational discrepancies “have convinced many that the canals of Mars are a psychophysiological rather than an astronomical problem.” However, like many scientific controversies, this also sparked new methods and thinking as it led to pioneering thoughts as to the ways in which understanding of geologic processes on Earth could be used to understand observations on Mars. In fact, Peal (1893) wrote, “The remarkable feature of the whole case seems to be that so far there has been little or no reference to terrestrial experience when discussing the problem of the distribution of land and water on Mars. The great recent geological discoveries bearing on the subject appear to have been overlooked, […].” Looking at Earth analogs has, in fact, become an integral tool for the advancement of our understanding of Martian processes and environmental conditions.

Noble gases have been instrumental in establishing a link between the SNC(O) meteorites and planet Mars. A superior (compared to the previous Viking measurements) analysis of the Martian atmosphere (MA) by the SAM instrument aboard the Mars Science Laboratory (MSL) has recently become available, which only strengthens this link. Nevertheless the results obtained on Martian meteorites still provide the most complete picture of noble gases on Mars, not just atmospheric Martian noble gases but also gases that can be confidently described as being of “interior” origin. Overall three major components of trapped noble gases have been clearly identified in Martian meteorites: (1) ~recent MA; (2) fractionated and possibly ancient MA; (3) interior (mantle?) noble gases. An additional, perhaps minor, component is only observed during crushing of shergottites. While the fractionated atmospheric component may tell us about processes like weathering, the difference between the atmosphere and the interior reservoir on Mars is unlike the difference observed on Earth and points to significant differences in the volatile history of the two planets. The nonradiogenic gases in the atmospheres of the two planets—apart from the ~2 orders of magnitude difference in absolute abundance—however, share similarities in their element abundance patterns, which sets them apart from solar wind or primordial noble gases in primitive meteorites and may indicate similar acquisition/loss processes. In addition, the atmospheric Xe isotopic composition for these two planetary bodies is quite unique (and remarkably similar), which points to a similar fractionation process, or set of processes, leading to the observed composition. A crucial point to be settled is whether the isotopic composition of the (assumed) atmospheric Xe in the unique, >4 Ga old, ALH 84001 differs from that of modern Martian atmospheric Xe. The indication that it may have a solar wind–like composition instead poses a problem for currently popular models for the early evolution of the MA (as well as that of the terrestrial atmosphere).