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The mixed Fe(II)/Fe(III) mineral magnetite [Fe3O4] of various stoichiometric and non‐stoichiometric compositions have been reported in Martian soils and rocks by several rover missions. Magnetite is an important paleomagnetic indicator mineral and can serve as a 'biogeobattery' as a consequence of its magnetic properties and the mixed valence state of iron in its structure. Here, we assess the extent of oxidative weathering of magnetite in presence of chlorate and bromate containing solutions that are likely important oxidants on Mars. Oxyhalogen species, chlorate and bromate, produced non‐stoichiometric magnetite [Fe(II)/Fe(III) < 0.5] in Mars‐relevant, near‐neutral pH fluids; no other ferric minerals were produced. The same results were observed in highly acidic fluids with or without oxyhalogens. Owing to its resistance to extensive oxidation, magnetite can serve as an important archive of geochemical, paleomagnetic, and astrobiological information in samples that will be returned by the Mars Sample Return mission. Plain Language Summary: Magnetite is an iron oxide that contains both Fe(II) and Fe(III) in its crystal structure. The Fe(II) to Fe(III) ratio in an ideal (i.e., stoichiometric) magnetite is 0.5, that decreases as Fe(II) in its structure oxidizes to Fe(III) thereby forming non‐ideal (i.e., non‐stoichiometric) magnetite. Owing to its unique structure, magnetite can serve as an important paleomagnetic indicator mineral and a source of energy for microorganisms. Therefore, understanding the survivability of magnetite in presence of the harsh oxidizing chemical environment on Mars is important. Here, we conduct laboratory experiments in Mars‐like fluids to test the reactivity of magnetite in presence of strong and effective oxidants that have previously been shown to be active on Mars. Our results show that magnetite is resistant to extensive oxidation in presence of chlorate and bromate solutions to an extent that is much greater than other Fe(II) minerals like iron sulfides, and forms non‐stoichiometric magnetite making it a useful target for analyses of samples from the Mars Sample Return mission aimed at understanding Mars' magnetic history and habitability. Key Points: Magnetite shows resistance to oxidation by oxyhalogen compounds (chlorate and bromate) in Mars‐relevant fluidsNon‐stoichiometric magnetite on Mars may be formed by aqueous alteration of stoichiometric magnetite by oxyhalogen compoundsMagnetite likely preserves geochemical, paleomagnetic and astrobiological information and is an important target mineral in Mars return samples [ABSTRACT FROM AUTHOR]

Crewed missions to the Moon may resume as early as 2026 with NASA's Artemis III mission, and lunar dust exposure/inhalation is a potentially serious health hazard that requires detailed study. Current dust exposure limits are based on Apollo‐era samples that spent decades in long‐term storage on Earth; their diminished reactivity may lead to underestimation of potential harm that could be caused by lunar dust exposure. In particular, lunar dust contains nanophase metallic iron grains, produced by "space weathering"; the reactivity of this unique component of lunar dust is not well understood. Herein, we employ a chemical reduction technique that exposes lunar simulants to heat and hydrogen gas to produce metallic iron particles on grain surfaces. We assess the capacity of these reduced lunar simulants to generate hydroxyl radical (OH*) when immersed in deionized (DI) water, simulated lung fluid (SLF), and artificial lysosomal fluid (ALF). Lunar simulant reduction produces surface‐adhered metallic iron "blebs" that resemble nanophase metallic iron particles found in lunar dust grains. Reduced samples generate ~5–100× greater concentrations of the oxidative OH* in DI water versus non‐reduced simulants, which we attribute to metallic iron. SLF and ALF appear to reduce measured OH*. The increase in observed OH* generation for reduced simulants implies high oxidative damage upon exposure to lunar dust. Low levels of OH* measured in SLF and ALF imply potential damage to proteins or quenching of OH* generation, respectively. Reduction of lunar dust simulants provides a quick cost‐effective approach to study dusty materials analogous to authentic lunar dust. [ABSTRACT FROM AUTHOR]

With the Artemis III mission scheduled to land humans on the Moon in 2025, work must be done to understand the hazards lunar dust inhalation would pose to humans. In this study, San Carlos olivine was used as an analog of lunar olivine, a common component of lunar dust. Olivine was dissolved in a flow-through apparatus in both simulated lung fluid and 0.1 M HCl (simulated gastric fluid) over a period of approximately 2 weeks at physiological temperature, 37°C. Effluent samples were collected periodically and analyzed for pH, iron, silicon, and magnesium ion concentrations. The dissolution rate data derived from our measurements allow us to estimate that an inhaled 1.0 μm diameter olivine particle would take approximately 24 years to dissolve in the human lungs and approximately 3 weeks to dissolve in gastric fluid. Results revealed that inhaled olivine particles may generate the toxic chemical, hydroxyl radical, for up to 5-6 days in lung fluid. Olivine dissolved in 0.1 M HCl for 2 weeks transformed to an amorphous silica-rich solid plus the ferric iron oxy-hydroxide ferrihydrite. Olivine dissolved in simulated lung fluid shows no detectable change in composition or crystallinity. Equilibrium thermodynamic models indicate that olivine in the human lungs can precipitate secondary minerals with fibrous crystal structures that have the potential to induce detrimental health effects similar to asbestos exposure. Our work indicates that inhaled lunar dust containing olivine can settle in the human lungs for years and could induce long-term potential health effects like that of silicosis. [ABSTRACT FROM AUTHOR]

A Correction to this paper has been published: https://doi.org/10.1007/s11214-021-00801-2 [ABSTRACT FROM AUTHOR]

In the Late Noachian to Early Hesperian period, rivers transported detritus from igneous source terrains to a downstream lake within Gale crater, creating a stratified stack of fluviolacustrine rocks that is currently exposed along the slopes of Mount Sharp. Controversy exists regarding the paleoclimate that supported overland flow of liquid water at Gale crater, in large part because little is known about how chemical and mineralogical paleoclimate indicators from mafic‐rock dominated source‐to‐sink systems are translated into the rock record. Here, we compile data from basaltic terrains with varying climates on Earth in order to provide a reference frame for the conditions that may have prevailed during the formation of the sedimentary strata in Gale crater, particularly focusing on the Sheepbed and Pahrump Hills members. We calculate the chemical index of alteration for weathering profiles and fluvial sediments to better constrain the relationship between climate and chemical weathering in mafic terrains, a method that best estimates the cooler limit of climate conditions averaged over time. We also compare X‐ray diffraction patterns and mineral abundances from fluvial sediments in varying terrestrial climates and martian mudstones to better understand the influence of climate on secondary mineral assemblages in basaltic terrains. We show that the geochemistry and mineralogy of most of the fine‐grained sedimentary rocks in Gale crater display first‐order similarities with sediments generated in climates that resemble those of present‐day Iceland, while other parts of the stratigraphy indicate even colder baseline climate conditions. None of the lithologies examined at Gale crater resemble fluvial sediments or weathering profiles from warm (temperate to tropical) terrestrial climates. Plain Language Summary: Ancient rivers and streams on Mars physically and chemically altered the surface, then transported and deposited sediments, resulting in sedimentary rock production in downstream basins, as we observe in the remnants of Gale crater. However, the climate that allowed surface water to flow across the martian surface for extended periods of time remains the subject of debate. The work presented here addresses the ancient climate of Gale crater by comparing the geochemistry and mineralogy of sediments and soils on Earth to those analyzed by the Curiosity rover, specifically focusing on mudstones targeted early in the rover's traverse. A chemical weathering proxy is calculated and compared to climatological and environmental variables from various places on Earth, ultimately demonstrating that temperature is the main variable driving the extent that rocks are weathered. The results of this work suggest that the paleoclimate of Gale crater was variable, with our terrestrial reference frame providing a baseline approximation of an ancient martian climate that shifted toward Icelandic‐like conditions from even more frigid temperatures over the course of sedimentation in the ancient lake. Key Points: Terrestrial sediments and weathering profiles from basaltic terrains display first‐order similarities with mudstones from Gale crater, MarsThe chemical index of alteration can be used as paleoclimate proxy and places constraints on the ancient climate of Gale crater, MarsThe paleoclimate of Gale crater, Mars, was variable and ranged from Icelandic‐like conditions to colder climates [ABSTRACT FROM AUTHOR]

Planetary Instrument for X-ray Lithochemistry (PIXL) is a micro-focus X-ray fluorescence spectrometer mounted on the robotic arm of NASA’s Perseverance rover. PIXL will acquire high spatial resolution observations of rock and soil chemistry, rapidly analyzing the elemental chemistry of a target surface. In 10 seconds, PIXL can use its powerful 120 μm-diameter X-ray beam to analyze a single, sand-sized grain with enough sensitivity to detect major and minor rock-forming elements, as well as many trace elements. Over a period of several hours, PIXL can autonomously raster-scan an area of the rock surface and acquire a hyperspectral map comprised of several thousand individual measured points. When correlated to a visual image acquired by PIXL’s camera, these maps reveal the distribution and abundance variations of chemical elements making up the rock, tied accurately to the physical texture and structure of the rock, at a scale comparable to a 10X magnifying geological hand lens. The many thousands of spectra in these postage stamp-sized elemental maps may be analyzed individually or summed together to create a bulk rock analysis, or subsets of spectra may be summed, quantified, analyzed, and compared using PIXLISE data analysis software. This hand lens-scale view of the petrology and geochemistry of materials at the Perseverance landing site will provide a valuable link between the larger, centimeter- to meter-scale observations by Mastcam-Z, RIMFAX and Supercam, and the much smaller (micron-scale) measurements that would be made on returned samples in terrestrial laboratories. [ABSTRACT FROM AUTHOR]

Lunar regolith samples collected during previous Apollo missions were found to contain components that were established to be toxic to humans; however, the health effects due to inhalation of lunar soil as a whole are still unknown. Macrophages residing in the alveolar sacs of the lungs constitute one of the last lines of defense against inhaled particulates before entry into the bloodstream. Here, we examine the macrophage response to lunar simulants that are similar in chemical composition to the lunar regolith. We assess cytotoxicity, cellular morphology, phagocytosis of simulants and expression of inflammatory markers. Overall, the exposure of macrophages to lunar simulants results in moderate cytotoxicity and marked alteration of cell morphology and uptake of the simulants. Interestingly, simulant exposure decreased proinflammatory gene expression, but may induce an anti‐inflammatory phenotype in the cells. These results illustrate that although macrophages phagocytose lunar simulants as a protective response, the simulants do induce a degree of macrophage cell death. Our study reveals some toxicity associated with lunar simulants and supports further evaluation of the inhalation of lunar regolith to understand the risks of exposure fully. In previous missions to the Moon, astronauts reported irritating effects of lunar surface dust upon inhalation, pointing to the need to understand the potential health effects of the lunar regolith. As alveolar macrophages are one of the last lines of defense against inhaled particulates in the lungs, we investigate the responses of a macrophage cell line after exposure to lunar soil simulants, and examined cell death, changes in cell morphology, and expression of inflammatory genes. [ABSTRACT FROM AUTHOR]

Recent robotic missions to Mars have offered new insights into the extent, diversity and habitability of the Martian sedimentary rock record. Since the Curiosity rover landed in Gale crater in August 2012, the Mars Science Laboratory Science Team has explored the origins and habitability of ancient fluvial, deltaic, lacustrine and aeolian deposits preserved within the crater. This study describes the sedimentology of a ca 13 m thick succession named the Pahrump Hills member of the Murray formation, the first thick fine‐grained deposit discovered in situ on Mars. This work evaluates the depositional processes responsible for its formation and reconstructs its palaeoenvironmental setting. The Pahrump Hills succession can be sub‐divided into four distinct sedimentary facies: (i) thinly laminated mudstone; (ii) low‐angle cross‐stratified mudstone; (iii) cross‐stratified sandstone; and (iv) thickly laminated mudstone–sandstone. The very fine grain size of the mudstone facies and abundant millimetre‐scale and sub‐millimetre‐scale laminations exhibiting quasi‐uniform thickness throughout the Pahrump Hills succession are most consistent with lacustrine deposition. Low‐angle geometric discordances in the mudstone facies are interpreted as 'scour and drape' structures and suggest the action of currents, such as those associated with hyperpycnal river‐generated plumes plunging into a lake. Observation of an overall upward coarsening in grain size and thickening of laminae throughout the Pahrump Hills succession is consistent with deposition from basinward progradation of a fluvial‐deltaic system derived from the northern crater rim into the Gale crater lake. Palaeohydraulic modelling constrains the salinity of the ancient lake in Gale crater: assuming river sediment concentrations typical of floods on Earth, plunging river plumes and sedimentary structures like those observed at Pahrump Hills would have required lake densities near freshwater to form. The depositional model for the Pahrump Hills member presented here implies the presence of an ancient sustained, habitable freshwater lake in Gale crater for at least ca 103 to 107 Earth years. [ABSTRACT FROM AUTHOR]

Two decades of intensive research have demonstrated that early Mars (2 Gyr) had an active sedimentary cycle, including well-preserved stratigraphic records, understandable within a source-to-sink framework with remarkable fidelity. This early cycle exhibits first-order similarities to (e.g., facies relationships, groundwater diagenesis, recycling) and first-order differences from (e.g., greater aeolian versus subaqueous processes, basaltic versus granitic provenance, absence of plate tectonics) Earth's record. Mars' sedimentary record preserves evidence for progressive desiccation and oxidation of the surface over time, but simple models for the nature and evolution of paleoenvironments (e.g., acid Mars, early warm and wet versus late cold and dry) have given way to the view that, similar to Earth, different climate regimes on Mars coexisted on regional scales and evolved on variable timescales, and redox chemistry played a pivotal role. A major accomplishment of Mars exploration has been to demonstrate that surface and subsurface sedimentary environments were both habitable and capable of preserving any biological record. ▪ Mars has an ancient sedimentary rock record with many similarities to but also many differences from Earth's sedimentary rock record. ▪ Mars' ancient sedimentary cycle shows a general evolution toward more desiccated and oxidized surficial conditions. ▪ Climatic regimes of early Mars were relatively clement but with regional variations leading to different sedimentary mineral assemblages. ▪ Surface and subsurface sedimentary environments on early Mars were habitable and capable of preserving any biological record that may have existed. [ABSTRACT FROM AUTHOR]

This paper provides an overview of Mars Exploration Rover Spirit Microscopic Imager (MI) operations and the calibration, processing, and analysis of MI data. The focus of this overview is on the last five Earth years (2005–2010) of Spirit's mission in Gusev crater, supplementing the previous overview of the first 450 sols of the Spirit MI investigation. Updates to radiometric calibration using in‐flight data and improvements in high‐level processing are summarized. Released data products are described, and a table of MI observations, including target/feature names and associated data sets, is appended. The MI observed natural and disturbed exposures of rocks and soils as well as magnets and other rover hardware. These hand‐lens‐scale observations have provided key constraints on interpretations of the formation and geologic history of features, rocks, and soils examined by Spirit. MI images complement observations by other Spirit instruments, and together show that impact and volcanic processes have dominated the origin and evolution of the rocks in Gusev crater, with aqueous activity indicated by the presence of silica‐rich rocks and sulfate‐rich soils. The textures of some of the silica‐rich rocks are similar to terrestrial hot spring deposits, and observations of subsurface cemented layers indicate recent aqueous mobilization of sulfates in places. Wind action has recently modified soils and abraded many of the rocks imaged by the MI, as observed at other Mars landing sites. Plain Language Summary: The Microscopic Imager (MI) on NASA's Spirit rover returned the highest‐resolution images of the Martian surface available at the time of the 2004–2010 mission. Designed to survive 90 Mars days (sols) and search for evidence of water in the past, Spirit returned data for 2210 sols, far exceeding all expectations. This paper summarizes the scientific insights gleaned from the thousands of MI images acquired during the last 5 years of the mission, supplementing the summary of the first 450 sols of the Spirit MI investigation published previously (Herkenhoff et al.,). Along with data from the other instruments on Spirit, MI images guided the scientific interpretation of the geologic history of the rocks and soils observed in Gusev crater on Mars. We conclude that the geologic history of the area explored by Spirit has been dominated by impacts and volcanism, and that water, perhaps very hot water, was involved in the evolution of some of the rocks and soils. More recently, winds have moved soil particles and abraded rocks, as observed elsewhere on Mars. These results have improved our understanding of Mars' history and informed planning of future missions to Mars. Key Points: During the Mars Exploration Rover Spirit mission, the Microscopic Imager returned 5,923 full‐frame imagesThese images have guided interpretations of the geologic history of Gusev crater on MarsA table summarizing the MI images chronologically is appended, including target/feature names and sequence identifiers for Pancam images that provide context [ABSTRACT FROM AUTHOR]

Mineral analogs to silicate phases common to planetary regolith, including olivine; the pyroxenes augite and diopside; the plagioclase feldspars labradorite, bytownite, and albite; the Johnson Space Center‐1A lunar regolith simulant; as well as quartz (used as a reference), were subjected to mechanical pulverization by laboratory milling for times ranging from 5 to 45 min. Pulverized minerals were then incubated in an aqueous solution containing the free radical spin trapping compound 5,5‐Dimethyl‐1‐Pyrroline‐N‐Oxide for times ranging from 5 to 30 min. These slurries were then analyzed by Electron Paramagnetic Resonance spectroscopy to quantify the amount of hydroxyl radical (the neutral charge form of the hydroxide ion, denoted as OH*) formed in solution. We find that all tested materials generate an Electron Paramagnetic Resonance spectrum indicating the formation of OH* with concentrations ranging between 0.1 and 1.5 μM. We also find that, in general, mineral pulverization time is inversely correlated to OH* generation, while OH* generation is positively correlated to mineral fluid incubation time for phases that have iron in their nominal chemical formulae, suggesting the possible action of Fenton reaction as a cofactor in increasing the reactivity of these phases. Our results add to a body of literature that indicates that the finely comminuted minerals and rocks present in planetary regolith are capable of generating highly reactive and highly oxidizing radical species in solution. The results provide the foundation for further in vitro and in vivo toxicological studies to evaluate the possible health risks that future explorers visiting the surfaces of planetary bodies may face from these reactive regolith materials. Plain Language Summary: Future missions to the Moon will face many challenges and obstacles. Exposure to lunar dust will pose health risks to humans due to the reactive nature of the dust. We have assessed the reactivity of various mineral phases analogous to those present in lunar dust. Iron‐rich mineral phases generate higher concentrations of hydroxyl radical relative to mineral phases with low amounts of iron. Humans working in the lunar mare may experience relatively more detrimental health effects related to regolith dust inhalation relative to those working in the lunar highlands. Key Points: Electron paramagnetic resonance spectroscopy measurements show minerals with high iron content generate 2‐5 times more OH* relative to minerals with low iron contentPlanetary regolith on airless bodies containing iron‐rich mineral phases has the potential to generate oxidizing species that may pose a hazard to future human explorersHigh reactivity levels of iron‐rich minerals should motivate the development of effective mitigation systems for humans traveling to the Moon, especially in the mare regions [ABSTRACT FROM AUTHOR]

The Palaeoarchean supracrustal belts in Greenland contain Earth’s oldest rocks and are a prime target in the search for the earliest evidence of life on Earth. However, metamorphism has largely obliterated original rock textures and compositions, posing a challenge to the preservation of biological signatures. A recent study of 3,700-million-year-old rocks of the Isua supracrustal belt in Greenland described a rare zone in which low deformation and a closed metamorphic system allowed preservation of primary sedimentary features, including putative conical and domical stromatolites1 (laminated accretionary structures formed by microbially mediated sedimentation). The morphology, layering, mineralogy, chemistry and geological context of the structures were attributed to the formation of microbial mats in a shallow marine environment by 3,700 million years ago, at the start of Earth’s rock record. Here we report new research that shows a non-biological, post-depositional origin for the structures. Three-dimensional analysis of the morphology and orientation of the structures within the context of host rock fabrics, combined with texture-specific analyses of major and trace element chemistry, show that the ‘stromatolites’ are more plausibly interpreted as part of an assemblage of deformation structures formed in carbonate-altered metasediments long after burial. The investigation of the structures of the Isua supracrustal belt serves as a cautionary tale in the search for signs of past life on Mars, highlighting the importance of three-dimensional, integrated analysis of morphology, rock fabrics and geochemistry at appropriate scales. In contrast to a previous study of 3,700-million-year-old rocks of the Isua supracrustal belt in Greenland, which presented fossil evidence of stromatolites (macroscopic remains of layered microbial communities), this study shows that these ‘stromatolites’ are features of deformation unconnected to the processes of organic life. [ABSTRACT FROM AUTHOR]

Previous missions to the lunar surface implicated potential dangers of lunar soil. In future explorations, astronauts may spend weeks or months on the Moon, increasing the risk of inhaling lunar dust. In an effort to understand the biological impact of lunar regolith, cell cultures derived from lung or neuronal cells were challenged with lunar soil simulants to assess cell survival and genotoxicity. Lunar soil simulants were capable of causing cell death and DNA damage in neuronal and lung cell lines, and freshly crushed lunar soil simulants were more effective at causing cell death and DNA damage than were simulants as received from the supplier. The ability of the simulants to generate reactive oxygen species in aqueous suspensions was not correlated with their cytotoxic or genotoxic affects. Furthermore, the cytotoxicity was not correlated with the accumulation of detectable DNA lesions. These results determine that lunar soil simulants are, with variable activity, cytotoxic and genotoxic to both neuronal and lung‐derived cells in culture. Plain Language Summary: Lunar dust adhering to their suits caused mild respiratory issues for Apollo astronauts returning from the Moon. Chronic or long‐term effects of such dust exposure could be a problem for future missions. We assessed the cellular effects of exposure to terrestrial materials produced to mimic some aspects of lunar dust (simulants). We found significant cell toxicity in neuronal and lung cell lines in culture, as well as DNA damage associated with the exposure. Unexpectedly, these effects did not reflect the ability of the simulants to generate free radicals. Key Points: Lunar soil may pose a health risk when inhaled by astronautsLunar soil simulants have cytotoxic and genotoxic effects on neuronal and lung epithelial cellsCytotoxicity of the soils was not correlated with the DNA damage they caused in neuronal and lung cells [ABSTRACT FROM AUTHOR]

Clay mineral-bearing locations have been targeted for martian exploration as potentially habitable environments and as possible repositories for the preservation of organic matter. Although organic matter has been detected at Gale Crater, Mars, its concentrations are lower than expected from meteoritic and indigenous igneous and hydrothermal reduced carbon. We conducted synthesis experiments motivated by the hypothesis that some clay mineral formation may have occurred under oxidized conditions conducive to the destruction of organics. Previous work has suggested that anoxic and/or reducing conditions are needed to synthesize the Fe-rich clay mineral nontronite at low temperatures. In contrast, our experiments demonstrated the rapid formation of Fe-rich clay minerals of variable crystallinity from aqueous Fe3+ with small amounts of aqueous Mg2+. Our results suggest that Fe-rich clay minerals such as nontronite can form rapidly under oxidized conditions, which could help explain low concentrations of organics within some smectite-containing rocks or sediments on Mars. [ABSTRACT FROM AUTHOR]

Trace element and Nd isotopic compositions of Late Cambrian to Middle Ordovician passive margin metasediments from the northernmost Taconic Allochthon of the northeast United States indicate a provenance consistent with a two-component mixture of an evolved Grenville source and a rift source generated during the Late Proterozoic opening of the Iapetus Ocean. Initial ∊Nd values for these preorogenic deposits range from -11.3 to -14.6 (average = -13.0). Samples of overlying mid-Ordovician Taconian sediments exhibit initial ∊Nd values between -6.1 and -9.8 (average = -8.5 ). The trace element and Nd isotopic compositions of these synorogenic samples are consistent with a mixture of a less evolved Grenville Province source and recycled preorogenic passive margin deposits. No mantle-derived (ophiolitic or andesitic) source is unambiguously recognized in the synorogenic samples, consistent with published geochemical studies of other Taconian foreland sequences from this region. Sedimentary rocks from the northern Appalachians record a clear change in provenance at ca. 458 Ma, coincident with the onset of Taconian orogenesis and similar to patterns observed in other sedimentary sequences throughout North America. [ABSTRACT FROM AUTHOR]

Gusev crater was selected as the landing site for the Spirit rover because of the possibility that it once held a lake. Thus one of the rover's tasks was to search for evidence of lake sediments. However, the plains at the landing site were found to be covered by a regolith composed of olivine-rich basaltic rock and windblown ‘global’ dust. The analyses of three rock interiors exposed by the rock abrasion tool showed that they are similar to one another, consistent with having originated from a common lava flow. Here we report the investigation of soils, rock coatings and rock interiors by the Spirit rover from sol (martian day) 1 to sol 156, from its landing site to the base of the Columbia hills. The physical and chemical characteristics of the materials analysed provide evidence for limited but unequivocal interaction between water and the volcanic rocks of the Gusev plains. This evidence includes the softness of rock interiors that contain anomalously high concentrations of sulphur, chlorine and bromine relative to terrestrial basalts and martian meteorites; sulphur, chlorine and ferric iron enrichments in multilayer coatings on the light-toned rock Mazatzal; high bromine concentration in filled vugs and veins within the plains basalts; positive correlations between magnesium, sulphur and other salt components in trench soils; and decoupling of sulphur, chlorine and bromine concentrations in trench soils compared to Gusev surface soils, indicating chemical mobility and separation. [ABSTRACT FROM AUTHOR]

In Extended Data Fig. 1 of this Letter, the map showed the field-work location incorrectly; this figure has been corrected online. [ABSTRACT FROM AUTHOR]