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The sample analysis at Mars instrument evolved gas analyzer (SAM‐EGA) has detected evolved water, H2, SO2, H2S, NO, CO2, CO, O2, and HCl from two eolian sediments and nine sedimentary rocks from Gale Crater, Mars. These evolved gas detections indicate nitrates, organics, oxychlorine phase, and sulfates are widespread with phyllosilicates and carbonates occurring in select Gale Crater materials. Coevolved CO2(160 ± 248–2373 ± 820 μgC(CO2)/g) and CO (11 ± 3–320 ± 130 μgC(CO)/g) suggest that organic C is present in Gale Crater materials. Five samples evolved CO2at temperatures consistent with carbonate (0.32 ± 0.05–0.70 ± 0.1 wt % CO3). Evolved NO amounts to 0.002 ± 0.007–0.06 ± 0.03 wt % NO3. Evolution of O2suggests that oxychlorine phases (chlorate/perchlorate) (0.05 ± 0.025–1.05 ± 0.44 wt % ClO4) are present, while SO2evolution indicates the presence of crystalline and/or poorly crystalline Fe and Mg sulfate and possibly sulfide. Evolved H2O (0.9 ± 0.3–2.5 ± 1.6 wt % H2O) is consistent with the presence of adsorbed water, hydrated salts, interlayer/structural water from phyllosilicates, and possible inclusion water in mineral/amorphous phases. Evolved H2and H2S suggest that reduced phases occur despite the presence of oxidized phases (nitrate, oxychlorine, sulfate, and carbonate). SAM results coupled with CheMin mineralogical and Alpha‐Particle X‐ray Spectrometer elemental analyses indicate that Gale Crater sedimentary rocks have experienced a complex authigenetic/diagenetic history involving fluids with varying pH, redox, and salt composition. The inferred geochemical conditions were favorable for microbial habitability and if life ever existed, there was likely sufficient organic C to support a small microbial population. The SAM instrument has detected evolved water, H2, SO2, H2S, NO, CO2, CO, O2, and HCl from Gale Crater sediments and sedimentary rockSAM detections are consistent with the presence of nitrate, organic C, carbonate, phyllosilicates, perchlorate, chlorate, and sulfateGale Crater materials have experienced a complex authigenetic/diagenetic history with fluids of varying pH, redox, and salt composition

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 (1σprecision). 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. A third radiometric age dating experiment has been conducted on MarsThe model formation age of plagioclase is greater than 4 Ga, while the model age for jarosite is less than 3 GaThe young jarosite age suggests the presence of liquid water in Gale Crater during the Amazonian period, most likely in the subsurface

K‐Ar and noble gas surface exposure age measurements were carried out on the Windjana sandstone, Kimberley region, Gale Crater, Mars, by using the Sample Analysis at Mars instrument on the Curiosity rover. The sandstone is unusually rich in sanidine, as determined by CheMin X‐ray diffraction, contributing to the high K2O concentration of 3.09 ± 0.20 wt % measured by Alpha‐Particle X‐ray Spectrometer analysis. A sandstone aliquot heated to ~915°C yielded a K‐Ar age of 627 ± 50 Ma. Reheating this aliquot yielded no additional Ar. A second aliquot heated in the same way yielded a much higher K‐Ar age of 1710 ± 110 Ma. These data suggest incomplete Ar extraction from a rock with a K‐Ar age older than 1710 Ma. Incomplete extraction at ~900°C is not surprising for a rock with a large fraction of K carried by Ar‐retentive K‐feldspar. Likely, variability in the exact temperature achieved by the sample from run to run, uncertainties in sample mass estimation, and possible mineral fractionation during transport and storage prior to analysis may contribute to these discrepant data. Cosmic ray exposure ages from 3He and 21Ne in the two aliquots are minimum values given the possibility of incomplete extraction. However, the general similarity between the 3He (57 ± 49 and 18 ± 32 Ma, mean 30 Ma) and 21Ne (2 ± 32 and 83 ± 24 Ma, mean 54 Ma) exposure ages provides no evidence for underextraction. The implied erosion rate at the Kimberley location is similar to that reported at the nearby Yellowknife Bay outcrop. Second in situ dating on Mars using SAM in MSLK‐Ar age discrepantCosmogenic isotope ages young and internally compatible

Results from the Sample Analysis at Mars‐evolved gas analyzer on board the Mars Science Laboratory Curiosityrover constrained the alteration history and habitability potential of rocks sampled across the Siccar Point unconformity in Gale crater. The Glasgow member (Gm) mudstone just below the unconformity had evidence of acid sulfate or Si‐poor brine alteration of Fe‐smectite to Fe amorphous phases, leaching loss of Fe‐Mg‐sulfate and exchange of unfractionated sulfur 34S (δ34S = 2‰ ± 7‰) with enriched 34S (20‰ ± 5‰, Vienna Cañon Diablo Troilite). Carbon abundances did not significantly change (322–661 μgC/g) consistent with carbon stabilization by amorphous Al‐ and Fe‐hydroxide phases. The Gm mudstone had no detectable oxychlorine and extremely low nitrate. Nitrate (0.06 wt.% NO3), oxychlorine (0.13 wt.% ClO4), high C (1,472 μg C/g), and low Fe/Mg‐sulfate concentration (0.24 wt.% SO3) depleted in 34S (δ34S = −27‰ ± 7), were detected in the Stimson formation (Sf) eolian sandstone above the unconformity. Redox disequilibrium through the detections of iron sulfide and sulfate supported limited aqueous processes in the Sf sandstone. Si‐poor brines or acidic fluids altered the Gm mudstone just below the unconformity but did not alter underlying Gm mudstones further from the contact. Chemical differences between the Sf and Gm rocks suggested that fluid interaction was minimal between the Sf and Gm rocks. These results suggested that the Gm rocks were altered by subsurface fluids after the Sf placement. Aqueous processes along the unconformity could have provided habitable conditions and in some cases, C and N levels could have supported heterotrophic microbial populations. The Curiosity Rover investigated the chemistry and mineralogy of rocks in the Glen Torridon region of Gale crater, Mars. Rocks sampled across an unconformity (representative of a time gap between when two sedimentary rocks were deposited) gave insight into how they were altered over time. The Glasgow mudstones, below the unconformity, were formed in a lake environment while the younger Stimson sandstones above the unconformity were formed from ancient sand dunes. Using the Sample Analysis at Mars Evolved Gas Analysis (SAM‐EGA) experiment, solid powdered samples from these rocks were heated and released gases (e.g., water, carbon dioxide, and sulfur dioxide) were tracked. These gases revealed a complex history of alteration through the rocks. The Glasgow mudstones were characterized by acidic or Si‐poor brine alteration, variable sulfur, low amounts of carbon, and no nitrate or oxychlorine. SAM‐EGA results from the Stimson sandstone showed rocks that were less altered, had higher levels of carbon, different sulfur compounds and sources, and some nitrate/oxychlorine. Together, these results suggested that the Glasgow rocks were altered by subsurface fluids after Stimson sandstone placement. Aqueous processes along the unconformity could have provided habitable conditions and in some cases, C and N levels could have supported heterotrophic microbial populations. Subsurface silica‐poor brines or acidic fluids altered mudstones just below the Siccar Point group unconformityStimson formation sandstone above the unconformity was exposed to limited aqueous alterationAqueous alteration processes along the unconformity could have provided habitable conditions and in some cases, sufficient microbial C and N Subsurface silica‐poor brines or acidic fluids altered mudstones just below the Siccar Point group unconformity Stimson formation sandstone above the unconformity was exposed to limited aqueous alteration Aqueous alteration processes along the unconformity could have provided habitable conditions and in some cases, sufficient microbial C and N

The Sample Analysis at Mars (SAM) suite instrument on board NASA's Curiosityrover has characterized the inorganic and organic chemical composition of seven samples from the Glen Torridon (GT) clay‐bearing unit. A variety of organic molecules were detected with SAM using pyrolysis (up to ∼850°C) and wet chemistry experiments coupled with evolved gas analysis (EGA) and gas chromatography‐mass spectrometry. SAM EGA and GCMS analyses revealed a greater diversity and abundance of sulfur‐bearing aliphatic and aromatic organic compounds in the sediments of this Gale crater unit than earlier in the mission. We also report the detection of nitrogen‐containing, oxygen‐containing, and chlorine‐containing molecules, as well as polycyclic aromatic hydrocarbons found in GT, although the sources of some of these organics may be related to the presence of chemical reagents in the SAM instrument background. However, sulfur‐bearing organics released at high temperature (≥600°C) are likely derived from Martian sources (e.g., igneous, hydrothermal, atmospheric, or biological) or exogenous sources and consistent with the presence of recalcitrant organic materials in the sample. The SAM measurements of the GT clay‐bearing unit expand the inventory of organic matter present in Gale crater and is also consistent with the hypothesis that clay minerals played an important role in the preservation of ancient refractory organic matter on Mars. These findings deepen our understanding of the past habitability and biological potential of Gale crater. Organic molecules are essential to all life as we know it. Clay minerals are known on Earth for their high organic preservation potential and can be key indicators of past habitable environments. On Mars, the Glen Torridon (GT) region in Gale crater was first identified from orbit as a priority target for the Mars Science Laboratory mission due to its abundant clay minerals. To evaluate the organic preservation potential of this region, seven rock samples were collected and characterized using the Sample Analysis at Mars (SAM) instrument onboard the Curiosityrover. The SAM investigation indicated the presence of various organic compounds, including the first observation on Mars of some sulfur‐containing and ring‐structured organics and the highest abundance of sulfur organics observed to date. Our investigation of the sources of these organics revealed that while some of the sulfur‐bearing organics are likely Martian, a portion may also be related to the presence of chemical reagents carried in SAM, making attribution to a definitive source challenging. Nevertheless, these new SAM results confirm that ancient organic matter is preserved in the clay mineral bearing sediments of GT. Its origin—either meteoritic, abiotic or biotic—has yet to be established. Curiosityexplored the Glen Torridon region of Gale crater, which has a smectite‐rich mineralogy with high organic preservation potentialThe greatest diversity and abundance of sulfur‐bearing organics to date were detected in the solid samples by the SAM instrumentS‐bearing organics extracted ≥600°C and some aromatic compounds likely come from martian refractory organic matter Curiosityexplored the Glen Torridon region of Gale crater, which has a smectite‐rich mineralogy with high organic preservation potential The greatest diversity and abundance of sulfur‐bearing organics to date were detected in the solid samples by the SAM instrument S‐bearing organics extracted ≥600°C and some aromatic compounds likely come from martian refractory organic matter

The Sample Analysis at Mars (SAM) instrument on board the Mars Science Laboratory Curiosity rover is designed to conduct inorganic and organic chemical analyses of the atmosphere and the surface regolith and rocks to help evaluate the past and present habitability potential of Mars at Gale Crater. Central to this task is the development of an inventory of any organic molecules present to elucidate processes associated with their origin, diagenesis, concentration, and long-term preservation. This will guide the future search for biosignatures. Here we report the definitive identification of chlorobenzene (150–300 parts per billion by weight (ppbw)) and C2to C4dichloroalkanes (up to 70?ppbw) with the SAM gas chromatograph mass spectrometer (GCMS) and detection of chlorobenzene in the direct evolved gas analysis (EGA) mode, in multiple portions of the fines from the Cumberland drill hole in the Sheepbed mudstone at Yellowknife Bay. When combined with GCMS and EGA data from multiple scooped and drilled samples, blank runs, and supporting laboratory analog studies, the elevated levels of chlorobenzene and the dichloroalkanes cannot be solely explained by instrument background sources known to be present in SAM. We conclude that these chlorinated hydrocarbons are the reaction products of Martian chlorine and organic carbon derived from Martian sources (e.g., igneous, hydrothermal, atmospheric, or biological) or exogenous sources such as meteorites, comets, or interplanetary dust particles. First in situ evidence of nonterrestrial organics in Martian surface sedimentsChlorinated hydrocarbons identified in the Sheepbed mudstone by SAMOrganics preserved in sample exposed to ionizing radiation and oxidative condition

Evolved gas analysis (EGA) data from the Sample Analysis at Mars (SAM) instrument suite indicated Fe‐rich smectite, carbonate, oxidized organics, Fe/Mg sulfate, and chloride in sedimentary rocks from the Glen Torridon (GT) region of Gale crater that displayed phyllosilicate spectral signatures from orbit. SAM evolved H2O data indicated that the primary phyllosilicate in all GT samples was an Fe‐rich dioctahedral smectite (e.g., nontronite) with lesser amounts of a phyllosilicate such as mixed layer talc‐serpentine or greenalite‐minnesotaite. CO2data supported the identification of siderite in several samples, and CO2and CO data was also consistent with trace oxidized organic compounds such as oxalate salts. SO2data indicated trace and/or amorphous Fe sulfates in all samples and one sample may contain Fe sulfides. SO2data points to significant Mg sulfates in two samples, and lesser amounts in several other samples. A lack of evolved O2indicated the absence of oxychlorine salts and Mn3+/Mn4+oxides. The lack of, or very minor, evolved NO revealed absent or very trace nitrate/nitrite salts. HCl data suggested chloride salts in GT samples. Constraints from EGA data on mineralogy and chemistry indicated that the environmental history of GT involved alteration with fluids of variable redox potential, chemistry and pH under a range of fluid‐to‐rock ratio conditions. Several of the fluid episodes could have provided habitable environmental conditions and carbon would have been available to any past microbes though the lack of significant N could have been a limiting factor for microbial habitability in the GT region. The Mars Science Laboratory Curiosity rover carried out a comprehensive investigation of the sedimentary rocks in the Glen Torridon (GT) region in Gale crater, Mars, to better understand Martian geologic history. The rover’s Sample Analysis at Mars instrument suite was used to heat samples from GT and detect gases that were evolved to help identify the volatile‐bearing mineralogy of the samples. Results indicated the presence of Fe‐rich smectite, carbonate, oxidized organics, Fe and Mg sulfate, and chloride while oxychlorine salts, Mn3+/Mn4+oxides, and nitrate/nitrite salts were either not detected or occurred in trace amounts. This mineralogy data implied that geochemical conditions and fluid‐to‐rock ratios varied over time and that the conditions of GT depositional and diagenetic environments would have been amenable to microbial life with sufficient carbon but nitrogen abundances could have been limiting. Sample Analysis at Mars data indicated Fe‐smectite, carbonate, oxidized organics, Fe/Mg sulfates, and chlorides in Glen Torridon (GT) rocksGT’s environmental history involved fluids of variable redox potential and chemistry under a range of fluid‐to‐rock ratiosFluid episodes could have provided habitable environments and carbon was present, but nitrogen could have been a limiting factor Sample Analysis at Mars data indicated Fe‐smectite, carbonate, oxidized organics, Fe/Mg sulfates, and chlorides in Glen Torridon (GT) rocks GT’s environmental history involved fluids of variable redox potential and chemistry under a range of fluid‐to‐rock ratios Fluid episodes could have provided habitable environments and carbon was present, but nitrogen could have been a limiting factor

Context.Accurate atomic data for the less abundance Fe-peak elements are required for use in X-ray astrophysical studies.