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The Mars 2020 Perseverance Rover imaged diagenetic textural features in four separate sedimentary units in its exploration of the 25‐m‐thick Shenandoah formation at Jezero Crater, Mars, that we interpreted as probable concretions. These concretions were most abundant in the Hogwallow Flats member of the Shenandoah formation and were restricted to the light‐toned, platy, sulfur‐cemented bedrock at outcrop surfaces, whereas the finely laminated, darker toned, mottled and deformed strata lack concretions. The concretions also had a wide range of morphologies including concentric, oblate, urn, and spheroidal shaped forms that were not clustered, and ranged in size from ∼1 to 16 mm with a median of 2.65 mm. The elemental composition of the concretions compared to the bedrock had greater abundance of magnesium and calcium salts, silicates, and possibly hematite. We compared these Jezero Crater concretions to the geochemistry of concretions from previously published studies and from two new terrestrial analog sites (Gallup Formation, New Mexico and Torrey Pines, California). In addition, we measured organic carbon content of three terrestrial sedimentary analogs of increasing age that contain concretions (Torrey Pines (Pleistocene), Gallup Formation (∼89 Ma), and Moodies Group (∼3.2 Ga)). All measured concretions contained significant concentrations of organic carbon with the maximum organic carbon content (∼2 wt. % Total organic carbon) found in the Moodies Group concretions. Organic carbon abundances in terrestrial concretions was controlled more by the formation mechanism and relative timing of concretion development rather than deposit age. These findings suggested that concretions at Jezero Crater reflect local sites of enhanced biosignature preservation potential. Plain Language Summary: The Perseverance Rover discovered concretions in its exploration of the rock packages at Jezero Crater, Mars and one of the sample return cores was collected from concretion‐rich bedrock. Concretions are resistant cement in the rock that are found in many shapes (usually spherical or oblate) and range from millimeter to meter size scales on Earth; they can be formed through inorganic water‐rock reactions or facilitated by microbial metabolisms. We documented the abundance, size, composition, and shape of the concretions to understand how these features were formed. We found that the concretions are mixtures of salts, clay minerals, and iron oxides. We compared these results to terrestrial concretions with similar mineral compositions and measured the organic carbon in four terrestrial analogs. Comparisons with terrestrial concretions in this study and the literature suggested that the concretion composition in Jezero Crater could have high organic preservation potential. Thus, the concretions in Jezero Crater may retain organic carbon and other biosignatures and might therefore be considered as high priority samples of astrobiological interest out of the current sample suite for return to Earth. Key Points: Jezero Crater concretions are variably enriched in Si, Ca, and Mg salts, and Fe oxidesTerrestrial concretions of similar mineralogy analyzed in this study contain significant organic carbon phasesBased on terrestrial analogs, Jezero Crater concretions may represent sites of enhanced biosignature preservation potential [ABSTRACT FROM AUTHOR]

Using relative reflectance measurements from the Mastcam‐Z and SuperCam instruments on the Mars 2020 Perseverance rover, we assess the variability of Fe mineralogy in Noachian/Hesperian‐aged rocks at Jezero crater. The results reveal diverse Fe3+ and Fe2+ minerals. The igneous crater floor, where small amounts of Fe3+‐phyllosilicates and poorly crystalline Fe3+‐oxyhydroxides have been reported, is spectrally similar to most oxidized basalts observed at Gusev crater. At the base of the western Jezero sedimentary fan, new spectral type points to an Fe‐bearing mineral assemblage likely dominated by Fe2+. By contrast, most strata exposed at the fan front show signatures of Fe3+‐oxides (mostly fine‐grained crystalline hematite), Fe3+‐sulfates (potentially copiapites), strong signatures of hydration, and among the strongest signatures of red hematite observed in situ, consistent with materials having experienced vigorous water‐rock interactions and/or higher degrees of diagenesis under oxidizing conditions. The fan top strata show hydration but little to no signs of Fe oxidation likely implying that some periods of fan construction occurred either during a reduced atmosphere era or during short‐lived aqueous activity of liquid water in contact with an oxidized atmosphere. We also report the discovery of alternating cm‐scale bands of red and gray layers correlated with hydration and oxide variability, which has not yet been observed elsewhere on Mars. This could result from syn‐depositional fluid chemistry variations, possibly as seasonal processes, or diagenetic overprint of oxidized fluids percolating through strata having variable permeability. Plain Language Summary: The oxidation states of the atmosphere and waters (whether rich or poor in oxidants such as oxygen) of Mars and their evolution are poorly constrained but can be recorded in the iron (Fe) mineralogy of rocks. Using data from the Perseverance rover, we analyzed the Fe mineralogy of ∼4–3 Ga old rocks from an ancient lake at Jezero crater. Oxidized Fe is found in igneous rocks and lowermost portions of sedimentary rocks, carried by clays and poorly crystalline oxides in the former and by sulfates and crystalline oxides in the latter, pointing to past action of oxidizing fluids, affecting more intensely the sedimentary rocks. Fe shows poor to no signs of oxidation in the uppermost strata, which might be evidence for a reducing atmosphere during sediment deposition or that the aqueous environment was too cold or too short‐lived to oxidize minerals. We also report Fe mineralogy variability at the cm‐scale in alternating colored layers, which has not been observed previously on Mars and could possibly mean that seasonal processes are recorded at Jezero crater. Key Points: In situ reflectance data measured with Mars 2020 show variable Fe mineralogy in sedimentary rocks at Jezero craterStrata exposed at the fan front experienced stronger oxidative water‐rock interactions compared to the upper fan and igneous crater floorWe identify cm‐scale color banding correlated with Fe‐oxide variability that likely indicates time variation in redox [ABSTRACT FROM AUTHOR]

In recent years, the Tunable Laser Spectrometer within the Sample Analysis at Mars (TLS‐SAM) instrument on board the Mars Science Laboratory (MSL) Curiosity rover has detected methane variations in the atmosphere at Gale crater. Methane concentrations appear to fluctuate seasonally as well as sub‐diurnally, which is difficult to reconcile with an as‐yet‐unknown transport mechanism delivering the gas from underground to the atmosphere. To potentially explain the fluctuations, we consider barometrically induced transport of methane from an underground source to the surface, modulated by temperature‐dependent adsorption. The subsurface fractured‐rock seepage model is coupled to a simplified 1‐D atmospheric mixing model to provide insights on the pattern of atmospheric methane concentrations in response to transient surface methane emissions, as well as to predict sub‐diurnal variation in methane abundance for the northern summer period, which is a candidate time frame for a MSL Curiosity sampling campaign. Our analysis suggests that there is a lower limit to the subsurface fracture density that can produce the observed methane patterns, below which the atmospheric methane variations would be out of phase with the observations. The best‐performing model scenarios indicate a significant, short‐lived methane pulse just prior to sunrise, the detection of which by TLS‐SAM would be a potential indicator of the contribution of barometric pumping to Mars' atmospheric methane variations. Plain Language Summary: One of the outstanding goals of current Mars missions is to detect and understand biosignatures (signs of ancient or present life, if they exist) such as methane. Methane has been detected multiple times in Mars' atmosphere close to the planet's surface by the Mars Science Laboratory (MSL) Curiosity rover, and its abundance appears to fluctuate seasonally and on a daily time scale. With the source of methane on Mars most likely located underground, it is difficult to reconcile these atmospheric variations with an as‐yet‐unknown transport mechanism delivering the gas to the atmosphere. In this manuscript, we simulate methane transport to the atmosphere from underground fractured rock driven by atmospheric pressure fluctuations. We also model adsorption of methane molecules onto the surface of pores in the rock, which is a temperature‐dependent process that may contribute to the apparent seasonality of methane abundance. We simulated methane emitted from the subsurface mixing into a simulated atmospheric column, which provides insight into the sub‐diurnal methane concentrations in the atmosphere. Our simulations predict short‐lived methane pulses prior to sunrise for Mars' upcoming northern summer period, which is a candidate time frame for MSL Curiosity's next sampling campaign. Key Points: Barometrically driven atmospheric methane abundance timing controlled by fracture topology and atmospheric dynamicsThere is a lower limit to fracture density (0.01%) that can produce observed methane patternsA late morning or early evening Tunable Laser Spectrometer within the Sample Analysis at Mars sample could constrain diurnal methane pattern and transport processes [ABSTRACT FROM AUTHOR]

In situ geologic context mapping based on rover and helicopter observations provides documentation of a nearly continuous record of geology and exposed surface structure over a 120 m‐wide corridor along the traverse of the Mars 2020/Perseverance rover. The results record the geologic context of Mars 2020 campaign sites and sample sites, including the local extent of bedrock outcrops, stratigraphy, attitude, and structure from imaging and rover‐based remote sensing, and outcrop lithology based on in situ proximity science. Mapping identifies a sequence of igneous lithologies including (a) early mafic, possibly intrusive, rocks; (b) pervasively fractured and deeply altered massive bedrock of undetermined protolith; (c) buried and exhumed lava flows with pahoehoe and aa textures; (d) several varieties of regolith; and (e) small impact craters. Plain Language Summary: Reconnaissance‐type geologic mapping along the traverse of Perseverance on the Jezero Crater floor is adapted from field geologic methods used on Earth and modified to account for the geometry of rover‐based imaging. The final field geologic map records bedrock and surficial geology, contacts, and structures over a 120‐m wide strip along the traverse. Most of the lithologies are igneous, including possible intrusive mafic rocks, deeply weathered massive rocks of unknown original lithology, and lava flows. Stratigraphy determined from mapping together with the observed inclination of layers identifies either uplift or draping of the section centered in the elevated older terrain. The final map information provides ground‐truth geologic context for the first eight samples collected for return to Earth. Key Points: In situ mapping from the rover observations on Mars uses field geologic mapping methodsDocuments the geologic context of samples and the crater floor traverse of PerseveranceDevelops methods applicable to future robotic and human traverses on planetary surfaces [ABSTRACT FROM AUTHOR]

The Máaz formation consists of the first lithologies in Jezero crater analyzed by the Mars 2020 Perseverance rover. This formation, investigated from Sols (Martian days) 1 to 201 and from Sols 343 to 382, overlies the Séítah formation (previously described as an olivine‐rich cumulate) and was initially suggested to represent an igneous crater floor unit based on orbital analyses. Using SuperCam data, we conducted a detailed textural, chemical, and mineralogical analyses of the Máaz formation and the Content member of the Séítah formation. We conclude that the Máaz formation and the Content member are igneous and consist of different lava flows and/or possibly pyroclastic flows with complex textures, including vesicular and non‐vesicular rocks with different grain sizes. The Máaz formation rocks exhibit some of the lowest Mg# (=molar 100 × MgO/MgO + FeO) of all Martian igneous rocks analyzed so far (including meteorites and surface rocks) and show similar basaltic to basaltic‐andesitic compositions. Their mineralogy is dominated by Fe‐rich augite to possibly ferrosilite and plagioclase, and minor phases such as Fe‐Ti oxides and Si‐rich phases. They show a broad diversity of both compositions and textures when compared to Martian meteorites and other surface rocks. The different Máaz and Content lava or pyroclastic flows all originate from the same parental magma and/or the same magmatic system, but are not petrogenetically linked to the Séítah formation. The study of returned Máaz samples in Earth‐based laboratories will help constrain the formation of these rocks, calibrate Martian crater counting, and overall, improve our understanding of magmatism on Mars. Plain Language Summary: The Mars 2020 Perseverance rover landed on Mars in the Jezero crater on 18 February 2021. The main goals of this mission are to constrain the geology of the Jezero crater and its delta, to search for biosignatures (evidence of ancient life), to sample rocks to return to Earth, and to prepare for human exploration. Here we study the rock formation observed at the landing site, named the Máaz formation. We conclude that this rock formation is igneous (=formed from cooling and crystallization of lava or magma) consisting of iron‐rich basaltic lava flows, formed through effusive (i.e., outpouring of lava without explosions) volcanism. When compared to other Martian magmatic rocks, these rocks show a large variety of textures (shape and size of minerals) and compositions, making them different from the Martian magmatic rocks studied so far. The various lava flows of the Máaz rocks are likely all related, but not related to the underlying Séítah rock formation. Perseverance has collected core samples from the Máaz and Séítah rocks that could be among the Martian rocks to be returned to Earth in the 2030s. Their study in Earth‐based laboratories will allow us to better understand the evolution of Martian magmatism. Key Points: The Máaz formation in Jezero crater consists of basaltic to basaltic‐andesite lava flows likely originating from the same parental magmaThe Máaz formation shows various igneous textures and has a different magmatic history than the other known Martian igneous rocksThe study of samples from the Máaz formation on Earth will help constrain the Martian cratering chronology and Martian igneous evolution [ABSTRACT FROM AUTHOR]

The SuperCam instrument onboard the Mars 2020 Perseverance rover investigates Martian geological targets by a combination of multiple spectroscopic techniques. As Raman, Visible‐Infrared Spectroscopy, and Laser‐Induced Breakdown Spectroscopy (LIBS) spectra deliver complementary information about the interrogated sample, the multivariate analysis of combined spectroscopic data sets is here proposed as a tool to optimize the SuperCam capability to discriminate mineral phases on Mars. For this purpose, the laboratory study of carbonate phases within the Ca‐Mg‐Fe ternary system were selected as representative case of study. After the characterization of model samples, the discrimination capability of mono analytical Raman, VISIR, and LIBS data sets was evaluated by applying a chemometric approach based on the combination of principal component analysis (for sample clustering) and Linear Discriminant Analysis (for mineral classification). Afterward, the low‐level combination (LL) of Raman, VISIR, and LIBS data was achieved by concatenating their spectra into a single data matrix. The mineral classification achieved by LL data sets outperformed the mono analytical ones, thus proving the complementarity between molecular and elemental spectroscopic techniques. Mineral classification was further improved by using a mid‐level data combination strategy. After evaluating benefits and limitations afforded by the proposed combination strategies, future developments are finally outlined. As such, the final objective of this research line is to develop a classification model based on data combination to optimize the capability of SuperCam in discriminating relevant minerals on Mars, this being a key requirement for the selection of the optimal targets to be cached for the future Mars Sample Return Mission. Plain Language Summary: The SuperCam instrument onboard the Perseverance rover is capable of analyzing Martian rocks and soils by a combination of Laser‐Induced Breakdown Spectroscopy (LIBS), Raman and Visible‐Infrared Spectroscopy (VISIR). Learning from terrestrial applications, the complementary information provided by the three spectroscopic techniques can be correlated to obtain a more accurate interpretation of the analyzed target. This approach could be particularly useful to discriminate carbonates, which are interesting minerals where to look for traces of past life. Having this in mind, several carbonate samples have been analyzed with laboratory Raman, LIBS, and VISIR instrument. After evaluating the advantages and limitations of each technique, their data were merged by using low‐level and mid‐level strategies that were successfully used previous works. This work proved that, when spectra are combined, the discrimination of carbonate phases is more accurate than when each technique is interpreted separately. This suggests the scientific results obtained by SuperCam on Mars could benefit from the development of tailored classification models based on data combination. Key Points: Data combination of Raman, Visible‐Infrared Spectroscopy, and Laser‐Induced Breakdown Spectroscopy spectra collected by SuperCam is proposedLow‐ and mid‐level data combination strategies based on principal component analysis (discrimination) + PC‐Linear Discriminant Analysis (classification are evaluated and compared)The low‐level combination method outperformed the mono analytical discrimination. The mid‐level one further improved the results [ABSTRACT FROM AUTHOR]

Perseverance explored two geological units on the floor of Jezero Crater over the first 420 Martian days of the Mars2020 mission. These units, the Máaz and Séítah formations, are interpreted to be igneous in origin, with traces of alteration. We report the detection of carbonate phases along the rover traverse based on laser‐induced breakdown spectroscopy (LIBS), infrared reflectance spectroscopy (IRS), and time‐resolved Raman (TRR) spectroscopy by the SuperCam instrument. Carbonates are identified through direct detection of vibrational modes of CO3 functional groups (IRS and TRR), major oxides content, and ratios of C and O signal intensities (LIBS). In Séítah, the carbonates are consistent with magnesite‐siderite solid solutions (Mg# of 0.42–0.70) with low calcium contents (<5 wt.% CaO). They are detected together with olivine in IRS and TRR spectra. LIBS and IRS also indicate a spatial association of the carbonates with clays. Carbonates in Máaz are detected in fewer points, as: (a) siderite (Mg# as low as 0.03); (b) carbonate‐containing coatings, enriched in Mg (Mg# ∼0.82) and spatially associated with different salts. Overall, using conservative criteria, carbonate detections are rare in LIBS (∼30/2,000 points), IRS (∼15/2,000 points), and TRR (1/150 points) data. This is best explained by (a) a low carbonate content overall, (b) small carbonate grains mixed with other phases, (c) intrinsic complexity of in situ measurements. This is consistent with orbital observations of Jezero crater, and similar to compositions of carbonates previously reported in Martian meteorites. This suggests a limited carbonation of Jezero rocks by locally equilibrated fluids. Plain Language Summary: Carbonates are mineral phases that generally form by alteration of primary, magmatic minerals. This alteration process may occur under a variety of environmental conditions, which affect the resulting carbonate phase: its abundance, composition, spatial distribution and the mineral phases it is associated with. Consequently, carbonates keep track of the environmental conditions under which they formed, and in particular, the amount of CO2 and liquid water involved in their formation. Understanding the history of both water and CO2 on Mars is critical to better understand the evolution of the red planet and its atmosphere, but also the origin of the water on Earth, and possibly the origin of life. Since the beginning of the Mars2020 mission in Jezero Crater, the SuperCam instrument has analyzed more than 200 rocks of the crater floor, and detected carbonates along Perseverance's traverse. Carbonates are found in low amounts, and are therefore complex to identify; we use SuperCam's combination of investigation techniques and a specifically developed methodology to strengthen the identification of carbonate phases and their characterization. Even though Jezero crater hosted a lake billions of years ago, the detected carbonates appear to have formed in smaller amounts of water, after the lake had disappeared. Key Points: Carbonates are detected along Perseverance's traverse in Jezero Crater with SuperCam using laser‐induced breakdown spectroscopy, IR and Raman spectroscopyCarbonate abundance is low overall, consistent with the weak carbonate signatures observed from orbit in the explored unitsThe detected carbonates have variable compositions within the magnesite‐siderite series, and likely reflect multiple alteration episodes [ABSTRACT FROM AUTHOR]

During the first 2934 sols of the Curiosity rover's mission 33,468 passive visible/near‐infrared (NIR) reflectance spectra were taken of the surface by the mast‐mounted Chemistry and Camera (ChemCam) instrument on a range of target types. ChemCam spectra of bedrock targets from the Murray and Carolyn Shoemaker formations on Mt. Sharp were investigated using principal component analysis and various spectral parameters including the band depth at 535 nm and the slope between 840 and 750 nm. Four end‐member spectra were identified. Passive spectra were compared to Laser Induced Breakdown Spectroscopy (LIBS) data to search for correlations between spectral properties and elemental abundances. The correlation coefficient between FeOT reported by LIBS and BD535 from passive spectra was used to search for regions where iron may have been added to the bedrock through oxidation of ferrous‐bearing fluids but no correlations were found. Rocks in the Blunts Point‐Sutton Island transition that have unique spectral properties compared to surrounding rocks, that is flat NIR slopes and weak 535 nm absorptions, are associated with higher Mn and Mg in the LIBS spectra of bedrock. Additionally, calcium‐sulfate cements, previously identified by Ca and S enrichments in the LIBS spectra of bedrock, were also shown to be associated with spectral trends seen in Blunts Point. A shift toward a steeper NIR slope is seen in the Hutton interval, indicative of changing depositional conditions or increased diagenesis. Plain Language Summary: The Chemistry and Camera (ChemCam) instrument on the Mars Science Laboratory Curiosity rover was built for use in "active" mode, in which a laser vaporizes a small amount of material from a targets' surface and the light emitted from the resulting plasma is used to quantify the relative amounts of various elements. ChemCam also collects "passive" spectra (without the use of the laser). These passive spectra use reflected sunlight to provide complementary mineralogical information. By looking at how passive and active spectral features relate and change, we can further our understanding of the composition of targets that the rover has encountered. Specifically, this methodology can help determine if Curiosity encountered rocks altered by fluids containing reduced iron. Comparison between passive spectral parameters and iron oxides reported by active spectroscopy identified two regions (Sutton Island to Blunts Point and Glasgow to Knockfarril Hill transitions) as areas of compositional interest and show evidence of variations in oxidation conditions. The passive spectra are also shown to be largely in agreement with data from Chemistry and Mineralogy, another instrument on Curiosity which provides mineralogical analysis of powdered samples. Key Points: Principal component and spectral parameter analysis of Chemistry and Camera (ChemCam) passive spectra highlight four spectral end‐members in Mt. Sharp group rocksA decrease in the near‐infrared slope is seen in the Hutton interval, suggesting a changing depositional environment or enhanced diagenesisBedrock containing Mg‐sulfates and Ca‐sulfate cements are highlighted in a multivariate survey of ChemCam passive spectra [ABSTRACT FROM AUTHOR]

Understanding the genesis of Martian soils is important to constrain the hydrogeologic history of the planet. Soils have the potential to record paleoenvironmental conditions, through the nature of secondary minerals formed during weathering. In situ X‐ray diffraction analyses in Gale crater have revealed that about one third of each soil sample is composed of amorphous materials containing hydrated phases. Here, we use the geochemical data from the ChemCam instrument to investigate the nature and origin of the hydrated amorphous phases. We report for the first time with ChemCam clues for the presence of sulfates within the amorphous component of soils. We show that sulfates are the main carrier of the soil hydration and possibly explain the nature of hydrogen and sulfur measured from orbit. These sulfates and the apparent lack of significant Al‐bearing weathering products are consistent with a model of soil formation including weathering of olivine in water‐limited acidic conditions. Plain Language Summary: The study of Martian soils is of considerable interest as the nature of the mineral phases they contain, formed by the action of water for some of them, can give information on the past environments of the planet. Mineralogical analyses in Gale crater have shown that about one third of soils are composed of poorly crystalline materials whose nature remains unclear, and that soil hydration could be associated with these phases. Here, we use the chemical analyses from the ChemCam instrument to investigate the composition of the hydrogen‐bearing products, and we report for the first time the presence of sulfates in soils with this instrument. We demonstrate that sulfates are the main contributor to the water content of soils and are probably the source of the hydrogen and sulfur measured from orbit. The presence of sulfates and the lack of significant other secondary materials, especially enriched in aluminum, suggest that soils have probably undergone an acidic aqueous alteration with a low quantity of water, favoring the dissolution of olivine as the precursor to sulfates. Key Points: The amorphous component of Gale crater soils contains hydrated sulfatesThe Eolian dust deposits are not the carrier of the identified hydrated sulfatesWater‐limited acidic conditions may have led to the formation of these phases [ABSTRACT FROM AUTHOR]

Glen Torridon (GT) is a recessive‐trough feature on the northwestern slope of "Mt. Sharp" in Gale crater, Mars with the highest Fe‐/Mg‐phyllosilicates abundances detected by the Curiosity rover to date. Understanding the origin of these clay minerals and their relationship with diagenetic processes is critical for reconstructing the nature and habitability of past surface and subsurface environments in Gale crater. We aim to constrain the distribution and extent of diagenesis using compositional and morphological trends observed by visible‐to‐near infrared reflectance spectra in GT from Mastcam and ChemCam, supported by high‐resolution images from the Mars Hand Lens Imager. Spectral features consistent with nontronite and fine‐grained red hematite are ubiquitous throughout lower GT, and are strongest where diagenetic features are limited, suggesting that both were formed early, before burial. Diagenetic features increase in both abundance and diversity farther up‐section, and we observe morphologic evidence for multiple episodes of diagenesis, with the edge of a diagenetic front partially preserved in the middle stratigraphic member, Knockfarril Hill. Near the contact between GT and the overlying Greenheugh pediment capping unit, we observe a lack of clay minerals with signatures consistent instead with coarse‐grained gray hematite, likely formed through late‐diagenetic alteration. We hypothesize that the sandstone‐dominant Stimson formation acted as a conduit for diagenetic fluid flow into the area and that the clay‐rich impermeable GT slowed the flow of those fluids, leading to enhanced alteration surrounding the clay‐rich portions of GT, including within the nearby Vera Rubin ridge. Plain Language Summary: The clay mineral‐rich region of Glen Torridon on Mt. Sharp provides information to reconstruct the past habitability of the ancient lake environment in Gale crater. Clay minerals have a unique structure that allow for organic matter to be preserved, so regions with high concentrations of clay minerals are of interest for planetary exploration. We use data from the Mastcam cameras, Chemistry and Camera instrument, and Mars Hand Lens Imager on the Mars Science Laboratory Curiosity rover to search for trends in rock composition and visual properties to investigate how they have been altered by surface and subsurface water over time. This work has shown that regions with high clay mineral abundances restrict groundwater from penetrating deep into rock units, helping preserve remnants of the early environments where the clay minerals formed, some remnants are exposed on the modern‐day surface. Additionally, we observe textural evidence, supported by inferred compositions from spectral data that multiple water‐rock interactions led to enhanced alteration and destruction of clay‐minerals along the edges of the clay‐rich regions. This suggests that there has been a complex history of water‐rock interactions in Gale crater, but that regions with high abundances of clay‐minerals may still have preserved signs of life. Key Points: Glen Torridon exhibits spectral signatures consistent with Fe‐bearing clay minerals and fine‐grained red hematite within all membersThe Hutton interval, on the uppermost edge of Glen Torridon, has no clay mineral spectral signatures and instead shows evidence of hematite coarseningClay minerals and fine‐grained hematite formed via early weathering and oxidation while coarse‐grained hematite formed via late diagenesis [ABSTRACT FROM AUTHOR]

Both the source of methane on Mars and the mechanism for transmission from the subsurface to the atmosphere are not fully understood. Previous seepage simulations have invoked relatively shallow subsurface sources to explain observed methane signatures on Mars. We propose that barometric‐pressure pumping through fracture networks could be an effective mechanism for methane transport from the deep subsurface on Mars. Using atmospheric pressure data gathered by Curiosity as input, we simulate methane gas transport from depths of 200 m to the surface. Even with such a deep source, our model reproduces the observed seasonality of methane, and the simulated surface methane fluxes fall within the range of previous estimates derived from atmospheric observations. Because 200 m is the likely minimum hospitable depth for living methanogenic microbes, our fracture network model indirectly reinvigorates the possibility of a microbial source of methane on Mars. Plain Language Summary: The existence of methane on Mars is a topic of significant interest because of its potential association with subsurface microbial life. Measurements of methane in the atmosphere of Mars indicate that its abundance fluctuates over time. Although the source of methane is unknown, it most likely comes from below the surface of Mars; however, the range of depths of potential methane sources is not well constrained. If methane is currently being produced by living microbes, it would have to be at depths of at least 200 m in order to support life. Nearly all prior modeling work in this area has considered relatively slow, inefficient methane transport mechanisms, which limits the methane sources to the shallow martian subsurface. In this paper, we describe and model a mechanism capable of transporting significant quantities of methane to the atmosphere from depths capable of supporting living methane‐producing microorganisms. We also find that the methane seepage pattern generated by our model is highly seasonal, and closely follows the pattern of atmospheric methane concentrations measured by the Curiosity rover. Key Points: Atmospheric pressure fluctuations on Mars can produce significant methane seepage from potentially habitable depths (up to 200 m)Modeled surface methane seepage patterns are highly seasonal and coincide with rover measurements of elevated concentrations at Gale craterMagnitude and timing of modeled surface flux is comparable to existing plume estimates, supporting a model of localized surface releases [ABSTRACT FROM AUTHOR]

During 2018 and 2019, the Mars Science Laboratory Curiosity rover investigated the chemistry, morphology, and stratigraphy of Vera Rubin ridge (VRR). Using orbital data from the Compact Reconnaissance Imaging Spectrometer for Mars, scientists attributed the strong 860 nm signal associated with VRR to the presence of red crystalline hematite. However, Mastcam multispectral data and CheMin X‐ray diffraction (XRD) measurements show that the depth of the 860 nm absorption is negatively correlated with the abundance of red crystalline hematite, suggesting that other mineralogical or physical parameters are also controlling the 860 nm absorption. Here, we examine Mastcam and ChemCam passive reflectance spectra from VRR and other locations to link the depth, position, and presence or absence of iron‐related mineralogic absorption features to the XRD‐derived rock mineralogy. Correlating CheMin mineralogy to spectral parameters showed that the ~860 nm absorption has a strong positive correlation with the abundance of ferric phyllosilicates. New laboratory reflectance measurements of powdered mineral mixtures can reproduce trends found in Gale crater. We hypothesize that variations in the 860 nm absorption feature in Mastcam and ChemCam observations of VRR materials are a result of three factors: (1) variations in ferric phyllosilicate abundance due to its ~800–1,000 nm absorption; (2) variations in clinopyroxene abundance because of its band maximum at ~860 nm; and (3) the presence of red crystalline hematite because of its absorption centered at 860 nm. We also show that relatively small changes in Ca‐sulfate abundance is one potential cause of the erosional resistance and geomorphic expression of VRR. Plain Language Summary: Results from near‐infrared spectral measurements showed that Vera Rubin ridge (VRR) in Gale crater, Mars, has a unique spectral signature compared to the surrounding Mt. Sharp units, which was confirmed using instruments onboard the Curiosity rover. This paper describes the spectral, compositional, and physical properties of eight rocks that were drilled and analyzed by the Curiosity rover, including three rocks that are on VRR. Quantitative mineralogy, determined using the CheMin instrument, found that all eight rocks had plagioclase, clinopyroxene, ferric phyllosilicates, and red crystalline hematite in significant abundances. These minerals all have unique spectral signatures that contributed to spectra obtained by the Mastcam multispectral imager of the eight drilled rocks. By comparing spectral parameters of drill tailings from the eight rocks to their quantitative mineralogy, this paper found that the spectral differences of VRR and surrounding units are the result of variations in ferric phyllosilicates, clinopyroxene, and red crystalline hematite. New lab spectral measurements successfully reproduced the same trends as seen in data from the Curiosity rover. The results of this work help us better understand how different minerals affect the spectral signals we measure on Mars, which is extremely important to understanding its geologic history. Key Points: Hematite likely controls the wavelength position of the ~860 nm absorption in Mastcam multispectral observations of drill targetsLab results show that the ~860 nm band depth increases with ferric phyllosilicate abundance due to its ~800–1,000 nm featureThe reflectance maximum near 860 nm in pyroxene affects the ~860 nm band depth in spectra of lab mixtures and drilled rocks on Mars [ABSTRACT FROM AUTHOR]

Curiosity investigated a topographic rise named Vera Rubin Ridge (VRR) in Gale Crater, for which a distinct hematite‐like signature was observed from orbit. However, the Chemistry and Camera (ChemCam) and Alpha Particle x‐ray Spectrometer (APXS) instruments on board the rover did not record any significant iron enrichment in the bulk of the ridge compared to previous terrains. For this study, we have reverified ChemCam iron calibration at moderate abundances and developed more accurate calibrations at high‐iron abundances using iron‐oxide mixtures in a basaltic matrix in order to complete the ChemCam calibration database. The high‐iron calibration was first applied to the analysis of dark‐toned diagenetic features encountered at several locations on VRR, which showed that their chemical compositions are close to pure anhydrous iron oxides. Then, we tracked iron abundances in the VRR bedrock and demonstrated that although there is no overall iron enrichment in the bulk of the ridge (21.2 ± 1.8‐wt.% FeOT) compared to underlying terrains, the iron content is more variable in its upper section with areas of enhanced iron abundances in the bedrock (up to 26.6 ± 0.85‐wt.% FeOT). Since the observed variability in iron abundances does not conform to the stratigraphy, the involvement of diagenetic fluid circulation was likely. An in‐depth chemical study of these Fe‐rich rocks reveals that spatial gradients in redox potential (Eh) may have driven iron mobility and reactions that precipitated and accumulated iron oxides. We hypothesize that slightly reducing fluids were probably involved in transporting ferrous iron. Mobile Fe2+ could have precipitated as iron oxides in more oxidizing conditions. Plain Language Summary: Curiosity investigated a positive relief ridge named Vera Rubin Ridge (VRR) located in the Gale Crater. Orbital data indicate the presence of hematite (an iron oxide) in this ridge. Surprisingly, no significant enrichment in iron was observed by the two rover instruments (Chemistry and Camera [ChemCam] and Alpha Particle x‐ray Spectrometer [APXS]) that determined the chemical compositions. Here, we have made a dedicated iron calibration for ChemCam Martian data for high‐iron abundances. For this, we prepared mixtures of basaltic powder and iron oxides (hematite, goethite, or magnetite) and analyzed them with a ChemCam laboratory unit. The objective was to increase the set of standards currently used for ChemCam iron quantification. This method has shown that dark‐toned concretions located in some VRR bedrock have an iron abundance similar to pure hematite. An iron survey along the ridge revealed that there is no overall enrichment compared to underlying terrains. However, iron abundances recorded in the upper part of the ridge are more variable. Areas of enhanced iron abundances do not follow the rock stratification, which suggests that the phenomenon responsible for the iron variability did not occur during the sediment deposition but rather occurred later, during diagenesis. Fluids percolating into the sediment are most likely responsible for iron mobility. Key Points: We present a dedicated ChemCam calibration for high‐iron abundances and apply it to Vera Rubin Ridge bedrock and diagenetic concretionsDark‐toned diagenetic features have iron contents close to pure anhydrous iron oxidesIron variability is observed among bedrock in the upper part of the ridge, attributed to iron mobility during diagenesis [ABSTRACT FROM AUTHOR]

Visible/short‐wave infrared spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions attributed to hematite at Vera Rubin ridge (VRR), a topographic feature on northwest Mt. Sharp. The goals of this study are to determine why absorptions caused by ferric iron are strongly visible from orbit at VRR and to improve interpretation of CRISM data throughout lower Mt. Sharp. These goals are achieved by analyzing coordinated CRISM and in situ spectral data along the Curiosity Mars rover's traverse. VRR bedrock within areas that have the deepest ferric absorptions in CRISM data also has the deepest ferric absorptions measured in situ. This suggests strong ferric absorptions are visible from orbit at VRR because of the unique spectral properties of VRR bedrock. Dust and mixing with basaltic sand additionally inhibit the ability to measure ferric absorptions in bedrock stratigraphically below VRR from orbit. There are two implications of these findings: (1) Ferric absorptions in CRISM data initially dismissed as noise could be real, and ferric phases are more widespread in lower Mt. Sharp than previously reported. (2) Patches with the deepest ferric absorptions in CRISM data are, like VRR, reflective of deeper absorptions in the bedrock. One model to explain this spectral variability is late‐stage diagenetic fluids that changed the grain size of ferric phases, deepening absorptions. Curiosity's experience highlights the strengths of using CRISM data for spectral absorptions and associated mineral detections and the caveats in using these data for geologic interpretations and strategic path planning tools. Plain Language Summary: Satellites orbiting Mars map the composition of the planet's surface, tell us about past environments, and guide rovers to interesting locations on the surface. The Curiosity rover investigated a ridge named Vera Rubin ridge where indications of the mineral hematite (Fe2O3) was suggested from orbital data. In this paper, we investigate why the hematite detection on the ridge was so clear from orbit and what the implications are for how the hematite formed. We found several factors influence the orbital data, but the biggest reason hematite at Vera Rubin ridge was so easily detected from orbit was because the bedrock there was unique. Water had interacted with rocks at the ridge sometime after they were deposited, and this interaction affected the properties of the hematite and made it more visible from orbit. Curiosity's data help us reinterpret the orbital data over Mt. Sharp and reveal hematite is probably present in most of the bedrock there. Furthermore, there are other areas with particularly clear hematite detections that likely formed in a similar manner as Vera Rubin ridge. We end this paper with a discussion of lessons learned from this experience for using orbital data to guide rovers in the future. Key Points: Areas on Vera Rubin ridge with deep ferric absorptions from orbit also have deep ferric absorptions in Curiosity spectral data setsFerric phases are more widespread on Mt. Sharp than originally reported. Diagenesis deepened ferric absorptions in several locationsCombining orbital and in situ observations enhances planetary exploration [ABSTRACT FROM AUTHOR]

Geochemical results are presented from Curiosity's exploration of Vera Rubin ridge (VRR), in addition to the full chemostratigraphy of the predominantly lacustrine mudstone Murray formation up to and including VRR. VRR is a prominent ridge flanking Aeolis Mons (informally Mt. Sharp), the central mound in Gale crater, Mars, and was a key area of interest for the Mars Science Laboratory mission. ChemCam data show that VRR is overall geochemically similar to lower‐lying members of the Murray formation, even though the top of VRR shows a strong hematite spectral signature as observed from orbit. Although overall geochemically similar, VRR is characterized by a prominent decrease in Li abundance and Chemical Index of Alteration across the ridge. This decrease follows the morphology of the ridge rather than elevation and is inferred to reflect a nondepositionally controlled decrease in clay mineral abundance in VRR rocks. Additionally, a notable enrichment in Mn above baseline levels is observed on VRR. While not supporting a single model, the results suggest that VRR rocks were likely affected by multiple episodes of postdepositional groundwater interactions that made them more erosionally resistant than surrounding Murray rocks, thus resulting in the modern‐day ridge after subsequent erosion. Plain Language Summary: Results from the ChemCam instrument on Vera Rubin ridge (VRR) in Gale crater, Mars, are presented and compared with observations from similar rocks leading up to the ridge. VRR is a prominent ridge, flanking the central mound, Aeolis Mons, in Gale crater, Mars. The ridge attracted early attention because it displays strong iron‐oxide spectral signatures. Surprisingly, ChemCam data show that VRR rocks do not show an overall increase in iron abundance relative to the comparable bedrock analyzed for almost 300 m in elevation leading up to the ridge. While similar overall, some notable variations were observed on VRR relative to lower‐lying rocks. In particular, geochemical variations suggest a strong decrease in clay content on the ridge, above which, a notable enrichment in Mn is observed. No single geological process confidently explains all observations on the ridge. Rather, we think that VRR rocks underwent a series of interactions with groundwater that caused the rocks of VRR to become more resistant to erosion than their surroundings, thus emerging as a ridge as the rocks around them eroded. This likely implies that groundwater persisted in Gale crater even long after the disappearance of the ancient lake. Key Points: A decrease in Li and Chemical Index of Alteration, reflecting clay mineral content, is observed across Vera Rubin ridge (VRR)A Mn‐rich interval is observed stratigraphically above the decrease in clay mineral content on VRRVRR likely resulted from increased induration from late‐stage fluid interactions long after the lake environment in Gale crater ceased [ABSTRACT FROM AUTHOR]

The Mars Science Laboratory (MSL) Curiosity rover is exploring the Murray formation, a sequence of heterolithic mudstones and sandstones recording fluvial deltaic and lake deposits that comprise over 350 m of sedimentary strata within Gale crater. We examine >4,500 Murray formation bedrock points, employing recent laboratory calibrations for ChemCam laser‐induced breakdown spectroscopy H measurements at millimeter scale. Bedrock in the Murray formation has an interquartile range of 2.3–3.1 wt.% H2O, similar to measurements using the Dynamic Albedo of Neutrons and Sample Analysis at Mars instruments. However, specific stratigraphic intervals include high H targets (6–18 wt.% H2O) correlated with Si, Mg, Ca, Mn, or Fe, indicating units with opal, hydrated Mg sulfates, hydrated Ca sulfates, Mn‐enriched units, and akageneite or other iron oxyhydroxides, respectively. One stratigraphic interval with higher hydrogen is the Sutton Island unit and Blunts Point unit contact, where higher hydrogen is associated with Fe‐rich, Ca‐rich, and Mg‐rich points. A second interval with higher hydrogen occurs in the Vera Rubin ridge portion of the Murray formation, where higher hydrogen is associated with Fe‐rich, Ca‐rich, and Si‐rich points. We also observe trends in the H signal with grain size, separate from chemical variation, whereby coarser‐grained rocks have higher hydrogen. Variability in the hydrogen content of rocks points to a history of water‐rock interaction at Gale crater that included changes in lake water chemistry during Murray formation deposition and multiple subsequent groundwater episodes. Plain Language Summary: We measured the water content of bedrock targets in the Murray formation, a sequence of mudstones and sandstones part of Gale crater's Mt. Sharp, by applying recent laboratory calibrations to measurements from the Curiosity ChemCam instrument. While most rocks contained 2.3–3.1 wt.% H2O, consistent with measurements by other Mars Science Laboratory instruments, we found some stratigraphic intervals contained high water content (6–18 wt.% H2O) rocks including the Vera Rubin ridge. Based on our analysis of the corresponding major element composition, these are likely clays, Ca sulfates, Mn‐enriched units, and akageneite or other iron oxyhydroxides. The variation in water content indicates a history of water‐rock interaction at Gale crater that included changes in lake water chemistry during Murray formation deposition and multiple subsequent groundwater episodes. Key Points: Murray formation bedrock points measured by ChemCam have an interquartile range of 2.3–3.1 wt.% H2OSpecific intervals like the Vera Rubin ridge contain high H and indicate phases including iron oxyhydroxides, akageneite, and jarositeVariations in water content indicate changes in depositional lake water chemistry and multiple subsequent groundwater episodes [ABSTRACT FROM AUTHOR]

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. Plain Language Summary: Boron and lithium were measured in cracks in the rocks that were filled with whitish, calcium sulfate. These were found in Gale crater using the ChemCam instrument on the Mars Science Laboratory Curiosity rover. Both elements are highly water soluble and may indicate late‐stage ground water activity. Boron's lower solubility compared to that of lithium means it forms salts relatively easily, while Li remains dissolved in the brine with progressive evaporation. In our study we find that on Vera Rubin ridge, boron detection frequency is inversely proportional to the concentration of lithium. This finding suggests that, based on their different solubilities, boron may have precipitated in the fractures before lithium. Lithium possibly moved away with the remaining brine, leaving boron behind as precipitates. Key Points: ChemCam analyses of calcium sulfate veins in Vera Rubin ridge (VRR) show the presence of boron and lithiumBoron detection frequency in the Ca‐sulfate veins increases in the Jura member of VRR and is inversely correlated with lithiumThe relationship between B and Li suggests an evaporative sequence formed during dehydration on higher elevations of VRR [ABSTRACT FROM AUTHOR]

The Dynamic Albedo of Neutrons instrument aboard the Mars Science Laboratory rover, Curiosity, has been used to map a stratigraphically conformable layer of high‐SiO 2 material in Gale crater. Previous work has shown that this material contains tridymite, a high‐temperature/low‐pressure felsic mineral, interpreted to have a volcanic source rock. We describe several characteristics including orientation, extent, hydration, and geochemistry, consistent with a volcaniclastic material conformably deposited within a lacustrine mudstone succession. Relationships with widely dispersed alteration features and orbital detections of hydrated SiO 2 suggest that this high‐SiO 2 layer extends at least 17 km laterally. Mineralogical abundances previously reported for this high‐SiO 2 material indicated that hydrous species were restricted to the amorphous (non‐crystalline) fraction, which is dominated by SiO 2. The low mean bulk hydration of this high‐SiO 2 layer (1.85 ± 0.13 wt.% water‐equivalent hydrogen) is consistent with silicic glass in addition to opal‐A and opal‐CT. Persistent volcanic glass and tridymite in addition to opal in an ancient sedimentary unit indicates that the conversion to more ordered forms of crystalline SiO 2 has not proceeded to completion and that this material has had only limited exposure to water since it originally erupted, despite having been transported in a fluviolacustrine system. Our results, including the conformable nature, large areal extent, and presence of volcanic glass, indicate that this high‐SiO 2 material is derived from the product of evolved magma on Mars. This is the first identification of a silicic volcaniclastic layer on another planet and has important implications for magma evolution mechanisms on single‐plate planets. Plain Language Summary: Using the Dynamic Albedo of Neutrons instrument aboard the Mars Science Laboratory rover, Curiosity, we mapped a silica‐rich layer throughout a small region in Gale crater known as Marias Pass. Previous work has shown that some rocks in Marias Pass contain minerals formed in explosive volcanic eruptions. We determined several key characteristics including orientation, extent, hydration, and elemental composition, which are consistent with material derived from a volcanic deposit. This layer is likely related to nearby silica‐rich material deposited by groundwater along subsurface fractures, and geometric relationships to hydrated silica identified from orbit suggest that this high‐silica layer extends over at least 17 km. Mineralogical data from previous work indicates the crystalline fraction is anhydrous. As such, we interpret the low hydration of this material, attributable to the amorphous (non‐crystalline) fraction, as being consistent with a significant abundance of volcanic glass in addition to other hydrated phases. The presence of volcanic glass indicates that this material has had limited exposure to water since its formation, because glasses tend to preferentially weather. Our results show that this layer is parallel to surrounding rocks, covers a large area, and contains volcanic glass, indicating that it derived from an explosive volcanic product. Key Points: A >1 m thick SiO 2‐ and tridymite‐rich layer in Gale crater likely extends over several kilometersThis layer is stratigraphically conformable, with low water content consistent with significant volcanic glassThis material is consistent with an evolved igneous material deposited in a lacustrine environment [ABSTRACT FROM AUTHOR]

NASA's Genesis Mission returned solar wind (SW) to the Earth for analysis to derive the composition of the solar photosphere from solar material. SW analyses control the precision of the derived solar compositions, but their ultimate accuracy is limited by the theoretical or empirical models of fractionation due to SW formation. Mg isotopes are "ground truth" for these models since, except for CAIs, planetary materials have a uniform Mg isotopic composition (within ≤1‰) so any significant isotopic fractionation of SW Mg is primarily that of SW formation and subsequent acceleration through the corona. This study analyzed Mg isotopes in a bulk SW diamond‐like carbon (DLC) film on silicon collector returned by the Genesis Mission. A novel data reduction technique was required to account for variable ion yield and instrumental mass fractionation (IMF) in the DLC. The resulting SW Mg fractionation relative to the DSM‐3 laboratory standard was (−14.4‰, −30.2‰) ± (4.1‰, 5.5‰), where the uncertainty is 2ơ SE of the data combined with a 2.5‰ (total) error in the IMF determination. Two of the SW fractionation models considered generally agreed with our data. Their possible ramifications are discussed for O isotopes based on the CAI nebular composition of McKeegan et al. (2011). [ABSTRACT FROM AUTHOR]

The Mars Science Laboratory Curiosity rover is traversing a sequence of stratified sedimentary rocks in Gale crater that contain varied eolian, fluviodeltaic, and lake deposits, with phyllosilicates, iron oxides, and sulfate salts. Here, we report the chloride salt distribution along the rover traverse. Chlorine is detected at low levels (<3 wt.%) in soil and rock targets with multiple MSL instruments. Isolated fine‐scale observations of high chlorine (up to ≥15 wt.% Cl), detected using the ChemCam instrument, are associated with elevated Na2O and interpreted as halite grains or cements in bedrock. Halite is also interpreted at the margins of veins and in nodular, altered textures. We have not detected halite in obvious evaporitic layers. Instead, its scattered distribution indicates that chlorides emplaced earlier in particular members of the Murray formation were remobilized and reprecipitated by later groundwaters within Murray formation mudstones and in diagenetic veins and nodules. Plain Language Summary: Chlorine is measured in soils and rocks in Gale crater by multiple instruments on the Mars Science Laboratory Curiosity rover. Fine‐scale points of enriched chlorine are detected by the ChemCam instrument in bedrock, nodules, and at the margins of veins in the Murray formation. Chlorine content is correlated with weight percent Na2O indicating halite composition, corroborated by CheMin and SAM data. The scattered distribution of chlorides in the Murray formation indicates they were dissolved by later groundwaters then recrystallized. The chlorides may have been emplaced as small‐scale primary deposits in particular members of the Murray formation, consistent with varying salinity in the waters that deposited the Murray. Key Points: Isolated Cl enrichments in bedrock, in nodular textures, and at calcium sulfate vein margins, correlated with Na, indicate haliteMapping of Cl along the Curiosity traverse in Gale Crater indicates Cl enrichments are more common in select Murray formation membersThe scattered, isolated occurrences of chlorides are consistent with late groundwater reworking and remobilization of original deposits [ABSTRACT FROM AUTHOR]

Mineral‐filled fractures (veins) are valuable indicators of deformation and fluid flow within a sedimentary package. Information obtained from vein morphology, texture, and chemistry may elucidate the sequence and nature of postdepositional fluid events. Additional information from vein patterns and interactions between veins and host rock provides insight into fracture formation mechanism(s). The widespread occurrence of veins and other diagenetic features in the sedimentary rock record preserved in Gale crater, Mars, indicates that postdepositional fluids were regionally active considerably later in time than the primary fluviolacustrine environments responsible for the deposition of Mount Sharp strata. Here we report a suite of veins within the Murray formation at the Pahrump Hills locality that were investigated using the scientific payload of the Mars Science Laboratory Curiosity rover. Based on an analysis of vein color, morphology, and texture, and corroborated by vein chemistry, we interpret three distinct vein types at Pahrump Hills: gray veins, white veins, and dark‐toned veins. These veins represent distinct, separate episodes of postdepositional fluid flow, suggesting a protracted history of fluid stability in Gale crater. Additionally, we utilize vein patterns across multiple lithologies at the Pahrump Hills field site to suggest hydrofracture as the primary mechanism of fracture formation. Key Points: Mineral‐filled fractures (veins) are identified and characterized at the Pahrump Hills locality of the Murray formation, Gale crater, MarsMorphological and chemical data on veins are used to infer multiple episodes of postdepositional fluid flow and hydrofracturing of rocksImplications for prolonged stability of depositional and diagenetic fluids in Gale crater are discussed [ABSTRACT FROM AUTHOR]

Abstract: We propose spark plasma sintering (SPS) as a technique to prepare reference targets for Raman and other spectroscopy instruments involved in future space missions and more generally in‐field work. We have tested the effect of SPS on different international standards that are available in the form of minerals and rocks powders. Advantages and potential issues of SPS were considered by analyzing the Raman signal and mechanical properties of the sintered targets. The shape is well controlled; the rupture toughness is enhanced, and the homogeneous distribution of the mineral phases is verified. A suite of calibration targets has thus been implemented for the SuperCam instrument on the National Aeronautics and Space Administration Mars 2020 rover, and SPS may be preferred for future missions as well. [ABSTRACT FROM AUTHOR]

Abstract: The Mars Science Laboratory rover, Curiosity, is equipped with ChemCam, a laser‐induced breakdown spectroscopy (LIBS) instrument, to determine the elemental composition of nearby targets quickly and remotely. We use a laboratory sample set including prepared mixtures of basalt with systematic variation in hydrated mineral content and compositionally well‐characterized, altered basaltic volcanic rocks to measure hydrogen by characterizing the H‐alpha emission line in LIBS spectra under Martian environmental conditions. The H contents of all samples were independently measured using thermogravimetric analysis. We found that H peak area increases with weight percent H for our laboratory mixtures with basaltic matrices. The increase is linear with weight percent H in the mixtures with structurally bound H up to about 1.25 wt.% H and then steepens for higher H‐content samples, a nonlinear trend not previously reported but potentially important for characterizing high water content materials. To compensate for instrument, environmental, and target matrix‐related effects on quantification of H content from the LIBS signal, we examined multiple normalization methods. The best performing methods utilize O 778‐ and C 248‐nm emission lines. The methods return comparable results when applied to ChemCam data of H‐bearing materials on Mars. The calibration and normalization methods tested here will aid in investigations of H by LIBS on Mars with ChemCam and SuperCam. Further laboratory work will aid quantification across different physical matrices and heterogeneous textures because of differences we observed in H in pelletized and natural rock samples of the same composition. [ABSTRACT FROM AUTHOR]

Abstract: Silica enrichments resulting in up to ~90 wt% SiO2 have been observed by the Curiosity rover's instruments in Gale crater, Mars, within the Murray and Stimson formations. Samples acquired by the rover drill revealed a significant abundance of an X‐ray amorphous silica phase. Laser‐induced breakdown spectroscopy (LIBS) highlights an overall correlation of the hydrogen signal with silica content for these Si‐enriched targets. The increased hydration of the high‐silica rocks compared to the surrounding bedrock is also confirmed by active neutron spectroscopy. Laboratory LIBS experiments have been performed to calibrate the hydrogen signal and show that the correlation observed on Mars is consistent with a silica phase containing on average 6.3 ± 1.4 wt% water. X‐ray diffraction and LIBS measurements indicate that opal‐A, amorphous hydrated silica, is the most likely phase containing this water in the rocks. Pyrolysis experiments were also performed on drilled samples by the Sample Analysis at Mars (SAM) instrument to measure volatile content, but the data suggests that most of the water was released during handling prior to pyrolysis. The inferred low‐temperature release of water helps constrain the nature of the opal. Given the geological context and the spatial association with other phases such as calcium sulfates, the opal was likely formed from multiple diagenetic fluid events and possibly represents the latest significant water‐rock interaction in these sedimentary rocks. [ABSTRACT FROM AUTHOR]

We model the fluids involved in the alteration processes recorded in the Sheepbed Member mudstones of Yellowknife Bay ( YKB), Gale crater, Mars, as revealed by the Mars Science Laboratory Curiosity rover investigations. We compare the Gale crater waters with fluids modeled for shergottites, nakhlites, and the ancient meteorite ALH 84001, as well as rocks analyzed by the Mars Exploration rovers, and with terrestrial ground and surface waters. The aqueous solution present during sediment alteration associated with phyllosilicate formation at Gale was high in Na, K, and Si; had low Mg, Fe, and Al concentrations-relative to terrestrial groundwaters such as the Deccan Traps and other modeled Mars fluids; and had near neutral to alkaline pH. Ca and S species were present in the 10−3 to 10−2 concentration range. A fluid local to Gale crater strata produced the alteration products observed by Curiosity and subsequent evaporation of this groundwater-type fluid formed impure sulfate- and silica-rich deposits-veins or horizons. In a second, separate stage of alteration, partial dissolution of this sulfate-rich layer in Yellowknife Bay, or beyond, led to the pure sulfate veins observed in YKB. This scenario is analogous to similar processes identified at a terrestrial site in Triassic sediments with gypsum veins of the Mercia Mudstone Group in Watchet Bay, UK. [ABSTRACT FROM AUTHOR]

Introduction: The Askival sample is a geochemically and texturally unique sample investigated by the Curiosity rover in Gale crater. Located at the Bressay site and analyzed between mission sols 2015 to 2021, Askival has a feldspathic cumulate texture, but presents geochemical evidence of aqueous alteration beyond initial crystallization and accumulation. An earlier target, Bindi, provides an important comparative sample as it also appears to be a feldspathic cumulate but lacks the alteration present in Askival. Methods: Geochemical analysis of Askival and Bindi was performed using the Chemistry and Camera (Chem-Cam) instrument on the MSL Curiosity rover [1]. ChemCam is a laser induced breakdown spectrometer (LIBS) instrument that performs geochemical remote sensing on targets up to 7 m away from the rover. LIBS analyses occur by creating an energized plasma at a micron-scale point on the target rock, allowing for sampling of different phases within coarse-grained targets such as Askival. Supporting imagery from the ChemCam remote micro-imager (RMI) allows these chemical analyses to be correlated with visual identification of different phases. Further geochemical analysis of Askival using the Alpha-Particle X-Ray Spectrometer (APXS) [2] and images from the Mars Hand Lens Imager (MAHLI) [3] provide complementary datasets. Results & Analysis: Texturally, Askival has strong resemblance to feldspar cumulate samples, with roughly 65% of the sample consisting of light-toned, subhedral crystals with some examples of elongation. This phase is separated and, in some cases, enclosed by a fine-grained darker matrix, which comprises approximately 30% of the sample. The remaining texture is comprised of a fibrous grey/brown phase that occurs only in a couple of visible areas of the sample, as well as a secondary light-toned phase observed as small veins occupying interstitial areas. Geochemically, the primary light-toned phase has a range of compositions which form a linear trend away from stoichiometric feldspar composition. The most prominent chemical divergence is an enrichment in silica, with some of the sampled LIBS points containing >80% SiO2. This enrichment correlates with a detected increase in H, and a decrease in alkali elements and enrichment in Mg. This is consistent with the production of a leached layer and precipitation of secondary Mg-phyllosilicates under low temperature acidic conditions [4]. Other rocks located at Bressay do not show similar alteration, and are not of the same cumulate origin, indicating either a diversity of sources within a single locality or that Bressay has a collection of samples that have undergone different transportation pathways. The secondary phase presents a diverse mafic composition, indicating multiple mineral endmembers contributing to the phase that are not visibly distinguished in the RMI imagery. Normative calculations support a composition made of Fe/Mg silicates including pyroxenes and amphibole, supporting a model of formation under an upper crustal setting. [ABSTRACT FROM AUTHOR]

Introduction: The Mars2020 Perseverance rover landed in Jezero crater on February 18th 2021. During the first ~380 sols (martian days), the rover explored two different formations: the Máaz and the Séítah formations, both representing igneous lithologies. Here we focus on the SuperCam (SCAM) results of the Máaz formation and compare these rocks to the martian meteorites, currently our only samples that we possess from Mars. The SCAM instrument is a mast-based, remote science instrument that measures rock chemistry with Laser Induced Breakdown Spectroscopy (LIBS, see [1]), mineralogy with Raman and VISIR (Visible Infrared), and textures using Remote Micro Imager (RMI; see [2]). Perseverance has explored the Máaz formation from Sols 1 to 201 and then from 343 until Sol 382, including the Artuby ridge from Sol 170 to 201 and from Sols 343 until Sol 382. This study also comprises the Content member (mb) of the Séítah formation, as it shows compositions similar to those of the Máaz lithologies. The Màaz formation: The Máaz rocks show varied igneous textures, mineralogies, and compositions, expected for basaltic lithologies. Máaz formation rocks display both vesicular and non vesicular textures, also including aphanitic and phaneritic textures (> 1 mm grains). Some of these rocks show a flowy texture and conchoidal fractures, indicating the presence of glass (e.g., Hastą"áadah target, Sol 87). Abraded patches (conducted in the three Máaz rocks that were sampled) of Guillaumes, Bellegarde, and Alfafa, show mostly an ophitic texture [e.g., 3, 4]. Bulk compositions and Mineralogy. We divided the Máaz compositions between fine and coarse-grained textures. Both Máaz textures and the Content mb show similar bulk composition with 52 wt.% SiO2, 9.0-13 wt.% Al2O3, 15 - 20 wt.% FeO, and Mg# of 17-21 (= 100*molar MgO/MgO+FeO). These compositions indicate that the Máaz rocks with different grain sizes and the Content member could be petrogenetically linked. The Artuby rocks are slightly more primitive with a SiO2 content of 45 wt.%, Al2O3 of 6.5 wt.%, CaO of 8.4 wt.%, and Mg# of 28. Several pure mineral LIBS analyses were identified using different stoichiometric conditions in the Máaz formation. Pyroxene has been recognized through LIBS analyses having 4 (±0.2) total cations with 6 O. The observed pyroxene include augite grains (Wo30-50En10-22Fs29-55) and Fe-rich grains (Wo3-9En4-18Fs73-93). One plagioclase grain was analyzed in the Content mb (An28Ab66Or6), but no olivine was detected in any of the abrasion patches. Comparison with martian meteorites: The ophitic textures and basaltic mineralogy observed in the Máaz and Content lithologies, are extremely common in martian meteorites, especially shergottites [5]. However, no recovered martian meteorites show vesicular textures: this difference of texture likely indicates more volatiles/degassing processes in Jezero rocks. This difference in texture likely reflects the more comprehensive view of the igneous rocks in Jezero relative to the martian meteorites. Although the Máaz lithologies show general basaltic compositions, they are more enriched in alkali elements most than martian meteorites, displaying similar compositions to Northwest Africa (NWA) 7034 and paired meteorites [6]. Máaz rocks resemble basaltic shergottites in regard to their CaO and Al2O3 contents, but they have lower MgO and Mg# rocks compared to most martian meteorites, they are most similar to Fe-rich meteorites, such as the basaltic shergottites Dhofar 378 [7], and Los Angeles [8], the gabbroic shergottite NWA 7320 [9], the augite rich NWA 8159 [10], and some NWA 7034 clasts [6]. The pyroxene composition resembles pyroxene analyzed in NWA 7320 [9] and augite-rich NWA 8159 [10]. We interpret the Máaz formation lithologies to be lavas with complex textures and compositions similar to pyroxene-bearing meteorites (with no olivine). Earthbased analyses of the Máaz samples [10,11] will help better constrain their formations and petrogenetic link to these martian meteorites and lead to be a broader view of the igneous history of Mars. [ABSTRACT FROM AUTHOR]