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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]

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]