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Sulfur plays a major role in martian geochemistry and sulfate minerals are important repositories of water. However, their hydration states on Mars are poorly constrained. Therefore, understanding the hydration and distribution of sulfate minerals on Mars is important for understanding its geologic, hydrologic, and atmospheric evolution as well as its habitability potential. NASA's Perseverance rover is currently exploring the Noachian-age Jezero crater, which hosts a fan-delta system associated with a paleolake. The crater floor includes two igneous units (the Séítah and Máaz formations), both of which contain evidence of later alteration by fluids including sulfate minerals. Results from the rover instruments Scanning Habitable Environments with Raman and Luminescence for Organics and Chemistry and Planetary Instrument for X-ray Lithochemistry reveal the presence of a mix of crystalline and amorphous hydrated Mg-sulfate minerals (both MgSO4·[3–5]H2O and possible MgSO4·H2O), and anhydrous Ca-sulfate minerals. The sulfate phases within each outcrop may have formed from single or multiple episodes of water activity, although several depositional events seem likely for the different units in the crater floor. Textural and chemical evidence suggest that the sulfate minerals most likely precipitated from a low temperature sulfate-rich fluid of moderate pH. The identification of approximately four waters puts a lower constraint on the hydration state of sulfate minerals in the shallow subsurface, which has implications for the martian hydrological budget. These sulfate minerals are key samples for future Mars sample return., Correspondence Address: S. Siljeström; RISE Research Institutes of Sweden, Stockholm, Sweden; email: sandra.siljestrom@ri.se

The Mars 2020 Perseverance rover has examined and sampled sulfate-rich clastic rocks from the Hogwallow Flats member at Hawksbill Gap and the Yori Pass member at Cape Nukshak. Both strata are located on the Jezero crater western fan front, are lithologically and stratigraphically similar, and have been assigned to the Shenandoah formation. In situ analyses demonstrate that these are fine-grained sandstones composed of phyllosilicates, hematite, Ca-sulfates, Fe-Mg-sulfates, ferric sulfates, and possibly chloride salts. Sulfate minerals are found both as depositional grains and diagenetic features, including intergranular cement and vein- and vug-cements. Here, we describe the possibility of various sulfate phases to preserve potential biosignatures and the record of paleoenvironmental conditions in fluid and solid inclusions, based on findings from analog sulfate-rich rocks on Earth. The samples collected from these outcrops, Hazeltop and Bearwallow from Hogwallow Flats, and Kukaklek from Yori Pass, should be examined for such potential biosignatures and environmental indicators upon return to Earth., We thank the entire Mars 2020 science, engineering, and leadership team. K. C. Benison and K. K. Gill acknowledge funding from National Aeronautics and Space Administration Grant 80NSSC20K0235 to K.C.B. T. Bosak is supported by NASA Grant 80NSSC20K0234 and the Simons Foundation Collaboration on the Origins of Life #327126. E. A. Cloutis acknowledges funding from the Canadian Space Agency (Grants 15FASTA05 and 22EXPCOI4), the Natural Sciences and Engineering Research Council of Canada (Grants RGPIN‐2015‐0452, RTI‐2020‐00157, and RGPIN‐2023‐03413), the Canada Foundation for Innovation and Research Manitoba (Grants CFI1504 and CFI‐2450). F. Fornaro was funded through the ASI/INAF Agreement n. 2023‐3‐HH. C. D. K. Herd and N. Randazzo acknowledge funding from the Canadian Space Agency (20EXPMARS), and the Natural Sciences and Engineering Research Council of Canada (Grant RGPIN‐2018‐04902 to C.D.K.H.). J. M. Madariaga and J. M. Frias acknowledge funding from the Spanish Agency for Research AEI/MCIN/FEDER Grant PID2022‐142750OB‐I00. M. Nachon was funded by NASA M2020 Participating Scientist Grant 80NSSC21K0329. S. Sharma, K. Hand, and K. Uckert acknowledge funding from the National Aeronautics and Space Administration (80NM0018D0004) to support research that was carried out at the Jet Propulsion Laboratory, California Institute of Technology. S. Siljeström acknowledges funding from the Swedish National Space Agency, contract 2021‐00092. A. Williams acknowledges funding from NASA 80NSSC21K0332.

The Perseverance rover has collected seven oriented samples of sedimentary rocks, all likely older than the oldest signs of widespread life on Earth, at the exposed base of the western fan in Jezero crater, Mars. The samples include a sulfate- and clay-bearing mudstone and sandstone, a fluvial sandstone from a stratigraphically low position at the fan front, and a carbonate-bearing sandstone deposited above the sulfate-bearing strata. All samples contain aqueously precipitated materials and most or all were aqueously deposited. Although the rover instruments have not confidently detected organic matter in the rocks from the fan front, the much more sensitive terrestrial instruments will still be able to search for remnants of prebiotic chemistries and past life, and study Mars’s past habitability in the samples returned to Earth. The hydrated, sulfate-bearing mudstone has the highest potential to preserve organic matter and biosignatures, whereas the carbonate-bearing sandstones can be used to constrain when and for how long Jezero crater contained liquid water. Returned sample science analyses of sulfate, carbonate, clay, phosphate and igneous minerals as well as trace metals and volatiles that are present in the samples acquired at the fan front would provide transformative insights into past habitable environments on Mars, the evolution of its magnetic field, atmosphere and climate and the past and present cycling of atmospheric and crustal water, sulfur and carbon.

The Mars 2020 Perseverance rover has explored fluvio-lacustrine sedimentary rocks within Jezero crater. Prior work showed that igneous crater floor Séítah and Máaz formations have mafic mineralogy with alteration phases that indicate multiple episodes of aqueous alteration. In this work, we extend the analyses of hydration to targets in the Jezero western fan delta, using data from the SHERLOC (Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals) Raman spectrometer. Spectral features, for example, sulfate and hydration peak positions and shapes, vary within, and across the crater floor and western fan. The proportion of targets with hydration associated with sulfates was approximately equal in the crater floor and the western fan. All hydrated targets in the crater floor and upper fan showed bimodal hydration peaks at ∼3,200 and ∼3,400 cm−1. The sulfate symmetric stretch at ∼1,000 cm−1 coupled with a hydration peak at ∼3,400 cm−1 indicate that MgSO4·nH2O (2 < n ≤ 5) is a likely hydration carrier phase in all units, perhaps paired with low-hydration (n ≤ 1) amorphous Mg-sulfates, indicated by the ∼3,200 cm−1 peak. Low-hydration MgSO4·nH2O (n = 1–2) are more prevalent in the fan, and hydrated targets in the fan front only had one peak at ∼3,400 cm−1. While anhydrite co-occurs with hydrated Mg-sulfates in the crater floor and fan front, hydrated Ca-sulfates are observed instead at the top of the upper fan. Collectively, the data imply aqueous deposition of sediments with formation of salts from high ionic strength fluids and subsequent aridity to preserve the observed hydration states., We thank the SHERLOC and Mars 2020 science and engineering teams for the data that enabled this study. This research was supported by funds to the SHERLOC instrument team and the NASA Mars 2020 mission. Y.P. and B.L.E. were supported by a Mars-2020 SHERLOC Co-Investigator grant to B.L.E. S.Si. acknowledges funding from the Swedish National Space Agency (contract 2021-00092 and 137/19). A.D.C. was supported by the Mars 2020 Returned Sample Science Participating Scientist Program (NASA award number 80NSSC20K0237). Support for R.C.W. and S.C. was provided by a SHERLOC Co-Investigator grant to R.C.W. and by NASA contract NNH13ZDA018O. Funding for R.S.J. was provided as an Advanced Curation project run by the NASA Astromaterials Acquisition and Curation Office, Johnson Space Center under the Jacobs, JETSII contract. MPZ was supported by Grant PID2022-140180OB-C21 funded by MCIN/AEI/10.13039/501100011033/FEDER, UE. Research efforts carried out at the Jet Propulsion Laboratory, California Institute of Technology by K.H., S.Sh., K.U. were funded under a contract with the National Aeronautics and Space Administration (80NM0018D0004). L.M. was supported by a Texaco Postdoctoral prize fellowship awarded by the division of Geological and Planetary Sciences of Caltech.

The Mars 2020 Perseverance rover has examined and sampled sulfate-rich clastic rocks from the Hogwallow Flats member at Hawksbill Gap and the Yori Pass member at Cape Nukshak. Both strata are located on the Jezero crater western fan front, are lithologically and stratigraphically similar, and have been assigned to the Shenandoah formation. In situ analyses demonstrate that these are fine-grained sandstones composed of phyllosilicates, hematite, Ca-sulfates, Fe-Mg-sulfates, ferric sulfates, and possibly chloride salts. Sulfate minerals are found both as depositional grains and diagenetic features, including intergranular cement and vein- and vug-cements. Here, we describe the possibility of various sulfate phases to preserve potential biosignatures and the record of paleoenvironmental conditions in fluid and solid inclusions, based on findings from analog sulfate-rich rocks on Earth. The samples collected from these outcrops, Hazeltop and Bearwallow from Hogwallow Flats, and Kukaklek from Yori Pass, should be examined for such potential biosignatures and environmental indicators upon return to Earth.

The NASA Mars 2020 Perseverance rover mission will collect a suite of scientifically compelling samples for return to Earth. On the basis of orbital data, the Mars 2020 science team identified two notional sample caches to study (1) the geology of Jezero crater, collected during the prime mission and (2) the ancient crust outside of Jezero crater, collected during a possible extended mission. Jezero crater geology consists of well-preserved, Early Hesperian to Late Noachian deltaic and lacustrine deposits sourced from a river system that drained Noachian terrain. The crater floor comprises at least two distinct units of sedimentary or volcanic origin whose relationship to the deltaic deposits is presently unclear. Remotely-sensed data reveal signatures of carbonate+olivine and clay minerals within crater floor and crater margin units. Samples from within Jezero that comprise the prime mission notional sample collection thus include: crater floor units; fine- and coarse-grained delta facies, the former with potential to preserve organic matter and/or biosignatures, the latter to possibly constrain the type and timing of sediment deposition; chemical sediments with the potential to preserve biosignatures; a sample of crater rim bedrock; and at least one sample of regolith. The region of southern Nili Planum, directly outside the western rim of Jezero crater, is geologically distinct from Jezero crater and contains diverse Early or even Pre-Noachian lithologies, that may contain records of early planetary differentiation, magnetism, paleoclimate and habitability. The notional sample collection from this region will include: layered and other basement rocks; megabreccias, which may represent blocks of (pre-)Noachian crust; basement-hosted hydrothermal fracture fill; olivine+carbonate rocks that are regionally significant and may be related to units within Jezero crater; and mafic cap unit rocks. The samples described are notional and may change with ongoing surface inve

Before Perseverance, Jezero crater's floor was variably hypothesized to have a lacustrine, lava, volcanic airfall, or aeolian origin. SuperCam observations in the first 286 Mars days on Mars revealed a volcanic and intrusive terrain with compositional and density stratification. The dominant lithology along the traverse is basaltic, with plagioclase enrichment in stratigraphically higher locations. Stratigraphically lower, layered rocks are richer in normative pyroxene. The lowest observed unit has the highest inferred density and is olivine-rich with coarse (1.5 millimeters) euhedral, relatively unweathered grains, suggesting a cumulate origin. This is the first martian cumulate and shows similarities to martian meteorites, which also express olivine disequilibrium. Alteration materials including carbonates, sulfates, perchlorates, hydrated silicates, and iron oxides are pervasive but low in abundance, suggesting relatively brief lacustrine conditions. Orbital observations link the Jezero floor lithology to the broader Nili-Syrtis region, suggesting that density-driven compositional stratification is a regional characteristic.

We present a synthesis of PIXL elemental data and SHERLOC Raman spectra collected on two targets investigated by the Perseverance rover during the first year of its exploration of Jezero Crater, Mars. The Bellegarde target (in the Máaz formation) and Dourbes target (in the Séítah formation) exhibit distinctive mineralogies that are an ideal case study for in situ analysis by SHERLOC and PIXL. Each instrument alone produces valuable data about the chemistry and spatial distribution of mineral phases at the sub-millimeter scale. However, combining data from both instruments provides a more robust interpretation that overcomes the limitations of either instrument, for example: 1) Detection of correlated calcium and sulfur in Bellegarde by PIXL is corroborated by the co-located detection of calcium sulfate by SHERLOC. 2) Detection of sodium and chlorine in Dourbes is consistent with either chloride or oxychlorine salts, but SHERLOC does not detect perchlorate or chlorate. 3) A Raman peak at 1120 cm−1 in Dourbes could be sulfate or pyroxene, but elemental abundances from PIXL at that location are a better match to pyroxene. This study emphasizes the importance of analyzing co-located data from both instruments together, to obtain a more complete picture of sub-millimeter-scale mineralogy measured in situ in Jezero crater, Mars, by the Perseverance rover.

The Committee on Space Research (COSPAR) Sample Safety Assessment Framework (SSAF) has been developed by a COSPAR appointed Working Group. The objective of the sample safety assessment would be to evaluate whether samples returned from Mars could be harmful for Earth's systems (e.g., environment, biosphere, geochemical cycles). During the Working Group's deliberations, it became clear that a comprehensive assessment to predict the effects of introducing life in new environments or ecologies is difficult and practically impossible, even for terrestrial life and certainly more so for unknown extraterrestrial life. To manage expectations, the scope of the SSAF was adjusted to evaluate only whether the presence of martian life can be excluded in samples returned from Mars. If the presence of martian life cannot be excluded, a Hold & Critical Review must be established to evaluate the risk management measures and decide on the next steps. The SSAF starts from a positive hypothesis (there is martian life in the samples), which is complementary to the null-hypothesis (there is no martian life in the samples) typically used for science. Testing the positive hypothesis includes four elements: (1) Bayesian statistics, (2) subsampling strategy, (3) test sequence, and (4) decision criteria. The test sequence capability covers self-replicating and non-self-replicating biology and biologically active molecules. Most of the investigations associated with the SSAF would need to be carried out within biological containment. The SSAF is described in sufficient detail to support planning activities for a Sample Receiving Facility (SRF) and for preparing science announcements, while at the same time acknowledging that further work is required before a detailed Sample Safety Assessment Protocol (SSAP) can be developed. The three major open issues to be addressed to optimize and implement the SSAF are (1) setting a value for the level of assurance to effectively exclude the presen

The NASA Mars 2020 Perseverance rover plans to collect a suite of scientifically compelling samples for return to Earth [1–3]. Strategic planning by the Mars 2020 Science Team has identified notional sample caches within the framework of the geology of Jezero crater and its surroundings [2]. Locations of interest were identified by considering remotely sensed data and traversability constraints [1]. Notional sample caches have been defined for the prime mission within Jezero crater, and an extended mission outside Jezero crater. Prime mission notional cache. Samples of interest include: deltaic, crater floor, crater rim, and regolith materials. Lithologies with high habitability and biosignature preservation potential, such as carbonates and/or chemical deposits, will also be targeted. Such samples would address several questions: What habitable niches were present at Jezero? Are biosignatures and/or prebiotic organics preserved? What was the timing of fluviolacustrine activity? How can Jezero lithologies facilitate absolute crater chronology calibration? What insights do these lithologies provide into Mars climate evolution? What is the origin and alteration history of regional Noachian crust? Extended mission notional cache. Nili Planum is geologically distinct from Jezero, containing diverse Early or Pre-Noachian rocks [4]. Samples of interest include: basement rocks; megabreccias; fractures cross-cutting basement; olivine- and carbonate-bearing rocks; and mafic cap rock. These samples could answer questions 1, 4 and 5 above, together with: What characteristics defined the early planetary evolution and habitability of Mars? How long did the Martian dynamo persist? How do outside-Jezero surfaces, including bedrock and ejecta enable crater chronology calibration? What were the local and regional effects of the Isidis impact? The samples to be collected by Perseverance align with community prio

A central objective of the NASA Mars 2020 Perseverance rover mission is to collect and document a suite of scientifically compelling samples for possible return to Earth by a subsequent mission [1]. Strategic planning by the Mars 2020 Science Team has thus far identified a set of notional sample caches. These arose from integrating the testable hypotheses that could be addressed by Mars 2020 within the framework of the geology of Jezero crater and its surroundings [2], identifying specific locations of high scientific interest by analysis of remotely sensed data, and traversability considerations [1]. Here we describe the general characteristics of the identified notional caches and compare them to the types of samples previously prioritized by the wider Mars science community [3]. While strategic planning will guide and streamline the decision-making processes once the rover lands at Jezero crater, the actual samples collected will depend on the landing location, the traverse taken, and decisions made by the Mars 2020 Science Team.