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For the first time on Mars, the crystalline magnesium‐sulfate mineral starkeyite (MgSO4‧4H2O) was definitively identified using the CheMin X‐ray diffraction instrument at Gale crater. At the Canaima drill site, starkeyite along with amorphous MgSO4‧nH2O are among the “polyhydrated Mg‐sulfates” interpreted in orbital reflectance spectra. Mg‐sulfates are good climate indicators as they are very responsive to changes in temperature and relative humidity. We hypothesize that, through evaporation, Mg‐sulfates formed at the end of brine evolution when ion concentrations became saturated and precipitated on the surface or near sub‐surface as either epsomite or meridianiite. These minerals were subsequently dehydrated later to starkeyite and amorphous MgSO4‧nH2O in response to a drier Mars. At Canaima, starkeyite is stable and would form during the warmer Mars summers. Due to very slow kinetics at the low Mars winter temperatures, starkeyite and amorphous MgSO4‧nH2O would be resistant to recrystallize to more hydrous forms and thus likely persist year‐round. During the course of analyses, starkeyite transforms into amorphous MgSO4‧nH2O inside the rover body due to the elevated temperature and greatly reduced relative humidity compared to the martian surface at the Canaima drill site. It is possible that crystalline sulfate minerals existed in earlier samples measured by CheMin but altered inside the rover before they could be analyzed. Starkeyite is most likely prevalent in the subsurface, whereas both starkeyite and amorphous MgSO4‧nH2O are likely present on the surface as starkeyite could partially transform into amorphous MgSO4‧nH2O due to direct solar heating. For the first time on Mars, starkeyite (MgSO4‧4H2O), one of the many possible naturally occurring Mg‐sulfate minerals, has been identified using instruments that determine the mineralogy and chemistry of samples on the Curiosityrover in Gale crater. Minerals form in response to conditions they are subjected to and can be used to infer temperature, pressure, water availability, and other factors that will influence their formation. As such, their presence can be used to help define current and past climate conditions on Mars. When Mg‐sulfate minerals first precipitate from brine that is evaporating on the surface, they form more hydrous varieties. In response to drier conditions, they will recrystallize to Mg‐sulfate forms with less water in them. When Mg‐sulfate minerals are desiccated under extremely dry conditions, they will lose their crystal structure and form an amorphous phase. This occurred inside the rover body during the analysis of the Canaima sample. It is likely that earlier samples may also have contained crystalline Mg‐sulfates but altered to an amorphous phase while in the rover body before analyses could take place. Mg‐sulfate in the subsurface is likely starkeyite but could partially transform on the surface to amorphous MgSO4‧nH2O due to direct solar heating. For the first time on Mars, starkeyite (MgSO4‧4H2O) was positively identifiedStarkeyite along with amorphous MgSO4‧nH2O are the “polyhydrated Mg‐sulfates” interpreted in orbital reflectance spectraMg‐sulfate mineralogy serves as an indicator of transition to a drier climate and helps outline the climatic and depositional changes on Mars For the first time on Mars, starkeyite (MgSO4‧4H2O) was positively identified Starkeyite along with amorphous MgSO4‧nH2O are the “polyhydrated Mg‐sulfates” interpreted in orbital reflectance spectra Mg‐sulfate mineralogy serves as an indicator of transition to a drier climate and helps outline the climatic and depositional changes on Mars

Martian soils are critically important for understanding the history of Mars, past potentially habitable environments, returned samples, and future human exploration. This study examines soil crusts on the floor of Jezero crater encountered during initial phases of the Mars 2020 mission. Soil surface crusts have been observed on Mars at other locations, starting with the two Viking Lander missions. Rover observations show that soil crusts are also common across the floor of Jezero crater, revealed in 45 of 101 locations where rover wheels disturbed the soil surface, two out of seven helicopter flights that crossed the wheel tracks, and four of eight abrasion/drilling sites. Most soils measured by the SuperCam laser‐induced breakdown spectroscopy (LIBS) instrument show high hydrogen content at the surface, and fine‐grained soils also show a visible/near infrared (VISIR) 1.9 μm H2O absorption feature. The Planetary Instrument for X‐ray Lithochemistry (PIXL) and SuperCam observations suggest the presence of salts at the surface of rocks and soils. The correlation of S and Cl contents with H contents in SuperCam LIBS measurements suggests that the salts present are likely hydrated. On the “Naltsos” target, magnesium and sulfur are correlated in PIXL measurements, and Mg is tightly correlated with H at the SuperCam points, suggesting hydrated Mg‐sulfates. Mars Environmental Dynamics Analyzer (MEDA) observations indicate possible frost events and potential changes in the hydration of Mg‐sulfate salts. Jezero crater soil crusts may therefore form by salts that are hydrated by changes in relative humidity and frost events, cementing the soil surface together. Martian soils are important for understanding the history of Mars as well as future sample return and human exploration. Soil crusts in Jezero crater, which are also broadly found across Mars, can be observed when they are disturbed, such as by rover wheels or coring/abrasion activities. Jezero crater soil crusts are examined using images from the Perseverance and Ingenuity cameras, as well as using data from the SuperCam, PIXL, Mastcam‐Z, and MEDA instruments. Soil crusts are common in Jezero crater and show characteristics including hydration at the surface and the presence of salts that might contain water. MEDA instrument measurements indicate that changes in the hydration state of salts may result during conditions measured at Jezero crater. Jezero crater soil crusts may therefore form by salts that are present on the surface that can add or lose water during changes in relative atmospheric humidity and frost events. These changes in the amount of water present in the salts may result in soil surfaces that are cemented together, forming the crusts observed at Jezero crater. A better understanding of Mars soil crusts will help in the understanding of samples returned to Earth from Mars, as well as future human exploration. Soil crusts are prevalent across the Jezero crater floorSoil surfaces are largely hydratedSoil crusts likely contain salts and may form during changes in atmospheric relative humidity at the surface Soil crusts are prevalent across the Jezero crater floor Soil surfaces are largely hydrated Soil crusts likely contain salts and may form during changes in atmospheric relative humidity at the surface

The first samples collected by the Mars 2020 mission represent units exposed on the Jezero Crater floor, from the potentially oldest Séítah formation outcrops to the potentially youngest rocks of the heavily cratered Máaz formation. Surface investigations reveal landscape‐to‐microscopic textural, mineralogical, and geochemical evidence for igneous lithologies, some possibly emplaced as lava flows. The samples contain major rock‐forming minerals such as pyroxene, olivine, and feldspar, accessory minerals including oxides and phosphates, and evidence for various degrees of aqueous activity in the form of water‐soluble salt, carbonate, sulfate, iron oxide, and iron silicate minerals. Following sample return, the compositions and ages of these variably altered igneous rocks are expected to reveal the geophysical and geochemical nature of the planet's interior at the time of emplacement, characterize martian magmatism, and place timing constraints on geologic processes, both in Jezero Crater and more widely on Mars. Petrographic observations and geochemical analyses, coupled with geochronology of secondary minerals, can also reveal the timing of aqueous activity as well as constrain the chemical and physical conditions of the environments in which these minerals precipitated, and the nature and composition of organic compounds preserved in association with these phases. Returned samples from these units will help constrain the crater chronology of Mars and the global evolution of the planet's interior, for understanding the processes that formed Jezero Crater floor units, and for constraining the style and duration of aqueous activity in Jezero Crater, past habitability, and cycling of organic elements in Jezero Crater. Here we provide a narrative of sample collection and associated in situ rover observations for the rocks collected by the Perseverance rover to provide a preliminary description of the first samples of the Mars 2020 mission. These rocks collected in Jezero Crater represent the first samples from Mars with a known geologic context, the first collected with the potential to be returned to Earth for laboratory analysis, and the first cores from rock outcrops on another planet. Remote and proximal analyses indicate that all crater floor outcrops investigated are igneous in origin. Laboratory analyses of these rocks will be useful to study the planet's interior at the time of emplacement, characterize martian magmatism, and place timing constraints on geologic processes, both in Jezero Crater and more widely on Mars. All collected rocks have interacted with water and contain secondary geochemical and mineralogical evidence that can be used to understand aqueous environments in the crater and the potential conditions of habitability for ancient life on Mars. Nine samples, consisting of four pairs of rock cores and a tube of atmospheric gas, were collected from the floor of Jezero Crater, MarsIn situ observations of crater floor outcrops, used as proxies for the samples, reveal aqueously altered igneous lithologiesPerseverance will leave one sample from each pair at the Three Forks depot and retain a second to be cached with future samples Nine samples, consisting of four pairs of rock cores and a tube of atmospheric gas, were collected from the floor of Jezero Crater, Mars In situ observations of crater floor outcrops, used as proxies for the samples, reveal aqueously altered igneous lithologies Perseverance will leave one sample from each pair at the Three Forks depot and retain a second to be cached with future samples

If the chemistry essential to life was present in water-containing environments on Mars, the processes that led to life on Earth may have also occurred on the red planet. Phosphate is one of the chemical nutrients thought to be essential for life and is also considered critical to reactions that may have led to life on Earth. However, low prebiotic availability of phosphate may have been a complicating factor in terrestrial abiogenesis, suggesting that a similar hurdle may have confronted the development of life on Mars. Phosphate available for biological reactions can be introduced into aqueous environments through dissolution of primary phosphate minerals during water–rock interactions, but little is known about the dissolution of the dominant phosphate minerals found in martian meteorites and presumably on Mars. Here we present dissolution rates, phosphate release rates and solubilities of phosphate minerals found in martian rocks as determined from laboratory measurements. Our experimental findings predict phosphate release rates during water–rock interactions on Mars that are as much as 45 times higher than on Earth and phosphate concentrations of early wet martian environments more than twice those of Earth. We suggest that available phosphate may have mitigated one of the hurdles to abiogenesis on Mars.