We report the in situ detection of amorphous hydrated silica in the Bills Bay abrasion patch, located in the eastern portion of the Margin Unit between the rim of Jezero crater and the western delta. Here, hydrated silica co-occurs with olivine, Fe-Mg carbonates, secondary Fe-Mg silicates, and hydrated Mg-sulfate as determined by UV Raman (SHERLOC) and X-ray fluorescence (PIXL) spectrometers onboard the Perseverance rover. Almost pure hydrated silica fills the intergranular space between olivine and carbonate-bearing domains. We performed Raman analysis of terrestrial opals with various crystallinities including opal-AN, AG, CT, and C. We found that the Si-O symmetric stretching Raman band at similar to 800 cm-1 is sensitive to opal crystallinity, yet insensitive to ambient temperature (at similar to 77-293 K) and silica hydration. We identified the crystal structure of the Bills Bay Hydrated Silica (BBHS) as opal-A. Furthermore, we developed a Raman methodology to quantify opal-A hydration. We found that the total amount of hydration in the BBHS phases was 1.7 +/- 0.2 wt. %. Most of this hydration, 1.5 +/- 0.2 wt. %, reflects the presence of silanol groups. Our analysis revealed that the Raman spectrum of BBHS closely resembles that of opal-A that has lost most of its molecular water. The composition and textures of the Bills Bay abrasion indicate that BBHS is derived from olivine carbonation. Opal-A is the only silica polymorph identified in the SHERLOC data. We hypothesized that silica precipitation occurred, either during the late stages of a major carbonation event or during a brief, subsequent aqueous alteration event unrelated to carbonation.

Two lithologic units have been mapped and studied on the floor of Jezero crater, Mars: Seitah, which consists of layered olivine-rich cumulates, and Maaz, a series of basaltic to trachyandesitic lava flows. While Seitah and Maaz are close in proximity and stratigraphy, their potential geologic and petrological relationship remains unclear. Here, we present observations from the Planetary Instrument for X-ray Lithochemistry (PIXL) of an olivine cumulate outcrop-Issole-within the Seitah formation. The rock analyzed at Issole is a wehrlite dominated by olivine (Fo46 +/- 1) and interstitial phases, including augite, late olivine, spinel, and feldspathic material. Compared to other outcrops from Seitah, Issole is more iron-rich and records substantial alteration processes. We combine mineral chemistry, textural analysis, and thermodynamic modeling to show that Seitah olivines crystallized from a basaltic parent magma, compositionally similar to the most primitive basalts in the Maaz formation. Crystallization of this parent magma produces residual melts that follow the magmatic differentiation trend defined by Maaz basalts. Moreover, the mineral assemblages predicted by our model during crystallization are consistent with observations from Seitah rocks but show some differences in composition. These differences can be reconciled by considering post-cumulus processes that modified the mineral assemblage in Seitah, including Fe-Mg exchange between olivine and pyroxene. Our results indicate that Seitah and Maaz are likely genetically related, and their formation involved both accumulation of crystals at depth and eruption of lavas. The emplacement of Seitah likely occurred as a near-surface, sill-like igneous intrusion into previously erupted Maaz lava flows. The relationship between Seitah and Maaz demonstrates that magmatic differentiation processes, similar to those responsible for the formation of some Martian meteorites, can produce highly diverse lithologies and mineral textures in the Martian crust.

As both a source of atmospheric H2 and a sink for liquid water, the serpentinization of olivine-bearing rocks is widely thought to have influenced the long-term evolution of the early martian atmosphere and hydrosphere. However, the mechanisms, timing, and global importance of this process are unconstrained, in part because the remnants of ancient serpentinizing systems have not been examined in situ. New geochemical and mineralogical data from multiple instruments aboard the Mars 2020 Perseverance rover record serpentinization and associated H2 production in ancient igneous rocks of the Máaz formation, exposed on the Jezero crater floor. These data, combined with petrogenetic constraints, indicate that serpentinization may have been driven by devolatilization of magmatic H2O, highlighting a potential link between H2 production and the style and tempo of magmatism within the ancient martian crust.

The "Planetary Instrument for X-ray Lithochemistry" (PIXL) X-ray spectrometer conducts in situ geochemical analyses of martian rocks and regolith interrogated by the Mars 2020 rover, Perseverance. In addition to quantifying primary rock-forming elements, PIXL can quantify trace elements that in turn can provide additional constraints on the geologic history of Mars. Accurate quantifications of trace elements can require additional analytical techniques to mitigate experimental, background, and crystalline effects within PIXL spectra. In this study, we focus on reducing the impact of these effects and investigate the potential presence of rare earth elements (REEs). The study specifically investigates cerium given its typical relative abundance in many geologic materials compared to other REEs and its potential to mimic fluorescence features produced by organics under deep UV excitation. A detailed analysis of PIXL targets analyzed through the first 887 martian days of the Perseverance mission did not produce any conclusive Ce detections. Phosphorus-enriched materials analyzed by PIXL are estimated to contain sub-675 ppm Ce and sulfate-enriched materials sub-450 ppm Ce. The method presented can help constrain limits on the abundance of additional trace elements of interest that also face a similar analytical burden. PIXL's potential to assess REE abundances, outside of yttrium, is limited for expected concentrations in surface materials. Determining most REE concentrations in materials interrogated by Perseverance will therefore likely require terrestrial analyses.

Hydrovolcanic tuffs formed through magma-water interactions in lacustrine or littoral environments have been found to contain micro-textural elements, including microtubules and granular textures, within glass fragments. The morphological and associated geochemical characteristics of these micro-textures show evidence that they are formed by microbially-mediated dissolution of basaltic glass in an aqueous setting, establishing them as likely biosignatures. Further, the terrestrial setting of these samples and their basaltic composition is analogous to environmental conditions expected to have existed throughout the history of Mars. We present the first report of putative biogenic alteration textures in basaltic glass from the PliocenePleistocene hydrovolcanoes of the Western Snake River Plain volcanic field, Idaho, USA. Samples collected from tuff cones, tuff rings, and maars which erupted into paleo-Lake Idaho contain microtubules and granular alteration comparable in morphology (diameter, length, curvature, internal contents, branching) and size distribution to those recorded in other terrestrial hydrovolcanic fields. Petrographic relationships between fresh glass containing microtubules, glass that has been fully altered to palagonite, and mineral-filled vesicles and fractures indicate that tubules formed under low-temperature aqueous alteration conditions during the palagonitization process and ongoing alteration mineral precipitation. Alteration minerals including calcite and zeolites show that these fluids likely did not exceed 80 degrees C in temperature. Major element mapping of vitric clasts in hydrovolcanic tuff revealed most elements are depleted or neutral within microtubule interiors relative to the surrounding glass, although iron and titanium were notably enriched in many tubules. We found little distinction in major element composition between microtexture-bearing and non-microtexture-bearing glasses, with the exception of some microtexture-bearing samples being depleted in Na2O compared to the non-microtexturebearing glass. Western Snake River Plain is relevant to Mars in terms of geochemical, mineralogical, and environmental context; and this setting is capable of preserving putative biosignatures. This work has implications for furthering our understanding of how these microtextures are formed and preserved, and for potential astrobiological investigation of Mars.

Planetary rovers can use onboard data analysis to adapt their measurement plan on the fly, improving the science value of data collected between commands from Earth. This paper describes the implementation of an adaptive sampling algorithm used by PIXL, the X-ray fluorescence spectrometer of the Mars 2020 Perseverance rover. PIXL is deployed using the rover arm to measure X-ray spectra of rocks with a scan density of several thousand points over an area of typically 5 x 7 mm. The adaptive sampling algorithm is programmed to recognize points of interest and to increase the signal-to-noise ratio at those locations by performing longer integrations. Two approaches are used to formulate the sampling rules based on past quantification data: 1) Expressions that isolate particular regions within a ternary compositional diagram, and 2) Machine learning rules that threshold for a high weight percent of particular compounds. The design of the rulesets are outlined and the performance of the algorithm is quantified using measurements from the surface of Mars. To our knowledge, PIXL's adaptive sampling represents the first autonomous decision-making based on real-time compositional analysis by a spacecraft on the surface of another planet.

The Mars 2020 rover, Perseverance , encountered a range of basaltic igneous rocks on the floor of Jezero crater, two of which are olivine cumulates, formed by accumulation of olivine crystals from basaltic magma. These olivine cumulates lie in a geomorphically distinct region, named Séítah, on the Jezero crater floor. To understand the origin of the olivine cumulates and their relationship with the adjacent basalts of the Máaz formation, we calculated the composition of the parent magma of one of the olivine cumulates, named Brac, based on chemical analyses and mineralogic interpretations from the Planetary Instrument for X‐ray Lithochemistry (PIXL) instrument. Acceptable Brac/Dourbes parent magmas are olivine tholeiite basalts with SiO 2 ∼ 45%, MgO ∼ 8%, FeO Tot ∼ 27%, Al 2 O 3 ∼ 6%, and total alkali oxides of ∼2.8% weight. These compositions are similar to one of the Máaz basalts, the rock Rimplas, which is stratigraphically close to Séítah, but chemically distinct from other Máaz basalts. Rimplas could (within uncertainty) be a sample of the Brac parent magma, but it is more likely that Rimplas and Brac had a common (or similar) parent magma. Geochemical similarities between Rimplas and the other Máaz basalts thus suggest that Brac (and other olivine‐rich rocks of Séítah) and the Máaz basalts could be geochemically related; they could have been cogenetic and possibly contemporaneous, or could have been derived (at different times) from similar or related mantle source(s).

The Jezero crater floor features a suite of related, iron-rich lavas that were examined and sampled by the Mars 2020 rover Perseverance, and whose textures, minerals, and compositions were characterized by the Planetary Instrument for X-ray Lithochemistry (PIXL). This suite, known as the Máaz formation (fm), includes dark-toned basaltic/trachy-basaltic rocks with intergrown pyroxene, plagioclase feldspar, and altered olivine and overlying trachy-andesitic lava with reversely zoned plagioclase phenocrysts in a K-rich groundmass. Feldspar thermal disequilibrium textures indicate that they were carried from their crustal staging area. Bulk and mafic minerals have very high FeO and low MgO to FeO total ratios, which are partially reproduced by thermodynamic models involving high-degree fractional crystallization of a gabbroic assemblage and possibly also assimilation of iron-rich basement. Together, these in situ constraints on petrogenesis provide a uniquely detailed record of intracrustal processes beneath Jezero crater during a time period not represented by Mars samples to date.

The Planetary Instrument for X-ray Lithochemistry (PIXL) onboard the Perseverance rover has characterized the composition of Martian regolith at a scale of hundreds of microns using micro-focus X-ray fluorescence spectroscopy. PIXL data reveal a diverse population of regolith grains with distinct spectral, chemical, and crystallographic properties, through which we identified the mineralogy of individual regolith components. Olivine, phyllosilicate, carbonate-bearing phases, Cr-Ti-spinel, plagioclase, and Fe-sulfate are all inferred from the data, and potential local and regional bedrock sources are proposed for each. PIXL also inspected dust and soil components, which were found to be geochemically similar to analogous components characterized elsewhere by preceding missions. Unlike other sites, regolith on the western fan front of Jezero crater contains fewer sulfates, but is highly enriched in Cl (up to 2.0 +/- 0.5 wt. %), which likely includes chlorides, chlorates, and/or perchlorates. PIXL also finds evidence of hydration in the regolith, potentially carried by salts, as interstitial water, and/or in adsorbed phases. PIXL's observations of diverse amorphous and crystalline components, multiple styles of aqueous alteration, and enrichments of brine-forming salts provide exciting new justification for the return of a Martian regolith sample to Earth for further study.

A major objective of the Mars 2020 mission is to sample rocks in Jezero crater that may preserve organic matter for later return to Earth. Using an ultraviolet Raman and luminescence spectrometer, the Perseverance rover detected luminescence signals with maximal intensities at 330 to 350 nanometers and 270 to 290 nanometers that were initially reported as consistent with organics. Here, we test the alternative hypothesis that the 330- to 350-nanometer and 270- to 290-nanometer luminescence signals trace Ce3+ in phosphate and silicate defects, respectively. By comparing the distributions of luminescence signals with the rover detections of x-ray fluorescence from P2O5 and Si-bearing materials, we show that, while an organic origin is not excluded, the observed luminescence can be explained by purely inorganic materials. These findings highlight the importance of eventual laboratory analyses to detect and characterize organic compounds in the returned samples.

Phosphorus is an essential component for life, and in-situ identification of phosphate minerals that formed in aqueous conditions directly contributes toward one of the main goals of the Mars 2020 Perseverance rover: to seek signs of ancient habitable environments. In Jezero crater, proximity science analyses within a conglomerate outcrop, “Onahu” demonstrate the presence of rare Fe3+-bearing phosphate minerals (likely beraunite, metavivianite, ferrolaueite, and/or santabarbaraite) embedded in a carbonate-rich matrix. While Fe-phosphates have been previously inferred on Mars, this work presents the most definitive in-situ identification of martian Fe-phosphate minerals to date, using textural, chemical, spectral, and diffraction analyses of discrete green-blue grains. The Fe-phosphate minerals’ textural context along with comparisons to Earth analogs suggest they likely formed after oxidation of the Fe2+-phosphate vivianite — the most common Fe-phosphate on Earth, often associated with microbial activity and organics. The Fe3+-phosphate assemblage after vivianite, and the presence of two distinct matrix domains in Onahu indicate that the conglomerate and corresponding sample collected by Perseverance (Otis_Peak) preserve a record of evolving habitable paleoenvironmental conditions on Mars. Once returned to Earth, analysis of the Fe-phosphates in the Otis_Peak sample will provide new insights into ancient habitable environments, and, if analogous to terrestrial vivianite-rich environments, potential links with microbial activity.

This paper reviews the phosphate phases in meteorites and those measured by landed spacecraft, what they reveal about past igneous and aqueous conditions on Mars, and important implications for potential prebiotic chemistry, past habitability, and potential biosignatures that could be detected in samples returned from Mars. A review of the 378 martian meteorites as of 2023 indicate that of the two most common phosphate minerals in Mars meteorites, merrillite and apatites, the apatite composition is largely F- and Cl-rich, with shergottites containing more OH. The phosphate concentrations examined across multiple missions show a relatively narrow range of phosphate, with higher concentrations observed in the Mount Sharp Group in Gale crater and Wishstone at Gusev crater and lower concentrations observed at Jezero crater floor and Jezero fan. Possible secondary phosphates detected on Mars, including Fe phosphates at Jezero crater and Gusev crater and Ca- and Al-bearing secondary phosphates, temperatures of formation of secondary phases and their dissolution rates and solubilities are reviewed and summarized. Despite this wealth of information about phosphates on Mars, due to their fine scale and relatively low concentrations, Mars Sample Return is needed to better understand phosphate and its implications for the igneous, aqueous, and astrobiological history of Mars.

Although Mars today does not have a core dynamo, magnetizations in the Martian crust and meteorites suggest a magnetic field was present prior to 3.7 billion years (Ga) ago. However, the lack of ancient, oriented Martian bedrock samples available on Earth has prevented accurate estimates of the dynamo’s intensity, lifetime, and direction. Constraining the nature and lifetime of the dynamo are vital to understanding the evolution of the Martian interior and the potential habitability of the planet. The Perseverance rover, which is exploring Jezero crater, is providing an unprecedented opportunity to address this gap by acquiring absolutely oriented bedrock samples with estimated ages from ~2.3 to > 4.1 Ga. As a first step in establishing whether these samples could contain records of Martian paleomagnetism, it is important to determine their ferromagnetic mineralogy, the grain sizes of the phases, and the form of any natural remanent magnetization. Here, we synthesize data from various Perseverance instruments to achieve those goals and discuss the implications for future laboratory paleomagnetic analyses. Using the rover’s instrument payload, we find that cored samples likely contain iron oxides enriched in Cr and Ti. The relative proportions of Fe, Ti, and Cr indicate that the phases may be titanomagnetite or Fe-Ti-Cr spinels that are ferromagnetic at room temperature, but we cannot rule out the presence of non-ferromagnetic ulvöspinel, ilmenite, and chromite due to signal mixing. Importantly, the inferred abundance of iron oxides in the samples suggests that even <1 mm-sized samples will be easily measurable by present-day magnetometers.

Basaltic hydrovolcanic environments on Earth produce abundant glass (sideromelane), which readily alters and acts as an important source of chemical energy for lithotrophic microorganisms; as such, these sites are significant for potential origins- of- life and early life research. Similar environments were identified on Mars and should be considered potential targets for astrobiological investigation. Pleistocene to recent phreatomagmatic and glaciovolcanic structures on Earth include tuff cones, tuff rings, maars, tuyas, and tindars. Such hydrovolcanic deposits contain abundant glass that is variably hydrothermally altered, and some areas contain published evidence of putative microbial habitation and microbially mediated alteration, including microtubules and granular alteration. We analyzed the literature on terrestrial hydrovolcanic environments and created a global database of 45 volcanic fields on Earth with compositions, alteration histories, and structures relevant to Mars. These sites have geochemistry, mineralogy, and syn- and post- eruptive environmental conditions that make them suitable targets for Mars- analogue astrobiological research. Relevant alteration products include palagonite, zeolites, clays, and calcite. Seven of these sites have evidence of microbially mediated alteration, which could be considered a useful biosignature in a Mars- analogue context. The sites are Wells Gray- Clearwater Volcanic Field, Canada; Fort Rock Volcanic Field, Western Snake River Plain Volcanic Field, and Upsal Hogback, USA; Reykjanes Volcanic Field and Western Volcanic Zone, Iceland; and Carapace Nunatak, Antarctica. Based on the properties of these already confirmed sites, along with comparing the remaining 38 Earth volcanic fields to volcanic rocks on Mars, we recommend 11 volcanic fields in particular from our database for future investigations: Auckland and South Auckland volcanic fields, New Zealand; O'ahu, Black Rock Desert, and Black Point, USA; Tuya Volcanic Field, Canada; Karapinar Volcanic Field, Turkiye; Vestmannaeyjar Archipelago, Iceland; Llancanelo Volcanic Field, Argentina; Sao Miguel Volcanic Field, Azores; and Icefall Nunatak, Antarctica. We recommend reviewing palagonitized tuff samples from these sites for evidence of microbial alteration, in addition to performing geochemical and mineralogical analyses to constrain their magmatic and alteration properties. By studying the rock record of hydrovolcanic environments on Earth to infer habitability and biological alteration, we contribute to establishing the conditions favorable for the origination, survival, and proliferation of life in a Mars- relevant setting.

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.

Global magmatic trends inferred from gamma-ray, visible/near-infrared, and thermal infrared spectrometers on Mars-orbiting spacecraft have been used to constrain planetary petrogenetic processes and global thermal evolution models. Inferred magmatic trends include temporal variations in the relative proportions of low-Ca and high-Ca pyroxenes, and in the abundances of potassium (and total alkalis), silica, FeO* (total iron expressed as FeO), and thorium. These patterns are evaluated for consistency with the compositions of surface igneous rocks of different ages analyzed by Mars rovers and of martian meteorites. Trends of decreasing low-Ca pyroxene/total pyroxene ratios and of decreasing potassium (and total alkalis), with time are generally supported by surface rock analyses. However, significant differences in the GRS-measured silica in Amazonian volcanoes and in martian meteorites of equivalent age result from contamination by silica-rich dust and are problematic for a silica trend. Comparison of FeO* in Noachian and Amazonian surface data shows no decrease. An inferred temporal trend in thorium is in conflict with the complex enrichment and depletion patterns of incompatible trace elements in martian meteorites of various ages. A dearth of analyses of Hesperian-age surface rocks precludes a firm evaluation of inferred Noachian-Hesperian trends and Hesperian-Amazonian trends, but abundant Noachian rocks and a few Hesperian rocks at rover sites, and Amazonian martian meteorites, collectively representing at least 16 surface locations, afford useful comparisons with orbital remote-sensing data.