Sulfate minerals on Mars have garnered attention due to their potential to unravel the planet's geological past and serve as repositories of biosignatures. Among these, hydrated sulfate minerals, including mirabilite (Na2SO4 & centerdot;10H2O), present unique challenges due to their instability under most Earth conditions. Water, air vapor, bacteria, archaea, algae, fungi, diatoms, protozoa, and organic compounds such as beta-carotene have been identified in mirabilite, highlighting its potential to trap biosignatures. This study investigates the preservation of such biosignatures in mirabilite from the Great Salt Lake in Utah, U.S.A., highlighting the challenge of rapid dehydration in hydrated sulfate minerals during laboratory analyses. By employing non-destructive preparation techniques and commonly available laboratory supplies, the stability of mirabilite was extended, enabling the application of advanced methods, including transmitted light and UV-vis light microscopy and laser Raman spectroscopy. Notably, mirabilite chips sealed within a sample chamber, submerged in mineral oil, or sealed in plastic wrap delayed dehydration to thenardite (Na2SO4), resulting in the best preservation of the original mirabilite. Raman spectroscopy of organic material within primary fluid inclusions revealed several distinct spectral patterns, including signatures consistent with beta-carotene, indicating the preservation of organic compounds and biological pigments in the hydrated mineral matrix. These findings have implications for future biosignature studies of mirabilite and other hydrated minerals on Earth, as well as Mars return samples and other extraterrestrial samples, where maintaining the integrity of hydrated minerals is key to detecting environmental conditions and potential signs of life.

Gypsum and its many forms are common in modern sediment and the ancient rock record. In particular, Permo-Triassic bedded gypsum and associated red beds from Pangea represent continental environments that persisted during a time of extraordinary climate change and mass extinction. Despite this significance, there is a paucity of work investigating textures of ancient gypsum, and in particular, diagenetic gypsum textures. Here, we describe gypsum textures from the Permian Cloud Chief Formation of the Palo Duro Basin in Texas, midcontinental United States. We interpret the Cloud Chief Formation gypsum to represent continental saline lakes and mudflats, based on their depositional textures and association with red-bed protosols. Additionally, we document, for the first time, the diagenetic features of the Cloud Chief Formation. Diagenesis is extensive, complex, and remarkably heterogeneous, with distinct textures of gypsum interlocking-crystal mosaics varying at a cm-scale and a mm-scale. The diagenetic history of the Cloud Chief Formation gypsum includes partial replacement by dolomite and subsequent gypsum replacement of the replacement dolomite rhombs, a process we name "gypsum dedolomitization." This work advances our understanding of the depositional and diagenetic histories of ancient gypsum and expands the known geographic extent of Permo-Triassic continental saline-lake systems.

Studies of microorganisms in extreme Mars-analog environments have generally overlooked fungi. Here, we document fungi in lake waters, slime, and halite of the acid-saline Lakes Magic and Gneiss in Western Australia with pH 1.4-3.5 and 7-32% total dissolved solids (TDS). Both extremotolerant fungi, including ascomycete Parengyodontium torokii, and relatively common fungi (mesophilic), including Penicillium breviocompactum and Trametes pubescens, were present. Our discovery of P. torokii in halite is among the first known fungal examples of such preservation, and we propose that it has the biological traits of a generalist species. Nine strains of the dominant P. torokii fungi were tested for growth on diverse salts. The presence of mesophilic fungal saprotrophs in these lakes, along with extremophilic fungi, algae, bacteria, and archaea, suggests transport of the former into indigenous lake populations. This reveals a distinction between habitability and preservation potential; not all biosignatures in lake waters or their halite represent organisms that were active in situ. Our results suggest that searches for biosignatures in extreme waters and salt minerals on Earth and Mars should include the possibility of fungi. Additionally, interpretations of microbial communities in both modern brines and the rock record should consider the likelihood of mixed indigenous and transported taxa.

Permian bedded halite of the Nippewalla Group of Kansas and the Opeche Shale of North Dakota, USA, formed in extremely acid saline lakes. However, a full understanding about the compositions of those brines is not known. Micron-scale crystals within primary fluid inclusions in halite give clues about the geochemistry of past lake waters. Here, we use petrographic, microthermometric, and Raman spectral observations of crystals in chevron and cumulate halite crystals from two subsurface cores to make interpretations about past Pangean lake water chemistry. Our results show that (1) entrapped crystals are situated within primary fluid inclusions and as solid inclusions along growth bands in host depositional halite; (2) the presence of entrapped crystals is heterogeneous amongst fluid inclusions of single growth bands; (3) crystals in fluid inclusions do not change size upon heating or cooling; (4) at least nine different sulfate minerals were identified, including Ca-sulfates, Sr-sulfate, Mg-sulfates, Fe-sulfates, and Al-sulfates; and (5) rare carbonate grains partially coated with hematite were observed in some inclusions. We conclude that these crystals precipitated, alongside halite, in complex sulfate-rich, metal-rich acid saline lake waters. Rare hematite-coated carbonate grains likely were blown into the lakes by winds. We propose that these petrographic and spectroscopic methods can be used to refine past water compositional data from other bedded evaporites. In addition, any salt minerals returned in samples from Mars should be evaluated for accidental daughter crystals to reach a better understanding of past Martian water compositions and habitability.

Late-stage Ca-sulfate-filled fractures are common on Mars. Notably, the Shenandoah formation in the western edge of Jezero crater preserves a variety of Ca-sulfate minerals in the fine-grained siliciclastic rocks explored by the Perseverance rover. However, the depositional environment and timing of the formation of these sulfates are unknown. To address this outstanding problem, we developed a technique to map the crystal orientations of these sulfates in situ at two stratigraphically similar locations in the Shenandoah formation, allowing us to constrain the burial depth and paleoenvironment at the time of their precipitation. Our crystal orientation mapping results and outcrop-scale fracture analyses reveal two different generations of Ca-sulfates: one likely precipitated in the shallow subsurface and a second one that formed at a burial depth below 80 meters. These results indicate that two studied locations capture two different times and distinct chemical conditions in the sedimentary history of the Shenandoah formation, providing multiple opportunities to evaluate surface and subsurface habitability.

The Perseverance rover has sampled mm-size lithic fragments containing olivine likely from at least two source regions from the surface of an inactive megaripple surface, and fine-grained material from the surface and to a depth of similar to 4-6 cm. Some of the mm-size grains lack a coherent diffraction pattern measured by PIXL, consistent with the presence of poorly ordered secondary phases that have been altered. Analysis of these materials on Earth will allow examination of materials that have experienced aqueous, potentially habitable environments that could contain biosignatures. Fluorescence of three different patterns was detected, consistent with inorganic emissions from silica defects or rare earth elements in certain mineral phases, although organic origin cannot be excluded. Analysis of Autofocus Context Imager and Wide Angle Topographic Sensor for Operations and eNgineering images of the subsurface material and MEDA thermal inertia measurements indicate average grain sizes of similar to 125 and similar to 150 mu m, respectively, for the bulk material within the megaripple. The fine-grained material in the sampling location indicates chemical compositions similar to previously proposed global components as well as airfall dust. In situ and associated atmospheric measurements provide evidence of recent processes likely including water vapor in soil crust formation. The sampled material will therefore help elucidate the formation of Martian soils; current surface-atmosphere interactions; the composition, shape, and size distribution of dust grains valuable for studies of past and present Martian climate and for assessing potential health and other risks to human missions; and ancient, aqueously altered environments that could have been habitable, and, if Mars contained life, possibly contain biosignatures.

The search for organic molecules on Mars is central to understanding the planet's past habitability and potential for ancient life. Although organic molecules have previously been detected on Mars, their nature, origin and preservation mechanisms remain debated. On the floor of the Jezero crater-an ancient delta-lake system on Mars-the Perseverance rover detected Raman features that may be due to organic compounds spatially associated with sulfates, although their origin is uncertain. Here we report the detection of similar Raman features in the Jezero fan top and attribute them to polycyclic aromatic hydrocarbons based on comparisons with laboratory data. We propose that these polycyclic aromatic hydrocarbons may have formed through endogenous igneous processes and were subsequently preserved by sulfate precipitation. These findings align with previous studies on Martian meteorites and at Gale crater, underscoring the role of sulfates in preserving organic matter on Mars. Returning these samples to Earth would be key to assess their astrobiological relevance.

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.

If you could time travel to the central U.S. 300 million years ago, you would find yourself at the equator of the supercontinent Pangea. At first you might enjoy a warm climate, surrounded by seas filled with life. But, after some millions of years, the seas would vanish as the climate turned increasingly hot, dry, and hostile. Billowing dust would engulf you, and nearly all life on Earth would vanish in an event called the Great Dying. How do we know? Geoscientists reconstruct past landscapes and climates by drilling into ancient sediments—tiny grains of sand and silt. These tiny particles tell us how fast the mountains rose and which way the wind blew. Microscopic fossils reveal water and air temperatures. And miniature bubbles trapped in salt preserve actual fossil water, from nearly 300 million years ago. Travel back in time with us to explore the Great Dying.

The Temperature-Time Tiger Team(T4) was charteredby NASA and ESA to evaluate the potential for degra-dation or alteration of the Mars Sample Return ( MSR)samples if they are exposed to temperatures between+30 degrees Cand+60 degrees C, and to what extent this alteration may reduce thescientific value of the samples. Thirteen scientists were se-lected to represent scientific disciplines expected to be mostaffected by sample heating. Team expertise helped in under-standing whether exposing samples to temperatures between+30 degrees C and+60 degrees C poses risk to the sample integrity and,therefore, to future scientific investigations.Key processes identified were as follows: the release ofvolatiles by desorption and sublimation and release from con-densed phases (interiors, decomposition, dehydration); chem-ical reactions including gas-gas and gas-solid; deliquescenceof hygroscopic salts; acid/base interactions (potential for ext-reme pH conditions); aqueous redox reactions, isotopicexchange (aqueous phases, minerals, gases, organic phases);condensation and freezing (in the after-heating cooling phase);and interactions with the sample tube materials. There ispotential for multiple interactions and overlapping effects.For inorganic materials and their records, over both longtime scales (hours to days) and short-time scales (minutesto hours), no temperature excursion above+30 degrees C could beaccommodated without loss of science. There would besome robust constituents (feldspars, quartz, pyroxenes, etc.)that are unaffected but also less robust constituents (salts,phyllosilicates, radicals, etc.) that would be affected acrossall temperature ranges 60 pound degrees C.For organic materials, in particular organic biosignatures,the risks reflect that preservation is reliant on a number ofprocesses, and a change in one component within a sampletube can affect another. For organic materials, over longtimescales of hours to days no temperature excursion above+30 degrees C could be accommodated without loss of science, butover shorter timescales (minutes to hours), raising the tem-perature to 40 degrees C could be manageable without major dis-ruption to science, whereas temperatures above 40 degrees C wouldlead to significant losses.The consideration of these findings by the MSR team willhelp maintain the fidelity of samples returned from Mars inthe future and maximize scientific return when they areanalyzed in Earth laboratories

Abstract 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.

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 Seitah and Maaz 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 center dot[3-5]H2O and possible MgSO4 center dot 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. The history of water on Mars is a puzzle that is of interest to scientists as well as the general public. Mars currently has water in the form of ice at the poles, trace amounts of gas in the atmosphere, and an unknown amount beneath the surface as ground water, bound in minerals, and in ice. However, there is strong evidence that ancient Mars may have had long-lived streams, rivers, and lakes. There is still much to learn about what Mars was like and how it transformed over time. One approach is to study the inventory of water at different times. In this work, we report the presence of hydrated magnesium sulfate (similar to Epsom salts) and dehydrated calcium sulfate that were formed by water flowing through cracks in volcanic rocks at the bottom of the 3.8-billion-year-old Jezero crater. These hydrated minerals trap water within themselves and record the history of how and when they formed. Returning samples of these minerals to Earth would allow researchers to explore the history of Mars' water and climate, and possibly evidence of ancient life with the most sensitive instruments possible. Sulfate phases detected by Scanning Habitable Environments with Raman and Luminescence for Organics and Chemistry and PIXL in igneous units consists of crystalline/amorphous Mg-sulfate minerals with 3-5 waters and anhydrous Ca-sulfate minerals Hydration of sulfate minerals sets a lower constraint on how much subsurface water is stored in sulfate minerals The sulfate minerals of Jezero crater floor were deposited in moderate pH, likely at low temperature, and during several episodes

Bedrock rivers adjust to the properties of the rock into which they incise, imprinting the geologic past on Earth's surface. We compared rock properties and channel form along the Dry Fork in the Allegheny Mountains, West Virginia, as it crosses between Mississippian sandstone and carbonate rock units, to investigate how the depositional history of channel- margin bedrock influences modern channel form. We used thin- section petrography to interpret site- specific depositional environments. We quantified rock strength with point- load testing, discontinuity spacing by measuring bed and fracture spacing, and channel form through cross- section surveys. Petrography indicates that the sandstone was likely deposited in an alluvial fan, while the carbonate formed in a shallow- marine environment. The sandstone has modestly higher point- load strength than the carbonate, but the units differ more dramatically in their discontinuity spacing. The sandstone is thinly (3- 10 cm) bedded and densely (50- 100 cm) fractured; the carbonate has thicker (45 cm) beds and sparser (180- 300 cm) fractures. Sandstone channel cross sections are wider, shallower, and rougher, whereas carbonate cross sections are narrower, deeper, and smoother. Results suggest that a transition from plucking- dominated erosion in the discontinuity- rich sandstone to abrasion- and/or dissolution- dominated erosion in the discontinuity- poor carbonate, rather than differences in rock strength, drives observed morphologic differences. Differences in discontinuity spacing might arise from differential bed thickness between the two units, both because bed boundaries are discontinuities and because thinner beds lead to more densely spaced fractures. We hypothesize that depositional dynamics-the unsteady deposition of an alluvial fan resulting in thin beds versus steady, shallow- marine deposition that deposited thicker beds-explain the observed differences in bed thickness, discontinuity spacing, and modern erosion process dominance and channel form, emphasizing how modern Earth- surface processes are contingent on the geologic past.

Perseverance roverMars 2020 Perseverance rover is currently exploring Jezero Crater on Mars, which contains an ancient lake-delta fan system with a high potential for past habitability. One of Perseverance’s primary science goals is to collect a set of scientifically return-worthy samples for return to Earth (Mars Sample Return; MSR) [1]. Between February 2021 and May 2024, Perseverance has sealed 24 tubes containing 21 rock cores, 2 regolith samples and one atmosphere sample. Of the 17 rock cores and regolith samples, 8 were collected on the crater floor, 9 at the fan front, 3 at fan top and 3 at the Margin. Additionally, 3 witness tube assemblies (WTAs), which will serve as blanks for contamination control, have been sealed. A total of ten tubes have been deposited in a depot in the Three Forks area. All rock and regolith samples are accompanied by a set of observations (Sample Threshold Observation Protocol, the STOP List) performed on abrasion patches or regolith near each sample collection site. These observations are documented in the Initial Reports and the Sample Dossier which are available through the Geosciences Node of the Planetary Data System (https://pds-geosciences.wustl.edu). Samples The eight rock cores collected on the crater floor include samples of the two major rock units of the crater floor, the Máaz formation (basaltic to basaltic-andesite) and the Séitah formation (olivine-cumulate). In addition to the primary igneous mineralogy such as olivine, pyroxene and feldspar, these samples contain alteration minerals such as sulfates, carbonates and perchlorates indicating interaction with liquid water in the past [2]. These samples will be important for understanding Mars igneous history and providing constraints on the timing of Jezero crater and the fan units. The alteration phases in the rocks will enable studies of water-rock interaction within Jezero crater.The seven rock cores collected from the Shenandoah formation at the fan front are all fine-grained sedimentary rocks that were likely deposited in a lacustrine environment [3]. If returned to Earth, these rocks would be the first sedimentary rocks from Mars to be studied in terrestrial laboratories. Three cores (Hazeltop, Bearwallow and Kukaklek) were collected at the layered outcrops Wildcat Ridge and the stratigraphically equivalent Hidden Harbor. These samples are fine-grained sandstones to siltstones and are mainly composed of sulfates and phyllosilicates. They also contain various diagenetic features such as calcium sulfate veins/veinlets (typically anhydrite) and putative concretions. Two cores (Swift Run and Skyland) were collected at the layered outcrop Skinner Ridge. They are medium- to coarse- grained sandstones containing pyroxene, feldspar, carbonates and serpentine. Finally, two cores (Shuyak and Mageik) were collected at the layered outcrop Amalik. They are fine-grained sandstones and mainly composed of olivine grains that have been altered to phyllosilicates, most likely a serpentine phase. There are also carbonates associated with these cores. The phyllosilicates, sulfates and other alteration phases present in the fan front rock cores could potentially have trapped organic matter and other biosignatures originating from the ancient lake or from the Jezero watershed. Thus, these samples will be exceptionally valuable for astrobiological investigations upon return from Mars.The two regolith samples (Atmo mountain and Crosswind) were collected at a megaripple, Observation Mountain, near Amalik at the delta front [4]. The samples consist of different-sized grains of varying compositions including olivine, altered olivine, feldspar, carbonates, sulfates and phosphates. These samples will enable studies of the regolith and dust of Mars.Three cores were collected at the fan top, Melyn, Otis Peak and Pilot Mountain [5]. They are all poorly sorted medium sandstone with clasts ranging up to pebble sizes and believed to be part of the Tenby formation, which likely represents a fluvial environment and overlies the fan front. They contain olivine, feldspar, pyroxene and alteration phases such as Mg-Fe carbonates, Mg-sulfates, Ca-sulfates, phyllosilicates and chlorinated phases. These samples represent some of the coarsest sedimentary material yet sampled by the rover. Their detrital clasts have diverse lithologies likely sourced from the Nili Planum region outside Jezero crater that contains some of the oldest known rocks on Mars (>~4 billion years old). Therefore, laboratory investigations of these samples will enable the study of a source-to-sink sedimentary system on Mars that will inform how surface environments, aqueous processes, and habitability evolved through time, both within the catchment and the fan. Finally, three cores were collected in the Margin unit with two cores collected in the eastern Margin (Pelican Point and Lefroy Bay) and one core in the western Margin (Comet Geyser) [6]. They are all medium to coarse sandstones expect Comet Geyser which could be either a coarse sandstone or aqueously altered igneous rock. The rocks contain a high portion of carbonates with silica as a likely cement. Also present are olivine, pyroxene, minor feldspar, altered silicates and phyllosilicates. The Margin unit has a high astrobiological interest due to its high carbonate signal as observed from space and in-situ and its potential as a shoreline deposit. Parts of carbonates and silica are microcrystalline which make them excellent for biosignature preservation.Perseverance is currently continuing its exploration of the Margin unit with the possible collection of one more sample. After finishing the Margin campaign, the next step is to explore the crater rim which will include some of the oldest rocks on Mars (>~4 billion years old).[1] Farley K.A. et al. Space Science Reviews, 216 (2020), [2] Farley, K.A. et al. Science, 377 (2022), [3] Bosak et al. Lunar Planetary and Science Conference (2024), [4] Hausrath, E.M et al. Lunar Planetary and Science Conference (2023), [5] Weiss B. et al. Lunar Planetary and Science Conference (2024), [6] Siljeström et al. Lunar Planetary and Science Conference (2024)

The Mars Sample Return mission intends to retrieve a sealed collection of rocks, regolith, and atmosphere sampled from Jezero Crater, Mars, by the NASA Perseverance rover mission. For all life-related research, it is necessary to evaluate water availability in the samples and on Mars. Within the first Martian year, Perseverance has acquired an estimated total mass of 355 g of rocks and regolith, and 38 μmoles of Martian atmospheric gas. Using in-situ observations acquired by the Perseverance rover, we show that the present-day environmental conditions at Jezero allow for the hydration of sulfates, chlorides, and perchlorates and the occasional formation of frost as well as a diurnal atmospheric-surface water exchange of 0.5–10 g water per m2 (assuming a well-mixed atmosphere). At night, when the temperature drops below 190 K, the surface water activity can exceed 0.5, the lowest limit for cell reproduction. During the day, when the temperature is above the cell replication limit of 245 K, water activity is less than 0.02. The environmental conditions at the surface of Jezero Crater, where these samples were acquired, are incompatible with the cell replication limits currently known on Earth.