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Lake Salda, a terrestrial analog for the paleolake in Jezero Crater on Mars, hosts active, subfossil, and fossil hydromagnesite microbialites, making it an ideal location to study microbialite formation and subsequent processes. Our understanding of this record is still limited by an incomplete knowledge of the macro‐ and mesoscale morphotypes of microbialites, along with their spatial distribution and correlation with microbial and geochemical processes that influence microbialite formation. In this study, we investigated the spatial distribution, morphotypes, mineralogy, geochemistry, and microbial diversity of the microbialites and identified six distinct zones (Zone I to Zone VI) with major microbialite build‐ups in Lake Salda. Newly identified microbialites were classified based on the macro‐ and mesostructures. Our work shows that the lake contains stromatolites, thrombolites, stromatolitic thrombolites, dendrolites, and microbially induced sedimentary structures. At macroscale, Lake Salda microbialites exhibit hemispheres, stacked domes, and laterally linked columnar structures while minicolumns, knobs, mesoclots, laminae, and botryoidal structures are common at mesoscale. The macro‐ and mesoscale distribution of different microbialite types spatially correlates with microbial community composition and water depth. Deep‐growing microbialites with a low abundance of Cyanobacteria (∼1%–4%) and high abundance of Firmicutes (28%–93%) exhibit steeply convex lamination, producing finger‐like minicolumnar mesostructures. In contrast, shallow‐growing microbialites with a low abundance of Firmicutes (0%–5%) and high abundance of Cyanobacteria (11%–37%) have well‐preserved gently convex millimeter‐scale lamination, resulting in cauliflower mesostructures. Palygorskite ((Mg, Al)2Si4O10(OH)) is identified in the diatom‐rich microbial layer of the deep‐growing microbialites. Regardless of the microbialite types, hydromagnesite and aragonite are present in the extracellular polymeric substance (EPS)‐rich zone of the shallow and deep‐growing microbialites. Overall, environmental changes (e.g., water depth and, accommodation space) play a major role in the formation and spatial distribution of different microbialite morphologies at the macro‐ and mesoscale. Differences in the relative abundance of dominant microorganisms between mesostructured types suggest that mesomorphology may be influenced by changes in microbial diversity. Spatial variations in the microbialite morphotypes, along with the abundant presence of entombed biomass (e.g., mineralized filaments), may indicate areas that have a high potential for the preservation of biosignatures. [ABSTRACT FROM AUTHOR]

With the development of the hyperspectral remote sensing technique, extensive chemical weathering profiles have been identified on Mars. These weathering sequences, formed through precipitation-driven leaching processes, can reflect the paleoenvironments and paleoclimates during pedogenic processes. The specific composition and stratigraphic profiles mirror the mineralogical and chemical trends observed in weathered basalts on Hainan Island in south China. In this study, we investigated the laboratory reflectance spectra of a 53-m-long drilling core of a thick basaltic weathering profile collected from Hainan Island. We established a quantitative spectral model by combining the genetic algorithm and partial least squares regression (GA-PLSR) to predict the chemical properties (SiO2, Al2O3, Fe2O3) and index of laterization (IOL). The entire sample set was divided into a calibration set of 25 samples and a validation set of 12 samples. Specifically, the GA was used to select the spectral subsets for each composition, which were then input into the PLSR model to derive the chemical concentration. The coefficient of determination (R2) values on the validation set for SiO2, Al2O3, Fe2O3, and the IOL were greater than 0.9. In addition, the effects of various spectral preprocessing techniques on the model accuracy were evaluated. We found that the spectral derivative treatment boosted the prediction accuracy of the GA-PLSR model. The improvement achieved with the second derivative was more pronounced than when using the first derivative. The quantitative model developed in this work has the potential to estimate the contents of similar weathering basalt products, and thus infer the degree of alteration and provide insights into paleoclimatic conditions. Moreover, the informative bands selected by the GA can serve as a guideline for designing spectral channels for the next generation of spectrometers.

Eruptions of the Askja Volcano in Northern Iceland in 1875 and 1961 blanketed the caldera with rhyolitic and basaltic tephra deposits, respectively, which preserved layers of seasonal snowpack as massive ice. Askja serves as an operational and geophysical analog to test ground‐penetrating radar field and analysis techniques for in situ resource utilization objectives relevant to the martian and lunar environments. We conducted ground‐penetrating radar surveys at center frequencies of 200, 400, and 900 MHz to map the thickness and extent of tephra deposits and underlying massive ice at three caldera sites. We identified up to 1 m of tephra preserving up to 4.4 m of massive ice. We measured the real dielectric permittivity of the overlying tephra and the total attenuation at each frequency of the tephra and ice. A key objective of our investigation was to determine if attenuation (or loss) could be used as an additional diagnostic signature of massive ice preserved at depth when compared to ice‐free stratigraphy. Loss rates of the ice‐rich subsurface decrease with increasing ice thickness relative to the overburden, which may constitute a possible signature. Attenuation also increased with increasing frequency. The tephra, ice, and other volcanic deposits at each of our three caldera sites and the ice‐free, pumice‐mantled 1961 Vikrahraun lava flow exhibited consistently low loss rates at all frequencies. This result highlights the ambiguity associated with identifying the unique signature of ice within low‐loss stratigraphies, a possible challenge for its identification in the martian or lunar subsurface using radar. Plain Language Summary: The Askja Volcano in Northern Iceland is considered to be a planetary analog for other terrestrial worlds such as Mars and the Moon. We conducted ground‐penetrating radar surveys of the Askja caldera where seasonal snowpack was buried by eruptions of low‐density ash and tephra in 1875 and 1961. This erupted volcanic material protected the snowpack long‐term, where it later densified into thick layers of ice. We successfully mapped up to 4.4 m of this ice preserved beneath up to 1 m of erupted material. Transmitted radar signals decay naturally as their distance from the source increases. Some materials such as water ice are less conducting than others and are therefore less lossy to this transmitted signal. We used the ice and tephra deposits at Askja as a test case to determine if large quantities of buried ice would result in a detectable signature that indicates its presence when compared to ice‐free regions. We found that increases in ice layer thickness relative to the overlying volcanic material result in columns of material with bulk properties that are less dissipative to the radar signal and therefore may indicate a signature of buried ice in the subsurface. Key Points: Multi‐frequency Ground‐penetrating radar (GPR) surveys identified massive ice up to 4.4 m thick buried by up to 1 m of tephra from two Holocene eruptions of AskjaGPR readily maps vertical and horizontal extents of subsurface ice and tephra overburden; ice concentration transitions are not detectedIce‐rich and ice‐free sites present a similar attenuation; ice‐rich sites demonstrate a lower attenuation rate with increasing ice thickness [ABSTRACT FROM AUTHOR]

Antarctic deserts are among the driest and coldest ecosystems of the planet; there, some microbes survive under these extreme conditions inside porous rocks, forming the so-called endolithic communities. Yet the contribution of distinct rock traits to support complex microbial assemblies remains poorly determined. Here, we combined an extensive Antarctic rock survey with rock microbiome sequencing and ecological networks and found that contrasting combinations of microclimatic and rock traits such as thermal inertia, porosity, iron concentration, and quartz cement can help explain the multiple complex microbial assemblies found in Antarctic rocks. Our work highlights the pivotal role of rocky substrate heterogeneity in sustaining contrasting groups of microorganisms, which is essential to understand life at the edge on Earth and for the search for life on other rocky planets such as Mars. [ABSTRACT FROM AUTHOR]

In the recent decade of astrobiological exploration of the Martian surface, there has been a shift from identifying habitable environments to finding markers indicative of biological activity. It requires a prior understanding of the physical and geochemical environment of the setting to decipher whether the conditions were conducive. Generally, quiescent surroundings of lacustrine basins are considered one of the best targets for the preservation of any biological signatures. However, due to logistical limitations, the geochemical information available is mostly restricted to small areas on the surficial level (or in the subsurface in case of layered deposits or impact craters) where sufficient satellite coverage is available and, in some areas, where rovers/landers have been deployed. In this context, terrestrial lacustrine basins offer valuable insights into the environment required for the formation of the minerals observed on the Martian surface. This study was carried out within Sambhar Lake located in the arid/semiarid climatic zone within the Thar desert. It is a hypersaline playa that has undergone several cycles of desiccation and re-filling, sharing its climate-controlled history with that of several paleolakes on Mars. We conducted physicochemical analysis of the samples collected from the lake and its surrounding area and compared our results with samples from the Curiosity rover (at Gale crater) and to those of the studies carried out in basalt-rich parent settings of Iceland. Our results suggest that Sambhar Lake is a Na-Cl type brine with climate-driven hydrology. The shallow cores and rock samples indicated that the area is rich in evaporites. We propose that even the sites with different parent material may be crucial in understanding the geological evolution of paleolakes on Mars and that Sambhar is a great example to study tectono-geomorphic evolution and the climate-induced transition of a lacustrine basin to a playa. Additionally, the lake is also desirable to study extremophiles and their adaptation to changing environmental variables for future planetary missions, including but not limited to, Mars. • Sambhar Lake is a good example to study the geological evolution of lacustrine basins into playas. • It is a hypersaline playa that has undergone cycles of desiccation and re-filling, comparable to several paleolakes on Mars. • It possesses several morphological and mineralogical characteristics that are of relevance to Martian evaporitic basins. • It hosts various extremophiles and may be explored for habitability potential of similar settings for future missions. [ABSTRACT FROM AUTHOR]

Spatter cones are a common mafic explosive volcanic feature observed on Earth associated with Hawaiian and Strombolian-style lava fountaining. Across Mars there are numerous explosive volcanic features assessed to be accumulations of cold pyroclasts (e.g., scoria cones, tuff rings) but identification of welded and fused explosive deposits (i.e., spatter) has only recently been investigated. We present evidence indicating the presence of a Martian spatter cone south of Pavonis Mons and a comparison to a spatter cone formed during the 2021 Fagradalsfjall eruption, Iceland. The morphology and morphometry of the possible Martian spatter cone are more consistent with agglutinated rock like the spatter cone formed during the Fagradalsfjall eruption than poorly consolidated tephra, characteristic of scoria cones. In addition, the size of the two spatter cones falls within anticipated dimensions based on a simple ballistic trajectory model. Evidence for spatter included high angled slopes, knobby yet layered surface textures, rounded boulder talus, and thermophysical properties consistent with material that is more indicative of rock than scoria. The evidence indicates that the volcanic feature South of Pavonis Mons should be classified as a spatter cone. Identification of a Martian spatter cone has implications for eruption dynamics, magmatic volatile content, and environmental conditions. • We present evidence for a Martian spatter cone South of Pavonis Mons. • The 2021 Fagradalsfjall eruption is used as a terrestrial analog. • Identification of a Martian spatter cone fills an observational gap. [ABSTRACT FROM AUTHOR]

Several icy bodies (e.g., Europa and Ceres) likely possess near‐surface brine reservoirs, which are considered to be sources of salts on their surfaces. Previous studies have proposed processes whereby an overlying ice layer captures salinity from a freezing, subsurface reservoir. However, few field investigations have been conducted to investigate chemical partitioning and aqueous chemistry in freezing brine reservoirs in terrestrial analogs. Here we report results of winter field surveys to ice‐covered, closed‐basin saline lakes in the Valley of the Gobi Lakes, Mongolia. We found that the surface ice exhibited complex features, including both pressure ridges formed by compressive forces and wet cracks formed by tensile forces. The latter provides salinity to the ice layer and surface. In addition to wet cracks, saline lake bottom‐water, along with suspended matter, was continuously captured within the pores of the ice layer during downward freezing. Using a combined mass balance and low‐temperature aqueous chemistry model, we reproduced the ice salinity due to entrapment of Na+, Cl−, and SO42−, suggesting that chemical partitioning of these species in freezing brine reservoirs on icy bodies can be understood based on our current knowledge. In the lake bottom‐water, the metastable phase of carbonates (i.e., amorphous Mg‐carbonate and monohydrocalcite) play key roles in controlling the concentrations of precipitable Mg2+ and Ca2+ and alkalinity, highlighting the importance of metastable phase of carbonate in the aqueous chemistry of subsurface brine reservoirs on icy bodies. Metastable phases might be indicators of freshly erupted materials from brine reservoirs. Plain Language Summary: Icy bodies that have subsurface brines in the Solar System attract attention because of their potential habitability. Recent observations by spacecraft and ground‐based telescopes have identified the existence of salt materials on such icy bodies, such as Europa and Ceres. The salt compositions may reveal the aqueous chemistry of the subsurface liquid reservoirs. However, transport of salt materials to the icy surface is poorly understood and has been subject to limited field investigations of terrestrial analogs. Here we report results from field surveys of ice‐covered saline lakes in Mongolia. We found that cracks and pores in the surface ice capture lake bottom‐water and suspended matter. Similar processes may operate on icy bodies and transport salt materials to the surface. Key Points: Freezing closed‐basin saline lakes could be terrestrial analogs of chemical partitioning of salinity in subsurface brines on icy bodiesSalinity in ice and aqueous chemistry in bottom lake water were investigated through field surveys and geochemical modelingMetastable carbonate minerals could control dissolved CO2 and alkalinity of freezing lake water, implying their importance in ocean worlds [ABSTRACT FROM AUTHOR]

Astronauts who undergo prolonged periods of spaceflight may develop a unique constellation of neuro-ocular findings termed Spaceflight Associated Neuro-Ocular Syndrome (SANS). SANS is a disorder that is unique to spaceflight and has no terrestrial equivalent. The prevalence of SANS increases with increasing spaceflight duration and although there have been residual, structural, ocular changes noted, no irreversible or permanent visual loss has occurred after SANS, with the longest spaceflight to date being 14 months. These microgravity-induced findings are being actively investigated by the United States' National Aeronautics Space Administration (NASA) and SANS is a potential obstacle to future longer duration, manned, deep space flight missions. The pathophysiology of SANS remains incompletely understood but continues to be a subject of intense study by NASA and others. The study of SANS is of course partially limited by the small sample size of humans undergoing spaceflight. Therefore, identifying a terrestrial experimental model of SANS is imperative to facilitate its study and for testing of preventative measures and treatments. Head-down tilt bed rest (HDTBR) on Earth has emerged as one promising possibility. In this paper, we review the HDTBR as an analog for SANS pathogenesis; the clinical and imaging overlap between SANS and HDTBR studies; and potential SANS countermeasures that have been or could be tested with HDTBR. [ABSTRACT FROM AUTHOR]

A better understanding of the combined impact of different space stressors on human health is urgently warranted, considering the upcoming long-duration missions beyond lower Earth orbit. Therefore, a growing number of particle accelerator facilities implement ground-based set-ups to study the effect of simulated space radiation with simulated psychological or physical stressors. The immune system is highly sensitive to these types of stressors and limited information is currently available on the impact of the complex space radiation environment on the astronauts' immune function. This pilot study presents a first step in the implementation of a ground-based set-up with neutron irradiation, which is considered to be an important secondary component in space radiation fields. The effect of dose rate on immune alterations was studied using the in vitro cytokine release assay. Whole blood samples (n = 8) were exposed to 0.125 or 1 Gy of neutron irradiation (fluence-weighted average energy: 29.8 MeV) at a lower dose rate (LDR) of 0.015 Gy/min and a higher dose rate (HDR) of 0.400 Gy/min. Immediately post-irradiation, blood samples were stimulated with lipopolysaccharide (LPS), heat-killed Listeria monocytogenes (HKLM) or lectin pokeweed mitogen (PWM), and incubated for 24 h. Cell-mediated immunity was examined by analysing interleukin-2 (IL-2), interferon-gamma (IFN-γ), tumour necrosis factor-alpha (TNF-α), and interleukin-10 (IL-10) plasma levels. Stimulants significantly increased all cytokine levels except IL-2, where only PWM induced a significant increase. In general, no statistically significant changes were observed in IL-2, IFN-γ, and TNF-α concentrations at different neutron doses and dose rates when compared to their stimulated, sham-irradiated controls. After PWM-stimulation, IL-10 levels were significantly increased at 0.125 Gy HDR and 1 Gy LDR. In a pooled analysis, the HDR significantly increased IL-2 titres (under PWM-stimulation) and IFN-γ titres (with all stimulants), but significantly decreased TNF-α secretion in unstimulated cultures. Due to the limited sample number, no strong conclusions could be made in this pilot study on the effect of neutron radiation as a single stressor on cytokine secretion in response to different stimuli. However, some interesting trends and dose rate effects were observed, which pave the way for future investigations on the synergistic effects of multiple space stressors on immune cell function.

The 1.88‐km‐diameter Lonar crater emplaced in the Deccan basalt is an excellent terrestrial analog of bowl‐shaped impact craters on Mars. It contains a pristine ejecta blanket with abundant basalt boulders. We measured the density, porosity, P and S wave velocities and attenuation, magnetic susceptibility, uniaxial compressive strength, and tensile strength of 313 core specimens from 65 basalt ejecta boulders. Using these values, we quantified the gross physical properties of preimpact target and applied them in the cratering equations and estimated the spall plate dimensions and ejection distances. The impact of 35‐m‐radius projectile with 20 km/s velocity on the basaltic target with 77.2‐MPa dynamic tensile strength, 4,163 m/s P wave velocity, and 2.56 g/cm3 density gives a spall thickness range (0.2 to 9.7 m) similar to the observed boulder sizes at Lonar crater. Because aqueous weathering and vesicularity are present in the target, the Lonar impact produced smaller spall sizes than those expected from a massive basalt target. We also measured the ejecta boulder sizes and shapes around a fresh impact crater (of similar size and target to Lonar) in Arcadia Planitia on Mars and calculated the spall thicknesses. The low‐velocity impact (5.5 km/s) of 50‐m‐radius projectile on the target similar to Lonar basalt gives a spall thickness range (1 to 25 m) similar to the observed boulder sizes at the Martian impact crater. The impact craters of similar sizes and targets on Earth and Mars produced different spall boulder size distributions reflecting the distinct impact conditions on these planets. Plain Language Summary: When a hypervelocity meteorite strikes the planetary surface, it produces a layer of large spall fragments (boulders) from the target's surface and become parts of the impact crater ejecta. The measurements of physical and geometric properties of these ejecta boulders are useful for quantifying the conditions of impact cratering. Hence, we measured these quantities using the basalt boulders at Lonar crater in India and quantified the gross physical properties of the preimpact target. These values were used in the impact cratering equations and theoretical spallation models to determine the size and velocity of the impactor that would produce the spall sizes similar to the observed boulder sizes at Lonar. Many fresh impact craters on Mars are also formed on targets comparable to Lonar crater. Hence, we used the Lonar target properties in the spallation model of a Martian impact crater of similar size to Lonar. The results suggest that a lower‐velocity impact into a Lonar‐like target would produce spall fragments similar to the observed boulder sizes around the Martian crater. In addition, the ejecta boulders of Lonar and the Martian impact craters provide clues to the extent of aqueous alteration in the target rocks. Key Points: The physical properties of basalt ejecta boulders at Lonar crater constrained the preimpact target propertiesThe theoretical spallation model supported by the measured target properties reproduced the observed ejecta boulder sizesThe larger size ejecta boulders at the Lonar‐size impact crater on Mars suggest low‐velocity impact on Lonar‐like target [ABSTRACT FROM AUTHOR]

Banded iron formations (BIFs) are major rock units having hematite layers intermittent with silica rich layers and formed by sedimentary processes during late Archean to mid Proterozoic time. In terrestrial environment, hematite deposits are mainly found associated with banded iron formations. The BIFs in Lake Superior (Canada) and Carajas (Brazil) have been studied by planetary scientists to trace the evolution of hematite deposits on Mars. Hematite deposits are extensively identified in Meridiani region on Mars. Many hypotheses have been proposed to decipher the mechanism for the formation of these deposits. On the basis of geomorphological and mineralogical studies, aqueous environment of deposition is found to be the most supportive mechanism for its secondary iron rich deposits. In the present study, we examined the spectral characteristics of banded iron formations of Joda and Daitari located in Singhbhum craton in eastern India to check its potentiality as an analog to the aqueous/marine environment on Mars. The prominent banding feature of banded iron formations is in the range of few millimeters to few centimeters in thickness. Fe rich bands are darker (gray) in color compared to the light reddish jaspilitic chert bands. Thin quartz veins (<4 mm) are occasionally observed in the hand-specimens of banded iron formations. Spectral investigations have been conducted in VIS/NIR region of electromagnetic spectrum in the laboratory conditions. Optimum absorption bands identified include 0.65, 0.86, 1.4 and 1.9 μm, in which 0.56 and 0.86 μm absorption bands are due to ferric iron and 1.4 and 1.9 μm bands are due to OH/H 2 O. To validate the mineralogical results obtained from VIS/NIR spectral radiometry, laser Raman and Fourier transform infrared spectroscopic techniques were utilized and the results were found to be similar. Goethite-hematite association in banded iron formation in Singhbhum craton suggests dehydration activity, which has altered the primary iron oxide phases into the secondary iron oxide phases. The optimum bands identified for the minerals using various spectroscopic techniques can be used as reference for similar mineral deposits on any remote area on Earth or on other hydrated planetary surfaces like Mars. [ABSTRACT FROM AUTHOR]

A detailed vibrational Raman-IR spectroscopic and diffractional analyses have been performed on basalts from two locations from Tenerife Island: (1) the Arenas Negras volcano which belongs to the historical eruption not showing visible alteration and (2) Pillow Lavas zone from Anaga Massif which shows a clearly fluid-rock interaction caused by submarine alteration. These places have been extensively studied due to its similarity with the surface of Mars. The analysis is based on the mineral detection of selected samples by a Micro-Raman study of the materials. The complementary techniques have confirmed the mineralogy detected by the Raman measurement. The results show a volcanic environment behavior with primary phases like olivine, pyroxene, and feldspar/plagioclase. Moreover, the presence of accessory minerals or secondary mineralization like phosphate, iron oxides, zeolite or carbonates shows the alteration processes on each outcrop. The variation in the crystallinity and amorphous phases is related to fluid-rock interaction caused by hydrothermal episodes and external weathering processes, which shows several analogies with the ancient volcanic activity from Mars. [ABSTRACT FROM AUTHOR]

The paleo-meanders in the Aeolis Dorsa (AD) region show that meandering channels can develop in the absence of vegetation. Three possible mechanisms other than vegetation could contribute to the bank cohesion required to promote meandering: permafrost, abundant mud, and chemical cementation. Banks at the meandering Quinn River show little vegetation cover. Almost all sediment samples collected from the Quinn River deposits contain at least 41% mud (silt/clay), which is much higher than for most meandering streams. Ion chromatography (IC) analysis and scanning electron microscope (SEM) images showed presence of salts in river waters and sediments which may induce fine sediment to flocculate and be deposited. We find that bank cohesion promoting meandering can be provided by silt/clay, the deposition of which may be induced by dissolved salts. The sinuous Usuktuk River in the continuous permafrost region near Barrow, Alaska exhibited no exposed permafrost on stream banks. Instead vegetation seemed to be the dominant control of bank erosion. We have not found evidence for ice control of bank cohesion in this or other terrestrial rivers of similar size and in meandering pattern to the Martian AD meanders. We conclude that bank cohesion in the AD meanders was probably provided by deposition of fine suspended sediment that was flocculated by dissolved salts. [ABSTRACT FROM AUTHOR]

NASA's search for habitable environments has focused on alteration mineralogy of the Martian crust and the formation of hydrous minerals, because they reveal information about the fluid and environmental conditions from which they precipitated. Extensive work has focused on the formation of alteration minerals at low temperatures, with limited work investigating metamorphic or high-temperature alteration. We have investigated such a site as an analog for Mars: a mafic dike on the Colorado Plateau that was hydrothermally altered from contact with groundwater as it was emplaced in the porous and permeable Jurassic Entrada sandstone. Our results show evidence for fluid mobility removing Si and K but adding S, Fe, Ca, and possibly Mg to the system as alteration progresses. Mineralogically, all samples contain calcite, hematite, and kaolinite; with most samples containing minor anatase, barite, halite, and dolomite. The number of alteration minerals increase with alteration. The hydrothermal system that formed during interaction of the magma (heat source) and groundwater would have been a habitable environment once the system cooled below ∼120 °C. The mineral assemblage is similar to alteration minerals seen within the Martian crust from orbit, including those at Gusev and Jezero Craters. Therefore, based on our findings, and extrapolating them to the Martian crust, these sites may represent habitable environments which would call for further exploration and sample return of such hydrothermally altered igneous materials. [ABSTRACT FROM AUTHOR]

NASA's search for habitable environments has focused on alteration mineralogy of the Martian crust and the formation of hydrous minerals, because they reveal information about the fluid and environmental conditions from which they precipitated. Extensive work has focused on the formation of alteration minerals at low temperatures, with limited work investigating metamorphic or high-temperature alteration. We have investigated such a site as an analog for Mars: a mafic dike on the Colorado Plateau that was hydrothermally altered from contact with groundwater as it was emplaced in the porous and permeable Jurassic Entrada sandstone. Our results show evidence for fluid mobility removing Si and K but adding S, Fe, Ca, and possibly Mg to the system as alteration progresses. Mineralogically, all samples contain calcite, hematite, and kaolinite; with most samples containing minor anatase, barite, halite, and dolomite. The number of alteration minerals increase with alteration. The hydrothermal system that formed during interaction of the magma (heat source) and groundwater would have been a habitable environment once the system cooled below ~120° C. The mineral assemblage is similar to alteration minerals seen within the Martian crust from orbit, including those at Gusev and Jezero Craters. Therefore, based on our findings, and extrapolating them to the Martian crust, these sites may represent habitable environments which would call for further exploration and sample return of such hydrothermally altered igneous materials.