The high mobility of Li allows it to be used as a tracer for groundwater processes, recording past aqueous conditions. On Earth, a relationship has been noted in multiple field sites between clay mineral abundances and elevated Li in bedrock. Observations from the Curiosity MSL mission at Gale crater on Mars showed a high-clay mineral and high-Li area near the Vera Rubin ridge (VRR) and Glen Torridon region, suggesting Li was perhaps substituting into clay minerals as was seen in these terrestrial field settings. However, the process of this substitution has not been examined in the laboratory using non-field samples, especially not with Mars-relevant mineralogy. To investigate this open question in the laboratory using Mars-relevant regolith and clay minerals, we conducted continuous flow packed-bed reactor experiments to test whether clay minerals affect the Li concentration of Mars regolith simulant MGS-1 during aqueous alteration. The mechanism for Li sorption was also investigated by conducting experiments with clays mixed with glass beads and investigating changes in other elements alongside Li via laser-induced breakdown spectroscopy (LIBS). We tested four dioctahedral clay minerals (kaolinite, illite, nontronite, mixed layer illite/smectite) and two trioctahedral clay minerals (talc, saponite) and found that both talc and illite are capable of increasing the amount of Li sorbed compared to MGS-1 simulant when exposed to Li-bearing groundwater. For MGS-1, the glass beads, and the clay minerals (talc, illite) the primary mechanism appears to be Li substitution for Mg, Al, and K, respectively. This has implications for ongoing Mars missions as well as astrobiology, specifically relating to understanding habitability of areas on Mars and identifying aqueous environments for future mission concepts.

Detection of organic molecules on Mars is challenging due to a variety of degradation processes occurring at the Martian surface, including UV irradiation. Nevertheless, the NASA’s Curiosity rover found evidence of organic molecules in clays, suggesting that these minerals might be particularly suitable to preserve organics on Mars. In this work, the photostability of L-histidine adsorbed at different pHs on nontronite under Martian-like UV irradiation was investigated in order to assess the preservation potential of this clay in the Martian environment. The interactions between L-histidine and nontronite were investigated via Infrared spectroscopy and X-Ray Diffraction, in order to understand the possible preservation mechanisms. Results indicate that L-histidine intercalates into the mineral interlayer at acidic pH, and undergoes minor degradation after UV exposure compared to the pure molecule. At basic pH, polymolecular layers are formed and no degradation is observed. These results show that nontronite acts as a photoprotective mineral for L-histidine both at acidic and basic pH, making it a suitable mineral target for organic detection on Mars.

The ancient climate of Mars changed from warm to cold surface conditions. This climate transition is demonstrated by geomorphological evidence but lacks suitable mineralogical indicators. We investigated the crystallographic properties of hematite (iron oxide) in Gale crater measured by the Curiosity rover and compared them with laboratory experiments. Hematite crystallite sizes are about 5 to 65 nm in the oldest sedimentary rocks investigated by the rover (the Murray formation) and less than 10 nm in the younger overlying strata (the Mirador and Carolyn Shoemaker formations). We attribute the larger crystallites in the Murray formation to postdepositional coarsening by groundwater in warm and wet conditions that persisted for several million years. Hematite with small crystallites co-occurs with goethite (iron oxyhydroxide) in the overlying layers, consistent with colder and water-limited conditions.

This study investigates the long-term calibration and validation of the Aerial Measuring System (AMS) fixed and rotary-wing aerial gamma-ray survey platforms. Each of the five aircraft are equipped with an array of 2.08 L NaI(Tl) scintillator detectors that are empirically calibrated using the large area calibration pads located in Grand Junction, Co. Two spectral extraction methods, the International Atomic Energy Agency (IAEA) published window method and the Gaussian method, are compared using calibration pad data. Aerial surveys conducted at Lake Mohave and Government Wash are also analyzed, with good agreement between the IAEA and Gaussian methods and ground truth measurements within two standard deviations. The study's findings showcase the stability and reliability of the AMS system for naturally occurring radioactive material (NORM) mapping for use in applications such as geologic mapping, environmental monitoring, and exploration as well as highlight the feasibility of the Gaussian based approach which has some advantages over the IAEA window method in that the Gaussian extractions may avoid some of the isotopic and altitude dependence of the terms in the IAEA window method.

Ancient Mars had surface liquid water and a dense carbon dioxide (CO2)-rich atmosphere. Such an atmosphere would interact with crustal rocks, potentially leaving a mineralogical record of its presence. We analyzed the composition of an 89-meter stratigraphic section of Gale crater, Mars, using data collected by the Curiosity rover. An iron carbonate mineral, siderite, occurs in abundances of 4.8 to 10.5 weight %, colocated with highly water-soluble salts. We infer that the siderite formed in water-limited conditions, driven by water-rock reactions and evaporation. Comparison with orbital data indicates that similar strata (deposited globally) sequestered the equivalent of 2.6 to 36 millibar of atmospheric CO2. The presence of iron oxyhydroxides in these deposits indicates that a partially closed carbon cycle on ancient Mars returned some previously sequestered CO2 to the atmosphere.

The NASA Mars 2020 Perseverance Rover Mission has collected samples of rock, regolith, and atmosphere within the Noachian-aged Jezero Crater, once the site of a delta-lake system with a high potential for habitability and biosignature preservation. Between sols 109 and 1,088 of the mission, 27 sample tubes have been sealed, including witness tubes. Each sealed sample tube has been collected along with detailed documentation provided by the Perseverance instrument payload, preserving geological and environmental context. Samples representative of the stratigraphy within each of four campaigns have been collected: samples from the Crater Floor Campaign represent a suite of potentially petrogenetically related igneous rocks displaying variable degrees of aqueous alteration; samples from the Fan Front record fluvial to deltaic sediments formed by the transport and deposition of materials from the Jezero watershed; regolith samples from the Fan Front preserve material possibly representative of global dust as well as diverse, locally derived clasts; Upper Fan samples record the latest stages of aqueous activity within Jezero; and samples from the Margin Campaign preserve lacustrine, littoral, or possibly igneous processes that may have occurred early in the history of the crater. Along with anticipated samples from the older rocks within the rim of Jezero Crater, Perseverance promises to deliver a suite of samples preserving a diversity of formation environments and ages. Upon return to Earth and analysis in terrestrial laboratories, these samples would address longstanding questions pertaining to the geologic evolution of Mars, its habitability, and the potential for life outside the Earth.

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 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.

For more than a decade, the CheMin X-ray diffraction instrument on the Mars Science Laboratory rover, Curiosity, has been returning definitive and quantitative mineralogical and mineral–chemistry data from ~3.5-billion-year-old (Ga) sediments in Gale crater, Mars. To date, 40 drilled rock samples and three scooped soil samples have been analyzed during the rover’s 30+ km transit. These samples document the mineralogy of over 800 m of flat-lying fluvial, lacustrine, and aeolian sedimentary rocks that comprise the lower strata of the central mound of Gale crater (Aeolis Mons, informally known as Mt. Sharp) and the surrounding plains (Aeolis Palus, informally known as the Bradbury Rise). The principal mineralogy of the sedimentary rocks is of basaltic composition, with evidence of post-depositional diagenetic overprinting. The rocks in many cases preserve much of their primary mineralogy and sedimentary features, suggesting that they were never strongly heated or deformed. Using aeolian soil composition as a proxy for the composition of the deposited and lithified sediment, it appears that, in many cases, the diagenetic changes observed are principally isochemical. Exceptions to this trend include secondary nodules, calcium sulfate veining, and rare Si-rich alteration halos. A surprising and yet poorly understood observation is that nearly all of the ~3.5 Ga sedimentary rocks analyzed to date contain 15–70 wt.% of X-ray amorphous material. Overall, this >800 m section of sedimentary rock explored in lower Mt. Sharp documents a perennial shallow lake environment grading upward into alternating lacustrine/fluvial and aeolian environments, many of which would have been habitable to microbial life.

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.

Gypsum is a common mineral at Gale crater on Mars, currently being explored by the Mars Science Laboratory (MSL) rover, Curiosity. In this paper, we summarize the associations of gypsum with other sulfate minerals (bassanite, anhydrite, jarosite, starkeyite, and kieserite) from the lowest levels of the crater’s northern moat zone (Aeolis Palus) up through ~0.8 km of the stratigraphic section in the lower slopes of the sedimentary mound developed around the central peak, Aeolis Mons (informally, Mount Sharp). The analysis is based on results from the CheMin X-ray diffraction instrument on Curiosity, supplemented with information from the rover’s versatile instrument suite. Gypsum does not occur with the same frequency as less hydrous Ca-sulfates, likely, in most cases, because of its dehydration to bassanite and possibly to anhydrite. All three of these Ca-sulfate phases often occur together and, along with other sulfates, in mixed assemblages that are evidence of limited equilibration on a cold, dry planet. In almost all samples, at least one of the Ca-sulfate minerals is present, except for a very limited interval where jarosite is the major sulfate mineral, with the implication of more acidic groundwater at a much later time in Gale crater’s history. Although observations from orbit reveal a sulfate-rich surface, currently active dark basaltic dunes at Gale crater have only small amounts of a single sulfate mineral, anhydrite. Gale crater has provided the most complete mineralogical analysis of a site on Mars so far, but the data in hand show that Gale crater mineralogy is not a blueprint with planet-wide application. The concurrent study of Jezero crater by the Mars 2020 mission and comparisons to what is believed to be the most extensive deposit of gypsum on Mars, in the dune fields at the north polar ice cap, show significant diversity. Unraveling the stories of gypsum and other sulfates on Mars is just beginning.

X-ray amorphous material comprises 15-73 wt.% of sedimentary rocks and eolian sediments in Gale crater. This material is variably siliceous and iron rich but aluminum poor. The presence of volatiles is consistent with the existence of incipient weathering products. To better understand the implications of this material for past aqueous conditions on Mars, here we investigate X-ray amorphous material formation and longevity within terrestrial iron rich soils with varying ages and environmental conditions using bulk and selective dissolution methods, X-ray diffraction, and transmission electron microscopy. Results indicate that in situ aqueous alteration is required to concentrate iron into clay-size fraction material. Cooler climates promote the formation and persistence of X-ray amorphous material whereas warmer climates promote the formation of crystalline secondary phases. Iron rich X-ray amorphous material formation and persistence on Mars are therefore consistent with past cool and relatively wet environments followed by long-term cold and dry conditions. The presence of iron-rich X-ray amorphous material on the Martian surface is consistent with in situ aqueous alteration indicative of cool and relatively wet conditions in the past, according to a comparison between material from various terrestrial soils and Gale crater

X-ray amorphous material that is variably Mg/Fe/Si-rich and Al-poor and that likely contains secondary alteration products is prevalent in Gale crater sediments and rocks (15-73 wt.%). However, the structure and origin of these materials and their implications for past environmental conditions remain unknown. In this study, we use transmission electron microscopy and synchrotron microprobe analyses to examine Mg/Fe/Si-rich and Al-poor ultramafic soils from the warm Mediterranean climate Klamath Mountains of California and cold subarctic climate Tablelands of Newfoundland, Canada to help interpret environmental conditions during the formation of chemically similar X-ray amorphous material in Gale crater, Mars. Primary glass is absent from the Klamath Mountains and Tablelands materials; secondary X-ray amorphous material includes globular amorphous silica and chemically heterogeneous nanospherical amorphous material and nanocrystalline phases. Globular amorphous silica is only present in soils that undergo extensive periods of cyclic freezing. Fe-containing X-ray amorphous material from the subarctic Tablelands is significantly richer in Mg and Si than X-ray amorphous material from the warmer Klamath Mountains. Fe-rich nanocrystallites contain more Mg and Si in the subarctic Tablelands but are more highly Fe-enriched in the warmer Klamath Mountains. Potential secondary nanocrystalline phyllosilicates are only observed in the warmest examined soil in the Klamath Mountains. These characteristics – the presence or absence of amorphous silica, the chemical composition of X-ray amorphous material, the abundance and composition of Fe-rich nanocrystallites, and the presence or absence of secondary phyllosilicates - provide helpful identifiers to interpret past environmental conditions during the formation of X-ray amorphous material on Mars.

. IntroductionMars orbiters have detected different sulfates in the new landing sites of the upcoming Mars missions, Jezero crater (Mars2020) [1] and Oxia Planum region (Exomars2022) [2]. Both missions incorporate the Raman instrument to study the mineral phases in the planet, but the Raman Laser Spectrometer (RLS) has the capability to spot at microscopic scale of 50 microns. Thus, the possibility to detect sulfate minerals with the RLS instrument in the drilled samples, taken at different depths in the Martian sub-surfaces, must be considered. The expected sulfate mineral phases could contain crystallized water, and it is known that hydrated compounds have Raman responses sensitive to the temperature, especially when decreasing [3] but also when increasing due to mineral transformations. For this reason, some Raman essays at different temperatures were made for the sulfates gypsum [CaSO4·2H2O], syngenite [K2Ca(SO4)2·H2O] and görgeyite [K2Ca5(SO4)6·H2O] at high and low temperatures.2. Sample descriptionThe samples gypsum, syngenite and görgeyite used were previously synthesized by García-Florentino et al. [4]. The gypsum and syngenite samples were obtained at room temperature by mixing the adequate liquids containing the ions at concentrations to attain saturation for each salt. Görgeyite was obtained by using hydrothermal conditions (90 ºC during 8 hours) with the appropriate ion concentrations.3. Materials and MethodsThe sulfate synthesized samples [4] were analyzed at spot sizes of 50 microns using a Renishaw inVia micro-Raman spectrometer, equipped with the 532 nm excitation laser and a highly sensitive CCD detector, with a mean spectral resolution of 1 cm-1. The spectrometer was coupled to a temperature-controlled stage THMS600/HFS600 Linkam Scientific Instrument (UK) for the automatic control of the measurement temperature. The high temperature program used consisted of an increment of 20 ºC.min-1 up to 400 ºC. Whereas the low temperature program consisted of a decrease of 10 ºC.min-1 up to -100 ºC. Each ramp was followed by a one-minute hold to allow the stabilization of the mineral phase under study. And the spectra were collected both at the end of the ramp and at the end of the hold4. Results and DiscussionAs a consequence of the temperature increase, the shift to lower or higher wavenumbers of the main Raman bands were observed in all the spectra. However, the drop in temperature did not cause any shift in the position of the sulfate Raman bands although changes in the form of the Raman bands were observed. Therefore, the following features were noted:Gypsum. The transition from gypsum to anhydrite III (AIII) at a temperature of 180 ºC was observed. The transformation was detected by the shift of the 1008 cm-1 main Raman band to 1025 cm-1 and together with the disappearance of the hydration bands. The AIII form is metastable, reaching its stable form (Anhydrite II and I) above 800 ºC [5]. Although the AI/II could not be completely isolated because the experiment only reached 400 ºC, the presence of both compounds can be easily observed by a deconvolution of the main Raman band collected at 400 ºC, obtaining the bands at 1017 and 1025 cm-1, the main Raman bands of AI/II and AIII, respectively.When temperature decreases, the Raman bands due to the sulfate modes do not change. However, the two water bands at 3405 and 3487 cm-1 change in shape (both are more thin when temperature increases) but not in the wavenumber of the maximum.Syngenite. This compound is stable when temperature increases until 100 ºC where the transformation to soluble anhydrite starts. Anhydrite(III) was not obtained in pure form, suggesting a kinetic control of the dehydration process. Above 360 ºC the main Raman band of anhydrite I/II (1017 cm-1) is observed. In addition, from 380 ºC the 981 cm-1 and all the hydration bands disappeared, because the syngenite suffered the transformation to arcanite [K2SO4] and langbeinite [K2Ca2(SO4)3], which main Raman bands are located at 985 and 978 cm-1, respectively [6].The temperature decrease do not affect the maximum of any bands of syngenite. However, the broad water band at room temperature is splitted in two bands at 3107 and 3298 cm-1 when temperature decreases below -40 ºC, being both more thinner when temperature continues decreasing.Görgeyite. Above 160 ºC the görgeyite Raman band at 1012 cm-1 decreased, due to the fact that part of this sulfate was transformed to syngenite (980 cm-1) and gypsum (1007 cm-1). The corresponding bands due to the crystallized water also decreased.The temperature decrease do not affect Raman bands related to sulfate modes, but the broad water band at room temperature splits at

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.

To investigate the effects of environment, composition, and crystal orientation on incipient surface alteration of forsterite and fayalite in a natural environment, polycrystalline forsterite and fayalite samples were emplaced in Mg/Fe-rich and Al-poor ultramafic soils under subarctic (Tablelands in Newfoundland, Canada; 3.9 ⁰C and ∼120 cm precipitation/year), Mediterranean (Klamath Mountains, California;≤12.8 ⁰C and ∼101-118 cm precipitation/year), and desert (Pickhandle Gulch, Nevada; ∼14.1 ⁰C and dry ∼14.4 cm/year) climates for one year. Incipient alteration after one year was examined using scanning electron microscopy, atomic force microscopy, electron backscatter diffraction, X-ray photoelectron spectroscopy, and visible and near-infrared reflectance spectroscopy.Alteration features on forsterite surfaces included flat-bottomed pits with steeply dipping walls likely developing on grain faces and representing surface retreat of individual grains and lining features likely developing along grain boundaries. Mg-leached surface layers formed under acidic to slightly alkaline conditions while Mg-enrichment was observed under alkaline conditions. Flat bottomed pit formation preferentially occurs on surfaces within 30° of perpendicular to the b-axis (on the [010] plane) of the olivine crystal lattice. Depth of flat-bottomed pits on forsterite surfaces follows the order Klamath Mountains > Tablelands >> Pickhandle Gulch, reflecting the importance of the climatic conditions. Warm, wet, and relatively acidic conditions enhanced forsterite dissolution over cold, wet, and slightly alkaline conditions, with minimal alteration observed under hot but arid and alkaline conditions. Greater surface roughness on flat-bottomed pit floors on Klamath Mountain forsterite surfaces are consistent with less-saturated soil-pore water reaction conditions.In contrast, fayalite disks buried in the Klamath Mountains show no evidence for etch-pit formation despite the warm, wet, and slightly acidic conditions. Elevated Fe/Si ratios from X-ray photoelectron spectroscopy measurements and evidence of M-OH bonds in visual and near infrared spectra are consistent with formation of a Fe-enriched hydroxylated layer limiting fayalite surface area available for water-rock interaction and retarding fayalite dissolution during aqueous alteration under oxidizing conditions. These results differ from previous laboratory experiments that show enhanced dissolution of fayalite relative to forsterite, showing the effect of natural, oxic, unsaturated weathering zones. These results will be helpful for interpreting observations of this widely studied mineral, including from the planet Mars.