Identification of carbonate-rich outcrops on Mars by the Spirit rover

Searching for Life in Hot Spring Carbonate Systems: Investigating Raman Spectra of Carotenoid-Bearing Organic Carbonaceous Inclusions from Travertines of Italy

Carotenoid pigments provide some of the most common exclusively biogenic markers on Earth, and these organic pigments may be present in extraterrestrial life. Raman spectroscopy can be used to identify carotenoids quickly and accurately through the inelastic scattering of laser light. In this study, we show that Raman spectra of organic matter found in hot spring bacterial assemblages exhibit "spectral overprinting" of the carotenoid spectrum by the carbon spectrum as the organic matter progressively breaks down. Here, we present how, with increasing thermal maturity, the relative intensity of the carotenoid spectrum increases, and as maturity increases a low-intensity carbon spectrum forms in the same region as the carotenoid spectrum. This carbon spectrum increases in intensity as the thermal maturity increases further, progressively obscuring the carotenoid spectrum until only the carbon spectrum can be observed. This means key carotenoid biogenic signatures in hot spring deposits may be hidden within carbon spectra. A detailed study of the transition from carotenoid to carbon, Raman spectra may help develop deconvolution processes that assist in positively identifying biogenic carbon over abiogenic carbon. Our results are relevant for the data analysis from the Raman spectroscopy instruments on the Perseverance (National Aeronautics and Space Administration [NASA]) and Rosalind Franklin (European Space Agency [ESA]) rovers.

Bacterial templated carbonate mineralization: insights from concave-type crystals induced by Curvibacter lanceolatus strain HJ-1

The elucidation of carbonate crystal growth mechanisms contributes to a deeper comprehension of microbial-induced carbonate precipitation processes. In this research, the Curvibacter lanceolatus HJ-1 strain, well-known for its proficiency in inducing carbonate mineralization, was employed to trigger the formation of concave-type carbonate minerals. The study meticulously tracked the temporal alterations in the culture solution and conducted comprehensive analyses of the precipitated minerals' mineralogy and morphology using advanced techniques such as X-ray diffraction, scanning electron microscopy, focused ion beam, and transmission electron microscopy. The findings unequivocally demonstrate that concave-type carbonate minerals are meticulously templated by bacterial biofilms and employ calcified bacteria as their fundamental structural components. The precise morphological evolution pathway can be delineated as follows: initiation with the formation of bacterial biofilms, followed by the aggregation of calcified bacterial clusters, ultimately leading to the emergence of concave-type minerals characterized by disc-shaped, sunflower-shaped, and spherical morphologies.

Multitechnique characterization of secondary minerals near HI-SEAS, Hawaii, as Martian subsurface analogues

Secondary minerals in lava tubes on Earth provide valuable insight into subsurface processes and the preservation of biosignatures on Mars. Inside lava tubes near the Hawaii-Space Exploration and Analog Simulation (HI-SEAS) habitat on the northeast flank of Mauna Loa, Hawaii, a variety of secondary deposits with distinct morphologies were observed consisting of mainly sodium sulphate powders, gypsum crystalline crusts, and small coralloid speleothems that comprise opal and calcite layers. These secondary deposits formed as a result of hydrological processes shortly after the formation and cooling of the lava tubes and are preserved over long periods of time in relatively dry conditions. The coralloid speleothem layers are likely related to wet and dry periods in which opal and calcite precipitates in cycles. Potential biosignatures seem to have been preserved in the form of porous stromatolite-like layers within the coralloid speleothems. Similar secondary deposits and lava tubes have been observed abundantly on the Martian surface suggesting similar formation mechanisms compared to this study. The origin of secondary minerals from tholeiitic basalts together with potential evidence for microbial processes make the lava tubes near HI-SEAS a relevant analog for Martian surface and subsurface environments.

Microbial Ecosystems in Movile Cave: An Environment of Extreme Life

Movile Cave, situated in Romania close to the Black Sea, constitutes a distinct and challenging environment for life. Its partially submerged ecosystem depends on chemolithotrophic processes for its energetics, which are fed by a continuous hypogenic inflow of mesothermal waters rich in reduced chemicals such as hydrogen sulfide and methane. We sampled a variety of cave sublocations over the course of three years. Furthermore, in a microcosm experiment, minerals were incubated in the cave waters for one year. Both endemic cave samples and extracts from the minerals were subjected to 16S rRNA amplicon sequencing. The sequence data show specific community profiles in the different subenvironments, indicating that specialized prokaryotic communities inhabit the different zones in the cave. Already after one year, the different incubated minerals had been colonized by specific microbial communities, indicating that microbes in Movile Cave can adapt in a relatively short timescale to environmental opportunities in terms of energy and nutrients. Life can thrive, diversify and adapt in remote and isolated subterranean environments such as Movile Cave.

Influence of pH and salts on DMF-DMA derivatization for future Space Applications

For gas chromatography - mass spectrometry (GC-MS) analyses performed in situ, pH and salts (e.g., chlorides, sulfates) may enhance or inhibit the detection of targeted molecules of interest for astrobiology (e.g. amino acids, fatty acids, nucleobases). Obviously, salts influence the ionic strength of the solutions, the pH value, and the salting effect. But the presence of salts may also produce complexes or mask ions in the sample (masking effect on hydroxide ion, ammonia, etc.). For future space missions, wet chemistry will be conducted before GC-MS analyses to detect the full organic content of a sample. The defined organic targets for space GC-MS instrument requirements are generally strongly polar or refractory organic compounds, such as amino acids playing a role in the protein production and metabolism regulations for life on Earth, nucleobases essential for DNA and RNA formation and mutation, and fatty acids that composed most of the eukaryote and prokaryote membranes on Earth and resist to environmental stress long enough to still be observed on Mars or ocean worlds in geological well-preserved records. The wet-chemistry chemical treatment consists of reacting an organic reagent with the sample to extract and volatilize polar or refractory organic molecules (i.e. dimethylformamide dimethyl acetal (DMF-DMA) in this study). DMF-DMA derivatizes functional groups with labile H in organics, without modifying their chiral conformation. The influence of pH and salt concentration of extraterrestrial materials on the DMF-DMA derivatization remains understudied. In this research, we studied the influence of different salts and pHs on the derivatization of organic molecules of astrobiological interest with DMF-DMA, such as amino acids, carboxylic acids, and nucleobases. Results show that salts and pH influence the derivatization yield, and that their effect depend on the nature of the organics and the salts studied. Second, monovalent salts lead to a higher or similar organic recovery compared to divalent salts regardless of pH below 8. However, a pH above 8 inhibits the DMF-DMA derivatization influencing the carboxylic acid function to become an anionic group without labile H. Overall, considering the negative effect of the salts on the detection of organic molecules, future space missions may have to consider a desalting step prior to derivatization and GC-MS analyses.

Carbonate precipitation and nitrogen fixation in AMG (Artificial Martian Ground) by cyanobacteria

This article describes experiments performed to study the survival, growth, specific adaptations and bioremediation potential of certain extreme cyanobacteria strains within a simulation of the atmospheric composition, temperature and pressure expected in a future Martian greenhouse. Initial species have been obtained from Mars-analogue sites in Georgia. The results clearly demonstrate that specific biochemical adaptations allow these autotrophs to metabolize within AMG (Artificial Martian Ground) and accumulate biogenic carbon and nitrogen. These findings may thus contribute to the development of future Martian agriculture, as well as other aspects of the life-support systems at habitable Mars stations. The study shows that carbonate precipitation and nitrogen fixation, performed by cyanobacterial communities thriving within the simulated Martian greenhouse conditions, are cross-linked biological processes. At the same time, the presence of the perchlorates (at low concentrations) in the Martian ground may serve as the initial source of oxygen and, indirectly, hydrogen via photo-Fenton reactions. Various carbonates, ammonium and nitrate salts were obtained as the result of these experiments. These affect the pH, salinity and solubility of the AMG and its components, and so the AMG's scanty biogenic properties improved, which is essential for the sustainable growth of the agricultural crops. Therefore, the use of microorganisms for the biological remediation and continuous in situ fertilization of Artificial Martian Ground is possible.

Environmental and Mineralogical Controls on Biosignature Preservation in Magnesium Carbonate Systems Analogous to Jezero Crater, Mars

Jezero Crater on Mars is a paleolacustrine environment where Mg-carbonates may host evidence of ancient life. To elucidate the environmental and mineralogical controls on biosignature preservation, we examined samples from five terrestrial analogs: Lake Salda (Turkey), Lake Alchichica (Mexico), Qinghai-Tibetan Plateau (China), Mg-carbonate playas (British Columbia, Canada), and a mine with fine-grained ultramafic tailings (Yukon, Canada). The mineralogical compositions of the samples varied, yet were often dominated by either aragonite (CaCO₃) or hydromagnesite [Mg₅(CO₃)₄(OH)₂·4H₂O]. Aragonite-rich samples from Alchichica, Mg-carbonate playas, and the ultramafic mine contained an abundance of entombed microbial biomass, including organic structures that resembled cells, whereas hydromagnesite-rich samples were devoid of microfossils. Aragonite often precipitates subaqueously where microbes thrive, thereby increasing the likelihood of biomass entombment, while hydrated Mg-carbonates typically form by evaporation in subaerial settings where biofilms are less prolific. Magnesite (MgCO₃), the most stable Mg-carbonate, forms extremely slowly, which may limit the capture of biosignatures. Hydrated Mg-carbonates are prone to transformation via coupled dissolution-precipitation reactions that may expose biosignatures to degradation. Although less abundant, aragonite is commonly found in Mg-carbonate environments and is a better medium for biosignature preservation due to its fast precipitation rates and relative stability, as well as its tendency to form subaqueously and lithify. Consequently, we propose that aragonite be considered a valuable exploration target on Mars.

Thermal Stability of (Bio)Carbonates: A Potential Signature for Detecting Life on Mars?

The environmental conditions that prevail on the surface of Mars (i.e., high levels of radiation and oxidants) are not favorable for the long-term preservation of organic compounds on which all strategies for finding life on Mars have been based to date. Since life commonly produces minerals that are considered more resilient, the search for biominerals could constitute a promising alternative approach. Carbonates are major biominerals on Earth, and although they have not been detected in large amounts at the martian surface, recent observations show that they could constitute a significant part of the inorganic component in the martian soil. Previous studies have shown that calcite and aragonite produced by eukaryotes thermally decompose at temperatures 15°C lower than those of their abiotic counterparts. By using carbonate concretions formed by microorganisms, we find that natural and experimental carbonates produced by prokaryotes decompose at 28°C below their abiotic counterparts. The study of this sample set serves as a proof of concept for the differential thermal analysis approach to distinguish abiotic from bio-related carbonates. This difference in carbonate decomposition temperature can be used as a first physical evidence of life on Mars to be searched by in situ space exploration missions with the resolution and the technical constraints of the available onboard instruments.

Aqueous alteration processes in Jezero crater, Mars-implications for organic geochemistry

The Perseverance rover landed in Jezero crater, Mars, in February 2021. We used the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument to perform deep-ultraviolet Raman and fluorescence spectroscopy of three rocks within the crater. We identify evidence for two distinct ancient aqueous environments at different times. Reactions with liquid water formed carbonates in an olivine-rich igneous rock. A sulfate-perchlorate mixture is present in the rocks, which probably formed by later modifications of the rocks by brine. Fluorescence signatures consistent with aromatic organic compounds occur throughout these rocks and are preserved in minerals related to both aqueous environments.

Nitrogen Incorporation in Potassic and Micro- and Meso-Porous Minerals: Potential Biogeochemical Records and Targets for Mars Sampling

We measured the N concentrations and isotopic compositions of 44 samples of terrestrial potassic and micro- and meso-porous minerals and a small number of whole-rocks to determine the extent to which N is incorporated and stored during weathering and low-temperature hydrothermal alteration in Mars surface/near-surface environments. The selection of these minerals and other materials was partly guided by the study of altered volcanic glass from Antarctica and Iceland, in which the incorporation of N as NH₄⁺ in phyllosilicates is indicated by correlated concentrations of N and the LILEs (i.e., K, Ba, Rb, Cs), with scatter likely related to the presence of exchanged, occluded/trapped, or encapsulated organic/inorganic N occurring within structural cavities (e.g., in zeolites). The phyllosilicates, zeolites, and sulfates analyzed in this study contain between 0 and 99,120 ppm N and have δ¹⁵N_air values of -34‰ to +65‰. Most of these minerals, and the few siliceous hydrothermal deposits that were analyzed, have δ¹⁵N consistent with the incorporation of biologically processed N during low-temperature hydrothermal or weathering processes. Secondary ion mass spectrometry on altered hyaloclastites demonstrates the residency of N in smectites and zeolites, and silica. We suggest that geological materials known on Earth to incorporate and store N and known to be abundant at, or near, the surface of Mars should be considered targets for upcoming Mars sample return with the intent to identify any signs of ancient or modern life.

An olivine cumulate outcrop on the floor of Jezero crater, Mars

The geological units on the floor of Jezero crater, Mars, are part of a wider regional stratigraphy of olivine-rich rocks, which extends well beyond the crater. We investigate the petrology of olivine and carbonate-bearing rocks of the Séítah formation in the floor of Jezero. Using multispectral images and x-ray fluorescence data, acquired by the Perseverance rover, we performed a petrographic analysis of the Bastide and Brac outcrops within this unit. We find that these outcrops are composed of igneous rock, moderately altered by aqueous fluid. The igneous rocks are mainly made of coarse-grained olivine, similar to some Martian meteorites. We interpret them as an olivine cumulate, formed by settling and enrichment of olivine through multi-stage cooling of a thick magma body.

Spectroscopic study of terrestrial analogues to support rover missions to Mars - A Raman-centred review

The 2020s could be called, with little doubt, the "Mars decade". No other period in space exploration history has experienced such interest in placing orbiters, rovers and landers on the Red Planet. In 2021 alone, the Emirates' first Mars Mission (the Hope orbiter), the Chinese Tianwen-1 mission (orbiter, lander and rover), and NASA's Mars 2020 Perseverance rover reached Mars. The ExoMars mission Rosalind Franklin rover is scheduled for launch in 2022. Beyond that, several other missions are proposed or under development. Among these, MMX to Phobos and the very important Mars Sample Return can be cited. One of the key mission objectives of the Mars 2020 and ExoMars 2022 missions is the detection of traces of potential past or present life. This detection relies to a great extent on the analytical results provided by complementary spectroscopic techniques. The development of these novel instruments has been carried out in step with the analytical study of terrestrial analogue sites and materials, which serve to test the scientific capabilities of spectroscopic prototypes while providing crucial information to better understand the geological processes that could have occurred on Mars. Being directly involved in the development of three of the first Raman spectrometers to be validated for space exploration missions (Mars 2020/SuperCam, ExoMars/RLS and RAX/MMX), the present review summarizes some of the most relevant spectroscopy-based analyses of terrestrial analogues carried out over the past two decades. Therefore, the present work describes the analytical results gathered from the study of some of the most distinctive terrestrial analogues of Martian geological contexts, as well as the lessons learned mainly from ExoMars mission simulations conducted at representative analogue sites. Learning from the experience gained in the described studies, a general overview of the scientific outcome expected from the spectroscopic system developed for current and forthcoming planetary missions is provided.

Characteristics, Origins, and Biosignature Preservation Potential of Carbonate-Bearing Rocks Within and Outside of Jezero Crater

Carbonate minerals have been detected in Jezero crater, an ancient lake basin that is the landing site of the Mars 2020 Perseverance rover, and within the regional olivine-bearing (ROB) unit in the Nili Fossae region surrounding this crater. It has been suggested that some carbonates in the margin fractured unit, a rock unit within Jezero crater, formed in a fluviolacustrine environment, which would be conducive to preservation of biosignatures from paleolake-inhabiting lifeforms. Here, we show that carbonate-bearing rocks within and outside of Jezero crater have the same range of visible-to-near-infrared carbonate absorption strengths, carbonate absorption band positions, thermal inertias, and morphologies. Thicknesses of exposed carbonate-bearing rock cross-sections in Jezero crater are ∼75-90 m thicker than typical ROB unit cross-sections in the Nili Fossae region, but have similar thicknesses to ROB unit exposures in Libya Montes. These similarities in carbonate properties within and outside of Jezero crater is consistent with a shared origin for all of the carbonates in the Nili Fossae region. Carbonate absorption minima positions indicate that both Mg- and more Fe-rich carbonates are present in the Nili Fossae region, consistent with the expected products of olivine carbonation. These estimated carbonate chemistries are similar to those in martian meteorites and the Comanche carbonates investigated by the Spirit rover in Columbia Hills. Our results indicate that hydrothermal alteration is the most likely formation mechanism for non-deltaic carbonates within and outside of Jezero crater.

Recognition of Sedimentary Rock Occurrences in Satellite and Aerial Images of Other Worlds—Insights from Mars

Sedimentary rocks provide records of past surface and subsurface processes and environments. The first step in the study of the sedimentary rock record of another world is to learn to recognize their occurrences in images from instruments aboard orbiting, flyby, or aerial platforms. For two decades, Mars has been known to have sedimentary rocks; however, planet-wide identification is incomplete. Global coverage at 0.25–6 m/pixel, and observations from the Curiosity rover in Gale crater, expand the ability to recognize Martian sedimentary rocks. No longer limited to cases that are light-toned, lightly cratered, and stratified—or mimic original depositional setting (e.g., lithified deltas)—Martian sedimentary rocks include dark-toned examples, as well as rocks that are erosion-resistant enough to retain small craters as well as do lava flows. Breakdown of conglomerates, breccias, and even some mudstones, can produce a pebbly regolith that imparts a “smooth” appearance in satellite and aerial images. Context is important; sedimentary rocks remain challenging to distinguish from primary igneous rocks in some cases. Detection of ultramafic, mafic, or andesitic compositions do not dictate that a rock is igneous, and clast genesis should be considered separately from the depositional record. Mars likely has much more sedimentary rock than previously recognized.

Fluorescein Based Three-channel Probe for the Selective and Sensitive Detection of CO32- Ions in an Aqueous Environment and Real Water Samples

We have constructed a novel fluorescein-based fluorescent chemosensor, FL-In, functionalised with an indole moiety and capable of sensing by both the optical "turn-on" and electrochemical detection of carbonate ions (CO₃^2-) in aqueous media. The probe exhibits excellent selectivity and a low detection limit (0.27 µM) regarding carbonate ions by a possible coordination and hydrolysis reaction mechanism. The developed probe successfully detected CO₃^2- ions in different samples of water. Also, in a simple filter paper experiment, we documented its ability to allow the monitoring of CO₃^2- with the naked eye.

Formation of Magnesium Carbonates on Earth and Implications for Mars

Magnesium carbonates have been identified within the landing site of the Perseverance rover mission. This study reviews terrestrial analog environments and textural, mineral assemblage, isotopic, and elemental analyses that have been applied to establish formation conditions of magnesium carbonates. Magnesium carbonates form in five distinct settings: ultramafic rock-hosted veins, the matrix of carbonated peridotite, nodules in soil, alkaline lake, and playa deposits, and as diagenetic replacements within lime-and dolostones. Dominant textures include fine-grained or microcrystalline veins, nodules, and crusts. Microbial influences on formation are recorded in thrombolites, stromatolites, crinkly, and pustular laminites, spheroids, and filamentous microstructures. Mineral assemblages, fluid inclusions, and carbon, oxygen, magnesium, and clumped isotopes of carbon and oxygen have been used to determine the sources of carbon, magnesium, and fluid for magnesium carbonates as well as their temperatures of formation. Isotopic signatures in ultramafic rock-hosted magnesium carbonates reveal that they form by either low-temperature meteoric water infiltration and alteration, hydrothermal alteration, or metamorphic processes. Isotopic compositions of lacustrine magnesium carbonate record precipitation from lake water, evaporation processes, and ambient formation temperatures. Assessment of these features with similar analytical techniques applied to returned Martian samples can establish whether carbonates on ancient Mars were formed at high or low temperature conditions in the surface or subsurface through abiotic or biotic processes. The timing of carbonate formation processes could be constrained by 147Sm-143Nd isochron, U-Pb concordia, 207Pb-206Pb isochron radiometric dating as well as 3He, 21Ne, 22Ne, or 36Ar surface exposure dating of returned Martian magnesium carbonate samples.

Earth-like Habitable Environments in the Subsurface of Mars

In Earth's deep continental subsurface, where groundwaters are often isolated for >10⁶ to 10⁹ years, energy released by radionuclides within rock produces oxidants and reductants that drive metabolisms of non-photosynthetic microorganisms. Similar processes could support past and present life in the martian subsurface. Sulfate-reducing microorganisms are common in Earth's deep subsurface, often using hydrogen derived directly from radiolysis of pore water and sulfate derived from oxidation of rock-matrix-hosted sulfides by radiolytically derived oxidants. Radiolysis thus produces redox energy to support a deep biosphere in groundwaters isolated from surface substrate input for millions to billions of years on Earth. Here, we demonstrate that radiolysis by itself could produce sufficient redox energy to sustain a habitable environment in the subsurface of present-day Mars, one in which Earth-like microorganisms could survive wherever groundwater exists. We show that the source localities for many martian meteorites are capable of producing sufficient redox nutrients to sustain up to millions of sulfate-reducing microbial cells per kilogram rock via radiolysis alone, comparable to cell densities observed in many regions of Earth's deep subsurface. Additionally, we calculate variability in supportable sulfate-reducing cell densities between the martian meteorite source regions. Our results demonstrate that martian subsurface groundwaters, where present, would largely be habitable for sulfate-reducing bacteria from a redox energy perspective via radiolysis alone. We present evidence for crustal regions that could support especially high cell densities, including zones with high sulfide concentrations, which could be targeted by future subsurface exploration missions.

A New Constraint on the Physicochemical Condition of Mars Surface during the Amazonian Epoch Based on Chemical Speciation for Secondary Minerals in Martian Nakhlites

Iddingsite in Martian nakhlites contains various secondary minerals that reflect water–rock interaction on Mars. However, the formation processes of secondary Fe minerals in iddingsite are unclear because they include carbonates precipitated under reductive and alkaline conditions and sulfates that are generally precipitated under oxidative and acidic conditions. Mineral types cannot coexist under equilibrium. Herein, we characterize the carbonate phase of meteorite Yamato 000593 as siderite and Mn-bearing siderite via field-emission electron probe microanalyzer (FE-EPMA). Then, we examined the distribution and speciation of trace Cr and S within the carbonates through synchrotron micro-focused X-ray fluorescence-X-ray absorption fine structure and scanning transmission X-ray microscopy (μ-XRF-XAFS/STXM) analysis to estimate the transition history of Eh-pH conditions during siderite formation to explain the coexistence of carbonate and sulfate phases in the nakhlite vein. Specifically, the distribution and speciation of S in the mesostasis and carbonate phases and the heterogeneous distribution of Mn-FeCO3 incorporating Cr(III) in the carbonate constrain the Eh-pH condition. The conditions and transition of the fluid chemistry determined herein based on speciation of various elements provide a new constraint on the physicochemical condition of the water that altered the nakhlite body during the Amazonian epoch.

Lansoprazole-Based Colorimetric Chemosensor for Efficient Binding and Sensing of Carbonate Ion: Spectroscopy and DFT Studies

The new benzimidazole based receptor Lansoprazole has been used to detect carbonate anion by naked-eye and Uv-Vis spectroscopy. This receptor revealed visual changes withCO 3 2 - anion in ethanol. No detectable color changes were observed upon the addition of any other tested anions. The lansoprazole chemosensor selectively recognizesCO 3 2 - ion over the other interference anions in the ethanol, followed by deprotonation and reflected 1:1 complex formation between the receptor and the carbonate ion. Lansoprazole exhibits splendid selectivity toward carbonate ion via a visible color change from colorless to yellow with a detection limit of 57 μM. The binding mode ofCO 3 2 - to receptor L is supported by Density Functional Theory calculation. Moreover, this receptor shows a practical visible colorimetric test strip for the detection of carbonate ions. The transition states calculation demonstrates the occurrence of reaction from L to L-CO 3 2 - after overcoming an energy barrier of 10.1 kcal/mol, and there is considerable interaction energy between L andCO 3 2 - (94.9 kJ/mol), both of which confirmed that receptor L has high sensitivity and selectivity to the carbonate ion. The theoretical studies were performed to acquire an electronic description of the complexation mechanism byCO 3 2 - as well as to study bonding and structure in the complex. The optimized structures and binding mechanisms were supported with a high correlation and agreement by spectroscopy and DFT calculations.

Stable Isotope Fractionation in a Cold Spring System, Utah, USA: Insights for Sample Selection on Mars

Stable δ¹³C isotope analysis at hot and cold springs suggests that rapid degassing overprints carbon isotopic biosignatures even when microbial activity produces biogenic textures in the minerals. Mineral precipitation and potential biosignature preservation are evaluated at a cold spring system in Ten Mile Graben, Utah, USA, with scanning electron microscopy, X-ray diffraction, and stable carbon isotopes. Putative biogenic mineral habits such as aragonite microspheres and botryoids, and biologic materials (EPS and diatom tests) are abundant in modern mats, but the δ¹³C values are between +2‰ and +7.8‰, consistent with rapid CO₂ degassing reported by other researchers. Multiple factors, however, influence isotopic signatures of mineral precipitates in this spring system, including rapid degassing, preferential microbial uptake of light carbon isotopes via multiple carboxylation pathways, hydrocarbon-charged fluid, and other inherited isotopic signatures in the fluid, particularly from dissolution of older limestones; therefore, it is not likely that this narrow range of isotopic ratios definitively shows an abiotic signature. A fossil vent preserves biogenic mineral habits, but not microbial body fossils. This study highlights the need for novel biosignature detection methods-and an understanding of what an abiotic signature definitively is-as we prepare for sample caching of carbonate rocks by the Mars2020 mission and future sample return.

Laboratory Analysis of Returned Samples from the AMADEE-18 Mars Analog Mission

Between February 1 and 28, 2018, the Austrian Space Forum, in cooperation with the Oman Astronomical Society and research teams from 25 nations, conducted the AMADEE-18 mission, a human-robotic Mars expedition simulation in the Dhofar region in the Sultanate of Oman. As a part of the AMADEE-18 simulated Mars human exploration mission, the Remote Science Support team performed analyses of the Dhofar area (Oman) in an effort to characterize the region as a potential Mars analog site. The main motivation of this research was to study and register selected samples collected by analog astronauts during the AMADEE-18 mission with laboratory analytical methods and techniques comparable with those that are likely to be used on Mars in the future. The 25 samples representing unconsolidated sediments obtained during the simulated mission were studied by using optical microscopy, Raman spectroscopy, X-ray diffraction, laser-induced breakdown spectroscopy, and laser-induced fluorescence spectroscopy. The principal results show the existence of minerals and alteration processes related to volcanism, hydrothermalism, and weathering. The analogy between the Dhofar region and the Eridana Basin region of Mars is clearly noticeable, particularly as an analog for secondary minerals formed in a hydrothermal seafloor volcanic-sedimentary environment. The synergy between the techniques used in the present work provides a solid basis for the geochemical analyses and organic detection in the context of future human-robotic Mars expeditions. AMADEE-18 has been a prime test bed for geoscientific workflows with astrobiological relevance and has provided valuable insights for future space missions.

Synergistic Ground and Orbital Observations of Iron Oxides on Mt. Sharp and Vera Rubin Ridge

Visible/short-wave infrared spectral data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) show absorptions attributed to hematite at Vera Rubin ridge (VRR), a topographic feature on northwest Mt. Sharp. The goals of this study are to determine why absorptions caused by ferric iron are strongly visible from orbit at VRR and to improve interpretation of CRISM data throughout lower Mt. Sharp. These goals are achieved by analyzing coordinated CRISM and in situ spectral data along the Curiosity Mars rover's traverse. VRR bedrock within areas that have the deepest ferric absorptions in CRISM data also has the deepest ferric absorptions measured in situ. This suggests strong ferric absorptions are visible from orbit at VRR because of the unique spectral properties of VRR bedrock. Dust and mixing with basaltic sand additionally inhibit the ability to measure ferric absorptions in bedrock stratigraphically below VRR from orbit. There are two implications of these findings: (1) Ferric absorptions in CRISM data initially dismissed as noise could be real, and ferric phases are more widespread in lower Mt. Sharp than previously reported. (2) Patches with the deepest ferric absorptions in CRISM data are, like VRR, reflective of deeper absorptions in the bedrock. One model to explain this spectral variability is late-stage diagenetic fluids that changed the grain size of ferric phases, deepening absorptions. Curiosity's experience highlights the strengths of using CRISM data for spectral absorptions and associated mineral detections and the caveats in using these data for geologic interpretations and strategic path planning tools.

Water on Mars—A Literature Review

To assess Mars’ potential for both harboring life and providing useable resources for future human exploration, it is of paramount importance to comprehend the water situation on the planet. Therefore, studies have been conducted to determine any evidence of past or present water existence on Mars. While the presence of abundant water on Mars very early in its history is widely accepted, on its modern form, only a fraction of this water can be found, as either ice or locked into the structure of Mars’ plentiful water-rich materials. Water on the planet is evaluated through various evidence such as rocks and minerals, Martian achondrites, low volume transient briny outflows (e.g., dune flows, reactivated gullies, slope streaks, etc.), diurnal shallow soil moisture (e.g., measurements by Curiosity and Phoenix Lander), geomorphic representation (possibly from lakes and river valleys), and groundwater, along with further evidence obtained by probe and rover discoveries. One of the most significant lines of evidence is for an ancient streambed in Gale Crater, implying ancient amounts of “vigorous” water on Mars. Long ago, hospitable conditions for microbial life existed on the surface of Mars, as it was likely periodically wet. However, its current dry surface makes it almost impossible as an appropriate environment for living organisms; therefore, scientists have recognized the planet’s subsurface environments as the best potential locations for exploring life on Mars. As a result, modern research has aimed towards discovering underground water, leading to the discovery of a large amount of underground ice in 2016 by NASA, and a subglacial lake in 2018 by Italian scientists. Nevertheless, the presence of life in Mars’ history is still an open question. In this unifying context, the current review summarizes results from a wide variety of studies and reports related to the history of water on Mars, as well as any related discussions on the possibility of living organism existence on the planet.

Habitability of Hydrothermal Systems at Jezero and Gusev Craters as Constrained by Hydrothermal Alteration of a Terrestrial Mafic Dike

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.

The Case for Ancient Hot Springs in Gusev Crater, Mars

The origin and age of opaline silica deposits discovered by the Spirit rover adjacent to the Home Plate feature in the Columbia Hills of Gusev crater remains debated, in part because of their proximity to sulfur-rich soils. Processes related to fumarolic activity and to hot springs and/or geysers are the leading candidates. Both processes are known to produce opaline silica on Earth, but with differences in composition, morphology, texture, and stratigraphy. Here, we incorporate new and existing observations of the Home Plate region with observations from field and laboratory work to address the competing hypotheses. The results, which include new evidence for a hot spring vent mound, demonstrate that a volcanic hydrothermal system manifesting both hot spring/geyser and fumarolic activity best explains the opaline silica rocks and proximal S-rich materials, respectively. The opaline silica rocks most likely are sinter deposits derived from hot spring activity. Stratigraphic evidence indicates that their deposition occurred before the emplacement of the volcaniclastic deposits comprising Home Plate and nearby ridges. Because sinter deposits throughout geologic history on Earth preserve evidence for microbial life, they are a key target in the search for ancient life on Mars.

Olivine-Carbonate Mineralogy of the Jezero Crater Region

A well-preserved, ancient delta deposit, in combination with ample exposures of carbonate outcrops, makes Jezero Crater in Nili Fossae a compelling astrobiological site. We use Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) observations to characterize the surface mineralogy of the crater and surrounding watershed. Previous studies have documented the occurrence of olivine and carbonates in the Nili Fossae region. We focus on correlations between these two well-studied lithologies in the Jezero crater watershed. We map the position and shape of the olivine 1 μm absorption band and find that carbonates are found in association with olivine which displays a 1 μm band shifted to long wavelengths. We then use Thermal Emission Imaging Spectrometer (THEMIS) coverage of Nili Fossae and perform tests to investigate whether the long wavelength shifted (redshifted) olivine signature is correlated with high thermal inertia outcrops. We find that there is no consistent correlation between thermal inertia and the unique olivine signature. We discuss a range of formation scenarios for the olivine and carbonate associations, including the possibility that these lithologies are products of serpentinization reactions on early Mars. These lithologies provide an opportunity for deepening our understanding of early Mars and, given their antiquity, may provide a framework to study the timing of valley networks and the thermal history of the Martian crust and interior from the early Noachian to today.

The origin of life as a planetary phenomenon

We advocate an integrative approach between laboratory experiments in prebiotic chemistry and geologic, geochemical, and astrophysical observations to help assemble a robust chemical pathway to life that can be reproduced in the laboratory. The cyanosulfidic chemistry scenario described here was developed by such an integrative iterative process. We discuss how it maps onto evolving planetary surface environments on early Earth and Mars and the value of comparative planetary evolution. The results indicate that Mars can offer direct evidence for geochemical conditions similar to prebiotic Earth, whose early record has been erased. The Jezero crater is now the chosen landing site for NASA's Mars 2020 rover, making this an extraordinary opportunity for a breakthrough in understanding life's origins.

Infrared Spectroscopic Detection of Biosignatures at Lake Tírez, Spain: Implications for Mars

The detection of potential biosignatures with mineral matrices is part of a multifaceted approach in the search for life on other planetary bodies. The 2020 ExoMars Rosalind Franklin rover includes within its payload three IR spectrometers in the form of ISEM (Infrared Spectrometer for ExoMars), MicrOmega, and Ma-MISS (Mars Multispectral Imager for Subsurface Studies). The use of this technique in the detection and characterization of biosignatures is of great value. Organic materials are often co-deposited in terrestrial evaporites and as such have been proposed as relevant analogs in the search for life on Mars. This study focuses on Ca-sulfates collected from the hypersaline Tírez Lake in Spain. Mid infrared and visible near infrared analysis of soils, salt crusts, and crystals with green and red layering indicative of microbial colonization of the samples was acquired from across the lake and identified the main mineral to be gypsum with inputs of carbonate and silica. Organic functional groups that could be attributed to amides and carboxylic acids were identified as well as chlorophyll; however, due to the strong mineralogical absorptions observed, these were hard to unambiguously discern. Taxonomical assignment demonstrated that the archaeal community within the samples was dominated by the halophilic extremophile Halobacteriaceae while the bacterial community was dominated by the class Nocardiaceae. The results of this research highlight that sulfates on Mars are a mixed blessing, acting as an effective host for organic matter preservation but also a material that masks the presence of organic functional groups when analyzed with spectroscopic tools similar to those due to fly on the 2020 ExoMars rover. A suite of complementary analytical techniques therefore should be used to support the spectral identification of any candidate extraterrestrial biosignatures.

Nucleic Acid Extraction and Sequencing from Low-Biomass Synthetic Mars Analog Soils for In Situ Life Detection

Recent studies regarding the origins of life and Mars-Earth meteorite transfer simulations suggest that biological informational polymers, such as nucleic acids (DNA and RNA), have the potential to provide unambiguous evidence of life on Mars. To this end, we are developing a metagenomics-based life-detection instrument which integrates nucleic acid extraction and nanopore sequencing: the Search for Extra-Terrestrial Genomes (SETG). Our goal is to isolate and sequence nucleic acids from extant or preserved life on Mars in order to determine if a particular genetic sequence (1) is distantly related to life on Earth, indicating a shared ancestry due to lithological exchange, or (2) is unrelated to life on Earth, suggesting convergent origins of life on Mars. In this study, we validate prior work on nucleic acid extraction from cells deposited in Mars analog soils down to microbial concentrations (i.e., 10⁴ cells in 50 mg of soil) observed in the driest and coldest regions on Earth. In addition, we report low-input nanopore sequencing results from 2 pg of purified Bacillus subtilis spore DNA simulating ideal extraction yields equivalent to 1 ppb life-detection sensitivity. We achieve this by employing carrier sequencing, a method of sequencing sub-nanogram DNA in the background of a genomic carrier. After filtering of carrier, low-quality, and low-complexity reads we detected 5 B. subtilis reads, 18 contamination reads (including Homo sapiens), and 6 high-quality noise reads believed to be sequencing artifacts.

Recovery of Fatty Acids from Mineralogic Mars Analogs by TMAH Thermochemolysis for the Sample Analysis at Mars Wet Chemistry Experiment on the Curiosity Rover

The Mars Curiosity rover carries a diverse instrument payload to characterize habitable environments in the sedimentary layers of Aeolis Mons. One of these instruments is Sample Analysis at Mars (SAM), which contains a mass spectrometer that is capable of detecting organic compounds via pyrolysis gas chromatography mass spectrometry (py-GC-MS). To identify polar organic molecules, the SAM instrument carries the thermochemolysis reagent tetramethylammonium hydroxide (TMAH) in methanol (hereafter referred to as TMAH). TMAH can liberate fatty acids bound in macromolecules or chemically bound monomers associated with mineral phases and make these organics detectable via gas chromatography mass spectrometry (GC-MS) by methylation. Fatty acids, a type of carboxylic acid that contains a carboxyl functional group, are of particular interest given their presence in both biotic and abiotic materials. This work represents the first analyses of a suite of Mars-analog samples using the TMAH experiment under select SAM-like conditions. Samples analyzed include iron oxyhydroxides and iron oxyhydroxysulfates, a mixture of iron oxides/oxyhydroxides and clays, iron sulfide, siliceous sinter, carbonates, and shale. The TMAH experiments produced detectable signals under SAM-like pyrolysis conditions when organics were present either at high concentrations or in geologically modern systems. Although only a few analog samples exhibited a high abundance and variety of fatty acid methyl esters (FAMEs), FAMEs were detected in the majority of analog samples tested. When utilized, the TMAH thermochemolysis experiment on SAM could be an opportunity to detect organic molecules bound in macromolecules on Mars. The detection of a FAME profile is of great astrobiological interest, as it could provide information regarding the source of martian organic material detected by SAM.

Exploring, Mapping, and Data Management Integration of Habitable Environments in Astrobiology

New approaches to blending geoscience, planetary science, microbiology-geobiology/ecology, geoinformatics and cyberinfrastructure technology disciplines in a holistic effort can be transformative to astrobiology explorations. Over the last two decades, overwhelming orbital evidence has confirmed the abundance of authigenic (in situ, formed in place) minerals on Mars. On Earth, environments where authigenic minerals form provide a substrate for the preservation of microbial life. Similarly, extraterrestrial life is likely to be preserved where crustal minerals can record and preserve the biochemical mechanisms (i.e., biosignatures). The search for astrobiological evidence on Mars has focused on identifying past or present habitable environments - places that could support some semblance of life. Thus, authigenic minerals represent a promising habitable environment where extraterrestrial life could be recorded and potentially preserved over geologic time scales. Astrobiology research necessarily takes place over vastly different scales; from molecules to viruses and microbes to those of satellites and solar system exploration, but the differing scales of analyses are rarely connected quantitatively. The mismatch between the scales of these observations- from the macro- satellite mineralogical observations to the micro- microbial observations- limits the applicability of our astrobiological understanding as we search for records of life beyond Earth. Each-scale observation requires knowledge of the geologic context and the environmental parameters important for assessing habitability. Exploration efforts to search for extraterrestrial life should attempt to quantify both the geospatial context and the temporal/spatial relationships between microbial abundance and diversity within authigenic minerals at multiple scales, while assimilating resolutions from satellite observations to field measurements to microscopic analyses. Statistical measures, computer vision, and the geospatial synergy of Geographic Information Systems (GIS), can allow analyses of objective data-driven methods to locate, map, and predict where the "sweet spots" of habitable environments occur at multiple scales. This approach of science information architecture or an "Astrobiology Information System" can provide the necessary maps to guide researchers to discoveries via testing, visualizing, documenting, and collaborating on significant data relationships that will advance explorations for evidence of life in our solar system and beyond.

Catalytic/Protective Properties of Martian Minerals and Implications for Possible Origin of Life on Mars

Minerals might have played critical roles for the origin and evolution of possible life forms on Mars. The study of the interactions between the "building blocks of life" and minerals relevant to Mars mineralogy under conditions mimicking the harsh Martian environment may provide key insight into possible prebiotic processes. Therefore, this contribution aims at reviewing the most important investigations carried out so far about the catalytic/protective properties of Martian minerals toward molecular biosignatures under Martian-like conditions. Overall, it turns out that the fate of molecular biosignatures on Mars depends on a delicate balance between multiple preservation and degradation mechanisms, often regulated by minerals, which may take place simultaneously. Such a complexity requires more efforts in simulating realistically the Martian environment in order to better inspect plausible prebiotic pathways and shed light on the nature of the organic compounds detected both in meteorites and on the surface of Mars through in situ analysis.

Towards the colonization of Mars by in-situ resource utilization: Slip cast ceramics from Martian soil simulant

Here we demonstrate that by applying exclusively Martian resources a processing route involving suspensions of mineral particles called slurries or slips can be established for manufacturing ceramics on Mars. We developed water-based slurries without the use of additives that had a 51 wt. % solid load resembling commercial porcelain slurries in respect to the particle size distribution and rheological properties. These slurries were used to slip cast discs, rings and vases that were sintered at temperatures between 1000 and 1130 °C using different sintering schedules, the latter were set-up according the results of hot-stage microscopic characterization. The microstructure, porosity and the mechanical properties were characterized by SEM, X-ray computer tomography and Weibull analysis. Our wet processing of minerals yields ceramics with complex shapes that show similar mechanical properties to porcelain and could serve as a technology for future Mars colonization. The best quality parts with completely vitrificated matrix supporting a few idiomorphic crystals are obtained at 1130 °C with 10 h dwell time with volume and linear shrinkage as much as ~62% and ~17% and a characteristic compressive strength of 51 MPa.

Computer-Aided Exploration of the Martian Geology

Motivated by growing amounts of data and enhanced resolution from orbiters and rovers, systems for computer-aided decision support are becoming invaluable in planetary exploration. This article illustrates the value of such systems for a case study on the exploration of the Martian geology, along with improvements in assessing the favorability for landing. Under the current technical status quo for landing and rover's mobility, results show that Eastern Margaritifer Terra and Meridiani Planum stand out due to their high density of scientific targets and flat surfaces. However, our approach allows us to scale the analysis using different scenarios for the entire planet, quantifying the substantial benefits should higher landing elevations and higher rover speeds be realized in the future. This analysis offers new insights into the interplay of technical and scientific constraints.

Optimizing Data Reduction Procedures in Spatial Heterodyne Raman Spectroscopy with Applications to Planetary Surface Analogs

A spatial heterodyne Raman spectrometer (SHRS) is a variant of a Michelson interferometer in which the mirrors of a Michelson are replaced with two stationary diffraction gratings. When light enters the SHRS, it is reflected off of diffraction gratings at frequency-dependent angles that produce crossed wavefronts in space that can be imaged using a plane array detector. The crossed wavefronts, which represent a superposition of interference fringes, are converted to a Raman spectrum upon applying a Fourier transform. In this work, a new approach to intensity calibration is discussed that originates from modeling the shot noise produced by the SHRS and converting the real noise to idealized white noise as predicted by theory. This procedure has two effects. First, the technique produces Raman spectra with white noise. Second, when the mean of the noise is normalized to one, the technique produces Raman spectra where the intensity axis is equivalent to signal-to-noise ratio. The data reduction technique is then applied to the measurement of materials of interest to the planetary science community, including minerals and inorganic salts, at a distance of 5 m from the collecting optic.

A Field Guide to Finding Fossils on Mars

The Martian surface is cold, dry, exposed to biologically harmful radiation and apparently barren today. Nevertheless, there is clear geological evidence for warmer, wetter intervals in the past that could have supported life at or near the surface. This evidence has motivated National Aeronautics and Space Administration and European Space Agency to prioritize the search for any remains or traces of organisms from early Mars in forthcoming missions. Informed by (1) stratigraphic, mineralogical and geochemical data collected by previous and current missions, (2) Earth's fossil record, and (3) experimental studies of organic decay and preservation, we here consider whether, how, and where fossils and isotopic biosignatures could have been preserved in the depositional environments and mineralizing media thought to have been present in habitable settings on early Mars. We conclude that Noachian-Hesperian Fe-bearing clay-rich fluvio-lacustrine siliciclastic deposits, especially where enriched in silica, currently represent the most promising and best understood astropaleontological targets. Siliceous sinters would also be an excellent target, but their presence on Mars awaits confirmation. More work is needed to improve our understanding of fossil preservation in the context of other environments specific to Mars, particularly within evaporative salts and pore/fracture-filling subsurface minerals.

Detecting Kerogen as a Biosignature Using Colocated UV Time-Gated Raman and Fluorescence Spectroscopy

The Mars 2020 mission will analyze samples in situ and identify any that could have preserved biosignatures in ancient habitable environments for later return to Earth. Highest priority targeted samples include aqueously formed sedimentary lithologies. On Earth, such lithologies can contain fossil biosignatures as aromatic carbon (kerogen). In this study, we analyzed nonextracted kerogen in a diverse suite of natural, complex samples using colocated UV excitation (266 nm) time-gated (UV-TG) Raman and laser-induced fluorescence spectroscopies. We interrogated kerogen and its host matrix in samples to (1) explore the capabilities of UV-TG Raman and fluorescence spectroscopies for detecting kerogen in high-priority targets in the search for possible biosignatures on Mars; (2) assess the effectiveness of time gating and UV laser wavelength in reducing fluorescence in Raman spectra; and (3) identify sample-specific issues that could challenge rover-based identifications of kerogen using UV-TG Raman spectroscopy. We found that ungated UV Raman spectroscopy is suited to identify diagnostic kerogen Raman bands without interfering fluorescence and that UV fluorescence spectroscopy is suited to identify kerogen. These results highlight the value of combining colocated Raman and fluorescence spectroscopies, similar to those obtainable by SHERLOC on Mars 2020, to strengthen the confidence of kerogen detection as a potential biosignature in complex natural samples. Key Words: Raman spectroscopy-Laser-induced fluorescence spectroscopy-Mars Sample Return-Mars 2020 mission-Kerogen-Biosignatures. Astrobiology 18, 431-453.

Wind-Driven Erosion and Exposure Potential at Mars 2020 Rover Candidate-Landing Sites

Aeolian processes have likely been the predominant geomorphic agent for most of Mars' history and have the potential to produce relatively young exposure ages for geologic units. Thus, identifying local evidence for aeolian erosion is highly relevant to the selection of landing sites for future missions, such as the Mars 2020 Rover mission that aims to explore astrobiologically relevant ancient environments. Here we investigate wind-driven activity at eight Mars 2020 candidate-landing sites to constrain erosion potential at these locations. To demonstrate our methods, we found that contemporary dune-derived abrasion rates were in agreement with rover-derived exhumation rates at Gale crater and could be employed elsewhere. The Holden crater candidate site was interpreted to have low contemporary erosion rates, based on the presence of a thick sand coverage of static ripples. Active ripples at the Eberswalde and southwest Melas sites may account for local erosion and the dearth of small craters. Moderate-flux regional dunes near Mawrth Vallis were deemed unrepresentative of the candidate site, which is interpreted to currently be experiencing low levels of erosion. The Nili Fossae site displayed the most unambiguous evidence for local sand transport and erosion, likely yielding relatively young exposure ages. The downselected Jezero crater and northeast Syrtis sites had high-flux neighboring dunes and exhibited substantial evidence for sediment pathways across their ellipses. Both sites had relatively high estimated abrasion rates, which would yield young exposure ages. The downselected Columbia Hills site lacked evidence for sand movement, and contemporary local erosion rates are estimated to be relatively low.

Smectite formation in the presence of sulfuric acid: Implications for acidic smectite formation on early Mars

The excess of orbital detection of smectite deposits compared to carbonate deposits on the martian surface presents an enigma because smectite and carbonate formations are both favored alteration products of basalt under neutral to alkaline conditions. We propose that Mars experienced acidic events caused by sulfuric acid (H2SO4) that permitted phyllosilicate, but inhibited carbonate, formation. To experimentally verify this hypothesis, we report the first synthesis of smectite from Mars-analogue glass-rich basalt simulant (66 wt% glass, 32 wt% olivine, 2 wt% chromite) in the presence of H2SO4 under hydrothermal conditions (~200 °C). Smectites were analyzed by X-ray diffraction, Mossbauer spectroscopy, visible and near-infrared reflectance spectroscopy and electron microprobe to characterize mineralogy and chemical composition. Solution chemistry was determined by Inductively Coupled Plasma Mass Spectrometry. Basalt simulant suspensions in 11-42 mM H2SO4 were acidic with pH ≤ 2 at the beginning of incubation and varied from acidic (pH 1.8) to mildly alkaline (pH 8.4) at the end of incubation. Alteration of glass phase during reaction of the basalt simulant with H2SO4 led to formation of the dioctahedral smectite at final pH ~3 and trioctahedral smectite saponite at final pH ~4 and higher. Anhydrite and hematite formed in the final pH range from 1.8 to 8.4 while natroalunite was detected at pH 1.8. Hematite was precipitated as a result of oxidative dissolution of olivine present in Adirondack basalt simulant. Formation of secondary phases, including smectite, resulted in release of variable amounts of Si, Mg, Na and Ca while solubilization of Al and Fe was low. Comparison of mineralogical and solution chemistry data indicated that the type of smectite (i.e., dioctahedral vs trioctahedral) was likely controlled by Mg leaching from altering basalt and substantial Mg loss created favorable conditions for formation of dioctahedral smectite. We present a model for global-scale smectite formation on Mars via acid-sulfate conditions created by the volcanic outgassing of SO2 in the Noachian and early Hesperian.

The Influence of Mineral Matrices on the Thermal Behavior of Glycine

On the Hadean-Early Archean Earth, the first islands must have provided hot and dry environments for abiotically formed organic molecules. The heat sources, mainly volcanism and meteorite impacts, were also available on Mars during the Noachian period. In recent work simulating this scenario, we have shown that neat glycine forms a black, sparingly water-soluble polymer ("thermomelanoid") when dry-heated at 200 °C under pure nitrogen. The present study explores whether relevant minerals and mineral mixtures can change this thermal behavior. Most experiments were conducted at 200 or 250 °C for 2 or 7 days. The mineral matrices used were phyllosilicates (Ca-montmorillonites SAz-1 and STx-1, Na-montmorillonite SAz-1-Na, nontronite NAu-1, kaolinite KGa-1), salts (NaCl, NaCl-KCl, CaCl2, artificial sea salt, gypsum, magnesite), picritic basalt, and three Martian regolith simulants (P-MRS, S-MRS, JSC Mars-1A). The main analytical method employed was high-performance liquid chromatography (HPLC). Glycine intercalated in SAz-1 and SAz-1-Na was well protected against thermomelanoid formation and sublimation at 200 °C: after 2 days, 95 and 79 %, respectively, had either survived unaltered or been transformed into the cyclic dipeptide (DKP) and linear peptides up to Gly6. The glycine survival rate followed the order SAz-1 > SAz-1-Na > STx-1 ≈ NAu-1 > KGa-1. Very good protection was also provided by artificial sea salt (84 % unaltered glycine after 200 °C for 7 days). P-MRS promoted the condensation up to Gly6, consistent with its high phyllosilicate content. The remaining matrices were less effective in preserving glycine as such or as peptides.

Exploring Fingerprints of the Extreme Thermoacidophile Metallosphaera sedula Grown on Synthetic Martian Regolith Materials as the Sole Energy Sources

The biology of metal transforming microorganisms is of a fundamental and applied importance for our understanding of past and present biogeochemical processes on Earth and in the Universe. The extreme thermoacidophile Metallosphaera sedula is a metal mobilizing archaeon, which thrives in hot acid environments (optimal growth at 74°C and pH 2.0) and utilizes energy from the oxidation of reduced metal inorganic sources. These characteristics of M. sedula make it an ideal organism to further our knowledge of the biogeochemical processes of possible life on extraterrestrial planetary bodies. Exploring the viability and metal extraction capacity of M. sedula living on and interacting with synthetic extraterrestrial minerals, we show that M. sedula utilizes metals trapped in the Martian regolith simulants (JSC Mars 1A; P-MRS; S-MRS; MRS07/52) as the sole energy sources. The obtained set of microbiological and mineralogical data suggests that M. sedula actively colonizes synthetic Martian regolith materials and releases free soluble metals. The surface of bioprocessed Martian regolith simulants is analyzed for specific mineralogical fingerprints left upon M. sedula growth. The obtained results provide insights of biomining of extraterrestrial material as well as of the detection of biosignatures implementing in life search missions.

Vaterite induced by Lysinibacillus sp. GW-2 strain and its stability

Studies on the formation and stability of vaterite by bacteria in experimental systems are of great importance for understanding the mechanism by which microbes contribute to carbonate mineralization. In this study, mineralization experiments using Lysinibacillus sp. strain GW-2 were carried out for 72h under shaking conditions and aging experiments using biotic and chemically synthesized vaterite were performed for 60days in distilled water and air. Our results indicate that Lysinibacillus sp. strain GW-2 can induce the formation of vaterite with spherical morphology from an amorphous calcium carbonate precursor. Biogenic vaterite was more stable than chemically synthesized vaterite in distilled water, perhaps due to organic matter secreted by bacteria that enwrapped the vaterite and prevented it from transforming into more stable phases. Infrared spectrophotometry of biogenic and chemically synthesized vaterite confirmed the presence of organic matter in biogenic vaterite.

The WISDOM Radar: Unveiling the Subsurface Beneath the ExoMars Rover and Identifying the Best Locations for Drilling

The search for evidence of past or present life on Mars is the principal objective of the 2020 ESA-Roscosmos ExoMars Rover mission. If such evidence is to be found anywhere, it will most likely be in the subsurface, where organic molecules are shielded from the destructive effects of ionizing radiation and atmospheric oxidants. For this reason, the ExoMars Rover mission has been optimized to investigate the subsurface to identify, understand, and sample those locations where conditions for the preservation of evidence of past life are most likely to be found. The Water Ice Subsurface Deposit Observation on Mars (WISDOM) ground-penetrating radar has been designed to provide information about the nature of the shallow subsurface over depth ranging from 3 to 10 m (with a vertical resolution of up to 3 cm), depending on the dielectric properties of the regolith. This depth range is critical to understanding the geologic evolution stratigraphy and distribution and state of subsurface H₂O, which provide important clues in the search for life and the identification of optimal drilling sites for investigation and sampling by the Rover's 2-m drill. WISDOM will help ensure the safety and success of drilling operations by identification of potential hazards that might interfere with retrieval of subsurface samples. Key Words: Ground penetrating radar—Martian shallow subsurface—ExoMars. Astrobiology 17, 565–584.