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The Committee on Space Research (COSPAR) Sample Safety Assessment Framework (SSAF) has been developed by a COSPAR appointed Working Group. The objective of the sample safety assessment would be to evaluate whether samples returned from Mars could be harmful for Earth's systems (e.g., environment, biosphere, geochemical cycles). During the Working Group's deliberations, it became clear that a comprehensive assessment to predict the effects of introducing life in new environments or ecologies is difficult and practically impossible, even for terrestrial life and certainly more so for unknown extraterrestrial life. To manage expectations, the scope of the SSAF was adjusted to evaluate only whether the presence of martian life can be excluded in samples returned from Mars. If the presence of martian life cannot be excluded, a Hold & Critical Review must be established to evaluate the risk management measures and decide on the next steps. The SSAF starts from a positive hypothesis (there is martian life in the samples), which is complementary to the null-hypothesis (there is no martian life in the samples) typically used for science. Testing the positive hypothesis includes four elements: (1) Bayesian statistics, (2) subsampling strategy, (3) test sequence, and (4) decision criteria. The test sequence capability covers self-replicating and non-self-replicating biology and biologically active molecules. Most of the investigations associated with the SSAF would need to be carried out within biological containment. The SSAF is described in sufficient detail to support planning activities for a Sample Receiving Facility (SRF) and for preparing science announcements, while at the same time acknowledging that further work is required before a detailed Sample Safety Assessment Protocol (SSAP) can be developed. The three major open issues to be addressed to optimize and implement the SSAF are (1) setting a value for the level of assurance to effectively exclude the presence of martian life in the samples, (2) carrying out an analogue test program, and (3) acquiring relevant contamination knowledge from all Mars Sample Return (MSR) flight and ground elements. Although the SSAF was developed specifically for assessing samples from Mars in the context of the currently planned NASA-ESA MSR Campaign, this framework and the basic safety approach are applicable to any other Mars sample return mission concept, with minor adjustments in the execution part related to the specific nature of the samples to be returned. The SSAF is also considered a sound basis for other COSPAR Planetary Protection Category V, restricted Earth return missions beyond Mars. It is anticipated that the SSAF will be subject to future review by the various MSR stakeholders.

Carbonate rocks record the oldest forms of life on Earth, and their geologic reconstruction requires multiple methods to determine physical and chemical processes before conclusions of ancient biosignatures are made. Since crystal orientation within rock fabric may be used to infer geologic settings, we present here a complementary Raman method to study the orientation of calcite (CaCO(3)) and dolomite [CaMg (CO(3))(2)] minerals. The relative peak intensity ratio of the carbonate lattice E(g) modes T and L reveals the crystallographic orientation of calcite and dolomite with respect to the incident light polarization. Our results for calcite show that when the incident laser light propagates down the crystallographic a/b axis: (1) the L mode is always greater in intensity than the T mode (I(T) < I(L)), and (2) the spectra are most intense at 45° and least intense at 90° polarization angles measured from around the c axis. Our results for dolomite show that (1) I(T) > I(L) when the incident light propagation is down the crystallographic c axis and (2) I(T) < I(L) when the incident light propagation is down the crystallographic a/b axis. This study reveals mineral orientation variation related to deposition and paragenesis within limestone and dolostone samples. The method presented yields information related to growth and deformation during diagenetic and metamorphic alteration and may be used in research seeking to identify the fabric parameters of any calcite or dolomite containing rock. The compositional and structural data obtained from Raman mapping is useful in structural geology, materials science, and biosignature research.

Airborne microplastics (MPs) could have negative impacts on human health and pollute water, soil, and sediment. This study explored the distributions, compositions, and morphology of airborne microplastics in the indoor and ambient air in New Jersey, United States. Microplastic fibers, films, and fragments of Polystyrene (PS), Polyethylene terephthalate (PET), Polyethyelene (PE), Polyvinyl chloride (PVC) and Polypropylene (PP) were identified in office, hallway, classroom, and single-family house in this study. The deposition rates of synthetic fibers with length from 35 μm to 1000 μm were highest in the single-family house ((1.96 ± 1.09) × 104 fibers/m2/day) and lowest in the classroom ((6.20 ± 0.57) × 103 fibers/m2/day), suggesting that residential houses are a major source of microplastic fibers. However, for film-like plastics with surface areas ranging from 200 μm2 to 5000 μm2, a high deposition rate of (8.13 ± 2.17) × 103 films/m2/day was observed in the classroom, whereas the lowest deposition rate of (4.45 ± 0.27) × 103 films/m2/day was found in the hallway, probably because plastic films such as PE are intensively used in the classroom environments. The deposition rate of microplastics in the ambient air acquired on a building roof was only about 2–8% of the indoor deposition rates. The microplastics with similar textures but different sizes were identified in both total atmospheric deposition and particulate samples (PM2.5 and PM10), suggesting degradation from microplastics to nanoplastics. The main microplastics found in indoor air samples were PE fragments or fibers, different from those in the outdoor ambient air that were dominated by PVC fragments. These results unravel the properties of airborne microplastics in urban environments that are important to understanding their fate, transport, and potential health risks.

Stromatolites have been a major focus in the search for ancient microbial biosignatures, however, the organic carbon biosignatures of dolomitized stromatolites have not yet been fully characterized and correlated with their dolomitizing conditions. The lack in detailed dolomitic stromatolite studies is likely because dolomitization rarely preserves microbial morphology, which hampers the characterization of fossils’ biogenicity, syngenicity and indigeneity to their host rock. The Cambrian Allentown Formation in New Jersey, USA is an excellent example of dolomitized stromatolites and thrombolites containing diagenetically modified microbial biosignatures. Based on XRD and EPMA data, the dolomite is near- to stoichiometric, and poorly to well ordered. The outcrop underwent early dolomitization in a marginal-marine setting and later burial diagenesis resulting in multi-generational dolomite formation: (1) The microspar dolomite formed by early diagenetic replacement at or near the surface, that produced finely crystalline dolomite, (2) The zoned dolomite formed penecontemporaneously with the microspar phase as rhombohedral crystals by infilling primary pore spaces within the microspar matrix. The rhombic crystals continued to grow outward in alternating stages of Fe-enriched and -depleted fluids, which were preserved in zoned rims and revealed by cathodoluminescence, and (3) The saddle dolomite formed during late stage deep burial with Fe- and Mn-rich fluids, and occurs as a void-filling, high temperature phase. Organic carbon, characterized using confocal Raman microscopy, has exclusive distribution within the microspar dolomite, and the D and G bands’ characteristics reveal similar style thermal alteration as host rock, indicating that the mapped organic carbon is indigenous and syngenetic with the Cambrian carbonates. The findings presented in this study reveal organic matter found within microspar of various dolomitized facies deriving from different pools of organic carbon. This study sheds light on biosignatures in secondary dolostones and may aid biosignature detection in older carbonate rocks on Earth and Mars.

To explore the freezing effect on iron (Fe) solubility in natural environments, especially in Polar regions, event based freshly fallen snow samples were collected at Newark, New Jersey on the US East Coast for two consecutive winter seasons (2014–2015 and 2015–2016). These samples were analyzed for the concentrations of soluble iron (Fesol) using UV-Vis Spectroscopy and filterable iron (Fefil) and total iron (Fetot) using Atomic Absorption Spectroscopy. The average fractional solubility of the Fesol (the portion that passes through a 0.22 μm pore-size filter) with respect to the total Fe in the samples was 23.3 ± 12.2%, with the majority of the soluble Fe being present as Fe(III). Approximately 48.5% of the total Fe existed as Fefil (the portion that passes through 0.45 μm pore size filter media). No significant correlation was found between the soluble ionic species and soluble Fe. Six snow events were kept frozen for 10 days, and analyzed in periodic intervals to study the post-freezing modification in Fe solubility. Events 1 and 2 showed increasing trend in the soluble Fe concentrations; however, the events 5, 6, 7, and 8 showed no noticeable increments. The pattern shown in Events 1 and 2 is associated with high fraction of Fefil and one unit pH drop, suggesting that the freeze-induced modification in Fe solubility could be linked with the amount of Fefil and the acidity change in the samples. To further investigate the freeze-induced compaction of particles, samples from three events 6, 7, and 10 were analyzed by SEM-STEM-EDS microscopy, and the results showed that due to freezing, in general, the particles in the ice-melt counterparts tend to compact and cluster and form larger aggregates compared to the particles in snow-melt. These results show, despite the freeze-induced compaction in snow was observed from STEM images, the snow freezing might not have significant effect in increasing Fe solubility from materials in the snow. These results further suggest that freezing process with fresh snow in high-latitude regions may not impose significant modification on Fe solubility in snow.

The hypersaline sediment and groundwater of playa lake, Lake Lucero, at the White Sands National Monument in New Mexico were examined for microbial community composition, geochemical gradients, and mineralogy during the dry season along a meter and a half depth profile of the sediment vs. the groundwater interface. Lake Lucero is a highly dynamic environment, strongly characterized by the capillary action of the groundwater, the extreme seasonality of the climate, and the hypersalinity. Sediments are predominantly composed of gypsum with minor quartz, thenardite, halite, quartz, epsomite, celestine, and clays. Geochemical analysis has revealed the predominance of nitrates over ammonium in all of the analyzed samples, indicating oxygenated conditions throughout the sediment column and in groundwater. Conversely, the microbial communities are primarily aerobic, gram-negative, and are largely characterized by their survival adaptations. Halophiles and oligotrophs are ubiquitous for all the samples. The very diverse communities contain methanogens, phototrophs, heterotrophs, saprophytes, ammonia-oxidizers, sulfur-oxidizers, sulfate-reducers, iron-reducers, and nitrifiers. The microbial diversity varied significantly between groundwater and sediment samples as their temperature adaptation inferences that revealed potential psychrophiles inhabiting the groundwater and thermophiles and mesophiles being present in the sediment. The dynamism of this environment manifests in the relatively even character of the sediment hosted microbial communities, where significant taxonomic distinctions were observed. Therefore, sediment and groundwater substrates are considered as separate ecological entities. We hope that the variety of the discussed playa environments and the microorganisms may be considered a useful terrestrial analog providing valuable information to aid future astrobiological explorations.

The Dallol volcano and its associated hydrothermal field are located in a remote area of the northern Danakil Depression in Ethiopia, a region only recently appraised after decades of inaccessibility due to severe political instability and the absence of infrastructure. The region is notable for hosting environments at the very edge of natural physical-chemical extremities. It is surrounded by a wide, hyperarid salt plain and is one of the hottest (average annual temperature Dallol : 36-38°C) and most acidic natural systems (pH Dallol ≈0) on Earth. Spectacular geomorphologies and mineral deposits produced by supersaturated hydrothermal waters and brines are the result of complex interactions between active and inactive hydrothermal alteration of the bedrock, sulfuric hot springs and pools, fumaroles and geysers, and recrystallization processes driven by hydrothermal waters, degassing, and rapid evaporation. The study of planetary field analog environments plays a crucial role in characterizing the physical and chemical boundaries within which life can exist on Earth and other planets. It is essential for the definition and assessment of the conditions of habitability on other planets, including the possibility for biosignature preservation and in situ testing of technologies for life detection. The Dallol area represents an excellent Mars analog environment given that the active volcanic environment, the associated diffuse hydrothermalism and hydrothermal alteration, and the vast acidic sulfate deposits are reminiscent of past hydrothermal activity on Mars. The work presented in this paper is an overview of the Dallol volcanic area and its hydrothermal field that integrates previous literature with observations and results obtained from field surveys and monitoring coupled with sample characterization. In so doing, we highlight its exceptional potential as a planetary field analog as well as a site for future astrobiological and exploration programs, This is a contribution to the Europlanet 2020 Research Infrastructure programme funded under the European Commission's Horizon 2020 programme (No. 654208

Stromatolites have been a major focus in the search for ancient microbial life, however, the organic carbon biosignatures of dolomitized stromatolites have not yet been fully characterized or correlated with their dolomitizing conditions. Although dolomitization rarely preserves microbial morphology, the presence of organic carbon can provide valuable information for characterization of fossils' biogenicity, syngenicity, and indigeneity to their host rock. The Cambrian Allentown Formation in New Jersey, USA, is an excellent example of dolomitized stromatolites and thrombolites containing diagenetically modified microbial biosignatures. Based on XRD and EPMA data, the dolomite composition is typically stoichiometric, with varying degrees of cationic ordering. The outcrop underwent early dolomitization in a marginal-marine setting and later burial diagenesis resulting in multi-generational dolomite formation: (1) microspar dolomite formed by early diagenetic replacement at or near the surface, (2) zoned dolomite formed penecontemporaneously with the microspar phase as rhombohedral crystals by infilling primary pore spaces within the microspar matrix. The rhombic crystals continued to grow outward in alternating stages of Fe-enriched and -depleted fluids, which were preserved in zoned rims and revealed by cathodoluminescence, and (3) saddle dolomite formed during late stage deep burial with Fe- and Mn-rich fluids, and occurs as a void-filling, high-temperature phase. Organic carbon, characterized using confocal Raman microscopy, has an exclusive distribution within the microspar dolomite, and the D and G bands' characteristics reveal similar thermal alteration to the host rock, indicating that the mapped organic carbon is indigenous and syngenetic with the Cambrian carbonates. The findings presented in this study reveal organic matter found within microspar of various dolomitized facies deriving from different source pools of organic carbon. This study sheds light on biosignatures in secondary dolostones and may aid biosignature detection in older carbonate rocks on Earth and Mars.

Astrobiology brings together scientific disciplines focused on deciphering the origin of life, its nature, evolution, and distribution in the universe. Exceptionally rapid progress in our understanding has been made over the past four decades, including new insights into how life could have emerged on Earth, the revelation that life can thrive in the most hostile terrestrial environments, evidence of the presence of liquid water throughout the universe, a controversial discovery of past life in a Martian meteorite that reinvigorated the search for life on Mars, and the discovery of Earth-like planets orbiting stars other than our Sun in the Milky Way. Although Earth is the only planet known to host life in our Solar System, continued advances in the field of astrobiology stimulate the search for life and its origin beyond our planet.

Lake Lucero is a gypsum-rich, hypersaline, ephemeral playa located on the southern part of the Alkali Flat at the White Sands National Monument (WSNM), New Mexico, USA. This modern playa setting provides a dynamic extreme environment that changes from a freshwater lake to a hypersaline dry desert during the year. We investigated the microbial diversity (bacteria, archaea, and microbial eukaryotes) of the Lake Lucero sediments using 16S- and 18S-based amplicon sequencing approach and explored the diversity patterns in different geochemical microenvironments. Our results indicated that similar microbial communities, in particular bacterial communities colonized, were remarkably consistent across our depth profiles. Therefore, these communities show a first-order relevance on the environmental conditions (moisture content, oxygen content, and mineral composition). We found that Proteobacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Gemmatimonadetes were the major bacterial phyla, while Cyanobacteria were present in relatively low abundances and appeared only at the surface. Genus level assessment reflected that Truepera, Delftia, and Pseudomonas were the predominant bacterial genera across all samples. Euryarchaeota was the major archaeal phylum in all the samples, while Candidatus Halobonum and Candidatus Nitrososphaera were the main genera. Diatoms were the dominant eukaryotic group in surface samples and Fungi, Ciliophora, Metazoa, and Nematodes were the other major groups. As expected, metabolic inference indicated that aerobic microbial communities were near surface colonizers, with anaerobic communities dominating with increasing depth. We demonstrated that these microbial communities could be used to characterize unique geochemical microenvironments enabling us to extrapolate these results into other terrestrial and possibly extraterrestrial environments with comparable geochemical characteristics.

The 2010 Arctic Mars Analog Svalbard Expedition (AMASE) investigated two distinct geologic settings on Svalbard, using methodologies and techniques to be deployed on Mars Science Laboratory (MSL). AMASE-related research comprises both analyses conducted during the expedition and further analyses of collected samples using laboratory facilities at a variety of institutions. The Sample Analysis at Mars (SAM) instrument suite on MSL includes pyrolysis ovens, a gas-processing manifold, a quadrupole mass spectrometer (QMS), several gas chromatography columns, and a Tunable Laser Spectrometer (TLS). An integral part of SAM development is the deployment of SAM-like instrumentation in the field. During AMASE 2010, two parts of SAM participated as stand-alone instruments. A Hiden Evolved Gas Analysis-Mass Spectrometer (EGA-QMS) system represented the EGA-QMS component of SAM, and a Picarro Cavity Ring Down Spectrometer (EGA-CRDS), represented the EGA-TLS component of SAM. A field analog of CheMin, the XRD/XRF on MSL, was also deployed as part of this field campaign. Carbon isotopic measurements of CO2 evolved during thermal decomposition of carbonates were used together with EGA-QMS geochemical data, mineral composition information and contextual observations made during sample collection to distinguish carbonates formation associated with chemosynthetic activity at a fossil methane seep from abiotic processes forming carbonates associated with subglacial basaltic eruptions. Carbon and oxygen isotopes of the basalt-hosted carbonates suggest cryogenic carbonate formation, though more research is necessary to clarify the history of these rocks.

We report data on the martian meteorite Northwest Africa (NWA) 7034, which shares some petrologic and geochemical characteristics with known martian meteorites of the SNC (i.e., shergottite, nakhlite, and chassignite) group, but also has some unique characteristics that would exclude it from that group. NWA 7034 is a geochemically enriched crustal rock compositionally similar to basalts and average martian crust measured by recent Rover and Orbiter missions. It formed 2.089 ± 0.081 billion years ago, during the early Amazonian epoch in Mars' geologic history. NWA 7034 has an order of magnitude more indigenous water than most SNC meteorites, with up to 6000 parts per million extraterrestrial H(2)O released during stepped heating. It also has bulk oxygen isotope values of Δ(17)O = 0.58 ± 0.05 per mil and a heat-released water oxygen isotope average value of Δ(17)O = 0.330 ± 0.011 per mil, suggesting the existence of multiple oxygen reservoirs on Mars.

Abiotic Martian Organics Understanding the sources and the formation mechanisms of organic carbon compounds on Mars has implications for our understanding of the martian carbon cycle. Steele et al. (p. 212 , published online 24 May) present measurements of organic material in 11 martian meteorites, including the Tissint meteorite, which fell in the Moroccan desert in July 2011. Ten of the meteorites contain complex hydrocarbons encased within igneous minerals. The results imply that the organics formed as the magma melt crystallized and are thus of abiotic origin.

The mapped area of Harmakhis Vallis, at the eastern Hellas Planitia region (35°30–42°50′S; 91°00–97°30′E), covers the surface area of about 212,000 km2. The region displays an enhanced modification of the initial topography formed by the Hellas impact. The long and complex history of degradation and alteration involves mass-wasting processes, volcanism and fluvial activity, confronting effects of climate-induced slow mass-wasting processes to effects caused by temporary, catastrophic events (impact cratering, volcanism, etc.). Geological mapping at scale of 1:1,500,000 (full scale at 1:540,000) have been carried out on multiple co-registered data sets available from the past and ongoing orbiter missions to Mars. The mapped geomorphic features of small- and medium-scales reveal in detail events that shaped the topography of the region throughout history, providing specific constraints on the geologic and climatic history of the region. This study highlights events from the most recent Martian history, including fluvial activity recorded in relation to a debris apron flanking Centauri Montes, and evidence of recent positive geothermal anomalies of a high heat-flux with relatively small spatial extents, on the timescale of several million years ago.

Barite (BaSO4) is a stable and widely distributed mineral in Earth&rsquo, s crust. As such, barite has the potential to preserve specific geochemical and morphological characteristics representative of conditions at the time of its formation, which could be useful for interpretations of Earth&rsquo, s ancient rocks and paleoenvironments. In this study, we used variations in saturation index, solution temperature, solution chemistry, presence of organics, and Mg2+ and Ca2+ ions to investigate variations in barite crystal morphology. Through 42 experiments, we simulated poorly understood, low temperature spring settings similar to Zodletone Spring in Anadarko Basin, Oklahoma. Using SEM/EDS, we identified barite rosettes, rounded barite, euhedral/square-shaped barite, and elliptical barite as the crystal morphologies that directly reflect different formational settings. The X-ray diffraction (XRD) patterns revealed different crystallographic characters of the four distinct barite crystal morphologies, in particular, the samples that precipitated from supersaturated SrSO4 solution exhibited double peaks at 43&deg, 2-Theta, which matched barite with strontium substitution as barite might have incorporated strontium in its structure. Barite crystals that formed in the presence of organics in the initial solution exhibited a double peak at 33&deg, 2-Theta, which was absent in other samples. Confocal Raman microscopy indicated that all of the samples had typical barium sulfate bands, with a few differences in bands between the samples, for example, the 638 cm&minus, 1 band showed splitting or a double band between different samples. The samples that precipitated from solution with organics had organic compounds from the experimental solution included in their composition. In both cases, C&ndash, H stretches from 2800 cm&minus, 1 to 3000 cm&minus, 1 were present as well as bands from 1350 cm&minus, 1 to 1500 cm&minus, 1, which are typical of organic compounds. Based on our experiments, the variation in barite crystal morphologies reflected changes in initial solution chemistry (or environmental settings).

The Estancia, White Sands, Guadalupe and Cuatrocienegas Dune Fields are among the largest known aeolian gypsum sand-dune accumulations on Earth and occupy closed-drainage basins within the Rio Grande Rift. High sedimentation rates of lacustrine gypsum occur in topographic depressions within the closed basins. The gypsum accumulations result from long-term, complex, interaction between tectonism, climate, and a hydrologic cycle that involves geochemical recycling of sulfur from older sedimentary rocks flanking and underlying the basins. Gypsum precipitation in lacustrine environments is strongly controlled by local groundwater/bedrock interaction. The ranges of δ34S values (per mil, vs. VCDT) for gypsum sand in the White Sands Dune Field (12.1 to 13.9‰), Guadalupe Dune Field (10.2 to 12.5‰) and Cuatrocienegas Dune Field (14.6 to 15.9‰) indicate that the main sources of dissolved sulfate are evaporite strata of Lower Permian, Middle Permian and Cretaceous ages, respectively. A spatial increase of δ34S values across the White Sands Dune Field, in the direction of prevailing winds, matches well with a stratigraphically upward increase of δ34S values recorded in Lake Otero (an ancient lake in the basin) strata. This finding supports previous suggestions that White Sands Dune Field evolved as a result of the step-wise deflation of previously stored sediments in Lake Otero. The modern gypsum dune fields are primarily wet eolian systems in which dune accumulation is controlled by a near-surface groundwater table, which promotes early cementation of the dune accumulations. Early cementation in the interdune surfaces and, to a lesser degree, on the dune surfaces reduces the amount of sand available for transport and slows rates of dune migration. Based on an average migration rate of 2 m/year, the time needed for a dune at White Sands to migrate the downwind distance of the dune field is approximately 6500 years, which matches well with other estimates of the initiation of the dune field at approximately 7000 years ago and indicates that White Sands likely evolved as a wet aeolian system. As on Earth, gypsum-rich dune fields apparently are rare on Mars. Gypsum has been identified only within the Olympia Undae Dune Field which encircles a portion of the Martian north polar residual ice cap. Analogous to terrestrial gypsum dunes, the gypsum within the Olympia Undae gypsum-rich dunes might have originated from transport and deposition via aeolian processes. In this model, gypsum-rich source sediment could have been formed by confined groundwater or surface water activity and later transported by the wind. Any subsequent gypsum precipitation in the source area could have been initiated by episodic melting of the Martian polar ice cap. It is likely that the gypsum was deposited in the Olympia Undae dunes after the main deflation events that led to formation of the siliciclastic components of the dune field.

In order to reconstruct paleo-environmental conditions for the saline playa lakes of the Rio Grande Rift, we investigated sediment sulfate sources using sulfur isotope compositions of dissolved SO 4 2 - ions in modern surface water, groundwater, and SO 4 2 - precipitated in the form of gypsum sediments deposited during the Pleistocene and Holocene in the Tularosa and Estancia Basins. The major sulfate sources are Lower and Middle Permian marine evaporites (δ34S of 10.9–14.4‰), but the diverse physiography of the Tularosa Basin led to a complex drainage system which contributed sulfates from various sources depending on the climate at the time of sedimentation. As inferred from sulfur isotope mass balance constraints, weathering of sulfides of magmatic/hydrothermal and sedimentary origin associated with climate oscillations during Last Glacial Maximum contributed about 35–50% of the sulfates and led to deposition of gypsum with δ34S values of −1.2‰ to 2.2‰ which are substantially lower than Permian evaporates. In the Estancia Basin, microbial sulfate reduction appears to overprint sulfur isotopic signatures that might elucidate past groundwater flows. A Rayleigh distillation model indicates that about 3–18% of sulfates from an inorganic groundwater pool (δ34S of 12.6–13.8‰) have been metabolized by bacteria and preserved as partially to fully reduced sulfur-bearing minerals species (elemental sulfur, monosulfides, disulfides) with distinctly negative δ34S values (−42.3‰ to −20.3‰) compared to co-existing gypsum (−3.8‰ to 22.4‰). For the Tularosa Basin microbial sulfate reduction had negligible effect on δ34S value of the gypsiferous sediments most likely because of higher annual temperatures (15–33 °C) and lower organic carbon content (median 0.09%) in those sediments leading to more efficient oxidation of H2S and/or smaller rates of sulfate reduction compared to the saline playas of the Estancia Basin (5–28 °C; median 0.46% of organic carbon). The White Sands region of the Tularosa Basin is frequently posited as a hydrothermal analogue for Mars. High temperatures of groundwater (33.3 °C) and high δ18O(H2O) values (1.1‰) in White Sands, however, are controlled predominantly by seasonal evaporation rather than the modern influx of hydrothermal fluids. Nevertheless, it is possible that some of the geochemical processes in White Sands, such as sulfide weathering during climate oscillations and upwelling of highly mineralized waters, might be considered as valid terrestrial analogues for the sulfate cycle in places such as Meridiani Planum on Mars.

The paradigm of an ancient warm, wet, and dynamically active Mars, which transitioned into a cold, dry, and internally dead planet, has persisted up until recently despite published Viking-based geologic maps that indicate geologic and hydrologic activity extending into the Late Amazonian epoch. This paradigm is shifting to a water-enriched planet, which may still exhibit internal activity, based on a collection of geologic, hydrologic, topographic, chemical, and elemental evidences obtained by the Viking, Mars Global Surveyor (MGS), Mars Odyssey (MO), Mars Exploration Rovers (MER), and Mars Express (MEx) missions. The evidence includes: (1) stratigraphically young rock materials such as pristine lava flows with few, if any, superposed impact craters; (2) tectonic features that cut stratigraphically young materials; (3) features with possible aqueous origin such as structurally controlled channels that dissect stratigraphically young materials and anastomosing-patterned slope streaks on hillslopes; (4) spatially varying elemental abundances for such elements as hydrogen (H) and chlorine (Cl) recorded in rock materials up to 0.33 m depth; and (5) regions of elevated atmospheric methane. This evidence is pronounced in parts of Tharsis, Elysium, and the region that straddles the two volcanic provinces, collectively referred to here as the Tharsis/Elysium corridor. Based in part on field investigations of Solfatara Crater, Italy, recommended as a suitable terrestrial analog, the Tharsis/Elysium corridor should be considered a prime target for Mars Reconnaissance Orbiter (MRO) investigations and future science-driven exploration to investigate whether Mars is internally and hydrologically active at the present time, and whether the persistence of this activity has resulted in biologic activity.

Light-toned layered deposits are widespread on Mars in different geographical and geological settings and many different processes have been suggested to explain their formation, including lacustrine, sub-ice volcanism, weathering of basalts, pyroclastic, impact base surge and dust airfall. Interplay between airfall and aeolian processes with groundwater fluctuations leading to episodes of evaporite precipitation, interaction between lacustrine deposition and hydrothermal vents or large mud volcanoes, groundwater upwelling leading to spring deposits precipitation and/or mud volcanoes deposition have been also proposed. In order to contribute to this discussion, we present the recently published results on the Equatorial Layered Deposits (ELDs) of Arabia Terra in Firsoff crater and on the adjacent plateau. We produced a detailed geological map that included a survey of the relative stratigraphic relations and crater count dating. We reconstructed the geometry of the layered deposits and inferred some compositional constraints. We analyzed the sedimentary structures and textures observable at the available scale both inside and outside the craters. ELDs drape and onlap the plateau materials of Late Noachian age while they are unconformably covered by Early and Middle Amazonian units. ELDs show the presence of polyhydrated sulfates. Layer morphologies, albedo, structure, composition and stratigraphic setting enable us to include the ELDs in Firsoff crater and the surrounding plateau in the wider frame of the sulfate-bearing layered deposits seen elsewhere on Mars at the Noachian-Hesperian transition. ELDs found in craters and in the plateau can be distinguished from each other on the basis of basin-scale morphologies (kilometers-thick crater bulges vs 100s meter-thick sheet drape deposits) and local-scale morphologies (rounded shape, sub-circular depressions, raised rims, bowl-shaped appearance and serrated layer vs flat-topped bodies or dune fields with cross stratification). These morphologic differences suggest that genetic processes might at least partly be different, too. In the crater ELDs consist of mounds made of breccia sometimes displaying an apical pit laterally grading into a light-toned layered unit disrupted in a meter-scale polygonal pattern. These units are frequently associated with fissure ridges suggestive of subsurface sources. We interpret the ELDs inside the craters as spring deposits, originated by fluid upwelling through the pathways likely provided by the fractures related to the crater formations, and debouching at the surface through the fissure ridges and the mounds leading to evaporite precipitation. On the plateau, ELDs consist of rare mounds, flat-lying deposits and cross-bedded dune-fields. We interpret these mounds as possible smaller spring deposits, the flat-lying deposits as playa deposits, and the cross-bedded dune-fields as aeolian deposits. Groundwater fluctuations appear to be the major factor controlling ELDs deposition, leading to different depositional environments depending on the physiography of the basin.

We have combined mineralogy, organic geochemistry and molecular microbiology to study hydrothermal deposits from Solfatara Crater, a geologically young volcanic formation (∼4,000 years old) display...

The equatorial layered deposits of Arabia Terra are investigated to understand their genesis and the controls on their evolution. We interpret the deposits found within the craters as having been formed by spring deposition based on the large-scale geometry, the presence of morphologies consistent with fluid expulsion, the composition, and the sedimentary structures. Outside of the craters, we found evidence of dune forms and cross-stratification suggestive of aeolian activity, possibly associated with playa deposition. Groundwater fluctuations are suggested as the control on deposition.

The White Sands National Monument from New Mexico (U.S.A) contains one of the largest known gypsum dune fields with unique, rapidly migrating, arid, evaporitic habitats. Deposits from dune sides and interdune areas were collected in order to determine the characteristics of microbial habitat and communities through mineral assemblages, microbial pigments along with investigations of nitrogen and sulfur cycles. The most abundant pigments, scytonemin and carotenoids, were common UV protective pigments. Predominance of nitrite and nitrate over ammonium nitrogen (2.16: 1) implies that nitrification processes might be important in this ecosystem. Ammonium oxidizers from groups of β-, γ-proteobacteria and archaea were detected in all deposits, thereby indicating microbial involvement in nitrification. Additionally, denitrifying organisms with nirS and nirK genes were also present in most of the analyzed samples. The presence of trace carbonate mineral phases in association with biofilm implies possible microbia...

[1] The High Resolution Stereo Color camera (HRSC) data over Hesperia Planum and its surroundings reveal important details of geologic episodes and water-related processes in this region. (1) The Noachian fluvial events of Hesperia Planum depression included accumulation of water and formation of a water/ice reservoir there. Later, the reservoir was depleted in several phases reflecting diminishing amounts of water. Climate changes and/or volcanism were important in these volatile releases. (2) The massive, 0.45–1.5 × 106 km3, erosion from the Hesperia depression before the main lava eruption possibly resulted in thick, 0.5–1.5 km, deposits in Hellas Planitia. (3) Measurements of the flooded craters within Hesperia Planum provide the estimates of the thickness of lavas there, about 250–500 m. The final volume of lavas within Hesperia Planum (0.4–0.7 × 106 km3) is comparable with the range of some terrestrial igneous provinces such as Columbia River Basalts. (4) Extended magmatism possibly triggered formation of the outflow channel in a few locations after the lava emplacement. During this episode, about 0.04 × 106 km3 of material (about 4.5–8.9% of the volume eroded in the episode of massive erosion) were removed. The thickness of the composite lava layer exposed on the walls of the outflow channels, a few hundreds of meters, corresponds well to the thickness estimates made by the measurements of the flooded craters. (5) Dispersed viscous flows (debris aprons, flow-like deposits) reflect the final fluvial events. Viscous flows from the subsurface sources in the Southwestern trough associate with Dao, Niger, and Harmakhis Valles. These flows represent the final volatile discharge from the Hesperia reservoir that mostly was depleted by the earlier events of massive erosion and formation of the outflow channels. Viscous surface flows are mostly associated with Reull Vallis and probably reflect redistribution of volatiles related to the late episodes of evolution of this outflow channel.

We report on the detection of discrete grains of crystalline graphite and graphite whiskers (GWs) in an Apollo 17 impact melt breccia. Multiple instances of graphite and GWs within a discrete area of the sample imply that these grains are not terrestrial contamination. Both graphite and GWs are indicative of high-temperature conditions and are probably the result of the impact processes responsible for breccia formation. This suggests that impact processes may be an additional formation mechanism for GWs in the solar system and indicates that the Moon contains a record of ancient carbonaceous material delivered at the time of the Late Heavy Bombardment.