Search

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.

Early Mars most likely had a diversity of environments in terms of pH, redox conditions, temperature, geochemistry, and mineralogy. Field research in terrestrial analog environments contribute to understand the habitability of this diversity of environments on Mars in the past, because terrestrial analogues are places on Earth characterized by environmental, mineralogical, geomorphological, or geochemical conditions similar to those observed on present or past Mars. So far, analogs have been referred to terrestrial locations closely similar to any of the geochemical environments that have been inferred on Mars, i.e., they are “place-analogs” that represent snapshots in time: one specific environmental condition at a very specific place and a very specific time. Because of this, each individual field analog site cannot be considered an adequate representation of the changing martian environmental conditions through time. Here we introduce the concept of “astrobiological time-analog”, referred to terrestrial analogs that may help understand environmental transitions and the related possible ecological successions on early Mars. As Mars lost most of its surface water at the end of the Hesperian, this wet-to-dry global transition can be considered the major environmental perturbation in the geological history of Mars, and therefore merits to be the first one to be assigned a “time-analog” for its better understanding and characterization. At the end of the Hesperian, several paleolakes on Mars were characterized by episodic inundation by shallow surface waters with varying salinity, evaporation, and full desiccation repeatedly over time, until the final disappearance of most surface water after the wet-to-dry transition. We show here that similar conditions can be tested through time in the terrestrial analog Tirez lagoon. Tirez was a small and seasonal endorheic athalassohaline lagoon that was located in central Spain. In recent years, the lagoon has totally dried out, offering for the first time the opportunity to analyze its desiccation process as a “time-analog” to similar events occurred during the wet-to-dry transition on early Mars. To do so, here we describe (i) the microbial ecology of Tirez when the lagoon was still active 20 years ago, with prokaryotes adapted to extreme saline conditions; (ii) the composition of the microbial community in the dried lake sediments today, in many case groups that thrive in sediments of extreme environments; and (iii) the molecular and isotopic analysis of the lipid biomarkers that can be recovered from the sediments today. We conclude that Tirez was habitable for a wide range of prokaryotes before and after its complete desiccation, in spite of the repeated seasonal dryness; and our results may inform about research strategies to search for possible biomarkers in Mars after all the water was lost. Our 25 yearlong analyses of the ecological transitions in the Tirez lagoon represent the first terrestrial astrobiological “time-analog” for desiccating saline lakes on early Mars

32 páginas.- 3 figuras.- 2 tablas.- 260 referencias, Nearly half a century ago, two papers postulated the likelihood of lunar lava tube caves using mathematical models. Today, armed with an array of orbiting and fly-by satellites and survey instrumentation, we have now acquired cave data across our solar system-including the identification of potential cave entrances on the Moon, Mars, and at least nine other planetary bodies. These discoveries gave rise to the study of planetary caves. To help advance this field, we leveraged the expertise of an interdisciplinary group to identify a strategy to explore caves beyond Earth. Focusing primarily on astrobiology, the cave environment, geology, robotics, instrumentation, and human exploration, our goal was to produce a framework to guide this subdiscipline through at least the next decade. To do this, we first assembled a list of 198 science and engineering questions. Then, through a series of social surveys, 114 scientists and engineers winnowed down the list to the top 53 highest priority questions. This exercise resulted in identifying emerging and crucial research areas that require robust development to ultimately support a robotic mission to a planetary cave-principally the Moon and/or Mars. With the necessary financial investment and institutional support, the research and technological development required to achieve these necessary advancements over the next decade are attainable. Subsequently, we will be positioned to robotically examine lunar caves and search for evidence of life within Martian caves; in turn, this will set the stage for human exploration and potential habitation of both the lunar and Martian subsurface., The following funding sources are recognized for supporting several of the contributing authors: Human Frontiers Science Program grant #RGY0066/2018 (for AAB), NASA Innovative Advanced Concepts Grant #80HQTR19C0034 (HJ, UYW, and WLW), and European Research Council, ERC Consolidator Grant #818602 (AGF), the Spanish Ministry of Science and Innovation (project PID2019-108672RJ-I00) and the "Ramon y Cajal" post-doctoral contract (grant #RYC2019-026885-I (AZM)), and Contract #80NM0018D0004 between the Jet Propulsion Laboratory, California Institute of Technology and the National Aeronautics and Space Administration (AA, MJM, KU, and LK).

Phosphorus is a key element in all forms of life. However, P on Earth is scarce as it is locked in low solubility phosphate minerals, raising the fundamental and long-lasting question about where early life got its P supply. Hydrothermal vents or extremely acidic hot springs have been commonly investigated as favourable environments for the emergence and evolution of primitive organisms. More recently, carbonate-rich lakes have been proposed to concentrate enough dissolved P to favour the formation of life (Toner & Catling 2020), thus providing a plausible solution to phosphate supply. In this study, we investigate P recycling and bioavailability in carbonate and iron-rich Archaean deposits (~3 Ga) to expand our understanding of the possible origin of life on Earth, and to test the astrobiological implications on other terrestrial planets, like Mars. Unlike Earth, carbonates on Mars are scarce (Bultel et al., 2019). Interestingly, the Jezero crater, where the rover Perseverance is currently searching for sights of ancient life, is one of the few locations showing abundant carbonates on Mars (Horgan et al., 2020). Thus, these Archaean deposits serve as a Jezero crater analogue for early life on Earth. Phosphorus recycling is driven by the redox chemistry of the water column. Accordingly, this study will explore the prevailing redox conditions (oxic-dysoxic, ferruginous and/or euxinic), and their fluctuation, in the water column at the time of deposition. This is important because ferruginous conditions may promote P fixation in the sediments due to the drawdown of iron particles and organic matter. By contrast, euxinic conditions may enhance the flux of bioavailable P in the water column due to the degradation of organic matter and the dissolution of Fe oxides, both effective P carriers to the sediment. To better approach P bioavailability in these carbonate and iron-rich deposits, combined geochemical analyses and biogeochemical modelling are used. On one hand, coupling iron and phosphorus speciation geochemical techniques allow for the sequential extraction of different forms of Fe and P and serve to quantify their concentrations (Poulton & Canfield, 2005; Thompson et al., 2019). On the other hand, biogeochemical models allow for the understanding of Ca-Fe-S-P interactions within variable redox conditions. Iron speciation results will determine whether the studied carbonates were deposited under euxinic or ferruginous conditions, relative to total iron (FeT), and will track the redox evolution upward stratigraphy. Phosphorus speciation results will quantify different operationally defined P sedimentary pools, including iron associated (PFe), authigenic (Pauth), detrital (Pdet), organic (Porg) and total (PT). Subsequently, Fe and P results will be modeled to address two fundamental research questions: a) shifts from ferruginous to euxinic conditions promoted the accumulation of dissolved phosphate, and b) iron reduction (microbial or abiotic) favoured the increase of alkalinity, contributing to carbonate precipitation. Paleoenvironmental reconstructions of early Earth play a key role in unravelling the co-evolution of life and the Earth system. Our understanding of the biogeochemical evolution of the P cycle during the Archean may shed light on whether carbonates on early Mars could have accumulated enough dissolved P to become favourable environments for the emergence and evolution of life. References: Bultel, B. et al. (2019). Journal of Geophysical Research: Planets, 124, 989–1007. Horgan, B. et al. (2020). Icarus 339, 113526. Poulton, S. W. & Canfield, D. E. (2005). Chemical Geology, 214, 209–221. Thompson, J. et al. (2019). Chemical Geology, 524, 383–393. Toner, J. D. & Catling, D. C. A. (2020). PNAS. 117, 883–888.

In situ investigations by the Mars Science Laboratory Curiosity rover have confirmed the presence of an ancient lake that existed in Gale crater for up to 10 million years. The lake was filled with sediments that eventually converted to a compacted sandstone. However, it remains unclear whether the infilling of the lake was the result of background sedimentation processes or represents punctual flooding events in a largely isolated lake. Here, we used the X-ray diffraction data obtained with the Chemistry and Mineralogy instrument onboard the Curiosity rover to characterize the degree of disorder of clay minerals in the Murray formation at Gale crater. Our analysis shows that they are structurally and compositionally related to glauconitic clays, which are a sensitive proxy of quiescent conditions in liquid bodies for extended periods of time. Such results provide evidence of long periods of extremely low sedimentation in an ancient brackish lake on Mars, the signature of an aqueous regime with slow evaporation at low temperatures. More in general, the identification of lacustrine glauconitic clays on Mars provides a key parameter in the characterization of aqueous Martian palaeoenvironments that may once have harboured life. We thank T. Bristow for excellent feedback that notably improved the clarity of an early version of this manuscript. We also thank the Mars Science Laboratory team members for their dedication to generating the Planetary Data System database, especially to the CheMin Team. E.L.-A. was supported by the program GRC-ED431C 2017/55 (Xunta de Galicia) granted to the XM-1 group of the Universidade de Vigo, and A.G.F. by the Project ‘MarsFirstWater’, European Research Council Consolidator grant no. 818602. Peerreview

The Radar Imager for Mars Subsurface Experiment instrument has conducted the first rover-mounted ground-penetrating radar survey of the Martian subsurface. A continuous radar image acquired over the Perseverance rover’s initial ~3-kilometer traverse reveals electromagnetic properties and bedrock stratigraphy of the Jezero crater floor to depths of ~15 meters below the surface. The radar image reveals the presence of ubiquitous strongly reflecting layered sequences that dip downward at angles of up to 15 degrees from horizontal in directions normal to the curvilinear boundary of and away from the exposed section of the Séitah formation. The observed slopes, thicknesses, and internal morphology of the inclined stratigraphic sections can be interpreted either as magmatic layering formed in a differentiated igneous body or as sedimentary layering commonly formed in aqueous environments on Earth. The discovery of buried structures on the Jezero crater floor is potentially compatible with a history of igneous activity and a history of multiple aqueous episodes.

Perseverance’s Mastcam-Z instrument provides high-resolution stereo and multispectral images with a unique combination of spatial resolution, spatial coverage, and wavelength coverage along the rover’s traverse in Jezero crater, Mars. Images reveal rocks consistent with an igneous (including volcanic and/or volcaniclastic) and/or impactite origin and limited aqueous alteration, including polygonally fractured rocks with weathered coatings; massive boulder-forming bedrock consisting of mafic silicates, ferric oxides, and/or iron-bearing alteration minerals; and coarsely layered outcrops dominated by olivine. Pyroxene dominates the iron-bearing mineralogy in the fine-grained regolith, while olivine dominates the coarse-grained regolith. Solar and atmospheric imaging observations show significant intra- and intersol variations in dust optical depth and water ice clouds, as well as unique examples of boundary layer vortex action from both natural (dust devil) and Ingenuity helicopter–induced dust lifting. High-resolution stereo imaging also provides geologic context for rover operations, other instrument observations, and sample selection, characterization, and confirmation.

Perseverance landed at the Octavia E. Butler landing site next to the Seitah dune region in Jezero crater on 18 February 2021, in close proximity...

Nunataks are permanent ice-free rocky peaks that project above ice caps in polar regions, thus being exposed to extreme climatic conditions throughout the year. They undergo extremely low temperatures and scarcity of liquid water in winter, while receiving high incident and reflected (albedo) UVA-B radiation in summer. Here, we investigate the geomicrobiology of the permanently exposed lithic substrates of nunataks from Livingston Island (South Shetlands, Antarctic Peninsula), with focus on prokaryotic community structure and their main metabolic traits. Contrarily to first hypothesis, an extensive sampling based on different gradients and multianalytical approaches demonstrated significant differences for most geomicrobiological parameters between the bedrock, soil, and loose rock substrates, which overlapped any other regional variation. Brevibacillus genus dominated on bedrock and soil substrates, while loose rocks contained a diverse microbial community, including Actinobacteria, Alphaproteobacteria and abundant Cyanobacteria inhabiting the milder and diverse microhabitats within. Archaea, a domain never described before in similar Antarctic environments, were also consistently found in the three substrates, but being more abundant and potentially more active in soils. Stable isotopic ratios of total carbon (δ 13C) and nitrogen (δ 15N), soluble anions concentrations, and the detection of proteins involved in key metabolisms via the Life Detector Chip (LDChip), suggest that microbial primary production has a pivotal role in nutrient cycling at these exposed areas with limited deposition of nutrients. Detection of stress-resistance proteins, such as molecular chaperons, suggests microbial molecular adaptation mechanisms to cope with these harsh conditions. Since early Mars may have encompassed analogous environmental conditions as the ones found in these Antarctic nunataks, our study also contributes to the understanding of the metabolic features and biomarker profiles of a potential Martian microbiota, as well as the use of LDChip in future life detection missions. This project has been funded by the Spanish Ministry of Science and Innovation (MICINN)/European Regional Development Fund (FEDER) project no. RTI2018-094368-B-I00; the European Research Council Consolidator grant no. 818602; and the Spanish State Research Agency (AEI) project no. MDM-2017-0737, Unidad de Excelencia “María de Maeztu” to Centro de Astrobiología.

2 páginas.- 1 figura.- 16 referencias, To the Editor — 2021 is the International Year of Caves and Karst. To honour this occasion, we wish to emphasize the vast potential embodied in planetary subsurfaces. While researchers have pondered the possibility of extraterrestrial caves for more than 50 years, we have now entered the incipient phase of planetary caves exploration....

Future efforts towards Mars exploration should include a discussion about the effects that the strict application of Planetary Protection policies is having on the astrobiological exploration of Mars, which is resulting in a continued delay in the search for Martian life. As proactive steps in the path forward, here we propose advances in three areas. First, we suggest that a redefinition of Planetary Protection and Special Regions is required for the case of Mars. Particularly, we propose a definition for special places on Mars that we can get to in the next 10–20 years with rovers and landers, where try to address questions regarding whether there is present-day near-surface life on Mars or not, and crucially doing so before the arrival of manned missions. We propose to call those special places “Astrobiology Priority Exploration” regions (APEX regions). Second, we stress the need for the development of robotic tools for the characterization of complex organic compounds as unequivocal signs of life, and particularly new generations of complex organic chemistry and biosignature detection instruments, including advances in DNA sequencing. And third, we advocate for a change from the present generation of SUV-sized landers and rovers to new robotic assets that are much easier to decontaminate such as microlanders: they would be very small with limited sensing capabilities, but there would be many of them available for launch and coordination from an orbiting platform. Implementing these changes will help to move forward with an exploration approach that is much less risky to the potential Mars biosphere, while also being much more scientifically rigorous about the exploration of the “life on Mars” question – a question that needs to be answered both for astrobiological discovery and for learning more definitive lessons on Planetary Protection.

Research on planetary caves requires cross-planetary-body investigations spanning multiple disciplines, including geology, climatology, astrobiology, robotics, human exploration and operations. The community determined that a roadmap was needed to establish a common framework for planetary cave research. This white paper is our initial conception

Martian subsurface habitability and astrobiology can be evaluated via a lava tube cave, without drilling. MACIE addresses two key goals of the Decadal Survey (2013-2022) and three MEPAG goals. New advances in robotic architectures, autonomous navigation, target sample selection, and analysis will enable MACIE to explore the Martian subsurface., Comment: This paper was submitted to the Planetary and Astrobiology Decadal Survey in August 2020

Bulletin of the AAS, 53 (4)

Charles D. Edwards (Jet Propulsion Laboratory, California Institute of Technology). Co-Authors: 1. Vlada Stamenkovic Jet Propulsion Laboratory, California Institute of Technology; 2. Penelope Boston NASA Ames; 3. Kennda Lynch LPI/USRA … et al.

The modern Martian surface is unlikely to be habitable due to its extreme aridity among other environmental factors. This is the reason why the hyperarid core of the Atacama Desert has been studied as an analog for the habitability of Mars for more than 50 years. Here we report a layer enriched in smectites located just 30 cm below the surface of the hyperarid core of the Atacama. We discovered the clay-rich layer to be wet (a phenomenon never observed before in this region), keeping a high and constant relative humidity of 78% (a 0.780), and completely isolated from the changing and extremely dry subaerial conditions characteristic of the Atacama. The smectite-rich layer is inhabited by at least 30 halophilic species of metabolically active bacteria and archaea, unveiling a previously unreported habitat for microbial life under the surface of the driest place on Earth. The discovery of a diverse microbial community in smectite-rich subsurface layers in the hyperarid core of the Atacama, and the collection of biosignatures we have identified within the clays, suggest that similar shallow clay deposits on Mars may contain biosignatures easily reachable by current rovers and landers., The reported research is a contribution from the Project “MarsFirstWater”, funded by the European Research Council, ERC Consolidator Grant No. 818602 to AGF and by the Human Frontiers Science Program grant nº RGY0066/2018 to AAB. This work was also supported by the grant PGC2018-094076-B-I00 to JW and CA from the Ministry of Science, Innovation and Universities of Spain.

Huang et al. (1) describe a supposed mechanism of water extraction from gypsum by cyanobacteria sampled from endoliths inhabiting Ca sulfates in the Atacama Desert, and cultivated in the laboratory. The authors claim that the phase transformation from gypsum (CaSO4·2H2O) to anhydrite (CaSO4) (G→A) occurred under “dry conditions” in the contact zone between a “dry biofilm” and the gypsum, where only {011} planes of gypsum are transformed to anhydrite, supposedly providing water for cyanobacteria. This work (1) has a number of major conceptual problems, as follows. First, the authors show the presence of gypsum and/or anhydrite in the inoculated Ca sulfate samples using X-ray diffraction and, incompletely, by Fourier transform infrared spectroscopy techniques (2), and not by Raman (3) or transmission electron microscopy. Selected area electron diffraction (SAED) data in ref. 1 do not allow any mineral identification, due to their differences with … [↵][1]1To whom correspondence may be addressed. Email: j.wierzchos{at}mncn.csic.es or oartieda{at}unex.es. [1]: #xref-corresp-1-1

The study area (148.155 km2, Figure 1) is located in the southern equatorial region of Mars, approximately centered at 26.0° S and 6.5° E. Although subjected to extensive surface erosion, this heavily cratered region, selected as a representative section of the densely cratered highlands [1], still shows evident signs of past water erosion in the form of valley networks that regularly dissect the surface. As such, is an ideal area to study the role of water in modifying the surface of the Martian highlands. The top elevation of the mapped region is located in the central and eastern areas, reaching a maximum elevation of 2,606 meters above the Martian datum (a.m.d.). The points of lower elevation in the area are locally inside impact craters (-678 m a.m.d.). We found two unusually large impact craters. One is at the northeast, about 180 km in diameter, and only its southern half is inside the area. The other is at the southeast, irregularly shaped, and 116 km in diameter. The topography in the mapped region is also defined by two large valley network systems which carve the surface flowing from south to north, and surround the positive relief at each flank. We have produced a 1:500.000 scale geomorphological map with unprecedented detail, using ArcGIS 10.3 Desktop Software (ESRI) to draw and compiled a combination of a mosaic of hi-resolution CTX images, complemented by available Context Camera (CTX) images for cover gaps [2], a mosaic composed by MOLA and HRSC topography [3], and THEMIS-IR day imagery [4]. We mapped the main morphological units to contribute to the understanding of the hydrology ofthis understudied region of Mars. We mainly focus on describing eleven different morphological unitsand four geomorphic features (Figure 2), related to the past presence of water, as both ice and liquid,to allow us to characterize the past environment and eventually to identify their presence andpersistence. Among these units we would like to highlight the watershed unit, formed by incisions on thesurface that we interpret as evidence of aqueous activity, in which water came from channels thatflowed by the runoff wall unit. We differentiate a few types of impact craters, highlighting the invertedcrater unit and the sediment-filled impact crater unit, both filled up with sedimentary materials maybesourced by paleo-lakes. We differentiate two ejecta units related to liquid and ice water reservoirs;and a polygonal ridged unit and a knobby terrain unit associated with permafrost environments. Acknowledgments: This research is a contribution of the Project ”MarsFirstWater”, EuropeanResearch Council, Consolidator Grant no. 818602. Authors also thank the Agencia Estatal deInvestigación (AEI) project no. MDM-2017-0737 Unidad de Excelencia ”María de Maeztu”, and ReyJuan Carlos University. References: [1] Forsberg-Taylor, et al., (2004). Journal of Geophysical Research: Planets, 109(E5). [2] Fergason R.L. et al. (2018) Astrogeology PDS Annex, USGS. [3] Dickson J.L. et al. (2018)49th LPSC, Abstract#2083. [4] Christensen, P. R et al. (2004). Space Science Reviews, 110 (1), 85–130.

The ExoMars Rosalind Franklin rover is scheduled to land in Oxia Planum, at the outlet of Coogoon Valles, in 2023. The site is located in the western Arabia Terra region, the most gradual transition of the planetary topographic dichotomy, also considered to be one of the oldest terrains of Mars (Davis et al., 2016). Despite the high potential of the area as a promising location to search for ancient life, some aspects of its regional geologic context remain elusive. The extremely complex hydrologic history of Coogoon Valles system (Molina et al., 2017) is one example of the difficulty in addressing its geologic record. The Arabia Terra surface is extensively modified, and the paucity of valley networks (Figure 1A) and the presence of many inverted structures (Hynek et al., 2010; Davis et al., 2016; Davis et al., 2019) seem to indicate a widespread denudation. Besides, some of the phyllosilicate-bearing light-toned layered materials found in the area could have been formed by weathered airborne transported volcanic tuffs or ashes, that may cover older features. The absence of obvious volcanic edifices near the study area, that could be a source for these materials (Kerber et al., 2012), does not exclude the presence of yet undiscovered volcanic sources in the vicinity. Some crater-like structures, which lack typical features of impact origin, could have been formed by tectonics, groundwater, thermokarst, or volcanic collapses (or a combination of all; Figure 2). Their morphology favors a volcanic origin (Molina et al., 2019), perhaps similar to the plain-style calderas described to the NE of Arabia Terra (Figure 2; Michalski and Bleacher, 2013). The distribution of relatively small water- and volcanic-related features in the region provides additional evidence for processes that are difficult to assess on a regional scale. We have performed a grid-based mapping (Ramsdale et al., 2017; Voelker and Ramsdale, 2019) in two perpendicular study areas that overlap in the landing site area (Figure 1). The northern study area was separated into 2,171 grids (each 20x20 km, yellow in Figure 1B). It follows the dichotomy scarp from the landing site until reaching the plain-style calderas to the northeast (Michalski and Bleacher, 2013). Here we looked for features related to volcanic and thermokarstic activity as depressions pits, flows, and ridges. The other study area (2,563 grids, white in Figure 1B) transverses the dichotomy from the landing site southbound to Sinus Sabaeus in the Noachian highlands, where records of fluvial activity are much more prevalent (Robas et al., 2019). In this case, we looked for modified craters and various water-related features. In addition to that, we mapped further landforms found in both study areas, as knob fields, light-toned deposits, and channels. To identify the different features we used the global mosaic composed of CTX images (Malin et al., 2007; Dickson et al., 2018), a topographic mosaic from MOLA and HRSC data (Smith et al. 2001; Jaumann, R. et al. 2007; Fergason et al., 2018), and the quantitative THEMIS-derived global thermal inertia mosaic (Christensen et al., 2004, 2013). Acknowledgments: This research is a contribution of the Project ”MarsFirstWater”, European Research Council Consolidator Grant no. 818602. The authors also thank the Agencia Estatal de Investigación (AEI) project no. MDM-2017-0737 Unidad de Excelencia ”María de Maeztu”, and Rey Juan Carlos University. References: Christensen P. R. et al., Space Sci Rev. 110, 85–130 (2004). Christensen P. R., R. L. Fergason, C. S. Edwards, J. Hill, in LPSC, 44, No. 1719, id. 2822 (2013). Davis J. M., M. Balme, P. M. Grindrod, R. M. E. Williams, S. Gupta, Geology. 44, 847–850 (2016). Davis J.M. et al, J Geophys Res Planets. 124(7), 1913–1934. (2019). Dickson J. L. , L. A. Kerber, C. I. Fassett, B. L. Ehlmann, in LPSC, 49, No. 2083, id. 2480 (2018). Fergason R. , T. Hare, J. Laura, Astrogeology PDS Annex, US Geological Survey (2018). Hynek B. M., M. Beach, M. R. T. Hoke, J Geophys Res Planets. 115 (2010). Jaumann R. et al., Planet Space Sci. 55, 928–952 (2007). Malin M. C. et al., Journal of Geophysical Research: Planets, 112, E5 (2018). Michalski J. R. , J. E. Bleacher, Nature. 502, 47–52 (2013). Molina A. et al., Icarus. 293, 27–44 (2017). Molina A., O. Prieto-Ballesteros, I. López, C. Robas, A. G. Fairén, in EANA Conf., 282577 (2019). Ramsdale J. D. et al., Planet Space Sci. 140, 49–61 (2017). Robas C., A. Molina, I. López, O. Prieto-Ballesteros, A. G. Fairén, in EANA Conf., 280888 (2019). Voelker M., J. D. Ramsdale, in Planetary Cartography and GIS, H. Hargitai, Ed. (Springer International Publishing, Cham, 2019), pp. 293–302.

The presence of organic matter in lacustrine mudstone sediments at Gale crater was revealed by the Mars Science Laboratory Curiosity rover, which also identified smectite clay minerals. Analogue experiments on phyllosilicates formed under low temperature aqueous conditons have illustrated that these are excellent reservoirs to host organic compounds against the harsh surface conditions of Mars. Here, we evaluate whether the capacity of smectites to preserve organic compounds can be influenced by a short exposure to different diagenetic fluids. We analyzed the stability of glycine embedded within nontronite samples previously exposed to either acidic or alkaline fluids (hereafter referred to as "treated nontronites") under Mars-like surface conditions. Analyses performed using multiple techniques showed higher photodegradation of glycine in the acid-treated nontronite, triggered by decarboxylation and deamination processes. In constrast, our experiments showed that glycine molecules were preferably incorporated by ion exchange in the interlayer region of the alkali-treated nontronite, conferring them a better protection against the external conditions. Our results demonstrate that smectite previously exposed to fluids with different pH values influences how glycine is adsorbed into their interlayer regions, affecting their potential for preservation of organic compounds under contemporary Mars surface conditions. The research leading to these results is a contribution from the Projects "icyMARS" and "MarsFirstWater", funded by the European Research Council, Starting Grant no. 307496 and Consolidator Grant no. 818602, respectively, to AGF. We acknowledge to S. Galvez-Martinez for help and support during XPS measurements and the technical staff of the Unidad de Tecnicas Geologicas (Universidad Complutense de Madrid) for the XRD measurements. This Project has been partially supported by Unidad de Excelencia "Maria de Maeztu", MDM-2017-0737, Centro de Astrobiologia (INTA-CSIC), OPB is supported by project ESP2017-89053-C2-1-P and EMM by project ESP2017-89053-C2-2-P. Peer review

The ancient rock record for Mars has long been at odds with climate modelling. The presence of valley networks, dendritic channels and deltas on ancient terrains points towards running water and fluvial erosion on early Mars 1 , but climate modelling indicates that long-term warm conditions were not sustainable 2 . Widespread phyllosilicates and other aqueous minerals on the Martian surface3–6 provide additional evidence that an early wet Martian climate resulted in surface weathering. Some of these phyllosilicates formed in subsurface crustal environments 5 , with no association with the Martian climate, while other phyllosilicate-rich outcrops exhibit layered morphologies and broad stratigraphies 7 consistent with surface formation. Here, we develop a new geochemical model for early Mars to explain the formation of these clay-bearing rocks in warm and wet surface locations. We propose that sporadic, short-term warm and wet environments during a generally cold early Mars enabled phyllosilicate formation without requiring long-term warm and wet conditions. We conclude that Mg-rich clay-bearing rocks with lateral variations in mixed Fe/Mg smectite, chlorite, talc, serpentine and zeolite occurrences formed in subsurface hydrothermal environments, whereas dioctahedral (Al/Fe3+-rich) smectite and widespread vertical horizonation of Fe/Mg smectites, clay assemblages and sulphates formed in variable aqueous environments on the surface of Mars. Our model for aluminosilicate formation on Mars is consistent with the observed geological features, diversity of aqueous mineralogies in ancient surface rocks and state-of-the-art palaeoclimate scenarios. A geochemical model for the state of early Mars suggests that short-term warm events grafted onto a generally cold climate could form Al-rich phyllosilicates in short-lived surface water bodies and Mg-rich ones in hydrothermal subsurface environments.

Here we inspect whether microbial life may disperse using dust transported by wind in the Atacama Desert in northern Chile, a well-known Mars analog model. By setting a simple experiment across the hyperarid core of the Atacama we found that a number of viable bacteria and fungi are in fact able to traverse the driest and most UV irradiated desert on Earth unscathed using wind-transported dust, particularly in the later afternoon hours. This finding suggests that microbial life on Mars, extant or past, may have similarly benefited from aeolian transport to move across the planet and find suitable habitats to thrive and evolve.

Extraformational sediment recycling (old sedimentary rock to new sedimentary rock) is a fundamental aspect of Earth's geological record; tectonism exposes sedimentary rock, whereupon it is weathered and eroded to form new sediment that later becomes lithified. On Mars, tectonism has been minor, but two decades of orbiter instrument-based studies show that some sedimentary rocks previously buried to depths of kilometers have been exposed, by erosion, at the surface. Four locations in Gale crater, explored using the National Aeronautics and Space Administration's Curiosity rover, exhibit sedimentary lithoclasts in sedimentary rock: At Marias Pass, they are mudstone fragments in sandstone derived from strata below an erosional unconformity; at Bimbe, they are pebble-sized sandstone and, possibly, laminated, intraclast-bearing, chemical (calcium sulfate) sediment fragments in conglomerates; at Cooperstown, they are pebble-sized fragments of sandstone within coarse sandstone; at Dingo Gap, they are cobble-sized, stratified sandstone fragments in conglomerate derived from an immediately underlying sandstone. Mars orbiter images show lithified sediment fans at the termini of canyons that incise sedimentary rock in Gale crater; these, too, consist of recycled, extraformational sediment. The recycled sediments in Gale crater are compositionally immature, indicating the dominance of physical weathering processes during the second known cycle. The observations at Marias Pass indicate that sediment eroded and removed from craters such as Gale crater during the Martian Hesperian Period could have been recycled to form new rock elsewhere. Our results permit prediction that lithified deltaic sediments at the Perseverance (landing in 2021) and Rosalind Franklin (landing in 2023) rover field sites could contain extraformational recycled sediment., With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

We present the hypothesis that microorganisms can change the freezing/melting curve of cold salty solutions by protein expression, as it is known that proteins can affect the liquid-to-ice transition, an ability that could be of ecological advantage for organisms on Earth and on Mars. We tested our hypothesis by identifying a suitable candidate, the well-known psycrophile and halotolerant bacteria Rhodococcus sp. JG3, and analyzing its response in culture conditions that included specific hygroscopic salts relevant to Mars-that is, highly concentrated magnesium perchlorate solutions of 20 wt % and 50 wt % Mg(ClO4)2 at both end members of the eutectic concentration (44 wt %)-and subfreezing temperatures (263 K and 253 K). Using a combination of techniques of molecular microbiology and aqueous geochemistry, we evaluated the potential roles of proteins over- or underexpressed as important players in different mechanisms for the adaptability of life to cold environments. We recorded the changes observed by micro-differential scanning calorimetry. Unfortunately, Rhodococcus sp. JG3 did not show our hypothesized effect on the melting characteristics of cold Mg-perchlorate solutions. However, the question remains as to whether our novel hypothesis that halophilic/psychrophilic bacteria or archaea can alter the freezing/melting curve of salt solutions could be validated. The null result obtained after analyzing just one case lays the foundation to continue the search for proteins produced by microorganisms that thrive in very cold, high-saline solutions, which would involve testing different microorganisms with different salt components. The immediate implications for the habitability of Mars are discussed., With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

Heterolithic, boulder-containing, pebble-strewn surfaces occur along the lower slopes of Aeolis Mons (“Mt. Sharp”) in Gale crater, Mars. They were observed in HiRISE images acquired from orbit prior to the landing of the Curiosity rover. The rover was used to investigate three of these units named Blackfoot, Brandberg, and Bimbe between sols 1099 and 1410. These unconsolidated units overlie the lower Murray formation that forms the base of Mt. Sharp, and consist of pebbles, cobbles and boulders. Blackfoot also overlies portions of the Stimson formation, which consists of eolian sandstone that is understood to significantly postdate the dominantly lacustrine deposition of the Murray formation. Blackfoot is elliptical in shape (62 × 26 m), while Brandberg is nearly circular (50 × 55 m), and Bimbe is irregular in shape, covering about ten times the area of the other two. The largest boulders are 1.5–2.5 m in size and are interpreted to be sandstones. As seen from orbit, some boulders are light-toned and others are dark-toned. Rover-based observations show that both have the same gray appearance from the ground and their apparently different albedos in orbital observations result from relatively flat sky-facing surfaces. Chemical observations show that two clasts of fine sandstone at Bimbe have similar compositions and morphologies to nine ChemCam targets observed early in the mission, near Yellowknife Bay, including the Bathurst Inlet outcrop, and to at least one target (Pyramid Hills, Sol 692) and possibly a cap rock unit just north of Hidden Valley, locations that are several kilometers apart in distance and tens of meters in elevation. These findings may suggest the earlier existence of draping strata, like the Stimson formation, that would have overlain the current surface from Bimbe to Yellowknife Bay. Compositionally these extinct strata could be related to the Siccar Point group to which the Stimson formation belongs. Dark, massive sandstone blocks at Bimbe are chemically distinct from blocks of similar morphology at Bradbury Rise, except for a single float block, Oscar (Sol 516). Conglomerates observed along a low, sinuous ridge at Bimbe consist of matrix and clasts with compositions similar to the Stimson formation, suggesting that stream beds likely existed nearly contemporaneously with the dunes that eventually formed the Stimson formation, or that they had the same source material. In either case, they represent a later pulse of fluvial activity relative to the lakes associated with the Murray formation. These three units may be local remnants of infilled impact craters (especially circular-shaped Brandberg), decayed buttes, patches of unconsolidated fluvial deposits, or residual mass-movement debris. Their incorporation of Stimson and Murray rocks, the lack of lithification, and appearance of being erosional remnants suggest that they record erosion and deposition events that post-date the exposure of the Stimson formation., With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

Organic chemistry is ubiquitous in the Solar System, and both Mars and a number of icy satellites of the outer Solar System show substantial promise for having hosted or hosting life. Here, we propose a novel astrobiologically focused instrument suite that could be included as scientific payload in future missions to Mars or the icy moons: the Complex Molecules Detector, or CMOLD. CMOLD is devoted to determining different levels of prebiotic/biotic chemical and structural targets following a chemically general approach (i.e., valid for both terrestrial and nonterrestrial life), as well as their compatibility with terrestrial life. CMOLD is based on a microfluidic block that distributes a liquid suspension sample to three instruments by using complementary technologies: (1) novel microscopic techniques for identifying ultrastructures and cell-like morphologies, (2) Raman spectroscopy for detecting universal intramolecular complexity that leads to biochemical functionality, and (3) bioaffinity-based systems (including antibodies and aptamers as capture probes) for finding life-related and nonlife-related molecular structures. We highlight our current developments to make this type of instruments flight-ready for upcoming Mars missions: the Raman spectrometer included in the science payload of the ESAs Rosalind Franklin rover (Raman Laser Spectrometer instrument) to be launched in 2022, and the biomarker detector that was included as payload in the NASA Icebreaker lander mission proposal (SOLID instrument). CMOLD is a robust solution that builds on the combination of three complementary, existing techniques to cover a wide spectrum of targets in the search for (bio)chemical complexity in the Solar System., This work has been funded by the project “MarsFirstWater,” European Research Council Consolidator grant number 818602 to Alberto G. Fairén; the Spanish Ministry of Economy and Competitiveness (MINECO) and EU FEDER program projects no. ESP2015-69540-R, RTI2018-094368-B-I00, BIO2016-79618-R, and ESP2017-89053-C2-1-P; With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

descripción no proporcionada por scopus, With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

This study reports in-situ sedimentologic evidence of giant floods in Gale crater, Mars, during the Noachian Period. Features indicative of floods are a series of symmetrical, 10 m-high gravel ridges that occur in the Hummocky Plains Unit (HPU). Their regular spacing, internal sedimentary structures, and bedload transport of fragments as large as 20 cm suggest that these ridges are antidunes: a type of sedimentary structure that forms under very strong flows. Their 150 m wavelength indicates that the north-flowing water that deposited them was at least 24 m deep and had a minimum velocity of 10 m/s. Floods waned rapidly, eroding antidune crests, and re-deposited removed sediments as patches on the up-flow limbs and trough areas between these ridges forming the Striated Unit (SU). Each patch of the SU is 50–200 m wide and long and consists of 5–10 m of south-dipping layers. The strike and dip of the SU layers mimic the attitude of the flank of the antidune on which they were deposited. The most likely mechanism that generated flood waters of this magnitude on a planet whose present-day average temperature is − 60 °C was the sudden heat produced by a large impact. The event vaporized frozen reservoirs of water and injected large amounts of CO and CH from their solid phases into the atmosphere. It temporarily interrupted a cold and dry climate and generated a warm and wet period. Torrential rainfall occurred planetwide some of which entered Gale crater and combined with water roaring down from Mt. Sharp to cause gigantic flash floods that deposited the SU and the HPU on Aeolis Palus. The warm and wet climate persisted even after the flooding ended, but its duration cannot be determined by our study., With funding from the Spanish government through the "María de Maeztu Unit of Excellence" accreditation (MDM-2017-0737)

© The Author(s) 2018., The hyperarid core of the Atacama Desert, the driest and oldest desert on Earth, has experienced a number of highly unusual rain events over the past three years, resulting in the formation of previously unrecorded hypersaline lagoons, which have lasted several months. We have systematically analyzed the evolution of the lagoons to provide quantitative field constraints of large-scale impacts of the rains on the local microbial communities. Here we show that the sudden and massive input of water in regions that have remained hyperarid for millions of years is harmful for most of the surface soil microbial species, which are exquisitely adapted to survive with meager amounts of liquid water, and quickly perish from osmotic shock when water becomes suddenly abundant. We found that only a handful of bacteria, remarkably a newly identified species of Halomonas, remain metabolically active and are still able to reproduce in the lagoons, while no archaea or eukaryotes were identified. Our results show that the already low microbial biodiversity of extreme arid regions greatly diminishes when water is supplied quickly and in great volumes. We conclude placing our findings in the context of the astrobiological exploration of Mars, a hyperarid planet that experienced catastrophic floodings in ancient times., The research leading to these results is a contribution from the Project “icyMARS”, funded by the European Research Council, Starting Grant No. 307496. A.G.F. and V.P. acknowledge funding support from Grant No. ESP2015-69540-R (MINECO/FEDER). We thank V. Souza-Egipsy and BIOPHYM (IEM-CSIC) for TEM observations; C. Arroyo (MNCN-CSIC), and the Geomaterials 2 Program (S2013/MIT_2914), financed by the Comunidad Autónoma de Madrid and the European Social Fund; and Y. Blanco for providing LDChip antibody microarrays.