Lipids constitute resistant biomarkers that have been proposed as pacemakers in the search for possible microbial life-forms in Mars' past. The extreme conditions on the surface of Mars-such as high levels of radiation and the presence of brines and/or perchlorates-must be taken into account when considering the preservation of hypothetical biomarkers. On Earth, alkaline lakes that are rich in microbialites and that have a high saturation index of carbonates have been proposed as analogs of the martian Noachian era. Here, we describe for the first time the lipid biomarker profile of stromatolites from the Alchichica soda lake in Mexico (n-alkanes, alkenes, fatty acids, and n-alkanols). Additionally, DNA sequencing was conducted to taxonomically characterize the Alchichica microbialites, while mineralogical analyses showed typical morphologies associated with aragonite. Microbialite samples were exposed to high doses of gamma (0.87 and 10.52 MGy) and UV (250 W/m2 for 140 h) radiation. Another experiment used salt solutions {brine conditions (NaCl + Na2SO4) and perchlorates [Mg(ClO4)2]} to explore the resilience of biomarkers to simulated martian primitive and present-day conditions. Our results suggest that different types and doses of radiation significantly degrade indigenous lipid biomarkers in microbialites (94% for 0.87 MGy, 99.5% for 10.52 MGy, and 93.5% for UV), with n-alkanes and fatty acids the best-preserved compounds even at higher radiation doses. While the presence of salts such as chloride and sulfate brines did not modify the preservation of fatty acids and alcohols, the presence of perchlorates alone favored their degradation. Our findings support the idea that remnants of past or present life on Mars may be better preserved in ancient chloride or sulfate saline environments.

The thickness and volume of the stratigraphic sequence in Mars' northern lowlands remain poorly constrained, despite their key role in recording the planet's geological and paleoclimatic evolution. Reliable thickness estimates are essential because they directly control calculations of volcanic effusion, surface flooding, and associated climate forcing. Here we present a revised volumetric assessment of the lowland stratigraphy - dominated by volcanic infill - based on integrated geological mapping and crater-statistical modeling. Our approach combines crater size-frequency distributions with volumetric reconstructions of buried craters and intercrater plains across both lowland and Noachian highland reference terrains. The results indicate that the minimum cumulative stratigraphic volume is at least three times greater than previous estimates, implying a proportional increase in volcanic outgassing of CO2, H2O, and SO2. These new quantitative conservative bounds provide improved constraints on early Martian volatile budgets and on mid- to late-Noachian atmospheric evolution, with implications for transient climate warming and late-stage lowland flooding.

The increasing production of biodiesel has led to a surplus of glycerol, a polluting by-product in need of valorization. In this study, we demonstrate that Citrobacter telavivensis T1.2D-1, an extremophile bacterium isolated from the Iberian Pyrite Belt, effectively converts glycerol into valuable compounds via dark anaerobic fermentation. Genomic and bioinformatic analyses confirmed the presence of the dha and pdu operons, responsible for 1,3-propanediol (1,3-PDO) synthesis, and the hyc operon and fdhF gene involved in hydrogen (H2) production. Batch fermentations revealed that optimal yields of both H2 (0.94 mol.mol-glycerol-1) and 1,3-PDO (0.66 mol‧mol-glycerol-1) were achieved at 25 °C using 2 g L-1 of supplied glycerol. Optimum yield of ethanol (1 mol‧mol-glycerol-1) was achieved using 12.5 g L-1 of supplied glycerol. Interestingly, 1,3-PDO and H2 production inversely correlated with ethanol formation, suggesting metabolic competition. Antibiotic sensitivity profiling revealed susceptibility to multiple antibiotics, supporting future genetic engineering efforts. We suggest opperating with reactors at low concentrations to produce 1,3-PDO and H2 with high yields, and at medium concentrations to generate ethanol. Our findings support C. telavivensis T1.2D-1 as a promising venue for the sustainable biotechnological production of biohydrogen and bio-based 1,3-PDO from glycerol, offering a dual solution to both energy demands and industrial waste management.

The search for life signatures beyond Earth is one of the main objectives of space exploration. Studies of analogous terrestrial ecosystems have shed light on the limits of life and on the adaptations of microbial communities to thrive in these extreme environments resembling Icy Moons. However, their findings tend to be compartmentalized, which hinders the drawing of broad conclusions about the drivers and challenges for life. This study aims to identify general characteristics of microbial communities inhabiting terrestrial analogs of Icy Moons, applying a novel meta-analysis on publicly available 16S rRNA amplicon sequencing data. We also seek to apply our findings to a new fundamental approach in the search for life in Europa and Enceladus, locations where life may exist. Our results suggest that depth, pH and hypersalinity are the key environmental drivers for microbial taxa distribution and molecular adaptations, with halophilic archaea showing ubiquitous presence. Integrating diverse datasets into a single meta-analysis allowed us to infer statistically significant microbial patterns related to adaptation to the Icy Moons’ analog conditions, notably that osmolytes and modified lipids emerged as a shared adaptive strategy, regardless of depth. Our findings are aimed to helping guide future life detection efforts in these extraterrestrial environments.

The United Nations Outer Space Treaty states that the exploration of celestial bodies must avoid "harmful contamination" which may impede scientific exploration by other parties to the treaty. To guide treaty compliance, Planetary Protection regulations promulgated by the Committee on Space Research set limits for microbial contamination of celestial bodies, particularly those that may harbor extant life (e.g., Mars). However, anthropogenically introduced chemicals and materials are not regulated but may cause "harmful contamination" and thus pose a potential threat to scientific exploration. On Earth, threats from anthropogenic chemicals and materials are often managed by considering both potential exposure to the substances and their hazardous properties. The lack of knowledge around hazards to possible extant life on Mars means that chemicals and materials should be designed and used so that their exposure concentrations are minimized. Here, we review possible emission, partitioning, persistence, and transport processes on Mars for anthropogenically introduced chemicals and materials and identify key knowledge gaps. We highlight difficulties and lessons learned from pollution policy development on Earth that could inform interplanetary chemical and material management. This work aims to support the expansion of the Planetary Protection guidelines to include a "No- or Low-Exposure by Design" approach to chemicals and materials on Mars.

Since the formation of Mars, its environmental conditions have changed. There is multiple and varied evidence that Mars was more similar to Earth at the beginning of its history. To contribute to the knowledge of the early conditions on Mars, it is important to study the geomorphological processes that shaped its surface and the period of time during which these processes operated. For this purpose, we have selected an area located between highlands and lowlands, in the southwest of Sinus Sabaeus (3ºE, 21ºS and 10ºE, 29.5ºS). This region is composed by a longitudinal valley, named Marikh Vallis, a central plateau, and two large craters with diameters of 198.8 and 121.7 km each, which we named Margulis and Roemer, respectively (IAU approval on April 21, 2021).To study these geomorphologies, we have included datasets in ArcGis, based on Context Camera images (CTX), with 6/pixel resolution. To obtain age constraints, we used the Crater Size Frequency Distribution (CSFD) counting technique using the "Craterstat" software, developed by the University of Berlin.The combined geomorphological and crater counting results suggest that the study area has undergone several resurfacing processes consistent with surface modification by liquid water and water ice. These processes also included glacial and periglacial processes, and some modifications due to subsurface water activity triggered by the melting of ice in the shallow subsurface. Most of these processes occurred during the Noachian and the Hesperian periods.Some of the identified morphologies, such as etched terrains, polygonal terrains, crater ejecta, and some valley types, are compatible with a Noachian to Hesperian origin under glacial and periglacial conditions. This fact is particularly relevant because it means that the studied morphologies may have formed under an icy and wet early Mars, suggesting that Sinus Sabaeus could be considered an attractive Martian location to explore in terms of habitability.

The incident ultraviolet (UV) irradiance on the surface of Mars is strongly sterilizing and plays a critical role in atmospheric and near-surface photochemistry. The Rover Environmental Monitoring Station (REMS) instrument, which includes the first UV sensor sent to Mars on board the Curiosity rover, has been measuring the UV irradiance at Gale Crater since 2012, providing ground-truth data regarding seasonal and short-term variability of the UV radiation at the surface of another planet. Here, we analyze the REMS UV measurements for a period of >5 Martian years to retrieve biological effective doses and other UV radiation quantities on the planetary surface that are key for different physicochemical processes. Our results reveal a previously unidentified complex UV radiation environment on the Martian surface, with dramatic short-term fluctuations capable of changing UV radiation doses by >30% in a few sols. We assess the viability of terrestrial microorganisms exposed to this UV radiation field and dispersed through the Martian atmosphere from a robotic spacecraft or human habitat. Our findings show that reducing microbial viability by 99% would require several hours of exposure to the Martian environment including during the daytime, a finding that may call for a reinforcement of planetary protection policies.

The smooth topography of the Martian Northern Lowlands has been classically equated to an ancient ocean basin. The High-Resolution Imaging Science Experiment (HiRISE) onboard the Mars Reconnaissance Orbiter (MRO) provides images of unprecedented resolution of the Martian surface at scales of 25 to 32 cm per pixel. Our analysis of HiRISE imaging reveals the presence of scour marks over the northern plains and other large basins, along with meter-sized boulders distributed in clusters and mounds. Here we show that the association of scour marks with clusters of boulders and mounds on the northern plains of Mars and the Hellas basin can be related to the dual processes of ice keel scouring and ice rafting of both glacial and non-glacial detritus. These processes are well documented on Earth, where they result in distinctive morphologies and sedimentary patterns recognizable on the ocean floor, comparable to those we identified on Mars. We conclude that the presence of icebergs floating in very cold oceans early in the history of the planet can explain the observed occurrence of scour marks and boulder distribution on the major lowlands of Mars.

Investigating the presence of oxygen on planets within our solar system and beyond is crucial for understanding the potential for life beyond Earth. Oxygen is a key ingredient for life as we know it and serves as a key indicator of habitability and planetary processes [1]. On Earth, the first lasting rise in atmospheric oxygen started ∼2.4 billion years ago and was a crucial process that fundamentally transformed the planet's atmosphere and oceans, leading to the evolution of complex life forms. However, geochemical evidence reveals the existence of intermittent oxic whiffs before that period, although the mechanisms that drove the production of such early oxygen are poorly constrained. Here, we present redox sensitive trace metal and Fe speciation data, as well as phosphorus phase partitioning results, for a 2.94 billion-year-old drill core from the Red Lake area, Canada. Results suggest dynamic oceanic Fe cycling between ferruginous conditions (anoxic Fe-rich), euxinic (anoxic S-rich) and short-lived episodes of oxygenated waters consistent with depleted (

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.

Phosphorus is an essential component for life, and in-situ identification of phosphate minerals that formed in aqueous conditions directly contributes toward one of the main goals of the Mars 2020 Perseverance rover: to seek signs of ancient habitable environments. In Jezero crater, proximity science analyses within a conglomerate outcrop, “Onahu” demonstrate the presence of rare Fe3+-bearing phosphate minerals (likely beraunite, metavivianite, ferrolaueite, and/or santabarbaraite) embedded in a carbonate-rich matrix. While Fe-phosphates have been previously inferred on Mars, this work presents the most definitive in-situ identification of martian Fe-phosphate minerals to date, using textural, chemical, spectral, and diffraction analyses of discrete green-blue grains. The Fe-phosphate minerals’ textural context along with comparisons to Earth analogs suggest they likely formed after oxidation of the Fe2+-phosphate vivianite — the most common Fe-phosphate on Earth, often associated with microbial activity and organics. The Fe3+-phosphate assemblage after vivianite, and the presence of two distinct matrix domains in Onahu indicate that the conglomerate and corresponding sample collected by Perseverance (Otis_Peak) preserve a record of evolving habitable paleoenvironmental conditions on Mars. Once returned to Earth, analysis of the Fe-phosphates in the Otis_Peak sample will provide new insights into ancient habitable environments, and, if analogous to terrestrial vivianite-rich environments, potential links with microbial activity.

Liquid water is thought to have been abundant on the surface of Mars early in its history, but today it exists only in the form of ice. The team behind the MarsFirstWater project are investigating the characteristics of water on early Mars, research which holds important implications for future space missions to the planet, as Professor Alberto Fairén explains.

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.

Abstract The Perseverance rover has collected seven oriented samples of sedimentary rocks, all likely older than the oldest signs of widespread life on Earth, at the exposed base of the western fan in Jezero crater, Mars. The samples include a sulfate‐ and clay‐bearing mudstone and sandstone, a fluvial sandstone from a stratigraphically low position at the fan front, and a carbonate‐bearing sandstone deposited above the sulfate‐bearing strata. All samples contain aqueously precipitated materials and most or all were aqueously deposited. Although the rover instruments have not confidently detected organic matter in the rocks from the fan front, the much more sensitive terrestrial instruments will still be able to search for remnants of prebiotic chemistries and past life, and study Mars's past habitability in the samples returned to Earth. The hydrated, sulfate‐bearing mudstone has the highest potential to preserve organic matter and biosignatures, whereas the carbonate‐bearing sandstones can be used to constrain when and for how long Jezero crater contained liquid water. Returned sample science analyses of sulfate, carbonate, clay, phosphate and igneous minerals as well as trace metals and volatiles that are present in the samples acquired at the fan front would provide transformative insights into past habitable environments on Mars, the evolution of its magnetic field, atmosphere and climate and the past and present cycling of atmospheric and crustal water, sulfur and carbon.

The Mars 2020 Perseverance Rover imaged diagenetic textural features in four separate sedimentary units in its exploration of the 25-m-thick Shenandoah formation at Jezero Crater, Mars, that we interpreted as probable concretions. These concretions were most abundant in the Hogwallow Flats member of the Shenandoah formation and were restricted to the light-toned, platy, sulfur-cemented bedrock at outcrop surfaces, whereas the finely laminated, darker toned, mottled and deformed strata lack concretions. The concretions also had a wide range of morphologies including concentric, oblate, urn, and spheroidal shaped forms that were not clustered, and ranged in size from similar to 1 to 16 mm with a median of 2.65 mm. The elemental composition of the concretions compared to the bedrock had greater abundance of magnesium and calcium salts, silicates, and possibly hematite. We compared these Jezero Crater concretions to the geochemistry of concretions from previously published studies and from two new terrestrial analog sites (Gallup Formation, New Mexico and Torrey Pines, California). In addition, we measured organic carbon content of three terrestrial sedimentary analogs of increasing age that contain concretions (Torrey Pines (Pleistocene), Gallup Formation (similar to 89 Ma), and Moodies Group (similar to 3.2 Ga)). All measured concretions contained significant concentrations of organic carbon with the maximum organic carbon content (similar to 2 wt. % Total organic carbon) found in the Moodies Group concretions. Organic carbon abundances in terrestrial concretions was controlled more by the formation mechanism and relative timing of concretion development rather than deposit age. These findings suggested that concretions at Jezero Crater reflect local sites of enhanced biosignature preservation potential. The Perseverance Rover discovered concretions in its exploration of the rock packages at Jezero Crater, Mars and one of the sample return cores was collected from concretion-rich bedrock. Concretions are resistant cement in the rock that are found in many shapes (usually spherical or oblate) and range from millimeter to meter size scales on Earth; they can be formed through inorganic water-rock reactions or facilitated by microbial metabolisms. We documented the abundance, size, composition, and shape of the concretions to understand how these features were formed. We found that the concretions are mixtures of salts, clay minerals, and iron oxides. We compared these results to terrestrial concretions with similar mineral compositions and measured the organic carbon in four terrestrial analogs. Comparisons with terrestrial concretions in this study and the literature suggested that the concretion composition in Jezero Crater could have high organic preservation potential. Thus, the concretions in Jezero Crater may retain organic carbon and other biosignatures and might therefore be considered as high priority samples of astrobiological interest out of the current sample suite for return to Earth. Jezero Crater concretions are variably enriched in Si, Ca, and Mg salts, and Fe oxides Terrestrial concretions of similar mineralogy analyzed in this study contain significant organic carbon phases Based on terrestrial analogs, Jezero Crater concretions may represent sites of enhanced biosignature preservation potential