Search

Planetary protection guidance for martian exploration has become a notable point of discussion over the last decade. This is due to increased scientific interest in the habitability of the red planet with updated techniques, missions becoming more attainable by smaller space agencies, and both the private sector and governments engaging in activities to facilitate commercial opportunities and human-crewed missions. The international standards for planetary protection have been developed through consultation with the scientific community and the space agencies by the Committee on Space Research's (COSPAR) Panel on Planetary Protection, which provides guidance for compliance with the Outer Space Treaty of 1967. In 2021, the Panel evaluated recent scientific data and literature regarding the planetary protection requirements for Mars and the implications of this on the guidelines. In this paper, we discuss the COSPAR Planetary Protection Policy for Mars, review the new scientific findings and discuss the next steps required to enable the next generation of robotic missions to Mars.

International audience; Enceladus is the first planetary object for which direct sampling of a subsurface water reservoir, likely habitable, has been performed. Over a decade of flybys and seven flythroughs of its watery plume, the Cassini spacecraft determined that Enceladus possesses all the ingredients for life. The existence of active eruptions blasting fresh water into space, makes Enceladus the easiest target in the search for life elsewhere in the Solar System. Flying again through the plume with more advanced instruments, landing at the surface near active sources and collecting a sample for return to Earth are the natural next steps for assessing whether life emerges in this active world. Characterizing this habitable world also requires detailed mapping and monitoring of its tidally-induced activity, from the orbit as well as from the surface using complementary platforms. Such ambitious goals may be achieved in the future in the framework of ESA large or medium-class missions in partnership with other international agencies, in the same spirit of the successful Cassini-Huygens mission. For all these reasons, exploring habitable ocean worlds, with Enceladus as a primary target, should be a priority topic of the ESA Voyage 2050 programme.

Nitrate-dependent Fe

Modern-day Mars is a dry, harsh environment with no surface water, but billions of years ago it might have been water-rich, like Earth. Scientists believe that, as water was lost on Mars, the remaining water would have become increasingly salty and rich in sulphur. By researching environments on Earth with a similar chemistry, we can develop hypotheses about whether life could have existed on Mars. In our research, we studied Colour Peak, a sulphur-rich, salty spring system in the Canadian High Arctic. This environment contains bacteria that use sulphur to get their energy. By studying water and sediment samples from this region, we confirmed that bacteria that used sulphur as an energy source could potentially have lived on Mars. These results can help scientists who are analysing data from Mars missions to identify evidence of former life on Mars.

Volcanic features and impact craters are ubiquitous features on Mars, and hydrothermal systems associated with the production of these features should have been abundant in Mars’s early history. These hydrothermal systems represent potentially habitable environments and are therefore a high priority for continued investigations of the Martian crust. Here we present a Mars analog study where basaltic magma intruded water-bearing sediments to produce a high-temperature (as high as ∼700°C) hydrothermal system, which we use to constrain the potential habitability of similar systems on Mars via mineralogy and geochemistry including S, C, and O isotopic systematics. Our analog site suggests evidence for a habitable environment once the system cooled below 120°C and the potential presence of microbial activity based on the combination of dolomite and C-isotopic systems in the same sample. These findings highlight the importance of future missions to investigate the interface of sediments with magmas and/or late-stage impact melts where microbial life may have taken hold when temperature conditions allowed.

Hydrothermal systems that formed as a result of impact events possess all the key requirements for life: liquid water, a supply of bio‐essential elements, and potential energy sources. Therefore, they are prime locations in the search for life on other planets. Here, we apply thermochemical modeling to determine secondary mineral formation within an impact‐generated hydrothermal system, using geochemical data returned for two soils on Mars found in regions that have previously experienced alteration. The computed mineral reaction pathways provide a basis for Gibbs energy calculations that enable both the identification of available geochemical energy, obtained from Fe‐based redox reactions, that could be utilized by potential microbial life within these environments, and an estimate of potential cell numbers. Our results suggest that water–rock interactions occurring within impact‐generated hydrothermal systems could support a range of Fe‐based redox reactions. The geochemical energy produced from these reactions would be substantial and indicates that crater environments have the potential to support microbial cell numbers similar to what has been identified in terrestrial environments.

Characterizing the microbiome of spacecraft assembly cleanrooms is important for planetary protection. We report two bacterial metagenome-assembled genome sequences (MAGs) reconstructed from metagenomes produced from cleanroom samples from the Kennedy Space Center’s Payload Hazardous Servicing Facility (KSC-PHSF) during the handling of the Phoenix spacecraft. Characterization of these MAGs will enable identification of the strategies underpinning their survival., Characterizing the microbiome of spacecraft assembly cleanrooms is important for planetary protection. We report two bacterial metagenome-assembled genomes (MAGs) reconstructed from metagenomes produced from cleanroom samples from the Kennedy Space Center’s Payload Hazardous Servicing Facility (KSC-PHSF) during the handling of the Phoenix spacecraft. Characterization of these MAGs will enable identification of the strategies underpinning their survival.

NASA’s search for habitable environments has focused on alteration mineralogy of the Martian crust and the formation of hydrous minerals, because they reveal information about the fluid and environmental conditions from which they precipitated. Extensive work has focused on the formation of alteration minerals at low temperatures, with limited work investigating metamorphic or high-temperature alteration. We have investigated such a site as an analog for Mars: a mafic dike on the Colorado Plateau that was hydrothermally altered from contact with groundwater as it was emplaced in the porous and permeable Jurassic Entrada sandstone. Our results show evidence for fluid mobility removing Si and K but adding S, Fe, Ca, and possibly Mg to the system as alteration progresses. Mineralogically, all samples contain calcite, hematite, and kaolinite; with most samples containing minor anatase, barite, halite, and dolomite. The number of alteration minerals increase with alteration. The hydrothermal system that formed during interaction of the magma (heat source) and groundwater would have been a habitable environment once the system cooled below ∼120 °C. The mineral assemblage is similar to alteration minerals seen within the Martian crust from orbit, including those at Gusev and Jezero Craters. Therefore, based on our findings, and extrapolating them to the Martian crust, these sites may represent habitable environments which would call for further exploration and sample return of such hydrothermally altered igneous materials.

The Dallol geothermal area in the northern part of the Danakil Depression (up to 124–155 meter below sea level) is deemed one of the most extreme environments on Earth. The area is notable for being part of the Afar Depression, an incipient seafloor-spreading center located at the triple junction, between Nubian, Somali and Arabian plates, and for hosting environments at the very edge of natural physical-chemical extremities. The northern part of the Danakil Depression is dominated by the Assale salt plain (an accumulation of marine evaporite deposits) and hosts the Dallol volcano. Here, the interaction between the evaporitic deposit and the volcanisms have created the unique Dallol hot springs, which are highly acidic (pH ~ 0) and saline (saturation) with maximum temperatures ranging between 90 and 109 °C. Here we report for the first time evidence of life existing with these hot springs using a combination of morphological and molecular analyses. Ultra-small structures are shown to be entombed within mineral deposits, which are identified as members of the Order Nanohaloarchaea. The results from this study suggest the microorganisms can survive, and potential live, within this extreme environment, which has implications for understanding the limits of habitability on Earth and on (early) Mars., European Union’s Horizon 2020 research and innovation program under Grant Agreement No 654208

Introduction The subsurface environment of Enceladus is potentially habitable: there is a global subsurface ocean [1], energy from hydrothermal activity [2] and bioessential elements [3]. Carbon, as a fundamental bioessential element, is critical for life, so understanding how it is processed within the Enceladus environment is crucial in assessing this moon’s potential habitability. Evidence from the south polar plumes suggests that carbon is likely to be bound within the silicate interior [4] and liberated through water-rock (silicate-ocean) interactions. Methods We have undertaken thermochemical modelling (CHIM-XPT) [5] of these interactions and tested different hypotheses for the formation of Enceladus. Both models reacted the silicate interior (with a CI chondrite composition [6]) with a fluid representative of the subsurface ocean: model 1) a dilute sodium chloride solution, based upon the assumption that the subsurface ocean originated as almost pure water [7]; model 2) a solution with a cometary composition (using data collected from 67P [8]), based upon the assumption that the ocean originated from melted cometary ice [9]. We have explored the full temperature and pressure ranges anticipated at the rock-water interface [2]. We have modelled the rock-water interactions: at the rock-water interface in the areas of hydrothermal activity; within the silicate interior, and in cooler areas of the ocean floor. In addition, we have run thermochemical models to cool the subsurface ocean fluid as it ascends from the ocean floor to the water-ice boundary; these results should be more comparable to the Cassini observations, as the plume material emanates from the ocean surface. Figure 1 - A cross section of the subsurface of Enceladus' South Polar Region, highlighting the area of study. The stars represent the different regions of study for the water-rock interaction models; each location represents different temperatures and pressure regimes. The arrows represent cooling and change in the chemical composition of the fluid as it moves from the ocean floor to the ice/ocean interface. Image Credit: R. E. Hamp Results/ Discussion With regards to the plausible chemistry of the Enceladus ocean, the model output agrees with the observations from the Cassini data; the dominant chemical species are sodium chloride, potassium chloride and sodium carbonates. The model has also revealed a possible formation mechanism for the silica nanoparticles within the subsurface ocean that could account for the detection of such particles in the Enceladus plumes [2]. This, in turn, validates our model and the simulant chemistry inputted. The cooling model results show that the pH of the ocean at the water/rock interface was significantly lower than that at the ocean/ice interface (8 compared with 10.5). Furthermore, the concentration of carbonates and sulfates decrease as they ascend though the water column, but the concentration of silica particles increases. The output from this work provides results very closely aligned to the concentrations of the chemical species detected by the Cassini Spacecraft. This work has also determined that a carbon cycle may operate at the rock-water interface, which could include a carbonate pump system and the formation of hydrocarbons up to C4. The availability of these chemical species and the potential for further ongoing reactions supports the evidence that the subsurface environment of Enceladus may be habitable. Summary We will present the outcomes from this modelling, which includes a theoretical composition for a modern day subsurface ocean, potential carbon cycling pathways and the effect of carbon species on the pH of the subsurface ocean fluid. We will also present the initial findings from modelling of the cooling of ocean fluids as they are transported from the ocean floor to the ocean/ice interface surface. [1] Thomas P. C. et al., (2016), Icarus, 264, 37-47 [2] Hsu H. W. et al., (2015), Nature, 519, 207-210 [3] McKay, C. P. et al., (2014) Astro-biology, 14, 352-355 [4] Glein C. R. & Waite J. H., (2020), Geophys Res Let, 47 [5] Reed, M. H., Spycher, N. F., Palandri, J., (2010) User guide for CHIM-XPT, University of Oregon, Oregon [6] Hamp R. E. et al., (2019), 50th LPSC 2019, Abstract 1091 [7] Brown R. H. et al, (2006) Science, 311, 1425-1428 [8] Hertier K. H., et al., (2017) RAS monthly notices, 469 [9] Neveu, M., et al., (2017) Geochim et Cosmochim, 212, 324-371

Authors acknowledge funding from the Science and Technology Facilities Council from the Grant ST/P000657/1. We would also like to acknowledge funding from a Leverhulme Trust Research Project Grant (RPG-2016-153) and thank the Polar Continental Shelf Program (Natural Resources Canada) for logistical field support in Nunavut. The transition of the martian climate from the wet Noachian era to the dry Hesperian (4.1–3.0 Gya) likely resulted in saline surface waters that were rich in sulfur species. Terrestrial analogue environments that possess a similar chemistry to these proposed waters can be used to develop an understanding of the diversity of microorganisms that could have persisted on Mars under such conditions. Here, we report on the chemistry and microbial community of the highly reducing sediment of Colour Peak springs, a sulfidic and saline spring system located within the Canadian High Arctic. DNA and cDNA 16S rRNA gene profiling demonstrated that the microbial community was dominated by sulfur oxidising bacteria, suggesting that primary production in the sediment was driven by chemolithoautotrophic sulfur oxidation. It is possible that the sulfur oxidising bacteria also supported the persistence of the additional taxa. Gibbs energy values calculated for the brines, based on the chemistry of Gale crater, suggested that the oxidation of reduced sulfur species was an energetically viable metabolism for life on early Mars. Publisher PDF

Finding evidence of life elsewhere in the Solar System is dependent on understanding biotic processes that could occur within potentially habitable environments. Here, we describe a suite of high-pressure flow-through reactors that have been developed to investigate biotic and abiotic processes within simulated sub-surface martian and icy moon environments.

The icy satellites of Jupiter and Saturn are perhaps the most promising places in the Solar System regarding habitability. However, the potential habitable environments are hidden underneath km-thick ice shells. The discovery of Enceladus’ plume by the Cassini mission has provided vital clues in our understanding of the processes occurring within the interior of exooceans. To interpret these data and to help configure instruments for future missions, controlled laboratory experiments and simulations are needed. This review aims to bring together studies and experimental designs from various scientific fields currently investigating the icy moons, including planetary sciences, chemistry, (micro-)biology, geology, glaciology, etc. This chapter provides an overview of successful in situ, in silico, and in vitro experiments, which explore different regions of interest on icy moons, i.e. a potential plume, surface, icy shell, water and brines, hydrothermal vents, and the rocky core.

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

Existing martian simulants are predominantly based on the chemistry of the average ‘global’ martian regolith as defined by data on chemical and mineralogical variability detected by orbiting spacecraft, surface rovers and landers. We have therefore developed new martian simulants based on the known composition of regolith from four different martian surface environments: an early basaltic terrain, a sulfur-rich regolith, a haematite-rich regolith and a contemporary Mars regolith. Simulants have been developed so that the Fe2+/Fe3+ ratios can be adjusted, if necessary, leading to the development of four standard simulants and four Fe-modified simulants. Characterisation of the simulants confirm that all but two (both sulfur-rich) are within 5 wt% of the martian chemistries that they were based on and, unlike previous simulants, they have Fe2+/Fe3+ ratios comparable to those found on Mars. Here we outline the design, production and characterisation of these new martian regolith simulants. These are to be used initially in experiments to study the potential habitability of martian environments in which Fe may be a key energy source.

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

Currently, the surface of Mars cannot sustain liquid water, but there is evidence suggesting that water was present in the Noachian. Although water might exist in the subsurface of Mars, it could not sustain in the present day unless it was highly saline. Thus, saline springs in polar desert environments are analogues with which to investigate martian conditions. An example of this is Axel Heiberg Island, located in a region of continuous permafrost in the Canadian High Arctic, which hosts sulfidic and highly saline springs. In this study, cultivation-dependant and independent techniques were used to investigate the microbial diversity of a sediment sample collected from a saline cold (3–8 °C) pool at Colour Peak Springs on Axel Heiberg. Both DNA and RNA were extracted from the samples, and the microbial community was characterised using the 16S rRNA gene from the extracted nucleic acids. The metabolic profile was characterised by screening DNA and cDNA for functional genes relating to the cycling of carbon (coxL, xoxF, cbbL), nitrogen (nifH, nosZ, nod) and sulfur (dsrB, soxB). The community profiles were used to inform enrichment strategies, allowing for the isolation and characterisation of several halophilic isolates including strains of Marinobacter, Halomonas, Halanaerobium and Loktanella. Through this work we have been able to develop an in-depth characterisation of the metabolic and phylogenetic diversity that is present and viable within this analogue site. This allows us to start building an understanding of the underlying mechanisms and strategies that enable organisms to persist in these environments.

Here, we report the draft genome sequence of a strain of Clostridium isolated from sediment collected from an estuarine environment. The strain was isolated using a minimal medium designed to select for chemoautotrophic microorganisms., Here, we report the draft genome sequence of a strain of Clostridium isolated from sediment collected from an estuarine environment. The strain was isolated using a minimal medium designed to select for chemoautotrophic microorganisms. The strain may represent a novel species within the genus Clostridium, and this genome sequence enables further investigation into the genetic and metabolic diversity of this organism.

A kombucha multimicrobial culture (KMC) was exposed to simulated Mars-like conditions in low-Earth orbit (LEO). The study was part of the Biology and Mars Experiment (BIOMEX), which was accommodated in the European Space Agency's EXPOSE-R2 facility, outside the International Space Station. The aim of the study was to investigate the capability of a KMC microecosystem to survive simulated Mars-like conditions in LEO. During the 18-month exposure period, desiccated KMC samples, represented by living cellulose-based films, were subjected to simulated anoxic Mars-like conditions and ultraviolet (UV) radiation, as prevalent at the surface of present-day Mars. Postexposure analysis demonstrated that growth of both the bacterial and yeast members of the KMC community was observed after 60 days of incubation; whereas growth was detected after 2 days in the initial KMC. The KMC that was exposed to extraterrestrial UV radiation showed degradation of DNA, alteration in the composition and structure of the cellular membranes, and an inhibition of cellulose synthesis. In the "space dark control" (exposed to LEO conditions without the UV radiation), the diversity of the microorganisms that survived in the biofilm was reduced compared with the ground-based controls. This was accompanied by structural dissimilarities in the extracellular membrane vesicles. After a series of subculturing, the revived communities restored partially their structure and associated activities.

The question of whether Earth is a unique location for life remains one of the most enduring questions of our time. Geochemical data suggests that habitable environments may exist, or may have existed, elsewhere in the Solar System with promising targets including Mars and icy bodies where liquid water is believed to exist (Kargel, 2000; Grotzinger et al., 2014; Glein et al., 2015). Furthermore, potential habitable Exoplanets have been discovered where potentially there is sufficient atmospheric pressure to maintain liquid water (Jenkins et al., 2015; Gillon et al., 2017; Orosei et al., 2018). Yet, for life to exist it is not solely dependent on liquid water as it also needs bio-essential elements, an energy source, and the environmental conditions, that are conducive to life (Nixon et al., 2013). To investigate the feasibility of life elsewhere in the Solar System a combination of field and laboratory based studies, in-situ space experiments, and theoretical modeling is required. Here, we present 14 original research papers, one mini review, and two hypothesis and theory papers highlighting the novel and diverse methods that are employed to investigate potential life beyond the Earth. The overall focus of this collection of work is to understand if terrestrial life could exist elsewhere in the Solar System, and if so, what evidence (bio-signatures) could be used to support or negate the hypothesis of life.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

The draft genomes of the nitrate-dependent iron-oxidizing bacteria Acidovorax sp. strain BoFeN1 and Paracoccus pantotrophus strain KS1 are presented., The draft genomes of the nitrate-dependent iron-oxidizing bacteria Acidovorax sp. strain BoFeN1 and Paracoccus pantotrophus strain KS1 are presented. These genomes supply supporting data to investigations of the mechanisms underlying this anaerobic form of microbial biogeochemical iron cycling.

This work considers the hypothetical viability of microbial nitrate-dependent Fe2+ oxidation (NDFO) for supporting simple life in the context of the early Mars environment. This draws on knowledge built up over several decades of remote and in situ observation, as well as recent discoveries that have shaped current understanding of early Mars. Our current understanding is that certain early martian environments fulfill several of the key requirements for microbes with NDFO metabolism. First, abundant Fe2+ has been identified on Mars and provides evidence of an accessible electron donor; evidence of anoxia suggests that abiotic Fe2+ oxidation by molecular oxygen would not have interfered and competed with microbial iron metabolism in these environments. Second, nitrate, which can be used by some iron oxidizing microorganisms as an electron acceptor, has also been confirmed in modern aeolian and ancient sediment deposits on Mars. In addition to redox substrates, reservoirs of both organic and inorganic carbon are available for biosynthesis, and geochemical evidence suggests that lacustrine systems during the hydrologically active Noachian period (4.1–3.7 Ga) match the circumneutral pH requirements of nitrate-dependent iron-oxidizing microorganisms. As well as potentially acting as a primary producer in early martian lakes and fluvial systems, the light-independent nature of NDFO suggests that such microbes could have persisted in sub-surface aquifers long after the desiccation of the surface, provided that adequate carbon and nitrates sources were prevalent. Traces of NDFO microorganisms may be preserved in the rock record by biomineralization and cellular encrustation in zones of high Fe2+ concentrations. These processes could produce morphological biosignatures, preserve distinctive Fe-isotope variation patterns, and enhance preservation of biological organic compounds. Such biosignatures could be detectable by future missions to Mars with appropriate instrumentation.

In nutrient limited soils, minerals constitute a major reservoir of bio-essential elements. Consequently, the release of nutritive elements during weathering is crucial. Bacteria have been shown to enhance weathering rates; however, there has been limited work that has focused on the bacterial weathering of bedrock or parent rock, which are the major sources of minerals, in nutrient limiting soils. In this study, both a culture-independent and culture-dependent approach was used to study the bacterial community at the interface between basaltic bedrock and nutrient limiting soil in Cadiar Idris region of Snowdonia National Park, United Kingdom. High throughput sequencing method, Ion Torrent, was used to characterise the bacterial community, which generated over 250,000 sequences. Taxonomical assignment demonstrated that approximately 50% (125,000 sequences) of the community consisted of the orders Actinomycetales, Burkholderiales, Clostridales, Bacillales, Rhizobiales and Acidobacterium, with unclassified sequences representing 44% ± 1.46% (110,000 ± 3650). Bacteria belonging to the genera Serratia, Pseudomonas, Bacillus, Paenibacillus, Chromobacterium, Janthinobacterium, Burkholderia and Arthrobacter, were isolated from the sample site. All of the isolates were able to grow in a minimal growth medium, which contained glucose, ammonium chloride with basalt as the sole source of bio-essential elements. Seventy percent of the isolates significantly enhanced basalt dissolution (p < 0.05). The rate of dissolution correlated to the production of oxalic acid and acidification of the growth medium. The findings of this work suggest that at the interface between bedrock and soil heterotrophic members of the bacterial community can enhance weathering, an essential part of biogeochemical cycling in nutrient limiting soil.

The authors thank the STFC for providing a studentship to PW for this work. This work was made possible with support from the UK Science and Technology Facilities Council (STFC; Grant No. ST/1001964/1). The mean air temperature of the Icelandic interior is below 10 °C. However, we have previously observed 16S rDNA sequences associated with thermophilic lineages in Icelandic basalts. Measurements of the temperatures of igneous rocks in Iceland showed that solar insolation of these low albedo substrates achieved a peak surface temperature of 44.5 °C. We isolated seven thermophilic Geobacillus species from basalt with optimal growth temperatures of ~65 °C. The minimum growth temperature of these organisms was ~36 °C, suggesting that they could be active in the rock environment. Basalt dissolution rates at 40 °C were increased in the presence of one of the isolates compared to abiotic controls, showing its potential to be involved in active biogeochemistry at environmental temperatures. These data raise the possibility of transient active thermophilic growth in macroclimatically cold rocky environments, implying that the biogeographical distribution of active thermophiles might be greater than previously understood. These data show that temperatures measured or predicted over large scales on a planet are not in themselves adequate to assess niches available to extremophiles at micron scales. Postprint

The dissolution of minerals plays an important role in the formation of soils and sediments. In nutrient limiting soils, minerals constitute a major reservoir of bio-essential cations. Of particular interest is granite as it is the major rock type of the continental land mass. Although certain bacteria have been shown to enhance weathering of granite-forming minerals, little is known about the dissolution of granite, at the whole rock scale, and the microbial community involved. In this study, both culture-independent and culture-dependent approaches were used to study the bacterial community at the interface between granite bedrock and nutrient limiting soil in Dartmoor National Park, United Kingdom. High throughput sequencing demonstrated that over 70% of the bacterial population consisted of the bacterial classes Bacilli, Beta-proteobacteria and Gamma-proteobacteria. Bacteria belonging to the genera Serratia, Pseudomonas, Bacillus, Paenibacillus, Chromobacterium and Burkholderia were isolated from the sample site. All of the isolates were able to grow in a minimal growth medium, which contained glucose and ammonium chloride, with granite as the sole source of bio-essential elements. Sixty six percent of the isolates significantly enhanced basalt dissolution (p < 0.05). Dissolution of Si, K, Ca and Mg correlated with production of oxalic acid and acidification. The results of this study suggest that microorganisms in nutrient limiting soils can enhance the rate of granite dissolution, which is an important part of the biogeochemical cycle.

In this experimental study, cells of the radiation-resistant bacterium Deinococcus radiodurans were exposed to several different sources of radiation chosen to replicate the charged particles found in the solar wind. Naked cells or cells mixed with dust grains (basalt or sandstone) differing in elemental composition were exposed to electrons, protons, and ions to determine the probability of cell survival after irradiation. Doses necessary to reduce the viability of cell population to 10% (LD(10)) were determined under different experimental conditions. The results of this study indicate that low-energy particle radiation (2-4 keV), typically present in the slow component of the solar wind, had no effect on dehydrated cells, even if exposed at fluences only reached in more than 1000 years at Sun-Earth distance (1 AU). Higher-energy ions (200 keV) found in solar flares would inactivate 90% of exposed cells after several events in less than 1 year at 1 AU. When mixed with dust grains, LD(10) increases about 10-fold. These results show that, compared to the highly deleterious effects of UV radiation, solar wind charged particles are relatively benign, and organisms protected under grains from UV radiation would also be protected from the charged particles considered in this study.

Shales play an important role in many earth system processes including coastal erosion, and they form the foundations of many engineering structures. The geobiology of the interior of pyrite-containing receding shale cliffs on the coast of northeast England was examined. The surface of the weathered shales was characterised by a thin layer of disordered authigenic iron oxyhydroxides and localised acicular, platy and aggregated gypsum, which was characterised by Raman spectroscopy, XAS and SEM. These chemical changes are likely to play an important role in causing rock weakening along fractures at the micron scale, which ultimately lead to coastal retreat at the larger scale. The surface of the shale hosts a novel, low-diversity microbial community. The bacterial community was dominated by Proteobacteria, with phylotypes closely associating with Methylocella and other members of the γ-subdivision. The second largest phylogenetic group corresponded to Nitrospira. The archaeal 16S rRNA phylotypes were dominated by a single group of sequences that matched phylotypes reported from South African gold mines and possessed ammonia monooxygenase (amoA) genes. Both the phylogenetic and the mineral data show that acidic microenvironments play an important role in shale weathering, but the shale has a higher microbial diversity than previously described pyritic acid mine drainage sites. The presence of a potentially biogeochemically active microbial population on the rock surface suggests that microorganisms may contribute to early events of shale degradation and coastal erosion.

Evidence indicates that Gale crater on Mars harboured a fluvio-lacustrine environment that was subjected to physio-chemical variations such as changes in redox conditions and evaporation with salinity changes, over time. Microbial communities from terrestrial environmental analogues sites are important for studying such potential habitability environments on early Mars, especially in laboratory-based simulation experiments. Traditionally, such studies have predominantly focused on microorganisms from extreme terrestrial environments. These are applicable to a range of Martian environments, however, they lack relevance to the lacustrine systems. In this study, we characterise an anoxic inter-tidal zone as a terrestrial analogue for the Gale crater lake system according to its chemical and physical properties, and its microbiological community. The sub-surface inter-tidal environment of the River Dee estuary, United Kingdom (53&deg, 21&prime, 15.40&Prime, N, 3&deg, 10&prime, 24.95&Prime, W) was selected and compared with available data from Early Hesperian-time Gale crater, and temperature, redox, and pH were similar. Compared to subsurface &lsquo, groundwater&rsquo, type fluids invoked for the Gale subsurface, salinity was higher at the River Dee site, which are more comparable to increases in salinity that likely occurred as the Gale crater lake evolved. Similarities in clay abundance indicated similar access to, specifically, the bio-essential elements Mg, Fe and K. The River Dee microbial community consisted of taxa that were known to have members that could utilise chemolithoautotrophic and chemoorganoheterotrophic metabolism and such a mixed metabolic capability would potentially have been feasible on Mars. Microorganisms isolated from the site were able to grow under environment conditions that, based on mineralogical data, were similar to that of the Gale crater&rsquo, s aqueous environment at Yellowknife Bay. Thus, the results from this study suggest that the microbial community from an anoxic inter-tidal zone is a plausible terrestrial analogue for studying habitability of fluvio-lacustrine systems on early Mars, using laboratory-based simulation experiments.

An epilithic microbial community was launched into low Earth orbit, and exposed to conditions in outer space for 548 days on the European Space Agency EXPOSE-E facility outside the International Space Station. The natural phototroph biofilm was augmented with akinetes of Anabaena cylindrica and vegetative cells of Nostoc commune and Chroococcidiopsis. In space-exposed dark controls, two algae (Chlorella and Rosenvingiella spp.), a cyanobacterium (Gloeocapsa sp.) and two bacteria associated with the natural community survived. Of the augmented organisms, cells of A. cylindrica and Chroococcidiopsis survived, but no cells of N. commune. Only cells of Chroococcidiopsis were cultured from samples exposed to the unattenuated extraterrestrial ultraviolet (UV) spectrum (>110 nm or 200 nm). Raman spectroscopy and bright-field microscopy showed that under these conditions the surface cells were bleached and their carotenoids were destroyed, although cell morphology was preserved. These experiments demonstrate that outer space can act as a selection pressure on the composition of microbial communities. The results obtained from samples exposed to >200 nm UV (simulating the putative worst-case UV exposure on the early Earth) demonstrate the potential for epilithic colonization of land masses during that time, but that UV radiation on anoxic planets can act as a strong selection pressure on surface-dwelling organisms. Finally, these experiments have yielded new phototrophic organisms of potential use in biomass and oxygen production in space exploration.

Many cyanobacteria are known to tolerate environmental extremes. Motivated by an interest in selecting cyanobacteria for applications in space, we launched rocks from a limestone cliff in Beer, Devon, United Kingdom, containing an epilithic and endolithic rock-dwelling community of cyanobacteria into low Earth orbit (LEO) at a height of approximately 300 kilometers. The community was exposed for 10 days to isolate cyanobacteria that can survive exposure to the extreme radiation and desiccating conditions associated with space. Culture-independent (16S rRNA) and culture-dependent methods showed that the cyanobacterial community was composed of Pleurocapsales , Oscillatoriales , and Chroococcales . A single cyanobacterium, a previously uncharacterized extremophile, was isolated after exposure to LEO. We were able to isolate the cyanobacterium from the limestone cliff after exposing the rock-dwelling community to desiccation and vacuum (0.7 × 10 −3 kPa) in the laboratory. The ability of the organism to survive the conditions in space may be linked to the formation of dense colonies. These experiments show how extreme environmental conditions, including space, can be used to select for novel microorganisms. Furthermore, it improves our knowledge of environmental tolerances of extremophilic rock-dwelling cyanobacteria.

14 páginas, 12 figuras, 2 tablas.-- et al., In the space experiments Lithopanspermia, experimental support was provided to the likelihood of the lithopanspermia concept that considers a viable transport of microorganisms between the terrestrial planets by means of meteorites. The rock colonising lichens Rhizocarpon geographicum and Xanthoria elegans, the vagrant lichen Aspicilia fruticulosa, and endolithic and endoevaporitic communities of cyanobacteria and bacteria with their natural rock substrate were exposed to space for 10 days onboard the Biopan facility of the European Space Agency (ESA). Biopan was closed during launch and re-entry. In addition, in the Stone facility, one sample of R. geographicum on its natural granitic substrate was attached at the outer surface of the re-entry capsule close to the stagnation point, only protected by a thin cover of glass textolite. Post-flight analysis, which included determination of the photosynthetic activity, LIVE/DEAD staining, and germination capacity of the ascospores, demonstrated that all three lichen were quite resistant to outer space conditions, which include the full spectrum of solar extraterrestrial electromagnetic radiation or selected wavelength ranges. This high resistance of the lichens to space appears to be due to their symbiotic nature and protection by their upper pigmented layer, the cortex. In contrast, the rock- or halite-inhabiting bacteria were severely damaged by the same exposure. After atmospheric re-entry, the granite of the Stone sample was transformed into a glassy, nearly homogenous material, with several friction striae. None of the lichen cells survived this re-entry process. The data suggest that lichens are suitable candidates for testing the concept of lithopanspermia, because they are extremely resistant to the harsh environment of outer space. The more critical event is the atmospheric re-entry after being captured by a planet. Experiments simulating the re-entry process of a microbe-carrying meteoroid did not show any survivors., This work was supported by grants from the Spanish Ministry of Education and Science through CSIC (CGL2006-04658/BOS to A. de los Ríos, CGL2007-62875/BOS to J. Wierzchos), UCM (CGL2006- 12179 to L. G. Sancho) and INTA (ESP2005-25292 to R. de la Torre), as well as by a grant of the Bundesministerium fuer Wirtschaft und Technologie through DLR (BMWi, 50WB0614 to S. Ott and J.P. de Vera) and the Heinrich-Hertz-Stiftung NRW.

Biomarker molecules, such as amino acids, are key to discovering whether life exists elsewhere in the Solar System. Raman spectroscopy, a technique capable of detecting biomarkers, will be on board future planetary missions including the ExoMars rover. Generally, the position of the strongest band in the spectra of amino acids is reported as the identifying band. However, for an unknown sample, it is desirable to define multiple characteristic bands for molecules to avoid any ambiguous identification. To date, there has been no definition of multiple characteristic bands for amino acids of interest to astrobiology. This study examinedL-alanine, L-aspartic acid, L-cysteine, L-glutamine and glycine and defined several Raman bands per molecule for reference as characteristic identifiers. Per amino acid, 240 spectra were recorded and compared using established statistical tests including ANOVA. The number of characteristic bands defined were 10, 12, 12, 14 and 19 for L-alanine (strongest intensity band: 832 cm-1), L-aspartic acid (938 cm-1), L-cysteine (679 cm-1),L-glutamine (1090 cm−1) and glycine (875 cm-1), respectively. The intensity of bands differed by up to six times when several points on the crystal sample were rotated through 360 °; to reduce this effect when defining characteristic bands for other molecules, we find that spectra should be recorded at a statistically significant number of points per sample to remove the effect of sample rotation. It is crucial that sets of characteristic Raman bands are defined for biomarkers that are targets for future planetary missions to ensure a positive identification can be made.

There is evidence that water may exist on Mars as brines in the subsurface. The chemistries of these brines will be greatly influenced by the local lithologies, which would impact on the organisms that could potentially live within them. There are multiple metabolisms that are theoretically viable under martian chemical conditions. In order to better establish which of these are capable of supporting persistent growth under martian conditions, we performed a series of enrichments using four geological simulants for Mars: a global composition, an early and unaltered basaltic composition, a sulfur-rich composition, and a haematite-rich composition. Enrichments were inoculated with sediment from Pyefleet mudflats in the Colne estuary (Essex, UK). Mudflat sediment was added to the simulant materials and a brine based on the chemistry of Rocknest. Enrichments were supplied with a H2/CO2 headspace at 1 bar pressure and incubated for 20 days. The enrichments were repeatedly subcultured into fresh simulant material and brines in order to effectively select for a community actively growing in this chemical environment. The enriched community was characterised through the isolation and identification of microbes, microscopy and the amplicon sequencing of 16S rRNA genes amplified from DNA extracted from each stage of the enrichment. Biotic and abiotic experiments were conducted to identify geochemical changes that occur due to the presence of microbial activity. We will present details on the communities enriched on the different martian simulants, metabolisms identified as present within the actively growing community and geochemical changes that were identified.