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Schroedl P, Silverstein M, DiGregorio D, Blättler CL, Loyd S, Bradbury HJ, Edwards RL, Marlow J. Carbonate chimneys at the highly productive point Dume methane seep: Fine-scale mineralogical, geochemical, and microbiological heterogeneity reflects dynamic and long-lived methane-metabolizing habitats. GEOBIOLOGY 2024; 22:e12608. [PMID: 38946067 DOI: 10.1111/gbi.12608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/27/2023] [Revised: 05/24/2024] [Accepted: 06/12/2024] [Indexed: 07/02/2024]
Abstract
Methane is a potent greenhouse gas that enters the marine system in large quantities at seafloor methane seeps. At a newly discovered seep site off the coast of Point Dume, CA, ~ meter-scale carbonate chimneys host microbial communities that exhibit the highest methane-oxidizing potential recorded to date. Here, we provide a detailed assessment of chimney geobiology through correlative mineralogical, geochemical, and microbiological studies of seven chimney samples in order to clarify the longevity and heterogeneity of these highly productive systems. U-Th dating indicated that a methane-driven carbonate precipitating system at Point Dume has existed for ~20 Kyr, while millimeter-scale variations in carbon and calcium isotopic values, elemental abundances, and carbonate polymorphs revealed changes in carbon source, precipitation rates, and diagenetic processes throughout the chimneys' lifespan. Microbial community analyses revealed diverse modern communities with prominent anaerobic methanotrophs, sulfate-reducing bacteria, and Anaerolineaceae; communities were more similar within a given chimney wall transect than in similar horizons of distinct structures. The chimneys represent long-lived repositories of methane-oxidizing communities and provide a window into how carbon can be transformed, sequestered, and altered over millennia at the Point Dume methane seep.
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Affiliation(s)
- Peter Schroedl
- Department of Biology, Boston University, Boston, Massachusetts, USA
| | | | - Daisy DiGregorio
- Department of Biology, Boston University, Boston, Massachusetts, USA
| | - Clara L Blättler
- Department of the Geophysical Sciences, University of Chicago, Chicago, Illinois, USA
| | - Sean Loyd
- Department of Geological Sciences, California State University Fullerton, Fullerton, California, USA
| | - Harold J Bradbury
- Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, Vancouver, British Columbia, Canada
| | - R Lawrence Edwards
- Department of Earth and Environmental Science, University of Minnesota, Minneapolis, Minnesota, USA
| | - Jeffrey Marlow
- Department of Biology, Boston University, Boston, Massachusetts, USA
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2
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Hart R, Cardace D. Mineral Indicators of Geologically Recent Past Habitability on Mars. Life (Basel) 2023; 13:2349. [PMID: 38137950 PMCID: PMC10744562 DOI: 10.3390/life13122349] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2023] [Revised: 11/25/2023] [Accepted: 12/05/2023] [Indexed: 12/24/2023] Open
Abstract
We provide new support for habitable microenvironments in the near-subsurface of Mars, hosted in Fe- and Mg-rich rock units, and present a list of minerals that can serve as indicators of specific water-rock reactions in recent geologic paleohabitats for follow-on study. We modeled, using a thermodynamic basis without selective phase suppression, the reactions of published Martian meteorites and Jezero Crater igneous rock compositions and reasonable planetary waters (saline, alkaline waters) using Geochemist's Workbench Ver. 12.0. Solid-phase inputs were meteorite compositions for ALH 77005, Nakhla, and Chassigny, and two rock units from the Mars 2020 Perseverance rover sites, Máaz and Séítah. Six plausible Martian groundwater types [NaClO4, Mg(ClO4)2, Ca(ClO4)2, Mg-Na2(ClO4)2, Ca-Na2(ClO4)2, Mg-Ca(ClO4)2] and a unique Mars soil-water analog solution (dilute saline solution) named "Rosy Red", related to the Phoenix Lander mission, were the aqueous-phase inputs. Geophysical conditions were tuned to near-subsurface Mars (100 °C or 373.15 K, associated with residual heat from a magmatic system, impact event, or a concentration of radionuclides, and 101.3 kPa, similar to <10 m depth). Mineral products were dominated by phyllosilicates such as serpentine-group minerals in most reaction paths, but differed in some important indicator minerals. Modeled products varied in physicochemical properties (pH, Eh, conductivity), major ion activities, and related gas fugacities, with different ecological implications. The microbial habitability of pore spaces in subsurface groundwater percolation systems was interrogated at equilibrium in a thermodynamic framework, based on Gibbs Free Energy Minimization. Models run with the Chassigny meteorite produced the overall highest H2 fugacity. Models reliant on the Rosy Red soil-water analog produced the highest sustained CH4 fugacity (maximum values observed for reactant ALH 77005). In general, Chassigny meteorite protoliths produced the best yield regarding Gibbs Free Energy, from an astrobiological perspective. Occurrences of serpentine and saponite across models are key: these minerals have been observed using CRISM spectral data, and their formation via serpentinization would be consistent with geologically recent-past H2 and CH4 production and sustained energy sources for microbial life. We list index minerals to be used as diagnostic for paleo water-rock models that could have supported geologically recent-past microbial activity, and suggest their application as criteria for future astrobiology study-site selections.
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Affiliation(s)
- Roger Hart
- Department of Physics and Engineering, Community College of Rhode Island, Lincoln, RI 02865, USA
- Department of Geosciences, University of Rhode Island, Kingston, RI 02881, USA;
| | - Dawn Cardace
- Department of Geosciences, University of Rhode Island, Kingston, RI 02881, USA;
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3
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Rempfert KR, Kraus EA, Nothaft DB, Dildar N, Spear JR, Sepúlveda J, Templeton AS. Intact polar lipidome and membrane adaptations of microbial communities inhabiting serpentinite-hosted fluids. Front Microbiol 2023; 14:1198786. [PMID: 38029177 PMCID: PMC10667739 DOI: 10.3389/fmicb.2023.1198786] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2023] [Accepted: 09/25/2023] [Indexed: 12/01/2023] Open
Abstract
The generation of hydrogen and reduced carbon compounds during serpentinization provides sustained energy for microorganisms on Earth, and possibly on other extraterrestrial bodies (e.g., Mars, icy satellites). However, the geochemical conditions that arise from water-rock reaction also challenge the known limits of microbial physiology, such as hyperalkaline pH, limited electron acceptors and inorganic carbon. Because cell membranes act as a primary barrier between a cell and its environment, lipids are a vital component in microbial acclimation to challenging physicochemical conditions. To probe the diversity of cell membrane lipids produced in serpentinizing settings and identify membrane adaptations to this environment, we conducted the first comprehensive intact polar lipid (IPL) biomarker survey of microbial communities inhabiting the subsurface at a terrestrial site of serpentinization. We used an expansive, custom environmental lipid database that expands the application of targeted and untargeted lipodomics in the study of microbial and biogeochemical processes. IPLs extracted from serpentinite-hosted fluid communities were comprised of >90% isoprenoidal and non-isoprenoidal diether glycolipids likely produced by archaeal methanogens and sulfate-reducing bacteria. Phospholipids only constituted ~1% of the intact polar lipidome. In addition to abundant diether glycolipids, betaine and trimethylated-ornithine aminolipids and glycosphingolipids were also detected, indicating pervasive membrane modifications in response to phosphate limitation. The carbon oxidation state of IPL backbones was positively correlated with the reduction potential of fluids, which may signify an energy conservation strategy for lipid synthesis. Together, these data suggest microorganisms inhabiting serpentinites possess a unique combination of membrane adaptations that allow for their survival in polyextreme environments. The persistence of IPLs in fluids beyond the presence of their source organisms, as indicated by 16S rRNA genes and transcripts, is promising for the detection of extinct life in serpentinizing settings through lipid biomarker signatures. These data contribute new insights into the complexity of lipid structures generated in actively serpentinizing environments and provide valuable context to aid in the reconstruction of past microbial activity from fossil lipid records of terrestrial serpentinites and the search for biosignatures elsewhere in our solar system.
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Affiliation(s)
- Kaitlin R. Rempfert
- Department of Geological Sciences, University of Colorado, Boulder, CO, United States
| | - Emily A. Kraus
- Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, CO, United States
| | - Daniel B. Nothaft
- Department of Geological Sciences, University of Colorado, Boulder, CO, United States
| | - Nadia Dildar
- Department of Geological Sciences, University of Colorado, Boulder, CO, United States
| | - John R. Spear
- Department of Civil and Environmental Engineering, Colorado School of Mines, Golden, CO, United States
- Department of Quantitative Biosciences and Engineering, Colorado School of Mines, Golden, CO, United States
| | - Julio Sepúlveda
- Department of Geological Sciences, University of Colorado, Boulder, CO, United States
| | - Alexis S. Templeton
- Department of Geological Sciences, University of Colorado, Boulder, CO, United States
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4
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Enya K, Yamagishi A, Kobayashi K, Yoshimura Y. Comparative study of methods for detecting extraterrestrial life in exploration mission of Mars and the solar system. LIFE SCIENCES IN SPACE RESEARCH 2022; 34:53-67. [PMID: 35940690 DOI: 10.1016/j.lssr.2022.07.001] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/12/2022] [Revised: 06/16/2022] [Accepted: 07/07/2022] [Indexed: 06/15/2023]
Abstract
The detection and analysis of extraterrestrial life are important issues of space science. Mars is among the most important planets to explore for extraterrestrial life, owing both to its physical properties and to its ancient and present environments as revealed by previous exploration missions. In this paper, we present a comparative study of methods for detecting extraterrestrial life and life-related substances. To this end, we have classified and summarized the characteristics targeted for the detection of extraterrestrial life in solar system exploration mission and the methods used to evaluate them. A summary table is presented. We conclude that at this moment (i) there is no realistic single detection method capable of concluding the discovery of extraterrestrial life, (ii) no single method has an advantage over the others in all respects, and (iii) there is no single method capable of distinguishing extraterrestrial life from terrestrial life. Therefore, a combination of complementary methods is essential. We emphasize the importance of endeavoring to detect extraterrestrial life without overlooking possible alien life forms, even at the cost of tolerating false positives. Summaries of both the targets and the detection methods should be updated continuously, and comparative studies of both should be pursued. Although this study assumes Mars to be a model site for the primary environment for life searches, both the targets and detection methods described herein will also be useful for searching for extraterrestrial life in any celestial environment and for the initial inspection of returned samples.
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Affiliation(s)
- Keigo Enya
- Institute of Space & Astronautical Science, Japan Aerospace Exploration Agency, 3-1-1 Yoshinodai, Chuou, Sagamihara, Kanagawa 252-5210, Japan.
| | - Akihiko Yamagishi
- School of Life Science, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi, Hachioji, Tokyo 192-0392, Japan
| | - Kensei Kobayashi
- Department of Chemistry, Yokohama National University, 79-5 Tokiwadai, Hodogaya, Yokohama 240-8501, Japan
| | - Yoshitaka Yoshimura
- Department of Life Science, Tamagawa University, 6-1-1 Tamagawagakuen, Machida, Tokyo 194-8610, Japan
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5
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Magnuson E, Altshuler I, Fernández-Martínez MÁ, Chen YJ, Maggiori C, Goordial J, Whyte LG. Active lithoautotrophic and methane-oxidizing microbial community in an anoxic, sub-zero, and hypersaline High Arctic spring. THE ISME JOURNAL 2022; 16:1798-1808. [PMID: 35396347 PMCID: PMC9213412 DOI: 10.1038/s41396-022-01233-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/28/2021] [Revised: 03/21/2022] [Accepted: 03/29/2022] [Indexed: 05/01/2023]
Abstract
Lost Hammer Spring, located in the High Arctic of Nunavut, Canada, is one of the coldest and saltiest terrestrial springs discovered to date. It perennially discharges anoxic (<1 ppm dissolved oxygen), sub-zero (~-5 °C), and hypersaline (~24% salinity) brines from the subsurface through up to 600 m of permafrost. The sediment is sulfate-rich (1 M) and continually emits gases composed primarily of methane (~50%), making Lost Hammer the coldest known terrestrial methane seep and an analog to extraterrestrial habits on Mars, Europa, and Enceladus. A multi-omics approach utilizing metagenome, metatranscriptome, and single-amplified genome sequencing revealed a rare surface terrestrial habitat supporting a predominantly lithoautotrophic active microbial community driven in part by sulfide-oxidizing Gammaproteobacteria scavenging trace oxygen. Genomes from active anaerobic methane-oxidizing archaea (ANME-1) showed evidence of putative metabolic flexibility and hypersaline and cold adaptations. Evidence of anaerobic heterotrophic and fermentative lifestyles were found in candidate phyla DPANN archaea and CG03 bacteria genomes. Our results demonstrate Mars-relevant metabolisms including sulfide oxidation, sulfate reduction, anaerobic oxidation of methane, and oxidation of trace gases (H2, CO2) detected under anoxic, hypersaline, and sub-zero ambient conditions, providing evidence that similar extant microbial life could potentially survive in similar habitats on Mars.
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Affiliation(s)
- Elisse Magnuson
- Natural Resource Sciences, McGill University, Ste-Anne-de-Bellevue, QC, Canada
| | - Ianina Altshuler
- School of Architecture, Civil and Environmental Engineering, Ecole Polytechnique Fédérale de Lausanne, Lausanne, Switzerland
| | | | - Ya-Jou Chen
- Natural Resource Sciences, McGill University, Ste-Anne-de-Bellevue, QC, Canada
| | - Catherine Maggiori
- Natural Resource Sciences, McGill University, Ste-Anne-de-Bellevue, QC, Canada
| | | | - Lyle G Whyte
- Natural Resource Sciences, McGill University, Ste-Anne-de-Bellevue, QC, Canada.
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6
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Abstract
Priorities for the exploration of Mars involve the identification and observation of biosignatures that indicate the existence of life on the planet. The atmosphere and composition of the sediments on Mars suggest suitability for anaerobic chemolithotrophic metabolism. Carbonates are often considered as morphological biosignatures, such as stromatolites, but have not been considered as potential electron acceptors. Within the present study, hydrogenotrophic methanogen enrichments were generated from sediments that had received significant quantities of lime from industrial processes (lime kiln/steel production). These enrichments were then supplemented with calcium carbonate powder or marble chips as a sole source of carbon. These microcosms saw a release of inorganic carbon into the liquid phase, which was subsequently removed, resulting in the generation of methane, with 0.37 ± 0.09 mmoles of methane observed in the steel sediment enrichments supplemented with calcium carbonate powder. The steel sediment microcosms and lime sediments with carbonate powder enrichments were dominated by Methanobacterium sp., whilst the lime/marble enrichments were more diverse, containing varying proportions of Methanomassiliicoccus, Methanoculleus and Methanosarcina sp. In all microcosm experiments, acetic acid was detected in the liquid phase. Our results indicate that chemolithotrophic methanogenesis should be considered when determining biosignatures for life on Mars.
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7
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Luo Y, Mischna MA, Lin JC, Fasoli B, Cai X, Yung YL. Mars Methane Sources in Northwestern Gale Crater Inferred From Back Trajectory Modeling. EARTH AND SPACE SCIENCE (HOBOKEN, N.J.) 2021; 8:e2021EA001915. [PMID: 35860450 PMCID: PMC9285602 DOI: 10.1029/2021ea001915] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/11/2021] [Revised: 10/26/2021] [Accepted: 10/27/2021] [Indexed: 06/15/2023]
Abstract
During its first seven years of operation, the Sample Analysis at Mars Tunable Laser Spectrometer (TLS) on board the Curiosity rover has detected seven methane spikes above a low background abundance in Gale crater. The methane spikes are likely sourced by surface emission within or around Gale crater. Here, we use inverse Lagrangian modeling techniques to identify upstream emission regions on the Martian surface for these methane spikes at an unprecedented spatial resolution. Inside Gale crater, the northwestern crater floor casts the strongest influence on the detections. Outside Gale crater, the upstream regions common to all the methane spikes extend toward the north. The contrasting results from two consecutive TLS methane measurements performed on the same sol point to an active emission site to the west or the southwest of the Curiosity rover on the northwestern crater floor. The observed spike magnitude and frequency also favor emission sites on the northwestern crater floor, unless there are fast methane removal mechanisms at work, or either the methane spikes of TLS or the non-detections of ExoMars Trace Gas Orbiter cannot be trusted.
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Affiliation(s)
- Y. Luo
- Division of Geological and Planetary SciencesCalifornia Institute of TechnologyPasadenaCAUSA
| | - M. A. Mischna
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
| | - J. C. Lin
- Department of Atmospheric SciencesUniversity of UtahSalt Lake CityUTUSA
| | - B. Fasoli
- Department of Atmospheric SciencesUniversity of UtahSalt Lake CityUTUSA
| | - X. Cai
- Columbia UniversityNew YorkNYUSA
| | - Y. L. Yung
- Division of Geological and Planetary SciencesCalifornia Institute of TechnologyPasadenaCAUSA
- Jet Propulsion LaboratoryCalifornia Institute of TechnologyPasadenaCAUSA
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8
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Harris RL, Schuerger AC, Wang W, Tamama Y, Garvin ZK, Onstott TC. Transcriptional response to prolonged perchlorate exposure in the methanogen Methanosarcina barkeri and implications for Martian habitability. Sci Rep 2021; 11:12336. [PMID: 34117335 PMCID: PMC8196204 DOI: 10.1038/s41598-021-91882-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2021] [Accepted: 05/28/2021] [Indexed: 02/05/2023] Open
Abstract
Observations of trace methane (CH4) in the Martian atmosphere are significant to the astrobiology community given the overwhelming contribution of biological methanogenesis to atmospheric CH4 on Earth. Previous studies have shown that methanogenic Archaea can generate CH4 when incubated with perchlorates, highly oxidizing chaotropic salts which have been found across the Martian surface. However, the regulatory mechanisms behind this remain completely unexplored. In this study we performed comparative transcriptomics on the methanogen Methanosarcina barkeri, which was incubated at 30˚C and 0˚C with 10-20 mM calcium-, magnesium-, or sodium perchlorate. Consistent with prior studies, we observed decreased CH4 production and apparent perchlorate reduction, with the latter process proceeding by heretofore essentially unknown mechanisms. Transcriptomic responses of M. barkeri to perchlorates include up-regulation of osmoprotectant transporters and selection against redox-sensitive amino acids. Increased expression of methylamine methanogenesis genes suggest competition for H2 with perchlorate reduction, which we propose is catalyzed by up-regulated molybdenum-containing enzymes and maintained by siphoning diffused H2 from energy-conserving hydrogenases. Methanogenesis regulatory patterns suggest Mars' freezing temperatures alone pose greater constraints to CH4 production than perchlorates. These findings increase our understanding of methanogen survival in extreme environments and confers continued consideration of a potential biological contribution to Martian CH4.
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Affiliation(s)
- Rachel L Harris
- Department of Geosciences, Princeton University, Princeton, NJ, USA.
- Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA.
| | - Andrew C Schuerger
- Department of Plant Pathology, University of Florida, Gainesville, FL, USA
| | - Wei Wang
- Lewis-Sigler Institute for Integrative Genomics, Department of Molecular Biology, Princeton University, Princeton, NJ, USA
| | - Yuri Tamama
- Department of Geosciences, Princeton University, Princeton, NJ, USA
| | - Zachary K Garvin
- Department of Geosciences, Princeton University, Princeton, NJ, USA
| | - Tullis C Onstott
- Department of Geosciences, Princeton University, Princeton, NJ, USA
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9
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Influence of tectonics on global scale distribution of geological methane emissions. Nat Commun 2020; 11:2305. [PMID: 32385247 PMCID: PMC7210894 DOI: 10.1038/s41467-020-16229-1] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2019] [Accepted: 04/17/2020] [Indexed: 11/08/2022] Open
Abstract
Earth's hydrocarbon degassing through gas-oil seeps, mud volcanoes and diffuse microseepage is a major natural source of methane (CH4) to the atmosphere. While carbon dioxide degassing is typically associated with extensional tectonics, volcanoes, and geothermal areas, CH4 seepage mostly occurs in petroleum-bearing sedimentary basins, but the role of tectonics in degassing is known only for some case studies at local scale. Here, we perform a global scale geospatial analysis to assess how the presence of hydrocarbon fields, basin geodynamics and the type of faults control CH4 seepage. Combining georeferenced data of global inventories of onshore seeps, faults, sedimentary basins, petroleum fields and heat flow, we find that hydrocarbon seeps prevail in petroleum fields within convergent basins with heat flow ≤ 98 mW m-2, and along any type of brittle tectonic structure, mostly in reverse fault settings. Areas potentially hosting additional seeps and microseepage are identified through a global seepage favourability model.
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10
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Corenblit D, Darrozes J, Julien F, Otto T, Roussel E, Steiger J, Viles H. The Search for a Signature of Life on Mars: A Biogeomorphological Approach. ASTROBIOLOGY 2019; 19:1279-1291. [PMID: 31584307 DOI: 10.1089/ast.2018.1969] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Geological evidence shows that life on Earth evolved in line with major concomitant changes in Earth surface processes and landforms. Biogeomorphological characteristics, especially those involving microorganisms, are potentially important facets of biosignatures on Mars and are generating increasing interest in astrobiology. Using Earth as an analog provides reasons to suspect that past or present life on Mars could have resulted in recognizable biogenic landforms. Here, we discuss the potential for, and limitations of, a biogeomorphological approach to identifying the subsets of landforms that are modulated or created through biological processes and thus present signatures of life on Mars. Subsets especially involving microorganisms that are potentially important facets of biosignatures on Mars are proposed: (i) weathering features, biocrusts, patinas, and varnishes; (ii) microbialites and microbially induced sedimentary structures (MISS); (iii) bioaccumulations of skeletal remains; (iv) degassing landforms; (v) cryoconites; (vi) self-organized patterns; (vii) unclassified non-analog landforms. We propose a biogeomorphological frequency histogram approach to identify anomalies/modulations in landform properties. Such detection of anomalies/modulations will help track a biotic origin and lead to the development of an integrative multiproxy and multiscale approach combining morphological, structural, textural, and geochemical expertise. This perspective can help guide the choice of investigation sites for future missions and the types and scales of observations to be made by orbiters and rovers.
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Affiliation(s)
- Dov Corenblit
- Université Clermont Auvergne, CNRS, GEOLAB - F-63000 Clermont-Ferrand, France
| | - José Darrozes
- Université Paul Sabatier, CNRS/IRD, GET - F-31062 Toulouse, France
| | - Frédéric Julien
- CNRS, ECOLAB, Université Paul Sabatier, CNRS, INPT, UPS, F-31062 Toulouse, France
| | - Thierry Otto
- CNRS, ECOLAB, Université Paul Sabatier, CNRS, INPT, UPS, F-31062 Toulouse, France
| | - Erwan Roussel
- Université Clermont Auvergne, CNRS, GEOLAB - F-63000 Clermont-Ferrand, France
| | - Johannes Steiger
- Université Clermont Auvergne, CNRS, GEOLAB - F-63000 Clermont-Ferrand, France
| | - Heather Viles
- School of Geography and the Environment, University of Oxford, Oxford, United Kingdom
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11
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Habitability of Mars: How Welcoming Are the Surface and Subsurface to Life on the Red Planet? GEOSCIENCES 2019. [DOI: 10.3390/geosciences9090361] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Mars is a planet of great interest in the search for signatures of past or present life beyond Earth. The years of research, and more advanced instrumentation, have yielded a lot of evidence which may be considered by the scientific community as proof of past or present habitability of Mars. Recent discoveries including seasonal methane releases and a subglacial lake are exciting, yet challenging findings. Concurrently, laboratory and environmental studies on the limits of microbial life in extreme environments on Earth broaden our knowledge of the possibility of Mars habitability. In this review, we aim to: (1) Discuss the characteristics of the Martian surface and subsurface that may be conducive to habitability either in the past or at present; (2) discuss laboratory-based studies on Earth that provide us with discoveries on the limits of life; and (3) summarize the current state of knowledge in terms of direction for future research.
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12
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Aeolian abrasion of rocks as a mechanism to produce methane in the Martian atmosphere. Sci Rep 2019; 9:8229. [PMID: 31160623 PMCID: PMC6546745 DOI: 10.1038/s41598-019-44616-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2018] [Accepted: 05/16/2019] [Indexed: 11/08/2022] Open
Abstract
Seasonal changes in methane background levels and methane spikes have been detected in situ a metre above the Martian surface, and larger methane plumes detected via ground-based remote sensing, however their origin have not yet been adequately explained. Proposed methane sources include the UV irradiation of meteoritic-derived organic matter, hydrothermal reactions with olivine, organic breakdown via meteoroid impact, release from gas hydrates, biological production, or the release of methane from fluid inclusions in basalt during aeolian erosion. Here we quantify for the first time the potential importance of aeolian abrasion as a mechanism for releasing trapped methane from within rocks, by coupling estimates of present day surface wind abrasion with the methane contents of a variety of Martian meteorites, analogue terrestrial basalts and analogue terrestrial sedimentary rocks. We demonstrate that the abrasion of basalt under present day Martian rates of aeolian erosion is highly unlikely to produce detectable changes in methane concentrations in the atmosphere. We further show that, although there is a greater potential for methane production from the aeolian abrasion of certain sedimentary rocks, to produce the magnitude of methane concentrations analysed by the Curiosity rover they would have to contain methane in similar concentrations as economic reserved of biogenic/thermogenic deposits on Earth. Therefore we suggest that aeolian abrasion is an unlikely origin of the methane detected in the Martian atmosphere, and that other methane sources are required.
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13
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Korablev O, Vandaele AC, Montmessin F, Fedorova AA, Trokhimovskiy A, Forget F, Lefèvre F, Daerden F, Thomas IR, Trompet L, Erwin JT, Aoki S, Robert S, Neary L, Viscardy S, Grigoriev AV, Ignatiev NI, Shakun A, Patrakeev A, Belyaev DA, Bertaux JL, Olsen KS, Baggio L, Alday J, Ivanov YS, Ristic B, Mason J, Willame Y, Depiesse C, Hetey L, Berkenbosch S, Clairquin R, Queirolo C, Beeckman B, Neefs E, Patel MR, Bellucci G, López-Moreno JJ, Wilson CF, Etiope G, Zelenyi L, Svedhem H, Vago JL. No detection of methane on Mars from early ExoMars Trace Gas Orbiter observations. Nature 2019; 568:517-520. [PMID: 30971829 DOI: 10.1038/s41586-019-1096-4] [Citation(s) in RCA: 88] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2018] [Accepted: 03/14/2019] [Indexed: 11/09/2022]
Abstract
The detection of methane on Mars has been interpreted as indicating that geochemical or biotic activities could persist on Mars today1. A number of different measurements of methane show evidence of transient, locally elevated methane concentrations and seasonal variations in background methane concentrations2-5. These measurements, however, are difficult to reconcile with our current understanding of the chemistry and physics of the Martian atmosphere6,7, which-given methane's lifetime of several centuries-predicts an even, well mixed distribution of methane1,6,8. Here we report highly sensitive measurements of the atmosphere of Mars in an attempt to detect methane, using the ACS and NOMAD instruments onboard the ESA-Roscosmos ExoMars Trace Gas Orbiter from April to August 2018. We did not detect any methane over a range of latitudes in both hemispheres, obtaining an upper limit for methane of about 0.05 parts per billion by volume, which is 10 to 100 times lower than previously reported positive detections2,4. We suggest that reconciliation between the present findings and the background methane concentrations found in the Gale crater4 would require an unknown process that can rapidly remove or sequester methane from the lower atmosphere before it spreads globally.
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Affiliation(s)
- Oleg Korablev
- Space Research Institute (IKI), Russian Academy of Sciences (RAS), Moscow, Russia.
| | | | - Franck Montmessin
- Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Paris, France
| | - Anna A Fedorova
- Space Research Institute (IKI), Russian Academy of Sciences (RAS), Moscow, Russia
| | | | - François Forget
- Laboratoire de Météorologie Dynamique (LMD), CNRS Jussieu, Paris, France
| | - Franck Lefèvre
- Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Paris, France
| | - Frank Daerden
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Ian R Thomas
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Loïc Trompet
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Justin T Erwin
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Shohei Aoki
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Séverine Robert
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Lori Neary
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Sébastien Viscardy
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Alexey V Grigoriev
- Space Research Institute (IKI), Russian Academy of Sciences (RAS), Moscow, Russia
| | - Nikolay I Ignatiev
- Space Research Institute (IKI), Russian Academy of Sciences (RAS), Moscow, Russia
| | - Alexey Shakun
- Space Research Institute (IKI), Russian Academy of Sciences (RAS), Moscow, Russia
| | - Andrey Patrakeev
- Space Research Institute (IKI), Russian Academy of Sciences (RAS), Moscow, Russia
| | - Denis A Belyaev
- Space Research Institute (IKI), Russian Academy of Sciences (RAS), Moscow, Russia
| | - Jean-Loup Bertaux
- Space Research Institute (IKI), Russian Academy of Sciences (RAS), Moscow, Russia.,Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Paris, France
| | - Kevin S Olsen
- Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Paris, France
| | - Lucio Baggio
- Laboratoire Atmosphères, Milieux, Observations Spatiales (LATMOS), UVSQ Université Paris-Saclay, Sorbonne Université, CNRS, Paris, France
| | - Juan Alday
- Department of Physics, Oxford University, Oxford, UK
| | - Yuriy S Ivanov
- Main Astronomical Observatory (MAO), National Academy of Sciences of Ukraine, Kiev, Ukraine
| | - Bojan Ristic
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Jon Mason
- School of Physical Sciences, The Open University, Milton Keynes, UK
| | - Yannick Willame
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Cédric Depiesse
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Laszlo Hetey
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Sophie Berkenbosch
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Roland Clairquin
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Claudio Queirolo
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Bram Beeckman
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Eddy Neefs
- Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Manish R Patel
- School of Physical Sciences, The Open University, Milton Keynes, UK
| | | | - Jose-Juan López-Moreno
- Instituto de Astrofìsica de Andalucía, Consejo Superior de Investigaciones Científicas (CSIC), Granada, Spain
| | | | - Giuseppe Etiope
- Instituto de Astrofisica e Planetologia Spaziali, INAF, Rome, Italy.,Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy.,Faculty of Environmental Science and Engineering, Babes-Bolyai University, Cluj-Napoca, Romania
| | - Lev Zelenyi
- Space Research Institute (IKI), Russian Academy of Sciences (RAS), Moscow, Russia
| | - Håkan Svedhem
- European Space Research and Technology Centre (ESTEC), ESA, Noordwijk, The Netherlands
| | - Jorge L Vago
- European Space Research and Technology Centre (ESTEC), ESA, Noordwijk, The Netherlands
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14
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Neveu M, Hays LE, Voytek MA, New MH, Schulte MD. The Ladder of Life Detection. ASTROBIOLOGY 2018; 18:1375-1402. [PMID: 29862836 PMCID: PMC6211372 DOI: 10.1089/ast.2017.1773] [Citation(s) in RCA: 89] [Impact Index Per Article: 14.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2017] [Accepted: 03/23/2018] [Indexed: 05/04/2023]
Abstract
We describe the history and features of the Ladder of Life Detection, a tool intended to guide the design of investigations to detect microbial life within the practical constraints of robotic space missions. To build the Ladder, we have drawn from lessons learned from previous attempts at detecting life and derived criteria for a measurement (or suite of measurements) to constitute convincing evidence for indigenous life. We summarize features of life as we know it, how specific they are to life, and how they can be measured, and sort these features in a general sense based on their likelihood of indicating life. Because indigenous life is the hypothesis of last resort in interpreting life-detection measurements, we propose a small but expandable set of decision rules determining whether the abiotic hypothesis is disproved. In light of these rules, we evaluate past and upcoming attempts at life detection. The Ladder of Life Detection is not intended to endorse specific biosignatures or instruments for life-detection measurements, and is by no means a definitive, final product. It is intended as a starting point to stimulate discussion, debate, and further research on the characteristics of life, what constitutes a biosignature, and the means to measure them.
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Affiliation(s)
- Marc Neveu
- NASA Postdoctoral Management Program Fellow, Universities Space Research Association, Columbia, Maryland
- NASA Headquarters, Washington, DC
| | - Lindsay E. Hays
- NASA Headquarters, Washington, DC
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
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15
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Yung YL, Chen P, Nealson K, Atreya S, Beckett P, Blank JG, Ehlmann B, Eiler J, Etiope G, Ferry JG, Forget F, Gao P, Hu R, Kleinböhl A, Klusman R, Lefèvre F, Miller C, Mischna M, Mumma M, Newman S, Oehler D, Okumura M, Oremland R, Orphan V, Popa R, Russell M, Shen L, Sherwood Lollar B, Staehle R, Stamenković V, Stolper D, Templeton A, Vandaele AC, Viscardy S, Webster CR, Wennberg PO, Wong ML, Worden J. Methane on Mars and Habitability: Challenges and Responses. ASTROBIOLOGY 2018; 18:1221-1242. [PMID: 30234380 PMCID: PMC6205098 DOI: 10.1089/ast.2018.1917] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/07/2018] [Accepted: 06/12/2018] [Indexed: 05/05/2023]
Abstract
Recent measurements of methane (CH4) by the Mars Science Laboratory (MSL) now confront us with robust data that demand interpretation. Thus far, the MSL data have revealed a baseline level of CH4 (∼0.4 parts per billion by volume [ppbv]), with seasonal variations, as well as greatly enhanced spikes of CH4 with peak abundances of ∼7 ppbv. What do these CH4 revelations with drastically different abundances and temporal signatures represent in terms of interior geochemical processes, or is martian CH4 a biosignature? Discerning how CH4 generation occurs on Mars may shed light on the potential habitability of Mars. There is no evidence of life on the surface of Mars today, but microbes might reside beneath the surface. In this case, the carbon flux represented by CH4 would serve as a link between a putative subterranean biosphere on Mars and what we can measure above the surface. Alternatively, CH4 records modern geochemical activity. Here we ask the fundamental question: how active is Mars, geochemically and/or biologically? In this article, we examine geological, geochemical, and biogeochemical processes related to our overarching question. The martian atmosphere and surface are an overwhelmingly oxidizing environment, and life requires pairing of electron donors and electron acceptors, that is, redox gradients, as an essential source of energy. Therefore, a fundamental and critical question regarding the possibility of life on Mars is, "Where can we find redox gradients as energy sources for life on Mars?" Hence, regardless of the pathway that generates CH4 on Mars, the presence of CH4, a reduced species in an oxidant-rich environment, suggests the possibility of redox gradients supporting life and habitability on Mars. Recent missions such as ExoMars Trace Gas Orbiter may provide mapping of the global distribution of CH4. To discriminate between abiotic and biotic sources of CH4 on Mars, future studies should use a series of diagnostic geochemical analyses, preferably performed below the ground or at the ground/atmosphere interface, including measurements of CH4 isotopes, methane/ethane ratios, H2 gas concentration, and species such as acetic acid. Advances in the fields of Mars exploration and instrumentation will be driven, augmented, and supported by an improved understanding of atmospheric chemistry and dynamics, deep subsurface biogeochemistry, astrobiology, planetary geology, and geophysics. Future Mars exploration programs will have to expand the integration of complementary areas of expertise to generate synergistic and innovative ideas to realize breakthroughs in advancing our understanding of the potential of life and habitable conditions having existed on Mars. In this spirit, we conducted a set of interdisciplinary workshops. From this series has emerged a vision of technological, theoretical, and methodological innovations to explore the martian subsurface and to enhance spatial tracking of key volatiles, such as CH4.
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Affiliation(s)
- Yuk L. Yung
- California Institute of Technology, Pasadena, California
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Pin Chen
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | | | | | | | - Jennifer G. Blank
- NASA Ames Research Center, Blue Marble Space Institute of Science, Mountain View, California
| | - Bethany Ehlmann
- California Institute of Technology, Pasadena, California
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - John Eiler
- California Institute of Technology, Pasadena, California
| | - Giuseppe Etiope
- Istituto Nazionale di Geofisica e Vulcanologia, Rome, Italy
- Faculty of Environmental Science and Engineering, Babes-Bolyai University, Cluj-Napoca, Romania
| | - James G. Ferry
- The Pennsylvania State University, University Park, Pennsylvania
| | - Francois Forget
- Laboratoire de Météorologie Dynamique, Institut Pierre Simon Laplace, CNRS, Paris, France
| | - Peter Gao
- University of California, Berkeley, California
| | - Renyu Hu
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Armin Kleinböhl
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | | | - Franck Lefèvre
- Laboratoire Atmospheres, Milieux, Observations Spatiales (LATMOS), IPSL, Paris, France
| | - Charles Miller
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Michael Mischna
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Michael Mumma
- NASA Goddard Space Flight Center, Greenbelt, Maryland
| | - Sally Newman
- California Institute of Technology, Pasadena, California
| | | | | | | | | | - Radu Popa
- University of Southern California, Los Angeles, California
| | - Michael Russell
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Linhan Shen
- California Institute of Technology, Pasadena, California
| | | | - Robert Staehle
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Vlada Stamenković
- California Institute of Technology, Pasadena, California
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | | | | | - Ann C. Vandaele
- The Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Sébastien Viscardy
- The Royal Belgian Institute for Space Aeronomy (BIRA-IASB), Brussels, Belgium
| | - Christopher R. Webster
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | | | | | - John Worden
- NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
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16
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Jones RM, Goordial JM, Orcutt BN. Low Energy Subsurface Environments as Extraterrestrial Analogs. Front Microbiol 2018; 9:1605. [PMID: 30072971 PMCID: PMC6058055 DOI: 10.3389/fmicb.2018.01605] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2018] [Accepted: 06/27/2018] [Indexed: 11/13/2022] Open
Abstract
Earth's subsurface is often isolated from phototrophic energy sources and characterized by chemotrophic modes of life. These environments are often oligotrophic and limited in electron donors or electron acceptors, and include continental crust, subseafloor oceanic crust, and marine sediment as well as subglacial lakes and the subsurface of polar desert soils. These low energy subsurface environments are therefore uniquely positioned for examining minimum energetic requirements and adaptations for chemotrophic life. Current targets for astrobiology investigations of extant life are planetary bodies with largely inhospitable surfaces, such as Mars, Europa, and Enceladus. Subsurface environments on Earth thus serve as analogs to explore possibilities of subsurface life on extraterrestrial bodies. The purpose of this review is to provide an overview of subsurface environments as potential analogs, and the features of microbial communities existing in these low energy environments, with particular emphasis on how they inform the study of energetic limits required for life. The thermodynamic energetic calculations presented here suggest that free energy yields of reactions and energy density of some metabolic redox reactions on Mars, Europa, Enceladus, and Titan could be comparable to analog environments in Earth's low energy subsurface habitats.
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Affiliation(s)
| | | | - Beth N. Orcutt
- Bigelow Laboratory for Ocean Sciences, East Boothbay, ME, United States
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17
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Webster CR, Mahaffy PR, Atreya SK, Moores JE, Flesch GJ, Malespin C, McKay CP, Martinez G, Smith CL, Martin-Torres J, Gomez-Elvira J, Zorzano MP, Wong MH, Trainer MG, Steele A, Archer D, Sutter B, Coll PJ, Freissinet C, Meslin PY, Gough RV, House CH, Pavlov A, Eigenbrode JL, Glavin DP, Pearson JC, Keymeulen D, Christensen LE, Schwenzer SP, Navarro-Gonzalez R, Pla-García J, Rafkin SCR, Vicente-Retortillo Á, Kahanpää H, Viudez-Moreiras D, Smith MD, Harri AM, Genzer M, Hassler DM, Lemmon M, Crisp J, Sander SP, Zurek RW, Vasavada AR. Background levels of methane in Mars’ atmosphere show strong seasonal variations. Science 2018; 360:1093-1096. [DOI: 10.1126/science.aaq0131] [Citation(s) in RCA: 189] [Impact Index Per Article: 31.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2017] [Accepted: 05/04/2018] [Indexed: 11/02/2022]
Abstract
Variable levels of methane in the martian atmosphere have eluded explanation partly because the measurements are not repeatable in time or location. We report in situ measurements at Gale crater made over a 5-year period by the Tunable Laser Spectrometer on the Curiosity rover. The background levels of methane have a mean value 0.41 ± 0.16 parts per billion by volume (ppbv) (95% confidence interval) and exhibit a strong, repeatable seasonal variation (0.24 to 0.65 ppbv). This variation is greater than that predicted from either ultraviolet degradation of impact-delivered organics on the surface or from the annual surface pressure cycle. The large seasonal variation in the background and occurrences of higher temporary spikes (~7 ppbv) are consistent with small localized sources of methane released from martian surface or subsurface reservoirs.
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18
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Abstract
Recurring discoveries of abiotic methane in gas seeps and springs in ophiolites and peridotite massifs worldwide raised the question of where, in which rocks, methane was generated. Answers will impact the theories on life origin related to serpentinization of ultramafic rocks, and the origin of methane on rocky planets. Here we document, through molecular and isotopic analyses of gas liberated by rock crushing, that among the several mafic and ultramafic rocks composing classic ophiolites in Greece, i.e., serpentinite, peridotite, chromitite, gabbro, rodingite and basalt, only chromitites, characterized by high concentrations of chromium and ruthenium, host considerable amounts of 13C-enriched methane, hydrogen and heavier hydrocarbons with inverse isotopic trend, which is typical of abiotic gas origin. Raman analyses are consistent with methane being occluded in widespread microfractures and porous serpentine- or chlorite-filled veins. Chromium and ruthenium may be key metal catalysts for methane production via Sabatier reaction. Chromitites may represent source rocks of abiotic methane on Earth and, potentially, on Mars.
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19
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High-Resolution Topographic Analyses of Mounds in Southern Acidalia Planitia, Mars: Implications for Possible Mud Volcanism in Submarine and Subaerial Environments. GEOSCIENCES 2018. [DOI: 10.3390/geosciences8050152] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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20
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Cabrol NA. The Coevolution of Life and Environment on Mars: An Ecosystem Perspective on the Robotic Exploration of Biosignatures. ASTROBIOLOGY 2018; 18:1-27. [PMID: 29252008 PMCID: PMC5779243 DOI: 10.1089/ast.2017.1756] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/29/2017] [Accepted: 11/27/2017] [Indexed: 05/09/2023]
Abstract
Earth's biological and environmental evolution are intertwined and inseparable. This coevolution has become a fundamental concept in astrobiology and is key to the search for life beyond our planet. In the case of Mars, whether a coevolution took place is unknown, but analyzing the factors at play shows the uniqueness of each planetary experiment regardless of similarities. Early Earth and early Mars shared traits. However, biological processes on Mars, if any, would have had to proceed within the distinctive context of an irreversible atmospheric collapse, greater climate variability, and specific planetary characteristics. In that, Mars is an important test bed for comparing the effects of a unique set of spatiotemporal changes on an Earth-like, yet different, planet. Many questions remain unanswered about Mars' early environment. Nevertheless, existing data sets provide a foundation for an intellectual framework where notional coevolution models can be explored. In this framework, the focus is shifted from planetary-scale habitability to the prospect of habitats, microbial ecotones, pathways to biological dispersal, biomass repositories, and their meaning for exploration. Critically, as we search for biosignatures, this focus demonstrates the importance of starting to think of early Mars as a biosphere and vigorously integrating an ecosystem approach to landing site selection and exploration. Key Words: Astrobiology-Biosignatures-Coevolution of Earth and life-Mars. Astrobiology 18, 1-27.
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