Special Issue "Planetary Exploration: Habitats and Terrestrial Analogs"

Quicklinks

A special issue of Life (ISSN 2075-1729). This special issue belongs to the section "Physics".

Deadline for manuscript submissions: closed (30 May 2014)

Special Issue Editors

Guest Editor
Prof. Dr. Dirk Schulze-Makuch

School of the Environment, Webster Hall 1148, Washington State University, Pullman, WA 99164, USA
Interests: planetary habitability; astrobiology; evolutionary biology; extreme environments; geobiology; space missions
Guest Editor
Dr. Alberto G. Fairen (Website)

Department of Astronomy, Cornell University, 426 Space Science Bldg, Ithaca, NY 14853, USA
Interests: mars evolution; exploration; hydrogeology; geochemistry; mineralogy; astrobiology

Special Issue Information

Dear Colleagues,

Planetary exploration is moving at a fast pace as we learn about environmental conditions on various planetary bodies in our solar system and beyond. Habitable conditions at some time during the history of the solar system have been proposed to have existed on Mars, Venus, and a number of icy moons of the outer solar system, some of which may still exist today. For this “LIFE” Special Issue, we particularly encourage submissions describing habitable conditions on planetary bodies and of how life could have interacted with them; also a description of analog environments on Earth from which we can learn about possible adaptations and life strategies on other planets and moons.

Prof. Dr. Dirk Schulze-Makuch
Dr. Alberto G. Fairen
Guest Editors

Submission

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. Papers will be published continuously (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are refereed through a peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Life is an international peer-reviewed Open Access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 600 CHF (Swiss Francs). English correction and/or formatting fees of 250 CHF (Swiss Francs) will be charged in certain cases for those articles accepted for publication that require extensive additional formatting and/or English corrections.

Keywords

  • planets
  • moons
  • habitat
  • analog environment
  • exploration
  • astrobiology

Published Papers (8 papers)

View options order results:
result details:
Displaying articles 1-8
Export citation of selected articles as:

Research

Jump to: Review

Open AccessArticle Photosynthesis in Hydrogen-Dominated Atmospheres
Life 2014, 4(4), 716-744; doi:10.3390/life4040716
Received: 10 June 2014 / Revised: 11 October 2014 / Accepted: 13 October 2014 / Published: 18 November 2014
Cited by 3 | PDF Full-text (1263 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The diversity of extrasolar planets discovered in the last decade shows that we should not be constrained to look for life in environments similar to early or present-day Earth. Super-Earth exoplanets are being discovered with increasing frequency, and some will be able [...] Read more.
The diversity of extrasolar planets discovered in the last decade shows that we should not be constrained to look for life in environments similar to early or present-day Earth. Super-Earth exoplanets are being discovered with increasing frequency, and some will be able to retain a stable, hydrogen-dominated atmosphere. We explore the possibilities for photosynthesis on a rocky planet with a thin H2-dominated atmosphere. If a rocky, H2-dominated planet harbors life, then that life is likely to convert atmospheric carbon into methane. Outgassing may also build an atmosphere in which methane is the principal carbon species. We describe the possible chemical routes for photosynthesis starting from methane and show that less energy and lower energy photons could drive CH4-based photosynthesis as compared with CO2-based photosynthesis. We find that a by-product biosignature gas is likely to be H2, which is not distinct from the hydrogen already present in the environment. Ammonia is a potential biosignature gas of hydrogenic photosynthesis that is unlikely to be generated abiologically. We suggest that the evolution of methane-based photosynthesis is at least as likely as the evolution of anoxygenic photosynthesis on Earth and may support the evolution of complex life. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
Open AccessArticle Mud Volcanoes of Trinidad as Astrobiological Analogs for Martian Environments
Life 2014, 4(4), 566-585; doi:10.3390/life4040566
Received: 9 June 2014 / Revised: 8 September 2014 / Accepted: 23 September 2014 / Published: 13 October 2014
Cited by 1 | PDF Full-text (2556 KB) | HTML Full-text | XML Full-text
Abstract
Eleven onshore mud volcanoes in the southern region of Trinidad have been studied as analog habitats for possible microbial life on Mars. The profiles of the 11 mud volcanoes are presented in terms of their physical, chemical, mineralogical, and soil properties. The [...] Read more.
Eleven onshore mud volcanoes in the southern region of Trinidad have been studied as analog habitats for possible microbial life on Mars. The profiles of the 11 mud volcanoes are presented in terms of their physical, chemical, mineralogical, and soil properties. The mud volcanoes sampled all emitted methane gas consistently at 3% volume. The average pH for the mud volcanic soil was 7.98. The average Cation Exchange Capacity (CEC) was found to be 2.16 kg/mol, and the average Percentage Water Content was 34.5%. Samples from three of the volcanoes, (i) Digity; (ii) Piparo and (iii) Devil’s Woodyard were used to culture bacterial colonies under anaerobic conditions indicating possible presence of methanogenic microorganisms. The Trinidad mud volcanoes can serve as analogs for the Martian environment due to similar geological features found extensively on Mars in Acidalia Planitia and the Arabia Terra region. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
Open AccessArticle Models of Formation and Activity of Spring Mounds in the Mechertate-Chrita-Sidi El Hani System, Eastern Tunisia: Implications for the Habitability of Mars
Life 2014, 4(3), 386-432; doi:10.3390/life4030386
Received: 31 May 2014 / Revised: 25 July 2014 / Accepted: 28 July 2014 / Published: 28 August 2014
Cited by 1 | PDF Full-text (14286 KB) | HTML Full-text | XML Full-text
Abstract
Spring mounds on Earth and on Mars could represent optimal niches of life development. If life ever occurred on Mars, ancient spring deposits would be excellent localities to search for morphological or chemical remnants of an ancient biosphere. In this work, we [...] Read more.
Spring mounds on Earth and on Mars could represent optimal niches of life development. If life ever occurred on Mars, ancient spring deposits would be excellent localities to search for morphological or chemical remnants of an ancient biosphere. In this work, we investigate models of formation and activity of well-exposed spring mounds in the Mechertate-Chrita-Sidi El Hani (MCSH) system, eastern Tunisia. We then use these models to explore possible spring mound formation on Mars. In the MCSH system, the genesis of the spring mounds is a direct consequence of groundwater upwelling, triggered by tectonics and/or hydraulics. As they are oriented preferentially along faults, they can be considered as fault spring mounds, implying a tectonic influence in their formation process. However, the hydraulic pressure generated by the convergence of aquifers towards the surface of the system also allows consideration of an origin as artesian spring mounds. In the case of the MCSH system, our geologic data presented here show that both models are valid, and we propose a combined hydro-tectonic model as the likely formation mechanism of artesian-fault spring mounds. During their evolution from the embryonic (early) to the islet (“island”) stages, spring mounds are also shaped by eolian accumulations and induration processes. Similarly, spring mounds have been suggested to be relatively common in certain provinces on the Martian surface, but their mode of formation is still a matter of debate. We propose that the tectonic, hydraulic, and combined hydro-tectonic models describing the spring mounds at MCSH could be relevant as Martian analogs because: (i) the Martian subsurface may be over pressured, potentially expelling mineral-enriched waters as spring mounds on the surface; (ii) the Martian subsurface may be fractured, causing alignment of the spring mounds in preferential orientations; and (iii) indurated eolian sedimentation and erosional remnants are common features on Mars. The spring mounds further bear diagnostic mineralogic and magnetic properties, in comparison with their immediate surroundings. Consequently, remote sensing techniques can be very useful to identify similar spring mounds on Mars. The mechanisms (tectonic and/or hydraulic) of formation and evolution of spring mounds at the MCSH system are suitable for the proliferation and protection of life respectively. Similarly, life or its resulting biomarkers on Mars may have been protected or preserved under the spring mounds. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
Open AccessCommunication Fluorine-Rich Planetary Environments as Possible Habitats for Life
Life 2014, 4(3), 374-385; doi:10.3390/life4030374
Received: 7 July 2014 / Revised: 4 August 2014 / Accepted: 5 August 2014 / Published: 18 August 2014
Cited by 2 | PDF Full-text (1655 KB) | HTML Full-text | XML Full-text
Abstract
In polar aprotic organic solvents, fluorine might be an element of choice for life that uses selected fluorinated building blocks as monomers of choice for self-assembling of its catalytic polymers. Organofluorine compounds are extremely rare in the chemistry of life as we [...] Read more.
In polar aprotic organic solvents, fluorine might be an element of choice for life that uses selected fluorinated building blocks as monomers of choice for self-assembling of its catalytic polymers. Organofluorine compounds are extremely rare in the chemistry of life as we know it. Biomolecules, when fluorinated such as peptides or proteins, exhibit a “fluorous effect”, i.e., they are fluorophilic (neither hydrophilic nor lipophilic). Such polymers, capable of creating self-sorting assemblies, resist denaturation by organic solvents by exclusion of fluorocarbon side chains from the organic phase. Fluorous cores consist of a compact interior, which is shielded from the surrounding solvent. Thus, we can anticipate that fluorine-containing “teflon”-like or “non-sticking” building blocks might be monomers of choice for the synthesis of organized polymeric structures in fluorine-rich planetary environments. Although no fluorine-rich planetary environment is known, theoretical considerations might help us to define chemistries that might support life in such environments. For example, one scenario is that all molecular oxygen may be used up by oxidation reactions on a planetary surface and fluorine gas could be released from F-rich magma later in the history of a planetary body to result in a fluorine-rich planetary environment. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
Figures

Open AccessCommunication Supercritical Carbon Dioxide and Its Potential as a Life-Sustaining Solvent in a Planetary Environment
Life 2014, 4(3), 331-340; doi:10.3390/life4030331
Received: 25 June 2014 / Revised: 30 July 2014 / Accepted: 31 July 2014 / Published: 8 August 2014
Cited by 11 | PDF Full-text (903 KB) | HTML Full-text | XML Full-text
Abstract
Supercritical fluids have different properties compared to regular fluids and could play a role as life-sustaining solvents on other worlds. Even on Earth, some bacterial species have been shown to be tolerant to supercritical fluids. The special properties of supercritical fluids, which [...] Read more.
Supercritical fluids have different properties compared to regular fluids and could play a role as life-sustaining solvents on other worlds. Even on Earth, some bacterial species have been shown to be tolerant to supercritical fluids. The special properties of supercritical fluids, which include various types of selectivities (e.g., stereo-, regio-, and chemo-selectivity) have recently been recognized in biotechnology and used to catalyze reactions that do not occur in water. One suitable example is enzymes when they are exposed to supercritical fluids such as supercritical carbon dioxide: enzymes become even more stable, because they are conformationally rigid in the dehydrated state. Furthermore, enzymes in anhydrous organic solvents exhibit a “molecular memory”, i.e., the capacity to “remember” a conformational or pH state from being exposed to a previous solvent. Planetary environments with supercritical fluids, particularly supercritical carbon dioxide, exist, even on Earth (below the ocean floor), on Venus, and likely on Super-Earth type exoplanets. These planetary environments may present a possible habitat for exotic life. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
Figures

Review

Jump to: Research

Open AccessReview Volcanogenic Fluvial-Lacustrine Environments in Iceland and Their Utility for Identifying Past Habitability on Mars
Life 2015, 5(1), 568-586; doi:10.3390/life5010568
Received: 2 June 2014 / Revised: 24 September 2014 / Accepted: 6 February 2015 / Published: 16 February 2015
PDF Full-text (1163 KB) | HTML Full-text | XML Full-text
Abstract
The search for once-habitable locations on Mars is increasingly focused on environments dominated by fluvial and lacustrine processes, such as those investigated by the Mars Science Laboratory Curiosity rover. The availability of liquid water coupled with the potential longevity of such systems [...] Read more.
The search for once-habitable locations on Mars is increasingly focused on environments dominated by fluvial and lacustrine processes, such as those investigated by the Mars Science Laboratory Curiosity rover. The availability of liquid water coupled with the potential longevity of such systems renders these localities prime targets for the future exploration of Martian biosignatures. Fluvial-lacustrine environments associated with basaltic volcanism are highly relevant to Mars, but their terrestrial counterparts have been largely overlooked as a field analogue. Such environments are common in Iceland, where basaltic volcanism interacts with glacial ice and surface snow to produce large volumes of meltwater within an otherwise cold and dry environment. This meltwater can be stored to create subglacial, englacial, and proglacial lakes, or be released as catastrophic floods and proglacial fluvial systems. Sedimentary deposits produced by the resulting fluvial-lacustrine activity are extensive, with lithologies dominated by basaltic minerals, low-temperature alteration assemblages (e.g., smectite clays, calcite), and amorphous, poorly crystalline phases (basaltic glass, palagonite, nanophase iron oxides). This paper reviews examples of these environments, including their sedimentary deposits and microbiology, within the context of utilising these localities for future Mars analogue studies and instrument testing. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
Open AccessReview Biota and Biomolecules in Extreme Environments on Earth: Implications for Life Detection on Mars
Life 2014, 4(4), 535-565; doi:10.3390/life4040535
Received: 7 July 2014 / Revised: 8 September 2014 / Accepted: 16 September 2014 / Published: 13 October 2014
Cited by 5 | PDF Full-text (1535 KB) | HTML Full-text | XML Full-text
Abstract
The three main requirements for life as we know it are the presence of organic compounds, liquid water, and free energy. Several groups of organic compounds (e.g., amino acids, nucleobases, lipids) occur in all life forms on Earth and are used as [...] Read more.
The three main requirements for life as we know it are the presence of organic compounds, liquid water, and free energy. Several groups of organic compounds (e.g., amino acids, nucleobases, lipids) occur in all life forms on Earth and are used as diagnostic molecules, i.e., biomarkers, for the characterization of extant or extinct life. Due to their indispensability for life on Earth, these biomarkers are also prime targets in the search for life on Mars. Biomarkers degrade over time; in situ environmental conditions influence the preservation of those molecules. Nonetheless, upon shielding (e.g., by mineral surfaces), particular biomarkers can persist for billions of years, making them of vital importance in answering questions about the origins and limits of life on early Earth and Mars. The search for organic material and biosignatures on Mars is particularly challenging due to the hostile environment and its effect on organic compounds near the surface. In support of life detection on Mars, it is crucial to investigate analogue environments on Earth that resemble best past and present Mars conditions. Terrestrial extreme environments offer a rich source of information allowing us to determine how extreme conditions affect life and molecules associated with it. Extremophilic organisms have adapted to the most stunning conditions on Earth in environments with often unique geological and chemical features. One challenge in detecting biomarkers is to optimize extraction, since organic molecules can be low in abundance and can strongly adsorb to mineral surfaces. Methods and analytical tools in the field of life science are continuously improving. Amplification methods are very useful for the detection of low concentrations of genomic material but most other organic molecules are not prone to amplification methods. Therefore, a great deal depends on the extraction efficiency. The questions “what to look for”, “where to look”, and “how to look for it” require more of our attention to ensure the success of future life detection missions on Mars. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)
Open AccessReview Río Tinto: A Geochemical and Mineralogical Terrestrial Analogue of Mars
Life 2014, 4(3), 511-534; doi:10.3390/life4030511
Received: 8 July 2014 / Revised: 22 August 2014 / Accepted: 28 August 2014 / Published: 15 September 2014
Cited by 7 | PDF Full-text (2068 KB) | HTML Full-text | XML Full-text
Abstract
The geomicrobiological characterization of the water column and sediments of Río Tinto (Huelva, Southwestern Spain) have proven the importance of the iron and the sulfur cycles, not only in generating the extreme conditions of the habitat (low pH, high concentration of toxic [...] Read more.
The geomicrobiological characterization of the water column and sediments of Río Tinto (Huelva, Southwestern Spain) have proven the importance of the iron and the sulfur cycles, not only in generating the extreme conditions of the habitat (low pH, high concentration of toxic heavy metals), but also in maintaining the high level of microbial diversity detected in the basin. It has been proven that the extreme acidic conditions of Río Tinto basin are not the product of 5000 years of mining activity in the area, but the consequence of an active underground bioreactor that obtains its energy from the massive sulfidic minerals existing in the Iberian Pyrite Belt. Two drilling projects, MARTE (Mars Astrobiology Research and Technology Experiment) (2003–2006) and IPBSL (Iberian Pyrite Belt Subsurface Life Detection) (2011–2015), were developed and carried out to provide evidence of subsurface microbial activity and the potential resources that support these activities. The reduced substrates and the oxidants that drive the system appear to come from the rock matrix. These resources need only groundwater to launch diverse microbial metabolisms. The similarities between the vast sulfate and iron oxide deposits on Mars and the main sulfide bioleaching products found in the Tinto basin have given Río Tinto the status of a geochemical and mineralogical Mars terrestrial analogue. Full article
(This article belongs to the Special Issue Planetary Exploration: Habitats and Terrestrial Analogs)

Journal Contact

MDPI AG
Life Editorial Office
St. Alban-Anlage 66, 4052 Basel, Switzerland
life@mdpi.com
Tel. +41 61 683 77 34
Fax: +41 61 302 89 18
Editorial Board
Contact Details Submit to Life
Back to Top