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Frontiers of Astrobiology, Volume II
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Frontiers of Astrobiology, Volume II

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

Deadline for manuscript submissions: closed (15 April 2022) | Viewed by 15274

Special Issue Editor

Dr. Christopher Bennett

E-Mail Website
Guest Editor
Department of Physics, University of Central Florida, Orlando, FL 32816, USA
Interests: astrochemistry; astrobiology; physical chemistry; planetary science; radiation chemistry
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

In this second volume of “Frontiers of Astrobiology”, we aim to bring together a collection of seminal papers that demonstrate the ongoing transcendence of this interdisciplinary field, which exemplify the current state of the art in the field. In addition to research articles covering experimental, observational, theoretical, and modeling approaches, we also encourage the submission of papers that focus on novel hypotheses and highlight current challenges or knowledge gaps, as well as long review articles. 

Although there is a wide range of topics that encompass this field, some relevant examples include: i) What do we know about the physical conditions and the chemical inventory of the early Earth, and how have these evolved over time? ii) What kinds of chemical processes may have occurred on the early Earth and what key steps were necessary for life to evolve (e.g., was there an RNA world, and if so, how did we arrive at it, or move on from it?)?, iii) What is the earliest evidence for life on Earth and how it evolved in time, and how robust is it? iv) What are the limits of life on Earth, and how does this affect our definition of habitable zones, planetary protection strategies, or panspermia? v) How might extraterrestrial life differ from terrestrial life, and are there certain traits that must be conserved? vi) Are there any special circumstances during the evolution of the Earth and its place in the solar system that made it especially conducive to the emergence of life? vii) With the next generations of telescopes currently being constructed, how may we begin to determine whether there is evidence of life, biosignatures, or technosignatures on nearby exoplanets? viii) How can we devise better tools to help to identify false positive (or negative) detections from observations or missions designed to look for evidence of biology/life on other worlds? ix) How does our increasing observational prowess provide constraints on whether or not we may be alone in the universe?

Dr. Christopher Bennett
Guest Editor

Manuscript Submission Information

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. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short 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 thoroughly refereed through a single-blind 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 monthly 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 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Astrobiology
  • Astrochemistry
  • Prebiotic chemistry and the primordial Earth
  • Origin of, evolution of, and earliest evidence of life
  • Definition of life
  • Limits of life/extremophiles
  • Habitability
  • Exoplanets
  • Panspermia
  • Planetary protection
  • Space missions
  • Remote sensing
  • Advances of analytical instrumentation
  • Biosignatures/technosignatures

Related Special Issue

Published Papers (5 papers)

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15 pages, 3084 KiB  
Article
Mineral Element Insiders and Outliers Play Crucial Roles in Biological Evolution
by Eli K. Moore, Daniella L. Martinez, Naman Srivastava, Shaunna M. Morrison and Stephanie J. Spielman
Life 2022, 12(7), 951; https://doi.org/10.3390/life12070951 - 24 Jun 2022
Viewed by 1632
Abstract
The geosphere of primitive Earth was the source of life’s essential building blocks, and the geochemical interactions among chemical elements can inform the origins of biological roles of each element. Minerals provide a record of the fundamental properties that each chemical element contributes [...] Read more.
The geosphere of primitive Earth was the source of life’s essential building blocks, and the geochemical interactions among chemical elements can inform the origins of biological roles of each element. Minerals provide a record of the fundamental properties that each chemical element contributes to crustal composition, evolution, and subsequent biological utilization. In this study, we investigate correlations between the mineral species and bulk crustal composition of each chemical element. There are statistically significant correlations between the number of elements that each element forms minerals with (#-mineral-elements) and the log of the number of mineral species that each element occurs in, and between #-mineral-elements and the log of the number of mineral localities of that element. There is a lesser correlation between the log of the crustal percentage of each element and #-mineral-elements. In the crustal percentage vs. #-mineral-elements plot, positive outliers have either important biological roles (S, Cu) or toxic biological impacts (Pb, As), while negative outliers have no biological importance (Sc, Ga, Br, Yb). In particular, S is an important bridge element between organic (e.g., amino acids) and inorganic (metal cofactors) biological components. While C and N rarely form minerals together, the two elements commonly form minerals with H, which coincides with the role of H as an electron donor/carrier in biological nitrogen and carbon fixation. Both abundant crustal percentage vs. #-mineral-elements insiders (elements that follow the correlation) and less abundant outsiders (positive outliers from the correlation) have important biological functions as essential structural elements and catalytic cofactors. Full article
(This article belongs to the Special Issue Frontiers of Astrobiology, Volume II)
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16 pages, 6017 KiB  
Article
Modeling Virus and Bacteria Populations in Europa’s Subsurface Ocean
by Adriana C. Gomez-Buckley, Gordon M. Showalter and Michael L. Wong
Life 2022, 12(5), 620; https://doi.org/10.3390/life12050620 - 21 Apr 2022
Cited by 4 | Viewed by 4661
Abstract
The search for life in the universe is often informed by the study of “extreme” environments on Earth, which provide analogs for habitable locations in the Solar System, and whose microbial inhabitants may therefore also serve as analogs for potential life forms in [...] Read more.
The search for life in the universe is often informed by the study of “extreme” environments on Earth, which provide analogs for habitable locations in the Solar System, and whose microbial inhabitants may therefore also serve as analogs for potential life forms in extraterrestrial milieus. Recent work has highlighted the ubiquity and importance of viral entities in terrestrial ecosystems, which calls for a greater understanding of the roles that viruses might play in hypothetical extraterrestrial biomes. While some studies have modeled the dynamics of viral and bacterial populations in icy ocean environments on Earth, previous work has yet to apply these findings to icy ocean worlds such as Jupiter’s moon Europa. It is commonly theorized that hydrothermal vents on Europa could produce the necessary reductants for chemosynthesis to take place on the ocean bottom. In the case that Europa’s ocean is a reductant-limited environment, how might reductants and organic matter reach the sub-ice region to power a more easily accessible ecosystem? Here, we propose a ‘viral elevator,’ a mechanism that functions similarly to the ‘viral shunt’ in Earth’s oceans, which could create and shuttle dissolved organic matter (DOM) to a hypothetical sub-ice biosphere through viral carriers. Current models of Europa’s ocean currents and stratification support the movement of DOM to the sub-ice biosphere. We adapt an existing model for bacterial and viral population dynamics in Earth’s Arctic sea ice to Europa and use parameters from various Arctic-based studies as proxies for Europa’s environment. We find that viral burst size has the most significant effect on the virus-to-bacteria ratio (VBR) and system longevity in closed systems (such as brine pockets within Europa’s icy crust), with higher burst sizes clearly increasing both. When applying our model to an open system with an influx of DOM from the viral elevator, we found that a steady-state system is attainable, with resulting sub-ice biofilms on the order of 0.1 mm thick (global equivalent layer). This has implications for future searches for life on Europa, given that life directly under the ice will be easier to detect and observe than life near the ocean bottom. Full article
(This article belongs to the Special Issue Frontiers of Astrobiology, Volume II)
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12 pages, 29961 KiB  
Article
New Signatures of Bio-Molecular Complexity in the Hypervelocity Impact Ejecta of Icy Moon Analogues
by Surendra V. Singh, Haritha Dilip, Jaya K. Meka, Vijay Thiruvenkatam, Vishakantaiah Jayaram, Mariyappan Muruganantham, Vijayan Sivaprahasam, Balabhadrapatruni N. Rajasekhar, Anil Bhardwaj, Nigel J. Mason, Mark J. Burchell and Bhalamurugan Sivaraman
Life 2022, 12(4), 508; https://doi.org/10.3390/life12040508 - 30 Mar 2022
Cited by 5 | Viewed by 2299
Abstract
Impact delivery of prebiotic compounds to the early Earth from an impacting comet is considered to be one of the possible ways by which prebiotic molecules arrived on the Earth. Given the ubiquity of impact features observed on all planetary bodies, bolide impacts [...] Read more.
Impact delivery of prebiotic compounds to the early Earth from an impacting comet is considered to be one of the possible ways by which prebiotic molecules arrived on the Earth. Given the ubiquity of impact features observed on all planetary bodies, bolide impacts may be a common source of organics on other planetary bodies both in our own and other solar systems. Biomolecules such as amino acids have been detected on comets and are known to be synthesized due to impact-induced shock processing. Here we report the results of a set of hypervelocity impact experiments where we shocked icy mixtures of amino acids mimicking the icy surface of planetary bodies with high-speed projectiles using a two-stage light gas gun and analyzed the ejecta material after impact. Electron microscopic observations of the ejecta have shown the presence of macroscale structures with long polypeptide chains revealed from LCMS analysis. These results suggest a pathway in which impact on cometary ices containing building blocks of life can lead to the synthesis of material architectures that could have played a role in the emergence of life on the Earth and which may be applied to other planetary bodies as well. Full article
(This article belongs to the Special Issue Frontiers of Astrobiology, Volume II)
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13 pages, 2002 KiB  
Article
Physicochemical Parameters Limiting Growth of Debaryomyces hansenii in Solutions of Hygroscopic Compounds and Their Effects on the Habitability of Martian Brines
by Jacob Heinz, Vita Rambags and Dirk Schulze-Makuch
Life 2021, 11(11), 1194; https://doi.org/10.3390/life11111194 - 5 Nov 2021
Cited by 7 | Viewed by 2068
Abstract
The availability of liquid water is a prerequisite for all lifeforms on Earth. In hyperarid subzero environments like the Dry Valleys in Antarctica or the near-subsurface of Mars liquid water might be provided temporarily by hygroscopic substances that absorb water from the atmosphere [...] Read more.
The availability of liquid water is a prerequisite for all lifeforms on Earth. In hyperarid subzero environments like the Dry Valleys in Antarctica or the near-subsurface of Mars liquid water might be provided temporarily by hygroscopic substances that absorb water from the atmosphere and lower the freezing point of water. To evaluate the potential of hygroscopic compounds to serve as a habitat, it is necessary to explore the microbial tolerances towards these substances and their life-limiting properties. Here we present a study investigating the tolerances of the halotolerant yeast Debaryomyces hansenii to various solutes. Growth experiments were conducted via counting colony forming units (CFUs) after inoculation of a liquid growth medium containing a specific solute concentration. The lowest water activities (aw) enabling growth were determined to be ~0.83 in glycerol and fructose-rich media. For all other solutes the growth-enabling aw was higher, due to additional stress factors such as chaotropicity and ionic strength. Additionally, we found that the solute tolerances of D. hansenii correlate with both the eutectic freezing point depressions and the deliquescence relative humidities of the respective solutes. Our findings strongly impact our understanding of the habitability of solute-rich low aw environments on Earth and beyond. Full article
(This article belongs to the Special Issue Frontiers of Astrobiology, Volume II)
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16 pages, 2701 KiB  
Perspective
Searching for Life, Mindful of Lyfe’s Possibilities
by Michael L. Wong, Stuart Bartlett, Sihe Chen and Louisa Tierney
Life 2022, 12(6), 783; https://doi.org/10.3390/life12060783 - 25 May 2022
Cited by 8 | Viewed by 3660
Abstract
We are embarking on a new age of astrobiology, one in which numerous interplanetary missions and telescopes will be designed, built, and launched with the explicit goal of finding evidence for life beyond Earth. Such a profound aim warrants caution and responsibility when [...] Read more.
We are embarking on a new age of astrobiology, one in which numerous interplanetary missions and telescopes will be designed, built, and launched with the explicit goal of finding evidence for life beyond Earth. Such a profound aim warrants caution and responsibility when interpreting and disseminating results. Scientists must take care not to overstate (or over-imply) confidence in life detection when evidence is lacking, or only incremental advances have been made. Recently, there has been a call for the community to create standards of evidence for the detection and reporting of biosignatures. In this perspective, we wish to highlight a critical but often understated element to the discussion of biosignatures: Life detection studies are deeply entwined with and rely upon our (often preconceived) notions of what life is, the origins of life, and habitability. Where biosignatures are concerned, these three highly related questions are frequently relegated to a low priority, assumed to be already solved or irrelevant to the question of life detection. Therefore, our aim is to bring to the fore how these other major astrobiological frontiers are central to searching for life elsewhere and encourage astrobiologists to embrace the reality that all of these science questions are interrelated and must be furthered together rather than separately. Finally, in an effort to be more inclusive of life as we do not know it, we propose tentative criteria for a more general and expansive characterization of habitability that we call genesity. Full article
(This article belongs to the Special Issue Frontiers of Astrobiology, Volume II)
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