The case for life on Mars

2008 ◽  
Vol 7 (2) ◽  
pp. 117-141 ◽  
Author(s):  
Dirk Schulze-Makuch ◽  
Alberto G. Fairén ◽  
Alfonso F. Davila
Keyword(s):  
Great Success ◽  
Detection Experiment ◽  
Microbial Life ◽  
Life On Mars ◽  
Extremophilic Microorganisms ◽  
Chain Of Evidence ◽  
Life Detection ◽  
Water On Mars ◽  
Cumulative Evidence ◽  
Early Biosphere

AbstractThere have been several attempts to answer the question of whether there is, or has ever been, life on Mars. The boldest attempt was the only ever life detection experiment conducted on another planet: the Viking mission. The mission was a great success, but it failed to provide a clear answer to the question of life on Mars. More than 30 years after the Viking mission our understanding of the history and evolution of Mars has increased vastly to reveal a wetter Martian past and the occurrence of diverse environments that could have supported microbial life similar to that on Earth for extended periods of time. The discovery of Terran extremophilic microorganisms, adapted to environments previously though to be prohibitive for life, has greatly expanded the limits of habitability in our Solar System, and has opened new avenues for the search of life on Mars. Remnants of a possible early biosphere may be found in the Martian meteorite ALH84001. This claim is based on a collection of facts and observations consistent with biogenic origins, but individual links in the collective chain of evidence remain controversial. Recent evidence for contemporary liquid water on Mars and the detection of methane in the Martian atmosphere further enhance the case for life on Mars. We argue that, given the cumulative evidence provided, life has and is likely to exist on Mars, and we have already found evidence of it. However, to obtain a compelling certainty a new mission is needed, one which is devoted to the detection of life on Mars.

scholarly journals Identifying molecules as biosignatures with assembly theory and mass spectrometry

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Stuart M. Marshall ◽  
Cole Mathis ◽  
Emma Carrick ◽  
Graham Keenan ◽  
Geoffrey J. T. Cooper ◽  
...  
Keyword(s):  
Mass Spectrometry ◽  
De Novo ◽  
Outer Space ◽  
Molecular Assembly ◽  
Detection Experiment ◽  
Complex Molecules ◽  
The World ◽  
Life Detection ◽  
Molecular Complexity ◽  
The Universe

AbstractThe search for alien life is hard because we do not know what signatures are unique to life. We show why complex molecules found in high abundance are universal biosignatures and demonstrate the first intrinsic experimentally tractable measure of molecular complexity, called the molecular assembly index (MA). To do this we calculate the complexity of several million molecules and validate that their complexity can be experimentally determined by mass spectrometry. This approach allows us to identify molecular biosignatures from a set of diverse samples from around the world, outer space, and the laboratory, demonstrating it is possible to build a life detection experiment based on MA that could be deployed to extraterrestrial locations, and used as a complexity scale to quantify constraints needed to direct prebiotically plausible processes in the laboratory. Such an approach is vital for finding life elsewhere in the universe or creating de-novo life in the lab.

scholarly journals Astrobiological Field Campaign to a Volcanosedimentary Mars Analogue Methane Producing Subsurface Protected Ecosystem: Imuruk Lake (Alaska)

2011 ◽  
Vol 2011 ◽  
pp. 1-8
Author(s):  
F. Gómez ◽  
O. Prieto-Ballesteros ◽  
D. Fernández-Remolar ◽  
J. A. Rodríguez-Manfredi ◽  
M. Fernández-Sampedro ◽  
...  
Keyword(s):  
Molecular Ecology ◽  
Point Of View ◽  
Land Bridge ◽  
High Hydrogen ◽  
Adverse Conditions ◽  
Life On Mars ◽  
Life Detection ◽  
National Preserve ◽  
Mars Exploration Rovers

Viking missions reported adverse conditions for life in Mars surface. High hydrogen signal obtained by Mars orbiters has increased the interest in subsurface prospection as putative protected Mars environment with life potential. Permafrost has attracted considerable interest from an astrobiological point of view due to the recently reported results from the Mars exploration rovers. Considerable studies have been developed on extreme ecosystems and permafrost in particular, to evaluate the possibility of life on Mars and to test specific automated life detection instruments for space missions. The biodiversity of permafrost located on the Bering Land Bridge National Preserve has been studied as an example of subsurface protected niche of astrobiological interest. Different conventional (enrichment and isolation) and molecular ecology techniques (cloning, fluorescence“in situ”probe hybridization, FISH) have been used for isolation and bacterial identification.

Possible evidence for panspermia: the labelled release experiment

2007 ◽  
Vol 6 (2) ◽  
pp. 95-108 ◽  
Author(s):  
Gilbert V. Levin
Keyword(s):  
Active Agent ◽  
Life Forms ◽  
Current Data ◽  
Release Experiment ◽  
Microbial Life ◽  
Martian Soil ◽  
Life On Mars ◽  
Biological Interpretation ◽  
Life Question ◽  
Chiral Specificity

Abstract30 years after the Viking Mission landed on Mars (20 July 1976) to search for life, despite the positive findings of the Labelled Release (LR) experiment, the issue remains unresolved. The controversial history, following the immediate dismissal of the LR’s evidence for microbial activity in the Martian soil, and the later claim to its having found living microorganisms are reviewed. The bearing of post-Viking-to-current data on the issue is discussed in the context of the scientific community’s growing interest in the long-dismissed possibility of microbial life on Mars. Objections raised over the years to the biological interpretation of the Mars LR, those currently maintained, and their rebuttals are reviewed. A case is presented that enough evidence now exists for an objective review by astrobiologists to resolve this key issue, a review, surprisingly, not yet held. The results could greatly influence NASA’s currently shifting plans for Mars exploration. A variation of the LR experiment to test for chiral specificity in the metabolism of substrates by the active agent found in the Martian soil, and thus having the capability of obtaining an unambiguous answer to the life question, is proposed. Confirmation of life on Mars by this experiment can also determine whether Martian and Earth life forms share a common heritage. Together with mounting evidence for the viable transfer of microorganisms between the two planets, this would be evidence for panspermia, and establish the presence of a common biosphere in which the two planets participate. Should Martian microorganisms show a different chiral specificity than that of Earth life then this would indicate separate origins of the two neighbouring life forms, thereby strongly implying that life occurs widely throughout the cosmos. Any one of these possible outcomes would be a paradigm-breaking event.

scholarly journals The Atacama Desert in Northern Chile as an Analog Model of Mars

2022 ◽  
Vol 8 ◽  
Author(s):  
Armando Azua-Bustos ◽  
Carlos González-Silva ◽  
Alberto G. Fairén
Keyword(s):  
Atacama Desert ◽  
Analog Model ◽  
Patchy Distribution ◽  
Microbial Life ◽  
Environmental Extremes ◽  
Life On Mars ◽  
Domains Of Life ◽  
Mars Analog ◽  
The Impact

The Atacama Desert is by far the driest and oldest desert on Earth, showing a unique combination of environmental extremes (extreme dryness, the highest UV radiation levels on Earth, and highly saline and oxidizing soils), explaining why the Atacama has been largely investigated as a Mars analog model for almost 20 years. Based on the source and the amount of water available for life and its analogy with Mars, two ecosystems are of interest in the Atacama: its Coastal Range and the much drier hyperarid core, which we here review in detail. Members of the three domains of life have been found across these ecosystems living at the limit of habitability, suggesting the potential dry limits for each domain and also unveiling the highly patchy distribution of microbial life in its most extreme regions. The thorough study of the Atacama has allowed us to understand how life has adapted to its extreme conditions, the specific habitats that life occupies in each case (thus suggesting the most likely places in which to search for evidence for life on Mars), and the number of biosignatures detected across this desert. Also, the characterization of west-to-east transects across this desert has shown to be of significant value to understand the potential adaptations that Martian microorganisms may have followed in an ever-drying planet. All of this explains why the Atacama is actively used as the testing ground of the technologies (detection instruments, rovers, etc.) that were sent and will be sent to Mars. We also highlight the need to better inform the exact locations of the sites studied to understand general trends, the need to identify the true native microbial species of the Atacama, and the impact of climate change on the most arid and most Martian desert of Earth.

scholarly journals Water on Mars—A Literature Review

Galaxies ◽  
2020 ◽  
Vol 8 (2) ◽  
pp. 40 ◽  
Author(s):  
Mohammad Nazari-Sharabian ◽  
Mohammad Aghababaei ◽  
Moses Karakouzian ◽  
Mehrdad Karami
Keyword(s):  
Living Organism ◽  
Underground Water ◽  
Microbial Life ◽  
Gale Crater ◽  
Subsurface Environments ◽  
History Of ◽  
Water On Mars ◽  
Living Organisms ◽  
River Valleys ◽  
Human Exploration

To assess Mars’ potential for both harboring life and providing useable resources for future human exploration, it is of paramount importance to comprehend the water situation on the planet. Therefore, studies have been conducted to determine any evidence of past or present water existence on Mars. While the presence of abundant water on Mars very early in its history is widely accepted, on its modern form, only a fraction of this water can be found, as either ice or locked into the structure of Mars’ plentiful water-rich materials. Water on the planet is evaluated through various evidence such as rocks and minerals, Martian achondrites, low volume transient briny outflows (e.g., dune flows, reactivated gullies, slope streaks, etc.), diurnal shallow soil moisture (e.g., measurements by Curiosity and Phoenix Lander), geomorphic representation (possibly from lakes and river valleys), and groundwater, along with further evidence obtained by probe and rover discoveries. One of the most significant lines of evidence is for an ancient streambed in Gale Crater, implying ancient amounts of “vigorous” water on Mars. Long ago, hospitable conditions for microbial life existed on the surface of Mars, as it was likely periodically wet. However, its current dry surface makes it almost impossible as an appropriate environment for living organisms; therefore, scientists have recognized the planet’s subsurface environments as the best potential locations for exploring life on Mars. As a result, modern research has aimed towards discovering underground water, leading to the discovery of a large amount of underground ice in 2016 by NASA, and a subglacial lake in 2018 by Italian scientists. Nevertheless, the presence of life in Mars’ history is still an open question. In this unifying context, the current review summarizes results from a wide variety of studies and reports related to the history of water on Mars, as well as any related discussions on the possibility of living organism existence on the planet.

scholarly journals Network-Based Prediction of Novel CRISPR-Associated Genes in Metagenomes

mSystems ◽  
2020 ◽  
Vol 5 (1) ◽  
Author(s):  
Jake L. Weissman ◽  
Philip L. F. Johnson
Keyword(s):  
Genome Editing ◽  
Viral Infections ◽  
Adaptive Immune System ◽  
Gene Families ◽  
Great Success ◽  
Theory Approach ◽  
Viral Pathogens ◽  
Microbial Life ◽  
Associated Proteins ◽  
Short Palindromic Repeat

ABSTRACT A diversity of clustered regularly interspaced short palindromic repeat (CRISPR)-Cas systems provide adaptive immunity to bacteria and archaea through recording “memories” of past viral infections. Recently, many novel CRISPR-associated proteins have been discovered via computational studies, but those studies relied on biased and incomplete databases of assembled genomes. We avoided these biases and applied a network theory approach to search for novel CRISPR-associated genes by leveraging subtle ecological cooccurrence patterns identified from environmental metagenomes. We validated our method using existing annotations and discovered 32 novel CRISPR-associated gene families. These genes span a range of putative functions, with many potentially regulating the response to infection. IMPORTANCE Every branch on the tree of life, including microbial life, faces the threat of viral pathogens. Over the course of billions of years of coevolution, prokaryotes have evolved a great diversity of strategies to defend against viral infections. One of these is the CRISPR adaptive immune system, which allows microbes to “remember” past infections in order to better fight them in the future. There has been much interest among molecular biologists in CRISPR immunity because this system can be repurposed as a tool for precise genome editing. Recently, a number of comparative genomics approaches have been used to detect novel CRISPR-associated genes in databases of genomes with great success, potentially leading to the development of new genome-editing tools. Here, we developed novel methods to search for these distinct classes of genes directly in environmental samples (“metagenomes”), thus capturing a more complete picture of the natural diversity of CRISPR-associated genes.

scholarly journals Acceleration of amino acid racemization by isovaline: possible implications for homochirality and biosignature search

2020 ◽  
Vol 19 (3) ◽  
pp. 276-282
Author(s):  
Stefan Fox ◽  
Annika Gspandl ◽  
Franziska M. Wenng
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Enantiomeric Excess ◽  
Terrestrial Planet ◽  
Microbial Life ◽  
Amino Acid Racemization ◽  
Geothermal Heating ◽  
Life On Mars ◽  
Volcanic Islands ◽  
Life On Earth

AbstractIn nature, abiotically formed amino acids are usually racemic. However, this is not true for the α,α-dialkyl amino acid isovaline (Iva), which has an L-enantiomeric excess in some specimens of carbonaceous meteorites. On the early Earth and Mars, such meteorites were sources of amino acids, including Iva. Therefore, a connection may exist between the possible chiral influence of non-racemic Iva and the origin of biological homochirality. On the surface of a young terrestrial planet, amino acids can be chemically altered in many ways. For example, high temperatures from geothermal heating can lead to racemization. Four billion years ago, active volcanism and volcanic islands provided suitable conditions for such reactions and perhaps even for early microbial life on Earth. In the current study, we investigated the influence of D- and L-Iva on the thermal racemization of L-alanine (L-Ala) and L-2-aminobutyric acid (L-Abu) in a simulated hot volcanic environment. The amino acids were intercalated in the clay mineral calcium montmorillonite (SAz-1). While Iva was resistant to racemization, partial racemization was observed for Ala and Abu after 8 weeks at 150°C. The experimental results – for example, accelerated racemization in the presence of Iva and different influences of the Iva enantiomers – suggest that the amino acid molecules interacted with each other, possibly in hydrogen-bonded dimers. Accelerated racemization of amino acids could have been an obstacle to the development of homochirality. Besides, it is also detrimental to the use of homochirality as a biosignature, for example, in the search for microbial life on Mars.

Chemical interpretation of Viking Lander 1 life detection experiment

Nature ◽  
1978 ◽  
Vol 271 (5646) ◽  
pp. 644-645 ◽  
Author(s):  
E. VERNON BALLOU ◽  
PETER C. WOOD ◽  
THEODORE WYDEVEN ◽  
MARJORIE E. LEHWALT ◽  
RUTH E. MACK
Keyword(s):  
Detection Experiment ◽  
Life Detection

scholarly journals Inhabited subsurface wet smectites in the hyperarid core of the Atacama Desert as an analog for the search for life on Mars

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Armando Azua-Bustos ◽  
Alberto G. Fairén ◽  
Carlos González Silva ◽  
Daniel Carrizo ◽  
Miguel Ángel Fernández-Martínez ◽  
...  
Keyword(s):  
Microbial Community ◽  
Atacama Desert ◽  
Martian Surface ◽  
Microbial Life ◽  
Clay Deposits ◽  
Life On Mars ◽  
Subsurface Layers ◽  
Active Bacteria ◽  
Halophilic Species ◽  
Diverse Microbial Community

Abstract The modern Martian surface is unlikely to be habitable due to its extreme aridity among other environmental factors. This is the reason why the hyperarid core of the Atacama Desert has been studied as an analog for the habitability of Mars for more than 50 years. Here we report a layer enriched in smectites located just 30 cm below the surface of the hyperarid core of the Atacama. We discovered the clay-rich layer to be wet (a phenomenon never observed before in this region), keeping a high and constant relative humidity of 78% (aw 0.780), and completely isolated from the changing and extremely dry subaerial conditions characteristic of the Atacama. The smectite-rich layer is inhabited by at least 30 halophilic species of metabolically active bacteria and archaea, unveiling a previously unreported habitat for microbial life under the surface of the driest place on Earth. The discovery of a diverse microbial community in smectite-rich subsurface layers in the hyperarid core of the Atacama, and the collection of biosignatures we have identified within the clays, suggest that similar shallow clay deposits on Mars may contain biosignatures easily reachable by current rovers and landers.

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