Perchlorate-Coupled Carbon Monoxide (CO) Oxidation by Moorella glycerini, an Obligately Anaerobic, Thermophilic, Nickel-Dependent Carboxydotroph

Many facultative and obligate anaerobes reduce perchlorate. Likewise, carbon monoxide (CO) oxidation has been documented in many aerobes, facultative anaerobes, and obligate anaerobes. A molybdenum-dependent CO dehydrogenase (Mo-CODH) and a nickel-dependent CO dehydrogenase (Ni-CODH) distinguish the former from the latter. Some Mo-dependent CO oxidizers (Mo-COX) couple CO oxidation to perchlorate reduction, but only at low concentrations of both under conditions that do not support growth in cultures. In contrast, CO-coupled perchlorate reduction has not been documented in Ni-dependent CO oxidizers (Ni-COX). To assess the potential for Ni-COX to reduce perchlorate, a model, obligately anaerobic homoacetogen, Moorella glycerini DSM 11254^T, was cultivated with or without perchlorate, usiing CO or glycerol as its sole carbon and energy source. It grew with glycerol with or without perchlorate, and its maximum cell densities were only weakly affected by the perchlorate. However, when CO (at a 30% headspace concentration) was used as a carbon and energy source, perchlorate reduction supported greater cell densities and more rapid growth rates. The stoichiometry of CO uptake, perchlorate reduction, and chloride production were consistent with the cryptic pathway for perchlorate reduction with chlorite as an end product. Chloride production occurred abiologically in the medium due to a reaction between chlorite and the sulfide used as a reducing agent. These results provide the first demonstration of CO-coupled perchlorate reduction supporting growth in Ni-COX, and they provide constraints on the potential for perchlorate-coupled, anaerobic CO oxidation in engineered systems as well as terrestrial systems and hypothetical, sub-surface, serpentinite-hosted systems on Mars.

Spectroscopic Detection of Biosignatures in Natural Ice Samples as a Proxy for Icy Moons

Some of the icy moons of the solar system with a subsurface ocean, such as Europa and Enceladus, are the targets of future space missions that search for potential extraterrestrial life forms. While the ice shells that envelop these moons have been studied by several spacecrafts, the oceans beneath them remain unreachable. To better constrain the habitability conditions of these moons, we must understand the interactions between their frozen crusts, liquid layers, and silicate mantles. To that end, astrobiologists rely on planetary field analogues, for which the polar regions of Earth have proven to be great candidates. This review shows how spectroscopy is a powerful tool in space missions to detect potential biosignatures, in particular on the aforementioned moons, and how the polar regions of the Earth are being used as planetary field analogues for these extra-terrestrial environments.

Memory Effect on the Survival of Deinococcus radiodurans after Exposure in Near Space

Near space (20 to 100 km in altitude) is an extreme environment with high radiation and extreme cold, making it difficult for organisms to survive. However, many studies had shown that there were still microbes living in this extremely harsh environment. It was particularly important to study which factors affected the survival of microorganisms living in near space after exposure to irradiation, as this was related to many studies, such as studies of radioresistance mechanisms, panspermia hypothesis, long-distance microbial transfer, and developing extraterrestrial habitats. Survival after radiation was probably influenced by the growth condition before radiation, which is called the memory effect. In this research, we used different growth conditions to affect the growth of Deinococcus radiodurans and lyophilized bacteria in exponential phase to maintain the physiological state at this stage. Then high-altitude scientific balloon exposure experiments were carried out by using the Chinese Academy of Sciences Balloon-Borne Astrobiology Platform (CAS-BAP) at Dachaidan, Qinghai, China (37°44'N, 95°21'E). The aim was to investigate which factors influence survival after near-space exposure. The results suggested that there was a memory effect on the survival of D. radiodurans after exposure. If the differences in growth rate were caused by differences in nutrition, the survival rate and growth rate were positively correlated. Moreover, the addition of paraquat and Mn2+ during the growth phase can also increase survival. This finding may help to deepen the understanding of the mechanics of radiation protection and provide relevant evidence for many studies, such as of long-distance transfer of microorganisms in near space. IMPORTANCE Earth's near space is an extreme environment with high radiation and extreme cold. Which factors affect the survival of microbes in near space is related to many studies, such as studies of radioresistance mechanisms, panspermia hypothesis, long-distance microbial transfer, and developing extraterrestrial habitats. We performed several exposure experiments with Deinococcus radiodurans in near space to investigate which factors influence the survival rate after near-space exposure; that is, there was a relationship between survival after radiation and the growth condition before radiation. The results suggested that there was a memory effect on the survival of D. radiodurans after exposure. This finding may help to deepen the understanding of the mechanism of radiation protection and provide relevant evidence for many studies, such as of long-distance transfer of microorganisms in near space.

The Impact of Harsh Stratospheric Conditions on Survival and Antibiotic Resistance Profile of Non-Spore Forming Multidrug Resistant Human Pathogenic Bacteria Causing Hospital-Associated Infections

Bacteria are constantly being lifted to the stratosphere due to air movements caused by weather phenomena, volcanic eruptions, or human activity. In the upper parts of the atmosphere, they are exposed to extremely harsh and mutagenic conditions such as UV and space radiation or ozone. Most bacteria cannot withstand that stress, but for a fraction of them, it can act as a trigger for selective pressure and rapid evolution. We assessed the impact of stratospheric conditions on the survival and antibiotic resistance profile of common non-spore-forming human pathogenic bacteria, both sensitive and extremely dangerous multidrug-resistant variants, with plasmid-mediated mechanisms of resistance. Pseudomonas aeruginosa did not survive the exposure. In the case of strains that were recovered alive, the survival was extremely low: From 0.00001% of Klebsiella pneumoniae carrying the ndm-1 gene and methicillin-resistant Staphylococcus aureus mecA-positive with reduced susceptibility to vancomycin (MRSA/VISA), to a maximum of 0.001% of K. pneumoniae sensitive to all common antibiotics and S. aureus sensitive to vancomycin (MRSA/VSSA). We noticed a tendency towards increased antibiotic susceptibility after the stratospheric flight. Antimicrobial resistance is a current real, global, and increasing problem, and our results can inform current understandings of antibiotic resistance mechanisms and development in bacteria.

Plausible Sources of Membrane-Forming Fatty Acids on the Early Earth: A Review of the Literature and an Estimation of Amounts

The first cells were plausibly bounded by membranes assembled from fatty acids with at least 8 carbons. Although the presence of fatty acids on the early Earth is widely assumed within the astrobiology community, there is no consensus regarding their origin and abundance. In this Review, we highlight three possible sources of fatty acids: (1) delivery by carbonaceous meteorites, (2) synthesis on metals delivered by impactors, and (3) electrochemical synthesis by spark discharges. We also discuss fatty acid synthesis by UV or particle irradiation, gas-phase ion-molecule reactions, and aqueous redox reactions. We compare estimates for the total mass of fatty acids supplied to Earth by each source during the Hadean eon after an extremely massive asteroid impact that would have reset Earth's fatty acid inventory. We find that synthesis on iron-rich surfaces derived from the massive impactor in contact with an impact-generated reducing atmosphere could have contributed ∼10² times more total mass of fatty acids than subsequent delivery by either carbonaceous meteorites or electrochemical synthesis. Additionally, we estimate that a single carbonaceous meteorite would not deliver a high enough concentration of fatty acids (∼15 mM for decanoic acid) into an existing body of water on the Earth's surface to spontaneously form membranes unless the fatty acids were further concentrated by another mechanism, such as subsequent evaporation of the water. Our estimates rely heavily on various assumptions, leading to significant uncertainties; nevertheless, these estimates provide rough order-of-magnitude comparisons of various sources of fatty acids on the early Earth. We also suggest specific experiments to improve future estimates. Our calculations support the view that fatty acids would have been available on the early Earth. Further investigation is needed to assess the mechanisms by which fatty acids could have been concentrated sufficiently to assemble into membranes during the origin of life.

Plausible Sources of Membrane-Forming Fatty Acids on the Early Earth: A Review of the Literature and an Estimation of Amounts

The first cells were plausibly bounded by membranes assembled from fatty acids with at least 8 carbons. Although the presence of fatty acids on the early Earth is widely assumed within the astrobiology community, there is no consensus regarding their origin and abundance. In this Review, we highlight three possible sources of fatty acids: (1) delivery by carbonaceous meteorites, (2) synthesis on metals delivered by impactors, and (3) electrochemical synthesis by spark discharges. We also discuss fatty acid synthesis by UV or particle irradiation, gas-phase ion-molecule reactions, and aqueous redox reactions. We compare estimates for the total mass of fatty acids supplied to Earth by each source during the Hadean eon after an extremely massive asteroid impact that would have reset Earth's fatty acid inventory. We find that synthesis on iron-rich surfaces derived from the massive impactor in contact with an impact-generated reducing atmosphere could have contributed ∼10² times more total mass of fatty acids than subsequent delivery by either carbonaceous meteorites or electrochemical synthesis. Additionally, we estimate that a single carbonaceous meteorite would not deliver a high enough concentration of fatty acids (∼15 mM for decanoic acid) into an existing body of water on the Earth's surface to spontaneously form membranes unless the fatty acids were further concentrated by another mechanism, such as subsequent evaporation of the water. Our estimates rely heavily on various assumptions, leading to significant uncertainties; nevertheless, these estimates provide rough order-of-magnitude comparisons of various sources of fatty acids on the early Earth. We also suggest specific experiments to improve future estimates. Our calculations support the view that fatty acids would have been available on the early Earth. Further investigation is needed to assess the mechanisms by which fatty acids could have been concentrated sufficiently to assemble into membranes during the origin of life.

Biophysical Manipulation of the Extracellular Environment by Eurotium halophilicum

Eurotium halophilicum is psychrotolerant, halophilic, and one of the most-extreme xerophiles in Earth's biosphere. We already know that this ascomycete grows close to 0 °C, at high NaCl, and-under some conditions-down to 0.651 water-activity. However, there is a paucity of information about how it achieves this extreme stress tolerance given the dynamic water regimes of the surface habitats on which it commonly occurs. Here, against the backdrop of global climate change, we investigated the biophysical interactions of E. halophilicum with its extracellular environment using samples taken from the surfaces of library books. The specific aims were to examine its morphology and extracellular environment (using scanning electron microscopy for visualisation and energy-dispersive X-ray spectrometry to identify chemical elements) and investigate interactions with water, ions, and minerals (including analyses of temperature and relative humidity conditions and determinations of salt deliquescence and water activity of extracellular brine). We observed crystals identified as eugsterite (Na₄Ca(SO₄)₃·2H₂O) and mirabilite (Na₂SO₄·10H₂O) embedded within extracellular polymeric substances and provide evidence that E. halophilicum uses salt deliquescence to maintain conditions consistent with its water-activity window for growth. In addition, it utilizes a covering of hair-like microfilaments that likely absorb water and maintain a layer of humid air adjacent to the hyphae. We believe that, along with compatible solutes used for osmotic adjustment, these adaptations allow the fungus to maintain hydration in both space and time. We discuss these findings in relation to the conservation of books and other artifacts within the built environment, spoilage of foods and feeds, the ecology of E. halophilicum in natural habitats, and the current episode of climate change.

Building the uracil skeleton in primitive ponds at the origins of life: carbamoylation of aspartic acid

A large set of nucleobases and amino acids is found in meteorites, implying that several chemical reservoirs are present in the solar system. The "geochemical continuity" hypothesis explores how protometabolic paths developed from so-called "bricks" in an enzyme-free prebiotic world and how they affected the origins of life. In the living cell, the second step of synthesizing uridine and cytidine RNA monomers is a carbamoyl transfer from a carbamoyl donor to aspartic acid. Here we compare two enzyme-free scenarios: aqueous and mineral surface scenarios in a thermal range up to 250 °C. Both processes could have happened in ponds under open atmosphere on the primeval Earth. Carbamoylation of aspartic acid with cyanate in aqueous solutions at 25 °C gives high N-carbamoyl aspartic acid yields within 16 h. It is important to stress that, while various molecules could be efficient carbamoylating agents according to thermodynamics, kinetics plays a determining role in selecting prebiotically possible pathways.

Unearthing terrestrial extreme microbiomes for searching terrestrial-like life in the Solar System

The possibility of life elsewhere in the universe has fascinated humankind for ages. To the best of our knowledge, life, as we know it, is limited to planet Earth; yet current investigation suggests that life might be more common than previously thought. In this review, we explore extreme terrestrial analogue environments in the search for some notable examples of extreme organisms, including overlooked microbial groups such as viruses, fungi, and protists, associated with limits of life on Earth. This knowledge is integral to provide the foundational principles needed to predict what sort of Earth-like organisms we might find in the Solar System and beyond, and to understand the future and origins of life on Earth.

Volcanically hosted venting with indications of ultramafic influence at Aurora hydrothermal field on Gakkel Ridge

The Aurora hydrothermal system, Arctic Ocean, hosts active submarine venting within an extensive field of relict mineral deposits. Here we show the site is associated with a neovolcanic mound located within the Gakkel Ridge rift-valley floor, but deep-tow camera and sidescan surveys reveal the site to be ≥100 m across-unusually large for a volcanically hosted vent on a slow-spreading ridge and more comparable to tectonically hosted systems that require large time-integrated heat-fluxes to form. The hydrothermal plume emanating from Aurora exhibits much higher dissolved CH₄/Mn values than typical basalt-hosted hydrothermal systems and, instead, closely resembles those of high-temperature ultramafic-influenced vents at slow-spreading ridges. We hypothesize that deep-penetrating fluid circulation may have sustained the prolonged venting evident at the Aurora hydrothermal field with a hydrothermal convection cell that can access ultramafic lithologies underlying anomalously thin ocean crust at this ultraslow spreading ridge setting. Our findings have implications for ultra-slow ridge cooling, global marine mineral distributions, and the diversity of geologic settings that can host abiotic organic synthesis - pertinent to the search for life beyond Earth.

Viruses in astrobiology

Viruses are the most abundant biological entities on Earth, and yet, they have not received enough consideration in astrobiology. Viruses are also extraordinarily diverse, which is evident in the types of relationships they establish with their host, their strategies to store and replicate their genetic information and the enormous diversity of genes they contain. A viral population, especially if it corresponds to a virus with an RNA genome, can contain an array of sequence variants that greatly exceeds what is present in most cell populations. The fact that viruses always need cellular resources to multiply means that they establish very close interactions with cells. Although in the short term these relationships may appear to be negative for life, it is evident that they can be beneficial in the long term. Viruses are one of the most powerful selective pressures that exist, accelerating the evolution of defense mechanisms in the cellular world. They can also exchange genetic material with the host during the infection process, providing organisms with capacities that favor the colonization of new ecological niches or confer an advantage over competitors, just to cite a few examples. In addition, viruses have a relevant participation in the biogeochemical cycles of our planet, contributing to the recycling of the matter necessary for the maintenance of life. Therefore, although viruses have traditionally been excluded from the tree of life, the structure of this tree is largely the result of the interactions that have been established throughout the intertwined history of the cellular and the viral worlds. We do not know how other possible biospheres outside our planet could be, but it is clear that viruses play an essential role in the terrestrial one. Therefore, they must be taken into account both to improve our understanding of life that we know, and to understand other possible lives that might exist in the cosmos.

Hydrothermal Processing of Microorganisms: Mass Spectral Signals of Degraded Biosignatures for Life Detection on Icy Moons

Life detection missions to the outer solar system are concentrating on the icy moons of Jupiter and Saturn and their inferred subsurface oceans. Access to evidence of habitability, and possibly even life, is facilitated by the ejection of subsurface material in plumes and outgassing fissures. Orbiting spacecraft can intersect the plume material or detect past sputtered remnants of outgassed products and analyze the contents using instruments such as mass spectrometers. Hydrothermalism has been proposed for the subsurface environments of icy moons, and the organic remains of any associated life would be expected to suffer some degradation through hydrothermalism, radiolysis, or spacecraft flyby impact fragmentation. Hydrothermalism is treated here for the first time in the context of the Europa Clipper mission. To assess the influence of hydrothermalism on the ability of orbiting mass spectrometers to detect degrading signals of life, we have subjected Earth microorganisms to laboratory hydrothermal processing. The processed microorganism samples were then analyzed using gas chromatography-mass spectrometry (GC-MS), and mass spectra were generated. Certain compound classes, such as carbohydrates and proteins, are significantly altered by hydrothermal processing, resulting in small one-ring and two-ring aromatic compounds such as indoles and phenols. However, lipid fragments, such as fatty acids, retain their fidelity, and their provenance is easily recognized as biological in origin. Our data indicate that mass spectrometry measurements in the plumes of icy moons, using instruments such as the MAss Spectrometer for Planetary Exploration (MASPEX) onboard the upcoming Europa Clipper mission, can reveal the presence of life even after significant degradation by hydrothermal processing has taken place.

The archaeal class Halobacteria and astrobiology: Knowledge gaps and research opportunities

Water bodies on Mars and the icy moons of the outer solar system are now recognized as likely being associated with high levels of salt. Therefore, the study of high salinity environments and their inhabitants has become increasingly relevant for Astrobiology. Members of the archaeal class Halobacteria are the most successful microbial group living in hypersaline conditions and are recognized as key model organisms for exposure experiments. Despite this, data for the class is uneven across taxa and widely dispersed across the literature, which has made it difficult to properly assess the potential for species of Halobacteria to survive under the polyextreme conditions found beyond Earth. Here we provide an overview of published data on astrobiology-linked exposure experiments performed with members of the Halobacteria, identifying clear knowledge gaps and research opportunities.

The emergence of interstellar molecular complexity explained by interacting networks

Recent years have witnessed the detection of an increasing number of complex organic molecules in interstellar space, some of them being of prebiotic interest. Disentangling the origin of interstellar prebiotic chemistry and its connection to biochemistry and ultimately, to biology is an enormously challenging scientific goal where the application of complexity theory and network science has not been fully exploited. Encouraged by this idea, we present a theoretical and computational framework to model the evolution of simple networked structures toward complexity. In our environment, complex networks represent simplified chemical compounds and interact optimizing the dynamical importance of their nodes. We describe the emergence of a transition from simple networks toward complexity when the parameter representing the environment reaches a critical value. Notably, although our system does not attempt to model the rules of real chemistry nor is dependent on external input data, the results describe the emergence of complexity in the evolution of chemical diversity in the interstellar medium. Furthermore, they reveal an as yet unknown relationship between the abundances of molecules in dark clouds and the potential number of chemical reactions that yield them as products, supporting the ability of the conceptual framework presented here to shed light on real scenarios. Our work reinforces the notion that some of the properties that condition the extremely complex journey from the chemistry in space to prebiotic chemistry and finally, to life could show relatively simple and universal patterns.

Organic carbon concentrations in 3.5-billion-year-old lacustrine mudstones of Mars

This work presents the first quantification of bulk organic carbon in Mars surface sedimentary rocks, enabled by a stepped combustion experiment performed by the Curiosity Rover in Gale crater, Mars. The mudstone sample analyzed by Curiosity represents a previously habitable lacustrine environment and a depositional environment favorable for preservation of organics formed in situ and/or transported from a wide catchment area. Here we present the abundance of bulk organic carbon in these mudstone samples and discuss the contributions from various carbon reservoirs on Mars.

The Sample Analysis at Mars instrument stepped combustion experiment on a Yellowknife Bay mudstone at Gale crater, Mars revealed the presence of organic carbon of Martian and meteoritic origins. The combustion experiment was designed to access refractory organic carbon in Mars surface sediments by heating samples in the presence of oxygen to combust carbon to CO₂. Four steps were performed, two at low temperatures (less than ∼550 °C) and two at high temperatures (up to ∼870 °C). More than 950 μg C/g was released at low temperatures (with an isotopic composition of δ¹³C = +1.5 ± 3.8‰) representing a minimum of 431 μg C/g indigenous organic and inorganic Martian carbon components. Above 550 °C, 273 ± 30 μg C/g was evolved as CO₂ and CO (with estimated δ¹³C = −32.9‰ to −10.1‰ for organic carbon). The source of high temperature organic carbon cannot be definitively confirmed by isotopic composition, which is consistent with macromolecular organic carbon of igneous origin, meteoritic infall, or diagenetically altered biomass, or a combination of these. If from allochthonous deposition, organic carbon could have supported both prebiotic organic chemistry and heterotrophic metabolism at Gale crater, Mars, at ∼3.5 Ga.

Bioinformation and Neutrino Communication

Communications among civilizations may include self-descriptive bioinformation because pathogen dynamics exist in their astrobiology and astrovirology, which could become pathogenic upon actual contact. This information is of mutual benefit, if reciprocated. However, in contrast, the strategic counter-scenario of self-hidden civilizations is also discussed. Civilizations, including extra-terrestrial civilizations have been divided and stratified into three levels, using a wide non-linear logarithmic scale. The levels are based on their energy expenditures: level 1 is at 4x10^19 erg/sec; level 2 is at 4x10^33 erg/sec; and level 3 is at 4x10^44 erg/sec. Terrestrial civilization is currently below the entry level I. Particularly advanced civilizations, which are above the highest level, may engineer interstellar travel and could move their planets across interstellar distances. Communication among civilizations has always been of keen interest. In terms of ability to communicate among advanced civilizations, neutrinos may be used for galactic and inter-galactic communication, in addition to or instead of using electromagnetic radiation. Thus, at this juncture, deliberation and debate are essential to proceed with development of civilization and communication.

Analytical Chemistry Throughout This Solar System

One of the greatest and most long-lived scientific pursuits of humankind has been to discover and study the planetary objects comprising our solar system. Information gained from solar system observations, via both remote sensing and in situ measurements, is inherently constrained by the analytical (often chemical) techniques we employ in these endeavors. The past 50 years of planetary science missions have resulted in immense discoveries within and beyond our solar system, enabled by state-of-the-art analytical chemical instrument suites on board these missions. In this review, we highlight and discuss some of the most impactful analytical chemical instruments flown on planetary science missions within the last 20 years, including analytical techniques ranging from remote spectroscopy to in situ chemical separations. We first highlight mission-based remote and in situ spectroscopic techniques, followed by in situ separation and mass spectrometry analyses. The results of these investigations are discussed, and their implications examined, from worlds as close as Venus and familiar as Mars to as far away and exotic as Titan. Instruments currently in development for planetary science missions in the near future are also discussed, as are the promises their capabilities bring. Analytical chemistry is critical to understanding what lies beyond Earth in our solar system, and this review seeks to highlight how questions, analytical tools, and answers have intersected over the past 20 years and their implications for the near future.

In Situ Raman Spectroscopy Monitoring of Material Changes During Proton Irradiation

Organic molecules are prime targets in the search for life on other planetary bodies in the Solar System. Understanding their preservation potential and detectability after ionic irradiation, with fluences potentially representing those received for several millions to billions of years at Mars or in interplanetary space, is a crucial goal for astrobiology research. In order to be able to perform in situ characterization of such organic molecules under ionic irradiation in the near future, a feasibility experiment was performed with polymer test samples to validate the optical configuration and the irradiation chamber geometry. We present here a Raman in situ investigation of the evolution of a series of polymers during proton irradiation. To achieve this goal, a new type of Raman optical probe was designed, which documented that proton irradiation (with a final fluence of 3.10¹⁴ at·cm^-2) leads to an increase in the background level of the signal, potentially explained by the scission of the polymeric chains and by atom displacements creating defects in the materials. To improve the setup further, a micro-Raman probe and a temperature-controlled sample holder are under development to provide higher spectral and spatial resolutions (by reducing the depth of field and laser spot size), to permit Raman mapping as well as to avoid any thermal effects.

Identifying the wide diversity of extraterrestrial purine and pyrimidine nucleobases in carbonaceous meteorites

The lack of pyrimidine diversity in meteorites remains a mystery since prebiotic chemical models and laboratory experiments have predicted that these compounds can also be produced from chemical precursors found in meteorites. Here we report the detection of nucleobases in three carbonaceous meteorites using state-of-the-art analytical techniques optimized for small-scale quantification of nucleobases down to the range of parts per trillion (ppt). In addition to previously detected purine nucleobases in meteorites such as guanine and adenine, we identify various pyrimidine nucleobases such as cytosine, uracil, and thymine, and their structural isomers such as isocytosine, imidazole-4-carboxylic acid, and 6-methyluracil, respectively. Given the similarity in the molecular distribution of pyrimidines in meteorites and those in photon-processed interstellar ice analogues, some of these derivatives could have been generated by photochemical reactions prevailing in the interstellar medium and later incorporated into asteroids during solar system formation. This study demonstrates that a diversity of meteoritic nucleobases could serve as building blocks of DNA and RNA on the early Earth.

The maintenance of ambiguity in Martian exobiology

How do scientists maintain their research programs in the face of not finding anything? Continual failure to produce results can result in declining support, scientific controversy and credibility challenges. We elaborate on a crucial mechanism for sustaining the credibility of research programs through periods of non-detection: the maintenance of ambiguity. By this, we refer to scientific strategies that resist closure or an experiment's premature end by creating doubt in negative findings and fostering hope for future positive results. To illustrate this concept, we draw upon the recent history of Martian exobiology. Since the 1960s, planetary scientists have continually tried and failed to find evidence of life on Mars. And yet, interest in extraterrestrial life detection remains high, with more missions to Mars underway. Through three destabilizing events of non-detection, we show how exobiologists sustained the search for Martian life by casting doubt on negative findings, pointing to other possible unexplored routes to success, and finally reconfiguring operations around new methods or goals. New approaches may take the form of shifts in scale, method and object of interest. By pivoting to a different scale, method or object, exobiologists have continued to study a subject continually lacking proof of existence and made important discoveries about life on Earth.

Catastrophe risk can accelerate unlikely evolutionary transitions

Intelligent life has emerged late in Earth's habitable lifetime, and required a preceding series of key evolutionary transitions. A simple model (the Carter model) explains the late arrival of intelligent life by positing these evolutionary transitions were exceptionally unlikely 'critical steps'. An alternative model (the neocatastrophism hypothesis) proposes that intelligent life was delayed by frequent catastrophes that served to set back evolutionary innovation. Here, we generalize the Carter model and explore this hypothesis by including catastrophes that can 'undo' an evolutionary transition. Introducing catastrophes or evolutionary dead ends can create situations in which critical steps occur rapidly or in clusters, suggesting that past estimates of the number of critical steps could be underestimated. If catastrophes affect complex life more than simple life, the critical steps will also exhibit a pattern of acceleration towards the present, suggesting that the increase in biological complexity over the past 500 Myr could reflect previously overlooked evolutionary transitions. Furthermore, our results have implications for understanding the different explanations (critical steps versus neo-catastrophes) for the evolution of intelligent life and the so-called Fermi paradox-the observation that intelligent life appears rare in the observable Universe.

Scaling laws in enzyme function reveal a new kind of biochemical universality

Known examples of life all share the same core biochemistry going back to the last universal common ancestor (LUCA), but whether this feature is universal to other examples, including at the origin of life or alien life, is unknown. We show how a physics-inspired statistical approach identifies universal scaling laws across biochemical reactions that are not defined by common chemical components but instead, as macroscale patterns in the reaction functions used by life. The identified scaling relations can be used to predict statistical features of LUCA, and network analyses reveal some of the functional principles that underlie them. They are, therefore, prime candidates for developing new theory on the “laws of life” that might apply to all possible biochemistries.

All life on Earth is unified by its use of a shared set of component chemical compounds and reactions, providing a detailed model for universal biochemistry. However, this notion of universality is specific to known biochemistry and does not allow quantitative predictions about examples not yet observed. Here, we introduce a more generalizable concept of biochemical universality that is more akin to the kind of universality found in physics. Using annotated genomic datasets including an ensemble of 11,955 metagenomes, 1,282 archaea, 11,759 bacteria, and 200 eukaryotic taxa, we show how enzyme functions form universality classes with common scaling behavior in their relative abundances across the datasets. We verify that these scaling laws are not explained by the presence of compounds, reactions, and enzyme functions shared across known examples of life. We demonstrate how these scaling laws can be used as a tool for inferring properties of ancient life by comparing their predictions with a consensus model for the last universal common ancestor (LUCA). We also illustrate how network analyses shed light on the functional principles underlying the observed scaling behaviors. Together, our results establish the existence of a new kind of biochemical universality, independent of the details of life on Earth’s component chemistry, with implications for guiding our search for missing biochemical diversity on Earth or for biochemistries that might deviate from the exact chemical makeup of life as we know it, such as at the origins of life, in alien environments, or in the design of synthetic life.

Neutrino communication, intergalactic transit, and Astrobiology

This is a brief summary, snapshot, of a few issues that relate to possible communication with Extraterrestrial Intelligence (ETI) using neutrinos. Essentially, more research is required to better understand possible detection and communication with intelligent life (Astrobiology and ETI). Because of the possible scarcity of life in any single galaxy, to enhance the possibility of life detection, inter-galactic transit neutrinos necessitate consideration. Neutrino-based potential communications are inferred as the optimal mechanism or venue for detection of communications from ETI as well as sending communications to ETI. A paradox exists within this central theme. On the one hand, neutrino technology should be further developed and used to receive signals from or to send signals to ETI, because they transit inter-galactic distances. On the other hand, however, neutrinos have a very low cross-section interaction and are very difficult to detect. This concise Editorial incorporates several diverse research areas. Various issues are briefly and conjointly mentioned to inform the reader of multiple fields required towards a deeper understanding of astrobiology, astro virology, and ETI. This understanding is required for future advances, just as innovations in classical physics, quantum mechanics, particle physics, biophysics, chemistry, biochemistry, and molecular biology were required for the breakthroughs and advances in biology and virology, from the last century to the present - thus, the need for innovations and applications in neutrino particle physics research.

A material-based panspermia hypothesis: The potential of polymer gels and membraneless droplets

The Panspermia hypothesis posits that either life's building blocks (molecular Panspermia) or life itself (organism-based Panspermia) may have been interplanetarily transferred to facilitate the origins of life (OoL) on a given planet, complementing several current OoL frameworks. Although many spaceflight experiments were performed in the past to test for potential terrestrial organisms as Panspermia seeds, it is uncertain whether such organisms will likely "seed" a new planet even if they are able to survive spaceflight. Therefore, rather than using organisms, using abiotic chemicals as seeds has been proposed as part of the molecular Panspermia hypothesis. Here, as an extension of this hypothesis, we introduce and review the plausibility of a polymeric material-based Panspermia seed (M-BPS) as a theoretical concept, where the type of polymeric material that can function as a M-BPS must be able to: (1) survive spaceflight and (2) "function", i.e., contingently drive chemical evolution toward some form of abiogenesis once arriving on a foreign planet. We use polymeric gels as a model example of a potential M-BPS. Polymeric gels that can be prebiotically synthesized on one planet (such as polyester gels) could be transferred to another planet via meteoritic transfer, where upon landing on a liquid bearing planet, can assemble into structures containing cellular-like characteristics and functionalities. Such features presupposed that these gels can assemble into compartments through phase separation to accomplish relevant functions such as encapsulation of primitive metabolic, genetic and catalytic materials, exchange of these materials, motion, coalescence, and evolution. All of these functions can result in the gels' capability to alter local geochemical niches on other planets, thereby allowing chemical evolution to lead to OoL events.