We have initiated a large project on identifying the requirements for developing a realistic and ground-up approach to simulating the formation of terrestrial planets in our solar system. As the first phase of this project, we present here the criteria that any model of planetesimal growth needs to fulfill in order to be self-consistent and produce reliable results. We demonstrate how these criteria emerge by revisiting runaway growth and carrying out a thorough analysis of its results. As our goal is to identify the pathway to a realistic model, we focus analysis on simulations where at the beginning, planetesimals are not artificially enlarged. We show how using uninflated planetesimals, as the first requirement for a realistic model, will result in a set of criteria naturally emerging from the evolution of the system. For instance, the growth times in simulations with uninflated planetesimals become comparable to the time of giant planet formation implying that any realistic simulation of planetesimal growth, in addition to using real-size planetesimals, needs to include the perturbation of the growing giant planets as well. Our analysis also points to a strong connection between the initial distribution of planetesimals and the final outcome. For instance, due to their natural expansion, initially isolated distributions, or a collection of initially isolated distributions, such as rings of planetesimals, do not produce reliable results. In a self-consistent and realistic model, where the initial conditions are supported by basic principles and do not include simplifying, ad hoc assumptions, the entire disk of planetesimals has to be simulated at once. We present the results of our analyses and discuss their implied criteria.

Ionizing radiation is known to have a destructive effect on biology by causing damage to DNA, cells and the production of reactive oxygen species, among other things. While direct exposure to high-radiation dose is indeed not favorable for biological activity, ionizing radiation can and, in some cases, is known to produce a number of biologically useful products. One such mechanism is the production of biologically useful products via charged particle-induced radiolysis. Energetic charged particles interact with the surfaces of planetary objects such as Mars, Europa and Enceladus without much shielding from their rarefied atmospheres. Depending on the energy of said particles, they can penetrate several meters deep below the surface and initiate a number of chemical reactions along the way. Some of the byproducts are impossible to produce with lower-energy radiation (such as sunlight), opening up new avenues for life to utilize them. The main objective of the manuscript is to explore the concept of a Radiolytic Habitable Zone (RHZ), where the chemistry of galactic cosmic ray-induced radiolysis can be potentially utilized for metabolic activity. We first calculate the energy deposition and the electron production rate using the GEANT4 numerical model, then estimate the current production and possible chemical pathways which could be useful for supporting biological activity on Mars, Europa and Enceladus. The concept of RHZ provides a novel framework for understanding the potential for life in high-radiation environments. By combining energy deposition calculations with the energy requirements of microbial cells, we have defined the RHZ for Mars, Europa and Enceladus. These zones represent the regions where radiolysis-driven energy production is sufficient to sustain microbial metabolism. We find that bacterial cell density is highest in Enceladus, followed by Mars and Europa. We discuss the implications of these mechanisms for the habitability of such objects in the solar system and beyond.

Spaceflight missions must limit biological contamination on both the outbound and return legs to comply with planetary protection requirements. Depending on the mission profile, contamination concerns may include the potential presence of bioactive molecules as defined by NASA’s Planetary Protection policies. Thus, the present study has examined the temperature and time requirements for sufficient inactivation/degradation of an infectious, heat-stable prion protein (Sup35NM), which serves as a model bioactive molecule. Bovine serum albumin was used to establish the method parameters and feasibility. Differential scanning calorimetry, Fourier transform infrared spectroscopy, analytical reversed-phase high-performance liquid chromatography, and mass spectrometry were utilized to analyze heat-treated samples, with non-treated samples serving as controls. Heat treatment at 400°C for 5 seconds was found to result in substantial decomposition of Sup35NM. In addition to the disruption of the protein backbone amide bonds, the side chain residues were also compromised. Fragments of molecular weight <4600 were observed by mass spectrometry but the impact of treatment on both the backbone and side chains of Sup35NM suggested that these fragments would not self-associate to create potentially pathogenic entities. The present methodology provided insight into the protein degradation process and can be applied to a variety of treatment strategies (e.g., any form of sterilization or inactivation) to ensure a lack of protein-based contamination of isolated extraterrestrial specimens.

Astrobiology is a scientific field that is very interdisciplinary and developing very fast, with many new discoveries generating a high level of attention in both the scientific community and the public. A central goal of astrobiology is to discover life beyond Earth which is, with our current instrumentation and knowledge, arguably within our reach. However, knowledge exchange crossing disciplinary boundaries is becoming increasingly challenging due to different usage of nomenclature and scientific controversies often limited to subdisciplines. There have been some efforts to compile organized databases of terms, concepts and other relevant material within some of the subfields contributing to astrobiology, for example through manually curated online portals designed to benefit students, teachers and practitioners of astrobiology-related research. However, the developments within the subfields and the potentially premature communication of research findings are too fast for objective research portals to remain reliable and up-to-date enough to enable well-informed scientific discussions. We suggest here a novel strategy for developing an online tracers portal as a self-maintaining and self-updating information platform, that would allow not only for a relatively unbiased selection of research results, but also provide fast access to latest scientific discoveries together with potential controversies, such that users of the tracers portal can form their own opinion on all available data rather than obtaining an already filtered and potentially biased selection of information.

The study explores the vertical stratification of microbial diversity and metabolic potential in Earth’s lower atmosphere. Using 16S rRNA sequencing data spanning the planetary boundary layer to the lower stratosphere, we conducted taxonomic profiling and metabolic pathways predictions. The aim was to elucidate microbial community dynamics and their ecological roles under diverse atmospheric conditions. Methods: 51 Publicly available datasets with 3584 samples were retrieved from repositories such as Sequencing Read Archive and European Nucleotide Archive, filtered for studies employing 16S rRNA sequencing. Quality control was performed using FastQC and Trimmomatic, followed by taxonomic classification with Qiime2 and the Silva132 database. Functional pathway predictions were derived using PICRUSt2, and statistical analyses included Kruskal-Wallis tests for diversity comparisons and Mann-Whitney U tests for pathway activity. Results: Microbial diversity decreased with altitude, with the Surface Layer exhibiting the highest Shannon diversity and the significantly decreased in Low Stratosphere. Taxonomic composition shifted along the elevation gradient, with Actinobacteria and Alphaproteobacteria predominant at lower altitudes. In contrast, Bacilli and Gammaproteobacteria became more dominant at higher elevations, though they maintained a notable presence at lower sites as well. Functional analysis revealed altitude-specific adaptations, including significant upregulation of CO2 fixation pathways in the Free Troposphere Transition Layer and secondary metabolite biosynthesis in the lower stratosphere. Discussion: These findings reveal distinct microbial metabolic profiles across atmospheric layers with varying conditions such as oxygen levels, UV radiation, and nutrient availability. While these differences may represent adaptive strategies, they could also reflect source environment characteristics or selective transport processes. The conserved metabolic pathways across altitude layers suggest functional resilience despite taxonomic divergence. These results have implications for astrobiology, providing analogs for microbial life in extraterrestrial environments like Mars or Europa. In summary, this study advances our understanding of aerobiomes’ ecological roles and their potential as models for life detection in extreme environments, bridging atmospheric microbiology with astrobiological exploration.

Here we present the resistance of two halophilic Archaea, Halorubrum (Hrr.) sp. AS12 and Haloarcula (Har.). sp. NS06, isolated from the brine in Lunenburg, Germany, to stress factors including desiccation, radiation and elevated perchlorate concentration. This is the first study to describe the stress resistance of halophilic Archaea isolated from the Lunenburg brine. While Hrr. sp. AS12 tolerates desiccation up to 45 days with a -log3 reduction in survival, Har. sp. NS06 displays a strong decline in viability and no detectable survival following 21 days. In contrast, Hrr. sp. AS12 was more sensitive towards X-Ray irradiation with a significant decline in viability (D10 228,2 ± 8,9 Gy) while Har. sp. NS06 showed a slight decline in survival following exposure to 1 kGy. The resistance of both strains against germicidal UV-C254nm radiation follows a similar pattern when compared to X-ray exposure with Hrr. sp. AS12 displaying more sensitivity to UV-C radiation (F10 111,6 ± 6,4 J/m2) compared to Har. sp. NS06 (F10 194,9 ± 13,7 J/m2). Exposure to He, Ar, and Fe heavy ions up to 500 Gy showed little effect on the survivability; however, the transport control of Hrr. sp. AS12 showed a strong decline (-log3 reduction) in survival. Both strains revealed increased growth in the presence of perchlorates (NaClO4 and MgClO4) with a clear preference to NaClO4 up to 5%. Our results provide a first insight into the stress resistance of these two isolates and will further develop our understanding of the parameters of life on Earth and potentially on other planets.

Based on present knowledge of atmospheric composition, a mechanism for the natural formation of vesicles in the lakes of Titan is proposed. It involves precipitation-induced spray droplets coated by a monolayer of amphiphiles. On interaction with the monolayer on the lake’s surface, bilayer membranes are being formed that encapsulate the liquid phase of the original droplet. The resulting vesicles develop thermodynamic stability by continuous compositional selection of various types of amphiphiles in a dynamic equilibrium, leading to an optimized vesicle stability. Different populations of stable vesicles may compete, initiating a long-term evolution process that could eventually result in primitive protocells. The existence of any type of vesicles on Titan would prove that early steps towards increasing order and complexity have taken place, which represent the necessary precondition for abiogenesis. A valid analytical approach could involve a laser device with combined light scattering analysis and surface enhanced Raman spectroscopy. It would allow for very sensitive detection of amphiphiles as well as for the observation of dispersed vesicles.

In ecological systems, be it a Petri dish or a galaxy, populations evolve from some initial value (say zero) up to a steady-state equilibrium, when the mean number of births and deaths per unit time are equal. This equilibrium point is a function of the birth and death rates, as well as the carrying capacity of the ecological system itself. We show that the occupation fraction versus birth-to-death rate ratio is S-shaped, saturating at the carrying capacity for large birth-to-death rate ratios and tending to zero at the other end. We argue that our astronomical observations appear inconsistent with a cosmos saturated with extraterrestrial intelligences, and thus search for extraterrestrial intelligence optimists are left presuming that the true population is somewhere along the transitional part of this S-curve. Since the birth and death rates are a-priori unbounded, we argue that this presents a fine-tuning problem. Further, we show that if the birth-to-death rate ratio is assumed to have a log-uniform prior distribution, then the probability distribution of the ecological filling fraction is bi-modal – peaking at zero and unity. Indeed, the resulting distribution is formally the classic Haldane prior, conceived to describe the prior expectation of a Bernoulli experiment, such as a technological intelligence developing (or not) on a given world. Our results formally connect the Drake equation to the birth–death formalism, the treatment of ecological carrying capacity and their connection to the Haldane perspective.

Glycine plays an essential role in a variety of biological and biochemical processes. As the smallest amino acid, glycine is especially important in studies of prebiotic chemistry and chemical evolution. The behaviour of glycine in aqueous solution under ionizing radiation fields is still not well understood. Understanding the reaction mechanism of glycine in an ionizing radiation environment may provide insights into the complex processes involved in prebiotic chemical synthesis. Such reaction conditions could provide clues about the environmental conditions that might favour the emergence of life. Numerical modelling based on reaction kinetics provides information on the feasibility of the reaction mechanisms. In this work, we developed a numerical model in Python that describes the behaviour of glycine, as prototype compound, in aqueous solution under gamma radiation. The model is based on a variety of reaction kinetics pathways that have been proposed to describe the principal reactions between glycine and the water radicals formed by ionizing radiation. The numerical results are consistent with the experiments of other researchers. We obtained similar numerical solutions from different reaction mechanisms that share the same initial reactions. The results suggest that the primary attack of water radicals on the glycine is the main factor that controls the general decay of the molar concentration of glycine and the secondary reactions do not have a strong influence, even at high doses of nearly 200 kGy. The numerical tests of the models indicate their stability with the changing initial condition of the molar concentration of glycine. This work contributes to the advancement of knowledge regarding the behaviour of glycine in aqueous solutions under ionizing radiation from a kinetic perspective. It also provides insights into their stability under conditions that are difficult to replicate in the laboratory. Finally, this work contributes to the evaluation of appropriate numerical methods for solving the system of stiff differential equations that describe the reaction mechanism of organic molecules under high radiation fields.

For near-future missions planed for Mars Sample Return (MSR), an international working group organized by the Committee on Space Research (COSPAR) developed the sample safety assessment framework (SSAF). For the SSAF, analytical instruments were selected by taking the practical limitations of hosting them within a facility with the highest level of biosafety precautions (biosafety level 4) and the precious nature of returned samples into account. To prepare for MSR, analytical instruments of high sensitivity need to be tested on effective Mars analogue materials. As an analogue material, we selected a rock core of basalt, a prominent rock type on the Martian surface. Two basalt samples with aqueous alteration cached in Jezero crater by the Perseverance rover are planned to be returned to Earth. Our previously published analytical procedures using destructive but spatially sensitive instruments such as nanoscale secondary ion mass spectrometry (NanoSIMS) and transmission electron microscopy coupled to energy-dispersive spectroscopy revealed microbial colonization at clay-filled fractures. With an aim to test the capability of an analytical instrument listed in SSAF, we now extend that work to conventional Fourier transform infrared (FT-IR) microscopy with a spatial resolution of 10 μm. Although Fe-rich smectite called nontronite was identified after crushing some portion of the rock core sample into powder, the application of conventional FT-IR microscopy is limited to a sample thickness of <30 μm. In order to obtain IR-based spectra without destructive preparation, a new technique called optical-photothermal infrared (O-PTIR) spectroscopy with a spatial resolution of 0.5 μm was applied to a 100 μm thick section of the rock core. By O-PTIR spectroscopic analysis of the clay-filled fracture, we obtained in-situ spectra diagnostic to microbial cells, consistent with our previously published data obtained by NanoSIMS. In addition, nontronite identification was also possible by O-PTIR spectroscopic analysis. From these results, O-PTIR spectroscopy is suggested be superior to deep ultraviolet fluorescence microscopy/μ-Raman spectroscopy, particularly for smectite identification. A simultaneous acquisition of the spatial distribution of structural motifs associated with biomolecules and smectites is critical for distinguishing biological material in samples as well as characterizing an abiotic background.

Astrobiology is often defined as the study of the origin, evolution, distribution and future of life on Earth and in the Universe and thought of as a discipline. In practice though, the delineation of astrobiology-related research and corresponding groups of researchers is far from straightforward. Here, we propose to apply text-mining methods to identify researcher communities depending on thematic similarities in their published works. After fitting a latent Dirichlet allocation topic model to the complete article corpus of three flagship journals in the field – Origins of Life and Evolution of Biospheres (1968–2020), Astrobiology (2001–2020), the International Journal of Astrobiology (2002–2020) – and computing author topic profiles, researcher communities are inferred from topic similarity networks to which community detection is applied. Such semantic social networks reveal, as we call them, ‘hidden communities of interest’ that gather researchers who publish on similar topics. The evolution of these communities is also mapped through time, bringing to light the significant shifts that the discipline underwent in the past 50 years.

The establishment of the possible presence of life on Mars (past or present) is based on the study of planetary analogues, which allow in situ analysis of the environments in which living organisms adapt to often extreme conditions. Although Mars has been a candidate for hosting life, based on observations made decades ago, it is thanks to the characteristics identified in environments, mainly volcanic, that it has been possible to calibrate instruments and detail the features of the red planet. In this paper, we present a review of the main characteristics of different planetary analogues, particularly deepening the study of Antarctica, to later expose the factors studied in Deception Island that have contributed to considering it as an analogue of Mars from different perspectives. Although geological and geomorphological studies on the analogies of the island already exist, detailed analyses that present the approach of astrobiological analogues are required, thus allowing further research.

Drosophila melanogaster has given enormous contributions to Space Biology Research. This organism is an important tool to be manipulated in genetic engineering and molecular experiments in order to understand different biological processes homologous to other multicellular systems, including humans. Their milestone contribution in microgravity conditions and radiation, the two most important variables in space, have allowed new knowledge and perspectives on the positive and negative effects on cellular, molecular and genetic levels. In this review, we expose the historical contribution of Drosophila melanogaster in Astrobiology.

The environmental conditions for the origin of life are still not well-constrained, but membrane-bound structures must have been key to the origin of life. Membranes composed of fatty acids are promising candidates due to their simplicity and plausible prevalence in prebiotic environments. To assess the stability of membranes composed of fatty acids with tail lengths ranging from 12 to 16 carbons at different temperatures and sodium chloride concentrations that may have existed on the early Earth, we conducted all-atom molecular dynamics (MD) simulations. In the absence of salt (freshwater), none of the fatty acids exhibited bilayer formation, whether below or above their chain melting temperature. However, elevating the salt concentration from 0.15 M (saline solution), 0.5 M (seawater), 1 M (seawater tide pools), 3 M (salty tide pools) and 5 M (Dead Sea) resulted in the formation of stable bilayers. The 16-carbon fatty acid required lower salt concentration, while shorter, 12-carbon chain necessitated higher salt levels. Increasing the salt concentration led to three main effects: (1) increased bilayer thickness, (2) reduced area per fatty acid and (3) elevated deuterium order parameter of the chains, resulting in more robust membranes. Our simulations indicated that the salt cations aggregated on the bilayer surfaces, effectively mitigating repulsive interactions among hydrophilic fatty acid head groups. These findings suggest that fatty acid bilayers are more likely present in ancient waters connected to saltwater reservoirs, or seawater tide pools with elevated salt concentrations.

Determining a reliable method to detect life on another planet is an essential first step in the pursuit of discovering extraterrestrial life. Polyhydroxyalkanoates (PHAs), bioplastic polymers created by microorganisms, are strong candidates for defining the presence of extraterrestrial life due to their water insolubility, strong ultraviolet resistance, high melting points and high crystallinity, amongst other qualities. PHAs are abundant on Earth, and their chemical properties can easily be distinguished from non-biological matter. Their widespread distribution and conferred resistance to astrobiologically relevant extreme environments render PHAs highly favourable candidates for astrobiological detection. Integrating detection of PHA biosignatures into current and future life-detection instruments would be useful for the planetary search for life. PHAs are analysed and characterized in laboratories by gas chromatography-mass spectrometry, infrared spectroscopy, Raman spectroscopy and immunoassay analysis in addition to other methods. We outline a path forward to integrate PHA detection in astrobiology missions to aid the search for extraterrestrial life.

Exopsychology is a sub-discipline of psychology concerned with how humans contemplateextraterrestrials as well as forming hypothesis about how these beings may think, feel and behave. While researching the former is undoubtedly a subject for empirical science, aspects of the latter remain uncertain. Given the contemporary scientific insight, it may still be possible to identify a set of cornerstones and eventually create a space of possible configurations of the extraterrestrial mind. Here, we identify three basic compatibility requirements: first, any form of life must navigate internal and external (environmental) demands and thus actively ensure the compatibility of its current state with the same demands. Second, any advanced cognitive development and the emergence of remotely detectable technosignatures require not only the relevant capabilities for manipulation but also compatibility with a permissive environment. Lastly, requirements also concern the compatibility of extraterrestrial thinking and behaviour with our search method. In its most basic understanding, search for extraterrestrial intelligence (SETI) searches for something done by somebody. However, the meaning of this simple formula and the psychological theory behind it is underdeveloped. Hence, psychological aid is needed to assist SETI in its effort to reveal whether galactic information indicates the presence of a mere object or activity of an identified subject with whom humans may establish contact. The fact that people believe in and search for extraterrestrials emphasizes that psychology should pay attention to this domain of phenomena. Hence, different imaginations of the extraterrestrial, ranging from benign to cruel, from superior to equally developed, are briefly discussed regarding their emergence and function as coping and motivating mechanisms for the uncertain search.

In this comprehensive review, Acidithiobacillus ferrooxidans, an acidophilic bacterium, has been thoroughly examined as a plausible analogue for microbial life in Venus's lower cloud layer. Given its ability to adapt to extreme conditions, including low pH environments and metal-rich settings, Acidithiobacillus ferrooxidans is considered a promising candidate for studying life analogues in Venus's clouds. This article comprehensively analyses the bacterium's distinctive phenotypic and genotypic features, investigating its metabolic pathways, adaptive strategies and potential ecological niche within Venusian cloud ecosystems. After careful consideration of the environmental parameters characterizing Venus, the unidentified UV absorber in its clouds, and the prospects for microbial life, this review underscores the imperative nature of future Venus missions and the pivotal role that Acidithiobacillus ferrooxidans may play in exploring the possible habitability of Venus and advancing astrobiological research.

The question of whether extraterrestrials exist has driven both the search for extraterrestrial intelligence (SETI) and some attempts of messaging to extraterrestrial intelligence (METI). Nevertheless, no data-driven or theory-based behavioural policy has been suggested. Here we simulate a comprehensive set of human–extraterrestrial strategic interactions, modelled as two-by-two game-theoretic matrices. We examine a sample of possible outcomes by relying on the theory of subjective expected relative similarity (SERS), which takes into account both the expected payoffs and the extent of strategic similarity – the prospects of the opponent making identical choices. Simulation results suggest: focusing messaging efforts on signalling of complete strategic similarity, monitoring potential alien communications for similarity-indicating signals, and using risk-averse decision rules for policy planning and decision-making. The discussion puts forward three guidelines for METI initiatives and addresses the relevance of the findings to human conflict management.

Hemoglycin, a space polymer of glycine and iron, has been identified in the carbonaceous chondritic meteorites Allende, Acfer 086, Kaba, Sutter's Mill and Orgueil. Its core form has a mass of 1494 Da and is basically an antiparallel pair of polyglycine strands linked at each end by an iron atom. The polymer forms two- and three- dimensional lattices with an inter-vertex distance of 4.9 nm. Here the extraction technique for meteorites is applied to a 2.1 Gya fossil stromatolite to reveal the presence of hemoglycin by mass spectrometry. Intact ooids from a recent (3000 Ya) stromatolite exhibited the same visible hemoglycin fluorescence in response to x-rays as an intact crystal from the Orgueil meteorite. X-ray analysis confirmed the existence in ooids of an internal three-dimensional lattice of 4.9 nm inter-vertex spacing, matching the spacing of lattices in meteoritic crystals. FTIR measurements of acid-treated ooid and a Sutter's Mill meteoritic crystal both show the presence, via the splitting of the Amide I band, of an extended anti-parallel beta sheet structure. It seems probable that the copious in-fall of carbonaceous meteoritic material, from Archaean times onward, has left traces of hemoglycin in sedimentary carbonates and potentially has influenced ooid formation.

Amino acids have been detected in some meteorites and are readily synthesized in prebiotic experiments. These molecules may have been precursors of oligomers and polymers in the early Earth. These reactions were likely to happen in the protected confined spaces on the porous surface of olivine and in the interlayer nanospace of montmorillonite. This study describes experimental and theoretical research on the sorption of l-alanine onto surfaces of silicate minerals, olivine and montmorillonite. Kinetics of the sorption of this amino acid at different pH media was performed. This sorption has been also studied at atomic scale by means of quantum mechanical calculations finding that this sorption is energetically favourable. These results strongly support the premise that minerals could have actively participated in prebiotic reactions.