Astrobiology最新文献

The "NASA definition" enjoys broad popularity among scientists, particularly in the astrobiology community: life is "a self-sustained chemical system capable of Darwinian evolution." Imprecise and difficult to implement, it nevertheless captures important features of life interesting to researchers and public audiences. A product of the Exobiology Discipline Working Group, it received a four-sentence introduction in a book foreword by Gerald Joyce. The only subsequent defense can be found in an online interview of Joyce. Additional commentary is limited, mostly critical, and occasionally incorrect. This article looks at the history of the definition and how it differs from earlier definitions of life as replication plus metabolism. The NASA definition focuses attention on information, molecular mechanisms, and "Darwinian evolution" through generalizations of replication. It retains traditional ambiguity about metabolism related to concepts of "self," "self-sustaining," and "capable." Understood in this context, the NASA definition identifies the current state of biology and suggests an agenda for future research. A "NASA working definition" may be more usefully constructed as follows: NASA will recognize life in a self-sustained chemical system demonstrating evolution by natural selection.

The origin of life is yet a compelling scientific mystery that has sometimes been attributed to high-pressure impacts by small solar system bodies such as comets, meteoroids, asteroids, and transitional objects. High-pressure torsion (HPT) is an innovative method with which to simulate the extreme conditions of astronomical impacts and offers insights relevant to prebiotic chemistry. In the present study, we investigated the polymerization and stability of adenosine monophosphate (AMP), a key precursor to ribonucleic acid (RNA), in dry and hydrated conditions (10 wt% water) under 6 GPa at ambient and boiling water temperatures. Comprehensive analyses with the use of X-ray diffraction, Raman spectroscopy, Fourier-transform infrared spectroscopy, nuclear magnetic resonance, scanning electron microscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry revealed no evidence of polymerization, while AMP partly transformed to other organic compounds such as nucleobase-derived fragments of adenine, phosphoribose fragments, dehydrated adenosine, protonated adenosine, and oxidized adenosine. The torque measurements during HPT further highlighted the mechanical behavior of AMP under extreme conditions. These findings suggest that, while HPT under the conditions tested does not facilitate polymerization, the formation of various compounds from AMP confirms the significance of astronomical impacts on the prebiotic chemistry of RNA on early Earth. Key Words: Ribonucleic acid (RNA)-Origin of life-Phase transformations-Chemical reactions-Small solar system bodies. Astrobiology 26, 1-9.

Advances in machine learning (ML) over the past decade have resulted in a proliferation of algorithmic applications for encoding, characterizing, and acting on complex data that may contain numerous multidimensional features. Recently, the emergence of deep-learning models trained across large datasets has created a new paradigm for ML in the form of Foundation Models (FMs). FMs are programs trained on large and broad datasets with an extensive number of parameters. Once built, these extremely powerful, flexible models can be utilized in less resource-intensive ways to build a variety of different downstream applications that can integrate previously disparate, multimodal data. The development of these applications can be done rapidly and with a much lower demand for ML expertise. Additionally, the necessary infrastructure and models themselves are already established within agencies such as NASA and ESA. At NASA, this work extends across several divisions of the Science Mission Directorate. Examples include the NASA Goddard and INDUS Large Language Models and the Prithvi Geospatial Foundation Model. Furthermore, ESA initiatives to bring FMs to Earth observations have led to the development of TerraMind. In February 2025, a workshop was held by NASA Ames Research Center and the SETI Institute to explore the potential of FMs in astrobiological research and identify the steps necessary to build and utilize such a model or models. Here, we share the findings and recommendations of that workshop and describe clear near-term and future opportunities in the development of a FM (or Models) for astrobiology applications. These applications would include a biosignature or life characterization task, a mission development and operations task, and a natural language task for integrating and supporting astrobiology research needs.

Planetary impact events have profoundly influenced the origin of life and the habitability of Earth in both constructive and destructive ways. The constructive effects of impacts include building Earth into a habitable world and providing the key ingredients for life, including carbon, hydrogen, nitrogen, oxygen, sulfur, and energy. The destructive effects of impacts include a cascade of transient environmental disruptions that were likely deleterious to life, such as the generation of extreme pressure and temperature conditions at the impact site, ocean vaporization, and ejection of material into the atmosphere. In this review, we retrace the evolving effects of Earth's impact history on Hadean and Archean habitability. We argue that, cumulatively, impacts encourage habitability, whereas, individually, they are more likely to cause significant transient ecological disruptions. Early in Earth's history, when large impacts were frequent, the beneficial cumulative effects likely dominated and resulted in a world primed for the development of life. We discuss novel tools that are being used to trace the origin and nature of these building blocks. From around the Archean onwards, as large impacts waned, they took on the role of occasional disruptors. We consider the ∼66 Ma Chicxulub impact as a case study for these sporadic post-Archean impacts and how they can cause transient environmental disruptions, create new subsurface habitats, and spur evolutionary developments in their wake.

Mars missions actively search for organic matter as potential biosignatures. Yet harsh conditions at the surface, including unfiltered ultraviolet (UV) light above 190 nm and oxidizing agents such as perchlorates, challenge the preservation of compounds relevant to astrobiology, such as nucleobases. Since current instruments primarily analyze samples from the uppermost surface layer, understanding the stability of organic matter under Mars-like surface conditions is essential. Nucleobases have interesting photochemical properties, as they can dimerize under UV light. Previous work showed that UV exposure of uracil under Mars-like conditions rapidly leads to more photostable dimers, with an enhanced photodecomposition yield when perchlorates are present. Additional chemical groups, including alkyne (C$\equiv$C) and nitrile (C$\equiv$N), emerge in the presence of calcium perchlorate and indicate novel photoproducts. The present work investigates the evolution of two other pyrimidine nucleobases, cytosine and thymine, in simulated UV martian conditions with and without calcium perchlorate. Infrared spectroscopy monitoring of the sample throughout the duration of the experiment showed that cytosine and thymine both form photoproducts under UV light, likely dimers for thymine. Moreover, both molecules seem to interact spontaneously with calcium perchlorates prior to any UV exposure, to form either a complex with cytosine or a change in the crystalline phase with thymine.

Biological activity has shaped environments across Earth with varying degrees of impact throughout geological time, which complicates efforts to distinguish signs of life in preserved structures. This challenge is further compounded in the ancient rock record, where diagenesis and alteration obscure biological signatures. To overcome these obstacles, it is necessary to understand the underlying processes that produce chemical and morphological features indicative of life. Traditional approaches to studying biological signatures in deep time typically focus on the binary question of "life" versus "non-life," often guided by predefined questions. Here, we emphasize a shift toward process-driven research that explores the relationships between fundamental scientific principles that govern these features, rather than traditional outcome-focused approaches. We lay groundwork for a more comprehensive exploration of life's role in shaping the rock record by addressing practical challenges and providing approaches for implementation.

The recent detection of proteinogenic amino acids and nucleobases in asteroid Bennu samples marks a pivotal discovery in astrobiology, yet the chemical pathways that govern their formation remain enigmatic. Here, we leverage computational chemistry and a systematic building-block approach, rooted in the hypothesis of hierarchical molecular assembly, to elucidate the thermodynamic properties and abundance trends observed in Bennu's organic inventory. Our framework not only rationalizes the distribution patterns of amino acids and nucleobases but also underscores its broader applicability in reconstructing the primordial synthesis of organic molecules on early Earth and Mars. By bridging cosmochemistry with prebiotic scenarios, this work advances our understanding of how extraterrestrial chemistry could have seeded life's molecular precursors.

On Mars, the amount of ultraviolet C (UVC) radiation that reaches the surface is sufficiently deleterious for life as we know it. However, it has been predicted that some ancient lakes on Mars had high concentrations of Fe³⁺, an ionic species known for a high absorption of UVC radiation. Some models of UV attenuation have already been established; however, there is a lack of reliable simulations that make the connection between this radiation absorption in an aqueous medium and its impact on the viability of microorganisms. This work proposes a simple model to estimate the viability of microorganisms irradiated in solution with different concentrations of Fe³⁺ and constrains the lethal UVC dose in these conditions. In experimental assays, the median lethal dose of Saccharomyces boulardii increased consistently with the model's predictions, which thereby demonstrated the model's predictive validity. This ability was then used in a case study to simulate the viability of life in a Fe³⁺-containing lake on ancient Mars. Although the actual conditions of this kind of environment are not known, the simulations showed that lakes with small water columns that contain Fe³⁺ should have been able to protect growing microorganisms. This model enhances the ability to assess potentially habitable conditions on ancient Mars. Key Words: Photoprotection-UVC radiation-Fe³⁺ ions-Mars-Astrobiology. Astrobiology xx, xxx-xxx.

The potential discovery of life beyond Earth presents unique communication challenges for astrobiology. These include ambiguous data, public misconceptions, and the dynamics of social media platforms. Building on National Aeronautics and Space Administration's 2021 Standards of Evidence (SoE) workshop, a diverse group of experts-scientists, science journalists, content creators, and scholars-were convened during February and March of 2024 for the Communicating Discoveries in the Search for Life in the Universe workshop. This report summarizes structured discussions focused on how to responsibly share findings with different public audiences. Key themes that emerged from the workshop included the following: communicating uncertainty, reaching consensus, and building trust between the scientific community and the public. Such efforts will involve navigating the rapidly evolving landscapes of social media and academic (peer-reviewed) journal publishing. Workshop participants emphasized the need for proactive communication, early-career training in science communication, and interdisciplinary partnerships, all of which can foster sound public understandings of astrobiology research and its myriad of practices, mitigate misinformation, and sustain ongoing support for the search for life. In brief, this report includes the workshop rationale and structure, insights gleaned from past case studies and hypothetical future scenarios, common themes that emerged from the breakout groups, a discussion of the relationship of workshop outcomes to SoE, and guidance for individuals, agencies, and institutions. Key Words: Astrobiology-Science communication-Biosignature detection. Astrobiology 25, 743-758.

Hydrothermal systems are widespread in our solar system. Identification of alteration mineral assemblages on Mars and potentially in ocean worlds such as Enceladus suggests the existence of extensive hydrothermal fluid-igneous rock interactions of astrobiological interest in different planetary bodies. Here, we studied the terrestrial analog Cerro Caliente, a band of geothermal alterations located in the glaciovolcanic environment of Deception Island (Antarctica), with the aim of determining the mobility of major chemical elements (e.g., alkalis, phosphorus) and its implications in the habitability potential of such environments. We verified that the rock texture, particularly rich in volcanic glass, plays a major role in geochemical mobility, with permafrost delimiting the impact of hydrothermal activity by reducing the permeability of the lapilli tuff deposit. We studied the mineralogy and geochemistry of the alteration band by comparing borehole samples in different locations that represent different thermal regimes along the hydrothermal alteration band. The alteration products are characteristic of palagonitization processes, which favor the release of elements useful for life, such as phosphorus, although the basic alkalinity of the medium caused its precipitation in the form of tricalcium phosphate. In addition, lipid biomarker analyses were performed to assess the existence of possible potential ecological niches associated with these environments. On Mars, the circulation of low-temperature CO₂-rich hydrothermal fluids through glass-bearing volcanic rocks results in a loss of silica content and a secondary mineral assemblage composed of palagonite, phyllosilicates, and zeolites, which establishes Cerro Caliente as a valid Mars analog for understanding such environments. In addition, our results support the hypothesis of a hydrothermal origin of phosphorous for the formation of Enceladus' phosphates recently detected in the plumes. We also determined that a fraction of the calcium in Cerro Caliente was sequestered as carbonates of biogenic origin, which produced a distinctive Raman signal that, together with the lipid content, would make it a relevant potential biosignature if similar findings were made in the search for life in such low-temperature hydrothermal environments. Key Words: Hydrothermal systems-Palagonitization-Phosphates-Lipid biomarkers-Mars-Ocean worlds. Astrobiology 25, 777-792.