Astrobiology最新文献

The alteration of martian deposits under extreme surface conditions remains a key challenge for their mineral-organic interpretation and paleoenvironmental reconstruction. This study investigates the spectral detection and alteration of mineral-organic signatures in Lake Salda hydromagnesite microbialites under martian sublimation and radiation (UV) conditions. Samples were analyzed using visible near-infrared and Fourier transform infrared (FTIR) spectroscopy, then sublimated via lyophilization and exposed to UV radiation in the Planetary Atmospheres and Surfaces Simulation Chamber. Sublimation reduced the intensity of water and carbonate vibrations and enhanced CH₂ ν₃ and PO₂^- ν₃ organic features; this demonstrated that interstitial water sublimation may reduce O-H spectral noise, improve organic visibility, and reveal volatile sublimation patterns for future Mars rovers, such as Rosalind Franklin. In a three-sol (74 h) simulation of martian UV radiation (200-400 nm) under 7 mbar of CO₂, FTIR spectral intensity was reduced, and organic CH₂ ν₃ and PO₂^- features were significantly degraded. These findings reveal spectral alterations under martian surface conditions and highlight organic biosignature vulnerability at equatorial latitudes, informing preservation protocols for future missions.

Return of Mars samples is a high priority in the planetary science community and has remained an enduring goal of planetary exploration programs. Development of sterilization techniques to prevent potential contamination of Earth's biosphere with unknown life-forms that could exist on planetary bodies requires the use of the most robust biological indicators. We argue that self-seeding proteinaceous particles (prions) represent the most robust biological agents found on Earth. To evaluate the impact of various sterilization techniques on prion activity, we used derivatives of yeast prion proteins Sup35 and Ure2, which are not harmful to humans. Our study demonstrated that effective antimicrobial modalities, which include prolonged dry heat (up to 200°C), vapor hydrogen peroxide, gamma irradiation (up to 100 kGy), and ambient air or wet He/water plasma (deposited energy density of up to 6.3 kJ/cm²), did not eliminate the biological activity of yeast prions. However, ultraviolet C (UVC) irradiation at a wavelength of 260-270 nm for 16-24 days eliminated Ure2 prion detection and biological activity, and prolonged UVC irradiation eliminated detection of Sup35 prions and reduced, although did not eliminate, their biological activity. These data suggest that UVC could be an essential component of in-flight sterilization techniques for all future planetary missions.

Ocean world plumes at Enceladus, Triton, and possibly Europa are astrobiologically significant. These active processes may transport fresh material from potentially habitable subsurface environments to the surface and atmosphere/exosphere, where they can be accessed by spacecraft and telescopic observations. However, it is currently unclear if chemical fractionation or other modification processes might occur during subsurface transport and eruption and potentially lead to changes in concentrations of habitability indicators relative to the source reservoir. To explore this phenomenon in a natural setting, we investigated the cold CO₂ geysers in Green River, Utah, which have eruptions driven by volatile exsolution. We collected samples from two geysers with different vent diameters and discharge volumes and compared the chemical composition of the erupted effluent and mineralogy of evaporite deposits with their respective pre-erupted waters; we also performed geochemical modeling to reconstruct the original chemical speciation of the source waters. Observed increases in electrical conductivity for both the erupted effluents may be due to an influx of warm fluids enriched in CO₂-charged brine entering the aquifer and initiating eruption via CO₂ exsolution and buoyant acceleration. Modeling results indicate source waters extremely rich in dissolved CO₂ with pH values significantly lower than those of erupted waters. The outgassing of CO₂ and significant levels of sulfate, Na/K ratio, and acidic pH suggest that the effluent from this geysering system may serve as a natural analog for putative plume deposits on Europa. The larger geyser (Crystal) had evaporites that were carbonate-rich, while the smaller geyser (Champagne) produced evaporites dominated by sulfate minerals. Furthermore, in a sample of erupted Champagne waters cooled rapidly in vacuum to replicate a frozen plume deposit, vitreous MgSO₄ was the primary constituent; this was not the main component in solution or identified in the evaporite or surrounding tufa. Overall, our observations suggest that geyser discharge volume, eruptive energy, and/or proximity to the host reservoir may all play a role in the composition of plume ejecta and surface deposits, and care should be taken in integrating both in situ and remote sensing observations to fully characterize plume deposits and make robust inferences of ocean composition. Key Words: Enceladus-Europa-Reflectance spectroscopy-Raman spectroscopy-Habitability indicator-Plume. Astrobiology xx, xxx-xxx.

The measured abundance (30-50 ppb) of long-chain (C₁₀-C₁₂) alkanes and their possible carboxylic acid precursors found in the ancient Cumberland mudstone in Gale Crater would have been substantially higher before the onset of exposure to ionizing radiation approximately 80 million years ago. Based on recent radiolysis experiments, we estimate conservatively that the Cumberland mudstone would have contained 120-7700 ppm of long-chain alkanes and/or fatty acids before ionizing radiation exposure. Such a high concentration of large organic molecules in martian sedimentary rocks cannot be readily explained by the accretion of organics from carbon-rich interplanetary dust particles and meteorites, nor by the deposition of hypothetical haze-derived organics from an ancient martian atmosphere. We discuss the feasibility of two additional mechanisms--one abiotic and one biological--that could have been capable of depositing this level of long-straight-chain organic molecules in the ancient martian mudstones: allochthonous transport of hydrothermally synthesized organics and autochthonous accumulation of organics from a hypothetical ancient Mars biosphere. To advance and test these and any additional working hypotheses put forth to explain such high concentrations of primary organics on Mars requires an understanding of the radiolytic degradation products expected for organics preserved in mineralogically comparable mudstones.

Exposure experiments that involve biological samples subjected to solar ultraviolet (UV) radiation (UVA, UVB, and UVC wavelengths) have advanced an understanding of biological responses in the harsh environment of space. These experiments provide insights about the role of such materials with regard to the origin and evolution of life and the development of protective strategies for long-term space habitation. A solar UV detector was developed to measure solar UV irradiance during exposure experiments as part of the Space Radiobiological Exposure Facility (SREF) on the China Space Station (CSS). This detector, which utilizes three SiC photodiodes, measures solar UV irradiance across three wavelength bands to determine UV doses received by exposed samples. Detector calibration is based on spectral solar irradiance data. From June 2023 to September 2024, the SREF completed three exposure missions that spanned a total duration of 465 days. Throughout these missions, the solar UV detector monitored the solar UV irradiance, which revealed periodic variations in the measured data that corresponded to changes in the solar beta angle and the CSS orbit. The cumulative radiation dose for the missions was 391 MJ m^-2 for UVA, 78.6 MJ m^-2 for UVB, and 30.1 MJ m^-2 for UVC.

Lacustrine sulfate- and carbonate-rich deposits have been detected at Jezero and Gale craters on Mars. The preservation of potential biosignatures in these sites may depend on the nature of precipitated salts and the early diagenetic history of in situ minerals. In this study, we explore a collection of Mars analog hypersaline depositional environments in British Columbia. Magnesium salts and other sulfate and carbonate salts precipitate from the variable water chemistry of Atlin Playa and a suite of lakes on the Cariboo Plateau. Authigenic and detrital grains were distinguished on the basis of their microscale morphology revealed by scanning electron microscopy. Authigenic minerals display distinct textures such as globular or prismatic clumps or delicately preserved cement that envelops angular, detrital grains. However, microscale authigenic textures become rare below the sediment-water interface due to early diagenetic dissolution and reprecipitation of salts during wet-dry cycles in the lakes. Such early diagenetic overprinting of salts could pose problems for identifying primary environments and any potential biosignatures they might have preserved in 3-4 billion-year-old rocks on Mars. The δ¹³C of organic matter and δ³⁴S of sulfate salts are reflective of source materials instead of diagenesis. Total organic carbon content is a function of the abundance of salt minerals, with a well-defined maximum in organic carbon content at an optimum salt content. Our findings demonstrate hypersaline lakes as key preservers of organic carbon and salts as a high-priority mineral target for finding organic carbon on Mars.

Lava tubes are recognized as strategic targets in the search for life on Mars. The Corona Lava Tube System in Lanzarote serves as a terrestrial analog for martian subsurface environments and an astronaut training site for the European Space Agency's (ESA) Planetary Analogue Geological and Astrobiological Exercise for Astronauts (PANGAEA) program. Here, we report the scientific outcomes of ESA's PANGAEA-X campaign, which combined in situ and laboratory-based analyses to investigate the biosignature potential of a black, sticky, organic-rich coating (CLT1), and white cotton-like mineral deposits (CLT3). The microbial diversity captured in real time using the MinION Nanopore device was validated and expanded through Illumina MiSeq and complementary laboratory techniques that included microscopy, mineralogy (X-ray powder diffraction, X-ray fluorescence), and organic geochemistry (gas chromatography/mass spectrometry, ¹³C NMR spectroscopy, thermogravimetry). Sample CLT1, enriched in organic matter derived from Euphorbia balsamifera milky juice fluid (latex) seepage, hosted halotolerant bacterial genera such as Salinisphaera and hydrocarbon-degrading Alcanivorax, supported by the presence of lipid biomarkers such as squalene, alkyl nitriles, and triterpenoids. CLT3, composed predominantly of gypsum with minor halite, exhibited scarce organic content but revealed acidophilic taxa such as Alicyclobacillus. This study demonstrates the effectiveness of integrating astronaut-led on-site DNA sequencing and geochemical fingerprinting, and traditional laboratory methods for astrobiological exploration. Our findings offer key insights into the microbial colonization, organic matter transformation, and biosignature preservation within lava tubes, with direct implications for future life detection missions on Mars and other planetary bodies. Key Words: Volcanic caves-Biosignatures-Organic matter-Geomicrobiology-Planetary exploration. Astrobiology 26, 30-47.

A closed-basin alkaline lake on the basaltic plateau of Tigray, Ethiopia, Lake Ashenge hosts living and fossil stromatolites composed primarily of magnesium-bearing calcite. In the present study, the morphogenetic and preservational processes that underlie stromatolite formation in such extreme environments were investigated, with implications for biosignature preservation. Using a combination of petrographic, spectroscopic, and microscopic techniques, we identified fossilized biomass, including microbial mat remnants, filamentous cyanobacteria, microfossil-like structures, and amorphous organic matter. Micritic and microsparitic Mg-calcite layers were found to preserve abundant sheaths, cyanobacterial filaments, and extracellular polymeric substances (EPS), which suggest a high fossilization potential. EPS-rich sheaths frequently contained stevensite (a Mg-silicate), which contributed to mold preservation. Subaqueous precipitation of Mg-calcite in the presence of organic biomass enhanced the entombment of microbial material and facilitated biosignature retention. Organic geochemical analyses revealed algaenan-like aliphatic structures associated with cyanobacterial cell walls, which are known for their resistance to degradation. These findings position Lake Ashenge as a relevant planetary field analog for ancient terrestrial and martian (habitable) lacustrine systems and advance our understanding of microbial fossilization pathways in alkaline settings. Since Mg-bearing phases, particularly Mg-calcite and stevensite, were found to be critical for biosignature preservation, such findings should guide sample collection and geological analyses on Mars, particularly in the framework of the Mars Sample Return mission.

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.