Astrobiology最新文献

{"title":"Prebiotic Nucleoside Phosphorylation in a Simulated Deep-Sea Supercritical Carbon Dioxide-Water Two-Phase Environment.","authors":"Shotaro Tagawa, Ryota Hatami, Kohei Morino, Shohei Terazawa, Caner Akıl, Kristin Johnson-Finn, Takazo Shibuya, Kosuke Fujishima","doi":"10.1089/ast.2024.0016","DOIUrl":"10.1089/ast.2024.0016","url":null,"abstract":"<p><p>Prebiotic synthesis of complex organic molecules in water-rich environments has been a long-standing challenge. In the modern deep sea, emission of liquid CO₂ has been observed in multiple locations, which indicates the existence of benthic CO₂ pools. Recently, a liquid/supercritical CO₂ (ScCO₂) hypothesis has been proposed that a two-phase ScCO₂-water environment could lead to efficient dehydration and condensation of organics. To confirm this hypothesis, we conducted a nucleoside phosphorylation reaction in a hydrothermal reactor creating ScCO₂-water two-phase environment. After 120 h of uridine, cytosine, guanosine, and adenosine phosphorylation at 68.9°C, various nucleoside monophosphates (NMPs), nucleotide diphosphates, and carbamoyl nucleosides were produced. The addition of urea enhanced the overall production of phosphorylated species with 5'-NMPs, the major products that reached over 10% yield. As predicted, phosphorylation did not proceed in the fully aqueous environment without ScCO₂. Further, a glass window reactor was introduced for direct observation of the two-phase environment, where the escape of water into the ScCO₂ phase was observed. These results are similar to those of a wet-dry cycle experiment simulating the terrestrial hot spring environment, indicating that the presence of ScCO₂ can create a comparatively dry condition in the deep sea. In addition, the high acidity present in the aqueous phase further supports nucleotide synthesis by enabling the release of orthophosphate from the hydroxyapatite mineral solving the phosphate problem. Thus, the present study highlights the potential of the unique ScCO₂-water two-phase environment to drive prebiotic nucleotide synthesis and likely induce condensation reactions of various organic and inorganic compounds in the deep-sea CO₂ pool on Earth and potentially other ocean worlds.</p>","PeriodicalId":8645,"journal":{"name":"Astrobiology","volume":" ","pages":"1151-1165"},"PeriodicalIF":3.5,"publicationDate":"2024-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142667024","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Self-Sustaining Living Habitats in Extraterrestrial Environments.","authors":"R Wordsworth, C Cockell","doi":"10.1089/ast.2024.0080","DOIUrl":"10.1089/ast.2024.0080","url":null,"abstract":"<p><p>Standard definitions of habitability assume that life requires the presence of planetary gravity wells to stabilize liquid water and regulate surface temperature. Here, the consequences of relaxing this assumption are evaluated. Temperature, pressure, volatile loss, radiation levels, and nutrient availability all appear to be surmountable obstacles to the survival of photosynthetic life in space or on celestial bodies with thin atmospheres. Biologically generated barriers capable of transmitting visible radiation, blocking ultraviolet, and sustaining temperature gradients of 25-100 K and pressure differences of 10 kPa against the vacuum of space can allow habitable conditions between 1 and 5 astronomical units in the solar system. Hence, ecosystems capable of generating conditions for their own survival are physically plausible, given the known capabilities of biological materials on Earth. Biogenic habitats for photosynthetic life in extraterrestrial environments would have major benefits for human life support and sustainability in space. Because the evolution of life elsewhere may have followed very different pathways from that on Earth, living habitats could also exist outside traditional habitable environments around other stars, where they would have unusual yet potentially detectable biosignatures.</p>","PeriodicalId":8645,"journal":{"name":"Astrobiology","volume":" ","pages":"1187-1195"},"PeriodicalIF":3.5,"publicationDate":"2024-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142715224","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Alunite in Cross Crater, Mars: Evidence for a Possible Site of Ancient Life.","authors":"Anthony J Ranalli, Gregg A Swayze","doi":"10.1089/ast.2024.0001","DOIUrl":"10.1089/ast.2024.0001","url":null,"abstract":"<p><p>Cross Crater is a 65-km impact crater located in the Noachian highlands of the Terra Sirenum region of Mars. Geochemical modeling has indicated that alunite detected on the southwest wall of Cross Crater could have been formed by a fumarole upwelling into Cross Crater Lake and could indicate that an environment favorable to the development of life may have existed several billion years ago. Alunite did not form when Noachian precipitation reacted with basalt nor when the sediments and groundwater resulting from this reaction were reacted with a fumarole. Only when Cross Crater Lake water was equilibrated with sulfuric acid, thought to be a major component of the atmosphere in the Hesperian, following reaction with fumarole groundwater, did alunite precipitate from solution. Kaolinite, silica, or an Al-smectite such as montmorillonite also formed. The proximity of Cross Crater to the Tharsis volcanic region relative to Columbus crater, where alunite has also been detected, may have resulted in larger amounts of magmatic water input to the lake from sources along fractures that extend westward from Tharsis. This could explain the more extensive deposit of alunite at Cross Crater relative to Columbus crater.</p>","PeriodicalId":8645,"journal":{"name":"Astrobiology","volume":" ","pages":"1096-1109"},"PeriodicalIF":3.5,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142493750","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Self-Shielding Enhanced Organics Synthesis in an Early Reduced Earth's Atmosphere.","authors":"Tatsuya Yoshida, Shungo Koyama, Yuki Nakamura, Naoki Terada, Kiyoshi Kuramoto","doi":"10.1089/ast.2024.0048","DOIUrl":"10.1089/ast.2024.0048","url":null,"abstract":"<p><p>Earth is expected to have acquired a reduced proto-atmosphere enriched in H₂ and CH₄ through the accretion of building blocks that contain metallic Fe and/or the gravitational trapping of surrounding nebula gas. Such an early, wet, reduced atmosphere that covers a proto-ocean would then ultimately evolve toward oxidized chemical compositions through photochemical processes that involve reactions with H₂O-derived oxidant radicals and the selective escape of hydrogen to space. During this time, atmospheric CH₄ could be photochemically reprocessed to generate not only C-bearing oxides but also organics. However, the branching ratio between organic matter formation and oxidation remains unknown despite its significance on the abiotic chemical evolution of early Earth. Here, we show via numerical analyses that UV absorptions by gaseous hydrocarbons such as C₂H₂ and C₃H₄ significantly suppress H₂O photolysis and subsequent CH₄ oxidation during the photochemical evolution of a wet proto-atmosphere enriched in H₂ and CH₄. As a result, nearly half of the initial CH₄ converted to heavier organics along with the deposition of prebiotically essential molecules such as HCN and H₂CO on the surface of a primordial ocean for a geological timescale order of 10-100 Myr. Our results suggest that the accumulation of organics and prebiotically important molecules in the proto-ocean could produce a soup enriched in various organics, which might have eventually led to the emergence of living organisms.</p>","PeriodicalId":8645,"journal":{"name":"Astrobiology","volume":" ","pages":"1074-1084"},"PeriodicalIF":3.5,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142456935","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Travel Times of a Descending Melting Probe on Europa.","authors":"Augusto Carballido","doi":"10.1089/ast.2024.0026","DOIUrl":"https://doi.org/10.1089/ast.2024.0026","url":null,"abstract":"<p><p>In this study, we calculated the travel times of a thermal probe that descends through Europa's ice shell. The ice column is simplified to a conductive layer. Using a cellular automaton model, the descent of the probe was simulated by tracking temperature changes, with cell interaction dictated by heat conduction and cell state transition rules determined by cell temperatures. Validation tests, including a soil column simulation, and comparison with experimental data, support the reliability of the model. Simulations were performed with 2 different cell sizes, 19 constant probe temperatures, and 5 ice thermal conductivities. A smaller cell size (<math><mrow><mtext>Δ</mtext><mi>z</mi><mo>=</mo><mn>3</mn><mo> </mo></mrow></math>mm) produced shorter travel times (between 22 days for a probe temperature <math><mrow><mrow><msub><mi>T</mi><mtext>p</mtext></msub></mrow><mo>=</mo><mn>600</mn><mi>K</mi></mrow></math> and ∼4 years for <math><mrow><mrow><msub><mi>T</mi><mtext>p</mtext></msub></mrow><mo>=</mo><mn>280</mn><mi>K</mi></mrow></math>) than a larger cell size (<math><mrow><mtext>Δ</mtext><mi>z</mi><mo>=</mo><mn>1</mn><mo> </mo></mrow></math>m), which produced travel times between 27 years (<math><mrow><mrow><msub><mi>T</mi><mtext>p</mtext></msub></mrow><mo>=</mo></mrow></math> 600K) and ∼10³ years (<math><mrow><mrow><msub><mi>T</mi><mtext>p</mtext></msub></mrow><mo>=</mo></mrow></math> 280K). The ice shell's thermal conductivity has a modest impact on descent times. The results are generally consistent with previous approaches that used more detailed probe engineering considerations. These results suggest that a probe relying solely on heat production may traverse Europa's conductive ice shell within a mission's timeframe.</p>","PeriodicalId":8645,"journal":{"name":"Astrobiology","volume":"24 11","pages":"1143-1149"},"PeriodicalIF":3.5,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142613894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Rapid Destruction of Lipid Biomarkers Under Simulated Cosmic Radiation.","authors":"Anaïs Roussel, Alexander A Pavlov, Jason P Dworkin, Sarah S Johnson","doi":"10.1089/ast.2024.0006","DOIUrl":"10.1089/ast.2024.0006","url":null,"abstract":"<p><p>Understanding how organics degrade under galactic cosmic rays (GCRs) is critical as we search for traces of ancient life on Mars. Even if the planet harbored life early in its history, its surface rocks have been exposed to ionizing radiation for about four billion years, potentially destroying the vast majority of biosignatures. In this study, we investigated for the first time the impact of simulated GCRs (using gamma rays) on several types of lipid biosignatures (including hopane C₃₀, sterane C₂₇, alkanes, and fatty acids [FAs]) in both the presence and absence of salts (NaCl, KCl, and MgCl₂). We measured that the lipids degraded 6-20 times faster than amino acids in similar conditions; moreover, when irradiated in the presence of a salt substrate, degradation was at least 4-6 times faster than without salt, which suggests that salty environments that are often preferred targets for astrobiology warrant caution. We detected radiolytic by-products only for FAs-in the form of alkanes and aldehydes. These results expand our understanding of the degradation of organic molecules in Mars analog environments and underscore the urgent need to direct rover missions to sampling sites protected from GCRs, for example, sites on Mars that have been recently exposed by a wind scarp retreat or meteoritic impact.</p>","PeriodicalId":8645,"journal":{"name":"Astrobiology","volume":" ","pages":"1063-1073"},"PeriodicalIF":3.5,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142456934","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Aeolian Biodispersal of Terrestrial Microorganisms on Mars Through Saltation Bombardment of Spacecraft.","authors":"Lori K Fenton, John R Marshall, Andrew C Schuerger, J Ken Smith, Karen L Kelley","doi":"10.1089/ast.2023.0125","DOIUrl":"10.1089/ast.2023.0125","url":null,"abstract":"<p><p>A major unknown in the field of planetary protection is the degree to which natural atmospheric processes remove terrestrial microorganisms from robotic and crewed spacecraft that could potentially contaminate Mars (i.e., forward contamination). We present experiments in which we measured the removal rate of <i>Bacillus subtilis</i> HA101 spores from aluminum surfaces under the bombardment of naturally rounded sand grains. To simulate grain impacts, we constructed a pneumatic sand-feed system and gun to accelerate grains to a desired speed, with independent control of impacting grain mass, flux, and angle. Spore counts of the resulting bombarded surfaces when using scanning electron microscopy indicate that although spores directly impacted by sand grains would likely be killed, those immediately adjacent to grain impacts might be released into the environment intact. The experiments demonstrate a linear relationship between the fractional dislodgement rate of spores and grain impact speed, which can be used to estimate input to microbial transport models (e.g., using numerical models of saltation). Even the slowest grain impacts (∼2.7 m/s) dislodged spores. Such slow events may be common and widespread on Mars, which suggests that microbial dislodgement by slow saltation near the surface is largely unavoidable.</p>","PeriodicalId":8645,"journal":{"name":"Astrobiology","volume":" ","pages":"1128-1142"},"PeriodicalIF":3.5,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142493749","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"A Machine-Learning Approach to Biosignature Exploration on Early Earth and Mars Using Sulfur Isotope and Trace Element Data in Pyrite.","authors":"Maria C Figueroa, Daniel D Gregory, Kenneth H Williford, David J Fike, Timothy W Lyons","doi":"10.1089/ast.2024.0019","DOIUrl":"10.1089/ast.2024.0019","url":null,"abstract":"<p><p>We propose a novel approach to identify the origin of pyrite grains and distinguish biologically influenced sedimentary pyrite using combined <i>in situ</i> sulfur isotope (δ³⁴S) and trace element (TE) analyses. To classify and predict the origin of individual pyrite grains, we applied multiple machine-learning algorithms to coupled δ³⁴S and TE data from pyrite grains formed from diverse sedimentary, hydrothermal, and metasomatic processes across geologic time. Our unsupervised classification algorithm, K-means++ cluster analysis, yielded six classes based on the formation environment of the pyrite: sedimentary, low temperature hydrothermal, medium temperature, polymetallic hydrothermal, high temperature, and large euhedral. We tested three supervised models (random forest [RF], Naïve Bayes, k-nearest neighbors), and RF outperformed the others in predicting pyrite formation type, achieving a precision (area under the ROC curve) of 0.979 ± 0.005 and an overall average class accuracy of 0.878 ± 0.005. Moreover, we found that coupling TE and δ³⁴S data significantly improved the performance of the RF model compared with using either TE or δ³⁴S data alone. Our data provide a novel framework for exploring sedimentary rocks that have undergone multiple hydrothermal, magmatic, and metamorphic alterations. Most significant, however, is the demonstrated potential for distinguishing between biogenic and abiotic pyrite in samples from early Earth. This approach could also be applied to the search for potential biosignatures in samples returned from Mars.</p>","PeriodicalId":8645,"journal":{"name":"Astrobiology","volume":" ","pages":"1110-1127"},"PeriodicalIF":3.5,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142493748","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Radiation-Driven Destruction of Thiophene and Methyl-Substituted Thiophenes.","authors":"Patrick D Tribbett, Yukiko Y Yarnall, Reggie L Hudson, Perry A Gerakines, Christopher K Materese","doi":"10.1089/ast.2024.0038","DOIUrl":"10.1089/ast.2024.0038","url":null,"abstract":"<p><p>Thiophene and two derivatives (2-methylthiophene and 3-methylthiophene) have been detected on the surface of Mars with the Sample Analysis at Mars instrument suite onboard NASA's Curiosity rover. Thiophene could serve as a secondary chemical biosignature since the secondary biosynthesis of thiophene is considered an important production pathway. However, it is critical to understand the abiotic formation and destruction of thiophene and its derivatives since these pathways could affect the molecules' stabilities on planetary surfaces over geological timescales. Here, we present the radiolytic destruction kinetics of thiophene, 2-methylthiophene, and 3-methylthiophene as single-component ices and when diluted in water ice at low temperatures. Using infrared spectroscopy, we determined the destruction rate constants and extrapolated our radiolytic half-lives to the surface of Mars, assuming the measured and modeled surface dose rates. We found that our rate constants strongly depend on temperature and presence of water ice. Based on our determined radiolytic half-life for thiophene under conditions most similar to those of thiophene groups in Martian macromolecules, we expect thiophene to be stable on the surface for significantly longer than the Martian surface exposure age of sites in Gale crater where thiophenes have been detected.</p>","PeriodicalId":8645,"journal":{"name":"Astrobiology","volume":" ","pages":"1085-1095"},"PeriodicalIF":3.5,"publicationDate":"2024-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142456933","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Preface to Eta-Earth Revisited: How Common Are Earth-like Habitats in the Galaxy?","authors":"Helmut Lammer, Manuel Scherf","doi":"10.1089/ast.2024.0116","DOIUrl":"10.1089/ast.2024.0116","url":null,"abstract":"","PeriodicalId":8645,"journal":{"name":"Astrobiology","volume":"24 10","pages":"893-896"},"PeriodicalIF":3.5,"publicationDate":"2024-10-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142557028","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}