Pub Date : 2023-04-12DOI: 10.1017/s1473550423000095
Tymofii Sokolskyi, Shiladitya DasSarma
Abstract The origin of carbon fixation is a fundamental question in astrobiology. While the Calvin cycle is the most active on the modern Earth, the reductive tricarboxylic acid (TCA) cycle (rTCA) pathway for carbon fixation has been proposed to have played an important role in early evolution. In this study, we examined the evolution of key enzymes in the rTCA, which are rare in extant organisms, occurring in a few groups of Bacteria and Archaea. We investigated one of the least common reactions of this pathway, cleavage of citrate into oxaloacetate and acetyl-CoA, which can be performed by either a two-enzyme system (CCS/CCL) or a single enzyme (ACL) that is assumed to be the result of fusion of the two active sites into a single polypeptide. For broader context, we also studied functionally diverged homologues of these enzymes, succinyl-CoA synthetase (SCS) and citrate synthase. Our phylogenetic analysis of these enzymes in Bacteria and Archaea shows that SCS, a homologue of CCS from distant bacterial taxa capable of citrate cleavage, are monophyletic, suggesting linked horizontal gene transfers of SCS and citrate cleavage enzymes. We also found evidence of the horizontal transfer of SCS from a clade of anaerobic Archaea (Archaeoglobi, Methanomicrobia or Crenarchaeota) to an ancestor of Cyanobacteria/Melainabacteria clade – both of which share a succinate semialdehyde shunt in their oxidative TCA cycles. We identified new bacterial and archaeal taxa for which complete rTCA cycles are theoretically possible, including Syntrophobacter, Desulfofundulus, Beggiatoa, Caldithrix, Ca. Acidulodesulfobacterales and Ca. Micrarchaeota. Finally, we propose a mechanism for syntrophically-regulated fluxes through oxidative and rTCA reactions in microbial communities particularly Haloarchaea-Nanohaloarchaea symbiosis and its implications for carbon fixation during retinal-based phototrophy and the Purple Earth hypothesis. We discuss how the inclusion of an ecological perspective in the studies of evolution of ancient metabolic pathways may be beneficial to understanding the origin of life.
碳固定的起源是天体生物学中的一个基本问题。虽然卡尔文循环是现代地球上最活跃的循环，但碳固定的还原性三羧酸循环(rTCA)途径被认为在早期进化中发挥了重要作用。在这项研究中，我们研究了在现存生物中罕见的rTCA关键酶的进化，这些酶发生在一些细菌和古细菌群中。我们研究了该途径中最不常见的反应之一，柠檬酸盐裂解成草酰乙酸和乙酰辅酶a，该反应可以通过双酶系统(CCS/CCL)或单酶系统(ACL)进行，这被认为是两个活性位点融合成单个多肽的结果。在更广泛的背景下，我们还研究了这些酶的功能分化同源物，琥珀酰辅酶a合成酶(SCS)和柠檬酸合成酶。我们对细菌和古细菌中这些酶的系统发育分析表明，SCS是来自能够裂解柠檬酸盐的遥远细菌分类群的CCS的同源物，是单系的，这表明SCS和柠檬酸盐裂解酶存在水平基因转移的联系。我们还发现了从厌氧古细菌分支(archaeoa archaebi, Methanomicrobia或Crenarchaeota)向蓝藻/黑藻分支的祖先水平转移SCS的证据-两者在其氧化TCA循环中共享琥珀酸半醛分流。我们发现了新的细菌和古细菌分类群，包括Syntrophobacter, Desulfofundulus, Beggiatoa, Caldithrix, Ca. Acidulodesulfobacterales和Ca. microarchaeota，理论上可能完整的rTCA循环。最后，我们提出了微生物群落中氧化和rTCA反应对共养调节通量的机制，特别是盐古菌-纳米盐古菌共生，以及它对视网膜光养过程中碳固定的影响和紫色地球假说。我们讨论了在古代代谢途径的进化研究中纳入生态学观点如何有助于理解生命的起源。
{"title":"Role of horizontal gene transfers and microbial ecology in the evolution of fluxes through the tricarboxylic acid cycle","authors":"Tymofii Sokolskyi, Shiladitya DasSarma","doi":"10.1017/s1473550423000095","DOIUrl":"https://doi.org/10.1017/s1473550423000095","url":null,"abstract":"Abstract The origin of carbon fixation is a fundamental question in astrobiology. While the Calvin cycle is the most active on the modern Earth, the reductive tricarboxylic acid (TCA) cycle (rTCA) pathway for carbon fixation has been proposed to have played an important role in early evolution. In this study, we examined the evolution of key enzymes in the rTCA, which are rare in extant organisms, occurring in a few groups of Bacteria and Archaea. We investigated one of the least common reactions of this pathway, cleavage of citrate into oxaloacetate and acetyl-CoA, which can be performed by either a two-enzyme system (CCS/CCL) or a single enzyme (ACL) that is assumed to be the result of fusion of the two active sites into a single polypeptide. For broader context, we also studied functionally diverged homologues of these enzymes, succinyl-CoA synthetase (SCS) and citrate synthase. Our phylogenetic analysis of these enzymes in Bacteria and Archaea shows that SCS, a homologue of CCS from distant bacterial taxa capable of citrate cleavage, are monophyletic, suggesting linked horizontal gene transfers of SCS and citrate cleavage enzymes. We also found evidence of the horizontal transfer of SCS from a clade of anaerobic Archaea (Archaeoglobi, Methanomicrobia or Crenarchaeota) to an ancestor of Cyanobacteria/Melainabacteria clade – both of which share a succinate semialdehyde shunt in their oxidative TCA cycles. We identified new bacterial and archaeal taxa for which complete rTCA cycles are theoretically possible, including Syntrophobacter, Desulfofundulus, Beggiatoa, Caldithrix, Ca. Acidulodesulfobacterales and Ca. Micrarchaeota. Finally, we propose a mechanism for syntrophically-regulated fluxes through oxidative and rTCA reactions in microbial communities particularly Haloarchaea-Nanohaloarchaea symbiosis and its implications for carbon fixation during retinal-based phototrophy and the Purple Earth hypothesis. We discuss how the inclusion of an ecological perspective in the studies of evolution of ancient metabolic pathways may be beneficial to understanding the origin of life.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":null,"pages":null},"PeriodicalIF":0.0,"publicationDate":"2023-04-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"134950355","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}
Pub Date : 2023-03-14DOI: 10.1017/s1473550423000083
Fernando de Sousa Mello, A. Friaça
Planetary geodynamics may have an important influence over planetary habitability and the boundaries of the circumstellar habitable zone (CHZ) in space and time. To investigate this we use a minimal parameterized model of the co-evolution of the geosphere and atmosphere of Earth-like planets around F, G, K and M main sequence stars. We found the CHZ for the present Solar System located between 0.92 and 1.09 au for a 1.0 M $_{oplus }$ Earth-like planet, extendible to 1.36 au for a 4.0 M $_{oplus }$ planet. In the literature, the CHZ varies considerably in width and border location, but the outer edges tend to be more spread out than the inner edges, showing a higher difficulty in determining the outer edge. Planetary mass has a considerable effect on planetary geodynamics, with low-mass planets cooling down faster and being less capable of maintaining a rich carbon dioxide atmosphere for several billions of years. Age plays a particularly important role in the width of the CHZ as the CHZ contracts in both directions: from the inner edge (as stellar luminosity increases with time), and from the outer edge (as planetary heat flux and seafloor spreading rate decrease with time). This strongly affects long-lived habitability as the 5 Gyr continuous CHZ may be very narrow or even non-existent for low-mass planets (<0.5 M $_{oplus }$ ) and fast-evolving high-mass stars (>1.1 M $_{odot }$ ). Because of this, the mean age of habitable terrestrial planets in our Galaxy today may be younger than Earth's age. Our results suggest that the best targets for future surveys of biosphere signatures may be planets between 0.5 and 4.0 M $_{oplus }$ , in systems younger than the Solar System. These planets may present the widest and long-lived CHZ.
行星地球动力学可能对行星的可居住性和星周可居住带的时空边界产生重要影响。为了研究这一点，我们使用了F、G、K和M主序星周围类地行星地圈和大气共同演化的最小参数化模型。我们发现，对于1.0 M $_{oplus }$类地行星，当前太阳系的CHZ介于0.92和1.09 au之间，对于4.0 M $_{oplus }$类地行星，CHZ可扩展到1.36 au。在文献中，CHZ的宽度和边界位置变化很大，但外缘往往比内缘更分散，表明确定外缘的难度更高。行星质量对行星地球动力学有相当大的影响，低质量的行星冷却得更快，在几十亿年的时间里维持富含二氧化碳的大气层的能力也更弱。年龄对CHZ的宽度起着特别重要的作用，因为CHZ从两个方向收缩:从内缘(随着恒星光度随时间增加)和从外缘(随着行星热通量和海底扩散率随时间减少)。这强烈影响了长期的可居住性，因为对于低质量行星(1.1 M $_{odot }$)， 5 Gyr连续CHZ可能非常狭窄甚至不存在。正因为如此，我们银河系中适宜居住的类地行星的平均年龄可能比地球的年龄要小。我们的结果表明，未来生物圈特征调查的最佳目标可能是0.5到4.0 M $_{oplus }$之间的行星，在比太阳系年轻的系统中。这些行星可能呈现出最宽、寿命最长的CHZ。
{"title":"Planetary geodynamics and age constraints on circumstellar habitable zones around main sequence stars","authors":"Fernando de Sousa Mello, A. Friaça","doi":"10.1017/s1473550423000083","DOIUrl":"https://doi.org/10.1017/s1473550423000083","url":null,"abstract":"\u0000 Planetary geodynamics may have an important influence over planetary habitability and the boundaries of the circumstellar habitable zone (CHZ) in space and time. To investigate this we use a minimal parameterized model of the co-evolution of the geosphere and atmosphere of Earth-like planets around F, G, K and M main sequence stars. We found the CHZ for the present Solar System located between 0.92 and 1.09 au for a 1.0 M\u0000 \u0000 $_{oplus }$\u0000 \u0000 \u0000 Earth-like planet, extendible to 1.36 au for a 4.0 M\u0000 \u0000 $_{oplus }$\u0000 \u0000 \u0000 planet. In the literature, the CHZ varies considerably in width and border location, but the outer edges tend to be more spread out than the inner edges, showing a higher difficulty in determining the outer edge. Planetary mass has a considerable effect on planetary geodynamics, with low-mass planets cooling down faster and being less capable of maintaining a rich carbon dioxide atmosphere for several billions of years. Age plays a particularly important role in the width of the CHZ as the CHZ contracts in both directions: from the inner edge (as stellar luminosity increases with time), and from the outer edge (as planetary heat flux and seafloor spreading rate decrease with time). This strongly affects long-lived habitability as the 5 Gyr continuous CHZ may be very narrow or even non-existent for low-mass planets (<0.5 M\u0000 \u0000 $_{oplus }$\u0000 \u0000 \u0000 ) and fast-evolving high-mass stars (>1.1 M\u0000 \u0000 $_{odot }$\u0000 \u0000 \u0000 ). Because of this, the mean age of habitable terrestrial planets in our Galaxy today may be younger than Earth's age. Our results suggest that the best targets for future surveys of biosphere signatures may be planets between 0.5 and 4.0 M\u0000 \u0000 $_{oplus }$\u0000 \u0000 \u0000 , in systems younger than the Solar System. These planets may present the widest and long-lived CHZ.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-03-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46114235","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}
Pub Date : 2023-02-24DOI: 10.1017/s1473550423000034
K. Szocik, Rakhat Abylkasymova
In this paper, we offer an outline of a feminist approach to considering the issue of extraterrestrial intelligence (ETI). Dominant ways of discussing ETI, particularly first-contact scenarios and protocols, are characterized by what feminism terms male bias. As with other cultural texts and disciplines, ETI studies can also be enriched by a feminist perspective. In this paper, we propose two possible applications of a feminist approach to considering ETI, such as using feminist categories to analyse our discourse about ETI, as well as understanding ETI in terms of sex and gender. We also propose a vision of ETI as genderless.
{"title":"Feminism and gender in thinking about extraterrestrial intelligence","authors":"K. Szocik, Rakhat Abylkasymova","doi":"10.1017/s1473550423000034","DOIUrl":"https://doi.org/10.1017/s1473550423000034","url":null,"abstract":"\u0000 In this paper, we offer an outline of a feminist approach to considering the issue of extraterrestrial intelligence (ETI). Dominant ways of discussing ETI, particularly first-contact scenarios and protocols, are characterized by what feminism terms male bias. As with other cultural texts and disciplines, ETI studies can also be enriched by a feminist perspective. In this paper, we propose two possible applications of a feminist approach to considering ETI, such as using feminist categories to analyse our discourse about ETI, as well as understanding ETI in terms of sex and gender. We also propose a vision of ETI as genderless.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-02-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44230721","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}
Pub Date : 2023-02-20DOI: 10.1017/s1473550423000022
B. Haezeleer, S. Fox, H. Strasdeit
The search for signs of life is a major objective in the exploration of Mars. Of particular interest are chemical biosignatures such as biomolecules. However, molecular biosignatures are susceptible to extreme environmental conditions such as heat, ionising radiation and strong oxidants. Therefore, a knowledge of the stability of possible biosignature molecules under present and past conditions on Mars is important, as well as the nature of possible alteration products. In the light of the long volcanically active history of Mars, we have studied the thermal behaviour of selected biological compounds, namely, haemin (an iron porphyrin closely related to the haem prosthetic group), cytochrome c (a small protein) and lecithin (a mixture of phospholipids). Samples were exposed to temperatures up to 900°C under an inert atmosphere of nitrogen, either in neat form or in mineral matrices. The matrix materials used were sodium chloride, gypsum (CaSO4 ⋅ 2H2O), Ca-montmorillonite (STx-1b), the Martian regolith simulant JSC Mars-1A and some mixtures thereof. Key results are: (1) The onset of significant decomposition for haemin, cytochrome c and lecithin occurs around 240°C. At slightly higher temperatures the disappearance of all characteristic infrared spectral bands indicates complete decomposition and loss of the primary biosignatures. (2) Haemin stoichiometrically releases CO2 and HCl during the initial thermal decomposition phase, at the end of which the iron porphyrin core is still intact. High-temperature products of haemin include graphite, α-iron and cementite (Fe3C). (3) Neat lecithin forms long-chain polyphosphates at 500°C, whereas lecithin‒NaCl mixtures form diphosphate (pyrophosphate). As these anions are absent and rare, respectively, in minerals, they may potentially serve as secondary biosignatures. (4) Heating a mixture of NaCl and JSC Mars-1A at 800°C in the presence of lecithin produces the aluminosilicate mineral sodalite (Na8[AlSiO4]6Cl2), which however appears to be of limited use as a secondary biosignature.
{"title":"Heat-induced changes in molecular biosignatures and the influence of Mars-relevant minerals","authors":"B. Haezeleer, S. Fox, H. Strasdeit","doi":"10.1017/s1473550423000022","DOIUrl":"https://doi.org/10.1017/s1473550423000022","url":null,"abstract":"\u0000 The search for signs of life is a major objective in the exploration of Mars. Of particular interest are chemical biosignatures such as biomolecules. However, molecular biosignatures are susceptible to extreme environmental conditions such as heat, ionising radiation and strong oxidants. Therefore, a knowledge of the stability of possible biosignature molecules under present and past conditions on Mars is important, as well as the nature of possible alteration products. In the light of the long volcanically active history of Mars, we have studied the thermal behaviour of selected biological compounds, namely, haemin (an iron porphyrin closely related to the haem prosthetic group), cytochrome c (a small protein) and lecithin (a mixture of phospholipids). Samples were exposed to temperatures up to 900°C under an inert atmosphere of nitrogen, either in neat form or in mineral matrices. The matrix materials used were sodium chloride, gypsum (CaSO4 ⋅ 2H2O), Ca-montmorillonite (STx-1b), the Martian regolith simulant JSC Mars-1A and some mixtures thereof. Key results are: (1) The onset of significant decomposition for haemin, cytochrome c and lecithin occurs around 240°C. At slightly higher temperatures the disappearance of all characteristic infrared spectral bands indicates complete decomposition and loss of the primary biosignatures. (2) Haemin stoichiometrically releases CO2 and HCl during the initial thermal decomposition phase, at the end of which the iron porphyrin core is still intact. High-temperature products of haemin include graphite, α-iron and cementite (Fe3C). (3) Neat lecithin forms long-chain polyphosphates at 500°C, whereas lecithin‒NaCl mixtures form diphosphate (pyrophosphate). As these anions are absent and rare, respectively, in minerals, they may potentially serve as secondary biosignatures. (4) Heating a mixture of NaCl and JSC Mars-1A at 800°C in the presence of lecithin produces the aluminosilicate mineral sodalite (Na8[AlSiO4]6Cl2), which however appears to be of limited use as a secondary biosignature.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-02-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45004542","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}
Pub Date : 2023-02-09DOI: 10.1017/S1473550423000046
Giulia Roccetti, T. Grassi, B. Ercolano, K. Molaverdikhani, A. Crida, D. Braun, A. Chiavassa
Free-floating planets (FFPs) can result from dynamical scattering processes happening in the first few million years of a planetary system's life. Several models predict the possibility, for these isolated planetary-mass objects, to retain exomoons after their ejection. The tidal heating mechanism and the presence of an atmosphere with a relatively high optical thickness may support the formation and maintenance of oceans of liquid water on the surface of these satellites. In order to study the timescales over which liquid water can be maintained, we perform dynamical simulations of the ejection process and infer the resulting statistics of the population of surviving exomoons around FFPs. The subsequent tidal evolution of the moons’ orbital parameters is a pivotal step to determine when the orbits will circularize, with a consequential decay of the tidal heating. We find that close-in ( $a lesssim 25$ RJ) Earth-mass moons with carbon dioxide-dominated atmospheres could retain liquid water on their surfaces for long timescales, depending on the mass of the atmospheric envelope and the surface pressure assumed. Massive atmospheres are needed to trap the heat produced by tidal friction that makes these moons habitable. For Earth-like pressure conditions (p0 = 1 bar), satellites could sustain liquid water on their surfaces up to 52 Myr. For higher surface pressures (10 and 100 bar), moons could be habitable up to 276 Myr and 1.6 Gyr, respectively. Close-in satellites experience habitable conditions for long timescales, and during the ejection of the FFP remain bound with the escaping planet, being less affected by the close encounter.
{"title":"Presence of liquid water during the evolution of exomoons orbiting ejected free-floating planets","authors":"Giulia Roccetti, T. Grassi, B. Ercolano, K. Molaverdikhani, A. Crida, D. Braun, A. Chiavassa","doi":"10.1017/S1473550423000046","DOIUrl":"https://doi.org/10.1017/S1473550423000046","url":null,"abstract":"\u0000 Free-floating planets (FFPs) can result from dynamical scattering processes happening in the first few million years of a planetary system's life. Several models predict the possibility, for these isolated planetary-mass objects, to retain exomoons after their ejection. The tidal heating mechanism and the presence of an atmosphere with a relatively high optical thickness may support the formation and maintenance of oceans of liquid water on the surface of these satellites. In order to study the timescales over which liquid water can be maintained, we perform dynamical simulations of the ejection process and infer the resulting statistics of the population of surviving exomoons around FFPs. The subsequent tidal evolution of the moons’ orbital parameters is a pivotal step to determine when the orbits will circularize, with a consequential decay of the tidal heating. We find that close-in (\u0000 \u0000 $a lesssim 25$\u0000 \u0000 \u0000 RJ) Earth-mass moons with carbon dioxide-dominated atmospheres could retain liquid water on their surfaces for long timescales, depending on the mass of the atmospheric envelope and the surface pressure assumed. Massive atmospheres are needed to trap the heat produced by tidal friction that makes these moons habitable. For Earth-like pressure conditions (p0 = 1 bar), satellites could sustain liquid water on their surfaces up to 52 Myr. For higher surface pressures (10 and 100 bar), moons could be habitable up to 276 Myr and 1.6 Gyr, respectively. Close-in satellites experience habitable conditions for long timescales, and during the ejection of the FFP remain bound with the escaping planet, being less affected by the close encounter.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-02-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49104513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}
Pub Date : 2023-01-31DOI: 10.1017/s1473550422000453
J. Chela-Flores
One of the main objectives of astrobiology is to understand the distribution of life in the universe, for microbial life, as well as for the search of extra-terrestrial intelligence, both of which would force upon us new problems in philosophy, including ethics and theology. The question of astrobiology and the humanities being such a broad topic, in the present paper we have limited our discussion of the Frontiers of Astrobiology and the Humanities to the single topic: ‘Independence of science (astrobiology) from philosophy and theology’. We have argued along the lines of this narrower thesis, but restricting our theological discussion strictly to a Judeo-Christian perspective.
{"title":"Frontiers of astrobiology and the humanities","authors":"J. Chela-Flores","doi":"10.1017/s1473550422000453","DOIUrl":"https://doi.org/10.1017/s1473550422000453","url":null,"abstract":"\u0000 One of the main objectives of astrobiology is to understand the distribution of life in the universe, for microbial life, as well as for the search of extra-terrestrial intelligence, both of which would force upon us new problems in philosophy, including ethics and theology. The question of astrobiology and the humanities being such a broad topic, in the present paper we have limited our discussion of the Frontiers of Astrobiology and the Humanities to the single topic: ‘Independence of science (astrobiology) from philosophy and theology’. We have argued along the lines of this narrower thesis, but restricting our theological discussion strictly to a Judeo-Christian perspective.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-01-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44812329","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}
Pub Date : 2023-01-25DOI: 10.1017/s1473550423000010
B. Nascimento-Dias
The main idea is to present the general aspects of the origin, evolution and distribution of life in the Universe from a Philosophy of Science perspective. The methodology used to develop this paper was through the intersection of favourable and unfavourable arguments from practitioners of science in the field of modern Astrobiology. The results were quite interesting and the historical crossover between the different arguments provides a great perspective on the research programme for the search for extraterrestrial life. Finally, although there is in fact no evidence that extraterrestrial life exists, the search for extraterrestrial life should not be considered as mere speculation. In the end, there are increasing indications that something extraordinary may be about to be found, whether on Mars, Europa, Enceladus or on some exoplanet.
{"title":"A philosophical perspective about the origin, evolution and distribution of life in the Universe","authors":"B. Nascimento-Dias","doi":"10.1017/s1473550423000010","DOIUrl":"https://doi.org/10.1017/s1473550423000010","url":null,"abstract":"\u0000 The main idea is to present the general aspects of the origin, evolution and distribution of life in the Universe from a Philosophy of Science perspective. The methodology used to develop this paper was through the intersection of favourable and unfavourable arguments from practitioners of science in the field of modern Astrobiology. The results were quite interesting and the historical crossover between the different arguments provides a great perspective on the research programme for the search for extraterrestrial life. Finally, although there is in fact no evidence that extraterrestrial life exists, the search for extraterrestrial life should not be considered as mere speculation. In the end, there are increasing indications that something extraordinary may be about to be found, whether on Mars, Europa, Enceladus or on some exoplanet.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44013682","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}
Pub Date : 2023-01-09DOI: 10.1017/s1473550422000441
K. Miki
Bioaerosol particles in the stratosphere are topics of interest for aerobiological and astrobiological studies. Although various studies have succeeded in sampling bioaerosol particles in the stratosphere, limited research has been conducted to evaluate how and why these bioaerosol particles can lift up to as high as the stratospheric level. This study tested different driving forces acting on particles in the stratosphere in order to simulate the motion of particles with various bioaerosol characteristics. The findings show that small pollen-sized particles can scarcely levitate in the stratosphere, although spore-sized and dust particles attached to microorganisms such as bacteria or fungus might be able to do so.
{"title":"Particle motion determines the types of bioaerosol particles in the stratosphere","authors":"K. Miki","doi":"10.1017/s1473550422000441","DOIUrl":"https://doi.org/10.1017/s1473550422000441","url":null,"abstract":"\u0000 Bioaerosol particles in the stratosphere are topics of interest for aerobiological and astrobiological studies. Although various studies have succeeded in sampling bioaerosol particles in the stratosphere, limited research has been conducted to evaluate how and why these bioaerosol particles can lift up to as high as the stratospheric level. This study tested different driving forces acting on particles in the stratosphere in order to simulate the motion of particles with various bioaerosol characteristics. The findings show that small pollen-sized particles can scarcely levitate in the stratosphere, although spore-sized and dust particles attached to microorganisms such as bacteria or fungus might be able to do so.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2023-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41497048","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}
Pub Date : 2022-12-15DOI: 10.1017/s147355042200043x
M. Ćirković
In a recent refreshing paper, Cowie (2022, The Philosophical Quarterly) analyses the hypothesis of artificial origin of the mysterious interstellar object 1I/2017 U1 ʻOumuamua, as well as the wider question of justification of the artefactual origin explanation for anomalous astronomical phenomena. This highly commendable philosophical project should be further developed in order to establish more general methodology for dealing with traces and manifestations of extraterrestrial intentional actors. In the present note, I demonstrate a couple of weaknesses of the standard account, mainly dealing with philosophy of technology, and suggest ways of improving upon it.
在最近的一篇令人耳目一新的论文中，Cowie (2022, The Philosophical Quarterly)分析了神秘星际物体1I/2017 U1 Oumuamua的人工起源假设，以及对异常天文现象的人工起源解释的更广泛的证明问题。应该进一步发展这一值得高度赞扬的哲学项目，以便建立更普遍的方法来处理外星有意行为者的痕迹和表现。在本文中，我展示了标准描述的几个弱点，主要涉及技术哲学，并提出了改进它的方法。
{"title":"Alien technology, conjunction and ergodicity","authors":"M. Ćirković","doi":"10.1017/s147355042200043x","DOIUrl":"https://doi.org/10.1017/s147355042200043x","url":null,"abstract":"\u0000 In a recent refreshing paper, Cowie (2022, The Philosophical Quarterly) analyses the hypothesis of artificial origin of the mysterious interstellar object 1I/2017 U1 ʻOumuamua, as well as the wider question of justification of the artefactual origin explanation for anomalous astronomical phenomena. This highly commendable philosophical project should be further developed in order to establish more general methodology for dealing with traces and manifestations of extraterrestrial intentional actors. In the present note, I demonstrate a couple of weaknesses of the standard account, mainly dealing with philosophy of technology, and suggest ways of improving upon it.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2022-12-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42893840","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}
Pub Date : 2022-12-06DOI: 10.1017/s1473550422000428
Graeme H. Smith
If a space-faring civilization embarks on a program to send probes to interstellar destinations, the first probe to arrive at such a destination is not likely to be one of the earliest probes, but one of much more advanced capability. This conclusion is based on a scenario in which an extraterrestrial civilization (ETC) embarks upon an interstellar program during which it launches increasingly sophisticated probes whose departure speed increases as a function of time throughout the program. Two back-of-the-envelope models are considered: one in which the launch velocity of an outgoing vehicle increases linearly with the time of launch, and a second in which the increase is exponential with launch date. In this paper consideration is directed to an hypothesized probe arriving within the Solar System from a non-terrestrial civilization. Within the above scenarios, a first-encounter probe will be one that was launched well after the initiation of an interstellar program by an ETC. Consequently, such a probe would be the product of a relatively advanced phase of that ETC's technology. The more distant the site from which an ETC is launching probes, the greater will be the technology gap between a first-encounter probe and terrestrial technology. One possible ramification may pertain to interpreting the nature of Unidentified Aerial Phenomena (UAP). Are flight characteristics of any UAP singular enough as to be consistent with an origin from a distant ETC?
{"title":"On the first probe to transit between two interstellar civilizations","authors":"Graeme H. Smith","doi":"10.1017/s1473550422000428","DOIUrl":"https://doi.org/10.1017/s1473550422000428","url":null,"abstract":"\u0000 If a space-faring civilization embarks on a program to send probes to interstellar destinations, the first probe to arrive at such a destination is not likely to be one of the earliest probes, but one of much more advanced capability. This conclusion is based on a scenario in which an extraterrestrial civilization (ETC) embarks upon an interstellar program during which it launches increasingly sophisticated probes whose departure speed increases as a function of time throughout the program. Two back-of-the-envelope models are considered: one in which the launch velocity of an outgoing vehicle increases linearly with the time of launch, and a second in which the increase is exponential with launch date. In this paper consideration is directed to an hypothesized probe arriving within the Solar System from a non-terrestrial civilization. Within the above scenarios, a first-encounter probe will be one that was launched well after the initiation of an interstellar program by an ETC. Consequently, such a probe would be the product of a relatively advanced phase of that ETC's technology. The more distant the site from which an ETC is launching probes, the greater will be the technology gap between a first-encounter probe and terrestrial technology. One possible ramification may pertain to interpreting the nature of Unidentified Aerial Phenomena (UAP). Are flight characteristics of any UAP singular enough as to be consistent with an origin from a distant ETC?","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":null,"pages":null},"PeriodicalIF":1.7,"publicationDate":"2022-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45900010","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}
京公网安备 11010802042870号
京ICP备2023020795号-1
扫码关注我们
求助内容：
应助结果提醒方式：