Pub Date : 2023-09-07DOI: 10.1017/s1473550423000198
Sergio Mosquera, Mack Ivey, Vincent F. Chevrier
Discoveries of transient liquid water in the Martian polar caps and the presence of liquid lakes and subsurface oceans in icy satellites have increased the interest of scientists in the capabilities of terrestrial extremophiles to grow and remain metabolically active in these extreme environments. The principal goal of this research is to understand the metabolic capacity of the anaerobic psychrophile, Desulfotalea psychrophila, cultured at subfreezing temperatures in media containing various concentrations of sulphate minerals. In this regard, our experiments focused on the detection of D. psychrophila survival and active metabolism, employing a biochamber that can recreate Martian temperatures. Using standard bacteriological methods for determining growth, combined with molecular and enzymatic determination of sulphate reduction, we have found that D. psychrophila is capable to carry out biological processes at temperatures down to −5°C, at concentrations that range from 0.35 to 18 wt% of MgSO4, 0.1 wt% of CaSO4 and 10 to 14 wt% of FeSO4 in which the highest sulphate concentration gradually returned the biosynthetic rate to basal limits, and the lowest temperature decreased bacterial cell division. These chemical salts, whose ions are classified as chaotropes, are known to act by maintaining water molecules in liquid state at subfreezing temperatures and by altering the stability of cellular components. This ‘chaotropic effect’ could potentially benefit the microbial metabolic activity up to a concentration in which cellular viability is jeopardized. Consequently, our hypothesis is directed towards the detection of metabolic activity as an indirect measurement of the potential influence of these ions in the flexibility/functionality of biological structures that at cold temperatures are highly rigid, compact and partially/non-functional due to water freezing. Studies of this type of microorganism are critical considering the possibility of survival and colonization of psychrophilic sulphate reducers in other planets and icy satellites.
{"title":"Detection of dsrAB operon expression in Desulfotalea psychrophila cells subjected to simulated Martian conditions of temperature and regolith's sulphate minerals composition","authors":"Sergio Mosquera, Mack Ivey, Vincent F. Chevrier","doi":"10.1017/s1473550423000198","DOIUrl":"https://doi.org/10.1017/s1473550423000198","url":null,"abstract":"\u0000 Discoveries of transient liquid water in the Martian polar caps and the presence of liquid lakes and subsurface oceans in icy satellites have increased the interest of scientists in the capabilities of terrestrial extremophiles to grow and remain metabolically active in these extreme environments. The principal goal of this research is to understand the metabolic capacity of the anaerobic psychrophile, Desulfotalea psychrophila, cultured at subfreezing temperatures in media containing various concentrations of sulphate minerals. In this regard, our experiments focused on the detection of D. psychrophila survival and active metabolism, employing a biochamber that can recreate Martian temperatures. Using standard bacteriological methods for determining growth, combined with molecular and enzymatic determination of sulphate reduction, we have found that D. psychrophila is capable to carry out biological processes at temperatures down to −5°C, at concentrations that range from 0.35 to 18 wt% of MgSO4, 0.1 wt% of CaSO4 and 10 to 14 wt% of FeSO4 in which the highest sulphate concentration gradually returned the biosynthetic rate to basal limits, and the lowest temperature decreased bacterial cell division. These chemical salts, whose ions are classified as chaotropes, are known to act by maintaining water molecules in liquid state at subfreezing temperatures and by altering the stability of cellular components. This ‘chaotropic effect’ could potentially benefit the microbial metabolic activity up to a concentration in which cellular viability is jeopardized. Consequently, our hypothesis is directed towards the detection of metabolic activity as an indirect measurement of the potential influence of these ions in the flexibility/functionality of biological structures that at cold temperatures are highly rigid, compact and partially/non-functional due to water freezing. Studies of this type of microorganism are critical considering the possibility of survival and colonization of psychrophilic sulphate reducers in other planets and icy satellites.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":" ","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-09-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45467334","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 : 2023-08-07DOI: 10.1017/s1473550423000162
Octavio A. Chon-Torres, J. Chela-Flores
We discuss in the context of astrobiology three aspects of the possible evolution of humanity. In addition, from astrobioethics -the study of the moral implications in astrobiology- we ask whether it is necessary to develop new concepts. Thus, it is concluded that we have already started our transition towards an interplanetary humanity; that our actions in the face of the discovery of extraterrestrial life will depend on the context in which we find ourselves; and that it is important to develop new and updated concepts for the scenarios to be faced by the eventual evolution of humanity in space.
{"title":"Astrobioethical reflections on humanity and its consideration as multi- and interplanetary","authors":"Octavio A. Chon-Torres, J. Chela-Flores","doi":"10.1017/s1473550423000162","DOIUrl":"https://doi.org/10.1017/s1473550423000162","url":null,"abstract":"\u0000 We discuss in the context of astrobiology three aspects of the possible evolution of humanity. In addition, from astrobioethics -the study of the moral implications in astrobiology- we ask whether it is necessary to develop new concepts. Thus, it is concluded that we have already started our transition towards an interplanetary humanity; that our actions in the face of the discovery of extraterrestrial life will depend on the context in which we find ourselves; and that it is important to develop new and updated concepts for the scenarios to be faced by the eventual evolution of humanity in space.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":" ","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-08-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43952626","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 : 2023-08-03DOI: 10.1017/s1473550423000174
C. Graney
This paper provides an overview of recent historical research regarding scientifically-informed challenges to the idea that the stars are other suns orbited by other inhabited earths – an idea that came to be known as ‘the Plurality of Worlds’. Johannes Kepler in the 17th century, Jacques Cassini in the 18th and William Whewell in the 19th each argued against ‘pluralism’ based on what in their respective times was solid science. Nevertheless, pluralism remained popular despite these and other scientific challenges. This history will be of interest to the astronomical community so that it is better positioned to avoid difficulties should the historical trajectory of pluralism continue, especially as it persists in the popular imagination.
{"title":"The challenging history of other Earths","authors":"C. Graney","doi":"10.1017/s1473550423000174","DOIUrl":"https://doi.org/10.1017/s1473550423000174","url":null,"abstract":"\u0000 This paper provides an overview of recent historical research regarding scientifically-informed challenges to the idea that the stars are other suns orbited by other inhabited earths – an idea that came to be known as ‘the Plurality of Worlds’. Johannes Kepler in the 17th century, Jacques Cassini in the 18th and William Whewell in the 19th each argued against ‘pluralism’ based on what in their respective times was solid science. Nevertheless, pluralism remained popular despite these and other scientific challenges. This history will be of interest to the astronomical community so that it is better positioned to avoid difficulties should the historical trajectory of pluralism continue, especially as it persists in the popular imagination.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":" ","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-08-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47240119","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 : 2023-07-13DOI: 10.1017/s1473550423000150
B. Fields, Sohom Gupta, M. Sandora
We propose the mathematical notion of information gain as a way of quantitatively assessing the value of biosignature missions. This makes it simple to determine how mission value depends on design parameters, prior knowledge and input assumptions. We demonstrate the utility of this framework by applying it to a plethora of case examples: the minimal number of samples needed to determine a trend in the occurrence rate of a signal as a function of an environmental variable, and how much cost should be allocated to each class of object; the relative impact of false positives and false negatives, with applications to Enceladus data and how best to combine two signals; the optimum tradeoff between resolution and coverage in the search for lurkers or other spatially restricted signals, with application to our current state of knowledge for solar system bodies; the best way to deduce a habitability boundary; the optimal amount of money to spend on different mission aspects; when to include an additional instrument on a mission; the optimal mission lifetime; and when to follow/challenge the predictions of a habitability model. In each case, we generate concrete, quantitative recommendations for optimizing mission design, mission selection and/or target selection.
{"title":"Information gain as a tool for assessing biosignature missions","authors":"B. Fields, Sohom Gupta, M. Sandora","doi":"10.1017/s1473550423000150","DOIUrl":"https://doi.org/10.1017/s1473550423000150","url":null,"abstract":"\u0000 We propose the mathematical notion of information gain as a way of quantitatively assessing the value of biosignature missions. This makes it simple to determine how mission value depends on design parameters, prior knowledge and input assumptions. We demonstrate the utility of this framework by applying it to a plethora of case examples: the minimal number of samples needed to determine a trend in the occurrence rate of a signal as a function of an environmental variable, and how much cost should be allocated to each class of object; the relative impact of false positives and false negatives, with applications to Enceladus data and how best to combine two signals; the optimum tradeoff between resolution and coverage in the search for lurkers or other spatially restricted signals, with application to our current state of knowledge for solar system bodies; the best way to deduce a habitability boundary; the optimal amount of money to spend on different mission aspects; when to include an additional instrument on a mission; the optimal mission lifetime; and when to follow/challenge the predictions of a habitability model. In each case, we generate concrete, quantitative recommendations for optimizing mission design, mission selection and/or target selection.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":" ","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-07-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"48149329","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 : 2023-07-06DOI: 10.1017/s1473550423000125
Matthew J. Roche, M. Fox‐Powell, R. Hamp, J. Byrne
Recent studies postulated the viability of a suite of metabolic pathways in Enceladus’ ocean motivated by the detection of H2 and CO2 in the plumes – evidence for available free energy for methanogenesis driven by hydrothermal activity at the moon's seafloor. However, these have not yet been explored in detail. Here, a range of experiments were performed to investigate whether microbial iron reduction could be a viable metabolic pathway in the ocean by iron-reducing bacteria such as Geobacter sulfurreducens. This study has three main outcomes: (i) the successful reduction of a number of crystalline Fe(III)-bearing minerals predicted to be present at Enceladus was shown to take place to differing extents using acetate as an electron donor; (ii) substantial bacterial growth in a simulated Enceladus ocean medium was demonstrated using acetate and H2(g) separately as electron donors; (iii) microbial iron reduction of ferrihydrite was shown to partially occur at pH 9, the currently accepted value for Enceladus’ ocean, whilst being severely hindered at the ambient ocean temperature of 0°. This study proposes the possibilities for biogeochemical iron cycling in Enceladus’ ocean, suggesting that a strain of iron-reducing bacteria can effectively function under Enceladus-like conditions.
{"title":"Iron reduction as a viable metabolic pathway in Enceladus’ ocean","authors":"Matthew J. Roche, M. Fox‐Powell, R. Hamp, J. Byrne","doi":"10.1017/s1473550423000125","DOIUrl":"https://doi.org/10.1017/s1473550423000125","url":null,"abstract":"\u0000 Recent studies postulated the viability of a suite of metabolic pathways in Enceladus’ ocean motivated by the detection of H2 and CO2 in the plumes – evidence for available free energy for methanogenesis driven by hydrothermal activity at the moon's seafloor. However, these have not yet been explored in detail. Here, a range of experiments were performed to investigate whether microbial iron reduction could be a viable metabolic pathway in the ocean by iron-reducing bacteria such as Geobacter sulfurreducens. This study has three main outcomes: (i) the successful reduction of a number of crystalline Fe(III)-bearing minerals predicted to be present at Enceladus was shown to take place to differing extents using acetate as an electron donor; (ii) substantial bacterial growth in a simulated Enceladus ocean medium was demonstrated using acetate and H2(g) separately as electron donors; (iii) microbial iron reduction of ferrihydrite was shown to partially occur at pH 9, the currently accepted value for Enceladus’ ocean, whilst being severely hindered at the ambient ocean temperature of 0°. This study proposes the possibilities for biogeochemical iron cycling in Enceladus’ ocean, suggesting that a strain of iron-reducing bacteria can effectively function under Enceladus-like conditions.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":" ","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-07-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44764096","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 : 2023-07-03DOI: 10.1017/s1473550423000149
Zachary S. Dean, Kristina Stott, W. Schubert, E. Seto, S. Chandrapati
Planetary Protection (PP) is the practice of safeguarding solar system bodies from terrestrial biological contamination and screening the Earth against potentially harmful extraterrestrial biological contamination. On Earth, cleanrooms and spacecraft surfaces are assayed using swabs and wipes that are then heat shocked for 15 min at 80°C to select for spores. The samples are further processed using the pour-plate method and Petri plates (TSA plates), with trypticase soy agar (TSA) serving as the growth medium. This sampling and processing procedure, called the NASA Standard Assay (NSA), is used by PP engineers around the world. Recent years have seen an increase in the incorporation of state-of-the-art technology, such as membrane filtration, into the NSA, with a push for implementing environmentally friendly technology into day-to-day activities. Dehydrated thin film media, such as Petrifilm Rapid Aerobic Count (RAC) plates, suit these goals as an alternative method to TSA plates. RAC plates show bacterial growth (and distinguish colonies from foreign particles such as bubbles) faster than TSA plates due to the incorporation of chromogenic colour indicators in the media. RAC plates also possess a much smaller environmental footprint than TSA plates, and are designed to evaluate even some of the challenging-to-detect environmental organisms, including spreaders that fill over 25% of the plate area in only a few hours. With these benefits in mind the PP Group at the NASA Jet Propulsion Laboratory took on the task of comparing RAC plates directly to TSA plates within the context of the NSA. Not only were the RAC plates able to detect surface environmental samples and in vitro spiked samples equivalent to NSA-processed TSA plates, but spreader organisms were countable on RAC plates at culture densities 10- to 100-fold greater than on TSA plates. In addition, RAC plates showed a robust, linear detection capability when challenged with membrane filter incorporation and organisms were easily acquired from RAC plates for archiving or post-processing experiments including MALDI-TOF bacterial identification. With their ease of use, small footprint, and both rapid and accurate bioburden measurements, RAC plates have the potential to overcome limitations posed by current PP culturing protocols.
{"title":"Dehydrated thin film media to rapidly estimate bioburden for planetary protection flight implementation","authors":"Zachary S. Dean, Kristina Stott, W. Schubert, E. Seto, S. Chandrapati","doi":"10.1017/s1473550423000149","DOIUrl":"https://doi.org/10.1017/s1473550423000149","url":null,"abstract":"Planetary Protection (PP) is the practice of safeguarding solar system bodies from terrestrial biological contamination and screening the Earth against potentially harmful extraterrestrial biological contamination. On Earth, cleanrooms and spacecraft surfaces are assayed using swabs and wipes that are then heat shocked for 15 min at 80°C to select for spores. The samples are further processed using the pour-plate method and Petri plates (TSA plates), with trypticase soy agar (TSA) serving as the growth medium. This sampling and processing procedure, called the NASA Standard Assay (NSA), is used by PP engineers around the world. Recent years have seen an increase in the incorporation of state-of-the-art technology, such as membrane filtration, into the NSA, with a push for implementing environmentally friendly technology into day-to-day activities. Dehydrated thin film media, such as Petrifilm Rapid Aerobic Count (RAC) plates, suit these goals as an alternative method to TSA plates. RAC plates show bacterial growth (and distinguish colonies from foreign particles such as bubbles) faster than TSA plates due to the incorporation of chromogenic colour indicators in the media. RAC plates also possess a much smaller environmental footprint than TSA plates, and are designed to evaluate even some of the challenging-to-detect environmental organisms, including spreaders that fill over 25% of the plate area in only a few hours. With these benefits in mind the PP Group at the NASA Jet Propulsion Laboratory took on the task of comparing RAC plates directly to TSA plates within the context of the NSA. Not only were the RAC plates able to detect surface environmental samples and in vitro spiked samples equivalent to NSA-processed TSA plates, but spreader organisms were countable on RAC plates at culture densities 10- to 100-fold greater than on TSA plates. In addition, RAC plates showed a robust, linear detection capability when challenged with membrane filter incorporation and organisms were easily acquired from RAC plates for archiving or post-processing experiments including MALDI-TOF bacterial identification. With their ease of use, small footprint, and both rapid and accurate bioburden measurements, RAC plates have the potential to overcome limitations posed by current PP culturing protocols.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":"12 3","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41268924","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 : 2023-06-26DOI: 10.1017/s1473550423000137
Ried Mackay
At the 2022 meeting of the American Society for Bioethics and Medical Humanities, a new affinity group was formed: astrobioethics. This is the branch of bioethics for space exploration, extraterrestrial environments and possible extraterrestrial organisms. Bioethics has traditionally operated from Western/Global North dominated thought structures and it is difficult to introduce alternative frameworks. However, astrobioethics is forming and is primed to include alternative frameworks, such as pre-Columbian Indigenous American philosophy/ethics and Global South frameworks and knowledge. The methods utilized include Indigenous research methodologies and standpoint, an overview of Indigenous American philosophy/ethics, and reflection on how this may impact astrobioethical considerations of space exploration. Indigenous philosophies and ethics consider space exploration and its associated risks and impacts on potential extraterrestrial lifeforms, systems and environments. The nuances of using terms like ‘colonization’ are considered and the paper concludes by considering how Méxica philosophical concepts and the four main Indigenous pragmatic dimensions can interact with established bioethical principles to guide future space exploration.
{"title":"Houston, we have a problem…or do we? The trajectory of astrobioethics and Indigenous thought","authors":"Ried Mackay","doi":"10.1017/s1473550423000137","DOIUrl":"https://doi.org/10.1017/s1473550423000137","url":null,"abstract":"\u0000 \u0000 \u0000 At the 2022 meeting of the American Society for Bioethics and Medical Humanities, a new affinity group was formed: astrobioethics. This is the branch of bioethics for space exploration, extraterrestrial environments and possible extraterrestrial organisms. Bioethics has traditionally operated from Western/Global North dominated thought structures and it is difficult to introduce alternative frameworks. However, astrobioethics is forming and is primed to include alternative frameworks, such as pre-Columbian Indigenous American philosophy/ethics and Global South frameworks and knowledge.\u0000 \u0000 \u0000 \u0000 The methods utilized include Indigenous research methodologies and standpoint, an overview of Indigenous American philosophy/ethics, and reflection on how this may impact astrobioethical considerations of space exploration.\u0000 \u0000 \u0000 \u0000 Indigenous philosophies and ethics consider space exploration and its associated risks and impacts on potential extraterrestrial lifeforms, systems and environments. The nuances of using terms like ‘colonization’ are considered and the paper concludes by considering how Méxica philosophical concepts and the four main Indigenous pragmatic dimensions can interact with established bioethical principles to guide future space exploration.\u0000","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":" ","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-06-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43844383","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 : 2023-06-14DOI: 10.1017/s1473550423000113
E. Mieli, A. Valli, C. Maccone
The authors use the mathematical tool of Maccone's lognormal distribution to further factor the Drake equation, which calculates the number of advanced civilizations in the galaxy, from the seven original levels of the Drake equation to 49 levels of overall analysis. The Maccone approach, in fact, supported by the central limit theorem, becomes more reliable the more levels are introduced. The resulting study necessarily draws upon an array of disciplines ranging from astronomy, chemistry and geology to biology, palaeontology and futurology. The final result calculates the number of planetary systems suitable for life in its various stages of development: those which have probably hosted life in the past and those which still host it at its various evolutionary levels. The final evolutionary level is the so-called galactic civilization (often called ETC, or extraterrestrial civilizations). The number of resulting galactic civilizations is divided between static civilizations, which do not move around the galaxy and whose Kardašëv rating is still low (<1.4), of which we find three examples (we ourselves plus, perhaps, two others), and potentially dynamic civilizations, which move around the galaxy and have a sufficiently high Kardašëv rating (≥1.4), of which we find 2000.
{"title":"Astrobiology: resolution of the statistical Drake equation by Maccone's lognormal method in 50 steps","authors":"E. Mieli, A. Valli, C. Maccone","doi":"10.1017/s1473550423000113","DOIUrl":"https://doi.org/10.1017/s1473550423000113","url":null,"abstract":"The authors use the mathematical tool of Maccone's lognormal distribution to further factor the Drake equation, which calculates the number of advanced civilizations in the galaxy, from the seven original levels of the Drake equation to 49 levels of overall analysis. The Maccone approach, in fact, supported by the central limit theorem, becomes more reliable the more levels are introduced. The resulting study necessarily draws upon an array of disciplines ranging from astronomy, chemistry and geology to biology, palaeontology and futurology. The final result calculates the number of planetary systems suitable for life in its various stages of development: those which have probably hosted life in the past and those which still host it at its various evolutionary levels. The final evolutionary level is the so-called galactic civilization (often called ETC, or extraterrestrial civilizations). The number of resulting galactic civilizations is divided between static civilizations, which do not move around the galaxy and whose Kardašëv rating is still low (<1.4), of which we find three examples (we ourselves plus, perhaps, two others), and potentially dynamic civilizations, which move around the galaxy and have a sufficiently high Kardašëv rating (≥1.4), of which we find 2000.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":" ","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-06-14","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49038543","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 : 2023-06-01DOI: 10.1017/s1473550423000101
S. Friederich, S. Wenmackers
Recent astrophysical findings suggest that the era during which the Universe is habitable has just begun. This raises the question whether the entire Universe may at some point in the future be filled with intelligent life. Hanson et al. (2021, The Astrophysical Journal922, 182) argued that we can be confident that the Universe will, by cosmic standards, soon be dominated by imperialist civilizations which expand rapidly, persist long and make drastic changes to the volumes they control. The main motivation for this ‘grabby civilizations’ hypothesis is that it supposedly provides a good explanation of why we are so early in cosmic history. In this paper, we criticize this motivation and suggest that it fails, for reasons analogous to why the notorious Doomsday argument fails. In the last part of the paper we broaden our discussion and argue that it may be rational to assign a rather low prior probability to the grabby civilizations hypothesis. For instance, if there are any civilizations that expand rapidly and indefinitely, they may well not make any drastic changes to the volumes they inhabit, potentially for strategic reasons. Hence, we call for epistemic caution and humility regarding the question of the long-term evolution of intelligence in the Universe.
{"title":"The future of intelligence in the Universe: a call for humility","authors":"S. Friederich, S. Wenmackers","doi":"10.1017/s1473550423000101","DOIUrl":"https://doi.org/10.1017/s1473550423000101","url":null,"abstract":"\u0000 Recent astrophysical findings suggest that the era during which the Universe is habitable has just begun. This raises the question whether the entire Universe may at some point in the future be filled with intelligent life. Hanson et al. (2021, The Astrophysical Journal922, 182) argued that we can be confident that the Universe will, by cosmic standards, soon be dominated by imperialist civilizations which expand rapidly, persist long and make drastic changes to the volumes they control. The main motivation for this ‘grabby civilizations’ hypothesis is that it supposedly provides a good explanation of why we are so early in cosmic history. In this paper, we criticize this motivation and suggest that it fails, for reasons analogous to why the notorious Doomsday argument fails. In the last part of the paper we broaden our discussion and argue that it may be rational to assign a rather low prior probability to the grabby civilizations hypothesis. For instance, if there are any civilizations that expand rapidly and indefinitely, they may well not make any drastic changes to the volumes they inhabit, potentially for strategic reasons. Hence, we call for epistemic caution and humility regarding the question of the long-term evolution of intelligence in the Universe.","PeriodicalId":13879,"journal":{"name":"International Journal of Astrobiology","volume":" ","pages":""},"PeriodicalIF":1.7,"publicationDate":"2023-06-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"45396938","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 : 2023-04-12DOI: 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。
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