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Never mind little green men: life on other planets might be purple. Nature 2024; 629:263. [PMID: 38698231 DOI: 10.1038/d41586-024-01261-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/05/2024]
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2
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Thompson B, Baker N. Keys, wallet, phone: the neuroscience behind working memory. Nature 2024:10.1038/d41586-024-01136-y. [PMID: 38632430 DOI: 10.1038/d41586-024-01136-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/19/2024]
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Burn R, Mordasini C, Mishra L, Haldemann J, Venturini J, Emsenhuber A, Henning T. A radius valley between migrated steam worlds and evaporated rocky cores. Nat Astron 2024; 8:463-471. [PMID: 38659612 PMCID: PMC11035145 DOI: 10.1038/s41550-023-02183-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/20/2023] [Accepted: 12/14/2023] [Indexed: 04/26/2024]
Abstract
The radius valley (or gap) in the observed distribution of exoplanet radii, which separates smaller super-Earths from larger sub-Neptunes, is a key feature that theoretical models must explain. Conventionally, it is interpreted as the result of the loss of primordial hydrogen and helium (H/He) envelopes atop rocky cores. However, planet formation models predict that water-rich planets migrate from cold regions outside the snowline towards the star. Assuming water to be in the form of solid ice in their interior, many of these planets would be located in the radius gap contradicting observations. Here we use an advanced coupled formation and evolution model that describes the planets' growth and evolution starting from solid, moon-sized bodies in the protoplanetary disk to mature Gyr-old planetary systems. Employing new equations of state and interior structure models to treat water as vapour mixed with H/He, we naturally reproduce the valley at the observed location. The model results demonstrate that the observed radius valley can be interpreted as the separation of less massive, rocky super-Earths formed in situ from more massive, ex situ, water-rich sub-Neptunes. Furthermore, the occurrence drop at larger radii, the so-called radius cliff, is matched by planets with water-dominated envelopes. Our statistical approach shows that the synthetic distribution of radii quantitatively agrees with observations for close-in planets, but only if low-mass planets initially containing H/He lose their atmosphere due to photoevaporation, which populates the super-Earth peak with evaporated rocky cores. Therefore, we provide a hybrid theoretical explanation of the radius gap and cliff caused by both planet formation (orbital migration) as well as evolution (atmospheric escape).
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Affiliation(s)
- Remo Burn
- Max-Planck-Institut für Astronomie, Heidelberg, Germany
| | | | - Lokesh Mishra
- Physikalisches Institut, Universität Bern, Bern, Switzerland
- Observatoire de Genève, Versoix, Switzerland
- Present Address: IBM Research, Rüschlikon, Switzerland
| | - Jonas Haldemann
- Physikalisches Institut, Universität Bern, Bern, Switzerland
| | | | - Alexandre Emsenhuber
- Universitäts-Sternwarte München, Ludwig-Maximilians-Universität München, Munich, Germany
- Present Address: Physikalisches Institut, Universität Bern, Bern, Switzerland
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5
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Witze A. Life in the cosmos: JWST hints at lower number of habitable planets. Nature 2023:10.1038/d41586-023-01983-1. [PMID: 37336984 DOI: 10.1038/d41586-023-01983-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/21/2023]
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6
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Kreidberg L. Search for distant atmosphere off to a rocky start. Nature 2023; 618:32-33. [PMID: 37259004 DOI: 10.1038/d41586-023-01738-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
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7
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Naoz S. Planet swallowed after venturing too close to its star. Nature 2023; 617:38-39. [PMID: 37138112 DOI: 10.1038/d41586-023-01385-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/05/2023]
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8
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Chen S. Mother-daughter duo work together to find new worlds. Nature 2023:10.1038/d41586-023-00580-6. [PMID: 36849819 DOI: 10.1038/d41586-023-00580-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023]
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9
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Way MJ, Ostberg C, Foley BJ, Gillmann C, Höning D, Lammer H, O’Rourke J, Persson M, Plesa AC, Salvador A, Scherf M, Weller M. Synergies Between Venus & Exoplanetary Observations: Venus and Its Extrasolar Siblings. Space Sci Rev 2023; 219:13. [PMID: 36785654 PMCID: PMC9911515 DOI: 10.1007/s11214-023-00953-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Accepted: 01/11/2023] [Indexed: 06/18/2023]
Abstract
Here we examine how our knowledge of present day Venus can inform terrestrial exoplanetary science and how exoplanetary science can inform our study of Venus. In a superficial way the contrasts in knowledge appear stark. We have been looking at Venus for millennia and studying it via telescopic observations for centuries. Spacecraft observations began with Mariner 2 in 1962 when we confirmed that Venus was a hothouse planet, rather than the tropical paradise science fiction pictured. As long as our level of exploration and understanding of Venus remains far below that of Mars, major questions will endure. On the other hand, exoplanetary science has grown leaps and bounds since the discovery of Pegasus 51b in 1995, not too long after the golden years of Venus spacecraft missions came to an end with the Magellan Mission in 1994. Multi-million to billion dollar/euro exoplanet focused spacecraft missions such as JWST, and its successors will be flown in the coming decades. At the same time, excitement about Venus exploration is blooming again with a number of confirmed and proposed missions in the coming decades from India, Russia, Japan, the European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA). Here we review what is known and what we may discover tomorrow in complementary studies of Venus and its exoplanetary cousins.
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Affiliation(s)
- M. J. Way
- NASA Goddard Institute for Space Studies, 2880 Broadway, New York, NY 10025 USA
- Theoretical Astrophysics, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden
| | - Colby Ostberg
- Department of Earth and Planetary Sciences, University of California, Riverside, CA 92521 USA
| | - Bradford J. Foley
- Department of Geosciences, Pennsylvania State University, University Park, PA USA
| | - Cedric Gillmann
- Department of Earth, Environmental and Planetary Sciences, Rice University, Houston, TX 77005 USA
| | - Dennis Höning
- Potsdam Institute for Climate Impact Research, Potsdam, Germany
- Department of Earth Sciences, Vrije Universiteit Amsterdam, Amsterdam, The Netherlands
| | - Helmut Lammer
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
| | - Joseph O’Rourke
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ USA
| | - Moa Persson
- Institut de Recherche en Astrophysique et Planétologie, Centre National de la Recherche Scientifique, Université Paul Sabatier – Toulouse III, Centre National d’Etudes Spatiales, Toulouse, France
| | | | - Arnaud Salvador
- Department of Astronomy and Planetary Science, Northern Arizona University, Box 6010, Flagstaff, AZ 86011 USA
- Habitability, Atmospheres, and Biosignatures Laboratory, University of Arizona, Tucson, AZ USA
- Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ USA
| | - Manuel Scherf
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstr. 6, 8042 Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
- Institute for Geodesy, Technical University, Graz, Austria
| | - Matthew Weller
- Lunar and Planetary Institute, 3600 Bay Area Blvd., Houston, TX 77058 USA
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Angerhausen D, Ottiger M, Dannert F, Miguel Y, Sousa-Silva C, Kammerer J, Menti F, Alei E, Konrad BS, Wang HS, Quanz SP. Large Interferometer for Exoplanets: VIII. Where Is the Phosphine? Observing Exoplanetary PH 3 with a Space-Based Mid-Infrared Nulling Interferometer. Astrobiology 2023; 23:183-194. [PMID: 36576793 DOI: 10.1089/ast.2022.0010] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
Phosphine could be a key molecule in the understanding of exotic chemistry that occurs in (exo)planetary atmospheres. While phosphine has been detected in the Solar System's giant planets, it has not been observed in exoplanets to date. In the exoplanetary context, however, it has been theorized to be a potential biosignature molecule. The goal of our study was to identify which illustrative science cases for PH3 chemistry are observable with a space-based mid-infrared nulling interferometric observatory like the Large Interferometer for Exoplanets (LIFE) concept. We identified a representative set of scenarios for PH3 detections in exoplanetary atmospheres that vary over the whole dynamic range of the LIFE mission. We used chemical kinetics and radiative transfer calculations to produce forward models of these informative, prototypical observational cases for LIFEsim, our observation simulator software for LIFE. In a detailed, yet first order approximation, it takes a mission like LIFE: (i) about 1 h to find phosphine in a warm giant around a G star at 10 pc, (ii) about 10 h in H2 or CO2 dominated temperate super-Earths around M star hosts at 5 pc, (iii) and even in 100 h it seems very unlikely that phosphine would be detectable in a Venus-Twin with extreme PH3 concentrations at 5 pc. Phosphine in concentrations previously discussed in the literature is detectable in 2 out of the 3 cases, and it is detected about an order of magnitude faster than in comparable cases with James Webb Space Telescope. We show that there is a significant number of objects accessible for these classes of observations. These results will be used to prioritize the parameter range for the next steps with more detailed retrieval simulations. They will also inform timely questions in the early design phase of a mission like LIFE and guide the community by providing easy-to-scale first estimates for a large part of detection space of such a mission.
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Affiliation(s)
- Daniel Angerhausen
- Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland
- National Center of Competence in Research PlanetS, Bern, Switzerland
- Blue Marble Space Institute of Science, Seattle, Washington, USA
| | - Maurice Ottiger
- Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland
| | - Felix Dannert
- Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland
| | - Yamila Miguel
- SRON Netherlands Institute for Space Research, Utrecht, The Netherlands
- Leiden Observatory, University of Leiden, Leiden, The Netherlands
| | - Clara Sousa-Silva
- Center for Astrophysics, Harvard-Smithsonian, Cambridge, Massachusetts, USA
- Division of Science, Mathematics, and Computing, Bard College, Annandale-on-Hudson, New York, USA
| | - Jens Kammerer
- Space Telescope Science Institute, Baltimore, Maryland, USA
| | - Franziska Menti
- Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland
| | - Eleonora Alei
- Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland
- National Center of Competence in Research PlanetS, Bern, Switzerland
| | - Björn S Konrad
- Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland
- National Center of Competence in Research PlanetS, Bern, Switzerland
| | - Haiyang S Wang
- Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland
- National Center of Competence in Research PlanetS, Bern, Switzerland
| | - Sascha P Quanz
- Department of Physics, Institute for Particle Physics and Astrophysics, ETH Zurich, Zurich, Switzerland
- National Center of Competence in Research PlanetS, Bern, Switzerland
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11
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Seidel JV, Nielsen LD, Sarkar S. JWST opens a window on exoplanet skies. Nature 2023; 614:632-633. [PMID: 36792896 DOI: 10.1038/d41586-023-00394-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/17/2023]
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12
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Witze A. How JWST revolutionized astronomy in 2022. Nature 2022; 612:600-1. [PMID: 36526914 DOI: 10.1038/d41586-022-01860-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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13
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Petrić Howe N, Thompson B. Huge data set shows 80% of US professors come from just 20% of institutions. Nature 2022:10.1038/d41586-022-03006-x. [PMID: 36131060 DOI: 10.1038/d41586-022-03006-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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14
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Thompson B, Petrić Howe N. Missing foot reveals world's oldest amputation. Nature 2022:10.1038/d41586-022-02854-x. [PMID: 36071232 DOI: 10.1038/d41586-022-02854-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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15
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Witze A. Webb telescope wows with first image of an exoplanet. Nature 2022:10.1038/d41586-022-02807-4. [PMID: 36050532 DOI: 10.1038/d41586-022-02807-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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16
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Hall S. Webb telescope spots CO 2 on exoplanet for first time: what it means for finding alien life. Nature 2022; 609:229-230. [PMID: 36038762 DOI: 10.1038/d41586-022-02350-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
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von Hegner I. First principles of terrestrial life: exemplars for potential extra-terrestrial biology. Theory Biosci 2022; 141:279-295. [PMID: 35907130 DOI: 10.1007/s12064-022-00373-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2021] [Accepted: 07/10/2022] [Indexed: 10/16/2022]
Abstract
The search for life elsewhere in the universe represents not only a potential expansion of our knowledge regarding life, but also a clarification of the first principles applicable to terrestrial life, which thus restrict the very search for extra-terrestrial life. Although there are no exact figures for how many species have existed throughout Earth's total history, we can still make inferences about how the distribution of this life has proceeded through a bell curve. This graph shows the totality of life, from its origin to its end. The system enclosing life contains a number of first principles designated the walls of minimal complexity and adaptive possibility, the fence of adaptation, and right-skewed extension. In this discussion of life, a framework will be formulated that, based on the dynamic relationship between mesophiles and extremophiles, will be imposed on exoworlds in order to utilize the graph's predictive power to analyze how extra-terrestrial life could unfold. In this framework the evolutionary variation does not depend on the specific biochemistry involved. Once life is 'up and running,' the various biochemical systems that can constitute terrestrial and extra-terrestrial life will have secondary significance. The extremophilic tail represents a range expansion in which all habitat possibilities are tested and occupied. This tail moves to the right not because of the biochemistry constitutions of organisms, but because it can do nothing else. Thus, it can be predicted that graphs of terrestrial and extra-terrestrial life will be similar overall. A number of other predictions can be made; for example, for worlds in which the atmospheric disequilibrium is approaching equilibrium, it is predicted that life may still be present because the extremophilic range expansion is stretched increasingly farther to the right. Because life necessarily arises at a left wall of minimal complexity, it is predicted that any origin of cellular life will have a close structural resemblance to that of the first terrestrial life. Thus, in principle, life may have originated more than once on Earth, and still exist. It is also predicted that there may be an entire subset of life existing among other domains that we do not see because, in an abstract sense, we are inside the graph. If we view the graph in its entirety, this subset appears very much like a vast supra-domain of life.
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Affiliation(s)
- Ian von Hegner
- Future Foundation Assoc., Egedal 21, 2690, Karlslunde, Denmark.
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18
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Witze A. Stunning new Webb images: baby stars, colliding galaxies and hot exoplanets. Nature 2022; 607:429-430. [PMID: 35821414 DOI: 10.1038/d41586-022-01931-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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19
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Witze A. Landmark Webb telescope releases first science image - astronomers are in awe. Nature 2022:10.1038/d41586-022-01906-6. [PMID: 35821407 DOI: 10.1038/d41586-022-01906-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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20
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Liquid water on planets with a primordial atmosphere can be long-lasting. Nat Astron 2022; 6:778-9. [PMID: 35789637 DOI: 10.1038/s41550-022-01700-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Super-Earths that retain their primordial atmospheres can have long-lasting temperate surfaces. If a layer of water can form on such a planet, it could be liquid for billions of years.
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21
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Small young star hosts a mammoth newborn planet. Nature 2022. [PMID: 35304885 DOI: 10.1038/d41586-022-00739-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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22
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Castelvecchi D. Earth-like planet spotted orbiting Sun's closest star. Nature 2022:10.1038/d41586-022-00400-3. [PMID: 35145291 DOI: 10.1038/d41586-022-00400-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract
Ammonia (NH3) in a terrestrial planet atmosphere is generally a good biosignature gas, primarily because terrestrial planets have no significant known abiotic NH3 source. The conditions required for NH3 to accumulate in the atmosphere are, however, stringent. NH3's high water solubility and high biousability likely prevent NH3 from accumulating in the atmosphere to detectable levels unless life is a net source of NH3 and produces enough NH3 to saturate the surface sinks. Only then can NH3 accumulate in the atmosphere with a reasonable surface production flux. For the highly favorable planetary scenario of terrestrial planets with hydrogen (H2)-dominated atmospheres orbiting M dwarf stars (M5V), we find that a minimum of about 5 ppm column-averaged mixing ratio is needed for NH3 to be detectable with JWST, considering a 10 ppm JWST systematic noise floor. When the surface is saturated with NH3 (i.e., there are no NH3-removal reactions on the surface), the required biological surface flux to reach 5 ppm is on the order of 1010 molecules/(cm2·s), comparable with the terrestrial biological production of methane (CH4). However, when the surface is unsaturated with NH3, due to additional sinks present on the surface, life would have to produce NH3 at surface flux levels on the order of 1015 molecules/(cm2·s) (∼4.5 × 106 Tg/year). This value is roughly 20,000 times greater than the biological production of NH3 on the Earth and about 10,000 times greater than Earth's CH4 biological production. Volatile amines have similar solubilities and reactivities to NH3 and hence share NH3's weaknesses and strengths as a biosignature. Finally, to establish NH3 as a biosignature gas, we must rule out mini-Neptunes with deep atmospheres, where temperatures and pressures are high enough for NH3's atmospheric production.
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Affiliation(s)
- Jingcheng Huang
- Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
- Department of Earth, Planetary and Atmospheric Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Sara Seager
- Department of Earth, Planetary and Atmospheric Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
- Department of Aeronautics and Astronautics, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Janusz J Petkowski
- Department of Earth, Planetary and Atmospheric Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Sukrit Ranjan
- Department of Earth, Planetary and Atmospheric Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
| | - Zhuchang Zhan
- Department of Earth, Planetary and Atmospheric Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts, USA
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Kipping D, Bryson S, Burke C, Christiansen J, Hardegree-Ullman K, Quarles B, Hansen B, Szulágyi J, Teachey A. An exomoon survey of 70 cool giant exoplanets and the new candidate Kepler-1708 b-i. Nat Astron 2022; 6:367-380. [PMID: 35399159 PMCID: PMC8938273 DOI: 10.1038/s41550-021-01539-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Accepted: 10/12/2021] [Indexed: 06/14/2023]
Abstract
Exomoons represent a crucial missing puzzle piece in our efforts to understand extrasolar planetary systems. To address this deficiency, we here describe an exomoon survey of 70 cool, giant transiting exoplanet candidates found by Kepler. We identify only one exhibiting a moon-like signal that passes a battery of vetting tests: Kepler-1708 b. We show that Kepler-1708 b is a statistically validated Jupiter-sized planet orbiting a Sun-like quiescent star at 1.6 au. The signal of the exomoon candidate, Kepler-1708 b-i, is a 4.8σ effect and is persistent across different instrumental detrending methods, with a 1% false-positive probability via injection-recovery. Kepler-1708 b-i is ~2.6 Earth radii and is located in an approximately coplanar orbit at ~12 planetary radii from its ~1.6 au Jupiter-sized host. Future observations will be necessary to validate or reject the candidate.
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Affiliation(s)
- David Kipping
- Department of Astronomy, Columbia University, New York, NY USA
| | - Steve Bryson
- NASA Ames Research Center, Mountain View, CA USA
| | - Chris Burke
- Department of Physics and Kavli Institute for Astrophysics and Space Research, Massachusetts Institute of Technology, Cambridge, MA USA
| | | | | | - Billy Quarles
- Department of Physics, Astronomy, Geosciences and Engineering Technology, Valdosta State University, Valdosta, GA USA
| | - Brad Hansen
- Mani Bhaumik Institute for Theoretical Physics, Department of Physics and Astronomy, UCLA, Los Angeles, CA USA
| | - Judit Szulágyi
- Institute for Particle Physics & Astrophysics, ETH Zurich, Zürich, Switzerland
| | - Alex Teachey
- Institute of Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan
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Abstract
Recent observations of the potentially habitable planets TRAPPIST-1 e, f, and g suggest that they possess large water mass fractions of possibly several tens of weight percent of water, even though the host star's activity should drive rapid atmospheric escape. These processes can photolyze water, generating free oxygen and possibly desiccating the planet. After the planets formed, their mantles were likely completely molten with volatiles dissolving and exsolving from the melt. To understand these planets and prepare for future observations, the magma ocean phase of these worlds must be understood. To simulate these planets, we have combined existing models of stellar evolution, atmospheric escape, tidal heating, radiogenic heating, magma-ocean cooling, planetary radiation, and water-oxygen-iron geochemistry. We present MagmOc, a versatile magma-ocean evolution model, validated against the rocky super-Earth GJ 1132b and early Earth. We simulate the coupled magma-ocean atmospheric evolution of TRAPPIST-1 e, f, and g for a range of tidal and radiogenic heating rates, as well as initial water contents between 1 and 100 Earth oceans. We also reanalyze the structures of these planets and find they have water mass fractions of 0-0.23, 0.01-0.21, and 0.11-0.24 for planets e, f, and g, respectively. Our model does not make a strong prediction about the water and oxygen content of the atmosphere of TRAPPIST-1 e at the time of mantle solidification. In contrast, the model predicts that TRAPPIST-1 f and g would have a thick steam atmosphere with a small amount of oxygen at that stage. For all planets that we investigated, we find that only 3-5% of the initial water will be locked in the mantle after the magma ocean solidified.
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Affiliation(s)
- Patrick Barth
- Centre for Exoplanet Science, University of St Andrews, St Andrews, UK
- SUPA, School of Physics & Astronomy, University of St Andrews, St Andrews, UK
- Max Planck Institute for Astronomy, Heidelberg, Germany
| | | | - Rory Barnes
- Astronomy Department, University of Washington, Seattle, Washington, USA
- NASA Virtual Planetary Laboratory Lead Team, USA
| | - Lena Noack
- Freie Universität Berlin, Institute of Geological Sciences, Berlin, Germany
| | - Paul Mollière
- Max Planck Institute for Astronomy, Heidelberg, Germany
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Limaye SS, Zelenyi L, Zasova L. Introducing the Venus Collection-Papers from the First Workshop on Habitability of the Cloud Layer. Astrobiology 2021; 21:1157-1162. [PMID: 34582698 DOI: 10.1089/ast.2021.0142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
We introduce the collection of papers from the first workshop on the habitability of the venusian cloud layer organized by the Roscosmos/IKI-NASA Joint Science Definition Team (JSDT) for Russia's Venera-D mission and hosted by the Space Research Institute in Moscow, Russia, during October 2-5, 2019. The collection also includes three papers that were developed independently of the workshop but are relevant to venusian cloud habitability.
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Affiliation(s)
- Sanjay S Limaye
- Space Science and Engineering Center, University of Wisconsin-Madison, Madison, Wisconsin, USA
| | - Lev Zelenyi
- Space Research Institute, Russian Academy of Sciences, Moscow, Russian Federation
| | - Ludmilla Zasova
- Space Research Institute, Russian Academy of Sciences, Moscow, Russian Federation
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Rivera-Valentín EG, Filiberto J, Lynch KL, Mamajanov I, Lyons TW, Schulte M, Méndez A. Introduction-First Billion Years: Habitability. Astrobiology 2021; 21:893-905. [PMID: 34406807 PMCID: PMC8403211 DOI: 10.1089/ast.2020.2314] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Accepted: 12/22/2020] [Indexed: 06/13/2023]
Abstract
The physical processes active during the first billion years (FBY) of Earth's history, such as accretion, differentiation, and impact cratering, provide constraints on the initial conditions that were conducive to the formation and establishment of life on Earth. This motivated the Lunar and Planetary Institute's FBY topical initiative, which was a four-part conference series intended to look at each of these physical processes to study the basic structure and composition of our Solar System that was set during the FBY. The FBY Habitability conference, held in September 2019, was the last in this series and was intended to synthesize the initiative; specifically, to further our understanding of the origins of life, planetary and environmental habitability, and the search for life beyond Earth. The conference included discussions of planetary habitability and the potential emergence of life on bodies within our Solar System, as well as extrasolar systems by applying our knowledge of the Solar System's FBY, and in particular Earth's early history. To introduce this Special Collection, which resulted from work discussed at the conference, we provide a review of the main themes and a synopsis of the FBY Habitability conference.
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Affiliation(s)
| | - Justin Filiberto
- Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA
| | - Kennda L. Lynch
- Lunar and Planetary Institute, Universities Space Research Association, Houston, Texas, USA
| | - Irena Mamajanov
- Earth-Life Science Institute, Tokyo Institute of Technology, Tokyo, Japan
| | - Timothy W. Lyons
- Department of Earth and Planetary Sciences, University of California Riverside, Riverside, California, USA
| | - Mitch Schulte
- Planetary Science Division, NASA Headquarters, Washington, District of Columbia, USA
| | - Abel Méndez
- Planetary Habitability Laboratory, University of Puerto Rico Arecibo, Arecibo, Puerto Rico
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Méndez A, Rivera-Valentín EG, Schulze-Makuch D, Filiberto J, Ramírez RM, Wood TE, Dávila A, McKay C, Ceballos KNO, Jusino-Maldonado M, Torres-Santiago NJ, Nery G, Heller R, Byrne PK, Malaska MJ, Nathan E, Simões MF, Antunes A, Martínez-Frías J, Carone L, Izenberg NR, Atri D, Chitty HIC, Nowajewski-Barra P, Rivera-Hernández F, Brown CY, Lynch KL, Catling D, Zuluaga JI, Salazar JF, Chen H, González G, Jagadeesh MK, Haqq-Misra J. Habitability Models for Astrobiology. Astrobiology 2021; 21:1017-1027. [PMID: 34382857 DOI: 10.1089/ast.2020.2342] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
Habitability has been generally defined as the capability of an environment to support life. Ecologists have been using Habitat Suitability Models (HSMs) for more than four decades to study the habitability of Earth from local to global scales. Astrobiologists have been proposing different habitability models for some time, with little integration and consistency among them, being different in function to those used by ecologists. Habitability models are not only used to determine whether environments are habitable, but they also are used to characterize what key factors are responsible for the gradual transition from low to high habitability states. Here we review and compare some of the different models used by ecologists and astrobiologists and suggest how they could be integrated into new habitability standards. Such standards will help improve the comparison and characterization of potentially habitable environments, prioritize target selections, and study correlations between habitability and biosignatures. Habitability models are the foundation of planetary habitability science, and the synergy between ecologists and astrobiologists is necessary to expand our understanding of the habitability of Earth, the Solar System, and extrasolar planets.
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Affiliation(s)
- Abel Méndez
- Planetary Habitability Laboratory, University of Puerto Rico at Arecibo, Puerto Rico, USA
| | | | - Dirk Schulze-Makuch
- Center for Astronomy and Astrophysics, Technische Universität Berlin, Berlin, Germany; German Research Centre for Geosciences, Section Geomicrobiology, Potsdam, Germany; Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Stechlin, Germany
| | | | - Ramses M Ramírez
- University of Central Florida, Department of Physics, Orlando, Florida, USA; Space Science Institute, Boulder, Colorado, USA
| | - Tana E Wood
- USDA Forest Service International Institute of Tropical Forestry, San Juan, Puerto Rico, USA
| | - Alfonso Dávila
- NASA Ames Research Center, Moffett Field, California, USA
| | - Chris McKay
- NASA Ames Research Center, Moffett Field, California, USA
| | - Kevin N Ortiz Ceballos
- Planetary Habitability Laboratory, University of Puerto Rico at Arecibo, Puerto Rico, USA
| | | | | | | | - René Heller
- Max Planck Institute for Solar System Research; Institute for Astrophysics, University of Göttingen, Germany
| | - Paul K Byrne
- North Carolina State University, Raleigh, North Carolina, USA
| | - Michael J Malaska
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
| | - Erica Nathan
- Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, Rhode Island, USA
| | - Marta Filipa Simões
- State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Taipa, Macau SAR, China
| | - André Antunes
- State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Taipa, Macau SAR, China
| | | | | | - Noam R Izenberg
- Johns Hopkins Applied Physics Laboratory, Laurel, Maryland, USA
| | - Dimitra Atri
- Center for Space Science, New York University Abu Dhabi, United Arab Emirates
| | | | | | | | | | - Kennda L Lynch
- Lunar and Planetary Institute, USRA, Houston, Texas, USA
| | | | - Jorge I Zuluaga
- Institute of Physics / FCEN - Universidad de Antioquia, Medellín, Colombia
| | - Juan F Salazar
- GIGA, Escuela Ambiental, Facultad de Ingeniería, Universidad de Antioquia, Medellín, Colombia
| | - Howard Chen
- Northwestern University, Evanston, Illinois, USA
| | - Grizelle González
- USDA Forest Service International Institute of Tropical Forestry, San Juan, Puerto Rico, USA
| | | | - Jacob Haqq-Misra
- Blue Marble Space Institute of Science, Seattle, Washington, USA
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Zhan Z, Seager S, Petkowski JJ, Sousa-Silva C, Ranjan S, Huang J, Bains W. Assessment of Isoprene as a Possible Biosignature Gas in Exoplanets with Anoxic Atmospheres. Astrobiology 2021; 21:765-792. [PMID: 33798392 DOI: 10.1089/ast.2019.2146] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The search for possible biosignature gases in habitable exoplanet atmospheres is accelerating, although actual observations are likely years away. This work adds isoprene, C5H8, to the roster of biosignature gases. We found that isoprene geochemical formation is highly thermodynamically disfavored and has no known abiotic false positives. The isoprene production rate on Earth rivals that of methane (CH4; ∼500 Tg/year). Unlike methane, on Earth isoprene is rapidly destroyed by oxygen-containing radicals. Although isoprene is predominantly produced by deciduous trees, isoprene production is ubiquitous to a diverse array of evolutionary distant organisms, from bacteria to plants and animals-few, if any, volatile secondary metabolites have a larger evolutionary reach. Although non-photochemical sinks of isoprene may exist, such as degradation of isoprene by life or other high deposition rates, destruction of isoprene in an anoxic atmosphere is mainly driven by photochemistry. Motivated by the concept that isoprene might accumulate in anoxic environments, we model the photochemistry and spectroscopic detection of isoprene in habitable temperature, rocky exoplanet anoxic atmospheres with a variety of atmosphere compositions under different host star ultraviolet fluxes. Limited by an assumed 10 ppm instrument noise floor, habitable atmosphere characterization when using James Webb Space Telescope (JWST) is only achievable with a transit signal similar or larger than that for a super-Earth-sized exoplanet transiting an M dwarf star with an H2-dominated atmosphere. Unfortunately, isoprene cannot accumulate to detectable abundance without entering a run-away phase, which occurs at a very high production rate, ∼100 times the Earth's production rate. In this run-away scenario, isoprene will accumulate to >100 ppm, and its spectral features are detectable with ∼20 JWST transits. One caveat is that some isoprene spectral features are hard to distinguish from those of methane and also from other hydrocarbons containing the isoprene substructure. Despite these challenges, isoprene is worth adding to the menu of potential biosignature gases.
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Affiliation(s)
- Zhuchang Zhan
- Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, Massachusetts, USA
| | - Sara Seager
- Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, Massachusetts, USA
- Department of Physics, MIT, Cambridge, Massachusetts, USA
- Department of Aeronautics and Astronautics, and MIT, Cambridge, Massachusetts, USA
| | - Janusz Jurand Petkowski
- Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, Massachusetts, USA
| | - Clara Sousa-Silva
- Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, Massachusetts, USA
| | - Sukrit Ranjan
- Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, Massachusetts, USA
| | | | - William Bains
- Department of Earth, Atmospheric, and Planetary Sciences, MIT, Cambridge, Massachusetts, USA
- Rufus Scientific, Royston, United Kingdom
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Witze A. The 2,000 stars where aliens would catch a glimpse of Earth. Nature 2021:10.1038/d41586-021-01692-7. [PMID: 34163085 DOI: 10.1038/d41586-021-01692-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract
Astrobiology is focused on the study of life in the universe. However, lifeless planetary environments yield biological information on the variety of ways in which physical and chemical conditions in the universe preclude the possibility of the origin or persistence of life, and in turn this will help explain the distribution and abundance of life, or lack of it, in the universe. Furthermore, many places that humans wish to explore and settle in space are lifeless, and studying the fate of life in these environments will aid our own success in thriving in them. In this synthetic review, I have three objectives, as follows: (1) To discuss the biological value and use of lifeless environments, (2) To explore the diverse planetary bodies and environments that can be lifeless and to categorize them, and (3) To propose sets of biological experiments that can be undertaken in different categories of lifeless worlds and environments and suggest concepts for mission ideas to realize these goals. They include origin of life and microbial inoculation experiments in lifeless but habitable environments. I suggest that the biological study of lifelessness is an underappreciated area in planetary sciences.
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Affiliation(s)
- Charles S Cockell
- UK Centre for Astrobiology, School of Physics and Astronomy, University of Edinburgh, Edinburgh, UK
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Sparks WB, Parenteau MN, Blankenship RE, Germer TA, Patty CHL, Bott KM, Telesco CM, Meadows VS. Spectropolarimetry of Primitive Phototrophs as Global Surface Biosignatures. Astrobiology 2021; 21:219-234. [PMID: 33216615 PMCID: PMC7876348 DOI: 10.1089/ast.2020.2272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/06/2020] [Accepted: 10/12/2020] [Indexed: 06/11/2023]
Abstract
Photosynthesis is an ancient metabolic process that began on early Earth and offers plentiful energy to organisms that can utilize it such that that they achieve global significance. The potential exists for similar processes to operate on habitable exoplanets and result in observable biosignatures. Before the advent of oxygenic photosynthesis, the most primitive phototrophs, anoxygenic phototrophs, dominated surface environments on the planet. Here, we characterize surface polarization biosignatures associated with a diverse sample of anoxygenic phototrophs and cyanobacteria, examining both pure cultures and microbial communities from the natural environment. Polarimetry is a tool that can be used to measure the chiral signature of biomolecules. Chirality is considered a universal, agnostic biosignature that is independent of a planet's biochemistry, receiving considerable interest as a target biosignature for life-detection missions. In contrast to preliminary indications from earlier work, we show that there is a diversity of distinctive circular polarization signatures, including the magnitude of the polarization, associated with the variety of chiral photosynthetic pigments and pigment complexes of anoxygenic and oxygenic phototrophs. We also show that the apparent death and release of pigments from one of the phototrophs is accompanied by an elevation of the reflectance polarization signal by an order of magnitude, which may be significant for remotely detectable environmental signatures. This work and others suggest that circular polarization signals up to ∼1% may occur, significantly stronger than previously anticipated circular polarization levels. We conclude that global surface polarization biosignatures may arise from anoxygenic and oxygenic phototrophs, which have dominated nearly 80% of the history of our rocky, inhabited planet.
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Affiliation(s)
- William B. Sparks
- SETI Institute, Mountain View, California, USA
- Space Telescope Science Institute, Baltimore, Maryland, USA
| | - Mary Niki Parenteau
- Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA
- NASA Ames Research Center, Moffett Field, California, USA
| | - Robert E. Blankenship
- Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA
- Department of Biology, Washington University in St. Louis, St. Louis, Missouri, USA
- Department of Chemistry, Washington University in St. Louis, St. Louis, Missouri, USA
| | - Thomas A. Germer
- National Institute of Standards and Technology, Gaithersburg, Maryland, USA
| | - Christian Herman Lucas Patty
- Institute of Plant Biology, Hungarian Academy of Sciences, Szeged, Hungary
- Space Research and Planetary Sciences, University of Bern, Bern, Switzerland
| | - Kimberly M. Bott
- Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA
- Department of Earth and Planetary Sciences, University of California, Riverside, Riverside, California, USA
| | - Charles M. Telesco
- Department of Astronomy, University of Florida, Gainesville, Florida, USA
| | - Victoria S. Meadows
- Virtual Planetary Laboratory, University of Washington, Seattle, Washington, USA
- Department of Astronomy, University of Washington, Seattle, Washington, USA
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Estrela R, Palit S, Valio A. Surface and Oceanic Habitability of Trappist-1 Planets under the Impact of Flares. Astrobiology 2020; 20:1465-1475. [PMID: 33320780 DOI: 10.1089/ast.2019.2126] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The discovery of potentially habitable planets around the ultracool dwarf star Trappist-1 naturally poses the question: could Trappist-1 planets be home to life? These planets orbit very close to the host star and are most susceptible to the UV radiation emitted by the intense and frequent flares of Trappist-1. Here, we calculate the UV spectra (100-450 nm) of a superflare observed on Trappist-1 with the K2 mission. We couple radiative transfer models to this spectra to estimate the UV surface flux on planets in the habitable zone of Trappist-1 (planets e, f, and g), assuming atmospheric scenarios based on a prebiotic and an oxygenic atmosphere. We quantify the impact of the UV radiation on living organisms on the surface and on a hypothetical planet ocean. Finally, we find that for non-oxygenic planets, UV-resistant life-forms would survive on the surface of planets f and g. Nevertheless, more fragile organisms (i.e., Escherichia coli) could be protected from the hazardous UV effects at ocean depths greater than 8 m. If the planets have an ozone layer, any life-forms studied here would survive in the habitable zone planets.
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Affiliation(s)
- Raissa Estrela
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
- Center for Radioastronomy and Astrophysics Mackenzie, Sao Paulo, Brazil
| | - Sourav Palit
- Center for Radioastronomy and Astrophysics Mackenzie, Sao Paulo, Brazil
- Department of Physics, Indian Institute of Technology Bombay (IITB), Mumbai, India
| | - Adriana Valio
- Center for Radioastronomy and Astrophysics Mackenzie, Sao Paulo, Brazil
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Volk K, Malhotra R. Dynamical instabilities in systems of multiple short-period planets are likely driven by secular chaos: a case study of Kepler-102. ACTA ACUST UNITED AC 2020; 160:98. [PMID: 33273743 DOI: 10.3847/1538-3881/aba0b0] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
We investigated the dynamical stability of high-multiplicity Kepler and K2 planetary systems. Our numerical simulations find instabilities in ~ 20% of the cases on a wide range of timescales (up to 5×109 orbits) and over an unexpectedly wide range of initial dynamical spacings. To identify the triggers of long-term instability in multi-planet systems, we investigated in detail the five-planet Kepler-102 system. Despite having several near-resonant period ratios, we find that mean motion resonances are unlikely to directly cause instability for plausible planet masses in this system. Instead, we find strong evidence that slow inward transfer of angular momentum deficit (AMD) via secular chaos excites the eccentricity of the innermost planet, Kepler-102 b, eventually leading to planet-planet collisions in ~ 80% of Kepler-102 simulations. Kepler-102 b likely needs a mass ≳ 0.1M ⊕, hence a bulk density exceeding about half Earth's, in order to avoid dynamical instability. To investigate the role of secular chaos in our wider set of simulations, we characterize each planetary system's AMD evolution with a "spectral fraction" calculated from the power spectrum of short integrations (~ 5 × 106 orbits). We find that small spectral fractions (≲ 0.01) are strongly associated with dynamical stability on long timescales (5 × 109 orbits) and that the median time to instability decreases with increasing spectral fraction. Our results support the hypothesis that secular chaos is the driver of instabilities in many non-resonant multi-planet systems, and also demonstrate that the spectral analysis method is an efficient numerical tool to diagnose long term (in)stability of multi-planet systems from short simulations.
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Turbet M, Bolmont E, Bourrier V, Demory BO, Leconte J, Owen J, Wolf ET. A Review of Possible Planetary Atmospheres in the TRAPPIST-1 System. Space Sci Rev 2020; 216:100. [PMID: 32764836 PMCID: PMC7378127 DOI: 10.1007/s11214-020-00719-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 01/14/2020] [Accepted: 07/04/2020] [Indexed: 06/11/2023]
Abstract
TRAPPIST-1 is a fantastic nearby (∼39.14 light years) planetary system made of at least seven transiting terrestrial-size, terrestrial-mass planets all receiving a moderate amount of irradiation. To date, this is the most observationally favourable system of potentially habitable planets known to exist. Since the announcement of the discovery of the TRAPPIST-1 planetary system in 2016, a growing number of techniques and approaches have been used and proposed to characterize its true nature. Here we have compiled a state-of-the-art overview of all the observational and theoretical constraints that have been obtained so far using these techniques and approaches. The goal is to get a better understanding of whether or not TRAPPIST-1 planets can have atmospheres, and if so, what they are made of. For this, we surveyed the literature on TRAPPIST-1 about topics as broad as irradiation environment, planet formation and migration, orbital stability, effects of tides and Transit Timing Variations, transit observations, stellar contamination, density measurements, and numerical climate and escape models. Each of these topics adds a brick to our understanding of the likely-or on the contrary unlikely-atmospheres of the seven known planets of the system. We show that (i) Hubble Space Telescope transit observations, (ii) bulk density measurements comparison with H2-rich planets mass-radius relationships, (iii) atmospheric escape modelling, and (iv) gas accretion modelling altogether offer solid evidence against the presence of hydrogen-dominated-cloud-free and cloudy-atmospheres around TRAPPIST-1 planets. This means that the planets are likely to have either (i) a high molecular weight atmosphere or (ii) no atmosphere at all. There are several key challenges ahead to characterize the bulk composition(s) of the atmospheres (if present) of TRAPPIST-1 planets. The main one so far is characterizing and correcting for the effects of stellar contamination. Fortunately, a new wave of observations with the James Webb Space Telescope and near-infrared high-resolution ground-based spectrographs on existing very large and forthcoming extremely large telescopes will bring significant advances in the coming decade.
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Affiliation(s)
- Martin Turbet
- Observatoire Astronomique de l'Université de Genève, 51 chemin de Pégase, 1290 Sauverny, Switzerland
| | - Emeline Bolmont
- Observatoire Astronomique de l'Université de Genève, 51 chemin de Pégase, 1290 Sauverny, Switzerland
| | - Vincent Bourrier
- Observatoire Astronomique de l'Université de Genève, 51 chemin de Pégase, 1290 Sauverny, Switzerland
| | - Brice-Olivier Demory
- Center for Space and Habitability, University of Bern, Gesellschaftsstrasse 6, 3012 Bern, Switzerland
| | - Jérémy Leconte
- Laboratoire d'astrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, 33615 Pessac, France
| | - James Owen
- Astrophysics Group, Department of Physics, Imperial College London, Prince Consort Rd, London, SW7 2AZ UK
| | - Eric T Wolf
- Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309 USA
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Haqq-Misra J, Kopparapu RK, Schwieterman E. Observational Constraints on the Great Filter. Astrobiology 2020; 20:572-579. [PMID: 32364797 DOI: 10.1089/ast.2019.2154] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
The search for spectroscopic biosignatures with the next generation of space telescopes could provide observational constraints on the abundance of exoplanets with signs of life. An extension of this spectroscopic characterization of exoplanets is the search for observational evidence of technology, known as technosignatures. Current mission concepts that would observe biosignatures from ultraviolet to near-infrared wavelengths could place upper limits on the fraction of planets in the Galaxy that host life, although such missions tend to have relatively limited capabilities of constraining the prevalence of technosignatures at mid-infrared wavelengths. Yet searching for technosignatures alongside biosignatures would provide important knowledge about the future of our civilization. If planets with technosignatures are abundant, then we can increase our confidence that the hardest step in planetary evolution-the Great Filter-is probably in our past. But if we find that life is commonplace while technosignatures are absent, then this would increase the likelihood that the Great Filter awaits to challenge us in the future.
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Affiliation(s)
| | | | - Edward Schwieterman
- Blue Marble Space Institute of Science, Seattle, Washington
- University of California at Riverside, Riverside, California
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O'Callaghan J. European space telescope to launch new era of exoplanet science. Nature 2019:10.1038/d41586-019-03800-0. [PMID: 33293707 DOI: 10.1038/d41586-019-03800-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Abstract
The search for an inhabited planet, beyond our own, is a driver of planetary exploration in our solar system and beyond. Using information from our own planet to inform search strategies allows for a targeted search. It is, however, worth considering some span in the strategy and in a priori expectation. An inhabited, Earth-like planet is one that would be similar to Earth in ways that extend beyond having biota. To facilitate a comparative cost/risk/benefit analysis of different potential search strategies, we use a metric akin to the Earth-similarity index. The metric extends from zero, for an inhabited planet that is like Earth in all other regards (i.e., zero differences), toward end-member values for planets that differ from Earth but maintain life potential. The analysis shows how finding inhabited planets that do not share other Earth characteristics could improve our ability to assess galactic life potential without a large increase in time-commitment costs. Search strategies that acknowledge the possibility of such planets can minimize the potential of exploration losses (e.g., searching for long durations to reach conclusions that are biased). Discovering such planets could additionally provide a test of the Gaia hypothesis-a test that has proven difficult when using only Earth as a laboratory. Finally, we discuss how an Earth2.0 narrative that has been presented to the public as a search strategy comes with nostalgia-laden baggage that does not best serve exploration.
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Affiliation(s)
- Adrian Lenardic
- Department of Earth, Environmental and Planetary Science, Rice University, Houston, Texas
| | - Johnny Seales
- Department of Earth, Environmental and Planetary Science, Rice University, Houston, Texas
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Léger A, Defrère D, Muñoz AG, Godolt M, Grenfell JL, Rauer H, Tian F. Searching for Atmospheric Bioindicators in Planets around the Two Nearby Stars, Proxima Centauri and Epsilon Eridani-Test Cases for Retrieval of Atmospheric Gases with Infrared Spectroscopy. Astrobiology 2019; 19:797-810. [PMID: 30985192 DOI: 10.1089/ast.2018.1938] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We tested the ability of thermal infrared spectroscopy to retrieve assumed atmospheric compositions for different types of planets orbiting Proxima Centauri and Epsilon Eridani. Six cases are considered, covering a range of atmospheric compositions and some diversity in the bulk composition (rocky, water ocean, hydrogen rich) and the spectral type of the parent star (M and K stars). For some cases, we applied coupled climate chemistry, or climate-only calculations; for other cases, we assumed the atmospheric composition, ground temperature, and surface reflectivity. The IR emission was then calculated from line-by-line radiative transfer models and used to investigate retrieval of input atmospheric species. For the six cases considered, no false positive of the triple bioindicator (H2O, CO2, and O2, in specified conditions) was found. In some cases, results show that the simultaneous acquisition of a visible spectrum would be valuable, for example, when CO2 is very abundant and its 9.4 μm satellite band hides the 9.6 μm O3 band in the IR. In each case, determining the mass appears mandatory to identify the planet's nature and have an idea of surface conditions, which are necessary when testing for the presence of life.
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Affiliation(s)
- A Léger
- 1 Institut d'Astrophysique Spatiale (IAS), University of Paris-Saclay, Orsay, France
- 2 Institut d'Astrophysique Spatiale (IAS), CNRS, Orsay, France
| | - D Defrère
- 3 Space Sciences Technology & Astrophysics Research (STAR) Institute, University of Liège, Liège, Belgium
| | - A García Muñoz
- 4 Centre for Astronomy and Astrophysics (ZAA), Berlin Institute of Technology (TUB), Berlin, Germany
| | - M Godolt
- 4 Centre for Astronomy and Astrophysics (ZAA), Berlin Institute of Technology (TUB), Berlin, Germany
| | - J L Grenfell
- 5 Department of Exoplanets and Atmospheres (EPA), German Aerospace Centre (DLR), Berlin, Germany
| | - H Rauer
- 4 Centre for Astronomy and Astrophysics (ZAA), Berlin Institute of Technology (TUB), Berlin, Germany
- 5 Department of Exoplanets and Atmospheres (EPA), German Aerospace Centre (DLR), Berlin, Germany
- 6 Institute of Geological Sciences, Free University of Berlin (FUB), Berlin, Germany
| | - F Tian
- 7 Department of Earth System Science, Tsinghua University, Beijing, China
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Ward LM, Stamenković V, Hand K, Fischer WW. Follow the Oxygen: Comparative Histories of Planetary Oxygenation and Opportunities for Aerobic Life. Astrobiology 2019; 19:811-824. [PMID: 31188035 DOI: 10.1089/ast.2017.1779] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Aerobic respiration-the reduction of molecular oxygen (O2) coupled to the oxidation of reduced compounds such as organic carbon, ferrous iron, reduced sulfur compounds, or molecular hydrogen while conserving energy to drive cellular processes-is the most widespread and bioenergetically favorable metabolism on Earth today. Aerobic respiration is essential for the development of complex multicellular life; thus the presence of abundant O2 is an important metric for planetary habitability. O2 on Earth is supplied by oxygenic photosynthesis, but it is becoming more widely understood that abiotic processes may supply meaningful amounts of O2 on other worlds. The modern atmosphere and rock record of Mars suggest a history of relatively high O2 as a result of photochemical processes, potentially overlapping with the range of O2 concentrations used by biology. Europa may have accumulated high O2 concentrations in its subsurface ocean due to the radiolysis of water ice at its surface. Recent modeling efforts suggest that coexisting water and O2 may be common on exoplanets, with confirmation from measurements of exoplanet atmospheres potentially coming soon. In all these cases, O2 accumulates through abiotic processes-independent of water-oxidizing photosynthesis. We hypothesize that abiogenic O2 may enhance the habitability of some planetary environments, allowing highly energetic aerobic respiration and potentially even the development of complex multicellular life which depends on it, without the need to first evolve oxygenic photosynthesis. This hypothesis is testable with further exploration and life-detection efforts on O2-rich worlds such as Mars and Europa, and comparison to O2-poor worlds such as Enceladus. This hypothesis further suggests a new dimension to planetary habitability: "Follow the Oxygen," in which environments with opportunities for energy-rich metabolisms such as aerobic respiration are preferentially targeted for investigation and life detection.
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Affiliation(s)
- Lewis M Ward
- 1 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California
| | - Vlada Stamenković
- 2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Kevin Hand
- 2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California
| | - Woodward W Fischer
- 1 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, California
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Abstract
One of the basic tenets of exobiology is the need for a liquid substratum in which life can arise, evolve, and develop. The most common version of this idea involves the necessity of water to act as such a substratum, both because that is the case on Earth and because it seems to be the most viable liquid for chemical reactions that lead to life. Other liquid media that could harbor life, however, have occasionally been put forth. In this work, we investigate the relative probability of finding superficial seas on rocky worlds that could be composed of nine different, potentially abundant, liquids, including water. We study the phase space size of habitable zones defined for those substances. The regions where there can be liquid around every type of star are calculated by using a simple model, excluding areas within a tidal locking distance. We combine the size of these regions with the stellar abundances in the Milky Way disk and modulate our result with the expected radial abundance of planets via a generalized Titius-Bode law, as statistics of exoplanet orbits seem to point to its adequateness. We conclude that seas of ethane may be up to nine times more frequent among exoplanets than seas of water, and that solvents other than water may play a significant role in the search for extrasolar seas.
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Affiliation(s)
- F J Ballesteros
- 1 Observatori Astronòmic, Universitat de València, Paterna (València), Spain
| | - A Fernandez-Soto
- 2 Instituto de Física de Cantabria (CSIC-UC), Santander, Spain
- 3 Unidad Asociada Observatori Astronòmic (IFCA-UV), Valencia, Spain
| | - V J Martínez
- 1 Observatori Astronòmic, Universitat de València, Paterna (València), Spain
- 3 Unidad Asociada Observatori Astronòmic (IFCA-UV), Valencia, Spain
- 4 Departament d'Astronomia i Astrofísica, Universitat de València, Burjassot (València), Spain
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Del Genio AD, Way MJ, Amundsen DS, Aleinov I, Kelley M, Kiang NY, Clune TL. Habitable Climate Scenarios for Proxima Centauri b with a Dynamic Ocean. Astrobiology 2019; 19:99-125. [PMID: 30183335 DOI: 10.1089/ast.2017.1760] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/14/2023]
Abstract
The nearby exoplanet Proxima Centauri b will be a prime future target for characterization, despite questions about its retention of water. Climate models with static oceans suggest that Proxima b could harbor a small dayside surface ocean despite its weak instellation. We present the first climate simulations of Proxima b with a dynamic ocean. We find that an ocean-covered Proxima b could have a much broader area of surface liquid water but at much colder temperatures than previously suggested, due to ocean heat transport and/or depression of the freezing point by salinity. Elevated greenhouse gas concentrations do not necessarily produce more open ocean because of dynamical regime transitions between a state with an equatorial Rossby-Kelvin wave pattern and a state with a day-night circulation. For an evolutionary path leading to a highly saline ocean, Proxima b could be an inhabited, mostly open ocean planet with halophilic life. A freshwater ocean produces a smaller liquid region than does an Earth salinity ocean. An ocean planet in 3:2 spin-orbit resonance has a permanent tropical waterbelt for moderate eccentricity. A larger versus smaller area of surface liquid water for similar equilibrium temperature may be distinguishable by using the amplitude of the thermal phase curve. Simulations of Proxima Centauri b may be a model for the habitability of weakly irradiated planets orbiting slightly cooler or warmer stars, for example, in the TRAPPIST-1, LHS 1140, GJ 273, and GJ 3293 systems.
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Affiliation(s)
| | - Michael J Way
- 1 NASA Goddard Institute for Space Studies , New York, New York
| | - David S Amundsen
- 1 NASA Goddard Institute for Space Studies , New York, New York
- 2 Department of Applied Physics and Applied Mathematics, Columbia University , New York, New York
| | - Igor Aleinov
- 1 NASA Goddard Institute for Space Studies , New York, New York
- 3 Center for Climate Systems Research, Columbia University , New York, New York
| | - Maxwell Kelley
- 1 NASA Goddard Institute for Space Studies , New York, New York
- 4 SciSpace LLC , New York, New York
| | - Nancy Y Kiang
- 1 NASA Goddard Institute for Space Studies , New York, New York
| | - Thomas L Clune
- 5 NASA Goddard Space Flight Center , Greenbelt, Maryland
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45
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Abstract
Life appears to have emerged relatively quickly on the Earth, a fact sometimes used to justify a high rate of spontaneous abiogenesis (λ) among Earth-like worlds. Conditioned upon a single datum-the time of earliest evidence for life (tobs)-previous Bayesian formalisms for the posterior distribution of λ have demonstrated how inferences are highly sensitive to the priors. Rather than attempt to infer the true λ posterior, we here compute the relative change to λ when new experimental/observational evidence is introduced. By simulating posterior distributions and resulting entropic information gains, we compare three experimental pressures on λ: (1) evidence for an earlier start to life, tobs, (2) constraints on spontaneous abiogenesis from the laboratory, and (3) an exoplanet survey for biosignatures. First, we find that experiments 1 and 2 can only yield lower limits on λ, unlike 3. Second, evidence for an earlier start to life can yield negligible information on λ if [Formula: see text]. Vice versa, experiment 2 is uninformative when [Formula: see text]. While experiment 3 appears the most direct means of measuring λ, we highlight that early starts inform us of the conditions of abiogenesis and that laboratory experiments could succeed in building new life. Altogether, the three experiments are complementary, and we encourage activity in all to solve this grand challenge.
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Affiliation(s)
- Jingjing Chen
- Department of Astronomy, Columbia University, New York, New York
| | - David Kipping
- Department of Astronomy, Columbia University, New York, New York
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46
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Díaz RF. A key piece in the exoplanet puzzle. Nature 2018; 563:329-30. [PMID: 30429560 DOI: 10.1038/d41586-018-07328-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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47
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Abstract
Characterizing the atmospheres of extrasolar planets is the new frontier in exoplanetary science. The last two decades of exoplanet discoveries have revealed that exoplanets are very common and extremely diverse in their orbital and bulk properties. We now enter a new era as we begin to investigate the chemical diversity of exoplanets, their atmospheric and interior processes, and their formation conditions. Recent developments in the field have led to unprecedented advancements in our understanding of atmospheric chemistry of exoplanets and the implications for their formation conditions. We review these developments in the present work. We review in detail the theory of atmospheric chemistry in all classes of exoplanets discovered to date, from highly irradiated gas giants, ice giants, and super-Earths, to directly imaged giant planets at large orbital separations. We then review the observational detections of chemical species in exoplanetary atmospheres of these various types using different methods, including transit spectroscopy, Doppler spectroscopy, and direct imaging. In addition to chemical detections, we discuss the advances in determining chemical abundances in these atmospheres and how such abundances are being used to constrain exoplanetary formation conditions and migration mechanisms. Finally, we review recent theoretical work on the atmospheres of habitable exoplanets, followed by a discussion of future outlook of the field.
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Affiliation(s)
- Nikku Madhusudhan
- Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
| | - Marcelino Agúndez
- Instituto de Ciencia de Materiales de Madrid, CSIC, C/Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Spain,
| | - Julianne I Moses
- Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA,
| | - Yongyun Hu
- Laboratory for Climate and Ocean-Atmosphere Sciences, Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing 100871, China,
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Figueira P, Faria JP, Adibekyan VZ, Oshagh M, Santos NC. A Pragmatic Bayesian Perspective on Correlation Analysis : The exoplanetary gravity - stellar activity case. ORIGINS LIFE EVOL B 2016; 46:385-393. [PMID: 27220496 DOI: 10.1007/s11084-016-9490-5] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2015] [Accepted: 01/12/2016] [Indexed: 11/26/2022]
Abstract
We apply the Bayesian framework to assess the presence of a correlation between two quantities. To do so, we estimate the probability distribution of the parameter of interest, ρ, characterizing the strength of the correlation. We provide an implementation of these ideas and concepts using python programming language and the pyMC module in a very short (∼ 130 lines of code, heavily commented) and user-friendly program. We used this tool to assess the presence and properties of the correlation between planetary surface gravity and stellar activity level as measured by the log([Formula: see text]) indicator. The results of the Bayesian analysis are qualitatively similar to those obtained via p-value analysis, and support the presence of a correlation in the data. The results are more robust in their derivation and more informative, revealing interesting features such as asymmetric posterior distributions or markedly different credible intervals, and allowing for a deeper exploration. We encourage the reader interested in this kind of problem to apply our code to his/her own scientific problems. The full understanding of what the Bayesian framework is can only be gained through the insight that comes by handling priors, assessing the convergence of Monte Carlo runs, and a multitude of other practical problems. We hope to contribute so that Bayesian analysis becomes a tool in the toolkit of researchers, and they understand by experience its advantages and limitations.
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Affiliation(s)
- P Figueira
- Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762, Porto, Portugal.
| | - J P Faria
- Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762, Porto, Portugal
- Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007, Porto, Portugal
| | - V Zh Adibekyan
- Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762, Porto, Portugal
| | - M Oshagh
- Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762, Porto, Portugal
- Institut für Astrophysik, Georg-August-Universität, Friedrich-Hund-Platz 1, 37077, Göttingen, Germany
| | - N C Santos
- Instituto de Astrofísica e Ciências do Espaço, Universidade do Porto, CAUP, Rua das Estrelas, 4150-762, Porto, Portugal
- Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 4169-007, Porto, Portugal
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49
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Seager S, Bains W. The search for signs of life on exoplanets at the interface of chemistry and planetary science. Sci Adv 2015; 1:e1500047. [PMID: 26601153 PMCID: PMC4643826 DOI: 10.1126/sciadv.1500047] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/14/2015] [Accepted: 02/05/2015] [Indexed: 05/04/2023]
Abstract
The discovery of thousands of exoplanets in the last two decades that are so different from planets in our own solar system challenges many areas of traditional planetary science. However, ideas for how to detect signs of life in this mélange of planetary possibilities have lagged, and only in the last few years has modeling how signs of life might appear on genuinely alien worlds begun in earnest. Recent results have shown that the exciting frontier for biosignature gas ideas is not in the study of biology itself, which is inevitably rooted in Earth's geochemical and evolutionary specifics, but in the interface of chemistry and planetary physics.
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Affiliation(s)
- Sara Seager
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Department of Physics, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - William Bains
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
- Rufus Scientific, Herts SG8 6ED, UK
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50
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Lawson PR, Poyneer L, Barrett H, Frazin R, Caucci L, Devaney N, Furenlid L, Gładysz S, Guyon O, Krist J, Maire J, Marois C, Mawet D, Mouillet D, Mugnier L, Pearson I, Perrin M, Pueyo L, Savransky D. On Advanced Estimation Techniques for Exoplanet Detection and Characterization Using Ground-based Coronagraphs. Proc SPIE Int Soc Opt Eng 2012; 8447. [PMID: 26347393 DOI: 10.1117/12.925099] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The direct imaging of planets around nearby stars is exceedingly difficult. Only about 14 exoplanets have been imaged to date that have masses less than 13 times that of Jupiter. The next generation of planet-finding coronagraphs, including VLT-SPHERE, the Gemini Planet Imager, Palomar P1640, and Subaru HiCIAO have predicted contrast performance of roughly a thousand times less than would be needed to detect Earth-like planets. In this paper we review the state of the art in exoplanet imaging, most notably the method of Locally Optimized Combination of Images (LOCI), and we investigate the potential of improving the detectability of faint exoplanets through the use of advanced statistical methods based on the concepts of the ideal observer and the Hotelling observer. We propose a formal comparison of techniques using a blind data challenge with an evaluation of performance using the Receiver Operating Characteristic (ROC) and Localization ROC (LROC) curves. We place particular emphasis on the understanding and modeling of realistic sources of measurement noise in ground-based AO-corrected coronagraphs. The work reported in this paper is the result of interactions between the co-authors during a week-long workshop on exoplanet imaging that was held in Squaw Valley, California, in March of 2012.
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Affiliation(s)
- Peter R Lawson
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Lisa Poyneer
- Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA 94550, USA
| | - Harrison Barrett
- College of Optical Sciences, University of Arizona, Tucson, AZ 85721, USA
| | - Richard Frazin
- Atmospheric, Oceanic and Space Sciences, Univ. Michigan, Ann Arbor, MI 48109, USA
| | - Luca Caucci
- College of Optical Sciences, University of Arizona, Tucson, AZ 85721, USA
| | - Nicholas Devaney
- Applied Optics Group, School of Physics, National University of Ireland, Galway, Ireland
| | - Lars Furenlid
- College of Optical Sciences, University of Arizona, Tucson, AZ 85721, USA
| | - Szymon Gładysz
- Fraunhofer Institute, Gutleuthausstrasse 1, 76275 Ettlingen, Germany
| | - Olivier Guyon
- Steward Observatory, The University of Arizona, Tucson, AZ 85721, USA ; Subaru Telescope, National Astronomical Observatory of Japan, Hilo, HI 96720, USA
| | - John Krist
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
| | - Jérôme Maire
- David Dunlap Inst., Univ. of Toronto, 50 St George St., Toronto, ON M5S 3H4, Canada
| | - Christian Marois
- NRC, Herzberg Institute of Astrophysics, Victoria, BC V9E 2E7, Canada
| | - Dimitri Mawet
- European Southern Observatory, Alonso de Córdova 3107, Vitacura, Casilla 19001, Chile
| | - David Mouillet
- IPAG, 414 rue de la Piscine, Domaine Univ., BP 53, 38041 Grenoble Cedex 09, France
| | - Laurent Mugnier
- ONERA, Division Optique Theorique et Appliquée, BP 72, 92322 Chatillon Cedex, France
| | - Iain Pearson
- College of Optical Sciences, University of Arizona, Tucson, AZ 85721, USA
| | - Marshall Perrin
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
| | - Laurent Pueyo
- JHU Department of Physics and Astronomy, 3400 N. Charles St, Baltimore, MD 21218, USA
| | - Dmitry Savransky
- Lawrence Livermore National Laboratory, 7000 East Ave, Livermore, CA 94550, USA
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