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Luo Y, Hu Y, Yang J, Zhang M, Yung YL. Coupled atmospheric chemistry, radiation, and dynamics of an exoplanet generate self-sustained oscillations. Proc Natl Acad Sci U S A 2023; 120:e2309312120. [PMID: 38091286 PMCID: PMC10743409 DOI: 10.1073/pnas.2309312120] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2023] [Accepted: 10/13/2023] [Indexed: 12/24/2023] Open
Abstract
Nonlinearity in photochemical systems is known to allow self-sustained oscillations, but they have received little attention in studies of planetary atmospheres. Here, we present a unique, self-oscillatory solution for ozone chemistry of an exoplanet from a numerical simulation using a fully coupled, three-dimensional (3D) atmospheric chemistry-radiation-dynamics model. Forced with nonvarying stellar insolation and emission flux of nitric oxide (NO), atmospheric ozone abundance oscillates by a factor of thirty over a multidecadal timescale. As such self-oscillations can only occur with biological nitrogen fixation contributing to NO emission, we propose that they are a unique class of biosignature. The resulting temporal variability in the atmospheric spectrum is potentially observable. Our results underscore the importance of revisiting the spectra of exoplanets over multidecadal timescales to characterizing the atmospheric chemistry of exoplanets and searching for exoplanet biosignatures. There are also profound implications for comparative planetology and the evolution of the atmospheres of terrestrial planets in the solar system and beyond. Fully coupled, 3D atmospheric chemistry-radiation-dynamics models can reveal new phenomena that may not exist in one-dimensional models, and hence, they are powerful tools for future planetary atmospheric research.
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Affiliation(s)
- Yangcheng Luo
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA91125
- Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing100871, China
- Laboratoire de Météorologie Dynamique/Institut Pierre-Simon Laplace, Sorbonne Université, École Normale Supérieure, Université Paris Sciences et Lettres, Ecole Polytechnique, Institut Polytechnique de Paris, Centre National de la Recherche Scientifique, Paris75005, France
| | - Yongyun Hu
- Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing100871, China
| | - Jun Yang
- Department of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing100871, China
| | - Michael Zhang
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA91125
| | - Yuk L. Yung
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA91125
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2
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Zieba S, Kreidberg L, Ducrot E, Gillon M, Morley C, Schaefer L, Tamburo P, Koll DDB, Lyu X, Acuña L, Agol E, Iyer AR, Hu R, Lincowski AP, Meadows VS, Selsis F, Bolmont E, Mandell AM, Suissa G. No thick carbon dioxide atmosphere on the rocky exoplanet TRAPPIST-1 c. Nature 2023; 620:746-749. [PMID: 37337068 PMCID: PMC10447244 DOI: 10.1038/s41586-023-06232-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2023] [Accepted: 05/17/2023] [Indexed: 06/21/2023]
Abstract
Seven rocky planets orbit the nearby dwarf star TRAPPIST-1, providing a unique opportunity to search for atmospheres on small planets outside the Solar System1. Thanks to the recent launch of the James Webb Space Telescope (JWST), possible atmospheric constituents such as carbon dioxide (CO2) are now detectable2,3. Recent JWST observations of the innermost planet TRAPPIST-1 b showed that it is most probably a bare rock without any CO2 in its atmosphere4. Here we report the detection of thermal emission from the dayside of TRAPPIST-1 c with the Mid-Infrared Instrument (MIRI) on JWST at 15 µm. We measure a planet-to-star flux ratio of fp/f⁎ = 421 ± 94 parts per million (ppm), which corresponds to an inferred dayside brightness temperature of 380 ± 31 K. This high dayside temperature disfavours a thick, CO2-rich atmosphere on the planet. The data rule out cloud-free O2/CO2 mixtures with surface pressures ranging from 10 bar (with 10 ppm CO2) to 0.1 bar (pure CO2). A Venus-analogue atmosphere with sulfuric acid clouds is also disfavoured at 2.6σ confidence. Thinner atmospheres or bare-rock surfaces are consistent with our measured planet-to-star flux ratio. The absence of a thick, CO2-rich atmosphere on TRAPPIST-1 c suggests a relatively volatile-poor formation history, with less than [Formula: see text] Earth oceans of water. If all planets in the system formed in the same way, this would indicate a limited reservoir of volatiles for the potentially habitable planets in the system.
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Affiliation(s)
- Sebastian Zieba
- Max-Planck-Institut für Astronomie, Heidelberg, Germany.
- Leiden Observatory, Leiden University, Leiden, The Netherlands.
| | | | - Elsa Ducrot
- Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, Gif-sur-Yvette, France
| | - Michaël Gillon
- Astrobiology Research Unit, University of Liège, Liège, Belgium
| | - Caroline Morley
- Department of Astronomy, University of Texas at Austin, Austin, TX, USA
| | - Laura Schaefer
- Department of Earth and Planetary Sciences, Stanford University, Stanford, CA, USA
| | - Patrick Tamburo
- Department of Astronomy, Boston University, Boston, MA, USA
- The Institute for Astrophysical Research, Boston University, Boston, MA, USA
| | - Daniel D B Koll
- Department of Atmospheric and Oceanic Sciences, Peking University, Beijing, People's Republic of China
| | - Xintong Lyu
- Department of Atmospheric and Oceanic Sciences, Peking University, Beijing, People's Republic of China
| | - Lorena Acuña
- Max-Planck-Institut für Astronomie, Heidelberg, Germany
- Aix-Marseille Université, CNRS, CNES, Institut Origines, LAM, Marseille, France
| | - Eric Agol
- Astrobiology Program, Department of Astronomy, University of Washington, Seattle, WA, USA
- NASA Nexus for Exoplanet System Science, Virtual Planetary Laboratory Team, University of Washington, Seattle, WA, USA
| | - Aishwarya R Iyer
- School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
| | - Renyu Hu
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
| | - Andrew P Lincowski
- Astrobiology Program, Department of Astronomy, University of Washington, Seattle, WA, USA
- NASA Nexus for Exoplanet System Science, Virtual Planetary Laboratory Team, University of Washington, Seattle, WA, USA
| | - Victoria S Meadows
- Astrobiology Program, Department of Astronomy, University of Washington, Seattle, WA, USA
- NASA Nexus for Exoplanet System Science, Virtual Planetary Laboratory Team, University of Washington, Seattle, WA, USA
| | - Franck Selsis
- Laboratoire d'Astrophysique de Bordeaux, Université de Bordeaux, CNRS, B18N, Pessac, France
| | - Emeline Bolmont
- Observatoire Astronomique de l'Université de Genève, Versoix, Switzerland
- Centre Vie dans l'Univers, Université de Genève, Geneva, Switzerland
| | - Avi M Mandell
- NASA Goddard Space Flight Center, Greenbelt, MD, USA
- Sellers Exoplanet Environments Collaboration, NASA Goddard Space Flight Center, Greenbelt, MD, USA
| | - Gabrielle Suissa
- Astrobiology Program, Department of Astronomy, University of Washington, Seattle, WA, USA
- NASA Nexus for Exoplanet System Science, Virtual Planetary Laboratory Team, University of Washington, Seattle, WA, USA
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3
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Mansfield M. Revealing the atmospheres of highly irradiated exoplanets: from ultra-hot Jupiters to rocky worlds. ASTROPHYSICS AND SPACE SCIENCE 2023; 368:24. [PMID: 37006965 PMCID: PMC10060346 DOI: 10.1007/s10509-023-04183-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/29/2022] [Accepted: 03/18/2023] [Indexed: 06/19/2023]
Abstract
Spectroscopy of transiting exoplanets has revealed a wealth of information about their atmospheric compositions and thermal structures. In particular, studies of highly irradiated exoplanets at temperatures much higher than those found in our solar system have provided detailed information on planetary chemistry and physics because of the high level of precision which can be obtained from such observations. Here we use a variety of techniques to study the atmospheres of highly irradiated transiting exoplanets and address three large, open questions in exoplanet atmosphere spectroscopy. First, we use secondary eclipse and phase curve observations to investigate the thermal structures and heat redistribution of ultra-hot Jupiters, the hottest known exoplanets. We demonstrate how these planets form an unique class of objects influenced by high-temperature chemical effects such as molecular dissociation and H- opacity. Second, we use observations of helium in the upper atmosphere of the exo-Neptune HAT-P-11b to probe atmospheric escape processes. Third, we develop tools to interpret JWST observations of highly irradiated exoplanets, including a data analysis pipeline to perform eclipse mapping of hot Jupiters and a method to infer albedos of and detect atmospheres on hot, terrestrial planets. Finally, we discuss remaining open questions in the field of highly irradiated exoplanets and opportunities to advance our understanding of these unique bodies in the coming years.
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Affiliation(s)
- Megan Mansfield
- Steward Observatory, University of Arizona, Tucson, 85715 AZ USA
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4
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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 SCIENCE REVIEWS 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] [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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5
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Abstract
Astronomers will soon begin searching for biosignatures, atmospheric gases or surface features produced by life, on potentially habitable planets. Since methane is the only biosignature that the James Webb Space Telescope could readily detect in terrestrial atmospheres, it is imperative to understand methane biosignatures to contextualize these upcoming observations. We explore the necessary planetary context for methane to be a persuasive biosignature and assess whether, and in what planetary environments, abiotic sources of methane could result in false-positive scenarios. With these results, we provide a tentative framework for assessing methane biosignatures. If life is abundant in the universe, then with the correct planetary context, atmospheric methane may be the first detectable indication of life beyond Earth. Methane has been proposed as an exoplanet biosignature. Imminent observations with the James Webb Space Telescope may enable methane detections on potentially habitable exoplanets, so it is essential to assess in what planetary contexts methane is a compelling biosignature. Methane’s short photochemical lifetime in terrestrial planet atmospheres implies that abundant methane requires large replenishment fluxes. While methane can be produced by a variety of abiotic mechanisms such as outgassing, serpentinizing reactions, and impacts, we argue that—in contrast to an Earth-like biosphere—known abiotic processes cannot easily generate atmospheres rich in CH4 and CO2 with limited CO due to the strong redox disequilibrium between CH4 and CO2. Methane is thus more likely to be biogenic for planets with 1) a terrestrial bulk density, high mean-molecular-weight and anoxic atmosphere, and an old host star; 2) an abundance of CH4 that implies surface fluxes exceeding what could be supplied by abiotic processes; and 3) atmospheric CO2 with comparatively little CO.
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6
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Quanz SP, Absil O, Benz W, Bonfils X, Berger JP, Defrère D, van Dishoeck E, Ehrenreich D, Fortney J, Glauser A, Grenfell JL, Janson M, Kraus S, Krause O, Labadie L, Lacour S, Line M, Linz H, Loicq J, Miguel Y, Pallé E, Queloz D, Rauer H, Ribas I, Rugheimer S, Selsis F, Snellen I, Sozzetti A, Stapelfeldt KR, Udry S, Wyatt M. Atmospheric characterization of terrestrial exoplanets in the mid-infrared: biosignatures, habitability, and diversity. EXPERIMENTAL ASTRONOMY 2021; 54:1197-1221. [PMID: 36915622 PMCID: PMC9998579 DOI: 10.1007/s10686-021-09791-z] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/29/2020] [Accepted: 08/20/2021] [Indexed: 06/13/2023]
Abstract
Exoplanet science is one of the most thriving fields of modern astrophysics. A major goal is the atmospheric characterization of dozens of small, terrestrial exoplanets in order to search for signatures in their atmospheres that indicate biological activity, assess their ability to provide conditions for life as we know it, and investigate their expected atmospheric diversity. None of the currently adopted projects or missions, from ground or in space, can address these goals. In this White Paper, submitted to ESA in response to the Voyage 2050 Call, we argue that a large space-based mission designed to detect and investigate thermal emission spectra of terrestrial exoplanets in the mid-infrared wavelength range provides unique scientific potential to address these goals and surpasses the capabilities of other approaches. While NASA might be focusing on large missions that aim to detect terrestrial planets in reflected light, ESA has the opportunity to take leadership and spearhead the development of a large mid-infrared exoplanet mission within the scope of the "Voyage 2050" long-term plan establishing Europe at the forefront of exoplanet science for decades to come. Given the ambitious science goals of such a mission, additional international partners might be interested in participating and contributing to a roadmap that, in the long run, leads to a successful implementation. A new, dedicated development program funded by ESA to help reduce development and implementation cost and further push some of the required key technologies would be a first important step in this direction. Ultimately, a large mid-infrared exoplanet imaging mission will be needed to help answer one of humankind's most fundamental questions: "How unique is our Earth?"
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Affiliation(s)
- Sascha P. Quanz
- ETH Zurich, Institute for Particle Physics and Astrophysics, Zurich, Switzerland
| | | | | | | | | | | | | | | | | | | | | | | | | | - Oliver Krause
- Max Planck Institute for Astronomy, Heidelberg, Germany
| | | | | | | | - Hendrik Linz
- Max Planck Institute for Astronomy, Heidelberg, Germany
| | - Jérôme Loicq
- Faculty of Aerospace Engineering, Delft University of Technology, Delft, Netherlands
| | | | - Enric Pallé
- Instituto de Astrofisica de Canarias, Santa Cruz de Tenerife, Spain
| | | | - Heike Rauer
- German Aerospace Center (DLR), Berlin, Germany
| | - Ignasi Ribas
- Institut de Ciencies de l’Espai, Barcelona, Spain
| | | | - Franck Selsis
- Laboratoire d’astrophysique de Bordeaux, Bordeaux, France
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7
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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 SCIENCE REVIEWS 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] [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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8
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Clouds will Likely Prevent the Detection of Water Vapor in JWST Transmission Spectra of Terrestrial Exoplanets. ACTA ACUST UNITED AC 2020. [DOI: 10.3847/2041-8213/ab6200] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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9
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Impact of Clouds and Hazes on the Simulated JWST Transmission Spectra of Habitable Zone Planets in the TRAPPIST-1 System. ACTA ACUST UNITED AC 2019. [DOI: 10.3847/1538-4357/ab5862] [Citation(s) in RCA: 59] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
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10
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Transit Signatures of Inhomogeneous Clouds on Hot Jupiters: Insights from Microphysical Cloud Modeling. ACTA ACUST UNITED AC 2019. [DOI: 10.3847/1538-4357/ab55d9] [Citation(s) in RCA: 45] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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11
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12
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Kreidberg L, Koll DDB, Morley C, Hu R, Schaefer L, Deming D, Stevenson KB, Dittmann J, Vanderburg A, Berardo D, Guo X, Stassun K, Crossfield I, Charbonneau D, Latham DW, Loeb A, Ricker G, Seager S, Vanderspek R. Absence of a thick atmosphere on the terrestrial exoplanet LHS 3844b. Nature 2019; 573:87-90. [DOI: 10.1038/s41586-019-1497-4] [Citation(s) in RCA: 84] [Impact Index Per Article: 16.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Accepted: 07/22/2019] [Indexed: 11/09/2022]
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13
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The L 98-59 System: Three Transiting, Terrestrial-size Planets Orbiting a Nearby M Dwarf. ACTA ACUST UNITED AC 2019. [DOI: 10.3847/1538-3881/ab2459] [Citation(s) in RCA: 67] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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14
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Lingam M, Loeb A. Relative Likelihood of Success in the Search for Primitive versus Intelligent Extraterrestrial Life. ASTROBIOLOGY 2019; 19:28-39. [PMID: 30556749 DOI: 10.1089/ast.2018.1936] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
We estimate the relative likelihood of success in the searches for primitive versus intelligent life on other planets. Taking into account the larger search volume for detectable artificial electromagnetic signals, we conclude that both searches should be performed concurrently, albeit with significantly more funding dedicated to primitive life. Based on the current federal funding allocated to the search for biosignatures, our analysis suggests that the search for extraterrestrial intelligence (SETI) may merit a federal funding level of at least $10 million per year, assuming that the average lifetime of technological species exceeds a millennium.
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Affiliation(s)
- Manasvi Lingam
- Institute for Theory and Computation, Harvard University , Cambridge, Massachusetts
| | - Abraham Loeb
- Institute for Theory and Computation, Harvard University , Cambridge, Massachusetts
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15
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Kane SR, Ceja AY, Way MJ, Quintana EV. CLIMATE MODELING OF A POTENTIAL EXOVENUS. THE ASTROPHYSICAL JOURNAL 2018; 869:46. [PMID: 30636775 PMCID: PMC6326386 DOI: 10.3847/1538-4357/aaec68] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The planetary mass and radius sensitivity of exoplanet discovery capabilities has reached into the terrestrial regime. The focus of such investigations is to search within the Habitable Zone where a modern Earth-like atmosphere may be a viable comparison. However, the detection bias of the transit and radial velocity methods lies close to the host star where the received flux at the planet may push the atmosphere into a runaway greenhouse state. One such exoplanet discovery, Kepler-1649b, receives a similar flux from its star as modern Venus does from the Sun, and so was categorized as a possible exoVenus. Here we discuss the planetary parameters of Kepler-1649b with relation to Venus to establish its potential as a Venus analog. We utilize the general circulation model ROCKE-3D to simulate the evolution of the surface temperature of Kepler-1649b under various assumptions, including relative atmospheric abundances. We show that in all our simulations the atmospheric model rapidly diverges from temperate surface conditions towards a runaway greenhouse with rapidly escalating surface temperatures. We calculate transmission spectra for the evolved atmosphere and discuss these spectra within the context of the James Webb Space Telescope (JWST) Near-Infrared Spectrograph (NIRSpec) capabilities. We thus demonstrate the detectability of the key atmospheric signatures of possible runaway greenhouse transition states and outline the future prospects of characterizing potential Venus analogs.
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Affiliation(s)
- Stephen R Kane
- Department of Earth Sciences, University of California, Riverside, CA 92521, USA
| | - Alma Y Ceja
- Department of Earth Sciences, University of California, Riverside, CA 92521, USA
| | - Michael J Way
- NASA Goddard Institute for Space Studies, New York, NY 10025, USA
- Department of Physics and Astronomy, Uppsala University, Uppsala, SE-75120, Sweden
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16
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Evolved Climates and Observational Discriminants for the TRAPPIST-1 Planetary System. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-4357/aae36a] [Citation(s) in RCA: 85] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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17
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18
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Detectability of Biosignatures in Anoxic Atmospheres with theJames Webb Space Telescope: A TRAPPIST-1e Case Study. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-3881/aad564] [Citation(s) in RCA: 70] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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19
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Ground-based Optical Transmission Spectroscopy of the Small, Rocky Exoplanet GJ 1132b. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-3881/aac6dd] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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20
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An Improved Transit Measurement for a 2.4 R ⊕ Planet Orbiting A Bright Mid-M Dwarf K2–28. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-3881/aabd75] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Redox Evolution via Gravitational Differentiation on Low-mass Planets: Implications for Abiotic Oxygen, Water Loss, and Habitability. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-3881/aab608] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
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Strategies for Constraining the Atmospheres of Temperate Terrestrial Planets with
JWST. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/2041-8213/aab896] [Citation(s) in RCA: 64] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Atmospheric escape from the TRAPPIST-1 planets and implications for habitability. Proc Natl Acad Sci U S A 2017; 115:260-265. [PMID: 29284746 DOI: 10.1073/pnas.1708010115] [Citation(s) in RCA: 133] [Impact Index Per Article: 19.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The presence of an atmosphere over sufficiently long timescales is widely perceived as one of the most prominent criteria associated with planetary surface habitability. We address the crucial question of whether the seven Earth-sized planets transiting the recently discovered ultracool dwarf star TRAPPIST-1 are capable of retaining their atmospheres. To this effect, we carry out numerical simulations to characterize the stellar wind of TRAPPIST-1 and the atmospheric ion escape rates for all of the seven planets. We also estimate the escape rates analytically and demonstrate that they are in good agreement with the numerical results. We conclude that the outer planets of the TRAPPIST-1 system are capable of retaining their atmospheres over billion-year timescales. The consequences arising from our results are also explored in the context of abiogenesis, biodiversity, and searches for future exoplanets. In light of the many unknowns and assumptions involved, we recommend that these conclusions must be interpreted with due caution.
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