1
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Abstract
A numerical model description of a hot Jupiter extended envelope based on the approximation of multi-component magnetic hydrodynamics is presented. The main attention is focused on the problem of implementing the completed MHD stellar wind model. As a result, the numerical model becomes applicable for calculating the structure of the extended envelope of hot Jupiters not only in the super-Alfvén and sub-Alfvén regimes of the stellar wind flow around and in the trans-Alfvén regime. The multi-component MHD approximation allows the consideration of changes in the chemical composition of hydrogen–helium envelopes of hot Jupiters. The results of calculations show that, in the case of a super-Alfvén flow regime, all the previously discovered types of extended gas-dynamic envelopes are realized in the new numerical model. With an increase in magnitude of the wind magnetic field, the extended envelope tends to become more closed. Under the influence of a strong magnetic field of the stellar wind, the envelope matter does not move along the ballistic trajectory but along the magnetic field lines of the wind toward the host star. This corresponds to an additional (sub-Alfvénic) envelope type of hot Jupiters, which has specific observational features. In the transient (trans-Alfvén) mode, a bow shock wave has a fragmentary nature. In the fully sub-Alfvén regime, the bow shock wave is not formed, and the flow structure is shock-less.
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2
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Konatham S, Martin-Torres J, Zorzano MP. Atmospheric composition of exoplanets based on the thermal escape of gases and implications for habitability. Proc Math Phys Eng Sci 2020; 476:20200148. [PMID: 33061789 PMCID: PMC7544335 DOI: 10.1098/rspa.2020.0148] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2020] [Accepted: 07/16/2020] [Indexed: 12/17/2022] Open
Abstract
The detection of habitable exoplanets is an exciting scientific and technical challenge. Owing to the current and most likely long-lasting impossibility of performing in situ exploration of exoplanets, their study and hypotheses regarding their capability to host life will be based on the restricted low-resolution spatial and spectral information of their atmospheres. On the other hand, with the advent of the upcoming exoplanet survey missions and technological improvements, there is a need for preliminary discrimination that can prioritize potential candidates within the fast-growing list of exoplanets. Here we estimate, for the first time and using the kinetic theory of gases, a list of the possible atmospheric species that can be retained in the atmospheres of the known exoplanets. We conclude that, based on our current knowledge of the detected exoplanets, 45 of them are good candidates for habitability studies. These exoplanets could have Earth-like atmospheres and should be able to maintain stable liquid water. Our results suggest that the current definition of a habitable zone around a star should be revisited and that the capacity of the planet to host an Earth-like atmosphere to support the stability of liquid water should be added.
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Affiliation(s)
- Samuel Konatham
- Group of Atmospheric Science, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Luleå, Sweden
| | - Javier Martin-Torres
- Group of Atmospheric Science, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Luleå, Sweden.,Instituto Andaluz de Ciencias de la Tierra (CSIC-UGR), Armilla, Granada, Spain.,School of Geosciences, University of Aberdeen, Meston Building, King's College, Aberdeen, UK
| | - Maria-Paz Zorzano
- Centro de Astrobiología (CSIC-INTA), Torrejón de Ardoz, Madrid, Spain.,Group of Atmospheric Science, Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology, Luleå, Sweden
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3
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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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4
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Gänsicke BT, Schreiber MR, Toloza O, Fusillo NPG, Koester D, Manser CJ. Accretion of a giant planet onto a white dwarf star. Nature 2019; 576:61-64. [PMID: 31802017 DOI: 10.1038/s41586-019-1789-8] [Citation(s) in RCA: 80] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2019] [Accepted: 09/13/2019] [Indexed: 11/09/2022]
Abstract
The detection1 of a dust disk around the white dwarf star G29-38 and transits from debris orbiting the white dwarf WD 1145+017 (ref. 2) confirmed that the photospheric trace metals found in many white dwarfs3 arise from the accretion of tidally disrupted planetesimals4. The composition of these planetesimals is similar to that of rocky bodies in the inner Solar System5. Gravitational scattering of planetesimals towards the white dwarf requires the presence of more massive bodies6, yet no planet has so far been detected at a white dwarf. Here we report optical spectroscopy of a hot (about 27,750 kelvin) white dwarf, WD J091405.30+191412.25, that is accreting from a circumstellar gaseous disk composed of hydrogen, oxygen and sulfur at a rate of about 3.3 × 109 grams per second. The composition of this disk is unlike all other known planetary debris around white dwarfs7, but resembles predictions for the makeup of deeper atmospheric layers of icy giant planets, with H2O and H2S being major constituents. A giant planet orbiting a hot white dwarf with a semi-major axis of around 15 solar radii will undergo substantial evaporation with expected mass loss rates comparable to the accretion rate that we observe onto the white dwarf. The orbit of the planet is most probably the result of gravitational interactions, indicating the presence of additional planets in the system. We infer an occurrence rate of approximately 1 in 10,000 for spectroscopically detectable giant planets in close orbits around white dwarfs.
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Affiliation(s)
- Boris T Gänsicke
- Department of Physics, University of Warwick, Coventry, UK. .,Centre for Exoplanets and Habitability, University of Warwick, Coventry, UK.
| | - Matthias R Schreiber
- Institute of Physics and Astronomy, Millennium Nucleus for Planet Formation (NPF), Universidad de Valparaíso, Valparaíso, Chile
| | - Odette Toloza
- Department of Physics, University of Warwick, Coventry, UK
| | | | - Detlev Koester
- Institut für Theoretische Physik und Astrophysik, Universität Kiel, Kiel, Germany
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5
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Abstract
The kinetic Monte Carlo method, used in astrochemistry to investigate suprathermal (hot) particles at the molecular level, is presented. Different modifications of this method, aimed at studying the influence of suprathermal particles in the processes occurring in gas and dust envelopes surrounding astrophysical objects — prestellar and protostellar cores of molecular clouds, planets, their moons, and comets in the Solar and extrasolar planetary systems — are considered. The important role of the fraction of suprathermal particles in astrochemical applications of this approach is demonstrated. The presence of these particles leads to local changes in the chemical composition; causes non-thermal emissions in gas and dust envelopes; enhances the chemical exchange between the gas and dust fractions of envelope; leads to the formation of extended hot coronae of planets; increases non-thermal atmospheric losses, thus determining the evolution of planetary atmosphere on astronomical time scales; and facilitates the formation of complex molecules in gas and dust envelopes of astrophysical objects.
The bibliography includes 146 references.
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6
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Affiliation(s)
- Matteo Brogi
- Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
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7
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The HST PanCET Program: Hints of Na i and Evidence of a Cloudy Atmosphere for the Inflated Hot Jupiter WASP-52b. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-3881/aaee89] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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8
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Allart R, Bourrier V, Lovis C, Ehrenreich D, Spake JJ, Wyttenbach A, Pino L, Pepe F, Sing DK, Lecavelier des Etangs A. Spectrally resolved helium absorption from the extended atmosphere of a warm Neptune-mass exoplanet. Science 2018; 362:1384-1387. [PMID: 30523080 DOI: 10.1126/science.aat5879] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 11/08/2018] [Indexed: 11/02/2022]
Abstract
Stellar heating causes atmospheres of close-in exoplanets to expand and escape. These extended atmospheres are difficult to observe because their main spectral signature-neutral hydrogen at ultraviolet wavelengths-is strongly absorbed by interstellar medium. We report the detection of the near-infrared triplet of neutral helium in the transiting warm Neptune-mass exoplanet HAT-P-11b by using ground-based, high-resolution observations. The helium feature is repeatable over two independent transits, with an average absorption depth of 1.08 ± 0.05%. Interpreting absorption spectra with three-dimensional simulations of the planet's upper atmosphere suggests that it extends beyond 5 planetary radii, with a large-scale height and a helium mass loss rate of ≲3 × 105 grams per second. A net blue-shift of the absorption might be explained by high-altitude winds flowing at 3 kilometers per second from day to night-side.
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Affiliation(s)
- R Allart
- Observatoire Astronomique de l'Université de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland.
| | - V Bourrier
- Observatoire Astronomique de l'Université de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland
| | - C Lovis
- Observatoire Astronomique de l'Université de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland
| | - D Ehrenreich
- Observatoire Astronomique de l'Université de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland
| | - J J Spake
- Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK
| | - A Wyttenbach
- Observatoire Astronomique de l'Université de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland.,Leiden Observatory, Leiden University, Postbus 9513, 2300 RA Leiden, Netherlands
| | - L Pino
- Observatoire Astronomique de l'Université de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland.,Dipartimento di Fisica e Astronomia "Galileo Galilei," Univ. di Padova, Vicolo dell'Osservatorio 3, Padova I-35122, Italy.,Anton Pannekoek Institute for Astronomy, University of Amsterdam, Science Park 904, 1098 XH Amsterdam, Netherlands
| | - F Pepe
- Observatoire Astronomique de l'Université de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland
| | - D K Sing
- Astrophysics Group, School of Physics, University of Exeter, Stocker Road, Exeter EX4 4QL, UK.,Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, MD, USA
| | - A Lecavelier des Etangs
- Institut d'Astrophysique de Paris, CNRS, UMR 7095, Sorbonne Université, 98 bis boulevard Arago, Paris F-75014, France
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9
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Nortmann L, Pallé E, Salz M, Sanz-Forcada J, Nagel E, Alonso-Floriano FJ, Czesla S, Yan F, Chen G, Snellen IAG, Zechmeister M, Schmitt JHMM, López-Puertas M, Casasayas-Barris N, Bauer FF, Amado PJ, Caballero JA, Dreizler S, Henning T, Lampón M, Montes D, Molaverdikhani K, Quirrenbach A, Reiners A, Ribas I, Sánchez-López A, Schneider PC, Zapatero Osorio MR. Ground-based detection of an extended helium atmosphere in the Saturn-mass exoplanet WASP-69b. Science 2018; 362:1388-1391. [PMID: 30523081 DOI: 10.1126/science.aat5348] [Citation(s) in RCA: 131] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2018] [Accepted: 11/16/2018] [Indexed: 11/02/2022]
Abstract
Hot gas giant exoplanets can lose part of their atmosphere due to strong stellar irradiation, and these losses can affect their physical and chemical evolution. Studies of atmospheric escape from exoplanets have mostly relied on space-based observations of the hydrogen Lyman-α line in the far ultraviolet region, which is strongly affected by interstellar absorption. Using ground-based high-resolution spectroscopy, we detected excess absorption in the helium triplet at 1083 nanometers during the transit of the Saturn-mass exoplanet WASP-69b, at a signal-to-noise ratio of 18. We measured line blueshifts of several kilometers per second and posttransit absorption, which we interpret as the escape of part of the atmosphere trailing behind the planet in comet-like form.
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Affiliation(s)
- Lisa Nortmann
- Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain. .,Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
| | - Enric Pallé
- Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
| | - Michael Salz
- Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
| | - Jorge Sanz-Forcada
- Centro de Astrobiología, Consejo Superior de Investigaciones Científicas-Instituto Nacional de Técnica Aeroespacial (CSIC-INTA), European Space Astronomy Centre campus, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
| | - Evangelos Nagel
- Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
| | | | - Stefan Czesla
- Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
| | - Fei Yan
- Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
| | - Guo Chen
- Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain.,Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008, China
| | - Ignas A G Snellen
- Leiden Observatory, Leiden University, Postbus 9513, 2300 RA, Leiden, Netherlands
| | - Mathias Zechmeister
- Institut für Astrophysik, Georg-August-Universität, 37077 Göttingen, Germany
| | - Jürgen H M M Schmitt
- Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
| | - Manuel López-Puertas
- Instituto de Astrofísica de Andalucía, Consejo Superior de Investigaciones Científicas (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
| | - Núria Casasayas-Barris
- Instituto de Astrofísica de Canarias, Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain.,Departamento de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Tenerife, Spain
| | - Florian F Bauer
- Institut für Astrophysik, Georg-August-Universität, 37077 Göttingen, Germany.,Instituto de Astrofísica de Andalucía, Consejo Superior de Investigaciones Científicas (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
| | - Pedro J Amado
- Instituto de Astrofísica de Andalucía, Consejo Superior de Investigaciones Científicas (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
| | - José A Caballero
- Centro de Astrobiología, Consejo Superior de Investigaciones Científicas-Instituto Nacional de Técnica Aeroespacial (CSIC-INTA), European Space Astronomy Centre campus, Camino bajo del castillo s/n, 28692 Villanueva de la Cañada, Madrid, Spain
| | - Stefan Dreizler
- Institut für Astrophysik, Georg-August-Universität, 37077 Göttingen, Germany
| | - Thomas Henning
- Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
| | - Manuel Lampón
- Instituto de Astrofísica de Andalucía, Consejo Superior de Investigaciones Científicas (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
| | - David Montes
- Departamento de Astrofísica y Ciencias de la Atmósfera, Facultad de Ciencias Físicas, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | | | - Andreas Quirrenbach
- Landessternwarte, Zentrum für Astronomie der Universität Heidelberg, Königstuhl 12, 69117 Heidelberg, Germany
| | - Ansgar Reiners
- Institut für Astrophysik, Georg-August-Universität, 37077 Göttingen, Germany
| | - Ignasi Ribas
- Institut de Ciències de l'Espai, Consejo Superior de Investigaciones Científicas (CSIC), Campus Universitat Autònoma de Barcelona, c/ de Can Magrans s/n, 08193 Bellaterra, Barcelona, Spain.,Institut d'Estudis Espacials de Catalunya, 08034 Barcelona, Spain
| | - Alejandro Sánchez-López
- Instituto de Astrofísica de Andalucía, Consejo Superior de Investigaciones Científicas (CSIC), Glorieta de la Astronomía s/n, 18008 Granada, Spain
| | - P Christian Schneider
- Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
| | - María R Zapatero Osorio
- Centro de Astrobiología, Consejo Superior de Investigaciones Científicas-Instituto Nacional de Técnica Aeroespacial (CSIC-INTA), Crta. de Ajalvir km 4, E-28850 Torrejón de Ardoz, Madrid, Spain
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10
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An Optical Transmission Spectrum for the Ultra-hot Jupiter WASP-121b Measured with the Hubble Space Telescope. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-3881/aaebff] [Citation(s) in RCA: 86] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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11
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Cohen O, Moschou SP, Glocer A, Sokolov IV, Mazeh T, Drake JJ, Garraffo C, Alvarado-GÓmez JD. EXOPLANET MODULATION OF STELLAR CORONAL RADIO EMISSION. THE ASTRONOMICAL JOURNAL 2018; 156:202. [PMID: 33510541 PMCID: PMC7839303 DOI: 10.3847/1538-3881/aae1f2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
The search for exoplanets in the radio bands has been focused on detecting radio emissions produced by the interaction between magnetized planets and the stellar wind (auroral emission). Here we introduce a new tool, which is part of our MHD stellar corona model, to predict the ambient coronal radio emission and its modulations induced by a close planet. For simplicity, the present work assumes that the exoplanet is stationary in the frame rotating with the stellar rotation. We explore the radio flux modulations using a limited parameter space of idealized cases by changing the magnitude of the planetary field, its polarity, the planetary orbital separation, and the strength of the stellar field. We find that the modulations induced by the planet could be significant and observable in the case of hot Jupiter planets - above 100% modulation with respect to the ambient flux in the 10 - 100 MHz range in some cases, and 2-10% in the frequency bands above 250 MHz for some cases. Thus, our work indicates that radio signature of exoplanets might not be limited to low-frequency radio range. We find that the intensity modulations are sensitive to the planetary magnetic field polarity for short-orbit planets, and to the stellar magnetic field strength for all cases. The new radio tool, when applied to real systems, could provide predictions for the frequency range at which the modulations can be observed by current facilities.
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Affiliation(s)
- Offr Cohen
- Lowell Center for Space Science and Technology, University of Massachusetts Lowell 600 Suffolk St., Lowell, MA 01854, USA
| | | | - Alex Glocer
- NASA/Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - Igor V Sokolov
- Center for Space Environment Modeling, University of Michigan, 2455 Hayward, Ann Arbor, Michigan USA
| | - Tsevi Mazeh
- School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel
| | - Jeremy J Drake
- Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, Massachusetts, USA
| | - C Garraffo
- Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, Massachusetts, USA
| | - J D Alvarado-GÓmez
- Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, Massachusetts, USA
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12
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Extremely Irradiated Hot Jupiters: Non-oxide Inversions, H− Opacity, and Thermal Dissociation of Molecules. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-4357/aadd9e] [Citation(s) in RCA: 139] [Impact Index Per Article: 23.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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13
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Fujii Y, Angerhausen D, Deitrick R, Domagal-Goldman S, Grenfell JL, Hori Y, Kane SR, Pallé E, Rauer H, Siegler N, Stapelfeldt K, Stevenson KB. Exoplanet Biosignatures: Observational Prospects. ASTROBIOLOGY 2018; 18:739-778. [PMID: 29938537 PMCID: PMC6016572 DOI: 10.1089/ast.2017.1733] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Accepted: 03/13/2018] [Indexed: 05/04/2023]
Abstract
Exoplanet hunting efforts have revealed the prevalence of exotic worlds with diverse properties, including Earth-sized bodies, which has fueled our endeavor to search for life beyond the Solar System. Accumulating experiences in astrophysical, chemical, and climatological characterization of uninhabitable planets are paving the way to characterization of potentially habitable planets. In this paper, we review our possibilities and limitations in characterizing temperate terrestrial planets with future observational capabilities through the 2030s and beyond, as a basis of a broad range of discussions on how to advance "astrobiology" with exoplanets. We discuss the observability of not only the proposed biosignature candidates themselves but also of more general planetary properties that provide circumstantial evidence, since the evaluation of any biosignature candidate relies on its context. Characterization of temperate Earth-sized planets in the coming years will focus on those around nearby late-type stars. The James Webb Space Telescope (JWST) and later 30-meter-class ground-based telescopes will empower their chemical investigations. Spectroscopic studies of potentially habitable planets around solar-type stars will likely require a designated spacecraft mission for direct imaging, leveraging technologies that are already being developed and tested as part of the Wide Field InfraRed Survey Telescope (WFIRST) mission. Successful initial characterization of a few nearby targets will be an important touchstone toward a more detailed scrutiny and a larger survey that are envisioned beyond 2030. The broad outlook this paper presents may help develop new observational techniques to detect relevant features as well as frameworks to diagnose planets based on the observables. Key Words: Exoplanets-Biosignatures-Characterization-Planetary atmospheres-Planetary surfaces. Astrobiology 18, 739-778.
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Affiliation(s)
- Yuka Fujii
- NASA Goddard Institute for Space Studies, New York, New York, USA
- Earth-Life Science Institute, Tokyo Institute of Technology, Ookayama, Meguro, Tokyo, Japan
| | - Daniel Angerhausen
- CSH Fellow for Exoplanetary Astronomy, Center for Space and Habitability (CSH), Universität Bern, Bern, Switzerland
- Blue Marble Space Institute of Science, Seattle, Washington, USA
| | - Russell Deitrick
- Department of Astronomy, University of Washington, Seattle, Washington, USA
- NASA Astrobiology Institute's Virtual Planetary Laboratory
| | - Shawn Domagal-Goldman
- NASA Astrobiology Institute's Virtual Planetary Laboratory
- NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
| | - John Lee Grenfell
- Department of Extrasolar Planets and Atmospheres (EPA), Institute of Planetary Research, German Aerospace Centre (DLR), Berlin, Germany
| | - Yasunori Hori
- Astrobiology Center, National Institutes of Natural Sciences (NINS), Mitaka, Tokyo, Japan
| | - Stephen R. Kane
- Department of Earth Sciences, University of California, Riverside, California, USA
| | - Enric Pallé
- Instituto de Astrofísica de Canarias, La Laguna, Tenerife, Spain
- Departamento de Astrofísica, Universidad de La Laguna, Tenerife, Spain
| | - Heike Rauer
- Department of Extrasolar Planets and Atmospheres (EPA), Institute of Planetary Research, German Aerospace Centre (DLR), Berlin, Germany
- Center for Astronomy and Astrophysics, Berlin Institute of Technology, Berlin, Germany
| | - Nicholas Siegler
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
- NASA Exoplanet Exploration Office
| | - Karl Stapelfeldt
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
- NASA Exoplanet Exploration Office
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14
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Helium in the eroding atmosphere of an exoplanet. Nature 2018; 557:68-70. [PMID: 29720632 DOI: 10.1038/s41586-018-0067-5] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Accepted: 03/09/2018] [Indexed: 11/08/2022]
Abstract
Helium is the second-most abundant element in the Universe after hydrogen and is one of the main constituents of gas-giant planets in our Solar System. Early theoretical models predicted helium to be among the most readily detectable species in the atmospheres of exoplanets, especially in extended and escaping atmospheres 1 . Searches for helium, however, have hitherto been unsuccessful 2 . Here we report observations of helium on an exoplanet, at a confidence level of 4.5 standard deviations. We measured the near-infrared transmission spectrum of the warm gas giant 3 WASP-107b and identified the narrow absorption feature of excited metastable helium at 10,833 angstroms. The amplitude of the feature, in transit depth, is 0.049 ± 0.011 per cent in a bandpass of 98 angstroms, which is more than five times greater than what could be caused by nominal stellar chromospheric activity. This large absorption signal suggests that WASP-107b has an extended atmosphere that is eroding at a total rate of 1010 to 3 × 1011 grams per second (0.1-4 per cent of its total mass per billion years), and may have a comet-like tail of gas shaped by radiation pressure.
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Helium discovered in the tail of an exoplanet. Nature 2018; 557:35-36. [DOI: 10.1038/d41586-018-04969-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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An Ultra-short Period Rocky Super-Earth with a Secondary Eclipse and a Neptune-like Companion around K2-141. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-3881/aaa5b5] [Citation(s) in RCA: 81] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Compositional Imprints in Density–Distance–Time: A Rocky Composition for Close-in Low-mass Exoplanets from the Location of the Valley of Evaporation. ACTA ACUST UNITED AC 2018. [DOI: 10.3847/1538-4357/aa9f1e] [Citation(s) in RCA: 155] [Impact Index Per Article: 25.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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18
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Observational Techniques with Transiting Exoplanetary Atmospheres. ASTROPHYSICS AND SPACE SCIENCE LIBRARY 2018. [DOI: 10.1007/978-3-319-89701-1_1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Tennyson J, Yurchenko SN. Laboratory spectra of hot molecules: Data needs for hot super-Earth exoplanets. ACTA ACUST UNITED AC 2017. [DOI: 10.1016/j.molap.2017.05.002] [Citation(s) in RCA: 64] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-3881/aa859c] [Citation(s) in RCA: 94] [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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The Cosmic Shoreline: The Evidence that Escape Determines which Planets Have Atmospheres, and what this May Mean for Proxima Centauri B. ACTA ACUST UNITED AC 2017. [DOI: 10.3847/1538-4357/aa7846] [Citation(s) in RCA: 103] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Madhusudhan N, Agúndez M, Moses JI, Hu Y. Exoplanetary Atmospheres-Chemistry, Formation Conditions, and Habitability. SPACE SCIENCE REVIEWS 2016; 205:285-348. [PMID: 28057962 PMCID: PMC5207327 DOI: 10.1007/s11214-016-0254-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
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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THE IMPRINT OF EXOPLANET FORMATION HISTORY ON OBSERVABLE PRESENT-DAY SPECTRA OF HOT JUPITERS. ACTA ACUST UNITED AC 2016. [DOI: 10.3847/0004-637x/832/1/41] [Citation(s) in RCA: 189] [Impact Index Per Article: 23.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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THE MUSCLES TREASURY SURVEY. III. X-RAY TO INFRARED SPECTRA OF 11 M AND K STARS HOSTING PLANETS. ACTA ACUST UNITED AC 2016. [DOI: 10.3847/0004-637x/824/2/102] [Citation(s) in RCA: 107] [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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Krissansen-Totton J, Bergsman DS, Catling DC. On Detecting Biospheres from Chemical Thermodynamic Disequilibrium in Planetary Atmospheres. ASTROBIOLOGY 2016; 16:39-67. [PMID: 26789355 DOI: 10.1089/ast.2015.1327] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Atmospheric chemical disequilibrium has been proposed as a method for detecting extraterrestrial biospheres from exoplanet observations. Chemical disequilibrium is potentially a generalized biosignature since it makes no assumptions about particular biogenic gases or metabolisms. Here, we present the first rigorous calculations of the thermodynamic chemical disequilibrium in Solar System atmospheres, in which we quantify the available Gibbs energy: the Gibbs free energy of an observed atmosphere minus that of atmospheric gases reacted to equilibrium. The purely gas phase disequilibrium in Earth's atmosphere is mostly attributable to O2 and CH4. The available Gibbs energy is not unusual compared to other Solar System atmospheres and smaller than that of Mars. However, Earth's fluid envelope contains an ocean, allowing gases to react with water and requiring a multiphase calculation with aqueous species. The disequilibrium in Earth's atmosphere-ocean system (in joules per mole of atmosphere) ranges from ∼20 to 2 × 10(6) times larger than the disequilibria of other atmospheres in the Solar System, where Mars is second to Earth. Only on Earth is the chemical disequilibrium energy comparable to the thermal energy per mole of atmosphere (excluding comparison to Titan with lakes, where quantification is precluded because the mean lake composition is unknown). Earth's disequilibrium is biogenic, mainly caused by the coexistence of N2, O2, and liquid water instead of more stable nitrate. In comparison, the O2-CH4 disequilibrium is minor, although kinetics requires a large CH4 flux into the atmosphere. We identify abiotic processes that cause disequilibrium in the other atmospheres. Our metric requires minimal assumptions and could potentially be calculated from observations of exoplanet atmospheres. However, further work is needed to establish whether thermodynamic disequilibrium is a practical exoplanet biosignature, requiring an assessment of false positives, noisy observations, and other detection challenges. Our Matlab code and databases for these calculations are available, open source.
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Affiliation(s)
- Joshua Krissansen-Totton
- 1 Department of Earth and Space Sciences/Astrobiology Program, University of Washington , Seattle, Washington
| | - David S Bergsman
- 2 Department of Chemical Engineering, Stanford University , Stanford, California
| | - David C Catling
- 1 Department of Earth and Space Sciences/Astrobiology Program, University of Washington , Seattle, Washington
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Cauley PW, Redfield S, Jensen AG, Barman T, Endl M, Cochran WD. OPTICAL HYDROGEN ABSORPTION CONSISTENT WITH A THIN BOW SHOCK LEADING THE HOT JUPITER HD 189733B. ACTA ACUST UNITED AC 2015. [DOI: 10.1088/0004-637x/810/1/13] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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Ehrenreich D, Bourrier V, Wheatley PJ, des Etangs AL, Hébrard G, Udry S, Bonfils X, Delfosse X, Désert JM, Sing DK, Vidal-Madjar A. A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b. Nature 2015; 522:459-61. [DOI: 10.1038/nature14501] [Citation(s) in RCA: 326] [Impact Index Per Article: 36.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2015] [Accepted: 04/27/2015] [Indexed: 11/09/2022]
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Misra A, Krissansen-Totton J, Koehler MC, Sholes S. Transient Sulfate Aerosols as a Signature of Exoplanet Volcanism. ASTROBIOLOGY 2015; 15:462-477. [PMID: 26053611 DOI: 10.1089/ast.2014.1204] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Geological activity is thought to be important for the origin of life and for maintaining planetary habitability. We show that transient sulfate aerosols could be a signature of exoplanet volcanism and therefore of a geologically active world. A detection of transient aerosols, if linked to volcanism, could thus aid in habitability evaluations of the exoplanet. On Earth, subduction-induced explosive eruptions inject SO2 directly into the stratosphere, leading to the formation of sulfate aerosols with lifetimes of months to years. We demonstrate that the rapid increase and gradual decrease in sulfate aerosol loading associated with these eruptions may be detectable in transit transmission spectra with future large-aperture telescopes, such as the James Webb Space Telescope (JWST) and European Extremely Large Telescope (E-ELT), for a planetary system at a distance of 10 pc, assuming an Earth-like atmosphere, bulk composition, and size. Specifically, we find that a signal-to-noise ratio of 12.1 and 7.1 could be achieved with E-ELT (assuming photon-limited noise) for an Earth analogue orbiting a Sun-like star and M5V star, respectively, even without multiple transits binned together. We propose that the detection of this transient signal would strongly suggest an exoplanet volcanic eruption, if potential false positives such as dust storms or bolide impacts can be ruled out. Furthermore, because scenarios exist in which O2 can form abiotically in the absence of volcanic activity, a detection of transient aerosols that can be linked to volcanism, along with a detection of O2, would be a more robust biosignature than O2 alone.
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Affiliation(s)
- Amit Misra
- 1 Department of Astronomy, University of Washington , Seattle, Washington
- 2 University of Washington Astrobiology Program, University of Washington , Seattle, Washington
| | - Joshua Krissansen-Totton
- 2 University of Washington Astrobiology Program, University of Washington , Seattle, Washington
- 3 Department of Earth and Space Sciences, University of Washington , Seattle, Washington
| | - Matthew C Koehler
- 2 University of Washington Astrobiology Program, University of Washington , Seattle, Washington
- 3 Department of Earth and Space Sciences, University of Washington , Seattle, Washington
| | - Steven Sholes
- 2 University of Washington Astrobiology Program, University of Washington , Seattle, Washington
- 3 Department of Earth and Space Sciences, University of Washington , Seattle, Washington
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Luger R, Barnes R, Lopez E, Fortney J, Jackson B, Meadows V. Habitable evaporated cores: transforming mini-Neptunes into super-Earths in the habitable zones of M dwarfs. ASTROBIOLOGY 2015; 15:57-88. [PMID: 25590532 DOI: 10.1089/ast.2014.1215] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We show that photoevaporation of small gaseous exoplanets ("mini-Neptunes") in the habitable zones of M dwarfs can remove several Earth masses of hydrogen and helium from these planets and transform them into potentially habitable worlds. We couple X-ray/extreme ultraviolet (XUV)-driven escape, thermal evolution, tidal evolution, and orbital migration to explore the types of systems that may harbor such "habitable evaporated cores" (HECs). We find that HECs are most likely to form from planets with ∼1 M⊕ solid cores with up to about 50% H/He by mass, though whether or not a given mini-Neptune forms a HEC is highly dependent on the early XUV evolution of the host star. As terrestrial planet formation around M dwarfs by accumulation of local material is likely to form planets that are small and dry, evaporation of small migrating mini-Neptunes could be one of the dominant formation mechanisms for volatile-rich Earths around these stars.
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Affiliation(s)
- R Luger
- 1 Astronomy Department, University of Washington , Seattle, Washington
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Kislyakova KG, Holmström M, Lammer H, Odert P, Khodachenko ML. Magnetic moment and plasma environment of HD 209458b as determined from Lyα observations. Science 2014; 346:981-4. [DOI: 10.1126/science.1257829] [Citation(s) in RCA: 100] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Kristina G. Kislyakova
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria
| | - Mats Holmström
- Swedish Institute of Space Physics, PO Box 812, SE-98128 Kiruna, Sweden
| | - Helmut Lammer
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria
| | - Petra Odert
- Institute of Physics, University of Graz, Universitätsplatz 5, A-8010 Graz, Austria
| | - Maxim L. Khodachenko
- Space Research Institute, Austrian Academy of Sciences, Schmiedlstrasse 6, A-8042 Graz, Austria
- Skobeltsyn Institute of Nuclear Physics, Moscow State University, Leninskie Gory, 119992 Moscow, Russia
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Lavvas P, Koskinen T, Yelle RV. ELECTRON DENSITIES AND ALKALI ATOMS IN EXOPLANET ATMOSPHERES. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/0004-637x/796/1/15] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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37
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Burrows AS. Highlights in the study of exoplanet atmospheres. Nature 2014; 513:345-52. [PMID: 25230656 DOI: 10.1038/nature13782] [Citation(s) in RCA: 71] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 06/23/2014] [Indexed: 11/09/2022]
Abstract
Exoplanets are now being discovered in profusion. To understand their character, however, we require spectral models and data. These elements of remote sensing can yield temperatures, compositions and even weather patterns, but only if significant improvements in both the parameter retrieval process and measurements are made. Despite heroic efforts to garner constraining data on exoplanet atmospheres and dynamics, reliable interpretation has frequently lagged behind ambition. I summarize the most productive, and at times novel, methods used to probe exoplanet atmospheres; highlight some of the most interesting results obtained; and suggest various broad theoretical topics in which further work could pay significant dividends.
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Affiliation(s)
- Adam S Burrows
- Astrophysical Sciences, Princeton University, 4 Ivy Lane, Princeton, New Jersey 08544, USA
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38
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Hatzes AP. The role of space telescopes in the characterization of transiting exoplanets. Nature 2014; 513:353-7. [PMID: 25230657 DOI: 10.1038/nature13783] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2014] [Accepted: 07/15/2014] [Indexed: 11/09/2022]
Abstract
Characterization studies now have a dominant role in the field of exoplanets. Such studies include the measurement of an exoplanet's bulk density, its brightness temperature and the chemical composition of its atmosphere. The use of space telescopes has played a key part in the characterization of transiting exoplanets. These facilities offer astronomers data of exquisite precision and temporal sampling as well as access to wavelength regions of the electromagnetic spectrum that are inaccessible from the ground. Space missions such as the Hubble Space Telescope, Microvariability and Oscillations of Stars (MOST), Spitzer Space Telescope, Convection, Rotation and Planetary Transits (CoRoT), and Kepler have rapidly advanced our knowledge of the physical properties of exoplanets and have blazed a trail for a series of future space missions that will help us to understand the observed diversity of exoplanets.
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Affiliation(s)
- Artie P Hatzes
- Thüringer Landessternwarte Tautenburg, Sternwarte 5, D-07778, Germany
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39
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Instrumentation for the detection and characterization of exoplanets. Nature 2014; 513:358-66. [DOI: 10.1038/nature13784] [Citation(s) in RCA: 87] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2014] [Accepted: 07/15/2014] [Indexed: 11/08/2022]
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Misra A, Meadows V, Crisp D. THE EFFECTS OF REFRACTION ON TRANSIT TRANSMISSION SPECTROSCOPY: APPLICATION TO EARTH-LIKE EXOPLANETS. ACTA ACUST UNITED AC 2014. [DOI: 10.1088/0004-637x/792/1/61] [Citation(s) in RCA: 84] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Moses JI. Chemical kinetics on extrasolar planets. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2014; 372:20130073. [PMID: 24664912 PMCID: PMC6380885 DOI: 10.1098/rsta.2013.0073] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
Chemical kinetics plays an important role in controlling the atmospheric composition of all planetary atmospheres, including those of extrasolar planets. For the hottest exoplanets, the composition can closely follow thermochemical-equilibrium predictions, at least in the visible and infrared photosphere at dayside (eclipse) conditions. However, for atmospheric temperatures approximately <2000K, and in the uppermost atmosphere at any temperature, chemical kinetics matters. The two key mechanisms by which kinetic processes drive an exoplanet atmosphere out of equilibrium are photochemistry and transport-induced quenching. I review these disequilibrium processes in detail, discuss observational consequences and examine some of the current evidence for kinetic processes on extrasolar planets.
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Affiliation(s)
- Julianne I Moses
- Space Science Institute, 4750 Walnut Street, Suite 205, Boulder, CO 80301, USA
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Encrenaz T. Infrared spectroscopy of exoplanets: observational constraints. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2014; 372:20130083. [PMID: 24664918 PMCID: PMC3982427 DOI: 10.1098/rsta.2013.0083] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The exploration of transiting extrasolar planets is an exploding research area in astronomy. With more than 400 transiting exoplanets identified so far, these discoveries have made possible the development of a new research field, the spectroscopic characterization of exoplanets' atmospheres, using both primary and secondary transits. However, these observations have been so far limited to a small number of targets. In this paper, we first review the advantages and limitations of both primary and secondary transit methods. Then, we analyse what kind of infrared spectra can be expected for different types of planets and discuss how to optimize the spectral range and the resolving power of the observations. Finally, we propose a list of favourable targets for present and future ground-based observations.
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Affiliation(s)
- Thérèse Encrenaz
- LESIA, Paris Observatory, CNRS, 5 place Janssen, Meudon 92195, France
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Tinetti G. Galactic planetary science. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2014; 372:20130077. [PMID: 24664916 PMCID: PMC3982425 DOI: 10.1098/rsta.2013.0077] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Planetary science beyond the boundaries of our Solar System is today in its infancy. Until a couple of decades ago, the detailed investigation of the planetary properties was restricted to objects orbiting inside the Kuiper Belt. Today, we cannot ignore that the number of known planets has increased by two orders of magnitude nor that these planets resemble anything but the objects present in our own Solar System. Whether this fact is the result of a selection bias induced by the kind of techniques used to discover new planets--mainly radial velocity and transit--or simply the proof that the Solar System is a rarity in the Milky Way, we do not know yet. What is clear, though, is that the Solar System has failed to be the paradigm not only in our Galaxy but even 'just' in the solar neighbourhood. This finding, although unsettling, forces us to reconsider our knowledge of planets under a different light and perhaps question a few of the theoretical pillars on which we base our current 'understanding'. The next decade will be critical to advance in what we should perhaps call Galactic planetary science. In this paper, I review highlights and pitfalls of our current knowledge of this topic and elaborate on how this knowledge might arguably evolve in the next decade. More critically, I identify what should be the mandatory scientific and technical steps to be taken in this fascinating journey of remote exploration of planets in our Galaxy.
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Mocquet A, Grasset O, Sotin C. Very high-density planets: a possible remnant of gas giants. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2014; 372:20130164. [PMID: 24664925 DOI: 10.1098/rsta.2013.0164] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/03/2023]
Abstract
Data extracted from the Extrasolar Planets Encyclopaedia (see http://exoplanet.eu) show the existence of planets that are more massive than iron cores that would have the same size. After meticulous verification of the data, we conclude that the mass of the smallest of these planets is actually not known. However, the three largest planets, Kepler-52b, Kepler-52c and Kepler-57b, which are between 30 and 100 times the mass of the Earth, have indeed density larger than an iron planet of the same size. This observation triggers this study that investigates under which conditions these planets could represent the naked cores of gas giants that would have lost their atmospheres during their migration towards the star. This study shows that for moderate viscosity values (10(25) Pa s or lower), large values of escape rate and associated unloading stress rate during the atmospheric loss process lead to the explosion of extremely massive planets. However, for moderate escape rate, the bulk viscosity and finite-strain incompressibility of the cores of giant planets can be large enough to retain a very high density during geological time scales. This would make those a new kind of planet, which would help in understanding the interior structure of the gas giants. However, this new family of exoplanets adds some degeneracy for characterizing terrestrial exoplanets.
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Affiliation(s)
- A Mocquet
- LPG-Nantes, UMR-CNRS 6112, Université de Nantes, , 2 rue de la Houssinière, 44322 Nantes Cedex 03, France
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Koskinen TT, Lavvas P, Harris MJ, Yelle RV. Thermal escape from extrasolar giant planets. PHILOSOPHICAL TRANSACTIONS. SERIES A, MATHEMATICAL, PHYSICAL, AND ENGINEERING SCIENCES 2014; 372:20130089. [PMID: 24664923 PMCID: PMC3982429 DOI: 10.1098/rsta.2013.0089] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
The detection of hot atomic hydrogen and heavy atoms and ions at high altitudes around close-in extrasolar giant planets (EGPs) such as HD209458b implies that these planets have hot and rapidly escaping atmospheres that extend to several planetary radii. These characteristics, however, cannot be generalized to all close-in EGPs. The thermal escape mechanism and mass loss rate from EGPs depend on a complex interplay between photochemistry and radiative transfer driven by the stellar UV radiation. In this study, we explore how these processes change under different levels of irradiation on giant planets with different characteristics. We confirm that there are two distinct regimes of thermal escape from EGPs, and that the transition between these regimes is relatively sharp. Our results have implications for thermal mass loss rates from different EGPs that we discuss in the context of currently known planets and the detectability of their upper atmospheres.
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Affiliation(s)
- Tommi T. Koskinen
- Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Boulevard, Tucson, AZ 85721-0092, USA
- e-mail:
| | - Panayotis Lavvas
- Groupe de Spectrométrie Moléculaire et Atmosphérique, UMR CNRS 6089, Université Reims Champagne-Ardenne, 51687 Reims, France
| | - Matthew J. Harris
- Department of Physics and Astronomy, University College London, Gower Street, London WC1E 6BT, UK
| | - Roger V. Yelle
- Lunar and Planetary Laboratory, University of Arizona, 1629 E. University Boulevard, Tucson, AZ 85721-0092, USA
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46
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Misra A, Meadows V, Claire M, Crisp D. Using dimers to measure biosignatures and atmospheric pressure for terrestrial exoplanets. ASTROBIOLOGY 2014; 14:67-86. [PMID: 24432758 PMCID: PMC3928785 DOI: 10.1089/ast.2013.0990] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
We present a new method to probe atmospheric pressure on Earth-like planets using (O2-O2) dimers in the near-infrared. We also show that dimer features could be the most readily detectable biosignatures for Earth-like atmospheres and may even be detectable in transit transmission with the James Webb Space Telescope (JWST). The absorption by dimers changes more rapidly with pressure and density than that of monomers and can therefore provide additional information about atmospheric pressures. By comparing the absorption strengths of rotational and vibrational features to the absorption strengths of dimer features, we show that in some cases it may be possible to estimate the pressure at the reflecting surface of a planet. This method is demonstrated by using the O2 A band and the 1.06 μm dimer feature, either in transmission or reflected spectra. It works best for planets around M dwarfs with atmospheric pressures between 0.1 and 10 bar and for O2 volume mixing ratios above 50% of Earth's present-day level. Furthermore, unlike observations of Rayleigh scattering, this method can be used at wavelengths longer than 0.6 μm and is therefore potentially applicable, although challenging, to near-term planet characterization missions such as JWST. We also performed detectability studies for JWST transit transmission spectroscopy and found that the 1.06 and 1.27 μm dimer features could be detectable (SNR>3) for an Earth analogue orbiting an M5V star at a distance of 5 pc. The detection of these features could provide a constraint on the atmospheric pressure of an exoplanet and serve as biosignatures for oxygenic photosynthesis. We calculated the required signal-to-noise ratios to detect and characterize O2 monomer and dimer features in direct imaging-reflected spectra and found that signal-to-noise ratios greater than 10 at a spectral resolving power of R=100 would be required.
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Affiliation(s)
- Amit Misra
- University of Washington Astronomy Department, Seattle, Washington, USA
- NAI Virtual Planetary Laboratory, Seattle, Washington, USA
- University of Washington Astrobiology Program, Seattle, Washington, USA
| | - Victoria Meadows
- University of Washington Astronomy Department, Seattle, Washington, USA
- NAI Virtual Planetary Laboratory, Seattle, Washington, USA
- University of Washington Astrobiology Program, Seattle, Washington, USA
| | - Mark Claire
- NAI Virtual Planetary Laboratory, Seattle, Washington, USA
- Department of Earth and Environmental Sciences, University of St Andrews, Fife, Scotland
- Blue Marble Space Institute of Science, Seattle, Washington, USA
| | - Dave Crisp
- NAI Virtual Planetary Laboratory, Seattle, Washington, USA
- Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
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47
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Ollivier M, Maurel MC. Planetary Environments and Origins of Life. BIO WEB OF CONFERENCES 2014. [DOI: 10.1051/bioconf/20140200001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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48
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Erkaev NV, Lammer H, Odert P, Kulikov YN, Kislyakova KG, Khodachenko ML, Güdel M, Hanslmeier A, Biernat H. XUV-exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets. Part I: atmospheric expansion and thermal escape. ASTROBIOLOGY 2013; 13:1011-29. [PMID: 24251443 PMCID: PMC3865622 DOI: 10.1089/ast.2012.0957] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/21/2012] [Accepted: 09/07/2013] [Indexed: 05/15/2023]
Abstract
The recently discovered low-density "super-Earths" Kepler-11b, Kepler-11f, Kepler-11d, Kepler-11e, and planets such as GJ 1214b represent the most likely known planets that are surrounded by dense H/He envelopes or contain deep H₂O oceans also surrounded by dense hydrogen envelopes. Although these super-Earths are orbiting relatively close to their host stars, they have not lost their captured nebula-based hydrogen-rich or degassed volatile-rich steam protoatmospheres. Thus, it is interesting to estimate the maximum possible amount of atmospheric hydrogen loss from a terrestrial planet orbiting within the habitable zone of late main sequence host stars. For studying the thermosphere structure and escape, we apply a 1-D hydrodynamic upper atmosphere model that solves the equations of mass, momentum, and energy conservation for a planet with the mass and size of Earth and for a super-Earth with a size of 2 R(Earth) and a mass of 10 M(Earth). We calculate volume heating rates by the stellar soft X-ray and extreme ultraviolet radiation (XUV) and expansion of the upper atmosphere, its temperature, density, and velocity structure and related thermal escape rates during the planet's lifetime. Moreover, we investigate under which conditions both planets enter the blow-off escape regime and may therefore experience loss rates that are close to the energy-limited escape. Finally, we discuss the results in the context of atmospheric evolution and implications for habitability of terrestrial planets in general.
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Affiliation(s)
- Nikolai V. Erkaev
- Institute of Computational Modelling, Siberian Division of the Russian Academy of Sciences, Krasnoyarsk, Russian Federation
- Siberian Federal University, Krasnoyarsk, Russian Federation
| | - Helmut Lammer
- Austrian Academy of Sciences, Space Research Institute, Graz, Austria
| | - Petra Odert
- Austrian Academy of Sciences, Space Research Institute, Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
| | - Yuri N. Kulikov
- Polar Geophysical Institute (PGI), Russian Academy of Sciences, Murmansk, Russian Federation
| | - Kristina G. Kislyakova
- Austrian Academy of Sciences, Space Research Institute, Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
| | - Maxim L. Khodachenko
- Austrian Academy of Sciences, Space Research Institute, Graz, Austria
- Institute of Nuclear Physics, Moscow State University, Moscow, Russian Federation
| | - Manuel Güdel
- Institute of Astrophysics, University of Vienna, Austria
| | | | - Helfried Biernat
- Austrian Academy of Sciences, Space Research Institute, Graz, Austria
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49
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Kislyakova KG, Lammer H, Holmström M, Panchenko M, Odert P, Erkaev NV, Leitzinger M, Khodachenko ML, Kulikov YN, Güdel M, Hanslmeier A. XUV-exposed, non-hydrostatic hydrogen-rich upper atmospheres of terrestrial planets. Part II: hydrogen coronae and ion escape. ASTROBIOLOGY 2013; 13:1030-48. [PMID: 24283926 PMCID: PMC3865724 DOI: 10.1089/ast.2012.0958] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/15/2023]
Abstract
We studied the interactions between the stellar wind plasma flow of a typical M star, such as GJ 436, and the hydrogen-rich upper atmosphere of an Earth-like planet and a "super-Earth" with a radius of 2 R(Earth) and a mass of 10 M(Earth), located within the habitable zone at ∼0.24 AU. We investigated the formation of extended atomic hydrogen coronae under the influences of the stellar XUV flux (soft X-rays and EUV), stellar wind density and velocity, shape of a planetary obstacle (e.g., magnetosphere, ionopause), and the loss of planetary pickup ions on the evolution of hydrogen-dominated upper atmospheres. Stellar XUV fluxes that are 1, 10, 50, and 100 times higher compared to that of the present-day Sun were considered, and the formation of high-energy neutral hydrogen clouds around the planets due to the charge-exchange reaction under various stellar conditions was modeled. Charge-exchange between stellar wind protons with planetary hydrogen atoms, and photoionization, lead to the production of initially cold ions of planetary origin. We found that the ion production rates for the studied planets can vary over a wide range, from ∼1.0×10²⁵ s⁻¹ to ∼5.3×10³⁰ s⁻¹, depending on the stellar wind conditions and the assumed XUV exposure of the upper atmosphere. Our findings indicate that most likely the majority of these planetary ions are picked up by the stellar wind and lost from the planet. Finally, we estimated the long-time nonthermal ion pickup escape for the studied planets and compared them with the thermal escape. According to our estimates, nonthermal escape of picked-up ionized hydrogen atoms over a planet's lifetime within the habitable zone of an M dwarf varies between ∼0.4 Earth ocean equivalent amounts of hydrogen (EO(H)) to <3 EO(H) and usually is several times smaller in comparison to the thermal atmospheric escape rates.
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Affiliation(s)
- Kristina G. Kislyakova
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
| | - Helmut Lammer
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria
| | | | | | - Petra Odert
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria
- Institute of Physics, University of Graz, Graz, Austria
| | - Nikolai V. Erkaev
- Institute of Computational Modelling, Siberian Division of the Russian Academy of Sciences, Krasnoyarsk, Russian Federation
| | | | - Maxim L. Khodachenko
- Space Research Institute, Austrian Academy of Sciences, Graz, Austria
- SINP, Moscow State University, Moscow, Russian Federation
| | - Yuri N. Kulikov
- Polar Geophysical Institute (PGI), Russian Academy of Sciences, Murmansk, Russian Federation
| | - Manuel Güdel
- Institute of Astrophysics, University of Vienna, Austria
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50
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Lammer H, Blanc M, Benz W, Fridlund M, Foresto VCD, Güdel M, Rauer H, Udry S, Bonnet RM, Falanga M, Charbonneau D, Helled R, Kley W, Linsky J, Elkins-Tanton LT, Alibert Y, Chassefière E, Encrenaz T, Hatzes AP, Lin D, Liseau R, Lorenzen W, Raymond SN. The science of exoplanets and their systems. ASTROBIOLOGY 2013; 13:793-813. [PMID: 24015759 DOI: 10.1089/ast.2013.0997] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/02/2023]
Abstract
A scientific forum on "The Future Science of Exoplanets and Their Systems," sponsored by Europlanet and the International Space Science Institute (ISSI) and co-organized by the Center for Space and Habitability (CSH) of the University of Bern, was held during December 5 and 6, 2012, in Bern, Switzerland. It gathered 24 well-known specialists in exoplanetary, Solar System, and stellar science to discuss the future of the fast-expanding field of exoplanetary research, which now has nearly 1000 objects to analyze and compare and will develop even more quickly over the coming years. The forum discussions included a review of current observational knowledge, efforts for exoplanetary atmosphere characterization and their formation, water formation, atmospheric evolution, habitability aspects, and our understanding of how exoplanets interact with their stellar and galactic environment throughout their history. Several important and timely research areas of focus for further research efforts in the field were identified by the forum participants. These scientific topics are related to the origin and formation of water and its delivery to planetary bodies and the role of the disk in relation to planet formation, including constraints from observations as well as star-planet interaction processes and their consequences for atmosphere-magnetosphere environments, evolution, and habitability. The relevance of these research areas is outlined in this report, and possible themes for future ISSI workshops are identified that may be proposed by the international research community over the coming 2-3 years.
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Affiliation(s)
- Helmut Lammer
- 1 Space Research Institute , Austrian Academy of Sciences, Graz, Austria
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