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Title: Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets

Abstract

The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could harbor liquid water on their surfaces. Ultraviolet observations are essential to measuring their high-energy irradiation and searching for photodissociated water escaping from their putative atmospheres. Our new observations of the TRAPPIST-1 Ly α line during the transit of TRAPPIST-1c show an evolution of the star emission over three months, preventing us from assessing the presence of an extended hydrogen exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape. However, TRAPPIST-1e to h might have lost less than three Earth oceans if hydrodynamic escape stopped once they entered the habitable zone (HZ). We caution that these estimates remain limited by the large uncertainty on the planet masses. They likely represent upper limits on the actual water loss because our assumptions maximize the X-rays to ultraviolet-driven escape, while photodissociation in the upper atmospheres should be the limiting process. Late-stage outgassing could also have contributedmore » significant amounts of water for the outer, more massive planets after they entered the HZ. While our results suggest that the outer planets are the best candidates to search for water with the JWST , they also highlight the need for theoretical studies and complementary observations in all wavelength domains to determine the nature of the TRAPPIST-1 planets and their potential habitability.« less

Authors:
;  [1];  [2];  [3];  [4];  [5];  [6];  [7];  [8]; ; ;  [9];  [10];  [11];  [12];  [13]
  1. Observatoire de l’Université de Genève, 51 chemin des Maillettes, 1290 Sauverny (Switzerland)
  2. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)
  3. Laboratoire AIM Paris-Saclay, CEA/DRF—CNRS—Univ. Paris Diderot—IRFU/SAp, Centre de Saclay, F-91191 Gif-sur-Yvette Cedex (France)
  4. Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125 (United States)
  5. Department of Physics, University of Warwick, Coventry CV4 7AL (United Kingdom)
  6. Center for Astrophysics and Space Science, University of California San Diego, La Jolla, CA 92093 (United States)
  7. Cavendish Laboratory, J J Thomson Avenue, Cambridge, CB3 0HE (United Kingdom)
  8. University of Bern, Center for Space and Habitability, Sidlerstrasse 5, CH-3012, Bern (Switzerland)
  9. Institut dAstrophysique et de Géophysique, Université de Liège, Allée du 6 Aout 19C, B-4000 Liège (Belgium)
  10. Laboratoire dAstrophysique de Bordeaux, Univ. Bordeaux, CNRS, B18N, allée Geoffroy Saint-Hilaire, F-33615 Pessac (France)
  11. NASA Johnson Space Center, 2101 NASA Parkway, Houston, Texas, 77058 (United States)
  12. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, Maryland 21218 (United States)
  13. Institute of Astronomy, Madingley Road, Cambridge CB3 0HA (United Kingdom)
Publication Date:
OSTI Identifier:
22663166
Resource Type:
Journal Article
Journal Name:
Astronomical Journal (Online)
Additional Journal Information:
Journal Volume: 154; Journal Issue: 3; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 1538-3881
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; DISSOCIATION; DWARF STARS; EXOSPHERE; HUMIDITY; HYDRODYNAMICS; HYDROGEN; IRRADIATION; LOSSES; MASS; ORBITS; PHOTOLYSIS; PLANETS; SATELLITE ATMOSPHERES; SATELLITES; STAR EVOLUTION; ULTRAVIOLET RADIATION; WATER; WAVELENGTHS

Citation Formats

Bourrier, V., Ehrenreich, D., Wit, J. de, Bolmont, E., Stamenković, V., Wheatley, P. J., Burgasser, A. J, Delrez, L., Demory, B.-O., Gillon, M., Jehin, E., Grootel, V. Van, Leconte, J., Lederer, S. M., Lewis, N., and Triaud, A. H. M. J. Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets. United States: N. p., 2017. Web. doi:10.3847/1538-3881/AA859C.
Bourrier, V., Ehrenreich, D., Wit, J. de, Bolmont, E., Stamenković, V., Wheatley, P. J., Burgasser, A. J, Delrez, L., Demory, B.-O., Gillon, M., Jehin, E., Grootel, V. Van, Leconte, J., Lederer, S. M., Lewis, N., & Triaud, A. H. M. J. Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets. United States. doi:10.3847/1538-3881/AA859C.
Bourrier, V., Ehrenreich, D., Wit, J. de, Bolmont, E., Stamenković, V., Wheatley, P. J., Burgasser, A. J, Delrez, L., Demory, B.-O., Gillon, M., Jehin, E., Grootel, V. Van, Leconte, J., Lederer, S. M., Lewis, N., and Triaud, A. H. M. J. Fri . "Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets". United States. doi:10.3847/1538-3881/AA859C.
@article{osti_22663166,
title = {Temporal Evolution of the High-energy Irradiation and Water Content of TRAPPIST-1 Exoplanets},
author = {Bourrier, V. and Ehrenreich, D. and Wit, J. de and Bolmont, E. and Stamenković, V. and Wheatley, P. J. and Burgasser, A. J and Delrez, L. and Demory, B.-O. and Gillon, M. and Jehin, E. and Grootel, V. Van and Leconte, J. and Lederer, S. M. and Lewis, N. and Triaud, A. H. M. J.},
abstractNote = {The ultracool dwarf star TRAPPIST-1 hosts seven Earth-size transiting planets, some of which could harbor liquid water on their surfaces. Ultraviolet observations are essential to measuring their high-energy irradiation and searching for photodissociated water escaping from their putative atmospheres. Our new observations of the TRAPPIST-1 Ly α line during the transit of TRAPPIST-1c show an evolution of the star emission over three months, preventing us from assessing the presence of an extended hydrogen exosphere. Based on the current knowledge of the stellar irradiation, we investigated the likely history of water loss in the system. Planets b to d might still be in a runaway phase, and planets within the orbit of TRAPPIST-1g could have lost more than 20 Earth oceans after 8 Gyr of hydrodynamic escape. However, TRAPPIST-1e to h might have lost less than three Earth oceans if hydrodynamic escape stopped once they entered the habitable zone (HZ). We caution that these estimates remain limited by the large uncertainty on the planet masses. They likely represent upper limits on the actual water loss because our assumptions maximize the X-rays to ultraviolet-driven escape, while photodissociation in the upper atmospheres should be the limiting process. Late-stage outgassing could also have contributed significant amounts of water for the outer, more massive planets after they entered the HZ. While our results suggest that the outer planets are the best candidates to search for water with the JWST , they also highlight the need for theoretical studies and complementary observations in all wavelength domains to determine the nature of the TRAPPIST-1 planets and their potential habitability.},
doi = {10.3847/1538-3881/AA859C},
journal = {Astronomical Journal (Online)},
issn = {1538-3881},
number = 3,
volume = 154,
place = {United States},
year = {2017},
month = {9}
}