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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: model experiment description paper 19 Aug 2019

Submitted as: model experiment description paper | 19 Aug 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Geoscientific Model Development (GMD).

TRAPPIST-1 Habitable Atmosphere Intercomparison (THAI). Motivations and protocol

Thomas Fauchez1,2,3, Martin Turbet4,5, Eric T. Wolf6,7, Ian Boutle8, Michael J. Way9,3, Anthony D. Del Genio9, Nathan J. Mayne10, Konstantinos Tsigaridis9,12, Ravi K. Kopparapu2,3, Jun Yang11, Francois Forget4, Avi Mandell2,3, and Shawn D. Domagal Goldman2,3 Thomas Fauchez et al.
  • 1Goddard Earth Sciences Technology and Research (GESTAR), Universities Space Research Association (USRA), Columbia Maryland, USA
  • 2NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
  • 3GSFC Sellers Exoplanet Environments Collaboration
  • 4Laboratoire de Méteorologie Dynamique, IPSL, Sorbonne Universités, UPMC Univ Paris 06, CNRS, 4 Place Jussieu, 75005 Paris, France
  • 5Observatoire Astronomique de l’Université de Genève, Université de Genève, Chemin des Maillettes 51, 1290 Versoix, Switzerland
  • 6Laboratory for Atmospheric and Space Physics, Department of Atmospheric and Oceanic Sciences, University of Colorado Boulder, Boulder, CO, USA
  • 7NASA Astrobiology Institute’s Virtual Planetary Laboratory, Seattle, WA, USA
  • 8Met Office, Exeter, UK
  • 9NASA Goddard Institute for Space Studies, New York, NY 10025, USA
  • 10University of Exeter, Exeter, UK
  • 11Dept. of Atmospheric and Oceanic Sciences, School of Physics, Peking University, Beijing, 100871
  • 12Center for Climate Systems Research, Columbia University, New York, NY, USA

Abstract. Upcoming telescopes such as the James Webb Space Telescope (JWST), the European Extremely Large Telescope (E-ELT), the Thirty Meter Telescope (TMT) or the Giant Magellan Telescope (GMT) may soon be able to characterize, through transmission spectroscopy, the atmospheres of rocky exoplanets orbiting nearby M dwarfs. One of the most promising candidates is the late M dwarf system TRAPPIST-1 which has seven known transiting planets for which Transit Timing Variation (TTV) measurements suggest that they are terrestrial in nature, with a possible enrichment in volatiles. Among these seven planets, TRAPPIST-1e seems to be the most promising candidate to have habitable surface conditions, receiving ~ 66 % of the Earth's incident radiation, and thus needing only modest greenhouse gas inventories to raise surface temperatures to allow surface liquid water to exist. TRAPPIST-1e is therefore one of the prime targets for JWST atmospheric characterization. In this context, the modeling of its potential atmosphere is an essential step prior to observation. Global Climate Models (GCMs) offer the most detailed way to simulate planetary atmospheres. However, intrinsic differences exist between GCMs which can lead to different climate prediction and thus observability of gas and/or cloud features in transmission and thermal emission spectra. Such differences should preferably be known prior to observations. In this paper we present a protocol to inter-compare planetary GCMs. Four testing cases are considered for TRAPPIST-1e but the methodology is applicable to other rocky exoplanets in the Habitable Zone. The four test cases included two land planets composed of pure N2 and pure CO2, respectively, and two aqua planets with a modern Earth and a CO2 rich composition. Currently there are 4 participating models (LMDG, ROCKE3D, ExoCAM, UM), however this protocol is intended to let other teams participate as well.

Thomas Fauchez et al.
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Status: final response (author comments only)
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Thomas Fauchez et al.
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Publications Copernicus
Short summary
Atmospheric characterization of rocky exoplanets orbiting within the habitable zone of nearby M dwarf stars is around the corner with the James Webb Space Telescope (JWST) expected to be launch in 2021. Global Circulation Model (GCM) are powerful tools to model exoplanet atmospheres and to predict their habitability. However, intrinsic differences between the models can lead to various predictions. This paper presents an experiment protocol to evaluate these differences.
Atmospheric characterization of rocky exoplanets orbiting within the habitable zone of nearby M...