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Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1

de Wit, Julien and Wakeford, Hannah R. and Lewis, Nikole K. and Delrez, Laetitia and Gillon, Michaël and Selsis, Frank and Leconte, Jérémy and Demory, Brice-Olivier and Bolmont, Emeline and Bourrier, Vincent and Burgasser, Adam J. and Grimm, Simon and Jehin, Emmanuël and Lederer, Susan M. and Owen, James E. and Stamenković, Vlada and Triaud, Amaury H. M. J. (2018) Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1. Nature Astronomy, 2 (3). pp. 214-219. ISSN 2397-3366. doi:10.1038/s41550-017-0374-z.

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Seven temperate Earth-sized exoplanets readily amenable for atmospheric studies transit the nearby ultracool dwarf star TRAPPIST-1 (refs 1,2). Their atmospheric regime is unknown and could range from extended primordial hydrogen-dominated to depleted atmospheres. Hydrogen in particular is a powerful greenhouse gas that may prevent the habitability of inner planets while enabling the habitability of outer ones. An atmosphere largely dominated by hydrogen, if cloud-free, should yield prominent spectroscopic signatures in the near-infrared detectable during transits. Observations of the innermost planets have ruled out such signatures. However, the outermost planets are more likely to have sustained such a Neptune-like atmosphere. Here, we report observations for the four planets within or near the system’s habitable zone, the circumstellar region where liquid water could exist on a planetary surface. These planets do not exhibit prominent spectroscopic signatures at near-infrared wavelengths either, which rules out cloud-free hydrogen-dominated atmospheres for TRAPPIST-1 d, e and f, with significance of 8σ, 6σ and 4σ, respectively. Such an atmosphere is instead not excluded for planet g. As high-altitude clouds and hazes are not expected in hydrogen-dominated atmospheres around planets with such insolation, these observations further support their terrestrial and potentially habitable nature.

Item Type:Article
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URLURL TypeDescription ReadCube access Paper
de Wit, Julien0000-0003-2415-2191
Wakeford, Hannah R.0000-0003-4328-3867
Lewis, Nikole K.0000-0002-8507-1304
Delrez, Laetitia0000-0001-6108-4808
Gillon, Michaël0000-0003-1462-7739
Selsis, Frank0000-0001-9619-5356
Demory, Brice-Olivier0000-0002-9355-5165
Bolmont, Emeline0000-0001-5657-4503
Bourrier, Vincent0000-0002-9148-034X
Burgasser, Adam J.0000-0002-6523-9536
Stamenković, Vlada0000-0003-2416-3683
Triaud, Amaury H. M. J.0000-0002-5510-8751
Additional Information:© 2018 Springer Nature Limited. Received 08 February 2017; Accepted 20 December 2017; Published 05 February 2018. This work is based on observations made with the NASA (National Aeronautics and Space Administration)/European Space Agency HST that were obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy. These observations are associated with programme GO-14873 (principal investigator J.d.W.), support for which was provided by NASA through a grant from the Space Telescope Science Institute. H.R.W. acknowledges funding from the European Research Council (ERC) under the European Union’s Seventh Framework Programme (FP7/2007–2013)/ERC grant agreement no. 336792, and funding under the Space Telescope Science Institute Giacconi Fellowship. This work was partially conducted while on appointment to the NASA Postdoctoral Program at Goddard Space Flight Center, administered by the Universities Space Research Association through a contract with NASA. L.D. acknowledges support from the Gruber Foundation Fellowship. E.J. and M.G. are Research Associates at the Belgian Fonds (National) de la Recherche Scientifique (FRS-FNRS). The research leading to these results has received funding from the ERC under the FP/2007–2013 ERC grant agreement no. 336480, and from a grant from the Concerted Research Actions, financed by the Wallonia-Brussels Federation. B.-O.D. acknowledges support from the Swiss National Science Foundation (PP00P2–163967). This work was also partially supported by a grant from the Simons Foundation (PI Queloz, grant no. 327127). This project has received funding from the ERC under the European Union’s Horizon 2020 research and innovation programme (grant agreement no. 679030/WHIPLASH). V.B. acknowledges the financial support of the Swiss National Science Foundation. We thank D. Taylor, K. Stevenson, N. Reid and K. Sembach for their assistance in the planning, execution and/or analysis of our observations. J.d.W., H.R.W. and N.K.L. thank also the Howards-Lewis Team and F. Dory for their support and contributions during the data-processing phase of this work. Author Contributions: J.d.W. and N.K.L. led the management of the survey. J.d.W. planned the observations. J.d.W and H.R.W. led the data reduction and analysis with the support of N.K.L., L.D., M.G. and B.-O.D. J.d.W. led the data interpretation with the support of H.R.W., N.K.L., V.S., J.L., J.E.O. and F.S. Every author contributed to the writing of the manuscript and/or the HST proposal behind these observations. The authors declare no competing financial interests.
Funding AgencyGrant Number
Space Telescope Science InstituteUNSPECIFIED
European Research Council (ERC)336792
NASA Postdoctoral ProgramUNSPECIFIED
Gruber FoundationUNSPECIFIED
Fonds de la Recherche Scientifique (FNRS)UNSPECIFIED
European Research Council (ERC)336480
Wallonia-Brussels FederationUNSPECIFIED
Swiss National Science Foundation (SNSF)PP00P2-163967
Simons Foundation327127
European Research Council (ERC)679030
Subject Keywords:Exoplanets
Issue or Number:3
Record Number:CaltechAUTHORS:20200122-154316623
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Official Citation:de Wit, J., Wakeford, H.R., Lewis, N.K. et al. Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1. Nat Astron 2, 214–219 (2018).
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:100857
Deposited By: Tony Diaz
Deposited On:23 Jan 2020 00:01
Last Modified:16 Nov 2021 17:57

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