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

Julien De Wit*, Hannah R. Wakeford, Nikole K. Lewis, Laetitia Delrez, Michaël Gillon, Frank Selsis, Jérémy Leconte, Brice Olivier Demory, Emeline Bolmont, Vincent Bourrier, Adam J. Burgasser, Simon Grimm, Emmanuël Jehin, Susan M. Lederer, James E. Owen, Vlada Stamenković, Amaury H.M.J. Triaud

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

69 Citations (Scopus)
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Abstract

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 3-6 . Hydrogen in particular is a powerful greenhouse gas that may prevent the habitability of inner planets while enabling the habitability of outer ones 6-8 . 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 9 . However, the outermost planets are more likely to have sustained such a Neptune-like atmosphere 10, 11 . 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 12-14 . 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 15, 16, these observations further support their terrestrial and potentially habitable nature.

Original languageEnglish
Pages (from-to)214-219
Number of pages6
JournalNature Astronomy
Volume2
Issue number3
Early online date5 Feb 2018
DOIs
Publication statusPublished - 1 Mar 2018

Keywords

  • exoplanets

ASJC Scopus subject areas

  • Astronomy and Astrophysics

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