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

Abstract : Seven temperate Earth-sized exoplanets readily amenable for atmospheric studies transit the nearby ultracool dwarf star TRAPPIST-1. 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.
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Nature Astronomy, Nature Publishing Group, 2018, 2 (3), pp.214 - 219. 〈10.1038/s41550-017-0374-z〉
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https://hal.archives-ouvertes.fr/hal-01729026
Contributeur : Marie-Paule Pomies <>
Soumis le : lundi 12 mars 2018 - 11:58:30
Dernière modification le : mercredi 19 septembre 2018 - 01:38:28

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Julien De Wit, Hannah Wakeford, Nikole Lewis, Laetitia Delrez, Michael Gillon, et al.. Atmospheric reconnaissance of the habitable-zone Earth-sized planets orbiting TRAPPIST-1. Nature Astronomy, Nature Publishing Group, 2018, 2 (3), pp.214 - 219. 〈10.1038/s41550-017-0374-z〉. 〈hal-01729026〉

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