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

By J. de Wit, H. Wakeford, N. Lewis, L. Delrez, M. Gillon, F. Selsis, J. Leconte, B. Demory, É. Bolmont, V. Bourrier and 7 more. 2018

196 citations recorded by the source corpus.

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 atmospheres3–6. Hydrogen in particular is a powerful greenhouse gas that may prevent the habitability of inner planets while enabling the habitability of outer ones6–8. 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 signatures9. However, the outermost planets are more likely to have sustained such a Neptune-like atmosphere10, 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 surface12–14. 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 insolation15, 16, these observations further support their terrestrial and potentially habitable nature.Hubble observations of the TRAPPIST-1 system exclude the presence of H2-dominated cloud-free atmospheres for the three planets within or around the system’s habitable zone. This result supports the hypothesis that these planets are terrestrial in nature.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

High Tide or Riptide on the Cosmic Shoreline? A Water-rich Atmosphere or Stellar Contamination for the Warm Super-Earth GJ 486b from JWST Observations (2023, background): “This has been confirmed by observations of terrestrial planets, including the TRAPPIST-1 planets (de Wit et al. 2016, 2018; Wakeford et al. 2019; Garcia et al. 2022; 17 NHFP Sagan Fellow.”
Disentangling the Planet from the Star in Late-Type M Dwarfs: A Case Study of TRAPPIST-1g (2018, methodology): “3 with the original published transmission spectrum in de Wit et al. (2018) which just looked at transit 1.”
Evolved Climates and Observational Discriminants for the TRAPPIST-1 Planetary System (2018, methodology): “The available data on this star in the UV to IR are limited to photometry and to measurements of Lyα from the Hubble Space Telescope (Bourrier et al. 2017).”
The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST (2019, background): “HST Wide Field Camera 3 transmission spectroscopy has ruled out H2-dominated atmospheres for most of the TRAPPIST-1 planets (de Wit et al. 2016, 2018), and instead they may have secondary outgassed atmospheres composed of relatively high mean molecular weight gases (Moran et al. 2018).”