Strict Limits on Potential Secondary Atmospheres on the Temperate Rocky Exo-Earth TRAPPIST-1 d

Strict Limits on Potential Secondary Atmospheres on the Temperate Rocky Exo-Earth TRAPPIST-1 d

The nearby TRAPPIST-1 system, with its seven small rocky planets orbiting a late-type M8 star, offers an unprecedented opportunity to search for secondary atmospheres on temperate terrestrial worlds. In particular, the 0.8 R _⊕ TRAPPIST-1 d lies at the edge of the habitable zone ( T _eq,A=0.3  = 262...

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Main Authors: Caroline Piaulet-Ghorayeb, Björn Benneke, Martin Turbet, Keavin Moore, Pierre-Alexis Roy, Olivia Lim, René Doyon, Thomas J. Fauchez, Loïc Albert, Michael Radica, Louis-Philippe Coulombe, David Lafrenière, Nicolas B. Cowan, Danika Belzile, Kamrul Musfirat, Mehramat Kaur, Alexandrine L’Heureux, Doug Johnstone, Ryan J. MacDonald, Romain Allart, Lisa Dang, Lisa Kaltenegger, Stefan Pelletier, Jason F. Rowe, Jake Taylor, Jake D. Turner
Format: Article
Language:English
Published: IOP Publishing 2025-01-01
Series:The Astrophysical Journal
Subjects:
Extrasolar rocky planets
Exoplanet atmospheres
Exoplanets
M dwarf stars
Stellar activity
Starspots
Online Access:https://doi.org/10.3847/1538-4357/adf207
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Summary:The nearby TRAPPIST-1 system, with its seven small rocky planets orbiting a late-type M8 star, offers an unprecedented opportunity to search for secondary atmospheres on temperate terrestrial worlds. In particular, the 0.8 R _⊕ TRAPPIST-1 d lies at the edge of the habitable zone ( T _eq,A=0.3  = 262 K). Here we present the first 0.6–5.2 μ m NIRSpec/PRISM transmission spectrum of TRAPPIST-1 d from two transits with JWST. We find that stellar contamination from unocculted bright heterogeneities introduces 500–1000 ppm visit-dependent slopes, consistent with constraints from the out-of-transit stellar spectrum. Once corrected, the transmission spectrum is flat within ±100–150 ppm, showing no evidence for a haze-like slope or molecular absorption despite NIRSpec/PRISM’s sensitivity to CH _4 , H _2 O, CO, SO _2 , and CO _2 . Our observations exclude clear, hydrogen-dominated atmospheres with high confidence (>3 σ ). We leverage our constraints on even trace amounts of CH _4 , H _2 O, and CO _2 to further reject high mean molecular weight compositions analogous to a haze-free Titan, a cloud-free Venus, early Mars, and both Archean Earth and a cloud-free modern Earth scenario (>95% confidence). If TRAPPIST-1 d retains an atmosphere, it is likely extremely thin or contains high-altitude aerosols, with water cloud formation at the terminator predicted by 3D global climate models. Alternatively, if TRAPPIST-1 d is airless, our evolutionary models indicate that TRAPPIST-1 b, c, and d must have formed with ≲4 Earth oceans of water, though this would not preclude atmospheres on the cooler habitable-zone planets TRAPPIST-1 e, f, and g.
ISSN:1538-4357

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