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

Piaulet-Ghorayeb, C; Benneke, B; Turbet, M; Moore, K; Roy, P; Lim, O; Doyon, R; Fauchez, TJ; Albert, L; Radica, M; Coulombe, L; Lafrenière, D; Cowan, NB; Belzile, D; Musfirat, K; Kaur, M; L’Heureux, A; Johnstone, D; MacDonald, RJ; Allart, R; Dang, L; Kaltenegger, L; Pelletier, S; Rowe, JF; Taylor, J

Climate Research Collection

Journal article

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

Abstract:: 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 (Teq,A=0.3 = 262 K). Here we present the first 0.6–5.2 μm 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 CH4, H2O, CO, SO2, and CO2. Our observations exclude clear, hydrogen-dominated atmospheres with high confidence (>3σ). We leverage our constraints on even trace amounts of CH4, H2O, and CO2 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.

Publication status:: Published

Peer review status:: Peer reviewed

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APA Style

Piaulet-Ghorayeb, C., Benneke, B., Turbet, M., Moore, K., Roy, P., Lim, O., Doyon, R., Fauchez, T. J., Albert, L., Radica, M., Coulombe, L., Lafrenière, D., Cowan, N. B., Belzile, D., Musfirat, K., Kaur, M., L’Heureux, A., Johnstone, D., MacDonald, R. J., … Taylor, J. (2025). Strict Limits on Potential Secondary Atmospheres on the Temperate Rocky Exo-Earth TRAPPIST-1 d. The Astrophysical Journal, 989(2).

MLA Style

Piaulet-Ghorayeb, C, et al. “Strict Limits on Potential Secondary Atmospheres on the Temperate Rocky Exo-Earth TRAPPIST-1 d.” The Astrophysical Journal, vol. 989, no. 2, 2025.

Chicago Style

Piaulet-Ghorayeb, C, B Benneke, M Turbet, et al. 2025. “Strict Limits on Potential Secondary Atmospheres on the Temperate Rocky Exo-Earth TRAPPIST-1 d.” The Astrophysical Journal 989 (2).
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