Strict limits on potential secondary atmospheres on the temperate rocky exo-Earth TRAPPIST-1 d
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| Format: | Preprint |
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2025
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| author | Piaulet-Ghorayeb, Caroline Benneke, Björn Turbet, Martin Moore, Keavin Roy, Pierre-Alexis Lim, Olivia Doyon, René Fauchez, Thomas J. Albert, Loïc Radica, Michael Coulombe, Louis-Philippe Lafrenière, David Cowan, Nicolas B. Belzile, Danika Musfirat, Kamrul Kaur, Mehramat L'Heureux, Alexandrine Johnstone, Doug MacDonald, Ryan J. Allart, Romain Dang, Lisa Kaltenegger, Lisa Pelletier, Stefan Rowe, Jason F. Taylor, Jake Turner, Jake D. |
| author_facet | Piaulet-Ghorayeb, Caroline Benneke, Björn Turbet, Martin Moore, Keavin Roy, Pierre-Alexis Lim, Olivia Doyon, René Fauchez, Thomas J. Albert, Loïc Radica, Michael Coulombe, Louis-Philippe Lafrenière, David Cowan, Nicolas B. Belzile, Danika Musfirat, Kamrul Kaur, Mehramat L'Heureux, Alexandrine Johnstone, Doug MacDonald, Ryan J. Allart, Romain Dang, Lisa Kaltenegger, Lisa Pelletier, Stefan Rowe, Jason F. Taylor, Jake Turner, Jake D. |
| contents | 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 Earth-radii planet TRAPPIST-1 d lies at the edge of the habitable zone (equilibrium temperature ~262 K). Here we present the first 0.6-5.2 micron NIRSpec/PRISM transmission spectrum of TRAPPIST-1 d from two transits with JWST. We find that stellar contamination from unocculted bright heterogeneities introduces 500-1,000 ppm visit-dependent slopes, consistent with constraints from the out-of-transit stellar spectrum. Once corrected, the transmission spectrum is flat within $\pm$100-150 ppm, showing no evidence for a haze-like slope or molecular absorption despite NIRSpec/PRISM's sensitivity to CH4, H2O, CO, SO2, and CO2. Our observations exclude clear, hydrogen-dominated atmospheres with high confidence (greater than 3$σ$). We leverage our constraints on even trace amounts of CH4, H2O, and CO2 to further reject high mean molecular weight compositions analogous to Titan, a cloud-free Venus, early Mars, and both Archean Earth and a cloud-free modern Earth scenario (greater than 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 less than approximately 4 Earth oceans of water, though this would not preclude atmospheres on the cooler habitable-zone planets TRAPPIST-1 e, f, and g. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2508_08416 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Strict limits on potential secondary atmospheres on the temperate rocky exo-Earth TRAPPIST-1 d Piaulet-Ghorayeb, Caroline Benneke, Björn Turbet, Martin Moore, Keavin Roy, Pierre-Alexis Lim, Olivia Doyon, René Fauchez, Thomas J. Albert, Loïc Radica, Michael Coulombe, Louis-Philippe Lafrenière, David Cowan, Nicolas B. Belzile, Danika Musfirat, Kamrul Kaur, Mehramat L'Heureux, Alexandrine Johnstone, Doug MacDonald, Ryan J. Allart, Romain Dang, Lisa Kaltenegger, Lisa Pelletier, Stefan Rowe, Jason F. Taylor, Jake Turner, Jake D. Earth and Planetary Astrophysics Solar and Stellar Astrophysics 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 Earth-radii planet TRAPPIST-1 d lies at the edge of the habitable zone (equilibrium temperature ~262 K). Here we present the first 0.6-5.2 micron NIRSpec/PRISM transmission spectrum of TRAPPIST-1 d from two transits with JWST. We find that stellar contamination from unocculted bright heterogeneities introduces 500-1,000 ppm visit-dependent slopes, consistent with constraints from the out-of-transit stellar spectrum. Once corrected, the transmission spectrum is flat within $\pm$100-150 ppm, showing no evidence for a haze-like slope or molecular absorption despite NIRSpec/PRISM's sensitivity to CH4, H2O, CO, SO2, and CO2. Our observations exclude clear, hydrogen-dominated atmospheres with high confidence (greater than 3$σ$). We leverage our constraints on even trace amounts of CH4, H2O, and CO2 to further reject high mean molecular weight compositions analogous to Titan, a cloud-free Venus, early Mars, and both Archean Earth and a cloud-free modern Earth scenario (greater than 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 less than approximately 4 Earth oceans of water, though this would not preclude atmospheres on the cooler habitable-zone planets TRAPPIST-1 e, f, and g. |
| title | Strict limits on potential secondary atmospheres on the temperate rocky exo-Earth TRAPPIST-1 d |
| topic | Earth and Planetary Astrophysics Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2508.08416 |