No thick atmosphere around TRAPPIST-1 b and c from JWST thermal phase curves

May 2026 • 2026NatAs..10..674G

Authors • Gillon, Michaël • Ducrot, Elsa • Bell, Taylor J. • Huang, Ziyu • Lincowski, Andrew P. • Lyu, Xintong • Maurel, Alice • Revol, Alexandre • Agol, Eric • Bolmont, Émeline • Dong, Chuanfei • Fauchez, Thomas J. • Koll, Daniel D. B. • Leconte, Jérémy • Meadows, Victoria S. • Selsis, Franck • Turbet, Martin • Charnay, Benjamin • Delrez, Laetitia • Demory, Brice-Olivier • Householder, Aaron • Zieba, Sebastian • Berardo, David • Dyrek, Achrène • Edwards, Billy • de Wit, Julien • Greene, Thomas P. • Hu, Renyu • Iro, Nicolas • Kreidberg, Laura • Lagage, Pierre-Olivier • Lustig-Yaeger, Jacob • Iyer, Aishwarya

Abstract • The survival of dense secondary atmospheres around temperate rocky planets orbiting low-mass red dwarfs remains an important open question. Here we show that the thermal phase curves of TRAPPIST-1 b and TRAPPIST-1 c, measured with the James Webb Space Telescope at 15 μm, are consistent with bare rocky surfaces rather than thick atmospheres. TRAPPIST-1 b exhibits a high dayside brightness temperature (490 ± 17 K), no significant nightside emission and no phase offset—features indicative of a dark, airless surface. TRAPPIST-1 c shows a cooler dayside (369 ± 23 K) and a similarly cold nightside, consistent with either a tenuous, oxygen-rich atmosphere or an equally airless, more reflective surface. Models with surface pressures above ~1 bar are strongly disfavoured for both planets. These results suggest divergent evolutionary pathways or atmospheric loss processes despite their similar compositions.

Links

• DATA https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html
• ELECTR https://doi.org/10.1038%2Fs41550-026-02806-9