Range of best-fit phase curve and eclipse models for TRAPPIST-1 b and c. The detrended data are shown with gray dots and binned data with black dots. Red curves show the light curve model for each JWST program that observed TRAPPIST-1 b and c at 15µm using MIRI F1500W; the shading spans the range of models drawn from the posterior distribution of the day flux, night flux and phase offset for planets b and c from Analysis # 1 at 2-σ. The top panel shows the phase curve from GO 3077; the second row displays the five visits from GO 1177 (PI: Greene); and the third row presents the four visits from GO 2304 (PI: Kreidberg), along with a zoom-in on the double occultation observed in GO 3077. The expected transit and eclipse timings for each planet from [19] are shown in vertical dashed and plain lines respectively (purple for b, orange for c, and green for g). — astro-ph.EP
We report JWST/MIRI 15 μm phase curves of TRAPPIST-1 b and c, revealing thermal emission consistent with their irradiation levels, assuming no efficient heat redistribution.
We find that TRAPPIST-1 b shows a high dayside brightness temperature (490 ± 17 K), no significantly detectable nightside emission (Fb,Night,max = 39+55−27 ppm), and no phase offset — features consistent with a low-albedo, airless ultramafic rocky surface.
TRAPPIST-1 c exhibits a lower dayside brightness temperature (369 ± 23 K), and a nightside flux statistically indistinguishable from that of TRAPPIST-1 b (Fc,Night,max = 62+60−43 ppm).
Atmosphere models with surface pressures ≥1 bar and efficient greenhouse effects are strongly disfavoured for both planets. TRAPPIST-1 b is unlikely to possess any substantial atmosphere, while TRAPPIST-1 c may retain a tenuous, greenhouse-poor O2-dominated atmosphere or be similarly airless with a more reflective surface.
These results suggest divergent evolutionary pathways or atmospheric loss processes, despite similar compositions. These measurements tightly constrain atmosphere retention in the inner TRAPPIST-1 system.
Michaël Gillon, Elsa Ducrot, Taylor J. Bell, Ziyu Huang, Andrew Lincowski, Xintong Lyu, Alice Maurel, Alexandre Revol, Eric Agol, Emeline Bolmont, Chuanfei Dong, Thomas J. Fauchez, Daniel D.B. Koll, Jérémy Leconte, Victoria S. Meadows, Franck Selsis, Martin Turbet, Benjamin Charnay, Laetita Delre, Brice-Olivier Demory, Aaron Householder, Sebastian Zieba, David Berardo, Achrène Dyrek, Billy Edwards, Julien de Wit, Thomas P. Greene, Renyu Hu, Nicolas Iro, Laura Kreidberg, Pierre-Olivier Lagage, Jacob Lustig-Yaeger, Aishwarya Iyer
Comments: 72 pages, 4 main text Figures, 20 Extended Data Figures, 6 Supplementary Figures. Accepted for publication in Nature Astronomy
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2509.02128 [astro-ph.EP] (or arXiv:2509.02128v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2509.02128
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From: Elsa Ducrot
[v1] Tue, 2 Sep 2025 09:23:03 UTC (12,845 KB)
https://arxiv.org/abs/2509.02128
Astrobiology,