TRAPPIST-1

JWST TRAPPIST-1 e/b Program: Motivation and First Observations

By Keith Cowing
Status Report
astro-ph.EP
December 9, 2025
Filed under , , , , , , , , , , ,
JWST TRAPPIST-1 e/b Program: Motivation and First Observations
Top: White light curves of observation 1, observation 3, and observation 15 from the NA reduction, both at native time resolution in black and binned to 25x in red for visibility. All transits are labeled by planet. Observation 1 also has a large flare that occurs right before the egress of planet e. Shown in the upper right is a schematic of our proposed setup, with the true overlapping planetary transit chords taken from Agol et al. (2021). Middle: Hα light curve from the NA reduction. Peaks in Hα correspond to flaring events, many of which are not visible in the white light curve, at least without hints to their location from the Hα signature. Note that the light curves are binned in time to 50x (to approximately 70 second bins) relative to that shown in the white light curve for visibility in the low signal single wavelengths shown. Bottom: Transmission spectrum of TRAPPIST-1 e (top) and TRAPPIST-1 b (bottom) for observation 1, observation 3, and observation 15 from left to right. — astro-ph.EP

One of the forefront goals in the field of exoplanets is the detection of an atmosphere on a temperate terrestrial exoplanet, and among the best suited systems to do so is TRAPPIST-1.

However, JWST transit observations of the TRAPPIST-1 planets show significant contamination from stellar surface features that we are unable to confidently model. Here, we present the motivation and first observations of our JWST multi-cycle program of TRAPPIST-1 e, which utilize close transits of the airless TRAPPIST-1 b to model-independently correct for stellar contamination, with the goal of determining whether TRAPPIST-1 e has an Earth-like mean molecular weight atmosphere containing CO2.

We present our simulations, which show that with the 15 close transit observations, we will be able to detect this atmosphere on TRAPPIST-1 e at ΔlnZ=5 or greater confidence assuming we are able to correct for stellar contamination using the close transit observations.

We also show the first three observations of our program. We find that our ability to correct for stellar contamination can be inhibited when strong stellar flares are present, as flares can break the assumption that the star does not change meaningfully between planetary transits.

The cleanest observation demonstrates the removal of stellar contamination contribution through an increased preference for a flat line over the original TRAPPIST-1 e spectrum, but highlights how minor data analysis assumptions can propagate significantly when searching for small atmospheric signals. This is amplified when using the signals from multiple planets, which is important to consider as we continue our atmospheric search.

Natalie H. Allen, Néstor Espinoza, V. A. Boehm, Caleb I. Cañas, Kevin B. Stevenson, Nikole K. Lewis, Ryan J. MacDonald, Brett M. Morris, Eric Agol, Knicole Colón, Hannah Diamond-Lowe, Ana Glidden, Amélie Gressier, Jingcheng Huang, Zifan Lin, Douglas Long, Dana R. Louie, Meredith A. MacGregor, Laurent Pueyo, Benjamin V. Rackham, Sukrit Ranjan, Sara Seager, Guadalupe Tovar Mendoza, Jeff A. Valenti, Daniel Valentine, Roeland P. van der Marel, Hannah R. Wakeford

Comments: 26 pages, 15 figures, accepted for publication in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2512.07695 [astro-ph.EP] (or arXiv:2512.07695v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2512.07695
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Submission history
From: Natalie Allen
[v1] Mon, 8 Dec 2025 16:35:58 UTC (36,129 KB)
https://arxiv.org/abs/2512.07695
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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