JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e
Jacob Lustig-Yaeger
The Astrophysical Journal Letters · 2025
JWST transmission spectroscopy of TRAPPIST-1e places observational constraints on whether this habitable-zone rocky planet retains a secondary atmosphere, finding no definitive detection but narrowing the viable atmospheric parameter space.
Brief
As part of the JWST-TST DREAMS (Determining if Rocky Exoplanets have Atmospheres via Multitransit Spectroscopy) program, Lustig-Yaeger et al. (2025) analyzed JWST transmission spectra of TRAPPIST-1e, a rocky planet receiving roughly Earth-equivalent stellar flux from the M8 dwarf TRAPPIST-1 (~40 light-years away). The study targets secondary atmospheres formed by outgassing rather than primordial hydrogen envelopes, which would have been stripped by the star's intense early UV and X-ray flux. While no definitive atmospheric detection is reported, the data constrain which atmospheric compositions and surface pressures remain consistent with observations. The results contribute to the critical empirical question of whether M-dwarf habitable-zone planets can retain atmospheres long enough to support surface liquid water.
Metadata
- Category
- Search
- Venue
- The Astrophysical Journal Letters
- Type
- Peer-reviewed
- Year
- 2025
- Authors
- Jacob Lustig-Yaeger
- Access
- Paywalled
- Programs
- JWST-TST DREAMS
- Instruments
- JWST NIRSpec
- Data sources
- JWST transmission spectra of TRAPPIST-1e
- Tags
- astrobiology, biosignature, exoplanet-atmospheres, habitability, SETI-prerequisites, transmission-spectroscopy
Key points
- TRAPPIST-1e occupies the habitable zone of its host M8 dwarf star and receives approximately 66% of Earth's insolation, making it among the most favorable rocky exoplanet targets for atmospheric characterization.
- The DREAMS program applies multi-transit co-addition of JWST transmission spectra to build signal-to-noise sufficient to detect or rule out secondary atmospheric signatures on rocky planets, a regime inaccessible to pre-JWST facilities.
- Secondary atmosphere constraints focus on high-mean-molecular-weight compositions (e.g., CO2-dominated or N2/CO2 mixtures), as low-mean-molecular-weight envelopes would have been stripped by TRAPPIST-1's historically active stellar environment.
- A flat or featureless transmission spectrum, the expected null result if no atmosphere exists, remains consistent with the observations, though thick CO2 or other high-MMW scenarios may be disfavored at some confidence level.
- TRAPPIST-1e joins TRAPPIST-1b and TRAPPIST-1c as DREAMS targets, enabling a comparative planetology approach across the system's irradiation gradient.
- Atmospheric retention around M-dwarf planets is the central upstream question for any biosignature search in these systems; this paper provides one of the first direct empirical tests for the habitable-zone case.
Most interesting
- TRAPPIST-1e is simultaneously one of the most Earth-like known exoplanets by flux and radius, and one of the most threatened by stellar activity, its host star flares at rates orders of magnitude higher than the Sun.
- The DREAMS acronym was constructed to match the program's goal: determining whether these planets are dead airless rocks or worlds with the atmospheric prerequisite for life.
- TRAPPIST-1 is so dim that each transit of TRAPPIST-1e removes less than 0.5% of the stellar flux, yet JWST's infrared sensitivity is sufficient to search for atmospheric spectral features within that window.
- Secondary atmospheres on rocky planets must be continuously replenished by volcanic outgassing to persist, meaning a positive detection would imply ongoing geological activity, not just atmospheric survival from formation.
- The TRAPPIST-1 system has been observed by JWST more intensively than any other multi-planet system, with results for individual planets arriving sequentially across 2023–2025 as transit observations accumulate.