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New JWST data narrows the search for an atmosphere on TRAPPIST-1e
The Earth-size exoplanet TRAPPIST-1e, located about 40 light-years away, has yielded its first detailed clues about a possible atmosphere thanks to observations from NASA’s James Webb Space Telescope (JWST). The planet orbits within the habitable zone of the red dwarf TRAPPIST-1, where surface temperatures could in principle allow liquid water — but only if an atmosphere capable of moderating temperature remains.
The Earth-size exoplanet TRAPPIST-1 e, depicted at the lower right, is silhouetted as it passes in front of its flaring host star in this artist’s concept of the TRAPPIST-1 system. Credit: NASA, ESA, CSA, J. Olmsted (STScI)
How the observations were made and why they matter
Researchers used JWST’s Near-Infrared Spectrograph (NIRSpec) to observe four transits of TRAPPIST-1e, collecting high-precision spectra as the planet passed in front of its star. During transit spectroscopy, starlight filters through any atmospheric shell and produces wavelength-dependent absorption features; repeated transits improve the signal and help identify molecular signatures such as water vapor, carbon dioxide or hydrogen.
Results published on 8 September 2025 in Astrophysical Journal Letters — from an international team that includes scientists at the University of Bristol, MIT and the Space Telescope Science Institute — rule out several scenarios while leaving others open. The data strongly exclude a primordial hydrogen-dominated envelope, but do not yet provide a definitive detection of a dense secondary atmosphere.
Key findings: no primordial hydrogen, hints of a secondary atmosphere
Primordial atmosphere ruled out
Analyses indicate TRAPPIST-1e no longer retains the light hydrogen-helium envelope it may have formed with. Stellar activity from the host red dwarf — including frequent flares and high-energy radiation — is expected to strip light gases early in a planet’s history. As co-author Dr. David Grant notes, the observations further eliminate a thick, hydrogen-rich primary atmosphere for planet e.
Possible secondary atmosphere and greenhouse implications
That absence leaves open the possibility of a heavier secondary atmosphere composed of molecules such as carbon dioxide, water vapor or nitrogen. Modeling work led by Dr. Ana Glidden suggests a CO2-dominated atmosphere like Venus is unlikely, but moderate amounts of CO2 could produce a greenhouse effect sufficient to allow stable liquid water in some scenarios. On a tidally locked world like TRAPPIST-1e — with a permanent dayside and nightside — modest greenhouse warming could support a global ocean or localized regions of melt surrounded by ice.
Dr. Hannah Wakeford, who helped design the JWST observing program, emphasizes that the new infrared data refine earlier Hubble measurements and provide unprecedented detail about the planet’s atmospheric possibilities, while stressing that some scenarios remain indistinguishable until more data arrive.
Next steps: more transits and comparative planet studies
Planned follow-up includes additional JWST observations of TRAPPIST-1e and comparative spectroscopy of neighboring planets in the same system, especially the hotter inner world TRAPPIST-1b. Comparing spectra across multiple planets will help separate stellar activity signals from true atmospheric features and constrain how atmospheres evolve under intense red-dwarf irradiation.
Principal investigator Dr. Néstor Espinoza comments that Webb’s infrared sensitivity is revealing details never previously accessible for Earth-sized exoplanets, and that the initial four transits are just the beginning of a larger campaign.
Expert Insight
Dr. Elena Martínez, an astrophysicist specializing in exoplanet atmospheres, adds: "The elimination of a hydrogen-rich primary atmosphere is an important zeroing-in step. What remains is a plausible set of secondary atmospheres that could allow liquid water, but confirming any one of them requires more transits and careful treatment of stellar contamination. JWST gives us the spectral reach to do that in the coming years."
Conclusion
JWST observations have advanced our understanding of TRAPPIST-1e by excluding a primordial hydrogen envelope and by revealing possible signatures consistent with a heavier secondary atmosphere. While the data do not yet confirm an atmosphere or surface oceans, they significantly narrow viable scenarios and prioritize follow-up observations. Continued transit spectroscopy with JWST and comparative studies of other TRAPPIST-1 planets will be critical to determine whether this nearby Earth-sized world could retain conditions suitable for liquid water and, ultimately, habitability.
Source: scitechdaily
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