When the James Webb Space Telescope (JWST) began observing exoplanets, few targets generated as much anticipation as the TRAPPIST-1 system – a compact arrangement of seven Earth-sized planets orbiting an ultracool red dwarf about 40 light-years away. Of these worlds, TRAPPIST-1 e has become a focal point because it resides in the star’s habitable zone, where conditions could theoretically allow liquid water.

In a recent SETI Live discussion, Dr. Moiya McTier spoke with Dr. Ana Glidden (MIT) and Dr. Néstor Espinoza (STScI) about JWST’s latest attempts to detect an atmosphere around TRAPPIST-1 e. Their findings underscore both the promise and the difficulty of studying small terrestrial planets at great distances, even with the most advanced instruments ever built.

Because TRAPPIST-1 e cannot be directly imaged, JWST relies on transmission spectroscopy, a method first pioneered in the early 2000s. During a planetary transit, a sliver of starlight passes through any atmosphere the planet may possess. Different molecules absorb different wavelengths, imprinting subtle spectral signatures. By measuring minuscule changes in the planet’s apparent size across wavelengths, scientists can infer the presence of gases such as carbon dioxide, methane, or water vapor.

For an Earth-sized planet orbiting a faint and magnetically active red dwarf, however, these signals are tiny – only tens of parts per million. Dr. Glidden and Dr. Espinoza are part of JWST’s DREAMS program (Deep Reconnaissance of Exoplanet Atmospheres using Multi-Instrument Spectroscopy), which aims to push JWST to its limits by observing a hot Jupiter, a warm Neptune, and the terrestrial TRAPPIST-1 e. The program has already delivered breakthroughs, including evidence of quartz clouds in the atmosphere of WASP-17 b.

In the case of TRAPPIST-1 e, analysis of four JWST transits points to two possible scenarios: the planet could possess a thin, nitrogen-dominated secondary atmosphere, or it might be largely airless. Importantly, the data show no strong signatures of carbon dioxide, ruling out a Venus-like or Mars-like carbon-dioxode-rich atmosphere. Yet the observations remain too limited to confirm the presence or absence of a more delicate gaseous envelope.

Complicating matters is the nature of the host star. Red dwarfs are small, making transits easier to detect, but they are also highly magnetically active. Their flares and coronal mass ejections could erode planetary atmospheres, and their fully convective interiors make predicting this activity challenging.

TRAPPIST-1 e is also likely tidally locked, meaning one side always faces the star. If even a modest atmosphere exists, it could redistribute heat and create a stable region near the sub-stellar point where liquid water might persist.

To refine their conclusions, the team is now collecting fifteen additional transits of TRAPPIST-1 e and observing TRAPPIST-1 b for comparison. This ambitious 130-hour effort aims to disentangle stellar variability from planetary signals, potentially leading to the first decisive confirmation – or rejection – of an atmosphere on an Earth-sized exoplanet.

For more details, read the full article by SETI Institute.