Astronomers using NASA's James Webb Space Telescope have detected faint methane signals around the Earth-sized exoplanet TRAPPIST-1e, but new analysis suggests these may originate from the host star rather than the planet. Located 39 light-years away in the habitable zone of a red dwarf star, TRAPPIST-1e remains a key target for potential signs of habitability. Researchers call for more data to confirm whether the planet has an atmosphere at all.
The TRAPPIST-1 system, discovered by the Transiting Planets and Planetesimals Small Telescope project, features seven Earth-sized planets orbiting a compact red dwarf star just 39 light-years from Earth. This setup fits within the orbit of Mercury, with each planet completing a revolution in mere days. Among them, TRAPPIST-1e stands out for its position in the habitable zone, where liquid water could exist if an atmosphere regulates temperatures.
Recent observations with the James Webb Space Telescope's Near-Infrared Spectrograph targeted transits of TRAPPIST-1e, capturing starlight filtered through any potential atmosphere. Over four transits, the data revealed tentative methane indications. However, Sukrit Ranjan, an assistant professor at the University of Arizona's Lunar and Planetary Laboratory, cautions that the star—an ultracool M dwarf, smaller and dimmer than the Sun—might produce these signals itself, as it can retain atmospheric gases.
"The basic thesis for TRAPPIST-1e is this: If it has an atmosphere, it's habitable," Ranjan said. "But right now, the first-order question must be, 'Does an atmosphere even exist?'"
Two papers in the Astrophysical Journal Letters detail these JWST findings, while a third by Ranjan's team models possible atmospheres. Their analysis, comparing scenarios to Saturn's methane-rich moon Titan, deems the planet's atmosphere unlikely, attributing the signal to stellar noise. "Based on our most recent work, we suggest that the previously reported tentative hint of an atmosphere is more likely to be 'noise' from the host star," Ranjan noted. Still, an atmosphere cannot be ruled out without further evidence.
The JWST, though not optimized for Earth-sized exoplanets, offers rare insights into such worlds. Upcoming efforts include NASA's Pandora mission, launching in early 2026 under Daniel Apai at the University of Arizona's Steward Observatory. This satellite will monitor host stars during transits to distinguish stellar from planetary effects. Additionally, the team plans dual-transit observations with airless TRAPPIST-1b to isolate atmospheric signatures.
"These observations will allow us to separate what the star is doing from what is going on in the planet's atmosphere—should it have one," Ranjan explained. These steps aim to clarify TRAPPIST-1e's potential for life-supporting conditions.