Astronomers have eyed TRAPPIST-1e as potentially one of the best candidates for life beyond Earth, but new findings suggest the very tools used to study it may be delivering misleading answers.
The TRAPPIST-1 system was discovered by the Belgian-led Transiting Planets and Planetesimals Small Telescope (TRAPPIST) project, a sky survey that collects data with the help of two Earth-based telescopes.
Thirty-nine light-years from Earth, the TRAPPIST system is smaller than ours, only extending about as far as the orbit of Mercury. Because of this, each year on a TRAPPIST world amounts to just a few days here on Earth. Of the seven planets orbiting the star, four reside in a possible habitable zone, with TRAPPIST-1e singled out for its early atmospheric readings.
However, a new paper argues that some of the promising conditions the planet is currently believed to possess may not be so ideal for alien life after all, throwing cold water on many astronomers’ hopes for TRAPPIST-1e’s potential habitability.
TRAPPIST-1: A Candidate for Life?
Scientists involved in the search for extraterrestrial life, or at least regions in space that could be habitable for such life forms, look for exoplanets that reside in a habitable “Goldilocks” zone, a region close enough to a star for surface water to remain liquid, but far enough away that it does not evaporate off as steam.
Presently, with our own watery world remaining the only planet known to host life, such liquid-water surface conditions are believed to offer the best opportunities in the search for life beyond Earth.
“The basic thesis for TRAPPIST-1e is this: If it has an atmosphere, it’s habitable,” said lead author Sukrit Ranjan of the University of Arizona Lunar and Planetary Laboratory. Unfortunately, though, the question of whether life could exist there isn’t so easily determined, and according to Ranjan, it first requires answering an even more fundamental question.
“Right now, the first-order question must be, ‘Does an atmosphere even exist?’” Ranjan says.
The James Webb Space Telescope’s Near-Infrared Spectrograph (NIRSpec) instrument has provided the best evidence to date for TRAPPIST-1e’s potential atmosphere. When the planet passes in front of its host star from the James Webb Space Telescope’s point of view, the planet—and any atmosphere it may contain—filters the star’s light. By spectroscopically analyzing changes in starlight, researchers can infer a planet’s atmospheric composition at great distances.
Questioning Habitability
In a new paper, building on two previous works published in The Astrophysical Journal Letters, Ranjan and his coauthors argue that more research is needed before scientists can really begin to feel optimistic about the prospects of TRAPPIST-1e as a habitable world. One major unresolved question is whether the tentative methane detections made by the James Webb Space Telescope really originate from the planet itself, or if they are instead coming from its host star.
The more planetary transits researchers observe, the more confidently they can interpret the results. So far, the team has studied four transits, which generally support the methane findings. Yet Ranjan notes that TRAPPIST-1’s diminutive size makes it difficult to determine the composition of TRAPPIST-1e’s atmosphere accurately, meaning caution remains essential.
“While the sun is a bright, yellow dwarf star, TRAPPIST-1 is an ultracool red dwarf, meaning it is significantly smaller, cooler and dimmer than our sun,” Ranjan explained. “Cool enough, in fact, to allow for gas molecules in its atmosphere. We reported hints of methane, but the question is, ‘is the methane attributable to molecules in the atmosphere of the planet or in the host star?’”
To determine how likely the methane signal was to be genuine, Ranjan and his team worked backward using theoretical models. They examined the conditions under which TRAPPIST-1e could have developed a methane-rich atmosphere and then estimated how probable those conditions would be. For habitability hopefuls, the news was not encouraging: the most plausible scenario resembled Saturn’s moon Titan—yet even that outcome appeared unlikely.
Looking Ahead
“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 said. “However, this does not mean that TRAPPIST-1e does not have an atmosphere – we just need more data.”
One issue with the research is that the primary tool for observing the system was not designed with small, Earth-like planets in mind. “It was designed long before we knew such worlds existed, and we are fortunate that it can study them at all,” Ranjan said. “There is only a handful of Earth-sized planets in existence for which it could potentially ever measure any kind of detailed atmosphere composition.”
Fortunately, better tools are on the horizon. NASA’s Pandora mission, set to launch next year, includes instruments specifically built for characterizing exoplanet atmospheres and monitoring stars for signs of habitable worlds. Additionally, refined techniques that compare TRAPPIST-1e’s signals to those of the airless TRAPPIST-1b may yield clearer results.
Ranjan concluded by saying, “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.”
The paper, “The Photochemical Plausibility of Warm Exo-Titans Orbiting M Dwarf Stars,” appeared in The Astrophysical Journal Letters on November 3, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.