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)
More research is needed before scientists can determine whether the recently observed methane signatures point to the presence of an atmosphere or are simply the result of contamination from the host star.
Of the seven Earth-sized planets circling the red dwarf star TRAPPIST-1, one world stands out to researchers because it moves through the star’s “Goldilocks zone” – a region where liquid water could exist – but only if the planet has its own atmosphere. And where there is water, there might be life.
Two recently scientific papers detail initial observations of the TRAPPIST-1 system obtained by a research group using NASA’s James Webb Space Telescope, published in the Astrophysical Journal Letters. In these publications, the authors, including Sukrit Ranjan with the University of Arizona’s Lunar and Planetary Laboratory, present a careful analysis of the results so far and offer several potential scenarios for what the planet’s atmosphere and surface may be like.
Two recent scientific papers present the first detailed observations of the TRAPPIST-1 system obtained with NASA’s James Webb Space Telescope. Published in the Astrophysical Journal Letters, these studies analyze the early data and outline several possible explanations for what the planet’s atmosphere and surface conditions might be. Their authors include Sukrit Ranjan of the University of Arizona’s Lunar and Planetary Laboratory.
Although the findings are promising and help advance efforts to understand this nearby Earth-sized exoplanet, Ranjan advises caution in a third paper. He notes that more detailed investigation is needed to confirm whether TRAPPIST-1e has an atmosphere at all and to determine if the faint signals of methane seen by Webb actually come from the planet rather than from its star.
The TRAPPIST system takes its name from the survey that found it, the “Transiting Planets and Planetesimals Small Telescope project”. It is located about 39 light-years from Earth and looks like a scaled-down version of our own solar system. The star and all seven planets could comfortably fit within the orbit of Mercury, and each TRAPPIST planet completes a “year” in just a few Earth days.
Searching for an Atmosphere
“The basic thesis for TRAPPIST-1e is this: If it has an atmosphere, it’s habitable,” said Ranjan, who is an assistant professor at LPL. “But right now, the first-order question must be, ‘Does an atmosphere even exist?'”
To answer this question, researchers aimed the space telescope’s powerful Near-Infrared Spectrograph, or NIRSpec, instrument at the TRAPPIST system as planet TRAPPIST-1e transited – i.e. passed in front of – its host star. During a transit, starlight filters through the planet’s atmosphere, if there is one, and is partially absorbed, allowing astronomers to deduce what chemicals it may contain. With each additional transit, the atmospheric contents become clearer as more data is collected.
The four transits of TRAPPIST-1e studied by the team revealed hints of methane. However, because TRAPPIST-1e’s star is a so-called M dwarf, about one-tenth the size of our sun and only slightly larger than Jupiter, its unique properties call for extra caution when interpreting data, Ranjan said.
“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,” he 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 rule on this question, Ranjan and colleagues simulated scenarios in which TRAPPIST-1e might have a methane-rich atmosphere and evaluated the probability for each of them. In the most likely scenario among the ones tested, the planet resembled Saturn’s methane-rich moon, Titan. However, the work showed that even that scenario was very unlikely.
“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.”
Advancing Tools and Techniques
Ranjan pointed out that while James Webb is revolutionizing exoplanet science, the telescope was not originally designed to study small, Earth-like exoplanets.
“It was designed long before we knew such worlds existed, and we are fortunate that it can study them at all,” he said. “There’s only a handful of Earth-sized planets in existence for which it could potentially ever measure any kind of detailed atmosphere composition.”
New answers could come from NASA’s Pandora mission, currently in development and slated for launch in early 2026. Led by Daniel Apai, professor of astronomy and planetary sciences at the U of A’s Steward Observatory, Pandora is a small satellite designed to characterize exoplanet atmospheres and their host stars. Pandora will monitor stars with potentially habitable planets before, during, and after they transit in front of their host stars.
In addition, researchers hope that an ongoing, larger round of observations and new analytical techniques could finally tip the scale in one way or another. Currently, the collaboration is focusing on a technique known as dual transit: by observing the star when both TRAPPIST-1e, and TRAPPIST-1b, the innermost and airless planet of the system, pass in front of their star at the same time.
“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 said.
References:
“The Photochemical Plausibility of Warm Exo-Titans Orbiting M Dwarf Stars” by Sukrit Ranjan, Nicholas F. Wogan, Ana Glidden, Jingyu Wang, Kevin B. Stevenson, Nikole Lewis, Tommi Koskinen, Sara Seager, Hannah R. Wakeford and Roeland P. van der Marel, 3 November 2025, The Astrophysical Journal Letters.
“JWST-TST DREAMS: Secondary Atmosphere Constraints for the Habitable Zone Planet TRAPPIST-1 e” by Ana Glidden, Sukrit Ranjan, Sara Seager, Néstor Espinoza, Ryan J. MacDonald, Natalie H. Allen, Caleb I. Cañas, David Grant, Amélie Gressier, Kevin B.
Stevenson, Natasha E. Batalha, Nikole K. Lewis, Douglas Long, Hannah R. Wakeford, Lili Alderson, Ryan C.
Challener, Knicole Colón, Jingcheng Huang, Zifan Lin, Dana R. Louie, Elijah Mullens, Kristin S. Sotzen, Jeff A. Valenti, Daniel Valentine, Mark Clampin, C.
Matt Mountain, Marshall Perrin and Roeland P. van der Marel, 8 September 2025, The Astrophysical Journal Letters.
“The Photochemical Plausibility of Warm Exo-Titans Orbiting M Dwarf Stars” by Sukrit Ranjan, Nicholas F. Wogan, Ana Glidden, Jingyu Wang, Kevin B. Stevenson, Nikole Lewis, Tommi Koskinen, Sara Seager, Hannah R. Wakeford and Roeland P. van der Marel, 3 November 2025, The Astrophysical Journal Letters.
Funding: NASA Headquarters, Space Telescope Science Institute
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