JWST data hints that Trappist-1e may have an atmosphere. More transits will test if this world could support liquid water.
Recent observations with NASA’s advanced JWST telescope have revealed a planet located 41 light-years from Earth that may possess an atmosphere. This planet orbits within the “habitable zone,” the region around a star where temperatures allow liquid water to remain on the surface of a rocky body. Water is essential because it is one of the fundamental requirements for sustaining life.
If upcoming observations verify these results, this would represent the first time a rocky planet in a star’s habitable zone has been confirmed to hold an atmosphere. The research is detailed in two studies published in the journal Astrophysical Journal Letters.
What defines the habitable zone
The habitable zone is characterized in part by the temperature range produced by a star’s heat. A planet must orbit at just the right distance, where conditions are not excessively hot or cold (earning the nickname “the Goldilocks zone”).
However, having the correct orbital distance is not enough. To retain liquid water, exoplanets (worlds that orbit stars beyond our solar system) generally require an atmosphere capable of creating a greenhouse effect. Greenhouse gases absorb and re-emit heat, keeping the planet warmer and preventing water from escaping into space.
Together with an international team of colleagues, we trained the largest telescope in space, NASA’s JWST, on a planet called Trappist-1 e. We wanted to determine whether this rocky world, which lies in its star’s habitable zone, hosts an atmosphere. The planet is one of seven rocky worlds known to orbit a small, cool “red dwarf” star called Trappist-1.
Rocky exoplanets are everywhere in our galaxy. The discovery of abundant rocky planets in the 2010s by the Kepler and Tess space telescopes has profound implications for our place in the Universe.
Most of the rocky exoplanets we’ve found so far orbit red dwarf stars, which are much cooler than the Sun (typically 2500°C/4,500°F, compared to the Sun’s 5,600°C/10,000°F). This isn’t because planets around Sun-like stars are rare, there are just technical reasons why it is easier to find and study planets orbiting smaller stars.
Red dwarfs also offer many advantages when we seek to measure the properties of their planets. Because the stars are cooler, their habitable zones, where temperatures are favorable to liquid water, are located much closer in comparison with our solar system, because the Sun is much hotter. As such, a year for a rocky planet with the temperature of Earth that orbits a red dwarf star can be just a few days to a week compared to Earth’s 365 days.
Measuring planetary atmospheres
One way to detect exoplanets is to measure the slight dimming of light when the planet transits, or passes in front of, its star. Because planets orbiting red dwarfs take less time to complete an orbit, astronomers can observe more transits in a shorter space of time, making it easier to gather data.
During a transit, astronomers can measure absorption from gases in the planet’s atmosphere (if it has one). Absorption refers to the process whereby certain gases absorb light at different wavelengths, preventing it from passing through. This provides scientists with a way of detecting which gases are present in an atmosphere.
Crucially, the smaller the star, the greater the fraction of its light is blocked by a planet’s atmosphere during transit. So red dwarf stars are one of the best places for us to look for the atmospheres of rocky exoplanets.
Located at a relatively close distance of 41 light-years from Earth, the Trappist-1 system has attracted significant attention since its discovery in 2016. Three of the planets, Trappist-1d, Trappist-1e, and Trappist-1f (the third, fourth, and fifth planets from the star) lie within the habitable zone.
JWST has been conducting a systematic search for atmospheres on the Trappist-1 planets since 2022. The results for the three innermost planets, Trappist-1b, Trappist-1c, and Trappist-1d, point to these worlds most likely being bare rocks with thin atmospheres at best. But the planets further out, which are bombarded with less radiation and energetic flares from the star, could still potentially possess atmospheres.
Challenges of stellar contamination
We observed Trappist-1e, the planet in the center of the star’s habitable zone, with JWST on four separate occasions from June-October 2023. We immediately noticed that our data was strongly affected by what’s known as “stellar contamination” from hot and cold active regions (similar to sunspots) on Trappist-1. This required a careful analysis to deal with. In the end, it took our team over a year to sift through the data and distinguish the signal coming from the star from that of the planet.
We are seeing two possible explanations for what’s going on at Trappist-1e. The most exciting possibility is that the planet has a so-called secondary atmosphere containing heavy molecules such as nitrogen and methane. But the four observations we obtained aren’t yet precise enough to rule out the alternative explanation of the planet being a bare rock with no atmosphere.
Should Trappist-1e indeed have an atmosphere, it will be the first time we have found an atmosphere on a rocky planet in the habitable zone of another star.
Atmosphere and habitability potential
Since Trappist-1e lies firmly in the habitable zone, a thick atmosphere with a sufficient greenhouse effect could allow for liquid water on the planet’s surface. To establish whether or not Trappist-1e is habitable, we will need to measure the concentrations of greenhouse gases like carbon dioxide and methane. These initial observations are an important step in that direction, but more observations with JWST will be needed to be sure if Trappist-1e has an atmosphere and, if so, to measure the concentrations of these gases.
As we speak, an additional 15 transits of Trappist-1e are underway and should be complete by the end of 2025. Our follow-up observations use a different observing strategy where we target consecutive transits of Trappist-1b (which is a bare rock) and Trappist-1e. This will allow us to use the bare rock to better “trace out” the hot and cold active regions on the star. Any excess absorption of gases seen only during Trappist-1e’s transits will be uniquely caused by the planet’s atmosphere.
So within the next two years, we should have a much better picture of how Trappist-1e compares to the rocky planets in our solar system.
References: “JWST-TST DREAMS: NIRSpec/PRISM Transmission Spectroscopy of the Habitable Zone Planet TRAPPIST-1 e” by Néstor Espinoza, Natalie H. Allen, Ana Glidden, Nikole K. Lewis, Sara Seager, Caleb I. Cañas, David Grant, Amélie Gressier, Shelby Courreges, Kevin B. Stevenson, Sukrit Ranjan, Knicole Colón, Brett M. Morris, Ryan J. MacDonald, Douglas Long, Hannah R. Wakeford, Jeff A. Valenti, Lili Alderson, Natasha E. Batalha, Ryan C. Challener, Jingcheng Huang, Zifan Lin, Dana R. Louie, Elijah Mullens, Daniel Valentine, C. Matt Mountain, Laurent Pueyo, Marshall D. Perrin, Andrea Bellini, Jens Kammerer, Mattia Libralato, Isabel Rebollido, Emily Rickman, Sangmo Tony Sohn and Roeland P. van der Marel, 8 September 2025, The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/adf42e
“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.
DOI: 10.3847/2041-8213/adf62e
Adapted from an article originally published in The Conversation.
Hannah Wakeford receives funding from UK Research and Innovation (UKRI) framework under the UK government’s Horizon Europe funding guarantee for an ERC Starter Grant (grant number EP/Y006313/1).
Ryan MacDonald has recieved funding from NASA through the NASA Hubble Fellowship grant HST-HF2-51513.001, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555.
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