Astronomers Confirm First Atmosphere on a Rocky Exoplanet in a Star's Habitable Zone, LHS 1140 b
A Harvard-led team detects escaping helium around super-Earth LHS 1140 b, the first confirmed atmosphere found on a rocky world in a habitable zone.
Overview
A team of astronomers has detected helium escaping from the upper atmosphere of LHS 1140 b, a rocky super-Earth orbiting a red dwarf star roughly 48 light-years from Earth, according to ScienceDaily. The finding, published in the journal Science on July 16, 2026, marks “the first time anyone has found an atmosphere on a rocky planet in the habitable zone of another star,” said lead author Collin Cherubim, who recently earned his Ph.D. in Earth and Planetary Sciences from Harvard University, according to ScienceDaily.
What We Know
LHS 1140 b is a super-Earth roughly 1.73 times the radius of Earth and 5.6 times its mass, orbiting the red dwarf star LHS 1140 in the constellation Cetus, according to EarthSky. First discovered in 2017, the planet completes an orbit every 24.7 days and receives about 42 percent of the stellar irradiation Earth gets from the Sun, according to Sci.News.
Cherubim and his colleagues had developed a theoretical model predicting that the upper atmosphere of LHS 1140 b would contain large amounts of helium slowly escaping into space, according to ScienceDaily. The team tested that prediction using an instrument called WINERED — the Warm Infrared Echelle Spectrograph to Realize Extreme Dispersion — mounted on the Magellan Clay Telescope at Las Campanas Observatory in Chile, according to Sci.News. The observations took advantage of an unusual event in which LHS 1140 b and its sibling planet, LHS 1140 c, crossed in front of their star during the same night, according to ScienceDaily. The Magellan Clay’s 6.5-meter primary mirror is the same size as the James Webb Space Telescope’s, but WINERED’s resolving power — roughly 28,000 to 70,000 depending on mode — far exceeds the roughly 2,700 offered by Webb’s Near Infrared Spectrograph, according to Astronomy.com. “The James Webb Space Telescope, the resolving power is just at most like a tenth of what this ground-based telescope is,” Cherubim said, per Astronomy.com.
The second planet, LHS 1140 c, showed no sign of an atmosphere, while LHS 1140 b produced a clear signal of escaping helium, according to ScienceDaily. LHS 1140 c is smaller and more heavily irradiated by the star than its sibling planet, according to EarthSky. Follow-up observations in 2025 detected no escaping helium from LHS 1140 b either, suggesting the atmospheric escape process is variable rather than constant, according to Sci.News. “After much careful analysis and consideration of the spectra, we determined that helium was escaping from LHS 1140b’s atmosphere in 2024 due to heating from stellar X-rays and extreme ultraviolet radiation,” said Shreyas Vissapragada, an astronomer at Carnegie Science Observatories. “However, our 2025 observations revealed no escaping helium, so the atmospheric escape appears to be variable,” he said, adding: “It is a rare privilege to witness the atmosphere of an extrasolar planet change on such short, human timescales!” according to Sci.News.
Astronomers estimate the atmosphere has survived for more than three billion years, according to ScienceDaily. David Charbonneau, head of the Harvard Department of Astronomy and an astronomer at the Center for Astrophysics | Harvard & Smithsonian, said he initially doubted the prediction would pan out, since the signal had never before been observed from a rocky world — but the results changed his mind. “Collin analyzed the planets we knew about and predicted that this one would have a helium atmosphere,” Charbonneau said. “Then he organized telescope time, got the data, and the detection was statistically rock solid,” according to ScienceDaily.
Robin Wordsworth, the Gordon McKay Professor of Environmental Science and Engineering and Professor of Earth and Planetary Sciences at Harvard and one of Cherubim’s dissertation advisors, framed the discovery as answering a two-decade-old question. “Twenty years ago we wondered whether other terrestrial-type planets even existed,” Wordsworth said. “Then we learned they’re common, and found some in the habitable zone. The next question was whether any of them had managed to keep an atmosphere. Now we know at least one has,” according to ScienceDaily.
What We Don’t Know
The composition of LHS 1140 b’s atmosphere below its helium-rich upper layer remains unknown. Jason Dittmann, an astronomer at the University of Florida, said the open question is whether the planet holds a persistent atmosphere or one that intermittently vents gas. “Because there’s helium there, and because the helium is escaping, the question is: Is LHS 1140b a bare rock with no atmosphere that sometimes burps up some gas that then immediately escapes, or is there a steady-state atmosphere there that will leak out stuff like the Earth does from time to time?” Dittmann said, according to Sci.News. He added that observations planned with the James Webb Space Telescope over the next four to five years will search for water, which would point to a more stable atmosphere, per Sci.News.
LHS 1140 b is now one of the targets under the Rocky Worlds Director’s Discretionary Time program, a joint Webb and Hubble effort dedicated to searching for atmospheres on rocky exoplanets orbiting dwarf stars, according to EarthSky. By comparison, Webb has already observed several planets in the nearby TRAPPIST-1 system in search of a stable atmosphere “but so far to no avail,” according to Astronomy.com.
Analysis
Since the first confirmed exoplanet detection in 1992, scientists have found more than 6,300 exoplanets, but confirming an atmosphere on a small, rocky one has remained elusive, according to Astronomy.com. The TRAPPIST-1 system’s seven Earth-sized worlds, about 40 light-years away, have drawn intense scrutiny in recent years, with Webb observing several of them in search of a stable atmosphere without success so far, according to Astronomy.com. Because LHS 1140 b is tidally locked, it would have a permanent day side, a permanent night side, and a permanent twilight band in between, according to Astronomy.com. Cherubim said his modeling suggests the planet has “a very strong cold trap on this planet that’s even colder than Earth’s cold trap” — the kind of barrier that, on Earth, keeps oceans from boiling off into space, according to Astronomy.com.
The discovery indicates that astronomers may be able to study the atmospheres of rocky exoplanets from the ground by looking for gases escaping into space, rather than relying solely on space telescopes, according to ScienceDaily. Cherubim said he hopes to identify the atmosphere’s complete chemical composition and eventually determine whether the planet has surface oceans or other features connected to habitability, and that he and his colleagues plan to use the same model to search for additional rocky worlds with atmospheres, according to ScienceDaily. “This has been a model validation, and hopefully it’s just the first of many more observations to come,” he said, according to ScienceDaily.