Astronomers have confirmed the first atmosphere on a rocky exoplanet in a star’s habitable zone, detecting helium leaking from LHS 1140 b, a world located 48 light-years away in the constellation Cetus. Researchers observed the atmospheric escape during planetary transits in 2024, marking a major milestone in the search for habitable worlds beyond our solar system.
While gas giants are large and relatively easy to spot, rocky planets are small and typically get stripped of their gases by the harsh radiation of their host stars. That dynamic changed when an international research team turned sensitive instruments toward a super-Earth orbiting a dim red dwarf in the constellation Cetus.
Detecting Helium Leaking from LHS 1140 b
The breakthrough centered on LHS 1140 b, a rocky super-Earth roughly 1.7 times the radius of Earth and about 5.6 times its mass. The planet orbits its host red dwarf every 24.7 days, placing it squarely within the system’s habitable zone where surface temperatures could potentially sustain liquid water. Researchers caught the signature of an atmosphere not by imaging clouds directly, but by watching helium escape into space as the planet crossed in front of its star.
Observations conducted in September 2024 using the WINERED infrared spectrograph on the Magellan Clay Telescope in Chile revealed that starlight filtering through the upper atmosphere dipped in brightness by about 1.24 per cent at specific wavelengths near 1,083.3 nanometres. The research team also detected absorption preceding the actual transit, pointing to a leading stream of escaping gas.
Contrasting Observations and Computer Model Predictions
Science often relies on follow-up data to test initial excitement, and LHS 1140 b provided a puzzle during subsequent observations. A second transit observed in 2025 failed to produce a detectable helium signature. Researchers suggest that escaping upper atmospheres can fluctuate as their host stars alter their high-energy ultraviolet and X-ray output. Independent analysis pipelines confirmed that the 2024 feature remained present while the 2025 signal stayed below the roughly 0.6 per cent detection threshold.
The detection closely matched computer simulations developed by Cherubim to model exoplanet evolution over billions of years.
Wordsworth noted that after learning terrestrial worlds were common, the next logical question was whether any had managed to keep an envelope of gas. The findings confirm that at least one habitable-zone rocky planet has done so.
What the Atmosphere Comprises and What Remains Unknown
While confirming an atmosphere marks a major technical milestone, scientists caution that the outer gas layer does not mirror Earth’s air. The upper atmosphere appears heavily enriched in helium while being depleted of hydrogen, a combination that makes conditions unlikely to support biological life in those upper layers.
Furthermore, LHS 1140 b is tidally locked to its host red dwarf, meaning one hemisphere experiences permanent daytime while the other sits in perpetual darkness. The planet is also roughly 70 per cent larger than Earth, resulting in surface gravity nearly twice as strong as our own. Researchers also do not yet know whether the surface is entirely covered by a deep global ocean or features exposed rocky terrain.
Despite these extreme conditions, computer models suggest that heavier molecules such as water vapor, carbon dioxide, carbon monoxide, and oxygen could reside closer to the surface beneath the helium envelope. Future observations aim to peer deeper into the atmosphere to determine whether those life-supporting elements are present.
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