Astronomers have obtained the clearest evidence so far for an atmosphere surrounding a rocky exoplanet inside its star’s habitable zone. The planet is LHS 1140 b, a temperate super-Earth located about 49 light-years away in the constellation Cetus. It orbits an old, relatively quiet red dwarf every 24.7 days, has approximately 5.6 times Earth’s mass and 1.73 times its radius, and receives about 42 percent as much stellar energy as Earth. Its estimated equilibrium temperature is around 226 kelvin, although the actual surface temperature would depend strongly on the atmosphere, cloud cover, reflectivity and heat redistribution. Being in the habitable zone therefore means that liquid water could be physically possible under suitable atmospheric conditions, not that the planet has been shown to be inhabited or even genuinely habitable. The researchers did not directly image the atmosphere or identify gases near the surface. Instead, they detected helium escaping from the planet’s extended upper atmosphere. During a transit in September 2024, when LHS 1140 b crossed in front of its star, some of the starlight passed through the tenuous gas surrounding the planet. Using the high-resolution WINERED spectrograph on the 6.5-metre Magellan Clay Telescope in Chile, the team found additional absorption near 10,833 angstroms, the wavelength of a triplet produced by metastable helium. The strongest component absorbed about 1.24 percent of the stellar light, corresponding to an opaque atmospheric region extending to roughly 1.5 times the planet’s visible radius. Absorption also appeared before the optical transit began, suggesting that escaping helium may form an extended stream ahead of the planet, with tentative evidence for a trailing tail as well. The most likely interpretation is that high-energy X-ray and extreme-ultraviolet radiation from the red dwarf heats the upper atmosphere and drives a hydrodynamic outflow into space. Models fitted to the observations imply a mass-loss rate of roughly 200 to 400 million grams per second. Despite sounding enormous, this rate is low enough for the planet to have retained a substantial atmosphere over billions of years, particularly because LHS 1140 is now comparatively inactive. The models also indicate that the escaping gas contains very little hydrogen relative to helium, with an inferred hydrogen-to-helium ratio of about one part in a thousand. This supports atmospheric-fractionation scenarios in which lighter hydrogen escapes more efficiently over time, gradually leaving the upper atmosphere enriched in helium. An important complication is that the helium signal was detected in the 2024 transit but not when the planet was observed again in 2025. The team independently reprocessed both datasets and investigated possible contamination from Earth’s atmosphere, instrumental effects and stellar activity, but concluded that these alternatives could not satisfactorily explain the 2024 feature. The difference between the two years is therefore interpreted as variable atmospheric escape, possibly caused by changes in the star’s high-energy emission or interactions between the stellar wind and the planet. The absence of helium in 2025 does not mean that the atmosphere disappeared; it means that the population of metastable helium producing this particular spectral line may vary considerably with time. Additional transits will be necessary to determine how frequently the signal appears and how strongly it changes. The same observing run also covered LHS 1140 c, a smaller planet orbiting much closer to the star and receiving about five times Earth’s irradiation. No corresponding helium absorption was detected around this inner world. That contrast is consistent with the expectation that the more strongly irradiated planet has lost most or all of its atmosphere, while the cooler and more massive LHS 1140 b has been able to retain one. More generally, the result provides observational evidence that at least some rocky or predominantly rocky planets around red dwarfs can preserve atmospheres despite prolonged exposure to stellar X-ray and ultraviolet radiation. This has been a major unresolved issue because many small planets examined around active M dwarfs appear to be airless or possess atmospheres too thin to detect. The detection does not yet reveal what the lower atmosphere is made of. The escaping upper layers appear helium-rich and hydrogen-poor, but heavier gases such as nitrogen, carbon dioxide and water vapour could remain trapped deeper down. Earlier JWST observations had already ruled out a large, clear hydrogen-dominated envelope and found tentative, low-significance evidence consistent with Rayleigh scattering from a nitrogen-rich atmosphere. Those data could not distinguish conclusively between a dense high-molecular-weight atmosphere and an almost airless planet. The new helium detection now makes the airless interpretation much less likely, although it still does not determine the surface pressure, climate or chemical composition of the lower atmosphere. LHS 1140 b’s mass and radius also indicate that it is less dense than a completely dry, Earth-composition planet. One possibility is a mostly rocky world surrounded by a substantial atmosphere; another is a water-rich planet containing perhaps 9 to 19 percent water by mass, far more than Earth. Because the planet is cool, atmospheric models predict that a strong cold trap could condense water in the lower atmosphere before it reaches altitudes where ultraviolet radiation could break it apart and allow the hydrogen to escape. If LHS 1140 b formed with a large water reservoir, it may therefore have preserved much of it. However, oceans have not been detected, and descriptions of the planet as an ocean world remain model-dependent rather than observationally established. The planet is also probably tidally locked, with one hemisphere permanently facing its star. Whether it could maintain liquid water would depend on the atmospheric pressure and circulation being sufficient to transport heat from the illuminated side to the nightside. Future JWST observations will attempt to search for lower-atmosphere molecules, particularly carbon dioxide, and to constrain the temperature structure and bulk composition more precisely. Even a detection of chemically unusual gases would require considerable caution: no atmospheric molecule by itself would demonstrate the presence of life without a detailed understanding of the planet’s geology, stellar environment and possible abiotic chemistry. In my view, the central result is not that astronomers have found a second Earth or a living world, because neither claim is supported. The real advance is methodological and physical: helium escaping at high altitude can reveal an atmosphere that is extremely difficult to detect through molecules closer to the surface. LHS 1140 b now appears to be the first clear example of a temperate, predominantly rocky exoplanet that has retained an atmosphere for billions of years. That turns it from an interesting habitable-zone candidate into one of the most valuable nearby laboratories for studying how atmospheres survive, evolve and possibly maintain liquid water around red dwarf stars. 👉 arxiv.org/html/2607.14326v1