A planet 48 light-years away has become the first rocky world in a star’s habitable zone with a confirmed atmosphere. The evidence did not come from seeing clouds or identifying gases close to the surface. It came from helium escaping above the planet and absorbing a narrow band of its star’s light.
The planet is LHS 1140 b, a large rocky world orbiting a cool red dwarf in the constellation Cetus. In a paper published in Science, Collin Cherubim and colleagues report a helium signal extending beyond the planet during one transit. The result confirms that atmospheric material is present, but it does not yet establish the composition, pressure or temperature of the air near the ground.
This is one study, not settled consensus. Its importance lies in the measurement itself: after years of searching, astronomers have detected an atmospheric species associated with a rocky habitable-zone planet.
LHS 1140 b sits in a useful but difficult middle ground
LHS 1140 b is about 1.7 times Earth’s radius and roughly 5.6 times its mass. Those measurements place it among the super-Earths, a broad class that appears to be common elsewhere even though our Solar System has no example. I wrote about that gap in our local inventory in an earlier piece on the more than 6,000 confirmed planets beyond the Sun.
The planet completes an orbit around its small star every 24.7 days. It receives an amount of energy that puts it within the system’s habitable zone, meaning liquid water could be possible under the right atmospheric and surface conditions. That phrase is often made to carry too much. A habitable-zone orbit is not evidence for oceans, biology or even a comfortable surface.
Nearby red-dwarf systems are useful laboratories because their planets pass in front of relatively small stars, producing deeper and more measurable transits. As the case of GJ 887 d also shows, identifying a nearby habitable-zone world is only the opening question. Whether it retained an atmosphere is a separate and harder one.
How a helium tail reveals an atmosphere
The team observed LHS 1140 b in 2024 with the WINERED infrared spectrograph on the Magellan Clay Telescope in Chile. During a transit, some starlight passed through material around the planet. At wavelengths near 1,083.3 nanometres, where an excited form of helium absorbs light, the star appeared about 1.24 per cent dimmer than expected.
Absorption also appeared before the planet itself began crossing the star. The researchers interpret this as a leading stream of escaping gas, with tentative evidence for material trailing behind. Helium atoms high in the atmosphere are heated by the star’s ultraviolet and X-ray radiation, then flow outward where a ground-based telescope can detect them.
This is indirect in the ordinary sense that no camera photographed an atmospheric shell. It is direct spectroscopic evidence of helium attached to the planet’s passage across the star. The team tested whether changing helium lines in the star or absorption in Earth’s atmosphere could imitate the signal, and reported that neither explanation matched the timing and motion of the feature.
The missing signal a year later matters
A second transit observed in 2025 did not produce a detectable helium signature. That may sound like a contradiction, but escaping atmospheres can vary as their host stars change. The 2025 data could still have contained a weaker signal below the observation’s roughly 0.6 per cent detection threshold.
The researchers processed both years again through an independent analysis pipeline. The 2024 feature remained and the 2025 feature remained absent. Their modelling suggests changes in the star’s high-energy output could alter the amount of helium occupying the extended upper atmosphere.
One successful transit and one non-detection make follow-up work especially important. More observations need to establish how often the helium appears, how it responds to the star and whether its shape around the planet repeats.
Escaping helium is not a sample of the surface air
The models describe a hot upper-atmospheric outflow, at roughly 5,200 to 5,900 kelvin, losing about 200 to 420 tonnes of material per second. They also favour an outflow strongly enriched in helium relative to hydrogen. These are model-dependent estimates, not readings from a weather station on the planet.
A helium-rich escape flow does not mean a person standing on LHS 1140 b would find helium-rich air. Lighter gases can separate by altitude and escape at different rates, while water, nitrogen, carbon dioxide and other heavier material may remain lower down. What I find most useful about this result is precisely that boundary: it answers whether atmospheric material exists while leaving most questions about the lower atmosphere open.
A 2024 analysis of James Webb Space Telescope observations found LHS 1140 b consistent with a water-rich world and tentatively favoured a nitrogen-bearing atmosphere over a hydrogen-dominated one. That was an interpretation of limited spectra, not an atmospheric confirmation. The helium detection now gives future Webb observations a firmer reason to look for carbon dioxide and other gases, but it does not decide between the remaining surface scenarios.
Why this first does not amount to evidence of life
Atmosphere detection is one rung on a long ladder. Astronomers still need to constrain the lower atmosphere, determine whether liquid water is present and work out how conditions vary across a planet likely locked with one face towards its star.
Even a living world may be difficult to recognise remotely. In an earlier article, I looked at how Earth supported life for billions of years before atmospheric oxygen became readily detectable from afar. LHS 1140 b is much less understood than that example. There is no reported biosignature here.
The immediate result is narrower and still significant. Helium escaping into space has shown that a rocky planet in a habitable-zone orbit can hold an atmosphere that astronomers can measure. The next useful evidence will come from repeated helium transits and from spectra capable of describing the gases that remain closer to the planet below.
