For almost a decade, the most closely watched rocky planet in the exoplanet catalogue has been LHS 1140 b: a super-Earth in the habitable zone of a quiet red dwarf about 48 light-years away, in the constellation Cetus. The open question was never whether it exists. We’ve known that since 2017. The question was whether a small planet sitting that close to a red dwarf could hold onto an atmosphere at all. A paper published in Science on July 16 gives the strongest answer yet, and it comes from an unexpected direction: the planet is losing gas. A Harvard-led team caught helium streaming off the top of its atmosphere. That leak, counterintuitively, is the best evidence we have that there’s an atmosphere down there to leak from.
Why “can it keep its air?” is the whole question
Red dwarfs are the most common stars in the galaxy, which makes their planets the most abundant potentially habitable real estate around. There’s a catch built into that abundance. Because these stars are faint and cool, their habitable zones sit close in, and young red dwarfs are violently active for hundreds of millions of years: strong X-ray and extreme-ultraviolet output, frequent flares. All of that radiation heats the top of a planet’s atmosphere until the lightest gases boil off into space. A world with Earth’s gravity might simply lose the fight.
So far the evidence hasn’t been encouraging. The first rocky planets JWST checked around red dwarfs, including the inner TRAPPIST-1 worlds, came back looking bare or nearly airless. And reading a rocky planet’s atmosphere is much harder than reading a gas giant’s. I got into why transmission spectroscopy works at all when JWST found methane on a Saturn-sized world with Earth-like temperatures back in May; for a small rocky planet the same trick has to pull a signal that’s a fraction of a percent, over a thin shell of gas. Nobody had a clean detection for a rocky planet in a habitable zone. That’s the gap this paper fills.
The planet itself
LHS 1140 b is a super-Earth: roughly 5.6 Earth masses and 1.73 Earth radii, on a 24.7-day orbit. It receives about 42% of the sunlight Earth gets, which for this cool star drops it neatly into the habitable zone, with an equilibrium temperature near 226 K (about −47°C). It’s dense, but not dense enough to be solid rock. JWST transmission spectroscopy in 2024 suggested that 10–20% of its mass could be water and floated a nitrogen-rich atmosphere over a possible ocean, maybe even a warm patch of liquid water on the star-facing side of an otherwise frozen “eyeball” world. Those hints were tentative; the nitrogen signal in particular still needs confirming.
A quick note on “habitable zone,” because the phrase does a lot of quiet overselling. It’s just the band of orbits where a planet could keep liquid water on its surface given a suitable atmosphere. It’s a statement about distance and starlight, not a promise of oceans. Sitting in it is necessary, not sufficient. You still need the air, which is the exact piece this detection speaks to.
You can’t photograph an atmosphere 48 light-years away
We don’t image these atmospheres. The ESO artist’s impression at the top of this piece is exactly that, an impression. What we actually measure is starlight. When the planet crosses in front of its star, a sliver of that light filters through the atmosphere’s edge on the way to us, and gases in that ring absorb specific wavelengths. The planet looks a hair bigger at exactly those colours, and the pattern tells you what’s in the gas.
The July result leans on one fingerprint: a line of helium in the near-infrared, at 10,833 ångströms (1.083 microns). This isn’t ordinary helium. It’s helium in a long-lived “metastable” state, and it only gets there when the star’s high-energy ultraviolet ionizes helium high in the atmosphere and it recombines. The practical consequence is that the 1083 nm line only appears where there’s a hot, puffed-up, irradiated upper atmosphere being actively stripped. It’s the standard tool for catching gas escaping from hot Neptunes and Jupiters. Aiming it at a temperate rocky planet is the new move.
The observation
The team used WINERED, a high-resolution near-infrared spectrograph, on the 6.5-metre Magellan Clay Telescope at Las Campanas Observatory in Chile — one of the few ground-based setups that can resolve that helium line cleanly for a planet this small. In September 2024 they watched the system for 6.5 hours and collected 70 spectra, 23 of them while the planet was transiting. During the transit the helium line deepened: extra absorption from helium sitting high above the planet, trailing off the way an escaping outflow should.
Losing gas is how you prove there’s gas
The reasoning runs like this. Helium is light, so it rises to the top of any atmosphere and escapes easily. To still be detecting it up there, transit after transit, the planet has to be replenishing it from a real reservoir below. A bare rock gives you nothing to work with. An escaping upper atmosphere means there’s a bulk atmosphere underneath, feeding it.
The composition of that escaping layer is a second clue. The team finds it helium-dominated and hydrogen-poor. That argues against a leftover primordial envelope, the puffy hydrogen-helium blanket a planet is born with. LHS 1140 b looks like it already shed its hydrogen and kept something heavier and more processed below: closer in kind to the secondary atmospheres of the rocky planets in our own solar system than to a mini-Neptune. What sits beneath the helium, whether water, nitrogen or CO₂, the escape measurement can’t say.
Lead author Collin Cherubim put the headline plainly: “An atmosphere is essential for a planet to support life as we know it. This is the first time anyone has found an atmosphere on a rocky planet in the habitable zone of another star.” His co-author Robin Wordsworth framed the longer arc: “20 years ago we wondered whether other terrestrial-type planets even existed. The next question was whether any of them had managed to keep an atmosphere. Now we know at least one has.”
That “first” deserves a caveat, and it’s a real one. Atmospheres have been reported on rocky planets before, but on scorched lava worlds like 55 Cancri e, nowhere near a habitable zone. This detection also reads the escaping top of the atmosphere, not its full chemistry. It’s the strongest case yet for a habitable-zone rocky world holding air. It is not a photograph of breathable sky.
The catch: the leak comes and goes
There’s an honest complication. When the team looked again in 2025, the helium was gone. No detection. The escape is variable, which isn’t really a contradiction so much as another data point. A red dwarf’s ultraviolet output rises and falls with flares and activity, and an outflow driven by that radiation should flicker along with it. An episodic or clumpy escape would look exactly like this. But it also means the signal isn’t a steady one you can re-check on demand, and one strong detection paired with a non-detection is a thinner foundation than anyone would want. This is a first firm footprint, not a closed case.
Pinning down what’s below the helium, and whether water vapour is in the mix, is a job for JWST, which can chase heavier molecules the ground-based helium line can’t reach.
What it changes for the rest of us
For anyone following the search for life, the upshot is a shift in the odds. The pessimistic version of the last few years ran roughly: red dwarfs are so common that if their rocky planets can’t keep atmospheres, the galaxy’s most abundant real estate is dead on arrival. LHS 1140 b is one counterexample, a rocky planet in a habitable zone that seems to have won at least part of the retention fight. One planet doesn’t settle the statistics. But it moves LHS 1140 b to the front of the queue for JWST time, and it proves out a cheap, ground-based technique for working out which small worlds are worth the expensive follow-up.
From my balcony in Nicosia I can’t add anything to this one. LHS 1140 is a faint red dwarf low in Cetus; no backyard telescope, my Seestar included, is going to pull it out, let alone catch a transit. This is professional-instrument territory. But it changes what I think about when I do look up. Around some fraction of those pinpricks, small rocky planets may be sitting in the habitable zone with real air over them, quietly leaking helium into the dark. We finally have one we can point to.