Scientists Detect First Atmosphere on a Rocky Habitable-Zone Planet, Raising Hopes for Life Beyond Earth

Astronomers have confirmed, for the first time, that a rocky planet sitting in its star's habitable zone has an atmosphere. The planet is called LHS 1140 b. It is 48 light-years away, about 5.6 times the mass of Earth, and orbits a quiet red dwarf star at a distance that puts its surface temperature in the range where liquid water could theoretically exist. A Harvard-led team detected helium escaping from it, confirming the atmosphere is real and has persisted for billions of years.

The study was published July 16 in the journal Science. Lead author Collin Cherubim, who recently completed his PhD at Harvard, said plainly: "This is the first time anyone has found an atmosphere on a rocky planet in the habitable zone of another star."

How the detection was made

Cherubim's team started with a model. He calculated which known exoplanets were most likely to retain a helium-rich upper atmosphere, then identified LHS 1140 b as the best candidate to test the prediction observationally.

The team used the WINERED spectrograph on the Magellan Clay telescope at Carnegie's Las Campanas Observatory in Chile. They observed LHS 1140 b during a rare simultaneous transit, when both it and its sibling planet passed in front of their star on the same night. The sibling showed nothing. LHS 1140 b showed helium escaping from its upper atmosphere, a signal that was, in Cherubim's words, "statistically rock solid."

The helium escape happens because the planet's star, though unusually calm for a red dwarf, still pumps out enough X-ray and ultraviolet radiation to heat the upper atmosphere and push lighter gases off into space. That the planet has held onto its atmosphere despite this process suggests it accumulated a substantial gas layer during formation and has kept it for a very long time.

What this does and does not mean

Helium alone cannot support life as we know it. The detection confirms an atmosphere exists — it does not tell us what the rest of that atmosphere contains. Earlier observations had suggested the possible presence of nitrogen, water vapor, and carbon dioxide below the helium layer, but none of that is confirmed. Cherubim was direct about this: "At this point, we have absolutely no evidence for life on the planet."

What the discovery does establish is that LHS 1140 b is not airless. That matters because an atmosphere is, as Cherubim put it, "essential for a planet to support life as we know it." It moderates temperature, enables chemistry, and in the right circumstances allows liquid water to exist at the surface. The planet is tidally locked, meaning one face permanently points toward its star, which complicates the habitability picture further. But at least there is something to study.

What comes next

Robin Wordsworth, professor of environmental science and engineering at Harvard and one of Cherubim's advisors, framed the arc of this research well: "Twenty years ago we wondered whether other terrestrial-type planets even existed. 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."

The team plans additional observations to characterize the full atmospheric composition of LHS 1140 b. Future ground-based and space-based telescopes, including the next generation of extremely large telescopes, could determine whether gases like oxygen, methane, or water vapor are present. Each observation will add detail to a picture that, right now, shows a planet that passed the first test: it has an atmosphere, it is rocky, and it is in the right place.

David Charbonneau, head of the Harvard Department of Astronomy, said it simply: Cherubim organized the telescope time, collected the data, and the detection held up. "Then he organized telescope time, got the data, and the detection was statistically rock solid." That is how science is supposed to work.