For the first time, astronomers have directly detected an atmosphere on a rocky exoplanet orbiting within the habitable zone of its star. The discovery marks a major milestone in the search for potentially life-supporting worlds beyond our solar system.
The planet, LHS 1140 b, lies 48 light-years from Earth and orbits a red dwarf star about one-third the size of the Sun. Originally discovered in 2017 by Jason Dittmann’s team, the planet is rocky with an iron core and sits within the so-called Goldilocks zone, the region where temperatures could allow liquid water to exist on the surface.
Now, a team led by Collin Cherubim of Harvard University has detected the planet’s atmosphere by analyzing the spectral signature of molecules as LHS 1140 b transited its star. Using the WINERED Spectrograph on the Magellan Observatory in Chile, they identified a clear helium signal, the first direct atmospheric detection for any rocky exoplanet.
“We have actually detected directly the helium present in the atmosphere itself, and that’s the first direct detection for any rocky exoplanet, which is really exciting,” Cherubim said. “And then there’s this added bonus that it’s in the habitable zone, which is super exciting for astrobiology and habitability and searching for life.”
The finding is significant for several reasons. Red dwarf stars are known for their intense flare activity and radiation, which can strip planetary atmospheres over time. LHS 1140 b’s ability to retain an atmosphere for billions of years, its star is roughly 6 billion years old, suggests that rocky planets around such stars can indeed hold on to their gaseous envelopes, a promising sign for the broader search for habitable exoplanets.
The team suspects the planet “probably also has a lot of water,” and its combination of rocky composition, suitable temperature, and confirmed atmosphere makes it one of the most promising targets for further study in the search for extraterrestrial life. However, Cherubim cautioned: “I’m not claiming this planet has life.”
The researchers hope to identify other gases in the atmosphere, such as water vapor, in future observations. They also note that the detection technique, usually reserved for gas giants, has now been successfully applied to a rocky planet for the first time, opening the door to characterizing many more similar worlds.
“This planet was found like 10 years ago, and we’re just now saying, okay, that’s an atmosphere,” said Dittmann, a co-author on the study. “We’re slowly narrowing the gap and checking these boxes. We’re finding a planet that’s rocky, a planet that’s of the right temperature, and now it’s like okay, we finally found one that has an atmosphere.”
The discovery was published in the journal Science.