Scientists have confirmed the first atmosphere on a rocky exoplanet in the habitable zone outside our solar system, a major milestone in the search for life beyond Earth. The planet, LHS 1140b, located 49 light-years away, orbits a small red dwarf star in the constellation Cetus and could have liquid water on its surface, researchers reported in the journal Science.
First confirmed atmosphere on a rocky exoplanet in the habitable zone
Dr. Collin Cherubim, the study's first author and formerly of Harvard University, said: "This is the first actually observationally confirmed atmosphere on a rocky planet in the habitable zone outside of our solar system." The discovery also marks the first direct identification of an atmospheric species for any rocky exoplanet, whether in a habitable zone or not.
Atmospheres have been found on gas giants and sub-Neptunes, and signs of envelopes have been seen on rocky exoplanets outside their star's habitable zone. However, LHS 1140b is the first rocky planet in the habitable zone with a confirmed atmosphere.
Key characteristics of LHS 1140b
LHS 1140b has a mass 5.6 times that of Earth and a radius 70% larger. While similar to Earth in composition and temperature, it is tidally locked, likely has more water, and possesses a very different atmosphere. Discovered in 2017, it orbits a quiet red dwarf that emits more ionizing radiation than the Sun but has few flares.
Cherubim said the planet now has all ingredients for habitability: a rocky surface, temperatures supporting liquid water, and an atmosphere to retain water and shield from radiation. "So it’s a really exciting place to keep looking, especially to look for signs of life," he added.
Detection of escaping helium
The team used an infrared spectrograph on the Magellan Clay telescope in Chile to observe LHS 1140b as it transited its star in 2024. They detected helium escaping from the planet's atmosphere, ruling out contamination from Earth's atmosphere. However, helium was not detected in 2025 observations, a surprise that led to re-analysis. Cherubim said: "Every false positive we could think of, we have confidently ruled out."
Implications and expert reactions
Professor Jayne Birkby of the University of Oxford called the discovery "fantastic," noting that red dwarf planets are common but often lose their atmospheres due to stellar activity. "That makes this discovery ... a crucial step towards understanding what it’s like living with a red dwarf," she said. She added that the varying signal shows how the atmosphere reacts to extreme ultraviolet radiation, raising questions about potential life and protective adaptations.
Dr. Yamila Miguel of Leiden Observatory said the planet's atmospheric loss is detectable, which is rare for a small rocky planet. However, she cautioned that the observations involve gas escaping from the upper atmosphere, not the lower atmosphere where life would evolve. "Therefore I do not think these results have any direct implications for detecting life on other planets," she said.
No atmosphere was found around LHS 1140c, another rocky planet orbiting the same star. The study positions LHS 1140b as a prime target for future astrobiology research.
