Astronomers have achieved a historic milestone by confirming the presence of an atmosphere around LHS 1140b, a rocky exoplanet located 49 light years away in the constellation Cetus. This marks the first time an atmosphere has been definitively detected on a rocky world within its star's habitable zone—the region where liquid water could exist on the surface.
First Confirmed Atmosphere on a Rocky Habitable-Zone Exoplanet
Dr. Collin Cherubim, formerly of Harvard University and lead author of the study published in Science, stated: "This is the first actually observationally confirmed atmosphere on a rocky planet in the habitable zone outside of our solar system." The discovery also represents the first direct identification of an atmospheric species for any rocky exoplanet, whether in a habitable zone or not.
LHS 1140b has a mass 5.6 times that of Earth and a radius 70% larger. While its overall composition and temperature resemble Earth's, the planet is tidally locked, likely has far more water, and possesses a very different atmosphere. Discovered in 2017, it orbits a small red dwarf star that is quieter and emits fewer flares than typical red dwarfs.
Helium Detection and Observational Details
The team observed LHS 1140b as it transited its star using an infrared spectrograph on the Magellan Clay telescope at Las Campanas Observatory in Chile. Data from 2024 revealed helium escaping from the planet's atmosphere. Cherubim noted that all possible false positives, including contamination from Earth's atmosphere, were ruled out. However, helium was not detected in 2025 observations, a surprise that prompted re-analysis. "Every false positive we could think of, we have confidently ruled out," Cherubim said.
Implications for Habitability and Future Research
Cherubim emphasized that LHS 1140b now has all the ingredients for a habitable environment: a rocky composition, a temperature supporting liquid water, and an atmosphere that prevents water loss and shields from radiation. "It's a really exciting place to keep looking, especially to look for signs of life," he added. No atmosphere was found around LHS 1140c, another rocky planet orbiting the same star.
Professor Jayne Birkby of the University of Oxford called the discovery "fantastic" and crucial for understanding planets around red dwarfs, which are the most common star type. She noted that the varying helium signal reveals how the atmosphere reacts to extreme ultraviolet radiation from the host star, potentially affecting surface conditions.
Dr. Yamila Miguel of Leiden Observatory added that the planet's atmospheric loss is detectable from Earth, which is rare for small, rocky worlds. However, she cautioned that the observations pertain to the upper atmosphere, not the surface where life would evolve, so direct implications for detecting life remain limited.
