Astronomers have confirmed the existence of an atmosphere surrounding LHS 1140 b, a rocky exoplanet orbiting within the habitable zone of a cool red dwarf star. Published in the journal Science, the study provides the strongest evidence yet that an Earth-like world in another star system has retained an atmosphere capable of enduring for more than three billion years, according to researchers at the Center for Astrophysics | Harvard & Smithsonian.
Astronomers Detect Atmosphere on Rocky Exoplanet in Habitable Zone
The exoplanet lies roughly 48 light-years from Earth. It is approximately 1.73 times larger than Earth and has a rocky composition. Because it receives a fraction of the stellar energy that Earth does, it orbits far enough from its host star to potentially allow liquid water to remain on its surface under the right conditions, fulfilling key criteria for a habitable environment.
Detecting Escaping Helium and Proving Atmospheric Retention
To determine whether the planet possessed an atmosphere, researchers used theoretical models predicting an upper atmosphere rich in helium that slowly escapes into space due to high-energy radiation from the host star. To test this hypothesis, the team utilized the Warm Infrared Echelle (WINERED) Spectrograph on the Magellan Telescope at the Las Campanas Observatory in Chile.
The breakthrough came during an unusual night of observations in September 2024, when LHS 1140 b and a second rocky planet in the same system, LHS 1140 c, transited their star simultaneously. While the second planet showed no atmospheric signal, instruments detected a faint stream of helium escaping from LHS 1140 b. Lead author Collin Cherubim noted that observing helium gas leaking into space indicates that the rocky world is not a barren rock, but instead maintains a substantial gaseous envelope.
Significance for the Search for Extraterrestrial Life
The discovery represents a major milestone in exoplanet research. While astronomers have previously identified thousands of exoplanets—including some rocky worlds in habitable zones—proving whether those bodies retained atmospheres had remained a significant challenge.
“Twenty years ago we wondered whether other terrestrial-type planets even existed,” said Robin Wordsworth, a Gordon McKay Professor of Environmental Science and Engineering and Professor of Earth and Planetary Sciences at Harvard, and one of Cherubim’s dissertation advisors. “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.”
Context, Limitations, and Future Observations
Although the presence of an atmosphere marks a crucial step toward assessing habitability, researchers emphasize that the environment of LHS 1140 b differs significantly from Earth’s. The detected helium originates from an outer layer driven off by stellar radiation, while deeper layers may contain heavier gases such as nitrogen, carbon dioxide, or carbon monoxide.
Follow-up observations conducted in 2025 did not detect the helium signal, suggesting that atmospheric escape rates may vary over time or temporarily fall below current observation limits. Moving forward, scientists plan to utilize more powerful instruments to fully characterize the planet’s complete chemical makeup and investigate whether it features surface oceans or other attributes compatible with supporting life.
