An international team of researchers has identified what is described as the most compelling evidence to date of an atmosphere surrounding a rocky exoplanet located within the habitable zone of its star. The planet, known as LHS 1140 b, orbits a red dwarf star approximately 48 to 49 light-years away in the constellation Cetus.
The discovery, published in the journal Science, marks a significant milestone in the search for potentially life-friendly worlds. While astronomers have confirmed over 6,000 exoplanets, previous attempts to detect atmospheres on rocky worlds within habitable zones—the range of orbital distances where liquid water could potentially exist—have been unsuccessful.
Detection and Atmospheric Composition
The presence of an atmosphere was determined by detecting escaping helium. Researchers led by Collin Cherubim of the Center for Astrophysics | Harvard & Smithsonian utilized the WINERED-spectrograph at the Magellan-Clay Telescope in Chile to analyze the system. By observing subtle changes in the color composition of light as the planet transited its star, the team identified a clear helium signal in September 2024.
According to the study, the upper atmosphere appears to be dominated by helium with little hydrogen. Researchers suspect that high-energy X-ray and ultraviolet radiation from the red dwarf star causes this helium to escape into space. While the upper atmosphere is helium-rich, scientists believe the lower, denser layers may contain heavier elements such as carbon, nitrogen, or oxygen. Some earlier analyses have even suggested the possibility that LHS 1140 b could be a “water world,” with water potentially accounting for up to 19 percent of its total mass.
System Dynamics and Variable Signals
A notable aspect of the observation is the variability of the helium signal. While a clear signal was recorded in 2024, subsequent measurements in 2025 indicated that the signal had disappeared. The research team views this fluctuation not as a failure, but as a crucial insight into the planet’s atmospheric dynamics. The changing signal suggests the atmosphere is undergoing active processes, potentially driven by the radiation environment of the host star.
LHS 1140 is characterized as an atypically quiet red dwarf compared to others of its class. Because red dwarfs are significantly smaller and cooler than the Sun, their habitable zones are located much closer to the star. LHS 1140 b completes an orbit in just 24.7 days. Despite this proximity, the planet remains in the habitable zone, receiving approximately 42 percent of the radiation that Earth receives from the Sun.
The system is estimated to be at least 3.1 billion years old. The successful detection of an atmosphere on a planet of this age provides evidence that rocky worlds orbiting red dwarfs—which constitute 70 percent of all stars in the Milky Way—can retain their gaseous envelopes despite the intense radiation environments typical of these stars.
Context and Future Research
LHS 1140 b is classified as a “super-Earth,” with approximately 5.6 times the mass and 1.7 times the diameter of our own planet. The significance of the discovery is underscored by the lack of a similar signal from a neighboring planet in the same system, LHS 1140 c, which is smaller, hotter, and appears to be an airless world.
Researchers caution that while the findings are significant, much remains to be learned. We don't know enough about the lower atmosphere of the planet to even say what substances it consists of—let alone anything about the surface or liquid water, said co-author Shreyas Vissapragada of the Carnegie Institution.
The team plans to conduct further observations to better understand the nature of the helium fluctuations and to refine models of the planet’s composition. For now, the discovery serves as a vital proof of concept, confirming that at least one rocky planet in a habitable zone has successfully maintained an atmosphere over billions of years.
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