Scientists have identified an atmosphere surrounding LHS 1140b, a rocky exoplanet located 49 light years away in the habitable zone of a small red dwarf star in the constellation Cetus. The discovery represents the first observationally confirmed atmosphere on a rocky planet within a habitable zone outside the solar system, and the first direct identification of an atmospheric species on any rocky exoplanet. The planet, which was discovered in 2017, has a mass 5.6 times that of Earth and a radius 70% larger.
Researchers observed LHS 1140b as it passed in front of its host star using an infrared spectrograph on the Magellan Clay telescope at Las Campanas Observatory in Chile. Data collected in 2024 revealed helium escaping from the planet’s upper atmosphere into space. The finding was unexpected when observations conducted in 2025 did not detect helium, prompting the research team to conduct additional analysis. Scientists stated they ruled out alternative explanations for the helium signal, including contamination from Earth’s atmosphere.
The planet contains several characteristics considered favorable for habitability. It maintains temperatures that could support liquid water, possesses an atmosphere capable of preventing water loss and shielding the surface from harmful radiation, and orbits a relatively quiet star with few flares. However, the planet differs from Earth in significant ways, including being tidally locked and potentially containing substantially more water. No atmosphere was detected around LHS 1140c, another rocky planet orbiting the same star.
The discovery holds particular significance because red dwarf stars, the most common stellar type, often emit high levels of ionizing radiation that typically strips atmospheres from their orbiting planets. The detection of an atmosphere around LHS 1140b represents a notable development in understanding planetary habitability in such systems. Experts noted the observation demonstrates how exoplanet atmospheres respond to extreme ultraviolet radiation from their host stars, though some researchers cautioned that the detected helium originates from the upper atmosphere rather than regions near the surface where life would be expected to develop.
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