A rocky planet 48 light-years from Earth has an atmosphere. This is not hypothesis, not model, but direct measurement: astronomers have detected helium escaping from the atmosphere of the planet LHS 1140 b. The study was published in July 2026 in the journal Science. This is the first time an atmosphere on a rocky planet in the habitable zone of another star has been directly confirmed.
What is LHS 1140 b?
LHS 1140 b orbits a red dwarf star in the constellation Cetus, roughly 48 to 49 light-years from the Sun. The planet has a mass 5.6 times Earth's and a radius 1.73 times larger, placing it in the super-Earth category. Critically, it sits within the habitable zone of its star: at this orbital distance, stellar radiation is such that liquid water on a rocky surface is theoretically possible.
Red dwarf stars are particularly interesting for the search for habitable planets. They make up 70 to 80 percent of all stars in the Milky Way and live far longer than Sun-like stars. Their habitable zone is closer to the star, making planetary transits more frequent and sharper. LHS 1140 b has been considered one of the most promising candidates in exoplanet research for several years.
How helium reveals an atmosphere
The Magellan Clay Telescope at Las Campanas Observatory in Chile observed LHS 1140 b during a transit in 2024, when the planet passed in front of its star. The Harvard University research team used the helium-10830 absorption line in the infrared spectrum: helium in the upper atmosphere of a planet absorbs starlight in a characteristic way that spectrographs can uniquely identify.
The signal was unambiguous. Helium is escaping from the outer atmospheric layer of the planet, a process called photoevaporation or atmospheric escape. This finding is direct evidence that LHS 1140 b possesses an atmosphere from which material can escape. Without an atmosphere, no such signal would occur.
An unexpected finding complicates interpretation: during a second transit window in 2025, the helium signal was no longer detectable. The authors interpret this as temporally variable atmospheric activity, possibly linked to fluctuating stellar activity or seasonal patterns on the planet. The signal's disappearance does not disprove the discovery but underscores that research on LHS 1140 b is still in its infancy.
What the discovery means and what it doesn't
Detecting an atmosphere does not mean LHS 1140 b is habitable. The atmosphere's composition remains unknown. At present, it is likely thin and dominated by nitrogen or carbon dioxide, not hydrogen-rich. Water, oxygen, or other biosignatures have not been detected.
What the discovery means: all previous measurements, including observations by the James Webb Space Telescope, had ranked LHS 1140 b as a promising candidate and provided hints of water vapor, but could not directly confirm the atmosphere itself. Only the Magellan measurement provides direct proof. For exoplanet research, whether rocky planets in habitable zones can retain atmospheres had been an open question: red dwarf stars are radiation-active and can strip atmospheres over billions of years. LHS 1140 b shows: in this case, the planet has retained an atmosphere.
In comparison: Rocky planets without atmospheres
The TRAPPIST-1 system is the most-observed planetary system with potentially habitable worlds. JWST observations in 2023 found no signs of a significant atmosphere around TRAPPIST-1c: infrared measurements showed little heat retention on the night side, suggesting a planet without a protective atmosphere. Similar results emerged for TRAPPIST-1b in earlier studies. The system's most promising candidates further out in the habitable zone have not yet been measured with comparable precision.
Mars provides an example of a planet that once had a thicker atmosphere and lost it. Roughly 3.5 to 4 billion years ago, Mars had, according to NASA reconstructions, a denser atmosphere and liquid water. Loss of its magnetic field and solar activity stripped the atmosphere away. Today, atmospheric pressure on Mars is roughly 0.6 percent of Earth's.
Kepler-186f, recognized in 2014 as the first Earth-sized planet in a habitable zone, lies 490 light-years away and is out of reach for current atmosphere measurements. LHS 1140 b, at 48 light-years, is far closer, making direct measurements possible for the first time.
From first discovery to first atmosphere: three decades
In 1995, Michel Mayor and Didier Queloz discovered the first exoplanet orbiting a Sun-like star: 51 Pegasi b, a gas giant, completely inhospitable but proof that other stars have planets. They received the 2019 Nobel Prize in Physics for this work.
In 2009, the Kepler Space Telescope launched and discovered nearly 2,700 confirmed exoplanets over ten years, including the first rocky planets in habitable zones: Kepler-22b in 2011, Kepler-186f in 2014. Both were too distant to measure their atmospheres.
In 2022, JWST began observations and characterized the atmospheres of nearby exoplanets with unprecedented precision for the first time. Earlier JWST data on LHS 1140 b had provided hints of water vapor but did not directly confirm the atmosphere itself. In 2026, roughly three decades after the first exoplanet discovery, the direct detection of an atmosphere on a rocky planet in the habitable zone has succeeded. What comes next: JWST is expected over the next four to five years to analyze the composition of this atmosphere and search for biosignatures.