Astronomers have directly detected an atmosphere around the rocky exoplanet LHS 1140-b, which orbits within the habitable zone of its host star. The discovery, based on observations from the Magellan Observatory in Chile, marks the first time an atmosphere has been confirmed on a rocky world residing in a region where liquid water could exist on its surface.

The detection hinges on the identification of helium in the planet’s atmosphere—a finding that constitutes the first direct evidence that a rocky exoplanet in a habitable zone can retain an atmosphere over time. A study detailing the discovery was published in the journal Science, offering new insight into planetary habitability beyond our solar system.

LHS 1140-b, located approximately 48 light years from the solar system, orbits a small red dwarf star. The planet is about 1.7 times the diameter of Earth and roughly 5.6 times more massive, classifying it as a “super-Earth.” It completes one orbit every 24.7 days at a distance of about 9 million miles from its star, which has surface temperatures ranging from 3,100°F to 5,800°F. Red dwarfs like this one are the most common type of star in the galaxy, with astronomers estimating that about three out of every four stars fall into this category.

The research team, led by Collin Cherubim, observed both LHS 1140-b and its sibling planet LHS 1140-c during 2024 and 2025 using the Warm Infrared Echelle (WINERED) Spectrograph at the Magellan Observatory in Chile. Observations in 2024 revealed a strong helium signal from LHS 1140-b, but no such detection occurred in 2025. In contrast, LHS 1140-c showed no signs of an atmosphere in either observing campaign.

Cherubim, currently a NASA Hubble Fellow at the University of Chicago, conducted the research while he was a PhD student at Harvard University. He developed theoretical models focusing on mass fractionation—a process in which lighter molecules escape a planet’s gravity into space while heavier ones remain. “Hydrogen is the lightest element and it's the easiest to blow off into space,” Cherubim said. “My model was predicting that if your planet is in this sweet spot where you're blowing enough hydrogen away, but not too much that you're dragging helium, which is a bit heavier, along with it, then you can actually create a helium-dominated atmosphere over time.”

He added, “This is a newly-predicted class of planets, which should have very unique chemistry.” Prior to this discovery, scientists had only inferred the possible presence of atmospheres on some rocky exoplanets in habitable zones through indirect evidence, such as moderate day-night temperature differences. “For rockier Earth-like planets, it has been a huge challenge in the field to detect any atmospheres at all,” Cherubim noted. “This is a huge question in the field that so much time and energy has been devoted to answering.”

The detection method relied on transit spectroscopy. “When the planet passes in front of the star, some of that starlight filters through the atmosphere of the planet,” Cherubim explained. “If there are any molecules or atoms like helium in the planet's atmosphere, they can absorb or block very specific wavelengths of light.” This technique enabled the team to isolate helium’s spectral signature during the 2024 observations.

Cherubim outlined the three primary criteria astronomers use to assess planetary habitability. “When we think about habitability, we think about three high-level things,” he said. “We think the planet needs to be rocky for the most part. It can't be a gas-rich thing where the surface is molten, or like Jupiter where it's just all gas.” He continued, “It's got to be the right temperature to support surface liquid water, at least for Earth-like life, and it needs an atmosphere to hold that water in and to shield the surface from radiation.”

“The new discovery is really the first claim ever of any rocky exoplanet atmosphere in the habitable zone that could potentially have liquid water and really support life,” Cherubim said. “With this discovery, we now know LHS 1140-b has all three of those things, which is really exciting.” He and his colleagues consider it likely that the planet harbors large amounts of liquid water on its surface. The research team also predicts that LHS 1140-b has maintained its atmosphere for billions of years, suggesting long-term stability.

Further bolstering its scientific value, LHS 1140-b is relatively close to Earth. “And it just happens to be a very nearby system to Earth, so it's very accessible,” he said. Astronomers have already used both the Hubble Space Telescope and the James Webb Space Telescope to search for biosignatures—chemical indicators of life—in the planet’s atmosphere.

So far, that search has not yielded any obvious signs of life, but Cherubim remains optimistic. “I think this is the best place to be looking for biosignatures,” he said. “We're really excited to see what comes out of that.”

The confirmation of an atmosphere on a rocky exoplanet in the habitable zone addresses a fundamental question in astrobiology: whether Earth-like worlds beyond our solar system can retain the conditions necessary for life. LHS 1140-b was discovered in 2017 using the transit method, and since then it has been a high-priority target for atmospheric study. With more than 6,200 exoplanets now known—and the first ever discovered in 1992 orbiting a distant pulsar—this finding represents a rare concrete step toward identifying potentially habitable environments.

Because the planet orbits a common red dwarf star and lies just 48 light years away, it offers a uniquely accessible laboratory for future observations. Upcoming data from space-based telescopes could reveal additional atmospheric components, test Cherubim’s helium-dominated model, and potentially uncover biosignature gases, making LHS 1140-b one of the most promising candidates in the search for life beyond Earth.