Astronomers detect first atmosphere around rocky planet in habitable zone

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Astronomers have found the strongest evidence yet that a rocky planet beyond our solar system has managed to hold onto an atmosphere — a crucial ingredient for life as we know it.

The discovery marks the first time scientists have detected an atmosphere surrounding a rocky planet orbiting in the habitable zone of another star, the region around a star where temperatures could enable liquid water to exist on a planet's surface. The findings, published July 16 in the journal Science , could help astronomers narrow the search for potentially habitable worlds beyond our cosmic backyard.

"It's absolutely exciting," Edward Schwieterman , associate professor of astrobiology at the University of California, Riverside, who was not involved in the study, told Live Science in an email. "We are getting closer to studying the atmospheres of worlds that could plausibly harbor life, with evidence of that life embedded in their observable spectra."

The planet, known as LHS 1140 b , lies about 48 light-years away from Earth and orbits a small, cool red dwarf star. At roughly 5.6 times Earth's mass, the exoplanet is classified as a super-Earth : a rocky planet larger than our own but much smaller than gas giants like Neptune.

It receives less than half the sunlight Earth gets, giving it an estimated surface temperature of around minus 53 degrees Fahrenheit (minus 47 degrees Celsius), according to previous estimates not accounting for an atmosphere. That makes the planet cold, but in the range astronomers consider potentially habitable.

Cosmic gas leak

Scientists have discovered thousands of exoplanets over the past few decades, including many rocky worlds. But determining whether those planets have atmospheres has proven far more difficult, because atmospheres around rocky planets are incredibly thin compared with those of giant planets, making them much harder to detect across vast cosmic distances.

Instead of looking for the atmosphere directly, the researchers behind the new study searched for a subtle clue that one existed: helium gas leaking into space. Using the WINERED spectrograph on the Magellan Clay Telescope in Chile, the team watched LHS 1140 b cross in front of its star and let a sliver of starlight filter through the planet's atmosphere on its way to Earth. As it did, the team looked for a tiny dip in the star’s light at the exact wavelength of infrared light that helium blocks — a telltale sign that gas was streaming off the planet and into space.

The prediction rested entirely on a mathematical model that had never been confirmed for a rocky planet. However, in September 2024, the team caught LHS 1140 b and a smaller, hotter neighboring planet, LHS 1140 c , transiting their star on the same night, less than 40 minutes apart. The researchers detected a clear helium signal from LHS 1140 b, while LHS 1140 c showed nothing.

NASA concept art depicting LHS 1140 b as a rocky super-Earth — a type of potentially habitable planet most similar to our own. (Image credit: NASA) The contrast matters: LHS 1140 c orbits much closer to its star than LHS 1140 b does and receives roughly five times the radiation, yet it's also smaller and less gravitationally bound — conditions that should make any escaping gas easier, not harder, to spot. Finding nothing there suggests LHS 1140 c's atmosphere was stripped away long ago, while LHS 1140 b, sitting farther out in cooler, calmer conditions, has managed to hold onto its own.

The discovery addresses a question astronomers have been working to answer for decades.

"Twenty years ago we wondered whether other terrestrial-type planets even existed," study co-author Robin Wordsworth , a professor of Earth and planetary sciences at Harvard, said in a statement . "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."

A step forward in the hunt for life

The find is especially notable because red dwarf stars like LHS 1140 can bombard nearby planets with high-energy radiation capable of stripping atmospheres away over time. Based on the star's estimated age of at least 3.1 billion years, the researchers say LHS 1140 b's atmosphere has likely persisted despite that bombardment, suggesting some rocky planets around these common stars can hang onto their atmospheres for far longer than once assumed.

But the researchers caution that detecting helium does not mean the planet is inhabited — or even that it is habitable. The observations reveal only the planet's thin upper atmosphere, not its full composition. Scientists still don't know whether LHS 1140 b has oxygen, carbon dioxide, water vapor or other gases that could make its surface more Earth-like and hospitable to life.

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Instead, the discovery opens a new way to study distant rocky worlds.

"The study demonstrates that, at least in some cases, we will be able to begin characterizing the atmospheres of potentially habitable planets," Schwieterman said. "If only rocky planets orbiting Sun-like stars retained atmospheres, we might have to wait one to two decades for the launch of the Habitable Worlds Observatory to search for biosignatures on rocky planets. I'm certainly excited about what comes next!"

Future observations will aim to determine what the rest of LHS 1140 b's atmosphere is made of and investigate whether it may harbor oceans or other features associated with habitability.