Astronomers just crossed a line the field has been circling for decades: they detected helium escaping from LHS 1140 b, and that is the strongest evidence yet that a rocky planet orbiting in its star's habitable zone has retained an atmosphere for billions of years. The results were published July 16 in the journal Science, and they represent the first time scientists have detected an atmosphere surrounding a rocky planet in the habitable zone of another star.

The trick is that the team did not “see” the atmosphere directly. Instead, they watched LHS 1140 b cross in front of its star and searched for a tiny dip in the star's light at the exact infrared wavelength that helium blocks. As the paper’s approach implies, helium streaming upward is a measurable fingerprint of a planet with an outer atmosphere strong enough to leak, even if the underlying atmosphere is thin. And crucially, they built the case using a comparison that worked out in their favor: on the same night in September 2024, the researchers also observed the smaller, hotter neighboring planet LHS 1140 c, and they detected nothing there, even though the conditions should have made escaping gas easier to detect.

Let’s ground the stake. LHS 1140 b sits about 48 light-years away and orbits a small, cool red dwarf star. It is roughly 5.6 times Earth's mass, which puts it in the “super-Earth” bucket: larger than Earth, but not a gas giant like Neptune. The planet receives less than half the sunlight Earth gets, so previous estimates (that did not account for an atmosphere) put its estimated surface temperature around minus 53 degrees Fahrenheit (minus 47 degrees Celsius). That is cold, but it is cold in the range astronomers consider potentially habitable, meaning the planet lies where temperatures could allow liquid water under the right atmospheric conditions.

This matters because atmospheres around rocky planets are incredibly thin compared with those of giant planets, making them much harder to detect across vast cosmic distances. For years, exoplanet hunters have found thousands of planets, including many rocky worlds. But the hard part is determining whether those planets actually have atmospheres, since thin skies do not give you big, easy signatures. The researchers behind this study aimed for a subtle clue rather than a direct readout: helium leaking into space. That method leans on a mathematical model that had never been confirmed for a rocky planet, which is why the observing details matter so much.

In September 2024, the team caught both LHS 1140 b and its smaller, hotter neighbor LHS 1140 c transiting their star on the same night, less than 40 minutes apart. Using the WINERED spectrograph on the Magellan Clay Telescope in Chile, they detected a clear helium signal from LHS 1140 b, while LHS 1140 c showed nothing. The contrast is not a throwaway detail. LHS 1140 c orbits much closer to its star and receives roughly five times the radiation, yet it is also smaller and less gravitationally bound. In plain terms, those conditions should have made any escaping gas easier, not harder, to spot. Finding nothing suggests LHS 1140 c’s atmosphere was stripped away long ago, while LHS 1140 b, sitting farther out in cooler, calmer conditions, managed to hold onto its own.

The “so what” is bigger than one planet. The find addresses a question astronomers have been working on for decades. As study co-author Robin Wordsworth, a professor of Earth and planetary sciences at Harvard, put it in a statement, “Twenty years ago we wondered whether other terrestrial-type planets even existed.” 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.” That line captures the evolution of the field: from “do rocky planets exist?” to “how many?” to “can they keep the ingredients that make life plausible?”

The note of caution is just as important for executives watching technology and mission pipelines: 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 do not 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. So this is evidence of atmospheric retention, not a discovery of life.

Still, the discovery changes the roadmap. 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 likely persisted despite that bombardment. That suggests some rocky planets around common red dwarf stars can hold onto their atmospheres for far longer than once assumed.

Looking forward, the study opens a new way to study distant rocky worlds. Edward Schwieterman, an associate professor of astrobiology at the University of California, Riverside, who was not involved in the study, told Live Science, “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.” 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. Schwieterman also highlighted the timing constraint for biosignature hunting: 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, and he said he is “certainly excited about what comes next.”

For leaders in space, investment, and applied science, the second-order implication is clear: atmosphere characterization on potentially habitable rocky planets is inching toward something closer to routine observability. That can reshape how boards think about sequencing, risk, and funding across the chain from instruments to telescopes to mission concepts. If helium escape can be read as a retention signal, then the next bottleneck is no longer “can we detect an atmosphere exists?” but “what is inside it, and how fast can we build a comparative dataset across targets?”