Pasadena, CA—A team of scientists led by Harvard University's Collin Cherubim and including Shreyas Vissapragada and other Carnegie astronomers has detected evidence of an atmosphere on a rocky planet orbiting in the habitable zone of its host star. Until now, the data showing rocky exoplanets with atmospheres has been extremely limited, so this observation—published this week in Science—is a breakthrough in our understanding of these worlds, their life cycles, and their potential habitability.
Theoretical models predict that atmospheres are a critical component for habitability, because they shield a planet from cosmic radiation, enable water to exist on its surface, and regulate dynamic climate cycles that can lead to clement conditions.
Atmospheres have been detected and characterized for hot gas giant planets. However, it has been a technological challenge to confirm the presence of atmospheres on rocky planets that orbit their stars at the right distance to have liquid water—the so-called "habitable zone." Telescopes, including NASA's JWST, are actively searching for atmospheres on small, rocky exoplanets, but these observations have mostly revealed airless worlds, making it unclear whether these planets are capable of retaining their atmospheres for long enough to enable life to arise and thrive.
"Red dwarf stars present a good opportunity for this kind of search because they are small and cool, so habitable-zone planets orbiting these stars are relatively accessible using the transit method, where we detect tiny, periodic dips in the host star's brightness every time the planet passes in front of it from our point of view," Vissapragada explained. "However, atmospheric signals from species like water and carbon dioxide—usually found in a planet's lower atmosphere—are extremely subtle and challenging to detect in these habitable-zone planets, even for flagship observatories like the JWST. So, our team decided on a different approach: to search for helium in the upper atmosphere, where signals can be a bit easier to detect."
On a mission to find a rocky habitable zone planet with evidence of an atmosphere, the research team—which also included Carnegie astronomers Johanna Teske, Nicole Wallack, William Misener, and Andrew McWilliam—zeroed in on a super-Earth called LHS 1140 b.
Discovered in 2017, LHS 1140 b orbits an older red dwarf star over a period of just 24.7 days. It has a mass just 5.6 times that of Earth and a radius about 1.7 times Earth's. This is consistent with a rocky world that has a bulk composition similar to our own planet's, making it a good target for the research team's goals. It receives 42 percent of the stellar radiation that Earth does, enabling the scientists to calculate that its temperature is right for having liquid water, although it is not yet known whether planets in this size range have surfaces like Earth's.
Using a powerful instrument called the WINERED spectrograph on the world-class Magellan Clay telescope at Carnegie's Las Campanas Observatory in Chile, the team observed LHS 1140 b in 2024 and saw evidence of helium escaping from its atmosphere—a stunning result.
"This was clear evidence of an atmosphere on a habitable-zone exoplanet," Vissapragada said. "It was an absolute thrill to see the transit spectra and slowly realize the implications of what we were looking at."
Spectra are a way of studying a celestial object's characteristics, including composition, speed, and motion. They take the light emitted by the host star and split it up into its component parts—the same way a prism creates a rainbow. When this light passes through the atmosphere of an exoplanet, astronomers can tell what elements are present there.
"After much careful analysis and consideration of the spectra, we determined that helium was escaping from LHS 1140 b's atmosphere in 2024 due to heating from stellar X-rays and extreme ultraviolet radiation," Vissapragada indicated. "However, our 2025 observations revealed no escaping helium, so the atmospheric escape appears to be variable. It is a rare privilege to witness the atmosphere of an extrasolar planet change on such short, human timescales!"
Combined with earlier observations and sophisticated models of exoplanet evolution, the team interpreted these results to indicate the presence of a highly layered atmosphere. They predict the planet has a helium-dominated and hydrogen-poor upper atmosphere, and other chemical species like water are trapped at lower altitudes closer to the surface.
The researchers also observed another planet in the same system, LHS 1140 c, which is both smaller and more highly irradiated. There was no evidence of an atmosphere, perhaps indicating that these two worlds may fall on opposite sides of the so-called "cosmic shoreline." On one side are planets that retain their atmospheres for billions of years, and on the other those with atmospheres that boil off quickly into space.
This exciting discovery is just one of many Carnegie-led and co-led projects and investigations of exoplanet atmospheres. Vissapragada, Teske, Wallack, Misener, McWilliam, and many others are using space- and ground-based telescopes, including JWST and the soon-to-launch Nancy Grace Roman Space Telescope, to push the boundaries of exoplanet characterization and understand what could make distant worlds capable of hosting life.
Other members of the LHS 1140 b team include: Tim Cunningham, Annabella G. Meech, David Charbonneau, and Robin Wordsworth from Harvard; Aaron Householder from MIT; Leonardo A. Dos Santos and Mercedes Lopez-Morales from the Space Telescope Science Institute; Zifan Lin from Washington University St. Louis; Michael Zhang from the University of Chicago; and Jason A. Dittmann from University of Florida Gainesville.
