Until now, evidence of atmospheres on this type of planet has been extremely limited. Theoretical models indicate that atmospheres play a fundamental role in habitability by shielding a planet’s surface from cosmic radiation, allowing liquid water to exist, and helping regulate climate.
Although astronomers have detected and characterized atmospheres around gas giant planets in recent years, confirming their presence on rocky planets orbiting at the right distance from their stars to sustain liquid water has remained a major technological challenge. Observatories such as the James Webb Space Telescope (JWST) have searched for these atmospheric signatures, but most observations have revealed airless worlds, leaving open the question of whether these planets can retain their atmospheres long enough for life to emerge and persist.
“Red dwarf stars present an excellent opportunity for this kind of search because they are small and cool, making habitable-zone planets around them relatively accessible using the transit method, which detects tiny, periodic dips in a star’s brightness each time a planet passes in front of it from our point of view,” explained Shreyas Vissapragada. “However, atmospheric signals from molecules such as water and carbon dioxide, which are typically found in the lower atmosphere, are extremely subtle and difficult to detect even with flagship observatories like JWST. So, we decided to take a different approach: searching for helium in the upper atmosphere, where the signals can be easier to observe.”
The research team, which also included Carnegie astronomers Johanna Teske, Nicole Wallack, William Misener, and Andrew McWilliam, focused their study on LHS 1140 b, a super-Earth discovered in 2017.
This exoplanet orbits an old red dwarf star every 24.7 days, has a mass 5.6 times that of Earth, and a radius 1.7 times larger. Its properties are consistent with those of a rocky planet with a composition similar to Earth’s, making it an ideal target for this study. In addition, it receives about 42% of the stellar radiation that Earth receives from the Sun—an amount that, according to current models, could allow liquid water to exist on its surface, although the nature of planets in this size range is still not well understood.
The Contribution of Las Campanas Observatory
The key evidence was obtained at Las Campanas Observatory in Chile using the high-resolution WINERED spectrograph installed on the Magellan Clay Telescope. During observations carried out in 2024, the team detected helium escaping from the atmosphere of LHS 1140 b, providing one of the strongest pieces of evidence to date for the existence of an atmosphere on a rocky planet located in the habitable zone of its host star.
“This was clear evidence of an atmosphere on a habitable-zone exoplanet,” said Vissapragada. “It was an absolute thrill to observe the transit spectra and gradually realize the implications of what we were looking at.”
Spectra allow astronomers to study the physical properties of celestial objects, including their composition, velocity, and motion. To do this, astronomers split the light from a star into its different wavelengths, much like a prism creates a rainbow. When that light passes through the atmosphere of an exoplanet during a transit, it leaves a characteristic signature that reveals which chemical elements are present, allowing researchers to identify components such as the helium detected in this study.