A new study suggests that a rocky planet located at an ideal distance from its star for potentially sustaining life is likely to possess an atmosphere.
This exoplanet, named LHS 1140 b, is situated approximately 49 light-years from Earth, positioning it as a relatively close neighbor given the Milky Way’s expansive span of over 100,000 light-years. Discovered in 2017, LHS 1140 b was already considered a significant candidate in the quest to find life-sustaining planets. Recently, researchers have detected helium leakage from this planet into space, enhancing the likelihood of life existing there, according to Collin Cherubim, a postdoctoral fellow at Harvard University.
Cherubim, the lead author of the study, explained the new findings in research published in Science on Thursday. He emphasized that LHS 1140 b meets three major criteria for habitability: it is rocky, maintains temperatures suitable for liquid water, and now shows evidence of an atmosphere.
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“This is the only planet that we know has all three of those things, and it happens to be relatively nearby,” Cherubim commented. “Another huge thing, which is really, really awesome, is that it happens to be orbiting a relatively quiet star,” meaning it is not frequently subjected to coronal mass ejections and other destructive eruptions.
While atmospheres have been observed on other rocky exoplanets, such findings are rare and often lack conclusiveness, considering the potential millions or billions of similar planets within the Milky Way.
The presence of an atmosphere is deemed crucial for a planet’s ability to harbor life, as it can protect the surface from radiation and retain water. The detection of helium escaping from LHS 1140 b marks a significant milestone, according to Laura Kreidberg, an astronomer at the Max Planck Institute for Astronomy in Heidelberg, Germany, who was not involved in the study.
Cherubim had hypothesized that small, rocky planets like LHS 1140 b might develop atmospheres rich in helium over time. To explore this, he compiled a list of known planets that met specific criteria for mass, radius, and temperature.
“LHS 1140 b was one of the relatively higher-probability predictions, and it just so happened to be the subject of lots of scrutiny because it’s this really exciting, rocky planet that’s near Earth, that’s in the habitable zone,” he noted. “I thought it was a good place to start.”
By using an infrared spectrograph on the Magellan Clay Telescope at the Las Campanas Observatory, Cherubim and his team searched for wavelengths of light indicating helium’s absorption of stellar radiation. Helium’s presence is crucial because, while abundant in the universe, small planets with thin atmospheres like Mars struggle to retain it. Therefore, detecting helium escaping into space from LHS 1140 b would suggest a thicker, multi-layered atmosphere capable of trapping water near the surface.
Upon analyzing the data, Cherubim confirmed that helium was indeed being heated by stellar x-rays and was leaking into space.
A surprising twist occurred when the helium detected in 2024 was no longer present upon re-examination in 2025.
“That was a pretty shocking finding,” Cherubim admitted. “It did cause me to go back to the original data in 2024 and say, ‘Oh, my gosh, did I miss something?’”
The absence of helium in 2025 is a concern, Kreidberg noted. “It would have been better if they confirmed it. But at the same time, this type of variability is not crazy. They’re going to follow it up, and I hope they see it again, and I think they will. I think it would be hard to explain this any other way.”
Several explanations for these differing observations exist, such as the planet’s atmosphere reacting to varied temperature levels during its orbit or changes in the star’s magnetic activity. The most plausible reason, Cherubim suggests, is that helium is only detectable in its excited state at such distances.
“It could be possible, in 2025, just as much helium was escaping, and we just didn’t see any of it because … the amount that was populated into this excited state was different,” he explained.
This discovery challenges some traditional beliefs in the astronomy community, Kreidberg remarked. It was generally thought that a planet the size and age of LHS 1140 b would have lost its helium long ago. The planet might be in a phase of transition, gradually losing helium to space and shrinking from its current sub-Neptune size to resemble Earth more closely.
“I think it is very possible that what we’re seeing is a snapshot of this evolution from the smallest gas giant to the biggest rocky planet,” Kreidberg stated.
LHS 1140 b is set to be examined under the Rocky Worlds Director’s Discretionary Time program, which utilizes the James Webb Space Telescope and Hubble Space Telescope to search for atmospheres on rocky planets. While this may resolve many unanswered questions about LHS 1140 b’s atmosphere, Cherubim can take pride in his work.
“This planet is one of the targets in their small sample of rocky worlds, where they’re looking for an atmosphere that they consider to be the most promising,” he said. “Well, they considered it. I kind of beat them to the punch and answered the question already.”
