Astronomers have detected leaking helium from the super-Earth exoplanet LHS 1140 b, providing the strongest evidence yet that this distant world retains a complex, multilayered atmosphere. The discovery marks a critical milestone in the search for Earth-like rocky planets capable of supporting life, confirming the presence of a protective gaseous envelope around a world situated in its star’s habitable zone.
Located just 49 light-years from Earth, LHS 1140 b has long intrigued scientists. Found in 2017, the planet orbits a cool red dwarf star and was immediately flagged as a prime candidate in the search for extraterrestrial life. The new findings, detailed in the journal Science, solidify the planet’s status by confirming it meets the three essential criteria for habitability: a rocky surface, temperatures suitable for liquid water, and a stable atmosphere.
The Significance of Leaking Helium
The detection of an exoplanet atmosphere is notoriously difficult. While signs of atmospheres have been spotted on other rocky exoplanets, such discoveries remain rare and often lack definitive proof. The presence of an atmosphere is considered essential to a planet’s ability to host life because it shields the surface from harmful stellar radiation while trapping water and heat. Laura Kreidberg, an astronomer at the Max Planck Institute for Astronomy in Heidelberg who was not involved in the new study, calls the detection of helium escaping from LHS 1140 b a milestone.
Collin Cherubim, a postdoctoral fellow at Harvard University and lead author of the study, had previously theorized that small, rocky planets could develop atmospheres rich in helium over time. To test this hypothesis, he compiled a list of known planets fitting specific criteria for mass, radius, and temperature. LHS 1140 b emerged as a high-probability target. “I thought it was a good place to start,” Cherubim says, noting the planet’s proximity to Earth and its placement in the habitable zone made it a subject of intense scientific scrutiny.
To make the detection, Cherubim and his colleagues utilized an infrared spectrograph mounted on the Magellan Clay Telescope at the Las Campanas Observatory in Chile. The instrument searched for specific wavelengths of light that indicate the absorption of stellar radiation by helium. While helium is one of the most abundant elements in the universe, smaller planets with thin atmospheres—such as Mars—struggle to retain it. Because helium is so light, it easily drifts away into space, often leaving behind only heavier gases like carbon dioxide. If LHS 1140 b is actively losing helium, it implies the existence of a much thicker, multilayered atmosphere beneath, likely with water trapped closer to the surface.
A Quiet Star and a Habitable Zone
The exoplanet’s host star plays a crucial role in its potential habitability. LHS 1140 b orbits a relatively quiet red dwarf, meaning the star is not prone to battering the planet with catastrophic coronal mass ejections and other violent eruptions that could strip away a protective atmosphere. “This is the only planet that we know has all three of those things, and it happens to be relatively nearby,” Cherubim says. “Another huge thing, which is really, really awesome, is that it happens to be orbiting a relatively quiet star.”
The combination of a stable stellar environment and a confirmed atmosphere makes LHS 1140 b an outlier among the millions, if not billions, of rocky planets estimated to exist in the Milky Way. The data revealed that helium is being heated by stellar X-rays and is subsequently leaking into space. However, the process is not entirely straightforward, presenting a new mystery for astronomers to unravel.
A Mysterious Disappearance in 2025
Despite the breakthrough, the detection came with a puzzling twist. While the helium signal was clearly visible in 2024 observations, it vanished when Cherubim used the telescope to examine the exoplanet atmosphere again in 2025. “That was a pretty shocking finding,” Cherubim admits. The absence prompted him to re-examine the original 2024 data to ensure no errors were made in the initial analysis.
Kreidberg noted this disappearance as the “one tummy rumble” she has regarding the study, though she acknowledged that such variability is not unprecedented in astronomical observations. “It would have been better if they confirmed it,” she says. “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.”
Researchers propose several explanations for the divergent observations. The atmosphere might be responding to different temperature levels during its orbit, or magnetic activity within the host star could have shifted. The most likely explanation, according to Cherubim, is that helium is only detectable at such vast distances when it exists in an excited state. “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 explains.
A Planet in Transition
The presence of escaping helium challenges long-held orthodoxies within the astronomy community. Scientists previously believed that a planet of LHS 1140 b’s size and age would have lost any primordial helium billions of years ago. The new data suggests the planet may currently be in a transitional period. As it continuously loses helium to space, it could be shrinking from its current sub-Neptune size to something that more closely resembles Earth.
“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 notes. This transitional phase offers astronomers a rare opportunity to observe planetary evolution in real-time, providing valuable data for models of how rocky worlds form and evolve over billions of years.
What Happens Next
The astronomical community will soon turn its most powerful instruments toward LHS 1140 b. The exoplanet is slated for observation as part of the Rocky Worlds Director’s Discretionary Time program, which is utilizing the James Webb Space Telescope (JWST) and the Hubble Space Telescope to search for evidence of atmospheres on rocky planets. These upcoming observations could resolve the lingering questions about the planet’s atmospheric composition and the mysterious disappearance of the helium signal.
While the JWST and Hubble could provide definitive answers, Cherubim takes pride in having already addressed the fundamental question of whether an atmosphere exists. “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 says. “Well, they considered it. I kind of beat them to the punch and answered the question already.”
For now, the detection of leaking helium stands as a testament to the capabilities of ground-based telescopes and the ingenuity of astronomers looking for Earth-like worlds. As researchers await the James Webb Space Telescope observations, LHS 1140 b remains a beacon of possibility—a nearby super-Earth that might just hold the keys to understanding how rocky planets acquire and keep the atmospheres necessary for life.
— Priya Nair, science desk, AXO News