‘Super-Earth’ planet shows signs it could have an atmosphere

An artist’s concept shows exoplanet LHS 1140b (right) surrounded by a helium-rich atmosphere. (Melissa Weiss/CfA/Harvard via CNN Newsource)

Scientists say they have detected promising signs that a planet orbiting a star 49 light-years from Earth could have an atmosphere, making it potentially suitable for life.

Called LHS 1140b, the object is about five times the mass of our planet, or a “super-Earth.” This planet orbits around its star in the “Goldilocks zone,” also known as the habitable zone, meaning its surface temperature is not too hot or too cold for liquid water to exist.

“We believe it is also predominantly a rocky planet, based on its mass and its radius measurements, which gives us a density estimate,” said Collin Cherubim, a planetary scientist and lead author of a paper on the finding, published July 16 in the journal Science.

“It appears to be consistent with Earth, meaning it might have an iron core and a silicate mantle, plus some sort of low-density component, which is probably a combination of water and, now we know, an atmosphere,” said Cherubim, a NASA Sagan Fellow at the University of Chicago. He conducted the research during his doctoral studies at Harvard University.

Astronomers have discovered more than 6,200 exoplanets since uncovering the first ones in the 1990s. The Hubble Space Telescope found evidence in 2001 of an atmosphere on a gas giant exoplanet orbiting a star about 150 light-years from Earth.

If further observations confirm the findings, LHS 1140b would mark the first discovery of an atmosphere on a rocky planet in the habitable zone of another star.

Signs of a habitable planet

Looking at the atmospheres of faraway rocky planets is difficult, because these celestial bodies are small and their atmospheres are thin. Astronomers must wait for a planet to move in front of its host star. Similar to an eclipse, as the light filters through the atmosphere, it can reveal the signature of a gas.

There is no evidence of life or a life-supporting atmosphere on LHS 1140b now, but Cherubim said he believes it’s a formidable candidate for potential signatures of extraterrestrial life.

“I think it’s the best place to look for life outside the solar system at this point,” he said. “It’s mostly rocky, it’s at the right temperature to support liquid water on the surface, and it has an atmosphere — those are the three key ingredients we look for.”

To spot the atmosphere, Cherubim first developed a model based on the widespread assumption that many planets form with atmospheres dominated by hydrogen and helium — the most abundant elements in the universe. As some of these planets evolve into rocky bodies, they lose most of their hydrogen but can hold onto helium, because it’s slightly heavier.

Cherubim used the model to find known exoplanets whose mass, radius and temperature would make them likely to have undergone this process, and then he searched for the telltale helium. Using the Magellan Clay telescope at Las Campanas Observatory in Chile, in September 2024, he found helium escaping from LHS 1140b.

“You’re stripping the hydrogen, keeping the helium, and you end up with this sort of helium world,” he said. “We believe LHS 1140b is in that sweet spot, where it lost its hydrogen and it kept its helium, which is now slowly escaping.”

Helium alone would likely not be suitable for supporting life, but it’s hoped that other gases, such as oxygen, may accompany it.

“We don’t have any other detections of any other molecules in the atmosphere yet, but I’m optimistic,” Cherubim said. “I would go ahead and bet that we will find something eventually.”

‘Can we maybe find water next?’

The host star of LHS 1140b is a red dwarf, the most common type of star in the universe. Because red dwarfs are smaller and cooler than other stars, it’s easier to check for atmospheres in planets that orbit them due to reduced brightness and glare. However, red dwarf stars are also more active than stars like our sun, and they can destroy atmospheres altogether. “They’re really feisty, ferocious stars that emit lots of X-rays and ultraviolet radiation,” Cherubim said, “which are really bad for atmospheres because they heat them up, expand them and blow them off into space.”

Confirming the existence of an atmosphere on a rocky planet orbiting a red dwarf would be particularly exciting, Cherubim said, because the possibility of that happening is an open question in astronomy. “Can rocky planets have atmospheres around red dwarfs? This is the first bona fide yes,” he said. “It’s kind of a sigh of relief for a lot of us. But the jury’s still out. Maybe this is a weird planet, and it’s an oddball, or maybe it’s the first of many. We don’t know yet.”

In a one-year follow-up observation of the planet in 2025, Cherubim and his team no longer detected helium. The study concluded this absence could be explained by a variability in the rate of escape of the helium, which would have put it below the instrument’s threshold of sensitivity. However, Cherubim admitted, “That’s a big mystery right now that we’re very actively thinking about.”

The researchers will start a new round of observations on LHS 1140b in the fall. “I’ve also applied for time on an even more sensitive instrument in Chile that I’m hoping will get approved,” Cherubim said. “Several other people are going to be looking at it, too. The James Webb Space Telescope is going to look at it. Hubble’s going to look at it. Basically, everybody who can see it is going to be training their eyes on it.”

Study coauthor Jason Dittmann shares Cherubim’s relief over the discovery. “I was starting to worry that maybe atmospheres around rocky planets weren’t that common or maybe red dwarfs weren’t very good planetary hosts,” Dittman, an assistant professor of astronomy at the University of Florida, said in an email. “So I think finding a positive example of a rocky planet with an atmosphere is really significant. It’s what we’ve been hoping to find for years. What else is there besides helium? Can we maybe find water next? Something else? The significance in this result lies in all the excitement about what other questions we can maybe ask next.”

For Dittmann, it’s especially thrilling that LHS 1140b will receive attention from so many scientists, because he led the team that discovered the exoplanet in 2017.

“It’s like my little planet is all grown up now,” he said. “I hope we’ll start seeing more rocky planet atmospheres over the next few years. I may end up eating those words, but if I had to put money down right now I’d say this is the first of, if not many, then several. And it’ll be really exciting to compare these planets to each other and see what makes them different.”

The follow-up problem

The LHS 1140b observations are groundbreaking, providing the strongest evidence so far for an atmosphere on a rocky exoplanet in the habitable zone, Ana Glidden, a postdoctoral researcher at the Massachusetts Institute of Technology’s Kavli Institute for Astrophysics and Space Research, said in an email.

“As LHS 1140 b orbits a quiet star and is a super-Earth, the odds of it holding onto an atmosphere are in its favor,” added Glidden, who was not involved with the study. “However, more observations are critical to confirm the result and to understand why helium was seen during the first observation, but not in the second.”

Michaël Gillon, research director of the Astrobiology Research Unit at Belgium’s University of Liège, called the study exciting with a potentially landmark result. But he warned no definitive proof exists that LHS 1140b possesses a substantial atmosphere. He also did not participate in the work.

“The helium signal was detected only once and was absent in follow-up observations in 2025,” Gillon wrote in an email. “The lack of a second detection calls for caution and before drawing conclusions about the nature of any underlying atmosphere, there is a need to establish that the helium signal is genuinely associated with the planet and reproducible.”

If the detection of helium can be confirmed, however, the implications would be profound, Gillon said. “Until now, we had only limited evidence for atmospheres on temperate rocky exoplanets,” he added. “Demonstrating that LHS 1140 b has retained a substantial atmosphere over billions of years would show that at least some habitable zone Super-Earths around red dwarfs can survive the intense early activity of their host stars.”

Such a result would significantly strengthen the prospects for finding truly habitable rocky worlds nearby, Gillon concluded, and would make LHS 1140b one of the highest-priority targets for the James Webb Space Telescope and future observatories.

By Jacopo Prisco, CNN