If This Planet Is Real, It Would Break So Many Records

Exoplanet hunters have had an eye on Alpha Centauri, the closest star system to Earth at just four light-years away, for decades. We know that it consists of two Sun-like stars, Alpha Centauri A and Alpha Centauri B, as well as a faint red dwarf star, Proxima Centauri. But while researchers have previously discovered three exoplanets orbiting Proxima Centauri, the search for more worlds orbiting the system’s other two stars has proven difficult. Until now: New evidence from the James Webb Space Telescope indicates there is a gas giant planet in orbit around Alpha Centauri A. And what’s more, it is likely in the star’s habitable zone.

Researchers described this tantalizing candidate planet in two studies published today on the preprint server arXiv, with the papers forthcoming in The Astrophysical Journal Letters.

If the planet is confirmed, it would break numerous records. It would be the first exoplanet ever observed around a star about the same age and temperature as our Sun, and the nearest exoplanet to Earth orbiting in the habitable zone of a Sun-like star. It would also be the closest planet to its host star ever to be imaged directly—it is likely just two astronomical units, or twice the distance between the Sun and the Earth, from its host star—rather than observed using indirect means.

“With this system being so close to us, any exoplanets found would offer our best opportunity to collect data on planetary systems other than our own,” Charles Beichman, co-lead author of the studies and an executive director of the NASA Exoplanet Science Institute, said in a statement.

“Yet, these are incredibly challenging observations to make, even with the world’s most powerful space telescope, because these stars are so bright, close, and move across the sky quickly,” he explained: The closer a planet is to its star, the harder it is to spot.

Researchers began the observations in August 2024, using a device on Webb’s Mid-Infrared Instrument known as a coronagraphic mask. It allows researchers to block out the glare of both Alpha Centauri A and Alpha Centauri B in observations in order to see any orbiting planets, revealing the evidence of this potential record-breaking exoplanet.

If the planet really does exist and orbits in Alpha Centauri A’s habitable zone—a point where liquid water can exist on a planet’s surface—its mid-infrared brightness indicates it’s a gas giant of about the same mass of Saturn. That unfortunately means we would not expect to find any signs of life, at least as we know it.

In fact it is very unlikely any world orbiting Alpha Centuari A could sustain liquid water in this zone, the researchers write, because “the elliptical orbit of the candidate giant planet sweeps through most of Alpha Centauri A’s habitable zone, making it unlikely that smaller rocky planets could survive.” That’s a bummer, because rocky exoplanets within habitable zones are the focus of the search for extraterrestrial life.

Nonetheless, the potential planet is “the most similar in temperature and age to the giant planets in our solar system and nearest to our home, Earth,” explained Sanghi Aniket Sanghi, a graduate student at the California Institute of Technology who was also co-lead author on the studies.

“Its very existence in a system of two closely separated stars would challenge our understanding of how planets form, survive, and evolve in chaotic environments,” Sanghi added.

It remains to be seen what future observations will reveal about the potential gas giant. Some—and especially fans of the James Cameron movie Avatar—may be particularly interested in learning if it has any moons, like the one on which the film’s Na’vi are supposed to live.