Alpha Centauri Might Have a Planet, Webb Telescope Finds

By: Colin Stuart August 7, 2025 0

Direct images from the James Webb Space Telescope show what could be a Saturn-mass planet around Alpha Centauri.

Saturn-like exoplanet 2 AU from host star — This artist's concept shows what the gas giant orbiting Alpha Centauri A could look like.
*NASA / ESA / CSA / STScI / R. Hurt (Caltech / IPAC)*

Using the James Webb Space Telescope, astronomers may have directly imaged a Saturn-mass gas giant in the habitable zone of a star in the solar system next door. While the planet itself isn’t habitable to life as we know it, moons around it could be.

Alpha Centauri is a triple-star system, made up of a pair of close-orbiting, Sun-like stars (A and B) as well as the red dwarf Proxima Centauri, the closest star to the Sun.

Astronomers have already found three planets swirling around Proxima Centauri, but now they may have spotted one circling Alpha Centauri A as well. The results are reported in two papers that will appear in The Astrophysical Journal Letters (paper 1, paper 2).

The relative proximity of the Alpha Centauri system to Earth was both a blessing and a curse: It allowed astronomers to directly image the planet, but that turned out to be far from straightforward. “These are incredibly challenging observations to make, even with the world's most powerful space telescope,” says team co-lead Charles Beichman (NASA Exoplanet Science Institute). “These stars are so bright, close, and move across the sky quickly.”

Three panels zoom in on possible planet around Alpha Centauri A — This image shows the Alpha Centauri star system from several different ground- and space-based observatories: the Digitized Sky Survey (DSS) at left, NASA's Hubble Space Telescope at center, and NASA's James Webb Space Telescope at right. The ground-based image from DSS shows the triple system as a single source of light, while Hubble resolves the two Sun-like stars in the system, Alpha Centauri A and Alpha Centauri B. The image from Webb's Mid-Infrared Instrument, which uses a coronagraphic mask to block the bright glare from Alpha Centauri A, reveals a potential planet orbiting the star.
*NASA / ESA / CSA / STScI / DSS / A. Sanghi (Caltech) / C. Beichman (JPL) / D. Mawet (Caltech); Image processing: J. DePasquale (STScI)*

The team made the discovery using Webb’s Mid Infrared Instrument (MIRI). It has a coronographic mask that can block out the intense glare of stars to observe fainter objects like planets in the vicinity. But this is tricky in a multiple-star system, with Alpha Centauri B's light needing to be blocked too. The team used Epsilon Muscae as a reference star to help untangle the planet's meager light from that of its host.

Interestingly, the planet's position matches a tentative detection made in 2019 by the Very Large Telescope’s NEAR experiment, raising the possibility that both sightings correspond to the same object. However, the planet failed to show up in two follow-up observations with Webb, casting doubt on the discovery. There's a chance, though, that the planet had simply moved too close to the star to been seen. Its orbit may be moderately eccentric and tilted compared to the orbital plane of the Alpha Centauri, further complicating the search. The planet's disappearing act is unlikely to be due to dust obscuration, as the team placed unprecedented limits on exozodiacal light in the system.

The team is planning further follow-up observations with Webb, and hopefully also with the Nancy Grace Roman Telescope when it launches in 2027.

Three panels zoom in on JWST images of Alpha Cen A — This three-panel image captures NASA's James Webb Space Telescope's observational search for a planet around the nearest Sun-like star, Alpha Centauri A. The image at left shows the bright glare of Alpha Centauri A and Alpha Centauri B. The middle panel shows the system with a coronagraphic mask placed over Alpha Centauri A to block its bright glare, though the way the light bends around the edges of the coronagraph creates ripples of light in the surrounding space. The telescope's optics (its mirrors and support structures) cause some light to interfere with itself, producing circular and spoke-like patterns. These complex light patterns, along with light from the nearby Alpha Centauri B, make it difficult to spot faint planets. In the panel at the right, astronomers have subtracted the known patterns (using reference images and algorithms) to clean up the image and reveal faint sources like the candidate planet.
*NASA / ESA / CSA / STScI / A. Sanghi (Caltech) / C. Beichman (JPL) / D. Mawet (Caltech); Image processing: J. DePasquale (STScI)*

“In my opinion, the authors have done a really careful job of analyzing their data,” says Sarah Casewell (University of Leicester, UK), who was not involved in the research. The proximity of the planet is also a real plus. “It will give us an opportunity to start to compare the composition with the gas giants in our solar system,” she says.

If the planet is eventually confirmed, it would be a record-breaking discovery as the planet orbits just two astronomical units away from its host star — right in the habitable zone.

"Of all the directly imaged planets, this would be the closest to its star seen so far,” says co-lead Aniket Sanghi (Caltech). It would also be the first directly imaged planet around a star that's the same age and temperature as the Sun.

A confirmed discovery would also impact our theories of how planetary systems are born and grow. "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 says.

But, for now, we'll just have to wait and see.

Editorial note (Aug. 13, 2025): The planet candidate's temperature was originally compared to Saturn's, but in fact Alpha Cen b is more than twice as warm.