This planet candidate, Alpha Centauri Ab, could be a gas giant, orbiting 1 to 2 times the distance between Sun and Earth, according to two papers to be published in the Astrophysical Journal Letters. If confirmed, this planet would be the closest to Earth that orbits in the habitable zone of a Sun-like star. However, because the planet is a gas giant, astronomers say it would not support life as we know it.
This artist’s concept shows what a gas giant orbiting Alpha Centauri A could look like. Image credit: NASA / ESA / CSA / STScI / Robert L. Hurt, Caltech & IPAC.
Located in the constellation of Centaurus, Alpha Centauri is the closest stellar system to Earth.
Also known as Rigil Kentaurus, Rigil Kent and Gliese 559, the system is made up of the bright binary star formed by Alpha Centauri A and Alpha Centauri B, plus the faint red dwarf star Alpha Centauri C.
The two brighter components are roughly 4.35 light-years away from us. Alpha Centauri C, better known as Proxima Centauri, is slightly closer at 4.23 light-years.
Compared to the Sun, Alpha Centauri A is of the same stellar type G2, and slightly bigger (1.1 times more massive than the Sun and about 1.5 times more luminous).
Alpha Centauri B, a K1-type star, is slightly smaller and less bright (0.9 times the mass of the Sun and about 45% of its visual luminosity).
Alpha Centauri A and B orbit a common center of gravity once every 80 years, with a minimum distance of about 11 times the distance between the Earth and the Sun.
Because these two stars are, together with Proxima Centauri, our nearest interstellar neighbors, they are among the best studied by astronomers.
And they are also among the prime targets in the hunt for potentially habitable planets.
“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,” said Dr. Charles Beichman, an astronomer at NASA’s Jet Propulsion Laboratory and the NASA Exoplanet Science Institute at Caltech’s IPAC astronomy center.
“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.”
This image shows the Alpha Centauri star system from several different ground- and space-based observatories: the Digitized Sky Survey (DSS), the NASA/ESA Hubble Space Telescope, and the NASA/ESA/CSA James Webb Space Telescope. 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 MIRI instrument, which uses a coronagraphic mask to block the bright glare from Alpha Centauri A, reveals a potential planet orbiting the star. Image credit: NASA / ESA / CSA / Aniket Sanghi, Caltech / Chas Beichman, NExScI, NASA & JPL-Caltech / Dimitri Mawet, Caltech / Joseph DePasquale, STScI.
The first observations of the system took place in August 2024, using the coronagraphic mask aboard Webb’s Mid-Infrared Instrument (MIRI) to block Alpha Centauri A’s light.
While extra brightness from the nearby companion star Alpha Centauri B complicated the analysis, the astronomers were able to subtract out the light from both stars to reveal an object over 10,000 times fainter than Alpha Centauri A, separated from the star by about two times the distance between the Sun and Earth.
While the initial detection was exciting, they needed more data to come to a firm conclusion.
However, additional observations of the system in February 2025 and April 2025 did not reveal any objects like the one identified in August 2024.
“We are faced with the case of a disappearing planet,” said Caltech Ph.D. student Aniket Sanghi.
“To investigate this mystery, we used computer models to simulate millions of potential orbits, incorporating the knowledge gained when we saw the planet, as well as when we did not.”
In these simulations, the team took into account both a 2019 sighting of the potential exoplanet candidate by ESO’s Very Large Telescope, the new data from Webb, and considered orbits that would be gravitationally stable in the presence of Alpha Centauri B, meaning the planet wouldn’t get flung out of the system.
“A non-detection in the second and third round of observations with Webb isn’t surprising,” Sanghi said.
“We found that in half of the possible orbits simulated, the planet moved too close to the star and wouldn’t have been visible to Webb in both February and April 2025.”
“Based on the brightness of the planet in the mid-infrared observations and the orbit simulations, it could be a gas giant approximately the mass of Saturn orbiting Alpha Centauri A in an elliptical path varying between 1 to 2 times the distance between Sun and Earth.”
“If confirmed, the potential planet seen in the Webb image of Alpha Centauri A would mark a new milestone for exoplanet imaging efforts,” Sanghi said.
“Of all the directly imaged planets, this would be the closest to its star seen so far.”
“It’s also the most similar in temperature and age to the giant planets in our Solar System, and nearest to our home, Earth.”
“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.”
If confirmed by additional observations, the results could transform the future of exoplanet science.
“This would become a touchstone object for exoplanet science, with multiple opportunities for detailed characterization by Webb and other observatories,” Dr. Beichman said.
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Charles Beichman et al. 2025. Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of Cen A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits. ApJL, in press; arXiv: 2508.03814
Aniket Sanghi et al. 2025. Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of Cen A. II. Binary Star Modeling, Planet and Exozodi Search, and Sensitivity Analysis. ApJL, in press; arXiv: 2508.03812
