NASA’s James Webb Space Telescope has provided new evidence of a giant planet orbiting Alpha Centauri A, one of three stars making up the Alpha Centauri triple star system, our solar system’s nearest stellar neighbor.
Only four light years away, the possibility of worlds in Alpha Centauri has long intrigued astronomers. Of the three, only Proxima Centauri, a faint red dwarf star, has been confirmed to harbor planets, while the status of the Sun-like binary stars Alpha Centauri A and Alpha Centauri B remains uncertain.
However, following a promising round of observations late last year, additional efforts to detect the suspected gas giant resulted in a cosmic cold case, as astronomers behind a recent pair of studies found that the object initially spotted by Webb’s powerful eye had seemingly vanished without a trace.
“We are faced with the case of a disappearing planet!” said Aniket Sanghi of Caltech in Pasadena, California, and the co-first author of the new papers.
James Webb Space Telescope MIRI
The Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope obtained the data used in the new research, described in a pair of papers accepted for publication. If the findings are confirmed, this would be the nearest known planet to Earth residing in the habitable zone—an orbital distance from its host star that is far enough for water to remain liquid, but not so close that it would evaporate.
“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 co-lead author Charles Beichman, of 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.”
“Webb was designed and optimized to find the most distant galaxies in the universe,” added Beichman. “The operations team at the Space Telescope Science Institute had to come up with a custom observing sequence just for this target, and their extra effort paid off spectacularly.”
Observing Alpha Centauri A
The team’s first observations of Alpha Centauri A took place in 2024, using a coronagraphic mask to dim the star’s light. Even so, the brilliance of Alpha Centauri B seeped into the imaging, requiring further work to subtract the excess light. Careful image processing revealed an object more than 10,000 times dimmer than Alpha Centauri A, located about twice the Earth-Sun distance from its star.
Despite the initial excitement, follow-up observations in February and April 2025 failed to locate the object again.
“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,” said co-first author Aniket Sanghi of Caltech in Pasadena, California.
The team’s simulations considered three key factors: the 2024 sighting, a previous 2019 potential exoplanet sighting made by the European Southern Observatory’s Very Large Telescope, and orbital paths stable enough to prevent Alpha Centauri B’s gravity from ejecting the object from the system.
A Complex Analysis
Determining the nature of the object required multiple layers of investigation. Webb performed several rounds of observations, after which the team analyzed the data and created detailed computer models. This process suggested that the object is likely a planet orbiting Alpha Centauri A, rather than being a false positive caused by a background galaxy, a passing asteroid, or an image artifact.
While the lack of detections in the follow-up observations might seem discouraging, the team’s simulations provided an alternative explanation.
“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,” said Sanghi.
Based on its brightness and the simulation results, the researchers believe the object is most likely a gas giant similar in mass to Saturn, following an elliptical orbit that varies between one and two times the distance of Earth’s orbit around the Sun.
Continuing Exoplanet Research
“If confirmed, the potential planet seen in the Webb image of Alpha Centauri A would mark a new milestone for exoplanet imaging efforts,” Sanghi says. “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.”
The team notes that confirmation would represent a major development for exoplanet research.
“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 said.
“This would become a touchstone object for exoplanet science, with multiple opportunities for detailed characterization by Webb and other observatories,” added Beichman.
Future observation platforms will be able to provide even greater insight into the potential gas giant. NASA plans to launch its Nancy Grace Roman Space Telescope sometime between fall 2027 and spring 2027. That spacecraft will feature new equipment for observing binary systems in the visible light spectrum, adding more context to the James Webb Space Telescope’s infrared data.
The papers, “Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits” and “Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of α Cen A. II. Binary Star Modeling, Planet and Exozodi Search, and Sensitivity Analysis,” have been accepted for publication in The Astrophysical Journal Letters, and preprint versions are currently available on arXiv.org.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. Contact him at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.