Scientists have announced signs of a possible new planet around Alpha Centauri A, part of the star system nearest to us. The candidate, informally named Alpha Centauri Ab, would orbit in the habitable zone, where liquid water could exist.
The find was made using the James Webb Space Telescope in August 2024. Webb’s Mid-Infrared Instrument, equipped with a coronagraph to block out starlight, revealed a faint object orbiting at around twice the Earth–Sun distance. At that separation, a planet could be warm enough for water, a tantalising prospect so close to home.
A signal that disappeared
What complicates the story is that the planet seemed to vanish. Webb picked up the faint signal in 2024 but saw nothing in follow-up observations in February and April 2025.
“We are faced with the case of a disappearing planet!” said Aniket Sanghi of the California Institute of Technology, who led the study. His team ran computer models of millions of possible orbits to see what might explain the signal. “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,” Sanghi explained.
The models also lined up with a 2019 detection by the European Southern Observatory’s Very Large Telescope, which adds weight to the idea that this planet might be real, simply slipping in and out of view as it traces an elliptical path around its star.
What the data suggests
Webb’s data points to a world about the size of Saturn. Unlike Earth, it would be a gas giant, and so not directly habitable. But astronomers note that large moons around such planets could, in theory, provide conditions suitable for life.
Charles Beichman of NASA’s Jet Propulsion Laboratory described the potential significance. “This would become a touchstone object for exoplanet science, with multiple opportunities for detailed characterisation by Webb and other observatories,” he said.
Why Alpha Centauri matters
Alpha Centauri is not just any star system. Sitting about four light years away, it is the nearest trio of stars to us, made up of Alpha Centauri A, Alpha Centauri B, and Proxima Centauri. Proxima already has known planets, one of which orbits in its habitable zone, but this new candidate would be the closest planet ever directly imaged around a Sun-like star. That makes it a prime target for studying how planetary systems form and evolve near stars like our own.
The system itself is tricky to observe. Alpha Centauri A and B sit close together, their light overlapping. Untangling faint planetary signals from the glare of two bright stars is a technical feat, and part of the reason astronomers tread carefully before declaring this a confirmed discovery.
The case is not closed. With Webb’s observations limited by the timing of its view and the planet’s possible orbit, astronomers will need more chances to watch Alpha Centauri A. If the planet exists, it should eventually emerge again from the star’s glare.
NASA’s upcoming Nancy Grace Roman Space Telescope, expected to launch in 2027, could add critical evidence by providing visible-light observations to complement Webb’s infrared data.
For now, the world nearest to us remains a mystery. A Saturn-sized neighbour in the habitable zone of Alpha Centauri A might be waiting to be confirmed. As Sanghi put it, the planet may have slipped from sight, but if it is real, it should reveal itself again in the years ahead.
The find was made using the James Webb Space Telescope in August 2024. Webb’s Mid-Infrared Instrument, equipped with a coronagraph to block out starlight, revealed a faint object orbiting at around twice the Earth–Sun distance. At that separation, a planet could be warm enough for water, a tantalising prospect so close to home.
A signal that disappeared
What complicates the story is that the planet seemed to vanish. Webb picked up the faint signal in 2024 but saw nothing in follow-up observations in February and April 2025.
“We are faced with the case of a disappearing planet!” said Aniket Sanghi of the California Institute of Technology, who led the study. His team ran computer models of millions of possible orbits to see what might explain the signal. “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,” Sanghi explained.
The models also lined up with a 2019 detection by the European Southern Observatory’s Very Large Telescope, which adds weight to the idea that this planet might be real, simply slipping in and out of view as it traces an elliptical path around its star.
What the data suggests
Webb’s data points to a world about the size of Saturn. Unlike Earth, it would be a gas giant, and so not directly habitable. But astronomers note that large moons around such planets could, in theory, provide conditions suitable for life.
Charles Beichman of NASA’s Jet Propulsion Laboratory described the potential significance. “This would become a touchstone object for exoplanet science, with multiple opportunities for detailed characterisation by Webb and other observatories,” he said.
Why Alpha Centauri matters
Alpha Centauri is not just any star system. Sitting about four light years away, it is the nearest trio of stars to us, made up of Alpha Centauri A, Alpha Centauri B, and Proxima Centauri. Proxima already has known planets, one of which orbits in its habitable zone, but this new candidate would be the closest planet ever directly imaged around a Sun-like star. That makes it a prime target for studying how planetary systems form and evolve near stars like our own.
The system itself is tricky to observe. Alpha Centauri A and B sit close together, their light overlapping. Untangling faint planetary signals from the glare of two bright stars is a technical feat, and part of the reason astronomers tread carefully before declaring this a confirmed discovery.
The case is not closed. With Webb’s observations limited by the timing of its view and the planet’s possible orbit, astronomers will need more chances to watch Alpha Centauri A. If the planet exists, it should eventually emerge again from the star’s glare.
NASA’s upcoming Nancy Grace Roman Space Telescope, expected to launch in 2027, could add critical evidence by providing visible-light observations to complement Webb’s infrared data.
For now, the world nearest to us remains a mystery. A Saturn-sized neighbour in the habitable zone of Alpha Centauri A might be waiting to be confirmed. As Sanghi put it, the planet may have slipped from sight, but if it is real, it should reveal itself again in the years ahead.
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