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Astronomers using NASA’s James Webb Space Telescope have found tantalizing evidence of a giant planet orbiting Alpha Centauri A—part of the stellar system closest to our Sun. Located just 4 light-years away, the Alpha Centauri triple star system has long been a prime target for exoplanet hunters.
The system consists of Alpha Centauri A and Alpha Centauri B—both Sun-like stars—and the faint red dwarf Proxima Centauri, which already has three confirmed planets. Alpha Centauri A is the third-brightest star in the night sky, and scientists have been eager to know whether more worlds might be hiding nearby.
Now, Webb’s Mid-Infrared Instrument (MIRI) has produced the strongest evidence yet of a gas giant orbiting Alpha Centauri A. If confirmed, it would be the closest planet found in the habitable zone of a Sun-like star—though its gas composition means it likely can’t support life as we know it.
“With this system being so close, any exoplanets found would offer our best opportunity to collect detailed data,” says Charles Beichman of NASA’s Jet Propulsion Laboratory and the NASA Exoplanet Science Institute at Caltech’s IPAC. “These are incredibly challenging observations, even for Webb, because the stars are so bright and move across the sky quickly.”
The First Sighting.
In August 2024, Webb used MIRI’s coronagraphic mask to block Alpha Centauri A’s intense light. The nearby glare of Alpha Centauri B complicated things, but scientists subtracted both stars’ light, revealing a faint object over 10,000 times dimmer than Alpha Centauri A—about twice the Sun–Earth distance away.
The team needed more data. They scheduled follow-up observations in February 2025 and April 2025. But strangely, the mysterious object was gone.
The “Disappearing” Planet Mystery.
“We are faced with the case of a disappearing planet!” says Aniket Sanghi, a PhD student at Caltech and co-first author of the discovery papers.
The team ran millions of computer simulations, including earlier hints of a planet from the Very Large Telescope in 2019. The models suggest that in half of all possible orbits, the planet would have moved too close to the star during the February and April observations, making it invisible to Webb.
From the mid-infrared brightness and orbital models, the candidate could be a Saturn-mass gas giant traveling in an elliptical orbit between 1 and 2 astronomical units (AU) from Alpha Centauri A.
If proven real, it would be the closest directly imaged planet to its host star ever seen, and one that shares similarities in temperature and age with our own solar system’s giants.
Why It Matters.
Its existence in a binary star system would challenge current theories about how planets form and survive in such chaotic environments.
“This would become a touchstone object for exoplanet science,” says Beichman. “We could study it in exquisite detail with Webb and other telescopes.”
One such observatory is NASA’s Nancy Grace Roman Space Telescope, launching between late 2026 and mid-2027. Roman’s visible-light capabilities could reveal the planet’s size and reflectivity, complementing Webb’s infrared data.
Whether this “vanishing” world truly exists remains to be confirmed—but if it does, it could reshape our understanding of planetary systems and bring us closer than ever to exploring a nearby alien giant.