Disappearing Planet Spotted Next Door in Alpha Centauri

Astronomers using NASA’s James Webb Space Telescope have spotted what could be a giant planet orbiting Alpha Centauri A, the nearest Sun-like star to Earth and part of the closest stellar system to our own.

The candidate world, glimpsed in August 2024, lies in the star’s habitable zone about twice the Earth-Sun distance away. If confirmed, it would be the closest planet ever directly imaged in the habitable zone of a Sun-like star. But there is a twist — the planet vanished in follow-up observations, leaving scientists to puzzle over its elusive orbit and the challenges of finding worlds in such a bright, complex system.

A Target Next Door

Alpha Centauri is a triple star system 4.37 light-years away, made up of Sun-like Alpha Centauri A and B and the faint red dwarf Proxima Centauri. While three planets are confirmed around Proxima, planets around A and B have been harder to prove. Alpha Centauri A is the third brightest star in the night sky and visible only from the Southern Hemisphere.

Webb’s Mid-Infrared Eye

Using the Mid-Infrared Instrument (MIRI) coronagraph, the team blocked Alpha Centauri A’s glare and subtracted out stray light from its companion star. This revealed an object more than 10,000 times fainter than the star, separated by about 1.5 arcseconds. “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 Charles Beichman of NASA’s Jet Propulsion Laboratory and the NASA Exoplanet Science Institute at Caltech’s IPAC. “The operations team had to come up with a custom observing sequence just for this target, and their extra effort paid off spectacularly.”

The Case of the Vanishing Planet

The object, dubbed S1, appeared only in the August 2024 images. Two later Webb observations, in February and April 2025, showed nothing similar. “We are faced with the case of a disappearing planet!” said Aniket Sanghi, a Caltech PhD student and co-first author. The team ran millions of orbital simulations, incorporating the August detection, the two non-detections, and a possible earlier sighting by the VLT’s NEAR experiment in 2019.

• About 50% of simulated orbits placed the planet too close to the star to be seen in both 2025 observations
• The best-fit orbits suggest a Saturn-mass gas giant moving between 1 and 2 astronomical units from Alpha Centauri A
• The planet’s temperature would be near 225 Kelvin, similar to the giant planets in our own system
• Its orbit is likely elliptical and inclined due to the gravitational pull of Alpha Centauri B

Why This Matters

“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.”

What Comes Next

The team hopes to observe again in August 2026, when the planet’s predicted position will be more favorable. By 2027, a background star will drift close enough to make searches harder. Future missions like NASA’s Nancy Grace Roman Space Telescope could complement Webb’s infrared data with visible-light measurements, offering new insights into the planet’s size and reflectivity.

Reference

Beichman, C., Sanghi, A., Mawet, D., et al. “Worlds Next Door: A Candidate Giant Planet Imaged in the Habitable Zone of Alpha Centauri A. I. Observations, Orbital and Physical Properties, and Exozodi Upper Limits.” Astrophysical Journal Letters (2025).

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