Webb finds evidence of a giant 'disappearing' planet around the Sun’s nearest twin

Alpha Centauri, a triple star system just four light-years away from Earth, has long been an area of interest in the search for exoplanets. Alpha Centauri contains three stars: Alpha Centauri A and B, both Sun-like stars, and Proxima Centauri, a faint red dwarf star. Research has confirmed the existence of three planets orbiting Proxima Centauri. But the brightness of Alpha Centauri A and B has made any such discovery around them an uphill task.

Now, Webb’s Mid-Infrared Instrument has found evidence of a planet orbiting Alpha Centauri A. The image from Webb, coupled with analysis from a research team and computer modeling, suggests that the planet could be a gas giant approximately the mass of Saturn, circling the star in an elliptical orbit that ranges from one to two times the Earth-Sun distance.

To see this planet, Webb utilized the coronagraphic mask aboard its MIRI to block out Alpha Centauri A’s light. Further efforts by the team helped filter out the light from Alpha Centauri B, revealing an object 10,000 times fainter than Alpha Centauri A, believed to be a planet.

This initial detection was made in August 2024. However, two other attempts in February and April 2025 failed to reveal any objects like the one previously identified. “We are faced with the case of a disappearing planet,” said PhD student Aniket Sanghi of Caltech and co-first author on two papers covering the team’s research. Simulations suggested that the planet’s proximity to the star at the time of the February and April observations could be the reason Webb couldn’t find the planet.

Future observations, potentially including those from the upcoming Nancy Grace Roman Space Telescope, could provide more information about the planet.