Recent observations from NASA’s James Webb Space Telescope revealed compelling evidence of a giant planet candidate orbiting Alpha Centauri A, a star in the nearest stellar system to the Sun. Led by assistant research professor Kevin Wagner, analysts at the University of Arizona’s Steward Observatory played a central role in confirming the findings. 

The Alpha Centauri system — which consists of Alpha Centauri A, Alpha Centauri B and the red dwarf Proxima Centauri — has long fascinated astronomers, with new findings making it even more enticing. 

Observations from JWST’s Mid-Infrared Instrument suggest that a gas giant could be orbiting Alpha Centauri A at roughly four light-years away. According to the UA’s Steward Observatory, this planet could be the closest known exoplanet orbiting a sun-like star within a potentially habitable zone. 

“Even though it’s most likely a gas giant, we’re still talking about a planet that could be orbited by moons in places where we could potentially envision life, existing right next door,” Wagner said. 

This milestone discovery began in 2019, when Wagner spotted unexplained points of light in the observatory known as the Very Large Telescope in Chile. In the following weeks, Wagner and his associates monitored the same points of light to rule out the data as noise or background artifacts. When the same point appeared years later on the opposite side of Alpha Centauri A in 2024 Webb Telescope data, the possibility of a genuine planetary orbit emerged.

“When you point the biggest telescope in the world at the brightest stars in the sky, you see some really weird things […]  eventually there was a point of light that just didn’t go away,” Wagner said. “We couldn’t explain it with any systematics, any models that we know of. So we can say it’s not random noise.” 

In more recent work, undergraduate researcher Connor Young described his own role in reprocessing and verifying the data. 

“My role has kind of just been trying to reverify that the planet candidate’s there […]. We’re like 75% sure,” Young said. “There’s a couple different things it could be [even though] it’s most likely a planet. But it could also be a big clump of dust, it could be just debris in general floating around there — but by the age of it, we don’t think that’s the case.”

Young explained that the team uses sophisticated computer code, now over 1,500 lines long, to reduce telescope images and filter out light from the stars themselves. This iterative process helps distinguish real celestial objects from dust, debris or image artifacts. Confirming a planet around Alpha Centauri is particularly difficult due to the brightness and proximity of its twin stars, Alpha Centauri A and B. 

“When all you have is a dot of light next to a star, you may or may not be looking at an actual planet, but when you see a dot of the same brightness several years later on the opposite side of the star, the story becomes much more compelling,” Wagner said. 

Tracking a single point of light as it shifts position over the long term provides astronomers with one of the strongest indicators of planetary motion. The Webb observations suggest that the candidate planet may be roughly the mass of Saturn, orbiting Alpha Centauri A in an elongated, one-to-two astronomical unit orbit. However, follow-up observations from this year failed to detect the planet, possibly because it had moved too close to its host star to be visible.

“The observations and orbital simulations provide us with a prediction for where the planet will be in the future, and the best time for us to go back and look at it will be in fall of next year,” Wagner said. 

Young emphasized the ongoing nature of scientific inquiry. The discovery is not yet confirmed, but each new data point brings astronomers closer to certainty. 

“Verification’s a little awkward of a process […]. We’re already pretty sure it’s there, but the closer we can get to a hundred, the better,” Young said. 

If confirmed, the Alpha Centauri A planet would mark one of the most remarkable exoplanet discoveries of the decade. Its presence raises exciting possibilities for future exploration of habitable moons within our galactic neighborhood.