NASA/ESA/CSA/STSci/ A. Sanghi (Caltech)/C. Beichman (JPL)/D. Mawet (Caltech/ J. DePasquale (STScI)
If Earth needs to borrow a cup of sugar, it's comforting to know that there may be a convenient, possibly habitable, world orbiting Alpha Centauri only 4.34 light years away - at least, if the findings from the James Webb Space Telescope pan out.
Alpha Centauri is one of those rare stars in our galaxy that has made it into popular culture. That's understandable, since it is our closest neighbor, and there's an off chance that there could be someone there wondering if there's life back here.
In fact, Alpha Centauri is a triple-star system made up of two stars, Alpha Centauri A and Alpha Centauri B that orbit around one another and a third, Proxima Centauri, that orbits the other two. Until now, only Proxima Centauri was known to have two and possibly three planets. One of these is in the habitable zone, the distance from its red dwarf sun where liquid water can exist, though it's very close in and periodically subjected to massive radiation bursts, so it's unlikely that any life exists there.
Alpha Centauri A, on the other hand, is much more interesting from an Earth perspective. It's a G2V star similar to the Sun, which is a kind that we know can support a life-bearing planet because we're the proof. The problem was that Alpha Centauri A didn't have any known planets, so it looked as though the entire star system was a busted flush.
That is, until the latest studies based on the Hames Webb observations were made public.
The problem with hunting for planets orbiting a G2 star is the same reason that most exoplanets have been found swinging around red dwarfs. Red dwarfs are small and dim. In addition, planets, especially in the habitable zone, tend to be closer in. This makes it relatively easy to notice changes in the light curve as an exoplanet passes in front of its star. A G2 star, on the other hand, is much brighter and the habitable zone farther away, with any planets with life-supporting potential having longer orbital periods, making them that much harder to detect.
So how do you find a suspected planet that's 10,000 times dimmer than the star it orbits? By being exceptionally clever.
The team used what is called coronagraphic imaging to remove Alpha Centauri A and the light scatter of Alpha Centauri B from the picture. This involved sighting on a third reference star that is similar to Alpha Centauri A but doesn't have a companion. Since this star has known properties, it can be used as a baseline for calculations to get rid of the light noise from Alpha Centauri A, light scattering, and interference from the telescope itself. What's left behind should be any planets in the vicinity. However, just to make sure, the astronomers also eliminated any nearby asteroids or spacecraft that might be in front of the star or any distant galaxies that might be behind it.
The next step took a bit more patience because, though they did find what might be a planet from observations in August 2024, it kept disappearing. That meant more observations in February and April 2025, which didn't find anything. So, it was back to the figurative drawing board as they created computer models that ran millions of possible simulated orbits until a stable one was found that could explain both the appearance of the object and its later disappearance due to its being too close to Alpha Centauri A to be seen.
From this, the team deduces that the new planet, if fully confirmed, is similar to Saturn or Jupiter in size and is in the habitable zone of the star, where its surface temperature is estimated as 225 K (-48 °C or -55 °F). Its orbit is a bit eccentric as it revolves around Alpha Centauri A once every two or three Earth years.
It's not at all likely that there's life on the planet, since it's a gas giant, but it might have a habitable moon or there may be other habitable zone planets in the vicinity, much as Earth has Venus and Mars in the solar system's habitable zone.
At any rate, being able to planet hunt in such close (in cosmic terms) proximity is heartening to scientists. Meanwhile, the questions of life and availability of cups of sugar available for borrowing remains on hold.
"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, NASA's Jet Propulsion Laboratory and the NASA Exoplanet Science Institute at Caltech's IPAC astronomy center. "Yet, these are incredibly challenging observations to make, even with the world's most powerful space telescope, because these stars are so bright, close, and move across the sky quickly. Webb was designed and optimized to find the most distant galaxies in the universe. The operations team at the Space Telescope Science Institute had to come up with a custom observing sequence just for this target, and their extra effort paid off spectacularly."