Using JWST, astronomers have found what looks to be a pretty decent candidate for a planet orbiting Alpha Centauri A! To be very clear, this planet is not yet confirmed, so it may not be real. But it looks pretty robust, and could be confirmed relatively soon. If so, YAY! A planet around the nearest Sun-like star in the Universe! Not only that, but it orbits the star in its habitable zone, meaning the temperature isn’t too hot or too cold. Interesting…

Alpha Centauri is one of the most famous stars in the sky because it’s the closest known stellar system to Earth. It’s actually a trinary star: two stars very much like the Sun orbit each other pretty close together, and a third, called Proxima Centauri, orbits the pair about 0.2 light-years out.

The pair orbiting each other are called Alpha Centauri A and B (or just Alpha Cen A and B for short). Alpha Cen A is very much like the Sun, being just a little bit more massive, bigger, and brighter. Alpha Cen B is a bit cooler, smaller, and dimmer. They orbit each other every 80 years on an elliptical path that brings them from about 1.7 billion km at their closest to about 5.3 billion at their most distant (roughly the distance of Saturn from the Sun to the distance of Neptune, respectively). From Earth, they appear pretty close together, about 20 arcseconds apart (for comparison, the Moon is about 1,800 arseconds across in our sky). 

Because they’re so close to us, about 4.3 light-years, they’ve long been a target not just of our science but of our imagination. Aliens from Alpha Cen is a scifi trope, used in countless novels, TV shows, and movies. But are planets there even possible?

Planets have been confirmed orbiting Proxima Cen, which itself is a dim red dwarf. These kinds of stars are really good at making planets, so in hindsight this discovery isn’t surprising (though still VERY cool, because Proxima Cen is a hair closer to us than the binary it orbits, making it the closest star to us in the Universe). So why not Alpha Cen A and/or B?

We know many binary stars have planets. Most are circumbinary, meaning the planet orbits both stars farther out than they orbit each other. Quite a few have been found orbiting one of the stars in a binary pair as well.

The stability of a planet orbiting one star in a binary is tricky. It has to orbit close enough to its host star that the gravity of the second star doesn’t yank on it too hard, ejecting it from the system. In general, it has to be about ¼ or less of the distance to the second star to remain stable (I discuss this in more detail in my book Under Alien Skies, by the way). There’s plenty of room around Alpha Cen A for a planet, then, as long as it doesn’t get too far out.

The star has been a target for planet hunters for a long time (in fact with another astronomer I proposed using STIS, a camera on Hubble, to look for one back in the 90s, but it got turned down as being too speculative, which, fair). In 2021 astronomers announced they found a candidate planet orbiting Alpha Cen A using the Very Large Telescope (or VLT), but the detection wasn’t strong enough to make a confident claim.

So another team of astronomers (including some from the VLT observations) decided to take a look using JWST (and published their results in two papers: Paper 1, Paper 2). The telescope sees infrared light, which is a big advantage in looking for planets; stars like Alpha Cen A don’t put out nearly as much light in the infrared as they do in the visible wavelengths (the kind we see), and warm planets are bright in infrared, so this maximizes the contrast. The team used JWST’s Mid Infrared Instrument (also called MIRI) to see what they could see.

This is actually a very tricky observation. Alpha Cen A is so bright that actually pointing the telescope at it accurately is difficult. To reduce its glare, they put it behind what’s called a coronagraphic mask, a small piece of metal designed to block a star’s light to allow fainter nearby objects to be seen. Not only that, but Alpha Cen B is also very bright and so close (about 8 arcseconds when the observations were taken) that its light overwhelms the telescope. To take care of that, the astronomers observed a very similar star (Epsilon Muscae, a red giant with similar colors as Alpha Cen B) so they could subtract it from the image of Alpha Cen B, minimizing its impact (I talk about this technique in BAN Issue 725).

Finally, they also planned on “rolling” JWST, which means rotating the observatory between observations so the image itself rotates. Features in the image (like blobs of light and such) can be due to the camera itself. If the spacecraft rolls and the features move around the star, then they’re part of the camera. If the features don’t move, then they’re something real in the sky.

They ran three observing campaigns; in August 2024, February 2025, and again in April 2025. After carefully processing the data, what they found is interesting indeed: in the August 2024 images there is a blob of light, about 1/20,000^th as bright as Alpha Cen A, just 1.5 arcseconds from the star. However, it was not seen in the later observations.

What is it? Well, that’s the big question. Unfortunately, the roll maneuvers didn’t work in the August ’24 observations. Damn the luck! This means they can’t be 100% sure the blob isn’t some weird camera artifact. However, they performed a lot of detailed analysis and conclude it’s unlikely to be an artifact. Nor is it likely to be an object in the foreground (like an asteroid in our solar system) or background (like a distant galaxy).

Ironically, the fact that it’s not seen in the other images means it may actually be a planet! That’s because planets move. They orbit their stars, so it’s possible in images taken months later the planet had moved enough that it was too close to the star to be seen.

Become a paying subscriber of Premium to get access to this post and other subscriber-only content.

Already a paying subscriber? Sign In.

A subscription gets you:

• • Three (3!) issues per week, not just one
• • Full access to the BAN archives
• • Leave comment on articles (ask questions, talk to other subscribers, etc.)