Alpha Centauri’s possible planet: a warm Neptune, a very large Earth.

Scientific American wonders whether we’ve just spotted a new planet orbiting Alpha Centauri, our sun’s nearest neighbor. If it’s there, that potential planet is in the just-right “Goldilocks zone” where water stays liquid enough for life to form, despite being a vast world the size of a small gas giant:

But even though it would be shrouded in gas and essentially bereft of any surface to stand on, its distance from its star would place it in the so-called “habitable zone” where liquid water could exist. No other planet has been directly seen in this starlight-drenched region around any other star, because of the associated glare.

The new findings were reported Wednesday in the journal Nature Communications. They come from an international consortium of planet hunters called Breakthrough Watch, via the inaugural science run of a one-of-a-kind “direct imaging” instrument called NEAR (New Earths in the AlphaCen Region), which operates on the European Southern Observatory’s (ESO) Very Large Telescope (VLT) in Chile. The effort is named for its chief funding organization, Breakthrough Initiatives—the brainchild of the Silicon Valley billionaire Yuri Milner, who also sponsors related projects to search the heavens for signs of alien civilizations and to send pint-sized interstellar probes to the Alpha Centauri system.

“Alpha Centauri presents us with a magical opportunity, because there is no better place in the sky to try to directly image small, potentially habitable planets,” says study co-author Pete Klupar, Breakthrough Initiatives’ chief engineer. “This was in some sense low-hanging fruit—for just $3 million, we were with our international partners able to build an instrument to take advantage of ESO’s billions of dollars invested in its telescopes. But it’s also like going after a needle in a haystack, which is why no one has ever done this before. Governments tend to build survey instruments, to look at large numbers of stars and guarantee a return on investment, whereas NEAR was purpose-built to just do this one, risky thing.”

Kevin Wagner, the study’s lead author and a postdoctoral Sagan Fellow at the University of Arizona, first saw the telltale evidence of a planet-like blip cresting far above NEAR’s instrumental noise. It happened while he was remotely processing a batch of data during a family vacation in Lake Jocassee, S.C. Measuring its brightness and sandwiching it between limits on planet masses and sizes calculated in previous studies by other groups, the Breakthrough Watch team estimated that—if the blip were indeed a planet—it would most likely be somewhere between Neptune and Saturn in size. By November, he and his colleagues were certain the find was worth publishing, even if it proved not to be a world at all.

“In a way, I hope we haven’t detected anything this time, too,” Wagner says. “Because what I’m most excited to find is an Earthlike planet in the habitable zone. The presence of a Neptune in the habitable zone of Alpha Centauri A would not rule out something smaller nearby, but it would limit some of the area in which we could hope for rocky worlds to exist there in the first place.”

You can read the Breakthrough Watch study here in Nature Communications.