Today researchers published an article in Nature describing the planet as “a small planet with a minimum mass of about 1.3 Earth masses orbiting Proxima with a period of approximately 11.2 days at a semi-major-axis distance of around 0.05 astronomical units. Its equilibrium temperature is within the range where water could be liquid on its surface.” (Proxima is a red dwarf. Its habitable zone is really close in.)
The discovery is the outcome of the Pale Red Dot Campaign to discover planets around Proxima, and involved observations from ground-based facilities like the European Southern Observatory’s HARPS instrument. More from the European Southern Observatory.
That Proxima b is in the habitable zone does not necessarily mean that it’s habitable, much less inhabited. It’s just that, unlike most other exoplanets discovered to date, we can’t rule out its habitability immediately. (Some estimates of the Sun’s habitable zone include Mars and Venus, which aren’t exactly pleasant places to live right now.) There are plenty of reasons why it may not be habitable: it’s tidally locked to its host star (as any planet in the habitable zone of a red dwarf would be), and Proxima puts out X-ray flares that could strip off any planetary atmosphere or oceans. On the other hand, it just might. But we’re unlikely to be able to find out for ourselves, as Charlie Stross points out in a badly needed reality check (written last Saturday, before the announcement but while rumours were swirling) — 4.25 light years is still very far away.
Proxima Centauri is a bit closer to our solar system than Alpha Centauri, a binary system that Proxima may be the third component of. In 2012 it was announced that a planet had been discovered around Alpha Centauri B, but that later turned out to be a false positive. Proxima b was discovered using the same method, but Bad Astronomer Phil Plait is more confident this time around: “In this case when I heard the news I was pretty skeptical, but after reading the paper it looks good to me. I’m satisfied the planet is real.”
Proxima Centauri has a planet. Sit down and absorb that news.