Yes, there is a planet at Alpha Centauri!

An artist’s conception of the Alpha Centauri System. Credit: ESO/L. Calçada/N. Risinger (

Science fiction fans the world over are vindicated as astronomers at the European Southern Observatory (ESO) have discovered a super-heated planet in the Alpha Centauri system. Better yet, it’s almost the same size as Earth!

Alpha Centauri is a triple star system just 4.3 light-years away, literally just next door in astronomical terms, since they are the closest stars to Earth besides the Sun. Two bright stars, Alpha Centauri A and B, orbit each other at about the distance between the Sun and Uranus, while the tiny red dwarf Proxima Centauri orbits them at a great distance. Now, ESO’s HARPS project has discovered a planet orbiting one of the stars, Alpha Centauri B.

The planet itself is known as Alpha Centauri Bb, and it may have a mass as small as 1.13 times Earth’s mass (and probably not much more). It is the smallest planet ever detected by radial velocity measurements and a very important step toward eventually discovering truly Earth-like planets. Finding small planets is hard, and this is the first time we’ve been able to make accurate measurements of a planet that is basically the same size as Earth.

But this planet is not Earth-like. It zips around Alpha Centauri B every 3.2 days, and it’s surface is so hot that it is probably made of molten rock obscured by a thick layer of dust. Finding slower-moving planets like our own is about five times as hard–but we’re getting there.

For now we can enjoy the fact that once we do have some way to travel interstellar distances (and there’s a half-decent chance we will by the end of this century), we’ll have someplace close by to go; and, if planets are as common as they appear, the nearest Earth-like planet might not be too far away, either. The fact that Alpha Centauri’s closeness makes it a favorite setting for science fiction, including, most recently, Avatar, makes it twice as fun. True, Alpha Centauri Bb isn’t quite Pandora, but it takes us one step closer.


About Alex R. Howe

I'm a full-time astrophysicist and a part-time science fiction writer.
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