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The Planet Next Door

Representations of Alpha Centauri A (larger) and B,
overlaying a real image of the system.
Credit: European Southern Observatory
Big, big astronomy news announced last week: a new planet has been discovered orbiting one of our closest stellar neighbors. A mere 4.4 light years away, Alpha Centauri Bb is both the closest and smallest extra-solar planet yet discovered. And while the planet is too hot to support life,  it's presence suggests there may be other, Earth-size planets in the same system—possibly in the habitable zone.

To learn more about the new planet, how it was found, and plans to find more planets in the Alpha Centauri system, check out this week's podcast.

Alpha Centauri Bb orbits around the star Alpha Centauri B, a member of the three-star Alpha Centauri system. The two brightest stars in the system, Alpha Centauri A and Alpha Centauri B, are similar to our sun. These two stars exist in a binary system, meaning they orbit very closet together, around a common central point. A third star, called Proxima Centauri, orbits in a wide loop around A and B, at a distance of about one trillion miles. Proxima Centauri is a red dwarf: an extremely small, cool, and thus very dim star. Despite being the closest star to our solar system, Proxima Centaur is not visible with the naked eye.

In many ways the new planet is unremarkable (it's not a planet made of diamonds as far as we can tell) but it's proximity to our own planet is enough to send the imagination soaring. What if there are planets in the Alpha Centauri system that are the right temperature to host life (why do you need liquid water to support life, anyway?)? What if we developed technologies that allowed a probe to reach the system? The discovery of Alpha Centauri Bb is a landmark on our journey to explore world beyond our own.


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