NPR logo Closest Star Harbors An Earth-Sized Planet


Closest Star Harbors An Earth-Sized Planet

Forget the debates, this is really important!

Astronomers have finally discovered a planet orbiting Alpha Centauri, the nearest star to the Sun. At a mere 4.4 light years away, scientists have long hoped that a planet would be found around this closest of stellar neighbors.

Alpha Centauri is actually a multiple star system and the planet is orbiting the star called Alpha Centauri B. The newly discovered world has a mass about that of our own Earth.

So — an Earth-sized planet orbiting the most nearby star — that is good news.

The bad news: it's a "hot" Earth. That means the planet's orbit is so small it's essentially parked right next to its star, with an orbit 25-times smaller than Earth's and a "year" that lasts just 3.2 days. Given such close proximity to Alpha Centauri B, surface temperatures on the planet would likely be around 2,000 degrees Fahrenheit. That's no place for a vacation.

Still, where there is one planet there may be another. Finding these low-mass worlds takes time and patience. Astronomers have to follow the wobble of the parent star, induced by the planet's gravity, across an entire orbit.

So maybe, just maybe, there is an Earth in an Earth-like orbit around Alpha Centauri. Stephane Udry of the University of Geneva, one of the co-authors of the paper put it best when she said, "Finding in our closest neighbor a one-Earth-mass planet really opens up the prospect for finding planets there in the habitable zone."