After years of searching, astronomers have finally spotted an Earth-mass planet in Alpha Centauri, the nearest star system to our own. Although the planet orbits too close to its parent star to host life, its discovery ups the chance of the system also hosting hospitable worlds.
Alpha Centauri looks like a single point of light from Earth, but it contains two bright stars that share a relatively close binary orbit, including one that looks a lot like our sun. This binary pair is in our cosmic backyard, about 4.3 light years away, spurring great interest in its ability to host planets.
"It is the most followed star in the search for planets," says Xavier Dumusque of the Geneva Observatory in Switzerland. Finding such worlds, however, proved to be a challenge. So far, planet hunters have ruled out the presence of gas giants akin to Jupiter in Alpha Centauri. Finding smaller planets with the methods available takes patience.
Using the La Silla Observatory in Chile, it still took Dumusque and colleagues four years to spot the planet around Alpha Centauri B, the smaller of the two stars.
. . . The team calculates that the new planet is 1.13 times the mass of Earth, which means it is likely to have a rocky composition. However, with a "year" of just over three Earth days, this rocky body is not our planet's twin.
"The surface temperature must be hundreds – thousands – of degrees. There is perhaps lava floating on the planet," says Dumusque. Still, planets tend not to be loners, so the Alpha Centauri system should have more. There's a chance these undetected worlds are in the habitable zone, the region around a star most likely to support life as we know it.