Astronomers identified more than 100 more worlds around other stars in 2012, but one especially hit home—because it is right next door. Scientists have spent more than a decade probing for planets around Alpha Centauri, a trio of stars just 4.4 light-years away. In October, Xavier Dumusque at the Observatory of Geneva and colleagues described a slight wobble in Alpha Centauri B, caused by the tug of an Earth-mass planet orbiting every three days around that yellowish, sunlike star.

Although the planet is probably rocky like Earth, it lies so close to Alpha Centauri B that its surface is surely molten. But where there is one planet there are usually more, Dumusque says. The worlds of the Alpha Centauri system will be among the few close enough to study for signs of life. NASA’s upcoming James Webb Space Telescope could dissect the planets' light and determine whether their atmospheres contain oxygen, water, and other biologically friendly ingredients. Other top 2012 planet finds:

One Planet, Four Suns: The concepts of sunrise and sunset must be confusing for any inhabitants of the planet PH1. It orbits two stars, which are also orbited by another stellar pair. The discovery was made by amateurs examining NASA data online.

Glittering Prize: Astronomers have found dozens of rocky worlds, but some rocks are more unusual than others. In October researchers determined that the nearby planet 55 Cancri e is composed largely of compressed carbon—making it, in essence, an enormous diamond.