While astronomers have found a number of exoplanets over the last few years that share one or two key traits with our own world — such as size or inferred surface temperature — they have yet to bag a bona fide "alien Earth." But that should change in 2013, scientists say.

"I'm very positive that the first Earth twin will be discovered next year," said Abel Mendez, who runs the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo.