For the first time, scientists have discovered planets roughly the size of ours outside our solar system. Kepler-20e and Kepler-20f are the smallest exoplanets yet found, Discovery reports. Because they're so close to the star they orbit, they don't appear habitable, but the finding is "next major milestone to finding habitable planets beyond our solar system," says a NASA scientist.
A year on Kepler-20e—that is, a full orbit of its star—takes about six days, while Kepler-20f completes its orbit in about 20 days, NASA reports. The planets were discovered using the Kepler space telescope, fulfilling the Kepler mission's "primary goal," says the head of the team that made the find. "This discovery demonstrates for the first time that Earth-size planets exist around other stars, and that we are able to detect them." (Read more Earth stories.)