There are other planets out there, and astronomers have a lot of methods for detecting them. Nearly 2000 planets have been found so far. The most successful method for finding them is using transits, where a planet physically passes in front of its parent star, producing a measurable dip in the star's light. Exoplanets appear to orbit nearly every kind of star, and we've even found planets that are the same size as Earth. Astronomers think there may be many billions of Earth-like planets in our galaxy. [11:49]