'Planet Nine' Is Still Just a Theory, NASA Cautions (Video)

The news that a planet about 10 times more massive than Earth may orbit the sun somewhere beyond Neptune has stirred up incredible excitement among scientists and the general public. In a video released by NASA, Jim Green, NASA's director of planetary science, cautions that it is still too early to claim that Earth's solar system has nine planets (again). "The idea of a new planet is certainly an exciting one for me as a planetary scientist, and I think for all of us," Green said in the video.