The 170-Year Search for a Planet Beyond Neptune
Clip: Season 46 | 2m 29s
Planet Nine’s existence is not the first time astronomers have predicted a planet they couldn’t see. Clyde Tombaugh was looking for Planet X when he accidentally found Pluto. After Voyager 2 flew by Neptune in 1989, new calculations determined there was no Planet X. But three years ago, a disturbance was detected at the far reaches of the Solar System.