Comet Shoemaker–Levy 9
The comet was discovered by astronomers Carolyn and Eugene M. Shoemaker and David Levy on March 24, 1993. It was found in a picture taken by the  Schmidt telescope at the Palomar Observatory, in California. When it was discovered, it was orbiting Jupiter. It was the first comet seen to be orbiting a planet. Scientists think that it had been orbiting the planet for 20 - 30 years before its discovery.