Comet Shoemaker–Levy 9

Comet Shoemaker-Levy 9 was a comet. It broke apart and crashed into Jupiter, in July 1994. The event was special because people could see, for the first time, how objects in the Solar System, outside Earth, collided. It caused a large amount of coverage in the media. The comet was carefully watched by astronomers worldwide. The crash gave new information about Jupiter. It also showed up its role in reducing space debris in the inner Solar System. The name came out of the discovers' last names.
Discovery of this comet.
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. 
Crash.
Calculations showed that its unusual broken up form was due to a previous closer approach to Jupiter in July 1992. At that time, the orbit of Shoemaker-Levy 9 passed within Jupiter's Roche limit. Jupiter's tidal forces had acted to pull the comet apart. The comet was later observed as a series of pieces up to in diameter. These fragments collided with Jupiter's southern hemisphere between July 16 and July 22, 1994. The pieces were moving at a speed of approximately 60 km/s. The impact scars were more easily seen than the Great Red Spot and they stayed for many months.