Original: Comet Shoemaker-Levy 9 (formally designated D\/1993 F2, nicknamed String of Pearls for its appearance) was a comet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects.
Simplified: Comet Shoemaker-Levy 9 (SL9, D\/1993 F2) was a comet that broke apart and smashed into Jupiter in July of 1994.