Original: Comet Shoemaker-Levy 9 (SL9, formally designated D/1993 F2) was a comet that broke apart and collided with Jupiter in July of 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.