Impact event such as Engelier and Gerin on Iapetus, Mamaldi on Rhea and Odysseus on Tethys and Herschel on Mimas form significant surface features. 2018 models developed to explain the unusual spin of Uranus support a long-held theory that this was caused by an oblique collision with massive object twice the size of Earth. On July 1994, Comet Shoemaker–Levy 9 was a comet that broke apart and collided with Jupiter, providing the first direct observation of an extraterrestrial collision of Solar System objects. The event served as a "wake-up call", and astronomers responded by starting programs such as Lincoln Near-Earth Asteroid Research
Great Comet of 1744 "dust striae" seen in the tails of some comets, such as Comet West and C/2006 P1 (McNaught). Chéseaux, on March 9, was the last known observer in the northern hemisphere to see the comet, but it remained visible for observers in the southern hemisphere, some of whom reported a tail length of approximately 90 degrees on March 18. The comet was not seen after April 22, 1744. The comet also was noted in Japanese astronomical records in the "Nihon Odai Ichiran" of the Kanpō era. Researchers have found in Chinese astronomical records that some Chinese observations describe audible sounds associated