When Shoemaker-Levy 9 apparently broke up on July 7, 1992, its distance from the center of Jupiter was about 91,000 km, or about 1.3 Jupiter radii. The fragments collided with Jupiter over a seven-day period starting with fragment "A" on July 16, 1994 and ending with fragment "W" on July 22. The period between the breakup and the collision was a little more than two years. During that time, the fragments of Shoemaker-Levy 9 moved farther and farther away from each other.

Comets usually orbit the Sun, but Shoemaker-Levy 9 was captured by Jupiter's gravity and appears to have orbited the planet for about two decades before the breakup. After Shoemaker-Levy 9 broke into fragments, it was in an orbit around Jupiter that had a period of two years. The energy lost in the breakup of the comet lowered the point of closest approach ("perijove") of the subsequent orbit to within one Jupiter radius of that planet's center.

According to David Levy, a half-mile-wide object should hit the Earth on the average of once every 100,000 years. However, small objects the size of a grain of sand or a piece of gravel hit the Earth each minute. The frequency with which a 100-meter asteroid/comet hits Earth is about once every 100 years. The chances could be higher or lower because these small objects are not easy to see with our telescopes, so their number is not well known.

The craters on the moon were caused by impacts with other objects. Craters on Earth are evidence that large objects have hit it. Many scientists believe that an asteroid or a comet was responsible for the extinction of the dinosaurs. The current theory of the formation of Earth's moon is linked to a collision or close encounter with a very large body. The oceans are believed to have formed from the impacts of many water-rich planetesimals and cometesimals.

A small asteroid fragment entered the sparsely-populated region of Tunguska, Siberia on June 30, 1908, causing destruction of many trees and reindeer. Craters on most solar system bodies provide evidence of collisions with asteroids or comets. If the impacted body is small, it can be forced into a different orbit and find itself captured by a nearby larger body. Some astronomers believe that the moons of Mars are really asteroids that ventured too close to the planet and were trapped by its gravity.

The fragments of Shoemaker-Levy 9 were traveling at an impact speed of 60 km/sec when they struck Jupiter with a kinetic energy equivalent to 600 times the world's estimated nuclear arsenal.

Scientists are still not certain whether the Shoemaker-Levy 9 was a comet or an asteroid. At present, many scientists favor a cometary origin. But we may never know the answer because comets and asteroids have so much in common. Comets and asteroids are both small bodies. Both are primordial, having formed 4.5 billion years ago. And they can be found near Jupiter. Comets generally contain a large amount of water; asteroids do not. Some analyses tend to favor that Shoemaker-Levy 9 was a comet. One such analysis shows the nuclei had comas before the impacts. However, some data still leave doubt as to the origin of Shoemaker-Levy 9. One finding, for example, reveals an absence of a strong indication of water in the impact debris.

The impacts into the Jovian atmosphere have provided scientists with a natural tracer of Jovian winds. The high-speed easterly and westerly jets turned the dark spots into "curly-cue" features. Hubble's ultraviolet observations showed the debris particles sinking into Jupiter's atmosphere. The observation provided a three-dimensional perspective of Jupiter's wind patterns. At lower altitudes the impact debris flowed east and west; in the higher stratosphere they moved primarily from the poles toward the equator because auroral heating drove them in that direction. Auroral heating is caused by the interaction of ions with Jupiter's strong magnetosphere, producing heat and light.

The individual impact sites are fading, leaving behind a thin band of debris in the Jovian atmosphere. The material left from Shoemaker-Levy 9 will continue to sink into the depths of Jupiter's atmosphere, leaving no permanent change in Jupiter's appearance.