Planetary habitability Jupiter orbits the Sun at about five times the distance between the Earth and the Sun. This is the rough distance we should expect to find good Jupiters elsewhere. Jupiter's "caretaker" role was dramatically illustrated in 1994 when Comet Shoemaker–Levy 9 impacted the giant. However, the evidence is not quite so clear. Research has shown that Jupiter's role in determining the rate at which objects hit Earth is significantly more complicated than once thought. The role of Jupiter in the early history of the Solar System is somewhat better established, and the source of significantly less debate. Early in the
Comet Shoemaker–Levy 9 thus a serendipitous discovery, but one that quickly overshadowed the results from their main observing program. Comet Shoemaker–Levy 9 was the ninth periodic comet (a comet whose orbital period is 200 years or less) discovered by the Shoemakers and Levy, hence its name. It was their eleventh comet discovery overall including their discovery of two non-periodic comets, which use a different nomenclature. The discovery was announced in IAU Circular 5725 on March 27, 1993. The discovery image gave the first hint that comet Shoemaker–Levy 9 was an unusual comet, as it appeared to show multiple nuclei in an elongated region