Oort cloud
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Comets are observed to come into the solar system from all directions, therefore the place from which the comets come is thought to be a giant sphere surrounding the solar system. This sphere is called the Oort Cloud after Jan Oort who postulated its existence in 1945. Thus comets are said to come from the Oort cloud. While some comets may come to the solar system from closer in, this place is called the Kuiper Belt and it is located past the orbit of Pluto. Kuiper Belt objects are suspected to be the source of the Jupiter family, a group of comets whose orbits take them between Jupiter and the sun in a short period of time (3-5 years). Comet Shoemaker-Levy 9 may have been one of those.