Comets have two "homes" or source areas. Most comets reside outside the Solar System, in a large spherical region called the Oort Cloud. It is named after Jan Oort, the Dutch astronomer who first proposed its existence. The Oort Cloud is very far away, between 5 to 8 trillion kilometers from the Sun. It probably contains trillions of comets, all of which are leftovers from the formation of the Solar System. Most comets stay in the Oort Cloud. However, when disturbed by gravity or collisions, a comet may drop into the Solar System, where we can see it.

The second home of comets is the Kuiper Belt, named after the American astronomer Gerard Kuiper. The Kuiper Belt is a ring of comets within the Solar System, between the orbits of Neptune and Pluto. Like the Oort Cloud, Kuiper Belt comets are remnants from the forming Solar System. They travel in toward the Sun when disturbed by the gravity of nearby planets. Halley’s Comet, which is visible from Earth about every 75 years, and Comet Hale-Bopp are both Kuiper Belt comets.