Kuiper belt and Oort cloud. Illustration showing the Kuiper belt (white band) and the Oort cloud (sphere) surrounding the solar system (Sun at centre). The Oort cloud, a postulated cloud of comet nuclei surrounding the solar system, is thought to extend over a light year from the Sun, up to a distance of about 100,000 astronomical units (AU). It forms a spherical shell with relatively empty areas (upper and lower centre) each side of the solar system. The existence of the Oort Cloud is inferred from the orbits of long-period comets that take millions of years to orbit the Sun. The Kuiper Belt is a disc of asteroid-like bodies in the plane of the solar system, but orbiting beyond Neptune. Pluto and some other dwarf planets are Kuiper Belt objects.