Oort cloud. Computer illustration of the Oort cloud of comet nuclei thought to form a spherical halo around the solar system. The Sun and solar system are at centre, but are not seen at this scale. The outer edge of the Oort cloud may be up to 100,000 astronomical units (the distance from the Earth to the Sun) from the Sun, or around 1.5 light years. The Oort cloud comprises billions of comet nuclei, small lumps of rock and ice. Some of these may fall into the solar system to become visible as comets. The bright horizontal band is the Kuiper Belt, a disc of asteroid-like bodies in the plane of the solar system.