In astronomy, the Hills cloud is a theoretical vast circumstellar disc, interior to the Oort cloud and roughly aligned with the solar ecliptic plane, whose outer border would be located at around 20,000 to 30,000 astronomical units (AU) from the Sun, and whose inner border, less well defined, is hypothetically located at 250–1500 AU, well beyond planetary and Kuiper Belt object orbits—but distances might be much greater. If it exists, the Hills cloud likely contains roughly five times as many comets as the Oort cloud.