A short-period comet is a comet with a period of less than 200 years. Short-period comets are now subdivided into Jupiter-type comets, such as comets Encke and Tempel 2, which have periods of less than 20 years; and intermediate-period or Halley-type comets, with periods between 20 and 200 years. Jupiter-type comets are believed to originate in the Kuiper belt, which surrounds the Sun at distances between about 30 astronomical units (the distance of Neptune) and 50 astronomical units (7.5 billion km, 4.7 billion miles). The gravitational influence of the outer planets, Neptune and Uranus, is thought occasionally to perturb some of the Kuiper belt objects causing them to take up the orbits characteristic of comets in the Jupiter family. Halley-type comets, together with long-period comets, however, appear to come from the Oort cloud.