Hills cloud

For the gravitational sphere of astronomical bodies, see Hill sphere.
Artist's view of the theoretical Oort cloud, Hills cloud, and Kuiper belt (inset)

In astronomy, the Hills cloud (also called the inner Oort cloud[1] and inner cloud[2]) is a theoretical vast circumstellar disc, interior to the Oort cloud, 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,[citation needed] well beyond planetary and Kuiper Belt object orbits—but distances might be much greater. If it exists, the Hills cloud likely contains roughly 5 times as many comets as the Oort cloud.[3]

  1. ^ see Oort cloud
  2. ^ Villemin, Gérard. "Astronomie, astéroïdes et comètes" (in French).
  3. ^ Duncan, Martin J.; Quinn, Thomas; Tremaine, Scott (1987). "The Formation and Extent of the Solar System Comet Cloud". The Astronomical Journal. 94: 1330. Bibcode:1987AJ.....94.1330D. doi:10.1086/114571.