オールトの雲
In astronomy, the Hills cloud (also called the inner Oort cloud and inner cloud) is a vast theoretical 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 , well beyond planetary and Kuiper Belt object orbits—but distances might be much greater. If it exists, the Hills cloud contains roughly 5 times as many comets as the Oort cloud.