a disk-shaped region on the edge of the solar system that contains masses of ice and icy rock, believed to be the source of comets with orbital periods of less than 200 years. Compare Oort cloud.
a region of the solar system far beyond the orbit of the dwarf planet Pluto in which billions of comets move in nearly circular orbits unless one is pulled into a highly eccentric elliptical orbit by a passing star. Compare Kuiper belt.
