Kuiper belt

The Kuiper belt, sometimes called the Edgeworth-Kuiper belt, is a circumstellar disc lying beyond the planets of the Sol system, extending from Neptune's orbit at thirty astronomical units out to roughly fifty. It resembles the asteroid belt but is far larger, twenty times as wide and twenty to two hundred times as massive, and it may hold as many as a hundred million individual objects, most of them remnants of the system's formation. Where asteroids tend toward rock and metal, Kuiper belt objects are mostly frozen volatiles: methane, ammonia and water. Three recognized dwarf planets sit there, Pluto, Haumea and Makemake, and some moons, Neptune's Triton among them, are thought to have started in the region. Short-period comets come from the belt. The long-period ones come from the Oort cloud, a vast shell of ancient icy bodies a thousand times farther out.