A ring of small, icy bodies orbiting the Sun beyond the outermost planet. The Kuiper belt, named after Dutch-born US astronomer Gerard Kuiper, who proposed its existence in 1951, is thought to be the source of comets that orbit the Sun with periods of less than 200 years. The first member of the Kuiper belt was seen in 1992. In 1995 the first comet-sized objects were discovered; previously the only objects found had diameters of at least 100 km (comets generally have diameters of less than 10 km). The belt is actually conceived as a disk-shaped region of icy bodies—including dwarf planets such as Pluto—and comets beyond the orbit of Neptune. It extends from about 30 to 55 AU and is probably populated with hundreds of thousands of icy bodies larger than 100 km (62 miles) across and an estimated trillion or more comets.