Another collection of a vast number of objects form a belt somewhat similar to the asteroid belt, but out beyond the orbit of Neptune between about 30 and 55 AU. The belt was named the Kuiper (Pronounced: Ku-I-per) belt after Gerard Kuiper, a pioneer in planetary astronomy. A number of Kuiper belt objects have been discovered with diameters between 100 and 400 km. The Kuiper belt is thought to be the origin of many short-period (<200 years) comets. Pluto and its moon, Charon, are similar to Kuiper belt objects, which is one reason why Pluto was demoted from full planet status.
Whereas objects in the main asteroid belt are mostly rocky objects, the Kuiper belt objects are thought to be mostly composed of ices. Besides water ice, there may be large quantities of frozen methane and ammonia. Besides Pluto, two other dwarf planets named Haumea and Makemake are considered to be part of the Kuiper belt.
The Kuiper belt object 2014 MU69 is a target for the New Horizons spacecraft now that it has passed Pluto.
In July 2005, a team of scientists announced the discovery of a Kuiper belt object that is similar in size to Pluto. It has been named Eris. It orbits the sun about once every 560 years, its distance varying from about 38 to 98 AU. (For comparison, Pluto travels from 29 to 49 AU in its solar orbit.) Eris has a small moon named Dysnomia. Eris, Pluto and the asteroid Ceres have been classified as dwarf planets.