The Kuiper Belt is named after Gerard Kuiper who postulated its existence in 1951. Kuiper suggested that some comets, which pass by the sun repeatedly (short-period comets), and approach the sun from within the same plane as that of the other planets, may originate in a region closer to the solar system than 100,000 AU, where the Oort Cloud is. He speculated that the region of space beyond Pluto could be populated with comets.
This picture shows the region of space where the Kuiper Belt is postulated to exist. In this picture, the observer is looking down on the solar system from above. The picture shows a region from the sun to 120 AU. The earth is so close to the center of the drawing that it does not show up.
The first object in the Kuiper Belt was discovered in 1992, proving that Gerard Kuiper's theory of 1951 was correct. Since then many objects have been discovered in this region, which is sometimes called "trans-Neptunian space" because even the planet Pluto could really be a Kuiper Belt object. The objects are usually very small, however, 10-50 km across, and not very bright. It takes hundreds of years for these objects to complete an orbit around the sun. Because they move so slowly, detecting them is difficult.
