Despite its unusual characteristics, Pluto's status as a planet was solid until 1992, when David Jewitt and J. Luu of the University of Hawaii discovered a strange object called 1992 QB1. QB1 is a small icy body, similar in size to an asteroid, orbiting one and a half times further from the sun than Neptune.
QB1 was the first clue that more objects than Pluto might populate the distant reaches of the solar system. Since 1992 nearly one hundred objects like QB1 have been found. They are thought to be similar to Pluto in composition, consisting primarily of ice and rock.
This swarm of Pluto-like objects beyond Neptune is known as the Kuiper Belt, named after Gerard Kuiper, who first proposed that such a belt existed.
Astronomers estimate that there are at least 35,000 Kuiper Belt objects (KBOs) greater than 62 miles (100 kilometers) in diameter. Pluto is practically indistinguishable from other objects in the Kuiper Belt. Aside from its large size, the only real difference is Pluto's reflectivity, which makes it much brighter than other KBOs.
