Kuiper Belt binary object 1998 WW31, illustration. One of the pair of objects is in the foreground; its companion is the dark, round object in the background. The objects are about the same size. Both are illuminated from behind by the Sun (white dot at upper left). The Kuiper Belt is a region of the Solar System that exists beyond the eight major planets, extending beyond the orbit of Neptune. It is similar to the asteroid belt, in that it contains many small bodies, which are remnants from the Solar System's formation. Unlike the asteroid belt, the Kuiper Belt is much larger, around 20 times as wide and 20 to 200 times as massive. Like other Kuiper Belt objects, 1998 WW31 orbits the Sun, completing a circuit every 301 years.