Figure 4-6The Kuiper Belt and Oort Cloud (a) The classical Kuiper belt of comets spreads from Neptune out 50 AU from the Sun. Most of the estimated 200 million Kuiper belt comets are believed to orbit in or near the plane of the ecliptic. The spherical Oort cloud with a radius of perhaps 50,000 AU and containing billions of comets, extends much farther out beyond the Kuiper belt than shown in this illustration. The top figures shows orbits of known Oort cloud and Kuiper belt objects, while the lower-left image summarizes the locations of various regions of the solar system. (b) Positions of known bodies in the Kuiper belt and Oort cloud.