Figure 15-35: The Kuiper Belt and Oort Cloud Short-period comets are thought to originate in the Kuiper belt, which begins just beyond the orbit of Neptune at 30 AU, and extends to about 50 AU from the Sun. Most of the Kuiper belt objects lie in a disk close to the plane of the solar system. The Oort cloud, by contrast, contains a doughnut-shaped distribution in the plane of the ecliptic, but also a spherical distribution of icy objects whose orbits are randomly oriented relative to the ecliptic. The inner edge of the doughnut-shaped distribution is about 2000 AU, and the Kuiper belt is so small compared to the Oort cloud that it would appear as a dot on the scale used in this figure. Long-period comets are thought to originate in the Oort cloud.

(NASA and A. Field/Space Telescope Science Institute)