What is the name of the cloud that contains many comets outside of the solar system?
In the name of Dutch scientist Jan Oort.
Most comets are thought to originate in the Kuiper belt and the Oort cloud.
Comets are often described as "dirty snowballs," being composed mostly of a loose clump of ice and rocks. They spend most of their time out toward the edge of the solar system, however, they have highly elliptical orbits which periodically bring them closer to the sun.
There are two main types of comets, short period comets, and long period comets. Short period comets have orbits of less than 200 years, and are thought to be Kuiper belt objects, like Pluto. The Kuiper belt sits just past Neptune, and in addition to comets, contains a variety of objects, including asteroids and dwarf planets.
Long period comets, on the other hand, can take thousands of years to orbit the sun, and are thought to originate within the Oort cloud. The Oort cloud was first proposed in 1950 by Jan Oort, a Danish astronomer. Unlike the Kuiper belt, which is a disk shaped ring, the Oort cloud is a spherical shell surrounding the solar system, and is estimated to contain trillions of icy objects.
The image above shows the relative size of the outer planets' orbits compared to the Oort cloud. Objects in the Oort cloud are loosely bound by the sun's gravity, and are more susceptible to gravitational influence by other nearby stars. Sometimes, these influences send Oort cloud comets hurtling toward the inner solar system.