Oort Cloud: Theoretical cloud of planetesimals at the far edge of the solar system

Astronomers believe it is way beyond the orbits of Pluto and the Kuiper belt. The Oort cloud is believed to be the source of long-period comets in the Solar System.

The Oort cloud may lie about 50,000 AU, or nearly a light-year, from the Sun. This means the cloud is nearly a quarter of the way to Proxima Centauri, the nearest star to the Sun.

The Kuiper belt and scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one-thousandth of the Oort cloud's distance. The outer limit of the Oort cloud defines the boundary of the Solar System and the region of the Sun's gravitational dominance.

The Dutch astronomer Jan Hendrik Oort published the Oort cloud idea in 1950. The Oort cloud was named after him, as were the Oort comet, and Oort constants.

The Oort cloud takes up a lot of space and is thought to have trillions of comets about tens of millions of kilometers apart.

The Oort cloud is made up of an inner Oort cloud and an outer Oort cloud. The outer cloud is weakly bound to the Sun; long-term comets are thought to come from there. The Inner cloud is also called the Hills cloud and maybe the maker of comets.

The objects in the Oort cloud are believed to consist of much ice. Since the object 1996 PW was found to be a rocky body in an orbit typical of long-period comets, it is believed that rocky objects might be in the Oort cloud.

Origins

The Oort cloud is thought to be the remains of a disk made out of gas that surrounded the Sun long ago.