Oort cloud

Definition

The Oort Cloud is a hypothetical, distant region of the Solar System that is believed to surround the Sun with a vast shell of icy bodies. It is thought to be the source of most long-period comets that enter the inner Solar System.

5 Must Know Facts For Your Next Test

1. The Oort Cloud is theorized to extend from about 2,000 to 100,000 astronomical units (AU) from the Sun.
2. It is divided into two regions: the inner spherical Oort Cloud and the outer toroidal Hills Cloud.
3. Dutch astronomer Jan Oort first proposed its existence in 1950.
4. Objects in the Oort Cloud are composed primarily of water ice, ammonia, and methane.
5. The gravitational influence of passing stars or galactic tides can perturb objects in the Oort Cloud, sending them toward the inner Solar System as comets.

Review Questions

• Who proposed the existence of the Oort Cloud?
• What are the primary components found in objects within the Oort Cloud?
• How can objects from the Oort Cloud become comets that enter the inner Solar System?

Related terms

Asteroid Belt:

A region between Mars and Jupiter filled with rocky bodies leftover from early Solar System formation.

Kuiper Belt:

A disk-shaped region beyond Neptune filled with small icy bodies and dwarf planets like Pluto.

Long-Period Comets:

Comets that take more than 200 years to complete an orbit around the Sun and are often believed to originate from the Oort Cloud.