What is the Oort Cloud?
The Oort Cloud is a vast, distant shell of icy objects thought to surround the solar system, far beyond Pluto. It is believed to be the source of long-period comets.
The Oort Cloud is thought to begin around 2,000 to 5,000 times the distance between Earth and the Sun and may extend more than 100,000 times that distance, up to about a quarter of the way to the nearest star. It may contain billions or even trillions of icy bodies.
No one has directly observed the Oort Cloud, because its objects are small, dark and incredibly far away. Its existence was proposed in 1950 by Dutch astronomer Jan Oort, who studied comets that arrive from all directions with very long orbits. Passing stars and the Milky Way's gravity can nudge objects inward, sending them toward the Sun as comets.
How far is it?
Even traveling at about 61,000 kilometers per hour, Voyager 1 will not reach the inner edge of the Oort Cloud for about 300 years, and it will take about 30,000 years to pass through it.
Did You Know?
Some long-period comets from the Oort Cloud take thousands or even millions of years to complete a single orbit around the Sun.