According to NASA, the Oort cloud is a spherical cloud of icy bodies that surrounds the solar system. It extends from around 5,000 astronomical units from the sun, or 5,000 times the distance from the sun to the Earth, out to 100,000 astronomical units. Most of the comets and many of the asteroids that pass near Earth originate in the Oort cloud.Continue Reading
Jan Oort, a Dutch astronomer, theorized in 1950 that many of the comets that enter the solar system come from a reservoir of frozen bodies existing at the outer periphery of the solar system. Astronomers estimate that this cloud may contain up to 2 trillion comets in solar orbits, and some of these orbits may last thousands of years. Occasionally, gravitational events or collisions may send one closer to the sun, bringing it near Earth's orbit. These objects rarely make return trips, although a few have settled into regular and more frequent orbital paths, such as Halley's Comet.
The objects in the Oort cloud are believed to be remnants from the original creation of the solar system, bodies made up of frozen gas that never managed to build up enough mass to become actual planets. The outer edge of the Oort cloud represents the outer edge of the solar system and the effective end of the sun's gravitational influence.Learn more about Astronomy