The Kuiper belt, sometimes called the Edgeworth–Kuiper belt, is a circumstellar disc in the Sol system beyond the planets, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from Sol. It is similar to the asteroid belt, but it is far larger—20 times as wide and 20 to 200 times as massive. Like the asteroid belt, it consists mainly of small bodies, or remnants from the Sol system's formation.
Although many asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water.
The Kuiper belt is home to three officially recognized dwarf planets: Pluto, Haumea, and Makemake. Some of the Sol system's moons, such as Neptune's Triton, are also thought to have originated in the region.
Prior to the protomolecule's discovery, Phoebe was thought to have originated from the Kuiper belt as well.
Short-period comets take less than 200 years to orbit the Sun and originate in the Kuiper Belt. Since their paths are deflected inward by the giant planets, most short-period comets orbit in the same region as the asteroid belt, located between the orbits of Mars and Jupiter. The relatively flat Kuiper Belt lies at the outer edge of the planets, beyond Neptune's orbit. Its radius is between 30 and 50 astronomical units (AU). There may be as many as 100 million objects in the Kuiper Belt.
Long-period comets require more than 200 years to orbit the Sun, generally taking many thousands to a few millions of years. They are usually only observed once. They come from the vast region in the outer reaches of our solar system known as the Oort Cloud. The Oort Cloud is a huge sphere of ancient, icy objects that envelops the region of the planets. The Oort Cloud extends a thousand times farther than the Kuiper Belt. It is 50,000 AU in radius.
- Crash Course - PBS Digital Studios - Youtube Channel- - "Introduction to Astronomy: Crash Course Astronomy #1" (video) - 1/15/2015
- Amazing Space "Sources of short-period and long-period comets" (photo) - 3/2014
- Space Facts "Kuiper Belt"
- Space Facts "Oort Cloud"