Comets are found in two main regions of the solar system: the Kuiper Belt and the Oort Cloud. There are two types of comets: short-period comets and long-period comets.
Short-period comets – comets that frequently return to the inner solar system – probably come from the Kuiper Belt beyond the orbit of Neptune. Astronomers estimate that this belt contains at least 200 million objects, which are thought to have remained essentially unchanged since the birth of the solar system 4.6 billion years ago.
Long-period comets, which can take thousands of years to complete their orbits, are thought to emanate from the Oort Cloud, a vast group of frozen bodies in the outer part of the solar system. The Oort Cloud is thought to extend 50,000 times the distance from the Earth to the Sun.
Oort Cloud comets, like their Kuiper Belt brothers, probably originated in the region of the solar system between Jupiter and Neptune, but were ejected from to the Oort Cloud by close encounters with the gravity of the giant planets.
Comets are kicked out of the Oort Cloud and the Kuiper Belt by the pull of the gravity of another object – a planet, a star, or another small body. They then begin their journey toward the inner solar system and the Sun.
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