Oort cloud

Comets

Comets are small, irregularly shaped bodies in the solar system composed mainly of ice and dust that typically measure a few kilometers across. They travel around the sun in very elliptical orbits that bring them very close to the Sun, and then send them out past Neptune. There are two categories of comet, based on the amount of time they take to orbit the Sun. Short-period comets take less than 200 years, and long-period comets take over 200 years, with some taking 100,000 to 1 million years to orbit the Sun.