Oort

Most comets are thought to originate in a huge cloud called the Oort Cloud.

The Oort Cloud is believed to surround our solar system and reach over halfway to the nearest star, Alpha Centauri, which is 150,000 astronomical units away.

Comet Siding Spring is one of the long-period comets, those that require more than 200 years to orbit the Sun. These comets come from the Oort Cloud, a sphere of about a trillion ancient, icy objects located hundreds to thousands of times farther than the planets' orbits.

The Oort Cloud is so far away from the Sun that its icy objects are not warmed much by the Sun's heat. The objects are frozen fossils from the early solar system.

Comets occasionally visit the inner solar system from their home in the Kuiper Belt or Oort Cloud.

Comets are part of the solar system. Scientists believe they come from one of two locations within the solar system: the Kuiper Belt and the Oort Cloud.

The comets that we see rarely — every few thousand years — come from the Oort Cloud.