Glossary term: Oort Cloud

Also known as Öpik–Oort cloud

Description: The Oort Cloud is a hypothetical region of the outer Solar System that is thought to be the origin of comets with long orbital periods. The Oort Cloud likely contains many billions of small icy bodies left over from the formation of the Solar System. This is thought to form the reservoir for long-period comets. Occasionally one of these frozen lumps will have its orbit disrupted by another icy body, or by the gravity of a star passing the Solar System. This may send the icy body falling towards the inner Solar System where it becomes a comet. The Oort Cloud probably extends from a few thousand astronomical units (AU) to perhaps over a hundred thousand AU, halfway to Proxima Centauri, the nearest star to the Sun. The inner Oort Cloud is likely a donut shape, but the outer Oort Cloud is probably a spherical shell.

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Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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