OORT CLOUD

Occupies space at a distance between 5,000 and 100,000 astronomical units. One astronomical units is 149,597,871 kilometers.

Dutch astronomer Jan Oort
1950
He noticed that comets all had the following in common.

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• Their orbits indicated that they didn't originate in interstellar space
• They come from all directions

Based on these observations he concluded that billions of potential cometary nuclei must exist in a spherical shell surrounding the solar system. It is yet to be directly observed.

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• The Oort Cloud contains about 2 trillion icy bodies.
• Most of the long-period comets that have been observed originate from the Oort Cloud.
• This cloud of particles is theorized to be the remains of the disc of material that formed the sun and planets.

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• It can be disrupted by the nearby passage of a star, nebula, or by actions of the disk of the Milky Way. Those actions knock cometary nuclei out of their orbits, and send them on a long rush toward the sun.

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• The objects in the Oort Cloud are thought to be fairly small. Measured cometary nuclei have diameters of 20km or less.

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