Oort Cloud
A vast, distant shell of icy objects thought to surround the Solar System and send long-period comets towards the Sun.
Far beyond the Kuiper Belt, perhaps thousands of times further from the Sun than Earth and stretching a large part of the way to the nearest stars, astronomers think there is an enormous cloud of icy bodies. It is called the Oort Cloud, after the Dutch astronomer Jan Oort, who proposed it in 1950 to explain where long-period comets come from. No one has ever seen an object in the cloud itself; it is far too distant and dark. Its existence is worked out from the orbits of comets that fall in from every direction.
The bodies are thought to have formed nearer the giant planets and been flung outwards by their gravity long ago. Every so often, a passing star or the pull of our galaxy nudges one inwards. It may take millions of years to arrive as a brilliant long-period comet. Comet Hale–Bopp, a spectacular sight in 1997, is an example; it will not return for over two thousand years.
No meteorites come from the Oort Cloud, as far as anyone knows. You recognise its comets by their very long, steep orbits rather than by anything visible.
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Level: Explorer Ages 10 and up