Oort cloud
Sign in to savetheoretical cloud of planetesimals at the far edge of the solar system
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The Oort cloud is a vast, theoretical shell of icy objects believed to surround our solar system at its outermost edge. It matters because it's thought to be the source of long-period comets that occasionally travel into the inner solar system, helping scientists understand the origins and structure of our cosmic neighborhood.
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The Oort cloud (pronounced /ɔːrt/ ORT or /ʊərt/ OORT), sometimes called the Öpik–Oort cloud, is theorized to be a cloud of billions of icy planetesimals surrounding the Sun at distances ranging from 2,000 to 200,000 AU (0.03 to 3.2 light-years). Its existence was proposed in 1950 by the Dutch astronomer Jan Oort, in whose honor the idea was later named. Oort proposed that the bodies in this cloud replenish and keep constant the number of long-period comets entering the inner Solar System—where they are eventually consumed and destroyed during close approaches to the Sun.
The cloud is thought to encompass two regions: a disc-shaped inner Oort cloud approximately aligned with the solar ecliptic (also called its Hills cloud) and a spherical outer Oort cloud enclosing the entire Solar System. Both regions lie well beyond the heliosphere and are in interstellar space. The innermost portion of the Oort cloud is more than a thousand times as far from the Sun as the Kuiper belt, the scattered disc and the detached objects—three nearer reservoirs of trans-Neptunian objects.