Oort cloud

Rare card · No. 27507

The Oort cloud (pronounced ORT or 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. 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. Both regions lie well beyond the heliosphere...

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