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Uranus's Rings

Uranus' ring particles are dark grey to black and form rings about 1–37 mi (2–60 km) wide and less than one kilometer thick. The rings are in the equatorial plane of Uranus, which is tilted at 98 degrees to the typical planetary attitude of the solar system (i.e., the plane of the orbit of the inner eight planets). This suggests that the rings formed after the planet was titled.

There is a ring hierarchy about Uranus. The inner eight rings are very thin and have no known shepard satellites. In an outward order, these rings are known as Delta, Gamma, Eta, Beta, Alpha, 4-ring, 5-ring, and 6-ring. The two outer rings have variable thickness and have shepard satellites (Cordelia on the inner edge and Ophelia on the outer edge). The outer rings are URI and Epsilon.

The Voyager 2 observations also indicate that the rings contain a large fraction of large particles; the average particle size in the rings was calculated to be between 8 and 28 in (20-70 cm). An appreciable amount of micron-sized dust seems to be distributed throughout the ring system. However, this dust is probably transitory; atmospheric drag on the dust particles from Uranus' hydrogen corona that was mentioned above is expected to decelerate them and cause them to spiral into the denser layers of Uranus' atmosphere after, at most, a few thousand years. Uranus has 10 known rings that are nearly circular and lie in or nearly in the plane of Uranus' equator. The Epsilon ring is not only the most distant ring from Uranus, but it is also the most elliptical and the widest one.

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Science EncyclopediaScience & Philosophy: Two-envelope paradox to VenusUranus - Observations From Earth, Results From The Flyby Of The Voyager 2 Spacecraft, Uranus's Magnetic Field - Discovery, Puck