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Uranian Satellites

Uranus' satellites all lie in the equatorial plane (like the rings). There are several groups of satellites. The inner satellites, of which there are ten, are irregular dark Figure 2. Diagram of offset and tilted magnetic field of Uranus. Illustration by Hans & Cassidy. Courtesy of Gale Group. objects (which may mean they are carbonaceous rock or are methane ice bodies coated with carbon material) under 93 mi (150 km) in diameter. The inner satellites are Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, and Puck. The outer satellites are all rather large satellites (292–982 mi [470–1580 km] in diameter) that are locked in 1:1 spin-orbit couples with Uranus. The outer satellites (Miranda, Ariel, Umbriel, Titania, and Oberon) are all spherical objects of water ice surrounding rock.

Voyager 2 discovered 10 satellites which all orbit Uranus closer to it than Miranda and are all smaller than Miranda. Surface albedo could be found for only Puck and Cordelia, which are 0.08 and 0.07, respectively, indicating that they are somewhat brighter than the ring particles. The other eight newly found satellites seem to be dark like Puck, Cordelia, and the rings. Cordelia and Ophelia, the two satellites closest to Uranus, seem to serve as "shepherd satellites" for the Epsilon ring, keeping its particles in the ring by their gravitational perturbations on them, thereby increasing this ring's orbital stability. Gravitational perturbations produced by several other satellites near the rings may make the rings more stable. Ophelia is slightly more and Cordelia slightly less than two Uranus radii from Uranus' center; this raises the possibility that the rings were formed by satellites inside Uranus' Roche limit that were torn to pieces by collisions or by tidal forces produced in them by Uranus.

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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