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With an average albedo of 0.21, Umbriel is the darkest of Uranus' five largest satellites. It also has a more uniform albedo than Titania and Oberon, showing only a few striking albedo features on the part of its surface imaged by Voyager 2. Umbriel also has extensive, heavily cratered terrain and several groups of canyons, scarps, and lineaments which seem to be of more recent origin than the craters which they cut. Evidence is also seen of resurfacing in and near several craters, indicating cryovolcanism. Much of its surface may have been resurfaced with dark material of uncertain origin (cryovolcanic, dark ejecta from a crater, or from an external source).

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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