### Discovery of Umbriel and Ariel **Date**: October 24, 1851 • **Location**: Rome, Italy Umbriel and Ariel, the third- and fourth-largest moons of Uranus, were discovered by William Lassell. Umbriel is the third-largest moon of Uranus. It was discovered on October 24, 1851, by William Lassell at the same time as neighboring moon Ariel. It was named after a character in Alexander Pope's 1712 poem The Rape of the Lock. Umbriel consists mainly of ice with a substantial fraction of rock, and may be differentiated into a rocky core and an icy mantle. The surface is the darkest among Uranian moons and appears to have been shaped primarily by impacts; however, the presence of canyons suggests early internal processes. The moon may have undergone an early endogenically driven resurfacing event that obliterated its older surface.

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