Umbriel

{{Infobox planet | name = Umbriel | alt_names = | mpc_name = Uranus II | pronounced = | adjectives = Umbrielian | image = PIA00040 Umbrielx2.47.jpg | image_scale = | image_alt = A round spherical body with its left half illuminated. The surface is dark and has a low contrast. There are only a few bright patches. The terminator is slightly to the right from the center and runs from the top to bottom. A large crater named Wunda with a bright ring on its floor can be seen at the top of the image near the terminator. A pair of large craters with bright central peaks can be seen along the terminator in the upper part of the body. The illuminated surface is covered by a large number of craters. | caption = Grayscale image of Umbriel from Voyager 2, January 1986. Umbriel's surface is heavily battered; the bright crater Wunda can be seen at the top of the image near the moon's equator | background = Thistle | discoverer = William Lassell | discovered = October 24, 1851 | orbit_ref = | periapsis =  km | apoapsis =  km | semimajor = | eccentricity = | period = | avg_speed = 4.67 km/s (calculated) | inclination = (to Uranus's equator) | satellite_of = Uranus | mean_diameter = km | mean_radius = (0.092 Earths) | surface_area = (0.008 Earths) | volume = (0.0008 Earths) | mass = | density = (calculated) | surface_grav = m/s2 (~0.0257 g) | escape_velocity = km/s{{efn|name=escape velocity|Escape velocity derived from the mass m, the gravitational constant G and the radius r : \sqrt{\frac{2Gm}{r} }.}} | rotation = presumed synchronous | axial_tilt = 0 | albedo = | magnitude = 15.1 | abs_magnitude = 2.10 | temp_name1 = solstice | mean_temp_1 = ≈ 75 K | max_temp_1 = 85 K | min_temp_1 = ? | atmosphere = no | surface_pressure = zero (presumed to be extremely low) | note = no }}

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.