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|Discovered by||William Lassell|
|Mean radius||266000 km|
|Orbital period||4.14 d|
|Is a satellite of||Uranus|
|Mean diameter||1169.4 km|
|Surface area||4,300,000 km2|
|Mean density||Unknown g/cm3|
|Surface gravity||? m/s2|
|Rotation period||4.14 d|
|Atmospheric pressure||0 kPa|
The name "Umbriel" and the names of all four satellites of Uranus then known were suggested by John Herschel in 1852 at the request of Lassell (). Lassell had earlier endorsed Herschel's 1847 naming scheme for the seven then-known satellites of Saturn and had named his newly-discovered eighth satellite Hyperion in accordance with Herschel's naming scheme in 1848.
It is also designated Uranus II.
So far the only close-up images of Umbriel are from the Voyager 2 probe, which made observations of the moon during its Uranus flyby in January, 1986. During the flyby the southern hemisphere of the moon was pointed towards the Sun so only it was studied.
Umbriel's surface is the darkest of the Uranian moons, and it is also the least geologically active. It is mostly composed of water ice, with the balance made up of silicate rock and methane ice. Most of its methane ice is on its surface. Coincidentally, Umbriel's dark colour suits its name: Umbriel is the 'dusky melancholy sprite' in Alexander Pope's The Rape of the Lock, and the name suggests the Latin umbra, shadow.
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