Umbriel is one of Uranus’ moons. It was discovered in 1851 by British astronomer William Lassell.

Diameter: 1.17 x 106 m
Mass: 1.27 x 1021 kg
Composition: Ice and rock
Orbit: 2.66 x 108 m from Uranus

Umbriel is the third largest of Uranus’ moons. 15 moons orbiting Uranus are known to exist; the largest five were discovered by observations from Earth, and the 10 smaller moons were discovered later by spacecraft missions.

All of Uranus’ moons are named after characters from either William Shakespeare or Alexander Pope. Umbriel takes its name from Pope’s poem “The Rape of the Lock”. Etymologically, Umbriel’s name comes from the Latin word “umbra”, meaning shadow. This is fitting as Umbriel is the darkest moon orbiting Uranus. It is much less reflective of the Sun’s light than Ariel, another of Uranus’ moons which was discovered at the same time, also by Lassell.

In composition Umbriel has a core of rock and an icy mantle. It has recognisable surface features such as its numerous overlapping impact craters. These were caused by violent collisions which were frequent in the early stages of our solar system when Umbriel was formed. They also provide evidence that the surface structure of Umbriel has not changed significantly since the time of its formation. Some of the most significant craters are named and catalogued; the largest, Wokolo, measures 210km in diameter. Another striking feature is Wunda, a crater which appears as a ring of very bright material near Umbriel’s equator.

Umbriel orbits Uranus in its equatorial plane and revolves in the same direction as the planet’s rotation. Umbriel’s orbital period is the same as its rotational period, at roughly four Earth days. This means that the same side of Umbriel is always facing towards Uranus. Along with Uranus and its other satellites, Umbriel takes around 84 Earth years to orbit the sun.

In 1986 the Voyager 2 spacecraft mission travelled past Uranus and took photos of Umbriel and other moons. Despite the technical difficulty associated with imaging moving objects whilst travelling past them, Voyager 2 was able to collect images of Umbriel with an impressive resolution of about 3km. This has been the only mission to Uranus and its moons to date.

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