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Umbriel

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Umbriel

 

Orbit: 265,980 km from Uranus
Orbital period: 99 hours
Gravity: 0.2 m/s²
Diameter: 1170 km
Mass:  1.27e21 kg
Umbriel is a moon of Uranus discovered on October 24, 1851, by William Lassell. It was discovered at the same time as Ariel and named after a character in Alexander Pope’s poem The Rape of the Lock
Umbriel and Oberon appear quite similar though  Oberon is 35% larger.  All of Uranus’ large moons are a mixture of about 40-50% water ice with the rest rock, a somewhat larger fraction of rock than  Saturn’s large moons such as Rhea. Umbriel’s heavily cratered surface has probably been stable since its  formation. It has far more and larger craters than do Ariel and Titania. Umbriel is very dark; it reflects only about half as much light as Ariel,  Uranus’  brightest satellite.
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Umbriel

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