Umbriels

Umbriels is a moon of Uranus. It is the third largest of Uranus's moons, with a diameter of approximately 1,169 kilometers. Umbriels was discovered by William Lassell on October 24, 1851. Its name comes from a character in Alexander Pope's The Rape of the Lock.

The surface of Umbriels is heavily cratered, indicating a long history of impacts. It appears to be the darkest of Uranus's major moons, with a low albedo. This darkness is thought to be due to a dark, possibly carbonaceous, surface coating that has accumulated over time. Unlike some other Uranian moons, Umbriels does not show significant signs of geological activity, such as large canyons or smooth plains, suggesting it has been geologically inactive for a very long time. The most prominent feature on its surface is Wunda, a large, bright crater.

Umbriels's composition is believed to be roughly half water ice and half rock. Its low density suggests a significant portion of its mass is made up of silicates and possibly carbonaceous materials. It orbits Uranus at a distance of about 266,000 kilometers and has a rotational period of about four Earth days, which is the same as its orbital period, meaning it is tidally locked with Uranus.