Umbriel

Umbriel is the third-largest moon orbiting the planet Uranus.

It is also the third-most massive moon in that system. This moon is quite a dark place in space. In fact, it has the darkest surface of all the moons around Uranus. Scientists believe it is made mostly of water ice. About 40% of its mass is made of a dense material like rock. This material might include carbon and heavy organic compounds called tholins.

The moon might have a rocky core at its center. This core could be surrounded by a thick mantle of ice.

The surface of Umbriel tells a story of many hits from space. It is covered in many impact craters from flying rocks. These craters are the second-most common among the moons of Uranus. Some craters are small, but others are huge. The largest known crater is named Wokolo, and it is 208 kilometers wide. Another famous feature is the Wunda crater near the equator. Wunda is about 131 kilometers across and has a bright ring on its floor.

This bright ring might be made of carbon dioxide ice. There are also canyons and dark patches called polygons on the surface. These shapes suggest that the inside of the moon was active a long time ago.

A man named William Lassell discovered Umbriel on October 24, 1851. He found it at the same time as the moon Ariel. The name Umbriel comes from a character in a poem. The poem is called "The Rape of the Lock" by Alexander Pope. It was written in 1712. Earlier, a man named William Herschel thought he saw four other moons. However, those observations were not confirmed by others. In 1852, John Herschel suggested names for the moons. He was the son of William Herschel.

Umbriel orbits Uranus at a distance of about 520,000 kilometers. It takes about 4.1 Earth days to complete one orbit. This moon is tidally locked to its planet. This means one face always points toward Uranus. The moon sits inside the magnetosphere of Uranus. This is a zone filled with charged particles. These particles hit the trailing side of the moon. This bombardment might be why the surface looks so dark.

Because Uranus tilts on its side, the moons have extreme seasons. Each pole spends 42 years in the dark and 42 years in the sun.

We have only seen Umbriel up close one single time. The Voyager 2 spacecraft flew past the moon in January 1986. This mission allowed scientists to map about 40% of the surface. Before this, we only knew about the moon from far away. Learning about Umbriel helps us understand how moons form. Most moons likely grew from a disk of material around a planet. Studying its dark surface helps us learn about space weathering. This is how particles in space change the look of a world over time.