Umbriel (moon)

Umbriel Earth Moon Comparison

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Voyager spacecraft

Umbriel is a moon of Uranus discovered on October 24, 1851, by William Lassell. It is the third-largest moon of Uranus and the fourth most massive, making it a significant subject of study in the astronomy community. Umbriel orbits Uranus at a distance of about 266,000 kilometers (165,000 miles), completing a full orbit in approximately 4.1 Earth days. Its discovery, along with that of Ariel, marked an important milestone in the exploration of the Uranian system.

Discovery and Naming

The discovery of Umbriel was made by William Lassell, an English astronomer, who used a 24-inch reflector telescope at his private observatory in Liverpool. The moon was named after a character in Alexander Pope's poem "The Rape of the Lock." The names of all four moons discovered by Lassell (Ariel, Umbriel, Titania, and Oberon) were suggested by John Herschel, son of William Herschel, who had discovered Uranus itself.

Physical Characteristics

Umbriel is distinguished by its dark surface, one of the darkest of the Uranian moons, which suggests a composition of water ice mixed with a dark material, possibly organic compounds. Its surface is heavily cratered, indicating a long history of impacts. The most prominent feature on Umbriel's surface is a ring of bright material on the floor of the Wunda crater. Unlike some of its sibling moons, Umbriel shows few signs of internal geological activity in the recent past.

Composition and Structure

Umbriel's density (about 1.4 g/cm³) suggests that it is roughly composed of equal parts water ice and a denser non-ice component. The non-ice portion could include rock and carbonaceous material, including heavy organic compounds. This composition is typical of the moons in the outer Solar System.

Surface Features

The surface of Umbriel is among the most heavily cratered in the Uranian moon system, with little to no evidence of endogenic resurfacing. This suggests that Umbriel's surface is ancient and has preserved the record of early Solar System impact history. The moon's most notable feature, Wunda crater, with its mysterious bright ring, stands out against the otherwise dark terrain.

Orbit and Rotation

Umbriel orbits Uranus at a distance that places it within the planet's magnetosphere intermittently. This means that it is directly exposed to the magnetic field and charged particles of Uranus, which may have effects on its surface. Like many moons in the Solar System, Umbriel is tidally locked with its planet, meaning the same side always faces Uranus.

Exploration

To date, the most significant source of information about Umbriel has come from the Voyager 2 spacecraft, which flew by Uranus in 1986. The flyby provided crucial data on Umbriel's surface, composition, and orbit. However, detailed exploration of Umbriel has been limited, and much about this moon remains a mystery. Future missions to the Uranian system could provide more insights into Umbriel and its place within the moons of Uranus.

See Also

• Moons of Uranus
• Astronomy
• William Lassell
• Voyager 2