Object Analysis

Umbriel is the third-largest and most heavily cratered moon of Uranus. It was discovered in 1851 by William Lassell. Umbriel is the darkest of the large Uranian satellites, reflecting only about 16% of the light that hits it. Its name comes from the "dusky melancholy sprite" in Alexander Pope's The Rape of the Lock.

The moon consists mainly of water ice with a substantial fraction of rock. Its surface is ancient and shows very little evidence of the geological "resurfacing" seen on Miranda or Ariel. It is covered in large impact craters, the most prominent of which is Wunda, a 131-km diameter crater with a mysterious ring of bright material on its floor.

The bright ring in Wunda is likely a deposit of fresh ice, possibly carbon dioxide ice, though its exact origin is unknown. Because Umbriel is so dark and geologically "quiet," it serves as a baseline for astronomers to understand the early bombardment history of the Uranian system, untouched by the internal heat that reshaped its siblings.