- satellite of Uranus discovered by Lassell in 1851. Umbriel has a 4.1 day, near-circular orbit in the plane of Uranus’s equator, at an average distance of 267,000km from the planet. Voyager 2’s 1986 visit to Uranus reveals Umbriel as a dark, crater-covered world with one or more bright patches, possibly sites where impacts have brought ice to the surface. Umbriel’s spectrum is also rich in lines indicating the presence of water. Umbriel is about 1200km in diameter.