Umbriel (GIF, 126K)

Uranus II

Umbriel [UM-bree-ul] is the darkest satellite of Uranus. It is about the same size as Ariel and has about the same density. The surface appears to be old with large craters and does not change much from one location to another. Near the top is a puzzling bright ring called the fluorescent cheerio. It is probably the floor of a crater.

Umbriel Statistics

Discovered by ............................... William Lassell
Date of discovery ...................................... 1851

Mass (kg) .......................................... 1.27e+21
Mass (Earth = 1) ................................. 2.1252e-04
Equatorial radius (km) ................................ 584.7
Equatorial radius (Earth = 1) .................... 9.1675e-02
Mean density (gm/cm^3) ................................. 1.52

Mean distance from Uranus (km) ...................... 265,970
Rotational period (days) ........................... 4.144177
Orbital period (days) .............................. 4.144177
Mean orbital velocity (km/sec) ......................... 4.67

Orbital eccentricity ................................. 0.0050
Orbital inclination .................................... 0.36°

Escape velocity (km/sec) .............................. 0.538

Visual geometric albedo ................................ 0.18
Magnitude (Vo) ........................................ 14.81

Uranus Ariel Titania

Author: Calvin J. Hamilton.