Ariel 

Discovered in 1851 by William Lassell, Ariel is the brightest satellite of Uranus. Ariel is 191,240 kilometers from Uranus and has an equatorial radius of 578.9 kilometers. The surface bears many heavy impact craters from millions of years of meteorite impact.

In addition, there are long, deep rift valleys that extend across the surface, much like that on Mars. The bases of the valleys have been smoothed by a fluid (not water), possibly ammonia, methane or carbon monoxide.

Physical Data Key Mass Mass Mass Mass compared to that of Earth. Radius Radius Radius Radius compared to that of Earth. Mean Density Average Density. Distance Distance to the planet's center. Magnitude The brightness of a star or object.

Orbital Data Key Rotational Period Number of days to make one complete rotation. Orbital Period Number of days to obital the planet. Mean Orbital Velocity Average obital speed. Orbital Eccentricity Eccentricity. Orbital Inclination The tilt of the moon or planet. Escape Escape Velocity. Albedo Visual geometric albedo.