Callisto 

Callisto, one of the four Galilean moons, is a satellite of Jupiter and was discovered by Simon Marius Galileo Galilei in 1610. Callisto is rather large compared with other satellites of the solar system with a radius of 2,400 kilometers. This makes it the second largest satellite of Jupiter and the third largest in the solar system!

Its crust is very ancient with millions of years of scarred impact craters and other prominent surface features. One of the surface landmarks of Callisto is the Valhalla region, discovered by Voyager 1 on March 6, 1979. This region is about 300 kilometers across and the remnant of a large meteorite that collided with Callisto. The Gipul Catena is a series of large impact craters with some reaching 40 kilometers across. The Asgard impact basin is another prominent surface feature on Callisto, with a radius 1700 km across (1,056 miles).

The interior of Callisto consists of water, rock and ice, all bound around a solid rocky core. Ice is prominent all around the surface of the moon because large meteorites had punctured deep into the surface and brought forth gushing streams that spread out and froze.

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.