Europa 

Europa is a moon of Jupiter discovered by Simon Marius and Galileo Galilei in 1610. The satellite is relatively smooth (general lack of craters on the surface), and is marked with many fractured ridges that extend across its plains. Scientists speculate that these ridges could be the result of the moon's expansion that shattered the icy crust into deep streaks; which in turn filled with water and froze. Some of the fractures formed ice plates or slabs that can reach lengths of 30 kilometers (18.5 miles) across.

Europa is a rather active moon evidenced by its internal activity that formed the dark crisscross features that line the surface. In addition, several craters were discovered that indicated that the moon has some deep layers of water and ice with tidal heating at a relatively shallow depth. The water ice layer extends some 5 kilometers (3 miles) into the moon and may have oceans at depths greater than 50 kilometers (30 miles).

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.