|Europa (natural color) as seen from Galileo.|
|Diameter|| 3,138 km|
|Distance from primary|| 670,900 km|
Europa is the smallest of Jupiter's four planet-sized moons, yet it is only slightly smaller than Earth's Moon. Its bright surface (roughly five times as reflective as the Moon), infrared water ice absorption bands, and the near absence of impact craters (only about five have been identified to date) indicate that the surface is ice rich and very young, perhaps only 30 million years old. Europa is covered by a water-ice shell no more than 150 kilometers thick. Calculations suggest that there could be liquid water at the base of this icy layer, leading to speculation that a primitive life form could have evolved in this dark, watery world. The thickness of the surface ice and the possible presence of liquid water have intrigued planetary scientists since the late 1970s.
Europa is about the size of Earth's Moon and is covered largely with smooth white and brownish-tinted ice, instead of large craters like so many other bodies in the Solar System. Scientists believe its cracked cue-ball appearance is due to stressing caused by the contorting tidal effects of Jupiter's strong gravity. They speculate that the warmth generated by tidal heating may have been sufficient to soften or even liquefy some portion of Europa's icy covering.
Europa has long been considered by scientists and celebrated in science fiction as one of the handful of places in the Solar System (along with Mars and Saturn's moon Titan) that could possess an environment where primitive forms of life could possibly exist.