The fourth-largest satellite of Jupiter and the second of the four Galilean satellites from the planet; also known as Jupiter II. Europa orbits in 3.551 days at a distance of 671 000 km. Its period of axial rotation is the same as its orbital period. Its diameter is 3122 km, making it only slightly smaller than our Moon. Europa's density of 3.01 g/cm3 indicates that it is mainly composed of silicate rock, mixed with at least 5% water. It has a bright, icy surface of albedo 0.67, dominated by networks of dark, linear cracks, some over 1000 km long. Many of these are curved and are termed flexus; they are thought to arise from tidal stresses. Impact craters on Europa are few and far between, indicating that the surface is young and perhaps being resurfaced by icy flows from below the surface. Indirect evidence suggests the widespread presence of liquid water below the icy crust, but neither the depth nor the extent of this subsurface sea are known.
Subjects: Astronomy and Astrophysics — Earth Sciences and Geography.