Europa:
This approximate true color view shows Europa, the second of the Galilean satellites of Jupiter, visible in small telescopes from Earth. It is roughly as large as Earth's moon and is in synchronous orbit around Jupiter. There are relatively few craters implying a relatively young surface. The surface has fairly low relief as well. The surface is mainly composed of water ice with various impurities embedded within. The mysterious linear features attest to stresses that are largely tidally generated. These features combined with other clues strongly point to the existence of a global sub-surface ocean of liquid water that may contain as much water as Earth's oceans. The water is probably located about 20km beneath the surface and may be up to 100km thick. The way in which the magnetic field varies around Europa even suggests the presence of electrically conducting salts in this ocean.