One of the four smallest Galilean moons and orbiting Jupiter named Europa, is also one of the sixth largest moon of Solar System.
It is made up of silicate rock and has a water-ice crust. Oxygen on this moon has also been discovered in its atmosphere. The surface of this moon contains massive cracks, streaks, and sometimes craters. Having one smooth surface spread through out.
It is expected water ocean exists beneath it, which could conceivably harbor extraterrestrial life making it one of likely candidate for future unmanned missions.
NASA have also pictured plumes of water coming out from its pole.
