Europa (moon)

Europa (IPA: listen ; Greek Ευρώπη) is the sixth nearest and fourth largest natural satellite of the planet Jupiter. Europa was discovered in 1610 by Galileo Galilei (and independently by Simon Marius shortly thereafter) and is the smallest of the four Galilean moons named in Galileo's honor.

Europa is primarily composed of silicate rock, has an outer layer of water, and likely has an iron core. At just over 3000 kilometers in diameter, it is slightly smaller than the Earth's moon and the sixth largest moon in the solar system. The satellite has a very tenuous oxygen atmosphere and one of the smoothest surfaces in the solar system. The young surface of the planet is straited by cracks and streaks, while craters are relatively infrequent. Due to an hypothesized water ocean beneath its icy surface, and an energy source provided by tidal heating, Europa has been cited as a possible host of extraterrestrial life. The heat energy ensures the ocean remains liquid and also drives geological activity.

The intriguing character of Europa has led to a number of ambitious exploration proposals; to date, only flyby missions have visited the moon. The Galileo mission provided the bulk of current data on the satellite, while the abortive Jupiter Icy Moons Orbiter, cancelled in 2005, was the most ambitious planned spacecraft. Conjecture on extraterrestrial life has ensured a high profile for the moon and led to continued lobbying for future missions.