Europa (yew-roe'-pə, ;
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
ice with probably some liquid
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 moon is striated by cracks and streaks, while craters are relatively infrequent. Due to a 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.
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