Europa is one of 79 and the 4th largest moon of Jupiter. It was discovered by Simon Marius in 1609, who named it “Europa”, after a princess from Greek Mythology. Its diameter is 3121.6km, just a bit smaller than Earth’s moon. It takes roughly 3.5 days for Europa to orbit Jupiter. Europa’s distance from Jupiter is about 670.900km.  Scientists believe that Europa has an iron core and an atmosphere (mostly oxygen). The surface is smooth and icy. Under the surface though, there’s a liquid ocean, which is kept warm by tidal heating, meaning that Jupiter’s gravitational pull makes it warm.