Outer Solar System: Europa
The giant planets of the outer solar system--Jupiter, Saturn, Uranus and Neptune--have more than 160 moons. Many of these are as interesting as the planets they orbit, and Europa, one of Jupiter's largest moons, is especially intriguing.
Beneath Europa's icy surface lies a tantalizing destination: a deep saltwater ocean. On Earth, life exists wherever there is water. Future missions to Europa may answer whether the same is true on this remote moon.