Why explore Jupiter?

The sheer complexity and dynamics of the Jupiter system set it apart. The planet itself contains ∼71% of all the planetary mass in our Solar System. The dynamic, constantly changing, storm-tossed, and lightning-scorched atmosphere belies a turbulent interior. A vast radiation-charged magnetosphere spreads over a domain as large as the full Moon, as seen from Earth, and is the largest structure in the Solar System other than the Sun. A small but dynamic ring system points to a complex dusty environment close in. Jupiter also controls the dynamical state of the Asteroid Belt and small comets in the Inner Solar System. At least 63 moons swarm about the planet (I remember when only 10 were known!), most of which are captured asteroids or dead comets, but there is also a population of small comets in temporary orbit, one of which, Shoemaker-Levy 9, slammed into the giant planet in 1994 with much fanfare.

It is the four large planet-like moons that grab our attention here. Io and Europa are the stars, due in good measure to their very dynamic geologic histories, but as this Atlas attests Ganymede and Callisto are almost equally compelling, if not for youthful vigor. All feature an unearthly beauty that transcends their rich geologic histories. The Galilean satellites have revealed several fundamental truths. Four hundred years ago they tipped the balance in favor of the Sun-centered planetary system we now know to be true.