Possible Sequence of Europa Exploration. Almost 30 years ago, Voyagers 1 and 2 (lower left) made their historic rendezvous with the Jupiter system, and first revealed Europa’s icy covered surface to human eyes. In 1995 the Galileo spacecraft went into orbit about Jupiter, and for years studied the giant planet and its major moons. From this mission, we learned that Europa is a world covered with a global ocean about 100 km (60 miles) deep, and that this ocean was capped, liked the Earth’s Arctic Ocean, with a shell of solid ice. To learn more about this ocean and the ice shell above, and especially to investigate ocean’s suitability to sustain life, will require the next step, a future mission dedicated to exploring Europa from orbit about the moon itself (center). Both NASA and ESA (the European Space Agency) are actively studying launching such a mission in the next 10 years. If such a mission is launched, and depending on what is found, future missions to Europa may involve landers or even autonomous vehicles — called cryobots (upper right) — that melt through the ice to explore the ocean below, perhaps sometime later in this century. Credit: NASA/JPL.