ABSTRACT

Galileo spacecraft data suggest that a global ocean exists beneath the frozen ice surface Jupiter’s moon Europa. Since the early 1970s, planetary scientists have used theoretical and observational arguments to deliberate the existence of an ocean within Europa and other large icy satellites. Galileo magnetometry data indicates an induced magnetic field at Europa, implying that a salt-water ocean exists today. A paucity of large craters argues for a surface on average only ~40–90 Myr old, and two multi-ring structures suggest impacts punched through an ice shell ~20 km thick. Europa’s ocean and surface are inherently linked through tidal deformation of the floating ice shell, and tidal flexing and nonsynchronous rotation may generate stresses that fracture and deform the surface to create ridges and bands. Dark spots, domes, and chaos terrain are probably related to tidally driven ice convection, along with partial melting within the ice shell. Europa’s geological activity and probable ocean-mantle contact could permit the chemical ingredients necessary for life to be present within the satellite’s ocean. Fascinating geology and geophysics, combined with high astrobiological potential, make Europa a top priority for future spacecraft exploration.