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J. F. Cooper (Raytheon ITSS / SSDOO Project, NASA Goddard Space Flight Center, Greenbelt, MD), C. B. Phillips (SETI Institute, Mountain View, CA), Europa Exploration Decadal Community Panel Team
Europa's tortured surface shows relatively few craters and appears only tens of millions of years old. The visible ice crust shows strong evidence of tidal stresses from gravitational coupling to Jupiter and other Galilean satellites. Linear and cycloidal fractures extend far across the surface with layer upon layer of such features indicating a long sequential history of surface deformation from tidal, radiogenic, and other heating of subsurface ices. Abundance of chaos regions, domes and pits possibly associated with diapiric plumes, localized regions of emergent flooding, and apparent extrusion of sulfate hydrates further point to the continuing existence of a sub-surface ocean to recent geologic times. Magnetometer data from many Europa flybys by the Galileo Orbiter are consistent with expected levels of electric current induction in a modern salty ocean. Various aspects of the surface chemical composition inferred from remote sensing are alternatively attributed to internal and exogenic sources. In any case the known energy inputs from solar UV and magnetospheric particle irradiation make the surface a chemical hotbed for rapid processing of ice and non-ice materials into astrobiologically interesting substances such as oxygen and hydrocarbons that could be conveyed to the ocean over millions of years. A profound question for the universality of life is whether biological organisms of any kind could evolve and thrive in such an environment, either near the highly irradiated frozen surface or within an underlying ocean inaccessible to direct sunlight. We define a series of key science questions and discuss how these might be further addressed by acquisition of new data from future missions to Europa such as the proposed Europa Orbiter, drop probes, surface landers, and cryobotic explorers of the sub-surface regions. Importance of continuing technological evolution in earth-based spectroscopic observations, and associated improvements in laboratory simulations under realistic Europan conditions, is also stressed.