INVITED: GEOLOGICAL EXPLORATION OF THE JUPITER SYSTEM

The Jupiter "system" includes the gas giant, Jupiter, its ring(s), and the satellites. The Galilean satellites (Io, Europa, Ganymede, and Callisto) are planet-size bodies that display diverse geological histories. Results from the Galileo orbiter suggest that all but Io could have liquid water beneath their "dirty" ice crusts. Europa contains more water than all of Earth and parts of its surface appear to have deformed, enabling water or slush to erupt onto the surface in geologically recent times, as driven by internally-generated tidal heat. Spectral reflectance data indicate that the surface includes various salts; moreover, it is likely that impacts by comets have implanted organic chemistry onto Europa. Given these characteristics, the National Research Council and NASA identified Europa and the Jupiter system as a high priority target for exploration, particularly as related to the search for life beyond Earth. Currently, various spacecraft options are being assessed, including the potential use of nuclear-powered systems, in order to obtain a uniform global image-set of Europa, conduct subsurface sounding experiments to determine the thickness of the ice crust, and characterize the magnetic field induced by Jupiter. Of particular interest is the possibility of a landed system for Europa to provide "ground truth" for remote sensing data from orbit and to make in situ measurements of the composition and physical state of the icy crust and its astrobiological potential.