Internal structures of the Galilean satellites

Internal structures of the Galilean satellites

. The interior characteristics of Jupiterís four largest moons have been inferred from gravitational and magnetic field measurements from the Galileo spacecraft. The satellites are shown according to their actual relative size, and compared with those of the Moon and Mercury (horizontal bars). With the exception of Callisto, the metal, rock and ice have separated, or differentiated, into distinct layers. Io, Europa and Ganymede all have metallic, or iron and nickel, cores surrounded by rock, or silicate, shells. Ioís rocky shell extends to the surface, while outer layers of water, in ice or liquid form, surround Europa and Ganymede. The surface of Io contains numerous active volcanoes, and Europaís thin, frozen crust of water ice probably covers a liquid ocean. Callisto seems to have a relatively uniform internal mixture of ice and rock. (Courtesy of NASA and JPL.)

Copyright 2010, Professor Kenneth R. Lang, Tufts University