Internal structure of the Galilean moons
Internal structure of the Galilean moons
These sectional views show possible internal structures of the Galilean moons. Ganymede is on the lower left, Callisto on the lower right, Io on the upper left and Europa on the upper right. The illustrations are based on models derived from measurements of the gravitational and magnetic fields by NASA's Galileo spacecraft. With the exception of Callisto, all satellites are thought to have cores of iron and nickel (shown in grey). These cores, again with the exception of Callisto, are surrounded by a rocky mantle (shown in brown). Io's rock or silicate mantle extends to the surface, while the rock layers of Ganymede and Europa are surrounded by water shells in ice or liquid form (shown in blue and white). Callisto appears as a relatively even mixture of comparable amounts of ice and rock, but it is now considered likely that Callisto also has a water layer with the volume of an ocean.
Credit:
NASA/JPL