Figure 13-3: Formation of the Galilean Satellites Heat from the protosun made it impossible for icy grains to survive within the innermost 2.5 to 4 AU of the solar nebula. In the same way, Jupiter’s heat evaporated any icy grains that were too close to the center of the “Jovian nebula.” Hence, the two inner Galilean satellites were formed primarily from rock, while the outer two incorporated both rock and ice.