In the absence of the moons tidal synchronization and circularization of the orbit could take place. But the other moons perturb Io's orbit and prevent if from becoming circular, so Jupiter keeps battling to synchronize it, and the net result is continuous tidal flexure. Closer view by Galileo indicates an icy surface covered with cracks that look like Arctic pack ice. Heat for melting is probably caused by tidal effects of Jupiter. Europa may be one of the few habitable places in the solar system.
Surface is heavier cratered, but less than Callisto.
May be evidence of episodes of melting brought on by tidal heating from Jupiter. There may be a sort of plate tectonics on Ganymede, causing surface to crack and slip. Difference with earth, though, in that the mantle and surface are mostly icy, rather than rocky. Images from Galileo spacecraft show all sorts of odd flow patterns and stress patterns on surface, caused perhaps by tidal stress and also by expansion and outflow of icy mantle material. Interior, like Ganymede, rocky core, thick mantle of ice and gravelly rock.