Tides on Europa. Diagram showing the gravitational flexion (tidal stretching) of Europa (blue) by two other satellites (grey) of Jupiter. The stretching is maximal at the points of closest approach to Io (left) and Ganymede (right). The tidal stretching slightly distorts Europa's shape from a sphere to an ovoid shape. This produces internal heat inside Europa, and may help to maintain an ocean of water under its icy surface. It may also account for the cracked appearance of this icy crust. Io, Europa and Ganymede are all tidally-locked by Jupiter, with one face facing Jupiter. They are also locked into resonant orbits, with Io orbiting four times for two Europa orbits and one Ganymede orbit.