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How can gravitational interactions keep the oceans of Jupiter’s moons warm?

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Habitable zone The habitable zones (green) for stars that are like the Sun (middle), hotter than the Sun (top), and cooler than the Sun (bottom). The red areas are those in which liquid surface water would be lost as a result of a runaway greenhouse effect, and the blue areas are those in which liquid surface water would be completely frozen.

Gravitational interactions keep the oceans of Jupiter’s moons warm through a process known as tidal heating.12

This mechanism occurs because of the moons' orbital configurations. When moons are in stable orbital resonances—such as the 1:2:4 ratio shared by Io, Europa, and Ganymede—their orbits are forced into eccentric (elliptical) paths. As a moon travels along this eccentric orbit, it experiences varying gravitational forces from its host planet.345

This changing gravitational pull causes the moon to undergo periodic, cyclic deformations—essentially a "flexing" of its interior. The dissipation of this mechanical energy through internal friction generates significant heat. In the case of Europa, this tidal energy is believed to be sufficient to maintain a global liquid water ocean beneath its icy crust. Similarly, this process is responsible for the intense volcanic activity observed on Io.45312

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