Tidal Heating & Subsurface Oceans: Structures & Vocabulary

Tidal heating converts repeated gravitational deformation into internal heat. On moons such as Io, Europa, and Enceladus, orbital eccentricity maintained by resonances prevents the body from settling into a constant tidal shape, allowing continuous flexing that can power volcanism or keep water liquid beneath ice.

As a moon moves through an eccentric orbit, the planet's tidal force changes in strength and direction. The moon repeatedly deforms, and internal friction converts some mechanical energy into heat. Resonant interactions with neighboring moons can continually restore eccentricity that tides would otherwise damp away.

Io's intense volcanism requires a major internal heat source, Europa's induced magnetic signature supports a global salty ocean, and Enceladus's south-polar heat flow and water-rich plumes demonstrate active internal heating. Orbital resonances quantitatively connect these observations to gravitational forcing.

The amount of heating depends on orbital eccentricity, distance from the planet, interior rigidity, dissipation efficiency, and resonance forcing. A differentiated ocean world may contain an ice shell, liquid layer, rocky mantle, and metallic core, each responding differently to periodic stress.