What source of energy might keep an ocean beneath the surface of Ganymede liquid?

Question

Quizplus · Accepted Answer

Ganymede, one of the moons of Jupiter, experiences tidal heating due to the gravitational forces of Jupiter and other nearby moons. This causes frictional heating within the moon's interior and can maintain a partially liquid ocean beneath its icy crust. In addition to tidal heating, Ganymede also has a small amount of radioactive decay occurring within its interior, which contributes to the heat budget and helps maintain the liquid ocean. Therefore, both tidal heating and radioactive decay are likely sources of energy that keep the ocean beneath Ganymede's surface liquid.

What Source of Energy Might Keep an Ocean Beneath the Surface