Europa and enceladus are both outside of the sun's habitable zone. however, they contain liquid water because they receive from their parent planets.

The correct answer is a tidal energy.

Explanation:

Astronomers have been thinking about an idea: for there to be an ocean beneath the surface of Enceladus and Europe, it is necessary to generate temperature. We know that the moon's core is relatively dead. So the energy will come, without further remedy, from the tidal forces that Saturn produces on its satellite.