How have the moons that JUICE will be visiting - Ganymede, Callisto and Europa - sustained a subsurface ocean despite being so far away from the Sun? Why haven’t they frozen over?
They are called ‘icy moons’ because they are made of frozen ice. But there is a mechanism inside the moons which generates heat, and then the ice can melt and become liquid. The question is, how is the heat generated inside?