This is a cutaway of the possible interior of an icy moon.
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Interior of Icy Moons
The diagram to the left shows a cutaway of the possible interior structure of an icy moon. The drawing illustrates what used to be postulated for Jupiter's moon Ganymede.
The composition of the icy moons is mostly ice, therefore there is probably a small core of some rocky material buried inside, overlain with mantles of ice of various phases.
The diagram shows that there may be an ocean of water beneath the surface crust. This is because one of the phases of ice is water. If the temperature inside an icy moon is just right, then there might be water inside. Such an environment might prove to be habitable for life. For Jupiter's moon Europa, this scenario may be very important.
The history of an icy moon involves cooling, however. So icy moons which may have had a water layer in the past might be completely frozen now.
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