MadSci Network: Astronomy |
There is no 'free lunch'! The energy that shows itself as heat in the oceans of Europa does indeed come from somewhere! Tidal energy is dissipated as heat when the motion of the liquid rubs against itself and solids, such as cliffs and ocean bottoms or what there may be lurking on Europa. The deformation and cracking of the surface ice also 'costs' some energy - it is all taken from the tidal bulge. Without the heating and deformation the tidal bulge would be that more vigorous and pronounced. Ultimately this energy comes from the potential energy of the moon Europa in its orbit around Jupiter. Our own Moon turns always one side to the Earth for the very same reason - its rotational energy has been dissipated by tidal heating to the extent that the period of rotation now is (nearly) the same as the period of its orbit around the Earth. The Earths rotation is also influenced by the presence of the Moon - the length of day is slowly changing over millions of years.
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