MadSci Network: Astronomy
Query:

Re: Tidally generated heat? Where does that come from?

Date: Tue Sep 2 02:50:01 2003
Posted By: Peter Thejll, Staff, Solar-Terrestrial Physics, Danish Meteorological Institute
Area of science: Astronomy
ID: 1062188573.As
Message:

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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