This is a question which I have been been tossing around for some time. By looking at gravitationally induced deformation of celectial bodies, I wonder one thing; where is the conservation of energy? Here's the deal: tides, in the oceans of earth or the siliciclastic crust of Io, are a manifestation of matters' affinity to itself. The moons gravity pulls water toward it's centre of mass, thus tides on earth. No big problem there. My question here is probably better illustrated by looking at tidal heating on Io (the Gallilean sattelite). It is known that Saturn's imense gravitational effects, coupled with gravitational pull from moons further from Saturn than Io generates extreme "push-pull" effects on Io, generating large quantities of heat due to friction within the sattelite. This heat is known to cause active volcanism on the moon. Following me? Good. This heat generated will then be lost to space as long wave rediation (infrared). Energy is lost from the Io system. The heat dissipates, the energy is gone. The energy of the system is A)Kinetic energy due to the angular momentum of Io and the other bodies and B) Gravitational potential energy. So if we are loosing heat out one end, we must also be gobbling up energy at the other. So does Io orbit closer and closer around Saturn with time, thus converting gravitational P.E. to heat? Or does Io's angular velocity decrease (Io looses K.E.)? I realise that in either case the stability of the orbit is affected.