<Dl> <Dt> Tidal friction </Dt> </Dl> <P> Ocean tides are converted to heat by frictional losses in the oceans and their interaction with the solid bottom and with the top ice crust . In late 2008, it was suggested Jupiter may keep Europa's oceans warm by generating large planetary tidal waves on Europa because of its small but non-zero obliquity . This generates so - called Rossby waves that travel quite slowly, at just a few kilometers per day, but can generate significant kinetic energy . For the current axial tilt estimate of 0.1 degree, the resonance from Rossby waves would contain 7.3 × 10 J of kinetic energy, which is two thousand times larger than that of the flow excited by the dominant tidal forces . Dissipation of this energy could be the principal heat source of Europa's ocean . </P> <Dl> <Dt> Tidal flexing </Dt> </Dl> <P> Tidal flexing kneads Europa's interior and ice shell, which becomes a source of heat . Depending on the amount of tilt, the heat generated by the ocean flow could be 100 to thousands of times greater than the heat generated by the flexing of Europa's rocky core in response to gravitational pull from Jupiter and the other moons circling that planet . Europa's seafloor could be heated by the moon's constant flexing, driving hydrothermal activity similar to undersea volcanoes in Earth's oceans . </P>

Which of jupiter's moons has water ice surface