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Unformatted text preview:  The slight eccentricity of Europa's orbit, maintained by the gravitational disturbances from the other Galileans, causes Europa's sub-Jovian point to oscillate about a mean position. As Europa comes slightly nearer to Jupiter, the planet's gravitational attraction increases, causing the moon to elongate towards it. As Europa moves slightly away from Jupiter, the planet's gravitational force decreases, causing the moon to relax back into a more spherical shape. The orbital eccentricity of Europa is continuously pumped by its mean-motion resonance with Io .  Thus, the tidal flexing kneads Europa's interior and gives the moon a source of heat, possibly allowing its ocean to stay liquid while driving subsurface geological processes.   The ultimate source of this energy is Jupiter's rotation, which is tapped by Io through the tides it raises on Jupiter and is transferred to Europa and Ganymede by the orbital resonance....
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- Fall '10