<P> First predicted shortly before the Voyager 1 flyby , the heat source for Io 's volcanism comes from tidal heating produced by its forced orbital eccentricity . This differs from Earth 's internal heating , which is derived primarily from radioactive isotope decay and primordial heat of accretion . Io 's eccentric orbit leads to a slight difference in Jupiter 's gravitational pull on the satellite between its closest and farthest points on its orbit , causing a varying tidal bulge . This variation in the shape of Io causes frictional heating in its interior . Without this tidal heating , Io might have been similar to the Moon , a world of similar size and mass , geologically dead and covered with numerous impact craters . </P>
what is the cause of volcanic activity on jupiter 's moon io
tidal heating produced by its forced orbital eccentricity