[OAB 58] The claim is that the existence of volcanoes on Io, Jupiter's closest large moon, demonstrates that the moon has not cooled off from the creation event, and that it therefore must be young. The fact is, however, that we know exactly what the heat source is which supplies Io. Because Io is so close to Jupiter, there are tremendous tidal forces which heat Io's interior by friction. That is why Io is the most volcanically active body in the solar system. In fact, calculations based on tidal heating predicted Io's volcanism before the Voyager spacecraft arrived at Jupiter and discovered it (see Peale, Casson, and Reynolds, Science, v.203, pp.892-894 (1979)).