Why does Jupiter’s moon Io have so many volcanoes?

Io is the most volcanically active body in the Solar System because it experiences intense tidal heating. Jupiter’s huge gravity and orbital resonances with Europa and Ganymede repeatedly flex Io’s interior, creating friction and heat. That energy keeps much of its interior partially molten, fueling constant volcanic eruptions and lava flows. The Galileo spacecraft and later observations revealed hundreds of active volcanic centers and dramatic plume activity. Io is a striking example of how gravity itself can power geology on a moon.