Which Jovian moon has volcanoes?

Which Jovian moon has volcanoes? Io—the innermost of Jupiter’s four large moons and the most volcanically active world in the Solar System.

Io’s volcanoes are powered by tidal heating. Jupiter’s enormous gravity, combined with repeated gravitational tugs from neighboring moons Europa and Ganymede, continually stretches and squeezes Io’s rocky interior. The resulting friction generates enough heat to melt rock and drive lava eruptions across the moon’s surface.

Galileo Galilei discovered Io in 1610, but its volcanoes were not observed until NASA’s Voyager 1 spacecraft flew past in 1979. The discovery transformed Io from a distant point of light into a world with hundreds of active volcanic centers, lava lakes, sulfur-rich deposits, and plumes that can rise hundreds of kilometers above the surface. Because eruptions constantly renew the landscape, Io has relatively few large impact craters.

A common mix-up is Europa, another Jovian moon. Europa is famous for evidence of a subsurface ocean and water-vapor plumes, while Io is the moon associated with active volcanoes and molten lava. Io is also slightly larger than Earth’s Moon, despite having a much more extreme volcanic environment.