Voyager image of a plume from the Pele volcano on Io, one of Jupiters four Galilean moons. This moon is the most active body in the solar system and is covered in volcanoes, including the heart-shaped Pele volcano seen in the center-right of the image. Io experiences intense gravitational tidal forces from Jupiter, which generate enormous heat in its interior. This heat causes heated rock to rise through layers containing sulfur and sulfur dioxide, leading to volcanic eruptions in plumes. Image obtained by the Voyager spacecraft.