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Io, the innermost large moon of Jupiter, is about the same size and density as Earth's Moon. Io is the most volcanically active body known in the Solar System. Eruptions are so common and so large that the entire surface can be buried under 100 meters of material every 1 million years (it takes submarine volcanoes about 80 million years to resurface about two-thirds of the Earth). Impact craters, which are common on many planets and moons, are absent on Io because of the frequent volcanic eruptions bury them.
These enhanced (false) color views of Io highlight details of the surface. Some areas on Io are truly red and are closely associated with very recent explosive eruptions and volcanic plumes. The most prominent red oval surrounds the volcano Pele (far right). Galileo images courtesy of NASA's Jet Propulsion Laboratory. The following pages provide an overview of many aspects of Io's volcanoes.