Jupiter's volcanic moon Io doesn't appear to have a subsurface ocean of magma, resolving some issues about how Io's volcanoes erupt and raising broader questions about similar magma oceans within other moons and planets.
Data from previous missions had made planetary scientists wonder whether, rather than just pockets of melt, Io contained a 31-mile (50-kilometer) deep layer of magma: a moon-wide ocean of molten rock. In the 1990s, NASA's Galileo mission performed magnetic induction measurements that suggested there was such a layer, while more recently, the distribution of volcanoes on Io mapped by NASA's Juno mission to Jupiter was considered suggestive of a global magma ocean distributing heat across the moon.
