How the tiny moon stores and moves its vast amounts of heat has long remained a mystery
An entire ocean of liquid magma, or perhaps a hot heart of solid metal, may be lurking in Io’s underworld.
The surface of Jupiter’s deepest moon is covered in burning lava lakes and riddled with hundreds active volcanoes , some of which eject molten rocks tens of kilometers in height. During many years the restless, mesmerizing hellscape of the moon attracted the attention of many planetary scientists.
Researchers are now investigating the nature of Io’s hellish interior to explain what is causing the spectacular volcanism on the moon’s fiery surface. “This is the largest volcanically active site in the solar system,” says planetary scientist Samuel Howell of NASA’s Jet Propulsion Laboratory in Pasadena, California. “But it’s still not entirely clear where this energy comes from.”
Researchers generally agree that Io gets most of its energy from the gravitational tug of war between its parent planet Jupiter and its sister moon Europa. These enormous forces pull the rocky body of Io, creating enormous heat of friction in its middle. But how this heat is stored and moved remains a mystery.
One explanation is that Io’s underworld may contain a vast ocean of liquid magma , said planetary scientist David Stevenson of the California Institute of Technology on December 15 at the fall meeting of the American Geophysical Union. While the exact size of the proposed molten sea remains uncertain, it should be relatively large, he said. “A magmatic ocean can be, say, 100 kilometers thick.”
In 2011, researchers reported that Io’s mantle may not be completely solid. Magnetic measurements of Io from the Galileo spacecraft showed that there must be an electrically conductive layer inside the Moon. Scientists write that global underground layer containing molten rock would meet the requirements.
But the researchers couldn’t tell whether the layer would consist of a continuous sea of magma or many small pockets of molten rock scattered across the solid rock, like a wet sponge.
Building on this previous work, Stevenson and Caltech geophysicist Yoshinori Miyazaki calculated that the mixed layer of magma and hard rock beneath Io’s crust would be fundamentally unstable under the predicted heating of the moon’s interior. According to Stevenson, the molten rock and solid rock will separate into separate layers, and the molten rock will merge into a subterranean sea. “The bottom line is that Io has a magma ocean.”
But there are other possibilities. “A lot of the information is consistent with a large global conductive layer that could be a magma ocean,” Howell says. “But I wouldn’t say there’s a consensus on how to interpret this data.”
Instead, the truth may lie in Io’s heart, where a core made of solid metal may be hidden , Howell said at the December 15 meeting. Previous studies have shown that Io has a metal-rich core . Howell and his colleagues calculated that a metallic core, which is about as hard as solid ice, and a rocky mantle, as viscous as Earth’s, could completely dissipate the enormous amount of heat that Io is estimated to emit. This would act as an energy releasing magma ocean.
Future measurements collected by an ongoing NASA mission Juno , as well as two future spacecraft — NASA’s Europa Clipper and the European Space Agency’s JUICE — could provide the data needed to determine whether any of the hypotheses, or some combination, are correct, Stevenson and Howell said. Until then, the mystery of what lives in Io’s dark depths may remain in purgatory.
