CHICAGO — An entire ocean of liquid magma, or perhaps a hot heart of solid metal, lies hidden in Hell.
The surface of Jupiter’s inner moon is scorched by burning lava lakes and suffocated by hundreds of active volcanoes, some erupting molten rock tens of kilometers high (SN: 8/6/14). Over the years, the moon’s restless, mesmerizing Hellscape has drawn the attention of many planetary scientists.SN: 5/3/22).
Now researchers are digging into the nature of Ion’s interior to explain what spectacular volcanism is doing on the moon’s surface. “It’s the hottest place in the solar system,” says planetary scientist Samuel Howell of NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “But where that energy comes from is not really clear.”
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Researchers generally agree that Io gets most of its power from the gravitational tug of war between its parent Jupiter and its sibling moon Europa. Those great forces drag on the rocky body of Ion, generating tremendous heat friction in its interior. But how that heat is stored and circulated remains a mystery.
One explanation is that Jupiter is a huge ocean of liquid magma, Caltech planetary scientist David Stevenson said on December 15 at a meeting of the American Geophysical Union. Although the size of the proposed sea melt remains uncertain, he said it would be a relatively large project. “The magma ocean is, you say, 100 kilometers thick.”
In 2011, researchers reported that Ion’s mantle may not be completely solid. Ion’s magnetic field measurements by Galileo indicated that there must be an electric field inside the moon. A global underground reservoir containing molten rock, the scientists wrote, would fit the bill.
But the researchers could not tell whether that layer was from a continuous sea of magma or several pockets of molten rock dispersed throughout the solid rock, like a stretch of sponge.
Building on that previous work, Stevenson and Caltech geophysicist Yoshinori Miyazaki calculated that the mixed layer of magma and solid rock beneath Ion’s crust is fundamentally unstable under the amount of heating they predict will occur inside the moon. The molten rock and the solid rock would split into separate layers, with the molten rock coalescing into the subsurface of the sea, Stevenson said. “The last conclusion is” [that] Io magma has an ocean. “
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But there are other possibilities. “A lot of information is related to a large, globally conductive layer that may be a magma ocean,” Howell says. “But I don’t mean the consent you translate into data.”
But the truth lies deep inside the heart of Io, where the solid metal core may be hiding, Howell told the Dec. 15 meeting. Previous research suggests that Io has a metal-rich core. Howell and colleagues calculate that a metallic core surrounded by ice as rigid as solid and a rocky mantle as viscous as Earth could fully dissipate the immense amounts of heat that Io is estimated to emit. That energy absorption would fill parts of the magma ocean.
Future measurements collected by NASA’s ongoing Juno mission as well as two future spacecraft — NASA’s Europa Clipper and Europa’s Space Shuttle — may provide the data needed to determine whether the hypothesis or some combination is correct, Stevenson and Howell said (SN: 12/15/22). Still, the mystery residing in the darkness of Ion must remain in purgatory.
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