NASA/JPL/University of Michigan/UCLA

New analysis of decade-old data has revealed a subsurface ocean of molten magma, bubbling in the crust of Jupiter's moon, Io.

The magma sea is buried deep beneath the surface and is 20 to 30 miles thick, meaning it makes up at least 10 percent of the moon's mantle by volume. The blisteringly hot reservoir, which feeds the moon's many active volcanoes, would probably exceed temperatures of 1,200 degrees Celsius.

So how did the team only just figure this out, when its Io-hunting spacecraft Galileo threw itself into the burning atmosphere of Jupiter way back in 2003?

When the spacecraft flew past the volcanic moon in October 1999 and February 2003 it picked up some odd signatures in the moon's magnetic field. At the time, the agency's astronomers couldn't adequately explain what they meant.


Years later and mineral physics researchers were looking into a group of rocks called "ultramafic" rocks, that form through the cooling of magma and are capable of carrying a substantial electrical current when they melt. That current would produce signals in a magnetic field.

This led UCLA's Krishan Khurana and her colleagues to the hypothesis that the strange signatures on Io could be attributed to current flowing through molten ultramafic rock in the core. Khurana tested the idea on lherzolite rocks -- igneous rocks found in Spitzbergen, Norway -- and found signatures consistent with those detected by Galileo.


Research into Io could give insight into the evolution of planet Earth. It has been suggested that both Earth and the Moon had subsurface oceans of magma when they were formed billions of years ago. They've long since cooled, leaving a few traces of magma at hotspots like the "Ring of Fire" around the Pacific Ocean.

By further studying Io, we could get a glimpse of Earth and the Moon in their earliest histories.


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