A new analysis of the data gathered by the Galileo space probe has revealed the presence of a partially molten magma ocean which is a layer about 30 miles thick below the surface of Io, one of the biggest Jupiter’s moons.
The Galileo spacecraft was launched from the Space Shuttle Atlantis on October 18, 1989, reached Jupiter on December 7, 1995 and collected data on the Jovian system until September 21, 2003, when it was thrown into Jupiter’s atmosphere, where it disintegrated. This choice was made to prevent any risk that the Jupiter’s satellites might be contaminated by terrestrial bacteria.
Io is one of the largest Jupiter’s satellites and it’s one of the four called Galileans because they were discovered almost exactly five hundred years ago by Galileo Galilei. Over the past decades some probes passed close to Io and the images taken by the Voyager probes showed volcanic activity on the surface of that moon.
The particular orbit of Io around Jupiter in resonance with two other large moons such as Europa and Ganymede create a tidal effect that generates the large amounts of energy required for the significant volcanic activity detected on Io. The observations made over the years have in fact led to estimate that the eruptions on Io produce a quantity of lava about a hundred times greater than Earth’s volcanoes. This is due to the fact that on Earth volcanoes are concentrated in some areas while on Io they’re scattered over all the surface.
The measurements of the Galileo spacecraft also concerned Io’s magnetic field but some of them had remained unexplained. In recent years however research on minerals physics investigated the properties of a group of rocks called ultramafic (or ultrabasic) indicating that those rocks may have an electrical charge when they are melted. The measurements made by the Galileo probe were consistent with one of those rocks called lherzolite. The estimated temperature of this ocean of magma could be more than 2,200 degrees Fahrenheit.
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Io gets hit by Jupiter’s extremely powerful magnetic field (the blue lines in the image) but the electromagnetic characteristics of the magma ocean cause its deflection to a vertical orientation within the moon. The changes in the resulting magnetic field allowed scientists to understand Io’s internal structure.
It’s possible that the Earth and the Moon had a magma ocean just like Io a few billion years ago, when they were recently formed. If that were the case that magma has cooled very long ago however any study that might increase our knowledge of volcanic phenomena is certainly useful.