Jupiter moon holds magma ocean

BBC : Io, one of Jupiter’s moons, is the most volcanic body in the solar system; it erupts 100 times more lava a year than does Earth, writes Jonathan Amos for BBC News. A reassessment of data from NASA’s Galileo probe suggests that this is due to a reservoir of magma at least 50 kilometers thick that probably makes up at least 10% of the moon’s mantle by volume. Unlike Earth, where volcanoes tend to collect at the boundaries of tectonic plates, Io has volcanoes all over its surface. Jupiter drives this volcanism by producing tides on the moon that squeeze and pull Io’s body, melting its rocks. In turn, Io dramatically distorts Jupiter’s magnetic field, although it wasn’t until several years after Galileo made its passes of the moon that physicists were able to determine why. The conductivity of rocks high in magnesium and iron increases by orders of magnitude when they melt; that conductivity was what allowed Io to influence its parent planet’s magnetic field so strongly.