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Physics - Jupiter's Moons - Io

In 1979 the Voyager Spacecraft flew past Jupiter and its moons; it found that Io had over 80 active volcanoes on its surface. Most people assumed that bodies of Io’s size, whether rocky like Io or icy like its companions, would be geologically dead like our own, similarly sized Moon.

This is because their small size makes them incapable of having retained enough primordial heat or generating adequate radiogenic heat to keep their lithospheres thin and to drive mantle convection sufficiently close to the surface for melts to escape.

However, it is now realized that the orbital resonance that exists between the three innermost Galilean satellites results in tidal heating. For every one orbit completed by Ganymede, Europa completes two and Io completes four, this means that the satellites repeatedly pass each other at the same points in their orbits, and the consequent internal stresses experienced by the satellites provide a source of heat that keeps their interiors warmer than they would otherwise be.

The effect is greatest for Io, which is closest to Jupiter and hence experiences the strongest tidal forces.

There are often more than a dozen volcanic eruptions on Io at any one time. These are identified by seeing ‘eruption plume’ powered by the explosive escape of Sulphur dioxide and rising 100-400 km above the surface. The record for the highest local temperature is at least 1400 ° C.

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