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Moons of our Solar System
Moons of our Solar System

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1.2 Present volcanism on other moons

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Figure 8 Io, caught in the act. 200-km-wide false-colour image taken by NASA’s Galileo spacecraft shows an incandescent lava flow at the Tvashtar volcano.
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This is an image of Io, caught in the act. 200-km-wide false-colour image taken by NASA’s Galileo spacecraft shows an incandescent lava flow at the Tvashtar volcano.

Figure 8 Io, caught in the act. 200-km-wide false-colour image taken by NASA’s Galileo spacecraft shows an incandescent lava flow at the ...

We know several moons in the Solar System to be volcanically active and see evidence in the form of recognisable surface deposits and by imaging of eruptions in progress.

What is driving Io?

Timing: Allow approximately 10 minutes.

Earth’s Moon froze long ago. What heat source could possibly be driving Io’s continuing volcanism, such as the eruption producing the plume visible on the left of this image, which is rising more than 100 km above the surface? Think back to the ‘Tidal heating explained’ video near the end of the first week.

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Figure 9 Voyager 1 image of Io showing an active plume from Loki volcano rising above the limb.
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This is a Voyager 1 image of Io showing an active plume from Loki volcano rising above the limb.

Figure 9 Voyager 1 image of Io showing an active plume from Loki volcano rising above the limb.

Answer

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Figure 10 Io image captured by Galileo in 1997.
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This is an image of Io captured by Galileo in 1997.

Figure 10 Io image captured by Galileo in 1997.

Thanks to orbital resonance with Europa, the varying tidal forces on Io caused by the eccentricity of its orbit around Jupiter are so strong that Io’s tidal bulges are expected to rise and fall by up to 100 m during a single orbit, and also migrate to and fro a little. This distortion generates an immense amount of heat, fuelling the most volcanic body in the Solar System.