A research team led by Katherine de Kleer (Caltech) has used the Atacama Large Millimeter/submillimeter Array (ALMA) to inventory the gases in the thin atmosphere of Jupiter’s moon Io. It was discovered that it contains many more heavy isotopes of sulfur and chlorine than the solar system average. This is because lighter isotopes are continually escaping from the upper atmosphere – a process that has been going on for quite some time (ScienceApril 18).
Io is the most volcanically active body in our solar system. It is in orbital resonance with two other large moons of Jupiter: Europa and Ganymede. In the time that Ganymede orbits Jupiter once, Europa completes exactly two orbits and Io completes four. This has caused Io’s orbit to be elliptical rather than circular, varying the gravitational pull that Jupiter exerts on this moon.
This results in strongly changing tides, comparable to the tides that the moon causes on Earth. They cause Io’s interior to heat up and volcanism to occur. Some of the sulfur released disappears into space under the influence of charged particles in Jupiter’s magnetosphere. The rest falls back to Io’s surface to be ‘reused’.
It turns out that the sulfur that disappears into space is isotopically a little lighter than the sulfur that is recycled in Io’s interior. As a result, the sulfur left on Io becomes isotopically heavier over time – how much heavier depends on the duration of the volcanism.
De Kleer and her team have now discovered that Io’s atmosphere contains so much more isotopically heavy sulfur that it must, in fact, have lost almost all of its original sulfur. Based on numerical models, they conclude that the Jupiter moon has been volcanically active for billions of years and the current orbital resonance with Ganymede and Europa has existed for just as long. (EE)
Studying volcanoes on Jupiter’s moon Io
