Jupiter has a permanent ring of auroral light surrounding each of its poles. Most of the charged particles responsible for the light have long been thought to originate from tiny, hyperactive Io, which burps out about a tonne of sulphur per second in its persistent, violent volcanic activity. However, the sun was thought to cause any variations in the rings via changes in the pressure of the solar wind.
But new observations suggest that Io can control these changes as well. “Variations we thought were connected to the sun we now see are connected to the volcanic activity,” says Bertrand Bonfond of the University of Liège in Belgium.