The Mysterious Inner Workings of Io, Jupiter’s Volcanic Moon

Scott Bolton’s first encounter with Io took place in the summer of 1980, right after he graduated from college and started a job at NASA. The Voyager 1 spacecraft had flown past this moon of Jupiter, catching the first glimpse of active volcanism on a world other than Earth. Umbrella-shaped outbursts of magmatic matter rocketed into space from all over Io’s surface. “They looked amazingly beautiful,” said Bolton, who is now based at the Southwest Research Institute in Texas. “It was like an artist drew it. I was amazed at how exotic it looked compared to our moon.”

Scientists like Bolton have been trying to understand Io’s exuberant volcanism ever since. A leading theory has been that just below the moon’s crust hides a global magma ocean, a vast contiguous cache of liquid rock. This theory dovetails neatly with ...