Hoping to understand them better, Earth-based astronomers have long tried to track where and when Io’s individual volcanoes flare up, then fade. One team including Julie Rathbun of the Planetary Science Institute in Tucson, Ariz., has monitored Io’s brightest volcanoes over two decades. But Dr. de Kleer’s survey captures far more detail.

“Her observations blow ours out of the water,” Dr. Rathbun says.

One pattern has already emerged. The moon’s trailing hemisphere — if you think of Io as a car driving in a circle around Jupiter, it’s the back windshield — seems to host far more bright, temporary eruptions than the other side of the moon.

This could be the result of Io’s crust differing f rom hemisphere to hemisphere , or because a single big eruption on the trailing hemisphere has triggered subsequent blasts. (Or, it could still be just a fluke in the data.)

Another suggestive pattern comes from Loki Patera, Io’s single most powerful volcano and a gaping window to the interior of the moon.

It brightens and fades about every 460 or 480 days, according to an analysis published by Dr. de Kleer and colleagues in the Geophysical Research Letters in May. If Loki Patera continues to wax and wane into the next few years as predicted, that time frame would match other cyclical variations in how Io orbits Jupiter — providing a suggestive link between changing tides exerted by Jupiter and the ebbs and flows of surface volcanoes.