On hundreds of clear nights over the past five years, giant telescopes on a dormant volcano in Hawaii have trained their gaze across space toward active volcanoes on a simmering hellscape of a moon that orbits Jupiter. It’s called Io.
“You just see so many volcanoes. It’s incredible,” said Katherine de Kleer, a planetary scientist at Caltech who has led the effort.
Last month de Kleer’s team released its full five-year record of Io’s volcanic activity in The Astronomical Journal. Their data show a pimple-ridden surface roiling with eruptions. Some hot spots glow continuously while other areas flare up, then die back down.
The researchers’ hope is that other planetary scientists may be able to glimpse or dig into the underlying rhythms of this world, the most volcanically active body in the solar system.
Witnessing eruptions on a faraway moon used to require more of a trek. Forty years ago the Voyager probes first spotted volcanoes on Io, a body that scientists expected would look dead and cratered. Instead, it turned out to be pockmarked with oozing hot spots.
The Galileo spacecraft took another close look starting in the 1990s, and the Juno mission, currently at Jupiter, glanced at a volcanic plume sprouting from Io’s surface in December. But these short visits didn’t let scientists study whether Io’s drumbeat of eruptions follows underlying patterns.
IO’S VOLCANOES are thought to be fueled by tidal heating, a stretching-and-squeezing process whereby gravitational forces treat the inside of Io like a stress ball as the moon swings around Jupiter. That same process might be the main energy source driving geologic activity on many small moons and planets throughout the galaxy.
Io’s eruptions are also thought to blast material into space, wafting plasma through the entire Jupiter system, where it swirls along magnetic field lines. Some ejecta from volcanoes even fall back on the surfaces of other moons like Europa, a prime candidate in the search for life.
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 de Kleer’s survey captures far more detail.
“Her observations blow ours out of the water,” Rathbun said.
The data from de Kleer’s team were captured at the W.M. Keck and Gemini observatories on Mauna Kea.
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 from 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 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.
Back on Earth, Rathbun said, she and other planetary scientists are proposing a NASA probe that would study Io’s volcanism up close. But she stressed the value of long-term monitoring.
“I really feel like we need to keep watching this. Five, ten years in the life of a volcano is nothing.”