Jupiter’s moon Io, the most volcanically active body in the solar system, is littered with hundreds of erupting volcanoes. High-resolution images now reveal several dozen lava lakes, researchers report in the February Journal of Geophysical Research: Planets. These lakes are far larger than their analogs on Earth, and their structure sheds light on how magma moves beneath the surface of Io. 

Io’s volcanism — probably present over the moon’s entire 4.6-billion-year existence — was discovered when the Voyager spacecraft flew by in 1979. The volcanic activity is caused by the intense gravitational pulls of Jupiter and nearby moons, which deform Io by tens of meters. “This squeezing is heating the body,” says Alessandro Mura, a planetary scientist at Italy’s National Institute for Astrophysics in Rome.

Using infrared images from NASA’s Juno spacecraft, which has orbited Jupiter since 2016, Mura’s team pinpointed more than 40 lava lakes ranging in diameter from about 10 to 100 kilometers. That’s much larger than the lava lakes found on Earth, which tend to measure tens to hundreds of meters across.  

Volcanic activity and lava flows are known to be more extreme on other worlds, says Einat Lev, a volcanologist at Columbia University’s Lamont-Doherty Earth Observatory in Palisades, N.Y., who was not involved in the research. “A lot of planetary flows are much bigger” than Earth’s, she says.

Previous studies have reported lava lakes on Io but with only limited detail, Mura and colleagues note. The researchers found that most of the newly analyzed lava lakes are hottest at their perimeters. This suggests that these lakes are largely capped by a cooler crust of solidified lava.

That idea makes sense given the conditions on Io, says Alfred McEwen, a planetary geologist at the University of Arizona in Tucson who was not involved in the research. “It’s very, very cold. A crust starts forming immediately.”

Molten lava remains exposed at the lake edges probably because of how the lakes interact with their surroundings, Mura and his colleagues propose. Io’s lava lakes sit within caldera-like features with steep or even vertical walls, so as a lake fills or drains, its outer crust scrapes against those walls, breaking up the crust there and exposing fresh lava.

The findings also shed light on how magma moves beneath Io’s surface and feeds these lakes. None of the analyzed lakes had a hot spot in the middle, Mura notes, suggesting that magma doesn’t simply upwell at a lake’s center. 

He and his team hope to understand whether multiple lava lakes are fed by a common magma reservoir. In that case, different lakes might change in size in lockstep. Such observations could help reveal details about the plumbing that powers Io’s volcanism, Mura says. “These can be a glimpse beneath the surface of Io.”