Synchronised volcanic eruptions on Io hint at a spongy interior

Five volcanoes on Jupiter’s moon Io erupted all at once in a cataclysm of lava. This means that they are probably all connected to the same underground magma network, which will help solve the mystery of Io’s insides.

At the end of 2024, researchers monitoring Io via NASA’s Juno spacecraft saw an unusually enormous lava flow near its south pole. “There was this one gigantic eruption and lava flow, and that’s what first caught our eye, but on second look, all these other hotspots lit up as well,” says Jani Radebaugh at Brigham Young University in Utah. “There’s so much magma that we can’t quite wrap our minds around it.”

The erupted lava spanned an area of about 65,000 square kilometres and released more energy than any eruption previously spotted on Io. “Picture standing at the edge of one of these features, and the valley that has been cold suddenly fills up with an entire lake of lava. As it fills up, you turn and look over your shoulder, and another massive crack opens up in the ground and fills with lava at exactly the same time,” says Radebaugh. “It would be terrifying, and so beautiful.”

The question, though, is where all that magma came from – we know very little about Io’s interior structure, so it is a tough one to answer. Previous work has shown that, contrary to researchers’ long-held expectations, Io doesn’t have a global magma ocean buried under its crust, so it is unclear how so much magma could bust through the surface all at once.

Radebaugh and her colleagues suggest that a sort of magma sponge may sit below huge regions of the surface, forming an interconnected network of pores that fill with lava and then spurt it out through the hotspots. We will need more observations to confirm this, though, and with Juno having moved further away from Io, it is unlikely we will get them anytime soon.

Despite Io’s small size – it is only slightly larger than Earth’s moon – the extreme nature of these eruptions makes them similar to volcanic events on Earth. “This is actually like early Earth when it was much hotter and more active, so Io can tell us a lot about our past,” says Radebaugh. While the source of this wildly powerful series of eruptions may remain a puzzle for now, when it’s solved it could help fill in a chapter of our own story.

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