Synchronised volcanic eruptions on Io hint at a spongy interior

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

In late 2024, researchers monitoring Io via NASA’s Juno spacecraft observed an unusually huge lava flow near its south pole. “There was this gigantic eruption and lava flow, and that’s what first caught our attention, but at second glance, all these other hot spots lit up as well,” says Jani Radebaugh of Brigham Young University in Utah. “There’s so much magma we can’t really think about it.”

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

The question, however, is where all this magma is coming from – we know very little about Io’s interior structure, so it’s difficult to answer. Previous work has shown that, contrary to researchers’ long-held expectations, Io does not have a global magma ocean buried beneath its crust. It is therefore unclear how so much magma could pass through the surface at once.

Radebaugh and his colleagues suggest that a kind of magma sponge may lie beneath large regions of the surface, forming an interconnected network of pores that fill with lava and then release it through hot spots. We’ll need more observations to confirm this, though, and since Juno has moved away from Io, we’re unlikely to get them any time soon.

Despite Io’s small size – it’s only slightly larger than Earth’s Moon – the extreme nature of these eruptions makes them similar to volcanic events on Earth. “It actually looks like early Earth, when it was much warmer and more active, so Io can tell us a lot about our past,” says Radebaugh. Although the source of this series of extremely powerful eruptions remains a mystery for now, once solved it could help fill a chapter in our own history.

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