NASA spacecraft flew by distant world. It saw unprecedented volcanism.

On Dec. 27, 2024, NASA’s Juno spacecraft swooped by the volcanic world Io. It witnessed a giant eruption.

As the space agency’s basketball court-sized craft orbits Jupiter, it swings near the gas giant’s intriguing moons, which allowed Juno to observe “a massive hot spot” near Io’s south pole. Juno’s JIRAM instrument, which can detect heat, observed a number of closely spaced hot spots, pointing to a giant eruption of lava from a vast underground chamber.

“The data supports that this is the most intense volcanic eruption ever recorded on Io,” Alessandro Mura, a Juno scientist from the National Institute for Astrophysics in Rome, said in a statement.

But that’s not all. Io, a realm about the size of Earth’s moon but blanketed in hundreds of active volcanoes, is no normal place.

“This is the most powerful volcanic event ever recorded on the most volcanic world in our solar system — so that’s really saying something,” said Scott Bolton, who leads the Juno mission.

This newly found volcanic feature covers an area of some 40,000 square miles, or 100,000 square kilometers. That smashes the previous record-holder, a feature called Loki Patera — considered the most active and persistent hot spot on Io — that hosts a lava lake spanning some 7,700 square miles (20,000 square kilometers).

The hot spot, which NASA notes is bigger than Lake Superior, is visible below.

Surface changes seen in the location of the detected hot spot between April 9, 2024, and Dec. 27, 2024.
Credit: NASA / JPL-Caltech / SwRI / MSSS / Image processing by Jason Perry

Io is blanketed in erupting volcanoes because it’s relentlessly locked in a tug-of-war between nearby objects, including the colossal Jupiter. “Not only is the biggest planet in the solar system forever pulling at it gravitationally, but so are Io’s Galilean siblings — Europa and the biggest moon in the solar system, Ganymede,” NASA explained in a statement. “The result is that Io is continuously stretched and squeezed, actions linked to the creation of the lava seen erupting from its many volcanoes.”

NASA’s recent flybys of Io, however, have revealed that it likely doesn’t contain a global magma ocean beneath its surface, as determined by new observations of the moon’s gravity. Instead, each of Io’s 400 or so volcanoes may harbor their own chamber of magma.

And NASA intends to further investigate this new site of prodigious volcanism. Juno will again fly by Io on March 3. Its cameras will be tuned to this compelling region of the moon, located some 484 million miles beyond Earth.