Juno reveals the hidden forces behind Jupiter's fiery moon Io

Io, the innermost of Jupiter’s four large moons, is the most volcanically active body in our solar system. Its surface is dotted with hundreds of volcanoes, some of which erupt with towering plumes of sulfur dioxide gas reaching up to 500 kilometers (310 miles) into space.

Scientists affiliated with NASA’s Juno mission have made an intriguing discovery about the moon’s intense volcanic activity.

The researchers have determined that Io’s fiery volcanoes are not fueled by a global magma ocean as previously believed. Instead, each volcano is powered by an individual chamber of molten magma.

This breakthrough ends a 44-year-old mystery surrounding the subsurface foundations of the moon’s most dramatic geological phenomena.

A new understanding of Io’s volcanoes

Io, which is similar in size to our own Moon, hosts approximately 400 volcanoes, which continuously belch out lava and plumes. This ongoing volcanic activity coats the surface in a fiery veneer.

The moon’s existence was first noted by Galileo Galilei in 1610, but it wasn’t until 1979 that its volcanic activity was identified, when imaging scientist Linda Morabito discerned a volcanic plume emanating from the moon’s surface.

Scott Bolton, Juno’s principal investigator from the Southwest Research Institute in San Antonio, elaborated on the significance of the research.

“Since Morabito’s discovery, planetary scientists have wondered how the volcanoes were fed from the lava underneath the surface,” said Bolton.

“Was there a shallow ocean of white-hot magma fueling the volcanoes, or was their source more localized? We knew data from Juno’s two very close flybys could give us some insights on how this tortured moon actually worked.”

The inner workings of the fiery moon Io

In the winters of 2023 and 2024, the Juno spacecraft conducted daringly close flybys of Io. It skimmed within approximately 930 miles of the moon’s mottled surface.

During these crucial missions, Juno linked up with NASA’s Deep Space Network and acquired meticulous, dual-frequency Doppler data. This data was used to gauge Io’s gravity and offered new insights into the effects of a phenomenon known as tidal flexing.

Under Jupiter’s sway: The tidal influence

Due to its proximity to Jupiter and rapid orbit, Io is subjected to an intense gravitational pull.

As Io swings closer and further away from Jupiter, the planet’s gravity exacts an unrelenting squeeze on the moon. This results in extreme tidal flexing, which generates immense internal heat energy.

“This constant flexing creates immense energy, which literally melts portions of Io’s interior,” explained Bolton.

“If Io has a global magma ocean, we knew the signature of its tidal deformation would be much larger than a more rigid, mostly solid interior. Thus, depending on the results from Juno’s probing of Io’s gravity field, we would be able to tell if a global magma ocean was hiding beneath its surface.”

The scientists compared the Doppler data with observations from previous missions to the Jovian system and ground-based telescopes. The team discovered evidence that did not support the presence of a shallow global magma ocean within Io.

“That’s what’s happening inside Io,” Bolton said. “That squeezing is generating heat, and it’s getting so hot that [Io’s] insides are literally melting and popping out. The eruptions are constant. It’s like a nonstop rainstorm. It’s just always erupting all over the place.”

Planetary formation and evolution

Study lead author Ryan Park is a Juno co-investigator and supervisor at the Solar System Dynamics Group at JPL.

Park elaborated on how Juno’s discovery does more than reshape our understanding of Io’s geology.

“It has implications for our understanding of other moons, such as Enceladus and Europa, and even exoplanets and super-Earths. Our new findings provide an opportunity to rethink what we know about planetary formation and evolution,” said Park.

Future exploration of volcanic moons

The discovery that Io’s volcanoes are fueled by individual magma chambers rather than a global magma ocean has significant implications for future planetary exploration.

The finding suggests that volcanic activity on other celestial bodies, such as Europa or Enceladus, could similarly arise from localized geological processes.

The research encourages a re-examination of the geological dynamics on moons across the solar system and beyond.

Moreover, understanding the internal mechanisms of Io’s volcanic activity provides a template for studying the geophysical behaviors of exoplanets.

Researchers believe that many super-Earths and exomoons might exhibit similar tidal flexing and localized heat generation due to the gravitational forces from their parent stars or planets.

By studying Io, scientists can develop new models for detecting and analyzing geological activity in distant worlds.

As Juno continues its mission, the spacecraft’s unique data will help refine exploration strategies for future missions targeting moons with suspected subsurface activity.

The full scientific paper is published in the journal Nature.

Image Credit: NASA/JPL-Caltech/ SwRI/ Gerald Eichstädt

Video Credit: NASA/JPL-Caltech/SwRI/Koji Kuramura/Gerald Eichstädt

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