Inside Io: NASA’s Juno Reveals Hidden Magma Chambers Fueling Endless Eruptions

Unveiling the Mystery of Io’s Volcanoes

About the size of Earth’s Moon, Io is known as the most volcanically active body in our solar system. The moon is home to an estimated 400 volcanoes, which blast lava and plumes in seemingly continuous eruptions that contribute to the coating on its surface.

Although the moon was discovered by Galileo Galilei on Jan. 8, 1610, volcanic activity there wasn’t discovered until 1979, when imaging scientist Linda Morabito of NASA’s Jet Propulsion Laboratory in Southern California first identified a volcanic plume in an image from the agency’s Voyager 1 spacecraft.

“Since Morabito’s discovery, planetary scientists have wondered how the volcanoes were fed from the lava underneath the surface,” said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. “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.”

This animated tour of Jupiter’s fiery moon Io, based on data collected by NASA’s Juno mission, shows volcanic plumes, a view of lava on the surface, and the moon’s internal structure. Credit: NASA/JPL-Caltech/SwRI/Koji Kuramura/Gerald Eichstädt

Juno’s Close Encounters with Io

The Juno spacecraft made extremely close flybys of Io in December 2023 and February 2024, getting within about 930 miles (1,500 kilometers) of its pizza-faced surface. During the close approaches, Juno communicated with NASA’s Deep Space Network, acquiring high-precision, dual-frequency Doppler data, which was used to measure Io’s gravity by tracking how it affected the spacecraft’s acceleration. What the mission learned about the moon’s gravity from those flybys led to the new paper by revealing more details about the effects of a phenomenon called tidal flexing.

Understanding Tidal Flexing

Io is extremely close to mammoth Jupiter, and its elliptical orbit whips it around the gas giant once every 42.5 hours. As the distance varies, so does Jupiter’s gravitational pull, which leads to the moon being relentlessly squeezed. The result: an extreme case of tidal flexing — friction from tidal forces that generates internal heat.

“This constant flexing creates immense energy, which literally melts portions of Io’s interior,” said 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 Juno team compared Doppler data from their two flybys with observations from the agency’s previous missions to the Jovian system and from ground telescopes. They found tidal deformation consistent with Io not having a shallow global magma ocean.

Implications for Planetary Science

“Juno’s discovery that tidal forces do not always create global magma oceans does more than prompt us to rethink what we know about Io’s interior,” said lead author Ryan Park, a Juno co-investigator and supervisor of the Solar System Dynamics Group at DOI: 10.1038/s41586-024-08442-5

The Juno mission, managed by NASA’s Jet Propulsion Laboratory (JPL), is dedicated to exploring Jupiter’s atmosphere, magnetic field, and moons. Led by principal investigator Scott Bolton of the Southwest Research Institute, Juno is part of NASA’s New Frontiers Program, overseen by NASA’s Marshall Space Flight Center for the Science Mission Directorate. Built and operated by Lockheed Martin Space in Denver, the spacecraft carries advanced instruments from various U.S. research institutions. The Italian Space Agency (ASI) contributed the Jovian InfraRed Auroral Mapper, enhancing Juno’s ability to study Jupiter’s powerful auroras and deep atmospheric processes.