Unveiling Io’s Volcanic Secrets: Insights from NASA’s Juno Mission

A recent study sheds light on why and how Io became the most volcanic body in the solar system. Researchers working with NASA’s Juno mission to Jupiter have revealed that the volcanoes on Io, Jupiter’s moon, are likely fueled by individual chambers of seething hot magma rather than a global ocean of magma. This discovery resolves a 44-year-old mystery about the underground origins of the moon’s most striking geological features.

A paper detailing the source of Io’s volcanism was published on Thursday, Dec. 12, in the journal Nature. These findings, along with other scientific results related to Io, were presented during a media briefing at the American Geophysical Union’s annual meeting in Washington, the largest gathering of Earth and space scientists in the U.S.

Roughly the size of Earth’s Moon, Io is recognized as the most volcanically active celestial body in the solar system. The moon hosts approximately 400 volcanoes, which erupt continuously, spewing lava and plumes that contribute to its ever-changing surface coating.

Although Galileo Galilei discovered Io on Jan. 8, 1610, its volcanic activity remained unknown until 1979. That year, Linda Morabito, an imaging scientist at NASA’s Jet Propulsion Laboratory in Southern California, identified a volcanic plume in an image captured by the Voyager 1 spacecraft.

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

“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.”

The Juno spacecraft performed extremely close flybys of Io in December 2023 and February 2024, approaching within about 930 miles (1,500 kilometers) of its pizza-like surface. During these flybys, Juno communicated with NASA’s Deep Space Network and collected high-precision dual-frequency Doppler data. This data allowed scientists to measure Io’s gravity by observing how it influenced the spacecraft’s acceleration. Insights into Io’s gravity field from these flybys unveiled new details about the effects of a phenomenon known as tidal flexing.

Prince of Jovian Tides

Io orbits close to the massive Jupiter, completing one revolution around the gas giant every 42.5 hours. Its elliptical orbit causes variations in Jupiter’s gravitational pull, leading to relentless squeezing of the moon. This process, known as tidal flexing, generates intense internal heat.

This five-frame sequence shows a giant plume erupting from Io’s Tvashtar volcano, extending 200 miles (330 kilometers) above the fiery moon’s surface. It was captured over an eight-minute period by NASA’s New Horizons mission as the spacecraft flew by Jupiter in 2007.
 Credit: NASA/Johns Hopkins APL/SwRI

“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 analyzed Doppler data from the two flybys and compared it with observations from NASA’s earlier missions to the Jovian system and ground-based telescopes. The results showed tidal deformation consistent with Io lacking a shallow global magma ocean.

“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 JPL. “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.”

There’s still more science to come. The spacecraft completed its 66th science flyby of Jupiter’s mysterious cloud tops on Nov. 24. Its next close approach to the gas giant is scheduled for 12:22 a.m. EST, Dec. 27. At perijove, the closest point in Juno’s orbit to Jupiter’s center, the spacecraft will be about 2,175 miles (3,500 kilometers) above Jupiter’s cloud tops. Since entering Jupiter’s orbit in 2016, Juno has traveled 645.7 million miles (1.039 billion kilometers).

More About Juno

JPL, a division of Caltech in Pasadena, California, manages the Juno mission for principal investigator Scott Bolton of the Southwest Research Institute in San Antonio. Juno is part of NASA’s New Frontiers Program, overseen by NASA’s Marshall Space Flight Center in Huntsville, Alabama, for the agency’s Science Mission Directorate in Washington. The Italian Space Agency (ASI) funded the Jovian InfraRed Auroral Mapper, while Lockheed Martin Space in Denver constructed and operates the spacecraft. Several scientific instruments on Juno were contributed by institutions across the U.S.

More information about Juno is available at:
https://science.nasa.gov/mission/juno



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