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| NASA's Juno spacecraft captured the north polar region of Jupiter's volcanic moon Io during its 57th close pass on Dec. 30, 2023, with data from recent flybys providing new insights into the moon's interior. |
A groundbreaking new study reveals that the volcanoes on Jupiter’s moon Io are powered by individual chambers of magma, rather than a global ocean of molten rock beneath the surface. This discovery, published on December 12, 2024, in Nature, addresses a longstanding mystery about Io’s geologic activity, one that has puzzled scientists for over four decades.
Io, which is roughly the size of Earth's Moon, holds the title of the most volcanically active body in our solar system. It is home to over 400 volcanoes, each contributing to its continually changing surface. These eruptions spew lava and plumes that define Io's distinctive "pizza-faced" appearance. Although the moon was first discovered by Galileo in 1610, its volcanic activity was not observed until 1979, when Linda Morabito, a scientist at NASA’s Jet Propulsion Laboratory, spotted a volcanic plume in an image from the Voyager 1 spacecraft.
For years, researchers debated whether Io’s volcanoes were powered by a global ocean of magma beneath the surface or by smaller, localized pockets of molten rock. Scott Bolton, the principal investigator for NASA's Juno mission, emphasized that this question was central to understanding Io's geological processes. “The data collected by Juno’s close flybys of Io gave us the opportunity to answer that question definitively,” he said.
In December 2023 and February 2024, the Juno spacecraft conducted close flybys of Io, coming within 930 miles (1,500 kilometers) of its surface. The spacecraft collected high-precision Doppler data by measuring how Io’s gravity affected the spacecraft’s acceleration. This data, in conjunction with earlier observations from previous missions and Earth-based telescopes, revealed that Io’s interior is not a molten ocean but rather contains distinct, localized magma chambers beneath its surface.
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| This five-frame sequence, captured by NASA's New Horizons mission during its 2007 flyby of Jupiter, shows a giant plume erupting from Io's Tvashtar volcano, reaching 200 miles (330 kilometers) above the moon's surface over an eight-minute period. |
The key to this discovery lies in understanding tidal flexing, a phenomenon caused by Io’s extreme proximity to Jupiter. Io’s elliptical orbit brings it close to the gas giant every 42.5 hours, subjecting it to immense gravitational forces. These forces create friction inside Io, generating enough heat to melt parts of its interior. The findings from Juno’s gravity measurements indicate that the tidal flexing does not produce a global magma ocean, as was once hypothesized, but instead causes localized pockets of magma that power the volcanoes.
Lead author Ryan Park, a Juno co-investigator from NASA’s Jet Propulsion Laboratory, explained the broader implications of the study. “Juno’s discovery that tidal forces do not always create global magma oceans has implications for our understanding of other moons, such as Enceladus and Europa, as well as exoplanets and super-Earths,” Park said. “It also provides new insights into planetary formation and evolution.”
The Juno spacecraft continues to provide valuable data about the Jovian system. Its next close approach to Jupiter is scheduled for December 27, 2024, when it will come within 2,175 miles (3,500 kilometers) of the gas giant’s cloud tops.
The Juno mission is managed by NASA’s Jet Propulsion Laboratory and is part of the agency’s New Frontiers Program. The spacecraft, built and operated by Lockheed Martin, has provided critical insights into Jupiter and its moons, deepening our understanding of the gas giant’s complex system.
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