Juno Mission Reveals Fiery Secrets of Jupiter’s Volcanic Moon

Recent findings from the Juno mission to Jupiter have shed light on the fascinating volcanic activity of Jupiter’s moon, Io. Scientists have revealed that the volcanoes on Io are likely powered by individual chambers of molten magma, rather than a vast ocean of magma beneath its surface. This groundbreaking discovery addresses a 44-year-old mystery concerning the geological features of this intriguing moon.

A comprehensive study on the source of Io’s volcanism was published on December 12 in the journal Nature. These findings, along with other significant results from Io research, were presented during a media briefing at the American Geophysical Union’s annual meeting in Washington, a premier gathering for Earth and space scientists across the nation.

Io, comparable in size to Earth’s Moon, is renowned for being the most volcanically active body within our solar system. It boasts approximately 400 volcanoes that continuously erupt, releasing lava and plumes that contribute to its distinctive surface.

The moon, which was first discovered by Galileo Galilei on January 8, 1610, did not reveal its volcanic nature until 1979. This was when 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.

“Since Morabito’s discovery, planetary scientists have wondered how the volcanoes were fed from the lava underneath the surface,” stated Scott Bolton, Juno’s principal investigator at the Southwest Research Institute in San Antonio. He further questioned whether a shallow ocean of molten magma was fueling these volcanoes or if the source was more localized. The data collected from Juno’s close flybys was expected to provide insights into the workings of this dynamic moon.

In December 2023 and February 2024, the Juno spacecraft performed close flybys of Io, approaching within about 930 miles (1,500 kilometers) of its surface. During these encounters, Juno communicated with NASA’s Deep Space Network to gather high-precision, dual-frequency Doppler data. This information was crucial for measuring Io’s gravity by observing its effects on the spacecraft’s acceleration.

The insights gained from these flybys revealed significant details about a phenomenon known as tidal flexing. Io’s proximity to the massive Jupiter and its elliptical orbit—completing an orbit around the gas giant every 42.5 hours—results in varying gravitational pull from Jupiter. This relentless squeezing causes an extreme case of tidal flexing, generating internal heat through friction.

“This constant flexing creates immense energy, which literally melts portions of Io’s interior,” Bolton explained. He noted that if Io possessed a global magma ocean, the signature of its tidal deformation would be much larger than that of a more rigid, mostly solid interior. Thus, the results from Juno’s measurements could determine the presence of a global magma ocean beneath the surface.

The Juno team analyzed Doppler data from their two flybys and compared it with observations from previous missions to the Jovian system and ground-based telescopes. They discovered tidal deformation consistent with Io lacking a shallow global magma ocean.

“Juno’s discovery that tidal forces do not always create global magma oceans prompts us to rethink our understanding of Io’s interior,” remarked lead author Ryan Park, a Juno co-investigator and supervisor of the Solar System Dynamics Group at JPL. He emphasized that these findings could have broader implications for understanding other moons, such as Enceladus and Europa, as well as exoplanets and super-Earths. “Our new findings provide an opportunity to rethink what we know about planetary formation and evolution,” he added.

Looking ahead, more scientific exploration is on the horizon. The Juno spacecraft completed its 66th science flyby over Jupiter’s enigmatic cloud tops on November 24. The next close approach to the gas giant is scheduled for 12:22 a.m. EST, December 27. At the time of perijove, when Juno’s orbit is nearest to Jupiter’s center, the spacecraft will be approximately 2,175 miles (3,500 kilometers) above the cloud tops. Since entering Jupiter’s orbit in 2016, the spacecraft will have logged an impressive 645.7 million miles (1.039 billion kilometers).