The remarkable results, published in the Journal of Geophysical Research: Planets, are based on data gathered during two close flybys in late 2023 and early 2024. These findings offer planetary scientists a unique perspective on how tidal forces generate heat within celestial bodies.
Io’s intense volcanic activity stems from ongoing tidal flexing. As the moon orbits in an elliptical path, Jupiter’s immense gravitational influence stretches and compresses its interior, producing substantial internal heat.
Until recently, researchers could only assess Io’s heat emissions at the surface level through infrared instruments. During the flybys on December 30, 2023, and February 3, 2024, Juno skimmed just 1,500 kilometers (930 miles) above the moon’s surface, utilizing its Microwave Radiometer (MWR) to examine conditions beneath the crust.
The instrument identified a sharp thermal gradient.
Temperatures surged by over 40°F just a few feet below the surface layer, a rise that cannot be attributed solely to solar radiation. The calculated background heat flow across Io measures between 1 to 3 watts per square meter. Although modest on a local scale, this energy release is up to 30 times greater than the average heat flow on Earth when considered across Io’s entire surface.
Researchers suggest that this data could point to cooling lava flows beneath a crust that measures 9 to 11 meters (30 to 35 feet) thick, covering about 10% of the moon’s surface at any given time.
“The Juno Microwave Radiometer directly observed Io’s heat output by looking beneath the surface,” stated Dr. Scott Bolton, Juno’s principal investigator at the Southwest Research Institute.
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“The unexpected ability to visualize beneath a rocky moon’s surface has significant implications for understanding volcanoes on Earth.”
Beyond measuring heat, the MWR instrument provided unanticipated insights into Io’s geology and topography.
While Io is renowned for its towering volcanic features, radar reflection data has shown that extensive areas consist of notably flat, wide plains extending over 100 kilometers. The surface material in these low-altitude zones appears highly porous and light.
Dr. Shannon Brown, the lead author of the study at NASA’s Jet Propulsion Laboratory, noted that the outer layer resembles pumice or fluffy volcanic ash rather than solid rock.
