NASA's Juno Measures Heat Beneath Jupiter's Fiery Moon Io For The First Time

NASA's Juno mission has made a major discovery beneath the surface of Jupiter's moon Io, the most volcanically active world in the solar system. Scientists have, for the first time, measured temperatures below Io's surface, offering new clues about how heat moves inside the moon, reported NASA.

The findings were published in the Journal of Geophysical Research: Planets. The study is based on data collected during two close flybys of Io by NASA's Juno spacecraft. The data also showed that most of Io's surface is remarkably smooth and made of material with very low density.

Io's intense volcanic activity is caused by tidal heating. As the moon travels in its slightly elliptical orbit, Jupiter's powerful gravity constantly stretches and squeezes it, producing large amounts of internal heat. Until now, scientists mainly relied on infrared observations, which measured only the temperature of the moon's surface. The new findings come from Juno's Microwave Radiometer (MWR), which can look below the surface.

Scott Bolton, the study's co-author and Juno's principal investigator at the Southwest Research Institute, said the Juno Microwave Radiometer directly observed Io's heat output by looking below the surface. He added that the discovery of being able to see beneath a rocky moon's surface could also help scientists study volcanoes on Earth by revealing similar underground temperature patterns.

The MWR instrument was originally designed to study Jupiter's deep atmosphere. During Juno's extended mission, it has also been used to observe Jupiter's moons Ganymede, Europa and Io.

Bolton said the technique is new because different microwave wavelengths explore different depths, allowing scientists to study the deep atmosphere of giant planets and the subsurface of icy and rocky moons. He added that while researchers expected to probe beneath the icy surfaces of Ganymede and Europa, being able to study volcanic rock beneath Io's surface was an unexpected discovery.

During flybys on December 30, 2023, and February 3, 2024, Juno came within about 930 miles (1,500 kilometres) of Io's surface.

Shannon Brown, the study's lead author at NASA's Jet Propulsion Laboratory, said the instrument measured Io's thermal emission from depths ranging from a few inches to several feet. She said the team found temperatures rising by more than 40 degrees Fahrenheit just a few feet below the surface, a change that could not be explained by sunlight alone.

Researchers said the heat may be moving steadily through the moon's crust or coming from cooling lava flows beneath a solidified crust.

Bolton said Io provides a unique opportunity to understand how tidal heating works across the universe. He added that scientists can now study how heat moves from the moon's interior to its surface, instead of only observing heat escaping through eruptions or from the surface itself.