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Io has 266 Active Volcanic Hotspots Linked by a Global Magma Ocean

Jupiter’s Io stands apart from the Solar System’s other moons, with its numerous volcanoes and its surface dominated by lava flows. Io’s surface volcanism was confirmed in 1979 when the Voyager spacecraft imaged it, but its volcanic nature isn’t duplicated anywhere else in our system. Tidal heating is behind the moon’s eruptive nature, driven by Jupiter’s powerful gravity, and by resonance with other moons. But is there a magma ocean inside Io?

A final answer to that question has been elusive, but new research supports the idea of a magma ocean.

NASA’s Juno mission has shifted its focus from Jupiter to the gas giant’s moons, beginning with the volcanic Io. It’s flybys are getting increasingly closer to the unique moon, and the decreasing distance is giving the spacecraft a better and better look. It’s identified 266 active volcanoes, and together, they’re evidence of a vast global ocean of magma according to new research.

A new study titled “Io’s polar volcanic thermal emission indicative of magma ocean and shallow tidal heating models” presented these results. The lead author is Ashley Gerard Davies from NASA’s Jet Propulsion Laboratory. “The extreme level of volcanic activity on Io, the most volcanically active object in the Solar System, is the result of tidally-induced internal heating,” the authors write. That’s not a new conclusion, but there’s more to the research.

Juno’s Jovial Infrared Auroral Mapper (JIRAM) instrument acquired the data behind this research. JIRAM is an image spectrometer, and was designed to probe Jupiter’s upper atmosphere in infrared, including the giant planet’s auroral regions. But now the focus has shifted to Io, and JIRAM is observing the moon’s widespread volcanic activity.

“Io is the most volcanic celestial body that we know of in our solar system,” said Scott Bolton, Juno principal investigator from the Southwest Research Institute in San Antonio. “By observing it over time on multiple passes, we can watch how the volcanoes vary – how often they erupt, how bright and hot they are, whether they are linked to a group or solo, and if the shape of the lava flow changes,” Bolton said in May 2023 when Juno came within about 35,500 km (22,000 miles) of Io.

Since then, Juno has closed the distance even more, and its latest pass brought it to within 12,000 km (7500 miles.) But it’s not just the proximity that is driving more discoveries. Juno follows a polar orbit, while previous observations of Io have been mostly confined to an equatorial plane. Why does that matter?

Scientists have been studying Io intently, trying to discover what drives its volcanic nature. They’ve developed detailed models of the moon, but haven’t been able to test them as rigorously as they can now. “Models predict enhanced heat flow at Io’s poles if tidal heating is deep in the mantle, and at lower latitudes if heating is predominantly in the asthenosphere, or a magma ocean is present,” the authors explain.

But now scientists have Juno’s data to work with, and its polar orbit is giving researchers a more complete look at the moon.

This figure from the research shows four images of Io from JIRAM. Two are from perijove 10 and show the south polar region at a resolution of 112 km/pixel (a & c.) The other two (c & d) are from perijove 43 and show the north polar region at a resolution of 21 km/pixel. Image b and d are JIRAM data overlain on Galileo/Voyager images. This new data from Io's poles is critical to understanding the moon's nature. Image Credit: Davies et al. 2023.
This figure from the research shows four images of Io from JIRAM. Two are from perijove 10 and show the south polar region at a resolution of 112 km/pixel (a & c.) The other two (c & d) are from perijove 43 and show the north polar region at a resolution of 21 km/pixel. Image b and d are JIRAM data overlain on Galileo/Voyager images. This new data from Io’s poles is critical to understanding the moon’s nature. Image Credit: Davies et al. 2023.

“The distribution of Io’s volcanic activity likely reflects the position and magnitude of internal tidal heating,” the authors write. Now that JIRAM has provided polar data, researchers have complete, global near-infrared coverage that reveals the
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