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New findings from NASA’s Juno probe provide a more complete picture of how widespread lava lakes are on Jupiter’s moon Io, and include for the first time insights into the volcanic processes at work there. These results come courtesy of Juno’s Infrared Auroral Mapper (JIRAM), an instrument provided by the Italian Space Agency that “sees” in infrared light. Researchers published a paper on Juno’s latest volcanic findings in Communications Earth and Environment.

Io has intrigued astronomers since 1610, when Galileo Galilei first discovered the Jovian moon, which is slightly larger than Earth. About 369 years later, NASA’s Voyager 1 spacecraft photographed a volcanic eruption on the Moon. Subsequent missions to Jupiter, with more flybys of Io, found additional jets – along with lava lakes. Scientists now believe that Io, which is stretched and squeezed like an accordion by neighboring moons and massive Jupiter itself, is the most volcanically active world in the Solar System. But while there are many theories about the types of volcanic eruptions on the Moon’s surface, little supporting data exists.

In both May and October 2023, Juno flew by Io, coming within about 21,700 miles (35,000 kilometers) and 8,100 miles (13,000 kilometers), respectively. Among Juno’s instruments to get a good look at the alluring moon was JIRAM.

Designed to capture the infrared light (not visible to the human eye) emanating from Jupiter’s depths, JIRAM probes the weather layer up to 30 to 45 miles (50 to 70 kilometers) below the gas giant’s cloud tops. But during Juno’s extended mission, the mission team also used the instrument to study the moons Io, Europa, Ganymede and Callisto. JIRAM Io images showed the presence of bright rings surrounding the floors of multiple hotspots.

“The high spatial resolution of JIRAM’s infrared images, combined with Juno’s favorable position during the flyby, revealed that Io’s entire surface is covered with lava lakes contained within caldera-like features,” said Alessandro Mura, with -juno researcher at the National Institute of Astrophysics in Rome. “In the region of Io’s surface for which we have the most complete data, we think about 3% of it is covered by one of these molten lava lakes.” (A caldera is a large depression formed when a volcano erupts and collapses .)

Fire-breathing lakes

Data from JIRAM’s Io flyby not only highlights the moon’s abundant lava supply, but also provides insight into what may be going on beneath the surface. Infrared images of several lava lakes on Io show a thin ring of lava at the boundary, between the central crust that covers most of the lava lake and the lake walls. Melt recycling is implied by the lack of lava flows along and beyond the lake rim, indicating that there is a balance between the melt that erupted into the lava lakes and the melt that flows back into the underground system.

“We now have an idea of ​​what the most common type of volcanism is on Io: huge lava lakes where magma moves up and down,” Mura said. “The lava crust is forced to break against the lake walls, forming the typical lava ring seen in Hawaiian lava lakes. The walls are probably hundreds of meters high, which explains why magma is not usually seen spilling out of the pateras” — cup-shaped features created by volcanism — “and moving across the surface of the moon.”

The JIRAM data suggest that most of the surface of these hotspots on Io is composed of a rocky crust that moves up and down cyclically as one contiguous surface due to central magma upwelling. In this hypothesis, as the crust touches the walls of the lake, friction keeps it from sliding, causing it to deform and eventually break, exposing lava just below the surface.

An alternative hypothesis remains: magma rises in the middle of the lake, spreads and forms a crust that sinks along the edge of the lake, exposing the lava.

“We are just starting to get into the JIRAM results from the close flybys of Io in December 2023 and February 2024,” said Scott Bolton, Juno’s principal investigator at the Southwest Research Institute in San Antonio. “The observations reveal fascinating new information about Io’s volcanic processes. Combining these new results with Juno’s long-term campaign to observe and map volcanoes at the never-before-seen North and South Poles, JIRAM is proving to be one of the most valuable tools for learning how this tortured world works.”

Juno completed its 62nd flyby of Jupiter — which includes a flyby of Io at an altitude of about 18,175 miles (29,250 kilometers) — on June 13. The 63rd flyby of the gas giant is scheduled for July 16.