Infrared images from the Juno spacecraft are rekindling debate about the inner workings of Jupiter’s hottest moon. Using NASA’s JIRAM instrument, the Juno probe has revealed detailed volcanic activity on Jupiter’s moon Io, revealing widespread lava lakes and dynamic volcanic processes. Historical and current missions have shaped our understanding of Io as the most volcanically active world in the Solar System, with Juno’s flybys providing high-resolution infrared images that show these features in unprecedented detail.

New discoveries by NASA’s Juno probe have provided a more complete picture of how common lava lakes are on Jupiter’s moon Io. They also include the first insights into the volcanic processes operating there. These results were obtained thanks to the Junon Infrared Auroral Mapper (JIRAM), an instrument provided by the Italian Space Agency that “sees” in infrared light. The researchers recently published a paper . Contact World and Environment About Juno’s recent volcanic discoveries.

Io has been intriguing astronomers since 1610, when Galileo Galilei first discovered Jupiter’s moon, which is slightly larger than Earth’s. Some 369 years later, NASA’s Voyager 1 spacecraft recorded a volcanic eruption on the moon. (See image below.) Subsequent missions to Jupiter, with more close flybys of Io, revealed additional plumes of smoke along with lava lakes. Scientists now believe that Io is the most volcanically active world in the Solar System, stretched and compressed like an accordion by nearby moons and massive Jupiter itself. While there are many theories about the types of volcanic eruptions on the lunar surface, there is little evidence to support this.

Close-up of Juno on Io

Juno flew by Io in May and October 2023, traveling about 21,700 miles (35,000 kilometers) and 8,100 miles (13,000 kilometers), respectively. Among Juno’s moon-gazing instruments was JIRAM.

Designed to capture infrared light (invisible to the human eye) emitted from deep inside Jupiter, JIRAM probes the layer of air 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. The JIRAM images of Io revealed the presence of bright rings surrounding the floors of several hot spots.

“The high spatial resolution of JIRAM’s infrared images, combined with Juno’s favorable location during the flybys, revealed that the entire surface of Io is covered by lava lakes within caldera-like structures,” said Alessandro Mura, one of Juno’s researchers, of the National Institute of Astrophysics in Rome. “In the region of Io’s surface where we have the most complete data, we estimate that about 3% of the surface 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 flyby of Io not only shed light on the moon’s abundant lava reserves, but also provide insight into what’s happening beneath the surface. Infrared images of some lava lakes on Io show a thin lava ring at the interface between the central crust and the lake walls, covering most of the lava lake. The absence of lava flows at the lake edge and beyond suggests melt recycling, suggesting a balance between melt being ejected into the lava lakes and melt being returned to the subsurface system.

“We now have a picture of the most common type of volcanism on Io: huge lava lakes where magma rises and falls,” Mura said. “The lava crust is forced against the lake walls, creating the typical lava ring seen in Hawaiian lava lakes. The walls would likely be hundreds of meters high, which explains why magma typically doesn’t flow out of pateras (cup-shaped structures formed by volcanism) and move across the moon’s surface.”

JIRAM data suggest that most of the surface of these hotspots on Io consists of a rocky crust that rotates up and down as a continuous surface due to the rise of central magma. According to this hypothesis, when the crust touches the lake walls, friction prevents it from sliding, causing it to deform and eventually break apart, exposing the lava just below the surface.

There is an alternative hypothesis: magma flows into the center of the lake, spreads, and forms a crust that descends along the lake’s edge, exposing the lava.

Continuing Juno’s research

“We are just beginning to analyze the JIRAM results from the December 2023 and February 2024 flybys of Io,” said Scott Bolton, Juno’s principal investigator from the Southwest Research Institute in San Antonio. “The observations are revealing exciting new information about volcanic processes on Io. By combining these new results with Juno’s long-term campaign to monitor and map volcanoes at Io’s never-before-seen north and south poles, JIRAM is proving to be one of the most valuable tools for studying how this troubled world works.”

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