NASA’s Juno probe gets a close-up view of lava lakes on Jupiter’s moon Io

New findings from NASA’s Juno probe provide a fuller picture of how widespread the lava lakes are on Jupiter’s moon Io and include insights for the first time into the volcanic processes at work there. These results are thanks to Juno’s Jovian Infrared Auroral Mapper (JIRAM) instrument, contributed by the Italian Space Agency, which “sees” in infrared light. Researchers have published an article about Juno’s latest volcanic discoveries Communication Earth and environment.

Io has intrigued astronomers since 1610, when Galileo Galilei first discovered Jupiter’s moon, which is slightly larger than Earth. Some 369 years later, NASA’s Voyager 1 spacecraft captured a volcanic eruption on the moon. Subsequent missions to Jupiter, with more Io flybys, discovered even more plumes, along with lava lakes. Scientists now believe that Io, stretched and compressed like an accordion by neighboring moons and massive Jupiter itself, is the most volcanically active world in the solar system. But while many theories exist about the types of volcanic eruptions on the moon’s surface, little supporting data exists.

In both May and October 2023, Juno flew past Io, coming within approximately 21,700 miles (35,000 kilometers) and 8,100 miles (13,000 kilometers), respectively. One of Juno’s instruments that allowed him to get a good look at the alluring moon was JIRAM.

JIRAM is designed to capture the infrared light (which is not visible to the human eye) coming from deep within Jupiter. JIRAM probes the weather layer up to 50 to 70 kilometers below the cloud tops of the gas giant. But during Juno’s extended mission, the mission team also used the instrument to study the moons Io, Europa, Ganymede and Callisto. The JIRAM Io images showed the presence of bright rings around the floors of numerous hotspots.

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

Fire-breathing lakes

JIRAM’s Io flyby data not only highlights the moon’s abundant lava reserves, but also offers a glimpse of what may be happening beneath the surface. Infrared images of several Io lava lakes show a thin circle of lava at the boundary, between the central crust covering most of the lava lake and the lake walls. Melt recycling is implied by the lack of lava flows on and off the lake edge, indicating that there is an equilibrium between melt erupted into the lava lakes and melt circulating back into the underground system.

“We now have an idea of ​​what the most common form of volcanism on Io is: huge lava lakes where magma goes 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 generally not observed flowing from the paterae” – bowl-shaped features created by volcanism – ‘and moving across the surface of the moon’.

JIRAM data suggest that most of the surface of these Io hotspots consists of a rocky crust that cyclically moves up and down as one continuous surface due to the central upwelling of magma. In this hypothesis, friction keeps the crust from slipping because the crust hits the walls of the lake, causing the crust to deform and eventually break, exposing lava just below the surface.

An alternative hypothesis remains in play: Magma bubbles up in the center of the lake, spreads and forms a crust that sinks along the edge of the lake, exposing lava.

“We are only now beginning to discover the JIRAM results from the close flybys of Io in December 2023 and February 2024,” said Scott Bolton, principal investigator for Juno at the Southwest Research Institute in San Antonio. “The observations reveal fascinating new information about Io’s volcanic processes. By combining these new results with Juno’s longer-term campaign to monitor and map the volcanoes at Io’s never-before-seen north and south poles, JIRAM proves to be one of the most valuable tools for learning how this tortured world works.”

Juno made its 62nd flyby of Jupiter – including an Io flyby at an altitude of about 18,175 miles (29,250 kilometers) – on June 13. The 63rd flight past the gas giant is scheduled for July 16.