Infrared images from NASA’s Juno spacecraft fuel debate about the inner workings of Io, Jupiter’s hottest volcanic moon.
The new findings provide a more complete picture of the extent of lava lakes on Io, and include information for the first time about the volcanic processes taking place there. These results come courtesy of Juno’s JIRAM (Jovian Infrared Auroral Mapper) instrument, provided by the Italian Space Agency, which “sees” in infrared light. The researchers have published a paper on Juno’s most recent volcanic discoveries 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. Some 369 years later, NASA’s Voyager 1 space probe captured a volcanic eruption on the moon. Subsequent Jupiter missions, with more flybys of Io, discovered additional 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 there are many theories about the types of volcanic eruptions that occur on the moon’s surface, there is little data to support them.
In May and October 2023, Juno passed by Io and came within about 35,000 and 13,000 kilometers, respectively. Among the Juno instruments that have managed to get a good look at the fascinating moon is JIRAM.
Designed to capture infrared light (not visible to the human eye) emerging from the depths of Jupiter, JIRAM explores the meteorological layer up to 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 images of Io showed the presence of bright rings surrounding the floors of numerous hot spots.
“The high spatial resolution of JIRAM’s infrared images, combined with Juno’s favorable position during flybys, revealed that the entire surface of Io is covered by lava lakes contained in the form of calderas,” Alessandro Mura, PhD, said in a statement. Juno co-investigator at 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 it is covered by one of these molten lava lakes.” (A caldera is a large depression that forms when a volcano erupts and collapses.)
Data from JIRAM’s Io flyby not only highlights the moon’s abundant lava reserves, but also provides insight into what may be happening beneath the surface. Infrared images of several lava lakes on Io show a thin circle of lava at the edge, between the central crust that covers most of the lava lake and the lake walls. Recycling of molten material is implied by the lack of lava flows at the edge of the lake and beyond it, indicating that there is a balance between molten material that has erupted in the lava lakes and molten material. which circulates back to the underground system.
“Now we have an idea of what the most common type of volcanism is on Io: huge lava lakes where magma rises and falls,” 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 they are generally not observes magma spilling from pateras (bowl-shaped features created by volcanism) “and moving across the moon’s surface.”
The JIRAM data suggest that most of the surface of these Io hot spots is composed of a rocky crust that moves up and down cyclically as a contiguous surface due to the central upwelling of magma. In this hypothesis, because 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.
An alternative hypothesis remains in play: magma is welling up in the middle of the lake, spreading and forming a sinking crust along the edge of the lake, exposing the lava.
“We are beginning to analyze JIRAM results from close flybys of Io in December 2023 and February 2024,” said Scott Bolton, Juno principal investigator at the Southwest Research Institute in San Antonio. “The observations show fascinating new information about Io’s volcanic processes. By combining these new results with Juno’s long-term campaign to monitor and map the never-before-seen volcanoes at Io’s north and south poles, JIRAM is proving be one of the most valuable tools to learn how this tortured world works.
Juno made its 62nd flyby of Jupiter (which included a flyby of Io at an altitude of approximately 29,250 kilometers) on June 13. The 63rd flyby of the gas giant is scheduled for July 16.
