The passages close to Jupiter’s volcanic moonIo, carried out by the Juno spacecraft NASA, are helping to solve the enduring mystery of why the tiny moon is the most volcanically active body in our solar system.
Similar in size to , Io has approximately 400 volcanoes that continually release plumes and lava that cover the moon’s surface.
The Juno mission, which has been orbiting and observing Jupiter and its moons since July 2016, made incredibly close flybys of Io in December 2023 and February of this year. The probe passed within 1,500 kilometers of the moon’s surface, capturing images and data.
Together, Juno’s flybys provided an unprecedented view of the smoldering moon, including observations of its poles for the first time. Researchers presented some of the results of analyzing data from the flyover last Wednesday (11) at the annual meeting of the American Geophysical Union in Washington, DC. An article detailing some of the findings was also published on Thursday (12) in the journal Nature.
“Io is one of the most intriguing objects in the entire solar system,” said study co-author Scott Bolton, Juno principal investigator and associate vice president of the Southwest Research Institute in San Antonio. “We can see that this body is completely covered by volcanoes at both poles and along its entire length, (which are) constantly erupting.”
The new data suggests that Io’s numerous volcanoes are likely powered by their own hot magma chambers, rather than being fed by a global magma ocean beneath the surface. The latter had been a prevailing hypothesis among astronomers.
The discovery could change how astronomers understand moons dominated by subsurface global oceans in our solar system, such as Jupiter’s moon Europa and planets beyond our solar system.
Detecting a cosmic pizza
Italian astronomer Galileo Galilei, known as the father of modern astronomy, discovered Io on January 8, 1610. But the moon’s intense volcanic activity was not detected until it passed by Jupiter and its moons in 1979, revealing the dynamic surface which resembled a pepperoni pizza, Bolton said.
That year, Linda Morabito, an imaging scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, became the first person to identify a volcanic plume by studying an image of Io captured by Voyager 1. The revelation triggered a mystery for decades as astronomers wondered about the origins of Io’s constant volcanic activity.
“Since the discovery of Morabito, planetary scientists have been wondering how volcanoes were fueled by lava beneath the surface,” Bolton said. “Was there a shallow ocean of incandescent magma feeding the volcanoes, or was its source more localized? We knew that data from Juno’s two very close flybys could give us some insights into how this tortured moon really worked.”
Flyover revelations
Io orbits around , which Bolton calls a “monster.” The moon’s orbit is imperfect, meaning that sometimes it comes closest to Jupiter during its orbit, and other times it is further away. Io completes an orbit around the planet every 42.5 hours.
Jupiter’s massive gravitational influence compresses Io as it orbits the planet, like a hand squeezing a rubber ball, which heats the moon. This phenomenon is called tidal flexing, or friction from tidal forces that generate internal heat.
“This is what’s happening inside Io,” Bolton said. “This squeeze is generating heat, and it’s getting so hot that Io’s interior is literally melting and exploding. The eruptions are constant. It’s like an endless storm. It’s always erupting everywhere.”
The constant flexing of Jupiter’s pull on Io generates immense energy, which would melt part of the moon’s interior, Bolton said. And if the melting were substantial enough, it would create a global ocean of magma that Juno could detect with its instruments. During its approaches, Juno captured high-precision Doppler data, which measured Io’s gravity by tracking how the close pass of the moon affected the spacecraft’s acceleration. The data was compared with observations from previous missions that flew by Jupiter and its moons, such as NASA’s Galileo spacecraft, as well as ground-based telescopes.
Together, the observations point to a rigid, mostly solid interior beneath Io’s surface rather than a global ocean of magma — solving a 45-year-old mystery started by Voyager 1 observations. Instead, the volcanoes are fed by vents more locations, and each has its own pocket of magma beneath.
“Juno’s discovery that tidal forces don’t always create global magma oceans makes us not only rethink what we know about Io’s interior,” said study lead author Ryan Park, a Juno co-investigator and group supervisor. of Solar System Dynamics at JPL, in a statement. “This has implications for our understanding of other moons, such as Enceladus and Europa (of Saturn), and even exoplanets and super Earths. Our new discoveries provide an opportunity to rethink what we know about planetary formation and evolution.”
The mission also helped capture a series of images showing Io’s “primordial fantastical earth surface,” said Heidi Becker, a planetary scientist at JPL who was not involved in the study. The images are bringing different features of Io into focus like never before, including islands spotted in huge lava lakes, like one called Loki Patera, which is so large that astronomers liken it more to a sea of lava on Io’s surface.
The Juno spacecraft continues to contribute new discoveries about Jupiter and its moons, having recently completed a flyby over Jupiter’s swirling clouds on November 24. Juno will next pass 2,175 miles (3,500 kilometers) above the center of Jupiter on December 27, logging 645.7 million miles (1.04 billion kilometers) since beginning its investigation of Jupiter eight years ago.
