In 1979, NASA Jet Propulsion Laboratory scientist Linda Morabito discovered volcanic activity on Jupiter’s inner moon, Io. But Io isn’t just volcanically active – it’s the most volcanically active body in the entire solar system, and scientists now have a better understanding of how the moon’s underground lava springs work.
NASA scientists have determined that Io’s roughly 400 active volcanoes are likely fed by separate chambers of hot magma, rather than a single massive underground shared magma ocean. The discovery, published in the journal Nature on December 12, solves a mystery that has puzzled researchers for more than four decades. The results of the study are forcing scientists to reconsider not only their understanding of Jupiter’s moon, but also other celestial bodies.
Io is about the same size as the Earth’s moon and is marked by seemingly continuous volcanic activity. Astronomer Galileo Galilei discovered it in 1610, and in 2011 – about four centuries later – NASA launched the Juno mission. The spacecraft has been exploring the Jovian system since 2016, transmitting stunning images to Earth, as well as amazing discoveries about the largest planet in the solar system.
“Since the discovery of Morabito, planetary scientists have been interested in how volcanoes are fed by lava below the surface,” said Scott Bolton, Juno principal investigator at the Southwest Research Institute in San Antonio, who participated in the study, in a statement from NASA JPL. “Was there a shallow ocean of hot magma feeding the volcanoes, or was the source more localized? We knew that the data from two very close flybys of Juno could give us some insight into how this tormented moon actually worked.”
In December 2023 and February 2024, Juno made the aforementioned flybys of Io, coming within 930 miles (1,500 kilometers) of its volcano-scarred surface. During these maneuvers, Juno collected data to draw conclusions about the moon’s gravity based on how it affects the spacecraft’s acceleration, revealing important information about Io’s “tidal bending”.
Tidal bending occurs when a celestial body is stretched and deformed by the gravitational pull of another nearby body. Friction during the movement generates heat, so this phenomenon is also known as tidal heating. Io, for example, moves in an elliptical orbit around Jupiter, and the change in distance from Jupiter (and thus Jupiter’s gravitational pull) along this orbit constantly compresses the moon, causing extreme tidal bending.
“This constant bending creates enormous energy that literally melts parts of Io’s interior,” Bolton said. “If Io has a global magma ocean, we knew that its tidal deformation would be much stronger than in a more rigid, predominantly solid interior. Thus, depending on the results of Juno’s probing of Io’s gravitational field, we will be able to determine whether a global magma ocean is hidden beneath its surface.” In other words, the greater the tidal deformation, the more likely it is that Io’s volcanoes were fed by a larger magma source, such as the ocean, and not just individual magma chambers.
Back on Earth, the team compared Juno’s data with the results of previous missions and ground-based telescopes. The researchers concluded that Io’s tidal deflections indicate the presence of separate magma chambers, not a single massive magma ocean.
“Juno’s discovery that tidal forces don’t always create global magma oceans doesn’t just prompt us to rethink what we know about Io’s interior,” said Ryan Park, a Juno co-investigator at JPL who co-lead the study. “This has implications for our understanding of other satellites such as Enceladus and Europa, and even exoplanets and super-Earths. Our new findings provide an opportunity to rethink what we know about the formation and evolution of planets.”
We can only wait to see what else Juno will learn about Jupiter during its next close flyby, scheduled for December 27.
