A careful statistical comparison of observations recorded by NASA’s Juno mission and the Planetary Science Institute’s Io Input Output observatory (IoIO) shows that IoIO observations reliably predict the density of Jupiter’s plasma disk, an important part of Jupiter’s magnetosphere, according to a new Geophysical Research Letters paper co-authored by Planetary Science Institute Senior Scientist Jeff Morgenthaler. Jian-Zhao Wang of the University of Colorado Boulder is the paper’s lead author.
Nearly all the material in Jupiter’s magnetosphere comes from its volcanic moon, Io. As ionized material spirals outward from Io, it curiously piles up into a complicated structure known as the Io plasma torus.
Detailed theoretical studies of the Io plasma torus (IPT) using space-based ultraviolet observations predict that it takes about 40 days for material to move through the outermost portion of the IPT, known as the “warm torus.” But detecting the warm torus from the ground is difficult. Rather, ground-based observatories like IoIO focus on emissions from the “ribbon,” which lies inside the warm torus.
A 40-day signal emerges
The paper demonstrates that major enhancements in the brightness of the IPT ribbon consistently occur about 40 days before enhancements in the density of Jupiter’s plasma disk.
“This paper provides important information about the Jupiter environment as the scientific community prepares for NASA’s Europa Clipper and ESA’s JUICE tours of Jupiter’s moons and magnetosphere,” Morgenthaler said.
Sharper context for upcoming missions
Like Juno, Europa Clipper and JUICE (Jupiter Icy Moons Explorer) will fly through Jupiter’s magnetosphere. The paper shows that IoIO can provide reliable predictions for the overall density of material these spacecraft will fly through. This greatly improves scientists’ ability to interpret the rare two-spacecraft measurements of Jupiter’s magnetosphere made possible by these missions.
“Observations of the torus can determine, for instance, whether Europa Clipper and JUICE are seeing denser plasma in the magnetosphere because more material is coming from Io or because there is a localized knot of plasma moving through the magnetosphere,” Morgenthaler said.
Jupiter as a plasma laboratory
“Detecting the latter would be very exciting, as it would enable study of the details of how plasma travels in Jupiter’s magnetosphere,” Morgenthaler said.
“The basic physical processes of plasma transport are the same in all planetary magnetospheres, but Jupiter is unique in that Io provides a significant internal source of mass. This makes many effects, like radial transport of plasma, much easier to measure accurately. The combination of IoIO, Europa Clipper and JUICE magnetospheric measurements at Jupiter can ultimately help us understand our home planet better.”
Publication details
Jian‐Zhao Wang et al, Temporal Variations of Jupiter’s Plasma Disk Observed by Juno, Geophysical Research Letters (2026). DOI: 10.1029/2026gl123313
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Planetary Science Institute
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Io’s volcanic output offers a 40‑day forecast of plasma density in Jupiter’s magnetosphere (2026, July 24)
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