Magnetic reconnection at dozens of small sites spread across 100 degrees of longitude buckles Jupiter’s ring-shaped current sheet into waves, overturning the picture of a smooth disk.

Jupiter is wrapped in a structure with no counterpart at Earth. Its magnetic field is so strong, and the plasma fed into it by the volcanoes of Io so abundant, that the field is stretched outward into a vast rotating disk — a magnetodisk, with a ring-shaped sheet of electric current running through its middle. Models have generally pictured that sheet as relatively smooth, a gently warped surface spinning with the planet.

Data from NASA’s Juno spacecraft, analysed by an international team led by researchers at Shandong University, says otherwise. During active periods the sheet is crumpled into a rippling, wave-like structure, and the thing doing the crumpling is magnetic reconnection.

An accidental census

The evidence came from counting crossings. Jupiter’s magnetic axis is tilted relative to its rotation axis, so as the planet turns — once every ten hours — the current sheet sweeps past a spacecraft in a fixed orbit. Juno would normally cross it twice per rotation: once going up, once coming down. That is what a smooth sheet produces.

During reconnection events, Juno crossed repeatedly. In one case it passed through the sheet four times within ten minutes. A spacecraft cannot cross a flat surface four times in ten minutes unless the surface is moving past it far faster than the planet’s rotation accounts for, or unless the surface is folded. Here the surface was folded.

Nearly every one of those crossings carried a reconnection signature, together with bursts of energised electrons and ions. Magnetic reconnection is the process by which oppositely directed magnetic field lines break and reconnect, converting stored magnetic energy into particle motion and heat; it powers solar flares and drives the substorms that produce Earth’s auroras. Finding its signature at crossing after crossing establishes that the ripples and the reconnection are the same phenomenon rather than two things happening at once.

Many small sites, not one big one

The structure the team describes is a kink-like surface wave running through the sheet, with individual ripples lasting from several minutes to more than an hour. The cause is not a single large reconnection event but numerous small reconnection sites distributed across roughly 100 degrees of Jovian longitude — close to a third of the way around the planet — each pushing the sheet away from its equilibrium position. The rippled sheet then rotates with Jupiter, carrying its corrugations around with it.

The contrast with Earth is the sharpest part of the result. In Earth’s magnetotail, reconnection at a localised site launches a kink wave that travels away from it, with a reasonably well-defined period — a recognisable wave propagating from a recognisable source. Jupiter’s motion has no fixed period and does not fit a simple travelling wave at all. With dozens of sites deforming the sheet at once across a third of the planet’s circumference, no single disturbance dominates, and what emerges is closer to a continuously agitated surface than to a wave train.

That difference is not a detail of Jovian trivia. Earth’s magnetosphere is the template from which most magnetospheric physics has been built, and a system where the same basic process produces a qualitatively different global behaviour is a test of how general that template is.

What a crumpled sheet might do

The authors suggest two consequences, both offered as possibilities rather than findings.

The first concerns Io. The moon’s volcanoes inject roughly a tonne of material per second into Jupiter’s magnetosphere, which is the ultimate source of the plasma that inflates the magnetodisk in the first place. How that material spreads outward and how it gets accelerated to high energies are long-standing questions, and a current sheet full of small reconnection sites offers a mechanism: each site is a place where magnetic energy is being converted into particle energy.

The second concerns the aurora. Jupiter’s polar auroras are the most powerful in the solar system and behave in ways that have resisted explanation, including emissions that do not line up with the solar-wind-driven patterns familiar from Earth. Magnetic field lines connect the current sheet to Jupiter’s ionosphere, so a sheet being deformed at many points simultaneously would map to a complicated and shifting pattern of activity in the polar atmosphere.

Neither claim is demonstrated here. The study establishes the structure; connecting it to Io’s plasma transport or to auroral morphology requires work the release does not describe.

Strengths and gaps

The methodological strength is that this is direct in-situ measurement. Juno carries a magnetometer and energetic-particle detectors and flies through the region in question, so the data are not inferred from remote sensing or from a model. Multiple events were analysed rather than one, which is what allows the authors to describe a general behaviour during active periods rather than a single anomaly.

The corresponding limitation is the one every spacecraft mission faces: a single spacecraft is a single point. Juno measures what happens where it is, and the global picture of a rippled sheet spanning 100 degrees of longitude is a reconstruction from a trajectory through it. The inference is reasonable — repeated crossings genuinely do require a folded surface — but the three-dimensional shape is modelled rather than imaged.

The release names Ruilong Guo of Shandong University as first and corresponding author, with co-authors Jinyan Zhao, Yuchen Xiao, Denis Grodent, Zhonghua Yao, Bertrand Bonfond and Quanqi Shi. It contains no direct quotations from any of them, so none appear in this article. Funding is credited to the National Natural Science Foundation of China and the Shandong Provincial Natural Science Foundation. No conflict-of-interest statement is included.

Juno arrived at Jupiter in 2016 on a mission originally scheduled for far less time than it has now spent there, and its polar orbit takes it through regions no previous spacecraft sampled. Results like this one are the dividend of an extended mission: not the headline images, but the slow accumulation of enough crossings to notice that something which was supposed to be smooth is not.

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Notes

1. Guo, R., et al. “Rippling current sheet generated by magnetodisk reconnection on Jupiter.” Science China Earth Sciences, 2026. DOI: 10.1007/s11430-025-1870-9.
2. Science China Press. “Juno spacecraft reveals a rippling current sheet in Jupiter’s magnetodisk generated by magnetic reconnection.” EurekAlert!, 6 October 2026. https://www.eurekalert.org/news-releases/1146641.