A planet's magnetic field is like an invisible shield: it catches charged particles from the solar wind and stretches out behind the planet into a long tail, like a fluttering scarf. For Earth, this tail is simple: a sheet of plasma, charged gas, flows along the middle, at the equator, while the regions near the poles are nearly empty, with magnetic field lines open to space. That scheme was thought to hold for all planets with magnetic fields, including Jupiter.
But from 2016 to 2022, the Juno probe gathered data at Jupiter, and the picture turned out different. On the night side, above 40 degrees magnetic latitude, instruments found a persistent layer of charged particles, similar to a current sheet. It consists of oxygen and sulfur ions — thrown out by the volcanic moon Io. The magnetic field in this layer is twisted differently from the equatorial current sheet: it bends the opposite way.
This means the old model of the magnetic tail will have to be revised. Jupiter spins very fast, and its magnetic field is more complex than we thought. The new data will help us understand how magnetic tails behave around other fast-rotating planets, and around distant exoplanets we can't yet see in detail.
The oxygen and sulfur ions in Jupiter's high-latitude layer came from Io — the most volcanically active body in the solar system: hundreds of volcanoes there erupt, blasting material into space.
In the film '2010: The Year We Make Contact', the crew of the spacecraft Alexei Leonov flies through clouds of sulfur and oxygen ejected by Io, the very material that fills Jupiter's magnetic tail.