What is the doughnut-shaped plasma region linked to Io called?

The doughnut-shaped plasma region linked to Io is called the Io plasma torus. It is a thick ring of ionized material surrounding Jupiter near Io’s orbit.

Io supplies the raw material through intense volcanic activity. Volcanic gases, especially sulfur dioxide, escape from the moon and are broken apart and ionized by collisions and ultraviolet radiation. Jupiter’s powerful magnetic field then sweeps these ions into co-rotation with the planet, producing a plasma torus rich in sulfur and oxygen ions, along with smaller amounts of sodium and chlorine.

The torus is not a solid ring and is not the same thing as Jupiter’s broader radiation belts. Its plasma is comparatively cool by magnetospheric standards, yet it remains extremely energetic and dense enough to influence the entire Jovian magnetosphere. Particles gradually diffuse outward, helping feed Jupiter’s vast magnetic environment.

Io’s volcanic activity makes the torus especially dynamic. Spacecraft observations have found warm, ribbon-like, and cold regions within it, reflecting differences in temperature and particle behavior. The “doughnut” description refers to the toroidal geometry around Jupiter, not to a hole or surface structure on Io itself.