Jupiter Science Results - Io Plasma Torus

The Io Plasma Torus (IPT), a doughnut-shaped ring of plasma rotating with the planet at the orbit of Jupiter's moon Io, was an object of special interest during the flyby. Its properties were measured both directly by the URAP instruments, and also remotely by the Ulysses Radio Science team. The IPT consists largely of ionised oxygen and sulfur atoms released as a neutral cloud by Io's volcanoes. The Ulysses measurements, taken a few hours after closest approach as the spacecraft crossed Jupiter's magnetic equator, indicate that the electron density of the IPT in the current epoch matched model predictions based on the older Voyager results quite well (Fig.7). On the other hand, the longitudinal distribution of plasma seen by Ulysses showed asymmetries not expected from the Voyager data, which, as mentioned in the introduction, were taken in a different region of the IPT.

Figure 7: Electron densities within
the Io Plasma Torus as determined by the URAP experiment. For comparison, model predictions based on Voyager data are also shown.