Jupiter Science Results - Energetic Particles

The energetic particle intensities measured by the Ulysses instruments during the flyby (Fig.8) were generally lower than observed by the Voyager spacecraft. A major discovery during the outbound pass was the existence at high latitudes of very strong counter-flowing streams of electrons and ions, constituting large currents that apparently feed into the auroral regions. Measured principally by the HI-SCALE experiment, these field-aligned particle beams are tightly confined to magnetic field lines which, as noted above, appear to be swept strongly tailward.

Figure 8: Overview of
HI-SCALE measurements of
ions and electrons in Jupiter's magnetosphere displayed as
an energy spectrogram (upper panel) and counting rates
(lower panel).

 

 

In the same regions, the COSPIN experiment observed periodic bursts of MeV electrons flowing away from the planet (Fig.9) . Preliminary estimates indicate that these bursts may represent a significant fraction of the population of relativistic electrons found in interplanetary space. Data from many of the Ulysses experiments point to the fact that the dusk-side magnetosphere, where the fields and plasmas rotate from the compressed day side into the magnetotail, is highly dynamic. Furthermore, signatures in the energetic particle data indicate that the high latitude region of the magnetosphere appears to be dominated by the interaction of the solar wind with the planet's magnetic field.

Figure 9: Data from the COSPIN experiment showing a quasi-periodic sequence of electron bursts observed on the outbound pass in the dusk sector of the magnetosphere. Shown for comparison are the simultaneous proton measurements.