Jupiter Science Results - Polar Cap Region

Because of its high-latitude trajectory, Ulysses was able to investigate the poleward extent of the Jovian radiation belts that contain durably trapped energetic electrons and ions. A surprising finding was that even close in to the planet (approximately 9 Jupiter radii), Ulysses apparently made an excursion out of the radiation belts at magnetic latitudes of only 48 degrees. Signatures in the data from many of the instruments are consistent with Ulysses having passed through a region in which magnetic field lines from the Jovian polar cap at one end were connected to interplanetary magnetic field lines at the other end. For example, the energetic particle sensors registered counting rates close to interplanetary background levels, while the SWOOPS plasma instruments noted a simultaneous drop-out in the magnetospheric electron population for a period of 1.5 hours. URAP DC electric field measurements indicate a drop in the plasma flow speed to very low levels.