Initial observations of plasma electrons from the Pioneer 10 flyby of Jupiter

Abstract

Initial results are presented from the electron measurements made by the Ames Research Center Plasma Analyzer during the inbound passage of Pioneer 10 in the vicinity of Jupiter. The observations indicate that as in the case of the earth's magnetosheath, there is an increase in electron temperature across the Jovian bow shock. During the second extended magnetosheath traversal (∼ 54 RJ to 46.5 RJ) the electron temperatures were generally higher than those observed during the first magnetosheath traversal (109 RJ to 96 RJ). These higher electron temperatures are in agreement with the measured higher magnitude of the magnetic field and ion density during this traversal. These observations are consistent with the contraction of the Jovian magnetosphere due to an increase in the solar wind dynamic pressure. In the outer Jovian magnetosphere the electron component of the thermal plasma was measured. These plasma electrons were associated with a peak in the electron counts at ∼ 4 eV and do not seem to be associated with the periodic behavior observed for the energetic electrons. The dayside magnetosphere is inflated with a high beta (β ∼ 1) plasma which in some respects is similar to that observed in the earth's magnetotail. The plasma electron measurements are consistent with a thick Jovian magnetosphere.