Plasma electron measurements in the outer Jovian magnetosphere

The existence of the plasma electrons in the outer Jovian magnetosphere reported by Intriligator and Wolfe (1974) is consistent with (1) the additional pressure needed to supplement the magnetospheric magnetic field in the outer magnetosphere so as to balance the solar wind and interplanetary magnetic field dynamic pressure across the magnetopause, (2) the drastic change in the plasma electron spectrum as soon as Pioneer 10 crossed the magnetopause from the magnetosheath into the magnetosphere, (3) the fact that the instrument aperture was at spacecraft ground, and (4) the fact that beyond about 2 AU the continuous observations of all ambient electron fluxes (solar wind electrons, secondary electrons, photoelectrons, etc.) are below the instrument threshold.