Protons and Electrons in Jupiter's Magnetic Field: Results from the University of Chicago Experiment on Pioneer 10

Abstract

Fluxes of high energy electrons and protons are found to be highly concentrated near the magnetic equatorial plane from distances of ~ 30 to ~ 100 Jovian radii (R_J). The 10-hour period of planetary rotation is observed as an intensity variation, which indicates that the equatorial zone of high particle fluxes is inclined with respect to the rotation axis of the planet. At radial distances [unknown] 20 R_J the synchrotron-radiation-producing electrons with energies ≳ 3 million electron volts rise steeply to a maximum intensity of ~ 5 x 10⁸ electrons per square centimeter per second near the periapsis at 2.8 R_J. The flux of protons with energies ≳ 30 million electron volts reaches a maximum intensity of ~ 4 x 10⁶ protons per square centimeter per second at ~ 3.5 R_J with the intensity decreasing inside this radial distance. Only for radial distances [unknown] 20 R_J does the radiation behave in a manner which is similar to that at the earth. Burst of electrons with energies up to 30 million electron volts, each lasting about 2 days, were observed in interplanetary space beginning approximately 1 month before encounter. This radiation appears to have escaped from the Jovian bow shock or magnetosphere.