Energetic particles in the Jovian magnetosphere

Abstract

This paper presents a detailed account of the Pioneer 10 encounter with Jupiter as viewed by the Goddard-University of New Hampshire cosmic ray experiment. Flux time histories of electrons and protons are given over a wide energy band. These show a marked variation with magnetic latitude, Significant removal of low-energy protons by Io is apparent in the inner magnetosphere (≲6 RJ). Proton and electron energy spectra are given at various Jovicentric distances. The electron spectra are remarkably hard and constant in slope in the 0.12- to 8.0-MeV interval, the electron spectral index having a value of 1.5–2.0 in the region outside 25 RJ. Proton spectra are shown to transform from a power law with indices in the 3–4.2 range to more nearly exponential forms in the inner regions (≲40 RJ). Extensive data are presented on the angular distributions of protons and electrons at various locations in the Jovicentric magnetosphere. In addition, a harmonic analysis of 1- to 2-MeV proton angular distributions has been performed. Simple corotation is shown to exist out to ∼23 RJ. Beyond this point, other effects are contributing significantly to the particle anisotropies. Alpha/proton ratios are given as a function of Jovian radius and are compared to the earth and solar wind values.