Energetic electron beams in Ganymede's magnetosphere

Abstract

We present energetic particle measurements obtained from the Galileo satellite's final close encounter with Jupiter's moon Ganymede. The encounter occurred on 28 December 2000, crossing Ganymede's plasma wake at midlatitudes. Field-aligned electron beams were observed in the region where trapped-like electron and ion distributions were measured. Given the altitude of the encounter (closest approach ∼2335 km), the observation of both trapped-like distributions and field-aligned electron beams is surprising and.suggests that the Ganymede magnetosphere is a more complex configuration than earlier charged particle results indicate. The location of the beams, their angular width, and their spectral characteristics suggest that they may be formed by the entry and subsequent quasi-chaotic drift of ambient Jovian electrons within Ganymede's magnetosphere. Copyright 2004 by the American Geophysical Union.