Observations of Energetic Ions from Comet Giacobini-Zinner

Abstract

During the encounter with comet Giacobini-Zinner, the energetic particle anisotropy spectrometer on the International Cometary Explorer spacecraft observed large fluxes of energetic ions, believed to result principally from ionization of the cometary atmosphere followed by pickup and acceleration by the ambient flow of the solar wind. These heavy cometary ions were observed from approximately 1 day before closest approach to about 2½ days afterward. Three regimes of differing ion characteristics have been identified. An outer region with a scale of ∼10⁶ kilometers contains variable fluxes of antisolar-streaming pick-up ions in the undisturbed solar wind. In the middle region, of ∼10⁵ kilometers, fluxes have less large-scale variability and broader angular and energy distributions. This region is separated from the outer zone by a sharp transition. The inner region has a scale of ∼10⁴ kilometers and is characterized by reduced fluxes and complex angular distributions.