Energetic ion observations of a cometary bow shock-like structure

Measurements made by the Energetic Particle Anisotropy Spectrometer (EPAS) on the International Cometary Explorer (ICE) spacecraft show distinct changes in energetic heavy ion properties at the transition between the pick-up and mass-loaded regions of comet P/Giacobini-Zinner. Travelling toward the comet nucleus, the ion flow is first deflected away from the comet-sun axis over a period of approximately 5 minutes. This is immediately followed by a broadening of the ion angular distribution over a comparable time and by a decrease in the ion bulk flow speed of about 100 km s⁻¹. The ion energy distribution broadens across the transitions, and the energy spectrum becomes harder.