Plasma wave, magnetic field and energetic ion observations in the ion pick-up region of comet giacobini-zinner

Abstract

Simultaneous plasma wave, magnetic field, and energetic ion observations made by the ICE spacecraft in the extended ion pick-up region surrounding comet Giacobini-Zinner are examined to determine the conditions under which two characteristics wave emissions, electrostatic waves at a few kHz, and electromagnetic waves at a few tens of Hz, are generated. The data are consistent with the view that the kHz electrostatic emissions result from an instability of the pick-up photoelectron “beam” produced when the angle α between the magnetic field and the solar wind velocity vector is less than ∼60°, while the behaviour of the tens of Hz electromagnetic waves suggests that they are generated by the pick-up ion “ring” which is present when α exceeds ∼60°.