Critical ionization velocity effects in the inner coma of comet Halley: Measurements by Vega-2

Plasma density and plasma wave measurements aboard the "Vega‐2" spacecraft discovered two plasma density enhancements in the inner coma of comet Halley that are accompanied by bursts of plasma waves in the lower‐hybrid frequency range. These events are explained by the critical ionization velocity (CIV) effects of Alfvén. The persistent bursty plasma wave activity and the intermittent plasma density growth toward the cometary nucleus indicate that the CIV effect contributes to the ionization of the cometary gas.