Some speculations about the origin of the high speed HCN jets in Comet Kohoutek (1973f)

The origin of the high speed HCN jets observed in Comet Kohoutek (1973f) is considered. It is argued that the occurrence of these jets with Doppler shifts corresponding to velocities of ≈3-5 km s^-1 with respect to the nucleus cannot be explained in terms of either (a) explosive outbursts of trapped sub-surface volatiles, (b) highly exothermic chemical reactions involving free radicals [or a combination of (a) and (b)] or (c) the outward expansion of the cometary atmosphere with additional heating. Instead, acceleration of the precursor ions of HCN by energetic electrons in the ionospheric current sheets or current arcs is suggested to play an important role. Also, a fraction of the HCN observed by electric discharges, associated with the ionosphere current system through the cometary atmosphere. It is not possible to make a realistic estimate of this fraction at the present time, but that it may be significant cannot be entirely excluded by the existing observations.