Kinetics of cometary plasma

Abstract

This paper presents an investigation of the kinetics of a coma, consisting of water vapor plasma and ice grains, illuminated by solar radiation. The photoelectric emission of electrons from ice grains strongly affects the composition of the coma. In deference to the recent emphasis on the character of openness of a complex plasma system, the investigation is based on the balance of the number density of the constituent species and energy of electrons and ions, and the charge neutrality. Accretion of electrons and ionic species by the ice particles, ionization of neutral species by solar radiation, the recombination of electrons and ions, the collisions between electrons, ions and neutral species, charge exchange between atomic ions and neutral molecules and photoelectric emission of electrons by ice grains have been considered in this study; further, the energy exchange associated with these processes has also been taken into account. An interesting conclusion, that the maximum charging of ice particles occurs for an optimum value of number density of ice particles, has been obtained; opposite charging of grains of different sizes has also been predicted in certain conditions. The validity of the theoretical model on the basis of the mean free path of electrons being less than the dimensions of the coma has also been discussed.