An analytic hybrid model of cometary plasma

The plasma environment of a comet is a very structured and dynamic environment, involving complex interactions between the gas from the comet, the solar wind and the interplanetary magnetic field. Reasonably realistic models aiming to catch the global structure of this environment therefore become equally complex, requiring large numerical simulations which provide detailed output for which extensive analysis is needed to disentangle the various processes. We present something much simpler, in effect a self-consistent analytic hybrid model with kinetic treatment of ions and fluid description of electrons. The model is stationary in time, spherically symmetric and (presently) collisionless, includes only plasma originating from the gas emanating from the comet nucleus, and (in common with most models) neglects direct plasma interaction with the nucleus itself. Any applicability is thus restricted to the inner part of the coma outside of the immediate vicinity of the nucleus of a moderately active comet. Ion distribution functions and their moments as well as the electron temperature are analytically calculated at any point within this region. A particularly interesting feature of the model is the energetics, describing the transfer of energy from the electron gas to the ions and thus relating the ion flow speed and the ion and electron temperatures to the mean energy an electron obtains when released from its parent molecule.