A SELF-CONSISTENT MODEL FOR THE PARTICLES AND FIELDS UPSTREAM OF AN OUTGASSING COMET .1. GYROTROPIC AND ISOTROPIC ION DISTRIBUTIONS

The magnetic field and solar wind flow parameters in the vicinity of a weakly outgassing comet are determined using a self-consistent model which treats the cometary ions kinetically. Two different assumptions are made concerning the cometary ion distribution function; the pickup cometary ions form either a velocity space gyrotropic ring distribution or a velocity space isotropic shell distribution in the solar wind frame of reference. The individual currents due to the solar wind and cometary ions, which determine the magnetic field, are calculated in each case. Using theoretically determined parameters which reflect the conditions expected at comet Kopff (a typical short-period comet and one possible target for the future CRAF/Cassini mission) for various heliocentric distances, we are able to determine how the global field and flow characteristic are influenced by the nature of the cometary ion distribution function.