My interest in comets also goes back a long ways. In the 1970's I speculated a bit in print about the origin of the strange brightness fluctuations of P/Schwassmann-Wachmann I and in general looked into the question of solar wind shock wave interactions with cometary comae. In the 1980's with Giotto and the others zooming in on P/Halley, I got more seriously involved and went on sabbatical and leave of absence to JPL for two years (1986-88) to peer over the shoulders of the Giotto experimenters there, Marcia Neugebauer, Bruce Goldstein and Ray Goldstein. I also crossed paths there with Bimla Buti who was visiting on sabbatical from India. This led to a paper with Bimla on the limitations of ideal MHD in comet physics, a model of the diamagetic cavity with Bruce and a major effort on energetic particle generation near the cavity boundary with Ray and others from the Mass Spectrometry team. We generated a recyling model involving multiple charge exchange interactions to provide the 300 eV heavy ions seen just inside the cavity.
Back home in 1989, I looked, with a graduate student, Zachi Klopman at the question of generation of the cavity in the light of more detailed analysis of the velocity profile published by Kettmann and others of MPI LIndau and came up with a unidimensional model that explains many of the observed phenomena. We found that including the nonuniformity of the velocity field creates a term of comparable magnitude and of opposite sign to the friction term, which implies that the attribution of cavity formation to friction/viscous interaction is not in general correct. A second conclusion is that there are cases in which a cavity will not be formed. These cases are, for example, comets with low gas production (small comets or comets that are quite far away from the sun)
More recently a graduate student, Zameret Gan Baruch, became interested in
the comet-solar wind interaction problem and embarked on a major simulation
study as her Ph.D. project. She spend altogether 18 months at the
Max-Planck-Institut fü Astrophysik in Munich, Germany where she honed
her simulation skills under the supervision of R. Wegmann and H. Schmidt.
Her model includes pressure anisotropy which is a major innovation in MHD
simulations of comets. She is now writing up her results for her dissertation.