A study of the icy tails of the distant comets

Properties are studied of the icy grain model for the tails of comets Baade 1955 VI and Haro-Chavira 1956 I, which have large perihelion distances. The general profiles and orientations of the tails are compared with a set of synchrones, or theoretical trajectories of particles ejected from a cometary nucleus at given instants of time. Several features observed in these comets are shown to be explained by the icy grain model, including jet activity in the coma and no appreciable broadening of the tail with increasing distance from the nucleus. It is demonstrated that the transition region between 2 and 3 AU, where water snow begins to experience rapid evaporation, has a significant effect on the dynamics of icy tails. It is suggested that the icy grains constituting these cometary tails may carry fine particles of meteoric dust which are released when the grains begin to disintegrate by evaporation.