Ejecta Pattern of the Impact of Comet Shoemaker–Levy 9

Abstract

The collision of Comet Shoemaker–Levy 9 (SL 9) with Jupiter created crescent-shaped ejecta patterns around impact sites. Although the observed impact plumes rose through a similar height of ∼3000 km, the radii of the created ejecta patterns differ from impact to impact and generally are larger for larger impacts. The azimuthal angle of the symmetry axis of the ejecta pattern is larger than that predicted by the models of oblique impacts, due to the action of the Coriolis force that rotates ejecta patterns counterclockwise from the south. We study the formation of ejecta patterns using a simple model of ballistic plume above a rotating plane. The ejected particles follow ballistic trajectories and slide horizontally for about an hour after reentry into the jovian atmosphere. The lateral expansion of the plume is stopped by the friction force, which is assumed to be proportional to the square of the horizontal velocity. Two different mass–velocity distributions used in the simulations produce qualitatively similar results. The simulated ejecta patterns fit very well the “crescents” observed at the impact sites. The sizes and azimuthal angles of symmetry axis of ejecta patterns depend on a parameterL, which has dimension of length and is related to the mass of the fragment. Thus more massive impacts produce larger ejecta patterns that are rotated through a wider angle.