The ejection of meteoroids from comets

The initial velocities of dust particles ejected from comets can often play a crucial role in the subsequent development of the resultant meteoroid stream. We seek to remedy some shortcomings of Whipple’s theory by including the effects of cooling by the sublimation of the ice and the adiabatic expansion of the escaping gases. We find that the inclusion of these effects does not yield results much different from Whipple’s original model. We pay particular attention to the particles with radii much greater than 2 μm that follow trajectories that are substantially different from the flow lines of the gas. We also investigate the effect of sublimation from a circular active area and find that even a very small active region results in large dust particles being ejected in a cone of semi-angle close to 34°. We show how the dust particles are ejected if the active area is in the form of a pit or depression. To make this paper useful to modellers of meteoroid stream evolution, we present empirical formulae which summarize the results of our numerical calculations.