Ejection of large particles from cometary nuclei in the shape of prolate ellipsoids

Abstract

The ejection of cometary grains from comets is examined. It is assumed that cometary grains are chunks of ice‐dust material. We focus on cometary nuclei in the shape of prolate ellipsoids. Two mechanisms are considered. The first one is the drag acting on the motionless grains lying on the surface of a comet's nucleus. It is a consequence of the cometary ice's gentle sublimation. The second one is related to the cometary jet‐like phenomenon. This mechanism is associated with the rapid flow of gas streams into space from subsurface cavities in a comet's nucleus through narrow gaps and channels. The different elongations of ellipsoidal nuclei are examined. The formula for the maximum radius of grain that can be lifted up from the comet's nucleus is derived. The obtained algorithm takes into account the different cometo‐centric latitudes of places from which the cometary grains are ejected. We show that for a fixed mass of nucleus the maximum size of grains is an increasing function of nuclear flattening. Numerical simulation is carried out for a large range of assumed cometary parameters. The obtained results are in good agreement with the observations of the Comet 103P/Hartley carried out by the Deep Impact spacecraft.