The importance of nucleus rotation in determining the largest grains ejected from comets

Abstract

The maximum diameter of large boulders ejected from the cometary nuclei is investigated using the classical model of dust grain as dragged out by radially expanding cometary gases. The importance of the inertial forces, and particularly those due to the rotation of the comet is shown. Although a larger dust grain can be lifted from the nucleus surface if the rotation is faster, the rotation period has to be larger than a certain value. A simple expression for this critical value of rotation period is given. Our results are applied to different comets and a comparison with the maximum radius values obtained by radar measurements is made. Finally, comet Churyumov-Gerasimenko, the target of the ROSETTA mission to arrive on 2014, is going to be analyzed and a range for the maximum diameter of the dust grains that can be lifted is proposed.