Modelling the large particle environment of comet 67P/Churyumov-Gerasimenko

A method is presented to simulate images of a cometary dust trail in consistency with observed gas and dust production rates. It is also applicable to dust tails including neckline and antitail phenomena. Our main objective is to analyse the amount of mm-sized and larger particles within a given image. These are interesting to us because their emission by comets may constitute a major source of interplanetary dust. The model is applied to 67P/Churyumov-Gerasimenko, the target of ESA's Rosetta mission. The employed parameters are consistent with a hydrodynamic coma model. Dust emitted during all apparitions of 67P since the Jupiter encounter in 1959 is taken into account. We compare simulated images with two images taken in May 2003 and April 2004. Both of these show a bright feature close to the projected orbit of the comet. We analyse the simulated images with respect to the age of the dust in this feature. We find that, within our model, the feature in 2003 is dominated by particles emitted during the same apparition. For 2004 we estimate that 25% of the intensity in the bright feature can be attributed to dust emitted during previous apparitions and 29% to particles emitted at true anomalies of (180 +/- 5)degrees before observation. Concerning the sizes of dust grains in the bright feature, we find that in 2003, particles with radii between about 10 mu m and 1 cm contribute nearly equally to the total intensity. In 2004 however, the structure is dominated by particles having sizes of 100 mu m to 1 mm. (c) 2005 COSPAR. Published by Elsevier Ltd. All rights reserved.