A Model of the Early Evolution of the 2007 Outburst of Comet 17P/Holmes

We have conducted a morphological analysis of the dust features generated during the first 5 weeks after the 2007 October outburst of comet 17P/Holmes. We used a computer simulation technique to generate synthetic images of dust ejecta released from discrete sources on a rotating nucleus. We found that the main “jets” are caused by discrete sources located near the south pole of the nucleus, while particle ejection is otherwise produced on the whole sunlit southern hemisphere, causing the observed dust shell in the sunward direction. The rotational parameters we derived (Φ = 213° and I = 90°, or the north pole pointing to R.A. = 38.8°, decl. = +35.1°) indicate that the subsolar latitude was near –90° at the outburst time. Assuming the same dust distribution function everywhere on the comet surface, and the same particle size dependence on the velocity, the ejection velocities for particles forming the “jets” must be remarkably different, by a factor of ~5 slower, than the background hemispherical particle emission. Based on a comparison of synthetic images with cometary images obtained during the 1892 outburst, we show that the rotational parameters are remarkably consistent during both 1892 and 2007 apparitions.