  The collision of Deep Impact with comet 9P/Tempel 1 generated a bright cloud
of dust which dissipated during several days after the impact. The brightness
variations of this cloud and the changes of its position and shape are governed
by the physical properties of the dust grains. We use a Monte Carlo model to
describe the evolution of the post-impact dust plume. The results of our
dynamical simulations are compared to the data obtained with FORS2, the FOcal
Reducer and low dispersion Spectrograph for the VLT of the European Southern
Observatory (ESO), to derive the particle size distribution and the total
amount of material contained in the dust ejecta cloud.
