Interpretation on Deep Impact results: Radial distribution of ejecta and the size distribution of large-sized grains

Abstract

Several observations of dust grains ejected from the comet 9P/Tempel 1 by the Deep Impact event strongly suggest that the evaporation and expansion of volatiles occurred and that the vapor accelerated some dust grains. When grains are accelerated by gas, size sorting should occur, that is, larger grains tend to stay closer to the nucleus, while smaller grains is pushed farther away. This means that the light at each distance is emitted from identical-sized grains. Hence, we can estimate the size distribution of grains based on the flux as a function of the distance from the nucleus. A simple evaluation indicates that the size distribution of grains with a size larger than ∼10 μm is expressed as a power law and the index is ∼-4. This is expected to be an alternative method to estimate the size distribution of grains, though detailed analyses and numerical simulations should be necessary to evaluate the error of this method.