The Grain Evolution Model for icy grains ejected from 9P/Tempel 1 by deep impact

Abstract

The GEM (Grain Evolution Model) is a unique model which follows the cometary icy grains from the moment of ejection until complete sublimation. The model takes into accounts the different forces acting on each and every grain from the initial distribution, as they are passing through the coma and sublimating. The GEM is sensitive to the wavelength and composition of the grains and therefore can anticipate which grains can better match the observations at a certain wavelength. The GEM can predict the brightness of the entire coma in steady state, or as in the Deep Impact Mission it can calculate the coma brightness at different cross sections of time while differentiating between the contribution of the nucleus and that of the grains. In this paper we will show that nearly pure ice grains, i.e. 1-5% of Pyroxene, match the observations from the Deep Impact Mission since they can give a reasonable explanation for the UV enhanced rapid and decline after 20-30 minutes. Furthermore nearly pure ice grains explain the sustained brightness in the UV that lasts 7-14 hours[20]. © 2009 Springer-Verlag Berlin Heidelberg.