Size Distribution of Cometary Dust, Meteoroids and Zodiacal Grains

Abstract

It is commonly accepted there is a strong relation among dust released from comets, meteoroids and dust in the zodiacal cloud. In this paper we investigate this relation starting from size distribution analysis of cometary dust grains. Size distribution of dust grains from comets is strongly time-dependent. A detailed analysis of this quantity was possible only with analysis of the dust tails of bright comets, or with the space missions to comet Halley. In the former case, the most successfull approach was the inverse approach (Fulle, 1987a) to the Finson-Probstein method (Finson and Probstein, 1968), which allowed to obtain the time-dependence of the size distribution of dust grains over periods of weeks for the comets Bennett 1970II (Fulle, 1987a), Arend-Roland 1957III, Seki-Lines 1962III (Fulle, 1987b), and Halley (Fulle et al., 1987a, b). The dust mass loss rates resulted regularly dependent on the Sun-Comet distance, whereas the number loss rates, ruled by smaller grains, resulted dominated by outbursts. These results were confirmed by space probes to comet Halley, which reported strong variations in time of the size distribution, probably due to fragmentation processes which are very active in the jets characterizing the inner coma (Zarnecki et al., 1986). To compare the size distribution of cometary grains to the same quantity of the zodiacal dust, we have to use averaged quantities. We assume the mean size distribution averaged over long times (weeks or months) given by the Finson-Probstein method as the mean distribution of cometary dust grains. This choice is supported by the strong correlation shown by the time-averaged size distributions obtained for the four comets already considered (Fulle et al., 1987a, b).