Velocity of individual large dust particles ejected from Comet P/Halley

Abstract

Five discrete events are presented which provide accurate information about the impact locations relative to the comet and lower mass limits of the individual particles. Ejection velocities of about 40 m/s were found for two particles in the 1-mg mass range and of not more than 10 m/s for particles in the 10-mg range for the most probable scenario, where the recorded heavy particles start their trajectories in sunward directed jets during a period around perihelion. The outflow velocities of the 10-mg particles are found to be significantly lower than predicted by gasdynamic calculations. The discrepancy can lead to an alternative interpretation of the observation assuming that the particles found near the nucleus were released from the nucleus a long time ago on a time scale of orbital periods. Similar-size particles were found in long dust trails of short-period comets. This alternative can influence the derivation of the particle size distribution and accumulated mass flux from the observations by the Giotto instruments.