NUMERICAL-SIMULATION OF THE EMISSION AND MOTION OF NEUTRAL AND CHARGED DUST FROM P/HALLEY

We have developed a numerical model to predict the distributions of Neutral or charged dust particles in P/Halley. The spatial and temporal variations of the plasma parameters and magnetic field, factors which govern the charging of the dust and its subsequent motion, were included. In computing the electric charge of the dust particles electron collection, photoemission, and secondary electron emission were taken into account. We found that the trajectories of charged dust particles with radii less than about 0.1 μm (10-14 g) were significantly different than the neutral dust trajectories. By charging the dust and including temporal fluctuations, the maximum particle-nucleus distances along the Giotto, Vega 1, and Vega 2 trajectories were increased and made more consistent with the measured values. Most of the model and in situ mass spectra were in good agreement except for a deficiency of the lowest mass model particles, and an offset in the total counting rate for two outbound mass spectra. The best agreement was obtained with a combination of two Lorentzian particle mass density functions with densities of 0.03-2.0 g cm-3 and 0.06-4.0 g cm-3, and a ratio of 100: 1 for the number of particles with the lower and higher density functions, respectively. We also needed particle ejection velocities of about 1.7 times the theoretical decoupling velocities, a high secondary electron yield, and small particles which were more absorbing than large particles. © 1991.