THE ELECTRIC CHARGING OF INTERSTELLAR DUST IN THE SOLAR-SYSTEM AND CONSEQUENCES FOR ITS DYNAMICS

The motion of the solar system relative to the local interstellar medi um causes a flux of neutral gas and dust into the solar system. When i nterstellar dust particles penetrate into the solar system, the mass d istribution of the grains is modified because smaller dust grains, whi ch have higher charge-to-mass ratios, are deflected by the Lorentz for ce in the solar magnetic field. In order to investigate the conditions of interstellar dust particles streaming into the heliosphere, the eq uilibrium surface potentials of interstellar dust grains are calculate d assuming that the grains are homogeneous spheres of different materi als. The following charging processes are considered: photoelectron em ission, sticking and penetration of plasma particles, and secondary el ectron emission due to bombardment of energetic plasma particles. We f ind that the dependences of the surface potentials on the heliocentric distance and the grain mass are weak except for the heliocentric dist ance range between the heliopause and the termination shock. We show t hat the influence of Lorentz forces on small dust grains with masses l ess than 10(-19) kg is strong enough to cause a significant deflection of the grains from their original direction of motion. Hence, we can expect that a selection of particles in a certain size interval can ta ke place already near the heliopause. Although the exact value of the charge varies with the material composition of dust, a selection effec t in the material composition of dust grains entering the solar system cannot be expected. Even if interstellar dust grains that can enter t he solar system are nonspherical, the surface potentials of the grains can be represented within the framework of the spherical dust model t hat is applied in this study.