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 medium causes a flux of neutral gas and dust into the solar system. When interstellar dust particles penetrate into the solar system, the mass distribution of the grains is modified because smaller dust grains, which have higher charge-to-mass ratios, are deflected by the Lorentz force in the solar magnetic field. In order to investigate the conditions of interstellar dust particles streaming into the heliosphere, the equilibrium surface potentials of interstellar dust grains are calculated assuming that the grains are homogeneous spheres of different materials. The following charging processes are considered: photoelectron emission, sticking and penetration of plasma particles, and secondary electron emission due to bombardment of energetic plasma particles. We find that the dependences of the surface potentials on the heliocentric distance and the grain mass are weak except for the heliocentric distance range between the heliopause and the termination shock. We show that the influence of Lorentz forces on small dust grains with masses less 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 take place already near the heliopause. Although the exact value of the charge varies with the material composition of dust, a selection effect in the material composition of dust grains entering the solar system cannot be expected. Even if interstellar dust grains that can enter the solar system are nonspherical, the surface potentials of the grains can be represented within the framework of the spherical dust model that is applied in this study.