Charging and Dynamics of Interstellar Dust at the Heliospheric Interface

The Sun is currently traversing the local interstellar medium at a relative velocity of approximately 26 km s⁻¹. Due to the Sun’s motion, interstellar dust grains from the interstellar medium are transported trough the heliosphere’s boundary, from the upwind direction.

Dust grains in a space environment are subject to a variety of charging mechanisms, which result in an overall equilibrium charge on their surface. In the interstellar medium and in the solar wind, the primary charging mechanisms are plasma collection, secondary electron emission, and photoelectric emission. The charge acquired by a dust grain depends on a number of factors, including the size, composition, and structure of the dust grain itself, as well as on the characteristics of the surrounding environment.

The magnetic field that the dust grains encounter when approaching the heliosphere, starts to change into the heliospheric magnetic field. Hence, the motion of individual grains near the heliospheric interface changes due to the influence of the Lorentz forces. The amount of trajectory deflection depends on the charge-to-mass ratio of a grain. Consequently, not all interstellar dust grains enter the solar system.

We discuss the dust charging with a particular focus on the influence of the space environment conditions that are expected at different locations throughout the heliosphere, including its boundary regions and including short-term and long-term variations of space environment conditions due to solar activity. These are necessary to calculate the dust trajectories in particular at the heliospheric interface. The results will help to explain the physical processes occurring at the boundary of the heliosphere.