Charging and Dynamics of Interstellar Dust throughout the Heliosphere

The heliosphere is a “bubble” of plasma that forms around the Sun through a pressure balance between the outflowing solar wind and the interstellar medium. 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 present in the interstellar medium are transported through 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 several factors, including the size, composition, and structure of the dust grain itself, as well as on the characteristics of the surrounding environment.

The trajectories of charged dust grains are influenced by the magnetic field in the environment they are moving through due to the emerging Lorentz force. When approaching the heliosphere, the interstellar magnetic field starts to get disturbed by the solar wind (heliospheric) magnetic field. The amount of trajectory deflection an inflowing interstellar dust grain experiences depends on its charge-to-mass ratio. 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 the boundary regions and including short-term and long-term variations of the environmental conditions due to the solar activity. Using these results, we show the influence of heliospheric properties on the dust grain trajectories at the heliospheric interface in specific. The results will help to understand the physical processes occurring at the boundary of the heliosphere.