Small Charged Grains Outside the Heliopause as a Source of Information About More Distant Regions: An Opportunity for the Interstellar Probe

The Interstellar Probe offers an unique chance to observe directly a wide range of sizes of both the interplanetary and the interstellar dust. Measurements in the outer solar system beyond the zone of the giant planets will provide an opportunity to study the dust components produced in the Kuiper-belt as well as the interstellar dust entering the heliosphere. Beyond the heliosphere, the observations will access also the small interstellar dust particles, which are deflected from entering the heliosphere due to a high surface charge-to-mass ratio.

We calculate numerically the velocity distributions of small (~ 10 nm) dust grains in the outer heliosheath, using simple models of the dust charging process and the magnetic field and plasma flow beyond the heliopause. The results are applied to the case of dust impact observations from a fast moving spacecraft like the Interstellar Probe. We find that even simple measurements of impact speed provide information about the plasma flow and the magnetc field structure in more distant regions of space. In particular, observations of small dust impacts can be used as a means of remote detection of structures like the heliospheric bow shock or transient waves. We also point out how different choices of the Interstellar Probe trajectory would affect the observations of small interstellar dust.