Lessons learned from Ulysses data analysis for future interstellar dust detectors in space

Due to the relative motion of the solar system through its local interstellar environment, interstellar dust can enter the heliosphere. The dust trajectories are influenced by gravitational forces, solar radiation pressure force and by the solar wind through the Lorentz force on charged dust grains. Finally, these interstellar micro-particles can be measured in the solar system by in situ cosmic dust instruments. 

One of the most extensive in situ interstellar dust databases stems from the Ulysses dust detector. However, distinguishing interplanetary from interstellar dust is a major challenge and the selection criteria may influence the conclusions made based on the interstellar dust dataset. 

In this work, we elaborate on how the selection criteria and mass determination methods influence the inferred ISD population bulk properties like the dust particle flux, flow direction, and the gas-to-dust mass ratio in the interstellar medium. We examine the largest dust grains that were selected as "interstellar" and we illustrate a methodology to infer the filtering at the heliosphere's outer regions (heliosheath) using in situ data in the solar system, simulations of dust transport in the heliosphere inside of the termination shock, and assumptions on the initial dust size distribution from astronomical observations. 

We conclude with lessons learned for future detectors, in particular the necessity to use velocity grids and large detector surface areas.