Exclusion of Tiny Interstellar Dust Grains from the Heliosphere

TL;DR

This study models how interstellar dust grains of different sizes are affected by the heliosphere's magnetic environment, revealing that small grains are excluded while larger ones can penetrate, skewing observed size distributions.

Contribution

It provides detailed 3-D simulations of interstellar dust grain trajectories through the heliosphere, incorporating realistic magnetic field orientations and heliosphere models.

Findings

Small grains (0.01 micron) are excluded at the heliopause.

Larger grains (0.1 micron) penetrate the heliosphere with asymmetric distribution.

Grain size distribution in the Solar System is skewed due to magnetic effects.

Abstract

The distribution of interstellar dust grains (ISDG) observed in the Solar System depends on the nature of the interstellar medium-solar wind interaction. The charge of the grains couples them to the interstellar magnetic field (ISMF) resulting in some fraction of grains being excluded from the heliosphere while grains on the larger end of the size distribution, with gyroradii comparable to the size of the heliosphere, penetrate the termination shock. This results in a skewing the size distribution detected in the Solar System. We present new calculations of grain trajectories and the resultant grain density distribution for small ISDGs propagating through the heliosphere. We make use of detailed heliosphere model results, using three-dimensional (3-D) magnetohydrodynamic/kinetic models designed to match data on the shape of the termination shock and the relative deflection of interstellar neutral H and He flowing into the heliosphere. We find that the necessary inclination of the ISMF relative to the inflow direction results in an asymmetry in the distribution of the larger grains (0.1 micron) that penetrate the heliopause. Smaller grains (0.01 micron) are completely excluded from the Solar System at the heliopause.