Interstellar Dust Transport Through the Heliosphere Including the Sector Region

Abstract

Interstellar dust has been detected in situ flowing through the heliosphere. However, our ability to derive the density and size distribution of the interstellar dust in the local interstellar medium from this directly detected dust requires modeling the transport of the grains as they interact with the solar wind magnetic field. The magnetic field in the sector region that contains the heliospheric current sheet has rapid polarity flips which can present an effectively very low averaged field strength to dust grains that have gyroradii tens of au in size. We present new calculations of dust transport through the heliosphere using models that include the sector region to assess the effects on dust transport. We show that the sector region can act as a window allowing even relatively small grains to penetrate deep into the heliosphere. We find the sector region reduces the variation in dust density with the solar cycle (as compared to models without the sector region), with very little concentration or dilution of the dust for grains larger than \sim 0.1$ $\mu$m for most of the solar cycle. We still find a substantial concentration of the dust in the ecliptic plane for a focusing overall polarity of the field at solar minimum. These models do not include the time dependence of the magnetic field during transport of grains through the heliosphere. Nevertheless, our results imply that observations of interstellar dust grains, even near Earth, could be fairly accurate in determining their size distribution in the surrounding interstellar medium.