Charging of Interstellar Dust Grains in the Out-of-Equilibrium Plasma of the Inner and Outer Heliosheath Regions

Thursday, 18 December 2014
Priscilla C Frisch1, Maher A Dayeh2, Mihir Indrajit Desai2, Herbert O Funsten3, Jacob Heerikhuisen4, Paul H Janzen5, David J McComas2, George Livadiotis2, Keiichi Ogasawara2, Nikolai V Pogorelov4, Daniel Brett Reisenfeld5, Nathan Schwadron6, Jonathan D Slavin7 and Gary Paul Zank4, (1)University of Chicago, Chicago, IL, United States, (2)Southwest Research Institute, San Antonio, TX, United States, (3)Los Alamos Natl Laboratory, Los Alamos, NM, United States, (4)University of Alabama in Huntsville, Space Science, Huntsville, AL, United States, (5)University of Montana, Missoula, MT, United States, (6)University of New Hampshire Main Campus, Space Science Center, Durham, NH, United States, (7)Harvard-Smithsonian CfA, Cambridge, MA, United States
Many of the energetic neutral atoms (ENAs) observed by the Interstellar Boundary Explorer (IBEX) are created in the inner and outer heliosheath regions, where the plasma is in a non-equilibrium state with properties that can be extracted from the IBEX ENA data. The energy distribution of the plasma is a composite of a thermal core, and a high energy non-thermal tail that can be described by a power-law with the index kappa. Interstellar dust grains with sizes 0.03-2.0 microns are contained in the flow of interstellar material through the heliosphere. These grains have reached the inner heliosphere only after traversing the magnetized plasmas of the inner and outer heliosheath regions, where impacts with ions and electrons control the grain charge and therefore the grain gyroradius and trajectory. Many studies of grain charging in the heliosheath regions exist, including 3D models that predict spatial distributions of grains of different masses from the grain charge, and models that set limits on the magnetic field strength in heliosheath regions based on observed grain mass. These studies were performed before IBEX measured the energy distribution of the heliosheath plasmas. In the heliosheath, grains are charged by the emission of secondary electrons after collisions with plasma particles, including electrons and ions, in addition to the photoejectron of electrons and other minor processes. We will present new models of dust grain charging in the non-equilibrium inner and outer heliosheath plasmas using the plasma energy distribution obtained from IBEX ENA data and theoretical models of the non-equilibrium electrons. Implications of this study for grain trajectories and the interstellar magnetic field strength will be discussed.