Pressure anisotropies in the very local interstellar medium

Abstract

Voyager 2 observations indicate that the plasma of the very local interstellar medium might be hotter than predicted by MHD models. However, based on experience with planetary magnetospheres, a region could exist on the interstellar side of the heliopause, where due to compression of the magnetic field the plasma density is depleted and the temperature is different in the directions parallel and normal to the magnetic field. The pressure anisotropy could also have a measurable effect on magnetic field draping around the heliopause and the resulting asymmetries of the structure of the global heliosphere. In this presentation we compare results from a conventional MHD model with a newly developed model based on the Chew-Goldberger-Low (CGL) approximation. The new model was constructed in such a way as to steer the system evolution away from kinetically unstable regions using information about the turbulence responsible for scattering and isotropization. It represents an important step toward developing a general purpose CGL framework for space and astrophysical applications. CGL results indicate that a plasma depletion layer develops in the outer heliosheath where the perpendicular temperature of the plasma is higher than the parallel temperature, while in the inner heliosheath certain regions can have an excess of parallel temperature.