Instabilities and Plasma Mixing at the Heliospheric Boundary

Abstract:

The stability of the heliopause (HP) that separates the tenuous heliosheath plasma from the relatively dense plasma of the local interstellar medium (LISM) is examined using a fully general model that includes all the important physical process pertaining to the heliosphere e.g., resonant charge exchange with neutral hydrogen, plasma flows and magnetic fields in the outer and inner heliosheath, and energetic neutral ENA) from the inner heliosheath. Charge exchange introduces Rayleigh Taylor (RT) like instability in the nose region of HP, the strong flow shear excites Kelvin-Helmholtz (KH) like instability in the flanks while mixed RT-KH modes are unstable in the shoulder region in between. ENA are found to be essential for the instability of flanks in the presence of magnetic field stabilization. Further, the mixing of the LISM plasma with solar wind (SW) plasma is across the HP caused by these instabilities is examined. The magnetic field in the OHS and IHS are oriented approximately parallel to each (on either side of HP). Such field lines normally do not experience reconnection However, we show that in the nonlinear phase, local mushroom like structures of RT and RT-KH mode will drag the OHS field lines across HP into the inner heliosheath. Driven by local plasma flows, these field lines will reconnect with magnetic field lines in the HIS. This reconnection of fields in OHS and IHS will greatly enhance the mixing of plasma across the HP. This scenario is examined using Sweet-Parker and Petscheck models of driven reconnection. The reconnection rates and mixing rates with collisional resistivity and anomalous resistivity are evaluated and compared with other mechanisms of mixing to assess the importance of reconnection in plasma mixing across HP.