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Approximate Mirror Symmetry in Heliospheric Plasma Flow Explains VOYAGER 2 Observations

The Sun and the undisturbed interstellar magnetic field and plasma velocity vectors (Bis,Vis) define a mirror symmetry plane of the flow at large heliospheric distances. We show that for the Bis direction defined by IBEX Ribbon center, the radial direction of Voyager 2 over the last decade, and the (thermal proton) plasma velocity measured by the spacecraft since 2010.5, are almost parallel to the (Bis,Vis)-plane, which coincides in practice with the Hydrogen Deflection Plane. These facts can be simply explained if approximate mirror symmetry is also maintained on the inner side of the heliopause. Such approximate symmetry is possible since the solar wind ram pressure is almost spherically symmetric and the plasma beta value in the inner heliosheath is high. In the proposed symmetry, the plasma flow speed measured by Voyager 2 in the inner heliosheath is expected to rotate more in the transverse than in the polar direction (explanation alternative to McComas & Schwadron (2014)), in evident agreement with available spacecraft data (our Fig.1).