The role of solar wind electrons at the solar wind termination shock

Voyager 2 plasma observations have recently revealed that, as predicted by theory, there exists a solar wind termination shock at 87 au. However, it is evidently different from classical expectations, for instance revealing the downstream solar wind protons still to be in a supersonic mode. In this paper we show that in order to explain the non-classical structure and facts of this shock, one has to start from a multi-fluid magnetohydrodynamic (MHD) approach describing the shock transition. Different from our earlier attempt, here we consider solar wind electrons as an additional extra fluid and allow for preferential heating of electrons compared to thermal solar wind protons at the shock. As we can then show, with this enlargement of the MHD theory by a separate electron fluid we are able to describe observed features of the solar wind termination shock. We arrive at the conclusion that the downstream solar wind thermal plasma is energetically dominated by the pressure of quasi-mass-less electrons.