The Return of the Bow Shock

Recently, whether a bow shock ahead of the heliospheric stagnation region exists or not has been a topic of discussion. This was triggered by measurements indicating that the Alfvén speed and the speed of fast magnetosonic waves are higher than the flow speed of the local interstellar medium (LISM) relative to the heliosphere and resulted in the conclusion that either a bow wave or a slow magnetosonic shock might exist. We demonstrate here that including the He + component of the LISM yields both an Alfvén and fast magnetosonic wave speed lower than the LISM flow speed. Consequently, the scenario of a bow shock in front of the heliosphere, as modeled in numerous simulations of the interaction of the solar wind with the LISM, remains valid.