Effects of charge exchange and photoionization on the interaction between the solar wind and unmagnetized planets

The effects of photoionization and charge exchange were compared by using three‐dimensional hybrid code simulations of the interaction between the solar wind and Venus. The direction of the shock altitude asymmetry in the direction of the convection electric field when photoionization was included was contrary to observations near Venus. However, when charge exchange was included, the direction of the asymmetry did agree with the observations. An analysis of the simulation results showed that the velocities of pickup ions and electrons differed near locations where charge exchange occurred. This velocity difference caused an electric current, and it generated a strong magnetic barrier on the side of the planet to which the convection electric field was pointing. This magnetic barrier acted as an obstacle to the solar wind, and the shock was inflated on this side.