TERMINATION OF THE SOLAR-WIND PROTON FLOW NEAR MARS BY CHARGE-EXCHANGE

One striking observation made during the Phobos-2 mission concerns the existence of a well-defined plasma boundary where the solar wind prot on flux terminates. Different mechanisms have been proposed to explain this interesting new feature. In the present study, we explore the po ssible influence of charge exchange on the loss of solar wind protons in the Martian exosphere as the reason of such a composition boundary. Unlike the cometary interaction, the charge exchange process is effec tive only in the vicinity of the subsolar point of the Martian ''magne topause'' where the streamlines cross the dense neutral atmosphere. Th e most recent model of the Martian upper atmosphere and the flow field obtained by numerical simulation are used to provide the basis for su ch a scenario.