The measurements carried out by the plasma spectrometer ASPERA, on-board the Phobos 2 spacecraft show that the Martian bow shock is characterized by a sudden increase of ionization of the neutral corona. It acts as a source of new ions that can strongly modify the process of ion heating behind the shock front. The loss of momentum of solar wind protons due to their interaction with exospheric ions may lead to an increase in the effective scale of the obstacle. ¿ American Geophysical Union 1993