Adv. .Space Res. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSR Vol. 15, No. E/9, pp. (g/9)423-(g/9)431, 1995 Copyright @ 1995 COSPAR Printed in Great Britain. All ri hts reserved. 0273-l 177/9&9.50 + 0.00 zyxwvutsrqp 0273-1177(94)00127-8 SOME FEATURES OF THE MARTIAN BOW SHOCK E. Dubinin,* D. Obod,* R. Lundin,** K. Schwingenschuh*** and R. Grardt zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA * Space Research Institute, 117810 Moscow, Profsojznaja str. 84132, Russia ** Swedish institute of Space Physics, P.O. Box 812, S-98128 Kit-ma, Sweden *** Space Research Ins&ute, Inffeldgasse 12, A-8010 Graz, Austria t Space Science Department, ESA, Keplerian 1, NL 2200 Noordwijk, The Netherlands ABSTRACT The Martian bow shock is immersed a dense and extended neutral atmosphere. This leads to a number of interesting features. The reflection of pickup ions from the electrostatic barrier at the shock front enhances the activity in the foreshock region. “Overreflection” of protons makes the phenomenon of Hot Diamagnetic Cavity a permanent feature of the Martian bow shock. Ion current carried by reflected ions twists the magnetic field. The bow shock acts as a source of new ions which take part in the process of ion thermalization behind the shock. The “injection” of newly created ions modifies the shock structure. UPSTREAM REGION The extended neutral corona around a planetary body can strongly affect the incoming solar wind. The ionization and subsequent pick-up of newly born exospheric ions could provide a mass-loading effect similar to near comets. The essential solar wind deceleration far upstream from the Martian bow shock was reported in /l/. This activity was attributed to the mass-loading by the hot oxygen corona. However, the process requires a much more massive oxygen corona than even the ‘extreme’ model predicts /2/. It was suggested that the shock reflection of H+ ions originating from the extended atomic hydrogen exosphere of Mars, could be responsible for the slowdown of the solar wind /2/. The measurements of the floating potential of the spacecraft, anticorrelated with the flux of collected electrons, have demonstrated that processes at the bow shock control the mass-loading in the upstream region /3/. Figure 1 shows electron number density derived from probe measurements for two orbits of the Phobos-2 spacecraft. The distinct mass-loading effect occurred while the spacecraft was moving (g/9)423