MAGNETIC-FIELD OVERSHOOTS IN THE MARTIAN BOW SHOCK

In 1989 the Phobos 2 spacecraft provided sufficient plasma and magneti c field data for statistical investigations of the Martian bow shock s tructure. Significant magnetic field overshoots were observed in more than 70% of the bow shock crossings detected in the terminator region. According to our studies based on the available low-resolution data s et, the features of the Martian overshoots are very similar to those o bserved in the terrestrial and Venusian bow shock: the magnitude incre ases with increasing Mach number and the thickness scales as the proto n gyroradius computed from the upstream solar wind speed and magnetic field strength. Our investigations seem to support the idea of Mellott and Livesey [1987] suggesting that overshoots may develop not only in supercritical shocks but also when the Mach number is below or around the critical value.