Venus express observations of an atypically distant bow shock during the passage of an interplanetary coronal mass ejection

On 10–11 September 2006 the Venus Express magnetometer detected a very strong Interplanetary Coronal Mass Ejection (ICME) event with an average field about 2 times higher than that of a typical ICME at 0.72 AU. While the effective obstacle to the solar wind is compressed to a smaller dimension during this ICME event, the bow shock is located far upstream of its nominal location. The observed shocks are weak and appear very dynamic. The location of the shock crossing can be found all along the Venus Express trajectory, which has an apocenter of 12 R_V. We attribute the atypical distant bow shock location as an effect of the extremely low Mach number during the ICME.