Three Dimensional MHD Modeling of Mercury’s Magnetosphere During ICMEs

NASA’sMESSENGERmission will enter its orbit about Mercury in 2011 and make observations of this magnetosphere during solar maximum when encounters with Interplanetary Coronal Mass Ejections (ICMEs) are most likely. We use the BATS-R-US MHD model, modified to simulate Mercury’s magnetosphere, to investigate the response of this small magnetosphere to ICME conditions. Mercury is treated as a sphere with limited conductance, and the spherical simulation grid is set to have an inner boundary just above one RM . A control case is established consisting of typical quiet time solar wind conditions. The low Alfven Mach number regime is then systematically explored using series of steady state simulations in which the IMF Bz is steadily decreased. We find that Alfven wing formation takes place during extreme ICME conditions as predicted by earlier analytic calculations. Finally, we simulate Mercury’s interaction with a realistic ICME event whose values are chosen to be consistent with an event measured by Helios 1 on June 20, 1981 at 0.34 AU.