Numerical modeling of the magnetic topology near Mars auroral observations

Magnetohydrodynamic (MHD) simulations of the Mars magnetic field topology are presented for the auroral observations reported from the Mars Express SPICAM instrument. It is found that the field lines closest to the assumed emission location are open. That is, they are connected to the interplanetary magnetic field, thus allowing access for solar wind electrons to bombard the upper atmosphere and create a auroral-like emission. The most likely population responsible for the creation of the emissions recorded by SPICAM is magnetosheath electrons. It is found that numerous closed magnetic field lines, connected to two strong crustal field regions, can straddle the terminator, leaving open the speculation that atmospheric photoelectrons could be responsible for nightside auroral-like emissions. However, for the particular case of the initially reported SPICAM auroral observations, the MHD results do not produce such terminator-crossing field lines near the emission region.