A dipole-like magnetosphere of Mars

The Martian magnetosphere is unique in our Solar system because it contains components of an induced and an intrinsic magnetosphere. Since we can not get a global snapshot of the magnetosphere at a given time we use a statistical picture based on a large number of plasma measurements. Depending on the choice of coordinate system used and the selection of the data we can observe different features of the Martian magnetosphere. If, for example, we map data in the Martian Solar Electric (MSE) coordinate system with a fixed direction of the cross-flow component of the interplanetary magnetic field (IMF), then we can separate the induced features of the magnetosphere of Mars which appears similar to the magnetosphere of Venus. If we map data in the geographic coordinate system, then effects caused by the local crustal magnetic field are emphasized and we can observe a mini crustal magnetosphere. If we use the Martian Solar Orbital (MSO) coordinate system and select together the spacecraft orbits with positive and negative B_y-component of the IMF, then the effects related to draped magnetic field and the high order harmonics of the crustal magnetic field are significantly weakened because of averaging over many spacecraft orbits. In this case, a dipole-like magnetosphere of Mars becomes visible indicating the existence of a weak planetary dipole field. If we select separately the orbits with positive and negative B_y-component of the IMF we observe a twist of the magnetotail in the direction determined by the sign of B_y that is typical for a hybrid magnetosphere with the induced and intrinsic components. The intrinsic and induced components are also well separated when we select the orbits with northward IMF. Then we observe the features that are somewhat similar to those at the Earth magnetosphere. When we use the MSO coordinates and separate by the phase of Mars rotation, the tail topology occurs more complex. This indicates that the effects of the local crustal magnetic field turn out as being also important.