Fig. 2.
Magnetic field lines near Mars when the Martian intrinsic dipolar magnetic field is (a) 0 nT, (b) 10 nT, (c) 30 nT and (d) 60 nT on the surface of Mars in the magnetic equator. The field line tracing was started on the spherical shell of 4000 km from the center of Mars. The color planes at the noon-midnight plane (y = 0) show the density of O2+ ions and they are added to see the correlation of density regions to the magnetic field lines. The red sphere has a radius of 3700 km. Note that the colour of the magnetic field lines which are behind the y = 0 colour plane is dark blue and they are not as bright as the field lines above the y = 0 plane.