If Mars has a small intrinsic magnetic moment, Mars' magnetosphere could vary on time scales of a few minutes due to reconnection with the solar wind magnetic field. The day-side magnetopause will be one or two reflected-ion Larmor radii from the bow shock. Substorms will have scale-times of about six minutes. Mars' high ionospheric conductance will virtually stop polar cap convection, and create a magnetic ''topological crisis'' unless convecting magnetic flux finds a dissipative way to return to the day-side. The strong magnetic shear induced by magnetospheric convection above the ionosphere could be tearing unstable. The magnetic field might diffusively ''percolate'' through the tearing layer. This shearing also draws field aligned currrents from the ionosphere which could inject few KeV heavy ionospheric ions into the magnetotail. ¿ American Geophysical Union 1989