Variability in Martian magnetic field topology

Martian crustal magnetic fields form localized mini-magnetosphere structures that extend in some regions well above the Martian ionosphere, interacting directly with the draped external interplanetary magnetic field (IMF). In some regions the crustal magnetic field lines are closed, locally shielding the ionosphere from external plasma. In other locations the crustal field lines are open, allowing exchange of plasma between the ionosphere and the surrounding plasma interaction region. The average magnetic topology as a function of geographic location has been mapped previously, using ~7 years of Mars Global Surveyor electron observations recorded at constant altitude and local time. In this previous work, pitch angle distributions of suprathermal electrons were examined for the presence of loss cones to determine whether field lines were open or closed. Here we apply the same technique to describe how magnetic topology varies with four external drivers: solar wind pressure, IMF orientation, solar EUV flux, and Martian season. We see that some locations on Mars change topology frequently depending upon external conditions, while others have a relatively static field topology.