Variations in Nightside Magnetic Field Topology at Mars

The Martian plasma environment contains a complex magnetic topology, with contributions from the interplanetary magnetic field (IMF) and crustal magnetic fields. The topology can control how plasma is exchanged between the solar wind and the Martian ionosphere. Here we use 7 years of suprathermal electron pitch angle distributions recorded by the Mars Global Surveyor (MGS) spacecraft to determine the topology at 2 am and 400 km on the Martian nightside as a function of geographic location and external drivers. Observations show that topology statistically varies with IMF direction, solar wind pressure, solar extreme ultraviolet (EUV) flux, and season. Changes in topology with IMF direction and season are consistent with changes in the likelihood of magnetic reconnection between individual crustal fields and the draped IMF. Changes in topology at a given location with solar wind pressure and solar EUV flux are consistent with reconfiguration of topological structures in the plasma environment.