Magnetic Topology at Mars as Inferred from Electron Pitch Angle Distributions Taken by the SWEA Instrument on MAVEN

Energy input from the solar wind can drive large fluxes of charged particle escape from Mars, but the solar wind's access to the Martian ionosphere is not uniform. Understanding where and under what conditions magnetic fields at Mars are open or closed to the IMF is vital for determining the ionospheric response to solar wind forcing. Studying this magnetic topology at Mars can inform us of the relevant plasma processes and the possible avenues of particle escape. One method of determining magnetic topology is through the use of electron pitch angle distributions (PADs), as the relative fluxes of electrons traveling parallel and perpendicular to the magnetic field can reveal the electron source. This indicates, for example, where solar wind electrons are entering the ionosphere or where ionospheric electrons are trapped close to the planet. This method was previously used to analyze topology with data from the MGS spacecraft (Brain et al., 2007), but this study was limited in scope due to the spacecraft orbit only sampling two local times (2 PM and 2 AM) and one altitude (400km). The MAVEN spacecraft orbit is not subject to these same limitations. In the study presented here we use PADs from the SWEA instrument on MAVEN to assess the magnetic topology across all local times and many altitudes. We first developed an algorithm to automatically label incoming and outgoing PAD signatures as being loss cones, beam distributions, or isotropic. By applying this algorithm to PADs taken at several different energies we are able to determine when magnetic field lines are open or closed. We then study how this magnetic topology varies across the surface of Mars and with changes in upstream solar wind conditions.