High Time and Spatial Resolution Observations of the Topology of Mars' Crustal Magnetic Fields

Mars has a patchwork of intense crustal magnetization that gives rise to magnetic fields that can dominate the plasma environment up to ~1000 km altitude in some locations. The strongest crustal fields, in the southern hemisphere centered near 180 deg longitude, form an arcade of reversing polarities that extends > 1000 kilometers east-west. The topology of these fields can be complex and dynamic, with closed loops connecting either nearby and distant crustal sources, and magnetic reconnection with the IMF temporarily forming open field lines. Electron energy-pitch angle distributions measured by the MAVEN Solar Wind Electron Analyzer (SWEA) can be used to infer magnetic topology and thus reveal the large-scale configuration of the magnetic field from measurements at one location. During normal operation, the instrument has a 2-second measurement cycle that provides ~8 km spatial resolution, which is too large to probe the transition region between closed and open field lines, for example. (Topology changes appear sharp and instantaneous at that scale.) However, it is possible to operate the instrument in a non-standard way to measure the electron angular distribution at a single energy with a time resolution of 0.03 seconds and a spatial resolution of 125 meters, which is comparable to the 50-eV electron gyroradius in a 100-nT field. High resolution observations from ~150 to 800 km altitude over strong crustal fields near the evening terminator were obtained on 12 orbits on January 27, 2019, and from May 27 to June 1, 2020. In this presentation, we show high resolution observations at 50 and 200 eV of the transition from closed to open topology and the structure of the magnetic footpoints of closed loops.