Global Mapping of Magnetic Field Topologies in the Martian Induced Magnetosphere

Abstract Mars hosts a global induced magnetosphere formed through the interaction between the solar wind and its upper atmosphere. Understanding the structure of the induced magnetosphere is essential for elucidating the processes governing atmospheric ion escape. Using 9 years of measurements by NASA's Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we investigate the magnetic fields with different topologies and construct their global distributions. We find that the distribution of magnetic topologies is primarily controlled by the solar wind, particularly in the nightside magnetotail. Specifically, draped field lines preferentially occur in the +E hemisphere, where the solar wind convective electric field () points away from Mars. In contrast, open‐to‐day and closed‐to‐day field lines preferentially occur in the −E hemisphere, where points toward the planet. Open‐to‐night field lines exhibit a weaker preference for the +E hemisphere, but only near the terminator, and this asymmetry diminishes farther downtail. A comparison with Venus reveals strong similarities, suggesting that such hemispheric asymmetries are an intrinsic property of induced magnetospheres. Furthermore, we show that field lines connected to the dayside ionosphere alone cannot fully account for the formation of the cold, dense ion trail, indicating that draped field lines also play an important role.