An equivalent source dipole model of the Martian crustal magnetic field using MGS, MAVEN, and Tianwen-1 data

Mars does not possess a present-day global magnetic field generated by an active dynamo; however, it exhibits intriguing localized crustal magnetic anomalies. High-resolution and reliable models of these remanent magnetic fields can offer critical insights into the planet’s internal dynamics and evolutionary history. This study presents a novel model of the Martian crustal magnetic field, derived from magnetic field data acquired by the Mars Global Surveyor (MGS), the Mars Atmosphere and Volatile Evolution (MAVEN) mission, and the orbiter of the Tianwen-1 mission. The model is constructed using the equivalent source dipole method, with dipole sources uniformly distributed on a spherical surface according to the Fibonacci sphere distribution. The inversion of the magnetic dipole moments involves two key steps. First, the radial components of the magnetic dipole moments are inverted using only the radial magnetic observations. Subsequently, the inverted radial magnetic moments serve as the initial model to derive the three-component magnetic moments through the iteratively reweighted least squares method with Huber weights. Our inversion scheme incorporates rigorous data selection criteria and novel mathematical methods to mitigate the influence of external magnetic sources. The inverted magnetic dipole moments are transformed into a spherical harmonic model, which demonstrates convergence of the magnetic power spectrum at the surface of Mars up to spherical harmonic degree 110, corresponding to a surface spatial resolution of approximately 190 km. The predicted values from our model are compared with on-site magnetic measurements taken by the InSight lander and the Zhurong rover of the Tianwen-1 mission.