Calibration of the Zero Offset of the Fluxgate Magnetometer on Board the Tianwen-1 Orbiter in the Martian Magnetosheath

High-precision measurements of the magnetic field are critical to explore the near-Mars environment. The Mars Orbiter MAGnetometer (MOMAG) is one of seven payloads on board the Tianwen-1 orbiter. Its zero offset needs regular calibration, and the Wang-Pan method I is applied to the MOMAG when the Tianwen-1 orbiter is in the solar wind. The orbiter will remain out of the solar wind over tens of days each year, a method is necessary to ensure the accuracy of the zero offset during this period. Recently, a new method was proposed by Wang (2022b), https://doi.org/10.3847/1538-4357/ac822c, which is referred to as the Wang method II for ease of description. Here, we test the performance of this method using the MOMAG data measured in the Martian magnetosheath. We find that the zero offset O-w determined by the Wang method II varies around the zero offset O-wp calculated by the Wang-Pan method I using the potential Alfv & eacute;nic fluctuations in the solar wind. After smoothing with a temporal window of 27 days, O-w is able to achieve an accuracy close to O-wp. If the data segment has no gaps and its duration is < 27 days, the smoothed O-w might have an error >2 nT, but the error tends to be smaller if the segment's duration is longer. Our tests suggest that the Wang method II is suitable for the in-flight calibration of the MOMAG when the Tianwen-1 orbiter remains out of the solar wind.