Enhancing Mars Gravity Field Solutions with China’s Tianwen-1 tracking data

China's Tianwen-1 (TW1) mission successfully entered Mars orbit in 2021. This mission provides a valuable tracking dataset for at least three more years to enhance the understanding of Mars' gravity field. The highly elliptical near-polar orbit of the TW1 orbiter offers unique sensitivity to long-wavelength gravity signals, complementing the contributions of low-altitude missions like the Mars Reconnaissance Orbiter (MRO). In this study, we first developed a new 50 degree and order Mars gravity field model using four months of TW1 radio tracking data combined with MRO data. We evaluated the improvement of gravity field determination through power spectrum analysis, gravity anomalies maps and trajectory precision assessment. The result shows significant improvements in accuracy up to degree and order 30, with an average enhancement of 38% in the zonal harmonic coefficients, as shown in Figure 1. There are obvious differences between the two gravity field models in gravity anomalies maps, as shown in Figure 2. The range of gravity anomaly errors improves after incorporating TW1 data, with the maximum error decreasing from 53.4 mGal to 46.4 mGal, and the average error improving from 8.4 mGal to 7.3 mGal. Orbit determination experiments confirm that the fused gravity field model enhances trajectory modeling for both MRO and TW1, as shown in Figure 3. Additionally, we processed all the tracking data currently accumulated by TW1 to obtain an 80th-degree Mars gravity field model, as shown in Figure 4. These findings highlight the scientific value of TW1 tracking data in advancing Mars' gravity field modeling.Figure 1. Power spectrum of the MRO50 and MTW50 gravity field models and their error estimates, along the Kaula’s rule and power spectrum of the a priori MGS95J gravity field modelFigure 2. From (a) to (b): maps of gravity anomalies of MRO50 and MTW50 gravity field models and their differences. The maps are centered on 0°E longitude (Hammer projection) Figure 3. Orbit fit difference rms on the MRO RTN frame using the MRO50 and MTW50 gravity field models for MROFigure 4. Power spectrum of the 80-degree gravity field model obtained with and without the Kaula’s rule and their error estimates, and power spectrum of the a priori MRO120D gravity field model