7th Asia-Pacific Conference on Plasma Physics, 12-17 Nov, 2023 at Port Messe Nagoya

Re-estimate the Mercury's dipole moment by employing a new technique
Zhaojin Rong1,2, Zhen Shi1,21Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese
Academy of Sciences, 2 College of Earth and Planetary Science, University of Chinese Academy ofSciencese-mail (speaker): rongzhaojin@mail.iggcas.ac.cn
The early surveys of Mercury 10 showed that Mercury
should have a global dipole magnetic field. The global
dipole field is not confirmed until the arrival ofMESSENGER spacecraft. MESSENGER into orbit
around Mercury in 2011, and operate successively for
four years. Using the magnetometer data of Mercury 10and MESSENGER, many researchers estimate the dipole
moment with different methods, and the yielded
moments are volatile. Based on some assumptions andcomplicated data processes, such as analyzing thedeviation position of the magnetic tail current plate near
Mercury and deducting the magnetic field outside themagnetosphere model, the current acceptable knowledge
demonstrates that the global magnetic dipole moment ofMercury is 195 nT*RM^-3 [1, 2], the dipole Angle isless than 3°, and the dipole center is shifted 480km to thenorth. Here, being different from previous studies, weuse a state-of-art method to diagnose the Mercury’s
dipolar field which is assumed to originate from amagnetic dipole. This method can effectively separate
and solve the dipole parameters (six parameters withthree dipole center, two dipole axis, and one dipole
moment), and gives the error of how much the dataset ofsampled magnetic field deviated from the dipole field [3].
By employing this method and the MESSENGER field
data, the dipole parameters are derived and compared atdifferent altitudes, latitudes and local times. We carefully
selected the study region relying on the derived errorsthat can be seen as the proxies of non-dipole fieldcomponents and the external fields. After the proper
selection of the study region, we found the region with
low-altitude (h<100 km), mid-latitude (40~50 degree),and night side location (20<local time<04) can yield
minimum fitting errors. The derived optimum dipole
parameters demonstrated that the dipole center is at[x=5.0;y=-16.0;z=480.5]km, the dipole moment is about
M=2.5*10^19 nA.m^2 (or 172 nT*RM^-3), the dipoletilt angle is 3.7 degree. Our yielded dipole moment isweaker than that estimated in previous studies. We
compared and discussed with previous results.
References[1] Anderson, B. J., Johnson, C. L., Korth, H., Purucker,M. E., Winslow, R. M., Slavin, J. A., et al. (2011). The
global magnetic field of Mercury from MESSENGER
orbital observations. Science, 333, 1859–
1862. https://doi.org/10.1126/science.1211001[2] Johnson, C. L., Purucker, M. E., Korth, H., Anderson,B. J., Winslow, R. M., Al Asad, M. M., et al.
(2012). MESSENGER observations of Mercury’smagnetic field structure. Journal of GeophysicalResearch, 117,
E00L14. https://doi.org/10.1029/2012JE004217[3] Rong, Z. J., Wei, Y., Klinger, L., Yamauchi, M., Xu,W. Y., Kong, D. L., et al. (2021). A new technique todiagnose the geomagnetic field based on a single circularcurrent loop model. Journal of Geophysical Research:
Solid Earth, 126,e2021JB022778. https://doi.org/10.1029/2021JB022778

Figure 1. The comparison of the predicted inverted
dipole model and the series of MESSENGER’s dataset