2014 Articles

Constraints on the secular variation of Mercury's magnetic field from the combined analysis of MESSENGER and Mariner 10 data

Philpott, Lydia C.; Johnson, Catherine L.; Winslow, Reka M.; Anderson, Brian J.; Korth, Haje; Purucker, Michael E.; Solomon, Sean C.

Observations of Mercury's internal magnetic field from the Magnetometer on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft have revealed a dipole moment of 190 nT R M3 offset about 480 km northward from the planetary equator, where R M is Mercury's radius. We have reanalyzed magnetic field observations acquired by the Mariner 10 spacecraft during its third flyby of Mercury (M10‐III) in 1975 to constrain the secular variation in the internal field over the past 40 years. With the application of techniques developed in the analysis of MESSENGER data, we find that the dipole moment that best fits the M10‐III data is 188 nT R M3 offset 475 km northward from the equator. Our results are consistent with no secular variation, although variations of up to 10%, 16%, and 35%, respectively, are permitted in the zonal coefficients g 10, g 20, and g 30 in a spherical harmonic expansion of the internal field.