ABSTRACT
In 1974, the three flybys of the Mariner 10 spacecraft revealed that Mercury has a global magnetic field. This was a surprise for many scientists since an internal dynamo process was deemed unlikely because of the planet’s relative small size and its old inactive surface (Solomon 1976). Either the iron core would have already solidified completely or the heat flux through the core-mantle boundary (CMB) would be too small to support dynamo action. The Mariner 10 measurements also indicated that Mercury’s magnetic field is special (Ness et al. 1974). Being 100 times smaller than the geomagnetic field, it seems too weak to be supported by an Earth-like core dynamo. And though the data were scarce, they nevertheless allowed to constrain that the internal field is generally large scale and dominated by a dipole but possibly also a sizable quadrupole contribution. Both the Hermean field amplitude and its geometry are unique in our solar system.
