"[15] Anderson et al. 2011, using high-quality MESSENGER data from many orbits around Mercury – as opposed to just a few high-speed flybys – found that the dipole moment is 195 ± 10 nT-RM3.

The origins of the magnetic field can be explained by the dynamo theory;[11] i.e., by the convection of electrically conductive molten iron in the planet's outer core.

There are still difficulties with this dynamo theory, including the fact that Mercury has a slow, 59-day-long rotation that could not have made it possible to generate a magnetic field.

The thermal gradient at the core–mantle boundary is subadiabatic, and hence the outer region of the liquid core is stably stratified with the dynamo operating only at depth, where a strong field is generated.

[20] Because of the planet's slow rotation, the resulting magnetic field is dominated by small-scale components that fluctuate quickly with time.

This geometry implies that the south polar region is much more exposed than in the north to charged particles heated and accelerated by solar wind–magnetosphere interactions.

In general, the inferred equivalent internal dipole field is smaller when estimated on the basis of magnetospheric size and shape (~150–200 nT R3).

[26] The MESSENGER spacecraft was expected to make more than 500 million measurements of Mercury's magnetic field using its sensitive magnetometer.

When Mariner 10 made a fly-by of Mercury back in 1974, its signals measured the bow shock, the entrance and exit from the magnetopause, and that the magnetospheric cavity is ~20 times smaller than Earth's, all of which had presumably decayed during the MESSENGER flyby.