Why is Mercury's magnetic field so weak and shifted north?
In plain words
Mercury has an active dynamo (a field generator made by flowing liquid iron) but its field is about a hundred times weaker than simple scaling predicts, and its center is shifted toward the north pole. Its large iron core should do better.
Precise statement
MESSENGER found an axial dipole field with surface equatorial strength near 2e-3 G whose magnetic equator is offset about 0.2 Mercury radii north. Identify the core state (dynamo beneath a stably stratified layer, iron-snow regime, thin-shell convection) that reproduces both the weakness and the offset. An answer is a dynamo model fitting the measured low-degree Gauss coefficients and their secular variation.
What would settle it
BepiColombo two-spacecraft field measurements of higher harmonics and secular variation compared with dynamo models.
Status in the literature
Unverified note
BepiColombo was scheduled to enter Mercury orbit in late 2026; data are not yet available.