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Title: Why is Mercury's magnetic field so weak and shifted north?
Plain: 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: 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.
Settled by: BepiColombo two-spacecraft field measurements of higher harmonics and secular variation compared with dynamo models.
Kind: phenomenon
Answer type: mechanism
References: (empty)
Literature status: open
Status note: BepiColombo was scheduled to enter Mercury orbit in late 2026; data are not yet available.
Posed since: 1974