Why is Mercury's magnetic field so weak and shifted north? · revision history

Revision 2

Accepted · core change · record

Changes against revision 1:

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 · changed · core
Revision 1: 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.
Revision 2: MESSENGER found an axial dipole field with surface equatorial strength near $2 \times 10^{-3}$ 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

Decisions