Physics
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p31a..04s&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P31A-04
Physics
1507 Core Processes (8115), 1510 Dynamo Theories, 5430 Interiors (8147), 5440 Magnetic Fields And Magnetism, 6235 Mercury
Scientific paper
Mariner 10 observed Mercury's magnetic field during 3 flybys of the planet between 1974 and 1975, revealing the presence of a magnetic field of internal origin with a dipole moment of ≈ 300nT-RM3 (1 RM = 2440 km). Such a field is probably too large to be explained by induction effects or remanent magnetization; however, energetic considerations suggest that it may be too small to be consistent with dynamo action, at least for an Earth-like dynamo. More specifically, energetic considerations provide an estimate of the toroidal magnetic field strength that the dynamo should generate: if the dynamo is Earth-like in the sense that it has similar toroidal-poloidal field strength scaling as the Earth, then the poloidal field should be much stronger than that observed. Before abandoning a dynamo explanation for Mercury's field, we question whether the same toroidal-poloidal scaling should hold for Mercury. If a dynamo is operating in Mercury's iron core, part of the core must be fluid. Thermal evolution calculations estimate that the solid inner core comprises between 0.5 and 0.8 of the total core radius, much larger than the Earth value of 0.35. As a result, the fluid convecting outer core where the dynamo is generated is much thinner for Mercury than for Earth. Here we use 3-D numerical dynamo modeling to investigate dynamos operating in thin shell geometries. We find that the magnetic fields produced by thin shell dynamos can have larger toroidal to poloidal field ratios than Earth-like dynamos. This suggests that a hydromagnetic dynamo may be consistent with the weak surface field observed at Mercury and alternative explanations may not be required.
Bloxham Jeremy
Hutchison William E.
Stanley Sabine
Zuber Maria T.
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