Magnetic fields and dynamos in terrestrial planets (Invited)

Details Magnetic fields and dynamos in terrestrial planets (Invited) Magnetic fields and dynamos in terrestrial planets (Invited)

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmdi33b..07c&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #DI33B-07

Physics

[1510] Geomagnetism And Paleomagnetism / Dynamo: Theories And Simulations, [5430] Planetary Sciences: Solid Surface Planets / Interiors

Scientific paper

Magnetic fields provide a probe into the deep interior of planets and put constraints on the structure and evolution of their cores. The most plausible explanation for the lack of present-day global field at Venus and Mars is that the heat flow at the core-mantle boundary is carried by thermal conduction along a sub-adiabatic temperature gradient and that these planets failed to nucleate an inner core, preventing compositional convection. Mercury most likely formed an inner core. The weakness of its field can be explained by stable stratification of the upper part of the fluid core. The early Martian dynamo was probably driven by secular cooling of the fluid core, in contrast to the present geodynamo, which is driven mainly by the latent heat and compositional flux of inner core growth. Dynamo simulations suggest that the two types of driving the flow do not result in strong differences in field geometry or field strength. However, in the case of volumetric cooling even a moderate north-south imbalance of the heat flow imposed by the mantle on the core can lead a dynamo that essentially operates in a single hemisphere. This can explain the strong concentration of Martian crustal magnetization on the Southern hemisphere, but it would preclude significant polar wander since the time when the crust was magnetized.

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