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Ann. Geophys., 22, 1829-1837, 2004
www.ann-geophys.net/22/1829/2004/
© European Geosciences Union 2004
Surface conductivity of Mercury provides current closure and may affect magnetospheric symmetry
P. Janhunen and E. Kallio
Finnish Meteorological Institute, Geophysical Research, Helsinki, Finland
Abstract. We study what effect a possible surface conductivity of Mercury has on
the closure of magnetospheric currents by making six runs with a
quasi-neutral hybrid simulation. The runs are otherwise identical but
use different synthetic conductivity models: run 1 has a fully
conducting planet, run 2 has a poorly conducting planet (
 m ) and runs 3-6 have one of the
hemispheres either in the dawn-dusk or day-night directions,
conducting well, the other one being conducting poorly. Although the
surface conductivity is not known from observations, educated guesses
easily give such conductivity values that magnetospheric currents may
close partly within the planet, and as the conductivity depends heavily
on the mineral composition of the surface, the possibility of
significant horizontal variations cannot be easily excluded. The
simulation results show that strong horizontal variations may produce
modest magnetospheric asymmetries. Beyond the hybrid simulation, we
also briefly discuss the possibility that in the nightside there may
be a lack of surface electrons to carry downward current, which may act
as a further source of surface-related magnetospheric asymmetry.
Key words. Magnetospheric physics (planetary magnetospheres;
current systems; solar wind-magnetosphere interactions).6
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