Geoscience Reference
In-Depth Information
2.7.
Mirror point asymmetry
Because of the expected dipole offset from the centre of the planet, causing
differently wide loss-cones in the two hemispheres, interhemispheric charge
flow may arise along Mercury's magnetic field.
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Such a charge flow will lead
to weak field-aligned currents connecting the hemispheres or to a parallel
electric potential distributed along the field lines, or both.
2.8.
Particle trapping
The maximum kinetic energy of the particles that can be trapped in
Mercury's magnetic field can be estimated by requiring the gyro radius be
less than some fraction of the size of the magnetosphere. The upper limit
to the energy of trapped protons is found to be of the order of 100 keV
with a fairly large uncertainty depending on the assumptions made both
about the size of the magnetosphere, the relevant fraction of its size, and
the magnitude of the magnetic field (which may vary significantly over the
gyro path). For heavier ion species the upper energy limit is lower, in inverse
proportion to the square root of the atomic mass. Electrons can likely be
trapped at energies up to several 100 MeV (i.e., beyond the energy range
of all magnetospheric electrons). Whether radiation belts exist at Mercury
is controversial. If they exist they are likely not present at all times, but
rather an occasional phenomenon. Possible radiation belts at Mercury have
also been discussed by, for example, Russell
et al.
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and Orsini
et al.
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2.9.
Wave activity at higher frequencies
2.9.1.
LF and MF waves
Energy transport within the Hermean magnetosphere is partly governed
by plasma wave activity, in particular Alfvenic activity. Alfven waves arise
where dynamic processes occur. They can transport energy, in the form of
electromagnetic energy, large distances before dissipating it through kinetic,
inertial, or wave breaking processes. BepiColombo will be the first mission
to Mercury where the detailed physics can be studied, i.e., energy trans-
port, acceleration processes, and dissipation. A number of wave emission
processes are expected. Hermean kilometric radiation (HKR) well below
1 MHz may be emitted from the “auroral” acceleration regions that are
known to exist at Mercury, and have a similar cause as the Auroral kilo-
metric radiation (AKR) near Earth. It is interesting to note that radio
emissions originating near Mercury below about 50-80 kHz will be trapped
