Geoscience Reference
In-Depth Information
2.1.4.
Current closure/dissipation at low altitude
Field-aligned currents are a fundamental mediator of energy and stress in
the magnetosphere. There is currently no clear understanding of how field-
aligned currents close at low altitude. Combined electric and magnetic field
measurements will provide new information on the closure mechanisms.
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2.1.5.
Plasma wave propagation
Propagation of whistler waves along the magnetic field lines guided by
plasma density structures will provide information on the magnetic field
and density structure of the Mercury magnetosphere. Further, the whistler
mode waves resonating with extremely high energy electrons suggest the
existence of energetic electrons associated with acceleration phenomena
such as substorms.
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2.2.
Dynamics of the magnetosphere
2.2.1.
Solar-wind-magnetosphere coupling
Mercury does not have any appreciable ionosphere.
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At Earth, the penetra-
tion of the solar wind electric field is weakened by a feedback mechanism
from the ionosphere. Such mechanism might be less ecient at Mercury.
The role of the ionosphere can be clarified by comparison to the Earth.
Further, by measuring the electric field as well as the magnetic field of
Eigen-frequency waves (i.e., field-line resonances), their phase difference
will yield information on the reflective properties of the ionosphere and/or
planetary surface.
2.2.2.
Response to solar wind
Since the Alfven Mach number can be less than unity, we may find quite
different responses of the magnetosphere, such as formation of a slow shock.
Also, distance variations along Mercury's eccentric orbit result in variations
of a factor 2 of the solar wind power. In the case the auroral radio emissions
exist, their power will provide a diagnostic of the global magnetospheric
response.
2.2.3.
Magnetosphere-exosphere coupling
Due to the lack of a thick atmosphere, plasma supply mechanisms from
Mercury can be quite different from those at Earth. Mercury's exosphere
could modify the magnetospheric plasma conditions. Plasma waves will
