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new aspects. In particular, the interconnection of the Mercury magneto-
sphere with the IMF B x component produces a hemispheric asymmetry,
as discussed by other authors (e.g., Refs. 5 and 7). The magnetosheath
ions crossing the dayside magnetopause are subjected to acceleration at
the rotational discontinuity, generated by the merging of the IMF with the
planetary magnetic field. This mechanism can generate particles with ener-
gies up to several tens of keV, and fluxes of the order of 10 10 cm 2 s 1 at
the magnetopause boundary, about 10% of which could reach the surface
of the planet (depending on the loss-cone).
The exact determination of these values is affected by several poorly
known parameters as the V A - SP / V A - SH ratio linked to the relative den-
sities on both sides of the rotational discontinuity at the magnetopause,
and the eciency of the magnetic merging at the dayside of Mercury.
The latter plays a very important role: in fact, the rate of the magnetic
merging, which can be either “bursty” or “steady”, can heavily affect
the plasma distribution inside the magnetosheath. A high rate of dayside
magnetic merging would lead to a fast depletion of the plasma density
inside the magnetosheath, causing a sensible deviation from the Spre-
iter's gasdynamic approximation. Under steady reconnection, the wide cusp
region of the B x -interconnected hemisphere could be almost always “open”,
and the magnetosheath density would be locally close to the upstream
solar wind value. In this case, the fluxes calculated in this work would
rapidly decrease, approaching the values of the unperturbed solar wind at
Mercury's orbit.
Acknowledgments
Authors wish to thank N. Tsyganenko, F. Toffoletto and T. Hill, together
with the NASA/Goddard Space Flight Center (NSSDC) for making
the magnetospheric T96, and TH93, models available to the scientific
community.
References
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37
(1989) 1461-1475.
99
2. M. Lockwood and M. F. Smith, J. Geophys. Res.
(1994) 8531-8553.
3. Massetti et al. , Icarus
(2003) 229-237.
4. J. R. Spreiter, A. L. Summers and A. Y. Alksne, Planet. Space Sci.
166
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(1966)
223-253.
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