Geoscience Reference
In-Depth Information
ON THE DYNAMICS OF CHARGED PARTICLES IN
THE MAGNETOSPHERE OF MERCURY
DOMINIQUE C. DELCOURT
∗,†
and KANAKO SEKI
‡,§
†
CETP-CNRS, Institut Pierre Simon Laplace
4 avenue de Neptune, 94107 Saint-Maur des Fosses, France
‡
Solar-Terrestrial Environment Laboratory, Nagoya University
Honohara 3-13, Toyokawa, Aichi 442-8507, Japan
∗
dominique.delcourt@cetp.ipsl.fr
§
seki@stelab.nagoya-u.ac.jp
We review some features of ion dynamics in Mercury's magnetosphere using
single-particle simulations. Not unexpectedly, the small spatial and temporal
scales of this magnetosphere lead to non-adiabatic transport features that have
a variety of implications such as extreme sensitivity to initial conditions upon
injection into the magnetosphere, formation of beamlets and of a thin cur-
rent sheet in the magnetotail, or large scale filtering due to the finite width of
the magnetosphere with respect to the ion Larmor radius. We show that ions
are rapidly transported and energized within Mercury's magnetosphere, with
possibly significant recycling of planetary material. The occurrence of reconnec-
tion in the magnetotail however, may substantially alter the global convection
pattern, and cause enhanced down-stream losses. We demonstrate that large
non-adiabatic energization may be achieved for electrons as well, in particular
during presumed expansion phases of substorms which lead to short-lived pre-
cipitation onto the planet surface and formation of bouncing electron clusters.
1. Introduction
Mariner-10 observations in 1974-1975 revealed an intrinsic magnetic field at
Mercury, with a reduced (by about 2 orders of magnitude) dipolar moment
as compared to that of Earth. The spatial and temporal scales of the result-
ing magnetosphere differ widely from those of the terrestrial one (by factors
of
30, respectively). The actual structure of Mercury's magneto-
sphere (in particular, the existence of large-scale plasma cells such as lobes,
plasma sheet or boundary layers) remains to be elucidated. Also, it is not
known if and to which amount ions originating from the planetary exosphere
contribute to the magnetospheric populations as is the case for ionospheric
ions at Earth. Although it is expected that the magnetopause is frequently
(up to 30% of the time) blown down to the planet surface due to enhanced
solar wind pressure, it is neither known whether the solar wind forms a
∼
7and
∼
17
