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| Titel |
Mapping of coma anisotropies to plasma structures of weak comets: a 3-D hybrid simulation study |
| VerfasserIn |
N. Gortsas, U. Motschmann, E. Kührt, J. Knollenberg, S. Simon, A. Boesswetter |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
0992-7689
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| Digitales Dokument |
URL |
| Erschienen |
In: Annales Geophysicae ; 27, no. 4 ; Nr. 27, no. 4 (2009-04-02), S.1555-1572 |
| Datensatznummer |
250016480
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| Publikation (Nr.) |
 copernicus.org/angeo-27-1555-2009.pdf |
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| Zusammenfassung |
| The effects of coma anisotropies on the plasma environment
of comets have been studied by means of a 3-D hybrid
model which treats electrons as a massless, charge-neutralizing fluid,
whereas ion dynamics are covered by a kinetic approach.
From Earth-based observations as well as from in-situ spacecraft measurements
the shape of the coma of many comets is ascertained to be anisotropic.
However, most plasma simulation studies deploy a spherically symmetric activity
pattern.
In this paper anisotropy is studied by considering three different coma shape models.
The first model is derived from the Haser model and is characterised by
spherically symmetry.
This reference model is then compared with two different neutral gas shape models:
the dayside restricted model with no nightside activity and a cone shaped
model with opening angle of π/2. In all models the
integrated surface activity is kept constant.
The simulations have been done for the Rosetta target
comet 67P/Churyumov-Gerasimenko for two heliocentric distances, 1.30 AU and 3.25 AU.
It is found that shock formation processes are modified as
a result of increasing spatial confinement. Characteristic plasma structures of comets
such as the bow shock, magnetic barrier region and the ion composition boundary
exhibit a shift towards the sun. In addition, the cone shaped model leads to a strong
increase of the mass-loaded region which in turn leads to a smooth deceleration
of the solar wind flow and an increasing degree of
mixture between the solar wind and cometary ion species.
This creates an additional transport channel of the magnetic field
from the magnetic barrier region away which in turn leads
to a broadening of this region. In addition, it leads to an ion composition
boundary which is only gradually developed. |
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