Geoscience Reference
In-Depth Information
THREE-DIMENSIONAL MHD SIMULATION
OF THE SOLAR WIND INTERACTION WITH COMETS
MEHDI BENNA
∗
and PAUL R. MAHAFFY
NASA — Goddard Space Flight Center, code 699
8800 Greenbelt Road, Greenbelt, MD 20771, USA
∗
mehdi.benna@gsfc.nasa.gov
A three-dimensional multi-fluid magnetohydronamic model of the interaction of
a cometary coma with the solar wind has been applied to an active Halley-class
gas source. The model includes both photo and electron impact ionization, ion
recombination, elastic collisions, Coulomb ion/electron interactions, cooling of
electrons by water vapor, and the coupling with the magnetic field. Heavy and
light ions are treated separately, as necessary. An adaptive mesh refinement
is employed to model both near-nucleus kilometer scale phenomena and the
much larger structures of the bow shock and the coma tail. With 5.8 million
computational cells and 25 levels of refinement, the structures in both the
inner coma (within 20,000 km from the nucleus) and in the outer coma were
satisfactorily resolved. The model output includes ion density, velocity, tem-
perature, and pressure, electron and neutral temperatures, and magnetic fields.
This model is compared to previous simulations and to the location of major
plasma boundaries from the 1986 Halley flyby missions. There is satisfactory
agreement from this model with the available mission data in features of the
plasma structure such as the location of the bow shock, the inner shock, and
the mass loading.
1. Introduction
Mass loading is a very common phenomenon in space plasmas. In the case
of comets, mass loading controls the structure and the dynamic of the inter-
action between the solar wind and the cometary atmosphere. During the
past decade some of the most sophisticated magnetohydrodynamic (MHD)
numerical simulations have been carried out to study the dynamics of the
solar wind comet atmosphere interaction and its mass-loading phenomena.
The article of Szego
et al.
1
provides an excellent review of mass-loading
phenomenon and their underling physics. We refer the reader to the papers
of Schmidt
et al.
2
and Gombosi
et al.
3
for cometary applications of mass-
loaded plasmas.
∗
Corresponding author.
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