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Ann. Geophys., 24, 1113-1135, 2006
www.ann-geophys.net/24/1113/2006/
© European Geosciences Union 2006
Plasma environment of Titan: a 3-D hybrid simulation study
S. Simon1, A. Bößwetter1, T. Bagdonat1, U. Motschmann1,2, and K.-H. Glassmeier3
1Institute for Theoretical Physics, TU Braunschweig, Germany
2Institute for Planetary Research, DLR, Berlin, Germany
3Institute for Geophysics and Extraterrestrial Physics, TU Braunschweig, Germany
Abstract. Titan possesses a dense atmosphere, consisting mainly of molecular
nitrogen. Titan's orbit is located within the Saturnian magnetosphere
most of the time, where the corotating plasma flow is
super-Alfvénic, yet subsonic and submagnetosonic. Since Titan does
not possess a significant intrinsic magnetic field, the incident
plasma interacts directly with the atmosphere and ionosphere. Due
to the characteristic length scales of the interaction region being
comparable to the ion gyroradii in the vicinity of Titan,
magnetohydrodynamic models can only offer a rough description of
Titan's interaction with the corotating magnetospheric plasma
flow. For this reason, Titan's plasma environment has been studied by
using a 3-D hybrid simulation code, treating the
electrons as a massless, charge-neutralizing fluid, whereas a
completely kinetic approach is used to cover ion dynamics. The
calculations are performed on a curvilinear simulation grid which is adapted
to the spherical geometry of the obstacle. In the model,
Titan's dayside ionosphere is mainly generated by solar UV radiation; hence,
the local ion production rate depends on the solar zenith
angle. Because the Titan interaction features the possibility of
having the densest ionosphere located on a face not aligned with the
ram flow of the magnetospheric plasma, a variety of different
scenarios can be studied. The simulations show the formation of a
strong magnetic draping pattern and an extended pick-up region, being
highly asymmetric with respect to the direction of the convective
electric field. In general, the mechanism giving rise to these structures
exhibits similarities to the interaction of the ionospheres of
Mars and Venus with the supersonic solar wind. The simulation results are in
agreement with data from recent Cassini flybys.
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