Abstract
Abstract. The interaction between Titan's ionosphere and the Saturnian magnetospheric plasma flow has been studied by means of a three-dimensional (3-D) hybrid simulation code. In the hybrid model, the electrons form a mass-less, charge-neutralizing fluid, whereas a completely kinetic approach is retained to describe ion dynamics. The model includes up to three ionospheric and two magnetospheric ion species. The interaction gives rise to a pronounced magnetic draping pattern and an ionospheric tail that is highly asymmetric with respect to the direction of the convective electric field. Due to the dependence of the ion gyroradii on the ion mass, ions of different masses become spatially dispersed in the tail region. Therefore, Titan's ionospheric tail may be considered a mass-spectrometer, allowing to distinguish between ion species of different masses. The kinetic nature of this effect is emphasized by comparing the simulation with the results obtained from a simple analytical test-particle model of the pick-up process. Besides, the results clearly illustrate the necessity of taking into account the multi-species nature of the magnetospheric plasma flow in the vicinity of Titan. On the one hand, heavy magnetospheric particles, such as atomic Nitrogen or Oxygen, experience only a slight modification of their flow pattern. On the other hand, light ionospheric ions, e.g. atomic Hydrogen, are clearly deflected around the obstacle, yielding a widening of the magnetic draping pattern perpendicular to the flow direction. The simulation results clearly indicate that the nature of this interaction process, especially the formation of sharply pronounced plasma boundaries in the vicinity of Titan, is extremely sensitive to both the temperature of the magnetospheric ions and the orientation of Titan's dayside ionosphere with respect to the corotating magnetospheric plasma flow.
Highlights
In the year 2004, ESA and NASA scientists celebrated the arrival of the Cassini spacecraft in the Saturnian system, marking the beginning of an extensive exploration of the giant planet and its complex system of rings and satellites
In agreement with the hybrid simulation results, it is illustrated that light Hydrogen ions are confined to the magnetospheric plasma flow wake directly beyond Titan, whereas the heavier ions move on cycloidal trajectories in Titan’s equatorial plane, the extension of the cyloids in the direction of the convective electric field depending on their masses
The main objective of the work presented in this paper is the study of the interaction between the multi-species Saturnian magnetospheric plasma flow and the multi-component ionosphere of Titan
Summary
In the year 2004, ESA and NASA scientists celebrated the arrival of the Cassini spacecraft in the Saturnian system, marking the beginning of an extensive exploration of the giant planet and its complex system of rings and satellites. Numerous ionospheric models, especially those designed by Keller et al (1992, 1994, 1998), Keller and Cravens (1994), and Cravens et al (2006) clearly illustrate that Titan’s ionosphere exhibits a complex ion chemistry and that interaction processes between different species make up a major feature of this region. These aspects can be taken into account by magnetohydrodynamic models of Titan’s plasma environment (cf Ma et al, 2004, 2006; Backes et al, 2005; Backes, 2005). The applicability of the different simulation approaches to the plasma environment of Titan will be analyzed in an extensive comparative discussion
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