Abstract
Abstract. The plasma environments of Mars and Titan have been studied by means of a 3-D hybrid simulation code, treating the electrons as a massless, charge-neutralizing fluid, whereas ion dynamics are covered by a kinetic approach. As neither Mars nor Titan possesses a significant intrinsic magnetic field, the upstream plasma flow interacts directly with the planetary ionosphere. The characteristic features of the interaction region are determined as a function of the alfvénic, sonic and magnetosonic Mach number of the impinging plasma. For the Martian interaction with the solar wind as well as for the case of Titan being located outside Saturn's magnetosphere in times of high solar wind dynamic pressure, all three Mach numbers are larger than 1. In such a scenario, the interaction gives rise to a so-called Ion Composition Boundary, separating the ionospheric plasma from the ambient flow and being highly asymmetric with respect to the direction of the convective electric field. The formation of these features is explained by analyzing the Lorentz forces acting on ionospheric and ambient plasma particles. Titan's plasma environment is highly variable and allows various different combinations of the three Mach numbers. Therefore, the Ion Composition Boundary may vanish under certain circumstances. The relevant physical mechanism is illustrated as a function of the Mach numbers in the upstream plasma flow.
Highlights
Since neither Mars nor Titan possesses a significant intrinsic magnetic field, the ionospheres of these planets are di-rectly exposed to the ambient plasma flow (Sauer et al, 1990; Riedler et al, 1991; Acuna et al, 1998; Lundin et al, 2004; Ness et al, 1982; Neubauer et al, 1984; Backes et al, 2005)
In the case of Titan being exposed to the solar wind, it will be shown that an Ion Composition Boundary is formed in analogy to the Martian situation: the solar wind is separated from the ionospheric plasma flow, the structure of the interaction region is symmetric in a plane perpendicular to the convective electric field and exhibits a pronounced asymmetry with respect to the direction of Econv=−ui×B (Brecht et al, 2000; Simon et al, 2006b)
We investigate the mechanism leading to the disappearence of the Ion Composition Boundary by presenting a set of 3-D hybrid simulations: In our first simulation run, the alfvenic Mach number MA, the sonic Mach number MS and the magnetosonic Mach number MMS of the upstream plasma flow are all larger than 1
Summary
Since neither Mars nor Titan possesses a significant intrinsic magnetic field, the ionospheres of these planets are di-. In the case of Titan being exposed to the solar wind, it will be shown that an Ion Composition Boundary is formed in analogy to the Martian situation: the solar wind is separated from the ionospheric plasma flow, the structure of the interaction region is symmetric in a plane perpendicular to the convective electric field and exhibits a pronounced asymmetry with respect to the direction of Econv=−ui×B (Brecht et al, 2000; Simon et al, 2006b). A second simulation scenario (MA>1, MS>1, MMS
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