The plasma environments of Mars and Titan have been studied by means of a3-D hybrid simulation code, treating the electrons as amassless, charge-neutralizing fluid, whereas iondynamics are covered by akinetic approach. As neither Mars nor Titan possesses a significant intrinsicmagnetic field, the upstream plasma flow interacts directly with theplanetary ionosphere. The characteristicfeatures of the interaction regionare determined as a function of the alfvénic, sonic and magnetosonic Machnumber of the impinging plasma. For the Martian interaction withthe solar wind as well as for the case of Titan being located outside Saturn'smagnetosphere in times of high solar wind dynamic pressure, all three Machnumbers are larger than 1. In such a scenario, the interactiongives rise to aso-called Ion Composition Boundary, separating the ionospheric plasma from theambient flow and being highly asymmetric with respect to the direction of theconvective electric field. The formation of these features is explained byanalyzing the Lorentz forces acting on ionospheric and ambient plasmaparticles. Titan's plasma environment is highly variable and allowsvarious different combinations of the three Mach numbers. Therefore, theIon Composition Boundary may vanish under certain circumstances.The relevant physicalmechanism is illustrated as a function of the Mach numbers in the upstreamplasma flow.
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