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Abstract

Multi-ion plasma is ubiquitous in the Solar System, in the heliosphere, and in the Universe in general. However, classical MHD theory fails to describe the microstructure and dynamics of multi-ion shocks. Consequently, more sophisticated physical models, like multi-fluid, hybrid or fully kinetic models are needed to capture nonlinear waves and dispersive shock waves in multi-ion plasma. In this talk, we present multi-fluid simulations of the Martian bow shock with planetary pickup protons, interplanetary shocks and the heliospheric termination shock with interstellar pickup ions, and the solar bow shock in the Local Interstellar Medium (LISM) with interstellar H⁺ and He⁺ ions. We validate the simulations with MAVEN solar wind data, New Horizons solar wind and pickup ion observations, and Voyager 2 magnetic field and solar wind plasma observations, respectively. We find that the Martian bow shock is subcritical and the shock structure is produced by a magnetosonic soliton. We compare our multi-fluid simulation of the termination shock with hybrid and PIC simulations and conclude that it is a subcritical dispersive shock wave where the shock structure is dominated by wave dispersion rather than kinetic effects, like ion reflection. We show that oblique shocks in the solar wind give rise to differential flow between solar wind ions and pickup ions downstream of shocks. We demonstrate that stream-stream interactions produce both shocks and rarefaction waves in the distant solar wind. Finally, we suggest that both a slow magnetosonic proton shock and a helium shock may exist ahead of the heliosphere in the LISM.