3D multispecies MHD studies of the interaction of the ionospheres of unmagnetized solar system bodies with the solar wind or magnetospheric plasma flows.

Abstract

We used 3D multi-species MHD models to study the solar wind interaction with the ionosphere of Mars and the magnetospheric interaction with the ionospheres of Europa and Titan. Mars, Europa and Titan are all considered to be non-magnetized bodies with an atmosphere. Therefore, the global scale solar wind/magnetospheric interactions with these solar system bodies are with the ionosphere/atmosphere systems directly. We have used a higher-order Godunov-type, finite-volume, upwind method with a Cartesian grid to solve the equations. Three models were used to study the solar wind interaction with Mars. Model 1 is a two-species MHD model, which considers protons in the solar wind and the dominant heavy ions ( O+2 ) in the ionosphere, separately. Model 2 is a three-species MHD model, which also considers the other major ion species (O<super>+</super>) in the Martian ionosphere. Model 3 is a three-species MHD model with surface dipole field added to study the impact of the crustal magnetic field on the solar wind interaction with Mars. The interaction of Europa with the Jovian magnetosphere has been studied by using a two-species ideal MHD model (model 1). This model considers the upstream plasma in the Jovian magnetosphere and the molecular oxygen ions in the ionosphere of Europa, separately. We also studied the possible effect of the surface sputtering by using another two-species MHD model (model 2). A three-dimensional three-species MHD model was used to study the interaction of Titan's ionosphere and Saturn's magnetosphere. The three generic species considered are light (e.g., H<super>+</super>, H+2 ), medium (e.g., N<super>+</super>, CH+5 ), and heavy (e.g., N+2 , HCNH<super>+</super>) ion species. The major advantages of the multi-species MHD models are as follows. The use of separate ionospheric and solar wind/magnetospheric constituents allowed us to calculate the mass loading terms more accurately. However, the more important aspect of the multi-species approach is that it allows us to establish how the solar wind/magnetospheric flow affects the ionospheric flow and structure and vice versa. For example we have been able to estimate the amount of ionospheric plasma flow into the solar wind/magnetosphere. We also found that the realistic ionosphere does present a harder obstacle to the incident flow, bending the magnetic field more and creating a stronger magnetic barrier. We are also able to determine the density distributions of the major ion species in both the ionosphere and the solar wind/magnetosphere. Although non-ideal MHD effects are present, the ideal MHD models still illustrate the overall picture including the most important features which are consistent with observations.