Authors: Federico Fraternale (The University of Alabama in Huntsville, Center for Space Plasma and Aeronomic Research), Nikolai V. Pogorelov (The University of Alabama in Huntsville, Center for Space Plasma and Aeronomic Research and Department of Space Science), Ratan K. Bera (The University of Alabama in Huntsville, Center for Space Plasma and Aeronomic Research)

This paper presents recent advancements in modeling the interaction between the solar wind (SW) and the local interstellar medium (LISM). Global modeling is necessary to interpret spacecraft observations of plasma and neutral atoms, considering the complex nature of this interaction at different scales. We present results from both multi-fluid and kinetic approaches for neutral atom description. Our updated MHD-plasma/kinetic neutrals model incorporates both hydrogen and helium atoms and ions, along with distinct electron fluid. Including helium significantly impacts the parameters of interstellar neutral hydrogen and protons, leading to significant influences on plasma and neutral atom distributions in SW regions. Furthermore, we conduct extensive hybrid simulations to examine the behavior of pick-up ions (PUIs) at the heliospheric termination shock (TS), where they experience preferential heating and acceleration. Describing the crossing of PUIs through the TS using fluid (MHD) models is highly inaccurate. Substantial improvement in modeling the SW-LISM interaction can be achieved by specifying kinetically-derived boundary conditions throughout the TS. These boundary conditions should be determined on the MHD scale, where the ion distribution function becomes nearly isotropic. We incorporate these boundary conditions consistently into the multi-fluid version of our model, solving conservation-law equations for the plasma mixture. We validate the results using data from New Horizons and Voyager and compare them with other existing approaches. Additionally, we present the first time-dependent simulation of the solar cycle using the new model, confirming the validity of the comet-like shape of the global heliosphere. Our findings and models are crucial for interpreting data from IBEX and future IMAP missions, including energetic neutral atoms (ENAs).