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)

The interaction between the solar wind (SW) and the local interstellar medium (LISM) involves a complex range of particle populations, energy distributions, and spatial scales. Capturing the global structure of this interaction, interpreting near-Earth observations, and probing the properties of the pristine LISM at thousands of au requires sophisticated, multi-component models.

The outer heliosheath (OHS) is characterized by large-scale gradients in plasma and neutral atoms, along with significant compressible perturbations driven by heliopause motion. Unique in situ measurements from the Voyager spacecraft offer rare insights into this region. Notably, in mid-2020 around 150 au, Voyager 1 (V1) detected a sudden increase in magnetic field strength—likely a shock or pressure front. Unlike previously observed GMIR-driven shocks, which display a typical jump-ramp profile, this event exhibited a distinct ‘hump’-like structure and a sustained magnetic field enhancement that has persisted to this day. Existing models have struggled to reproduce this feature, prompting new hypotheses.

Using data-driven MHD simulations, we show that V1 observations can be explained by a combination of solar cycle-driven outward motion of the heliopause generating a large-scale compressed region and pressure front; finer-scale compressible waves catching up from behind; and the influence of unperturbed LISM conditions.

Accurately interpreting such in situ data is also essential for constraining the unmeasured properties of the unperturbed LISM. This requires kinetic modeling of neutral hydrogen and helium atoms. We present our latest 3D MHD-plasma/kinetic-neutrals model, which treats pickup protons, electrons, and both singly and doubly charged helium ions as separate, self-consistently coupled fluids. These populations interact via six charge-exchange processes and photoionization with kinetically treated H and He atoms. We describe the model’s implementation, including updated charge-exchange cross-section fits, and demonstrate its capabilities and performance. Finally, we investigate how suprathermal ion populations, when consistently incorporated into charge-exchange modeling, affect H wall structure, atom filtration, and background plasma properties.