The interaction between the solar wind (SW) and the local interstellar medium (LISM) determines the heliosphere’s structure and global properties. Observational data and models indicate that the very local interstellar medium (VLISM) – the portion of LISM affected by the presence of the heliosphere – is highly dynamic. The region of space in front of the heliopause (HP) occupied by the VLISM is also known as the outer heliosheath (OHS).
The VLISM is partially ionized, multi-species, and collisional with respect to Coulomb collisions on scales larger than a few AU. Charge-exchange processes are fundamental in the OHS where they slow down the interstellar atoms and produce secondary ions that are quickly decelerated, creating a region of compressed plasma, draped interstellar magnetic fields (ISMF), and hydrogen and helium walls. Charge exchange and elastic collisions couple neutrals and ions, thereby setting the fundamental spatial and temporal scales of this system. The solar cycle sets a large-scale periodicity in the system, whereas a compressible turbulence cascade exists down to kinetic scales. The Voyagers (V1, V2) have been sampling the VLISM plasma since their crossing of the HP (2012/121 AU, 2018/119 AU for V1 and V2, respectively). In situ Voyager data continue to prompt new theoretical studies and lay out critical challenges for modeling and simulations.
This proposal addresses critical open questions about the physics of shocks, turbulence, the properties of electrons and associated plasma oscillations and radio emissions in the VLISM. The Voyagers have observed all of these interrelated phenomena, but the relationship between their underlying physical mechanisms and the global structure of the heliosphere remains poorly understood.
Our Team to investigate the origin, properties, and evolution of shocks, turbulence, kinetic instabilities, particle distribution functions, plasma oscillations, and radio emission in the OHS by means of theoretical models, numerical simulations, and new analysis of Voyager/PWS/MAG data.