Authors: G.P. Zank (Department of Space Science and Center for Space Plasma and Aeronomic Research (CSPAR), The University of Alabama in Huntsville), Lingling Zhao (Department of Space Science and Center for Space Plasma and Aeronomic Research (CSPAR), The University of Alabama in Huntsville), and M. Nakanotani (Department of Space Science and Center for Space Plasma and Aeronomic Research (CSPAR), The University of Alabama in Huntsville)

The Very Local Interstellar Medium (VLISM) is that part of the interstellar medium bordering the heliopause (HP) that is influenced by solar heliospheric processes (Zank 2015). These processes include the deposition of fast and/or hot H atoms of supersonic and subsonic solar wind origin and the subsequent creation of solar pickup ions (PUIs) and the transmission of solar shock waves across the HP and their later propagation into the ISM. While both of these were predicted (Zank et al 1996, Zank & Mueller, 2003), the unexpected observation of highly compressible VLISM turbulence within 10 au upwind of the HP (Burlaga et al 2015) and its subsequent absence and replacement with incompressible turbulence some > 20 au beyond the HP (Burlaga et al 2018) was not predicted. The inner heliosheath is comprised almost equally by incompressible Alfvenic and compressible fast magnetosonic modes (Burlaga et al 2006, Richardson & Burlaga 2013, Fraternale et al 2019, Zhao et al 2019, 2024). Zank et al 2017 showed that fast compressible mode turbulence can be transmitted across the HP but not Alfvenic turbulence to generate compressible turbulence immediately upwind of the HP. Zank et al 2019 further showed that mode conversion in the low plasma beta VLISM was responsible for producing the incompressible turbulence observed further from the HP by Voyager 1. This was further confirmed by the analysis of Zhao et al 2020 and Fraternale et al 2019 and Burlaga et al 2022 reported strikingly similar results for the Voyager 2 observations in the VLISM. In this presentation, we will review the existing theoretical models and extensions to explain VLISM turbulence and relate it to current observational studies using Voyager 1 & 2 data.