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Shocks in the Very Local Interstellar Medium
Abstract Large-scale disturbances generated by the Sun’s dynamics first propagate through the heliosphere, influence the heliosphere’s outer boundaries, and then traverse and modify the very local interstellar medium (VLISM). The existence of shocks in the VLISM was initially suggested by Voyager observations of the 2-3 kHz radio emissions in the heliosphere. A couple of decades later, both Voyagers crossed the definitive edge of our heliosphere and became the first ever spacecraft to sample interstellar space. Since Voyager 1’s entrance into the VLISM, it sampled electron plasma oscillation events that indirectly measure the medium’s density, increasing as it moves further away from the heliopause. Some of the observed electron oscillation events in the VLISM were associated with the local heliospheric shock waves. The observed VLISM shocks were very different than heliospheric shocks. They were very weak and broad, and the usual dissipation via wave-particle interactions could not explain their structure. Estimates of the dissipation associated with the collisionality show that collisions can determine the VLISM shock structure. According to theory and models, the existence of a bow shock or wave in front of our heliosphere is still an open question as there are no direct observations yet. This paper reviews the outstanding more »
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Publication Date:
NSF-PAR ID:
10392983
Journal Name:
Space Science Reviews
Volume:
218
Issue:
4
ISSN:
0038-6308
5. Voyager 1 (V1) has been exploring the heliospheric boundary layer in the very local interstellar medium (VLISM) since August 2012. This study presents a broadband multi-scale analysis of VLSIM magnetic turbulence between 124 and 144 au from the Sun, as observed by V1 during the period from 2013.36 to 2019.0. We use high resolution 48-s data and show the existence of physically relevant fluctuations on scales as small as the ion inertial length in the thermal plasma. In the fine-scale regime below $\sim 10^{-3}$ au, an evidence is provided of the intermittent turbulence cascade which retains a significant level of magnetic compressibility. Observed fluctuations are compatible with the presence of filamentary structures and sawtooth-like waveforms of mixed compressible/transverse nature. A striking example of small-scale enhanced turbulence (wavelengths in the range of $\sim 1-10^3$ ion inertial lengths) is observed in front of the shock wave that overtook V1 on DOY 237, 2014 at 140 au from the Sun. This event starts on DOY 178, 2014, and suggests the presence of an ion foreshock. Besides, small-scale intermittency has been growing smoothly since 2018.5. Our analysis suggests that local processes are contributing to the production of turbulence in this regime. We identified themore »