2021/05/10 by Stella Koch Ocker, S. K. Ocker, J. M. Cordes +10 · 1 citation
Physics and Astronomy · #Astrophysics and Star Formation Studies #Ionosphere and magnetosphere dynamics #Solar and Space Plasma Dynamics #astro-ph.EP #astro-ph.GA #physics.plasm-ph #physics.space-ph
paper · pdf · doi:10.1038/s41550-021-01363-7
This is a preprint of an article published in Nature Astronomy. The final authenticated version is available online at: https://doi.org/10.1038/s41550-021-01363-7
crossref issued 2021/05/10 · crossref published 2021/05/10 · crossref published-online 2021/05/10 · openalex publication_date 2021/05/10 · crossref created 2021/05/10 · openalex created_date 2021/05/24 · arxiv created 2021/12/13 · arxiv updated 2021/12/14 · crossref deposited 2022/12/02 · crossref indexed 2026/07/24 · openalex updated_date 2026/08/05
In 2012, Voyager 1 became the first in situ probe of the very local interstellar medium. The Voyager 1 Plasma Wave System has given point estimates of the plasma density spanning about 30 astronomical units (au) of interstellar space, revealing a large-scale density gradient and compressive turbulence outside the heliopause. Previous studies of the plasma density relied exclusively on the detection of discrete plasma oscillation events that are triggered ahead of shocks propagating outwards from the Sun, which were used to infer the plasma frequency and hence density. We present the detection of a class of very weak, narrowband plasma wave emission in the Voyager 1 Plasma Wave System data that persists from 2017 onwards and enables a steadily sampled measurement of the interstellar plasma density over about 10 au with an average sampling time of 3 days, or 0.03 au. We find au-scale density fluctuations that trace turbulence in the interstellar medium between episodes of previously detected plasma oscillations. Possible mechanisms for the narrowband emission include thermally excited plasma oscillations and quasi-thermal noise, and could be clarified by new findings from Voyager or a future interstellar mission. The persistence of the emission suggests that Voyager 1 may be able to continue tracking the interstellar plasma density in the absence of shock-generated plasma oscillation events.