Effects of solar transients observed in the VLISM

The plasma wave instruments on both Voyager spacecraft have observed electron plasma oscillations in the very local interstellar medium (VLISM).  The generally accepted explanation of these events is that the electron foreshock of shocks in the VLISM comprise electron beams in the range of 10 to 100 eV that are unstable to Langmuir waves, or electron plasma oscillations.  Further, at least some of these events have been tied to solar transients departing the Sun more than a year earlier that evolve as they propagate outward.  These disturbances are led by shocks and the impulse of these on the heliospause results in some of the shock impulse continuing into the VLISM.  Previously, Voyager 1 had detected the most distant evidence of these transients at about 145 AU.  In August 2025 Voyager 2 detected electron plasma oscillations near 140 AU. A simple model of the propagation of this disturbance suggests a transient from the Sun in 2022 as its source, near the beginning of the current solar maximum.  New Horizons observed a series of shocks in 2022 – 2023 at heliocentric distances near 55 AU that could be related to the Voyager 2 event. Given these events occur early in solar cycle 25, it is possible additional shocks will be detected by Voyager and enable us to extend the distance over which these disturbances can travel in the VLISM.

We further relate some of the transients observed by the Voyager plasma wave instruments to global models of the VLISM density and magnetic field (Fraternale et al., 2026).  For example, these models show the increased density and magnetic field associated with the so-called pf2 (pressure front 2) described by Burlaga et al. (2021).  We can now show that the 2-3 kHz radio emissions observed by the Voyagers in the early 1980’s, 1990’s, and 2000’s are related to density structures just beyond the heliopause presumed to be associated with global merged interaction regions stemming from very active solar conditions.