50 years of Interstellar Dust Measurements from Voyager

The Plasma Wave Subsystem (PWS) onboard the Voyager spacecraft have continuously recorded dust impacts over the past ~50 years, from the inner solar system to the very local interstellar medium. Not originally intended for this measurement, PWS detects a large surge in voltage when a dust particle impacts the spacecraft body, is vaporized and ionized, and becomes an expanding cloud of charge which is measured by the electric field antenna. While Voyager 2 lost the ability to measure dust impacts after it experienced a waveform receiver failure around 60 AU, Voyager 1 has recorded impacts along its entire trajectory. Dust impacts are very characteristic within the waveform data and can be automatically selected, although a human-in-the-loop method needs to be used to verify each dust impact signal. The rate of dust impacts has varied throughout the Voyager 1 flight. At a radial distance of 30 AU, Voyager 1 measured dust at a rate of 3 +/- 1 impacts per hour. At 70 AU, that increased to a peak of 6 +/- 3 impacts per hour, then started to fall off again after passing the Termination Shock and again after crossing the Heliopause. The last group of measurements showed impact rates of about 3 +/- 2 per hour. Converting to flux units gives values in the range of what Ulysses obtained for interstellar dust, indicating the Voyager impacts are of the same origin. We present the full set of dust impact measurements as well as compare with New Horizons measurements over radial distance and model simulations that utilize different dust grain size distributions to bring more insight to the Voyager dust data set.