Interstellar Dust Detected by Voyager 1 Over Heliocentric Radial Distances From 5 to 132 AU

Abstract:

The plasma wave instruments on the Voyager 1 and 2 spacecraft can detect the impact of high velocity dust particles when they strike the spacecraft body. The impacts are recognizable by a characteristic voltage pulse that they produce in the wideband electric field waveform data. Although the wideband receiver on Voyager 2 is no longer working, Voyager 1 has been collecting wideband data for over 37 years, starting near the Jupiter flyby at 5 AU and continuing to the most recent data beyond 132 AU. During this time a persistent level of dust impacts have been detected at a rate of about 3 to 7 impacts/ hour. We interpret these impacts as being due to interstellar dust. Using the cross-sectional area of the spacecraft high-gain antenna, 10.75 m², as the effective impact area, and the velocity of the spacecraft relative to the 26 km/s arrival velocity of the interstellar dust, this impact rate corresponds to a flux of about (0.75 to 1.65) x 10^-4 m^-2 s^-1. Although we do not have good knowledge of the mass of the dust particles, this flux agrees well with the interstellar dust flux published by Grün et al. [1993] from the dust detector on the Ulysses spacecraft at 5 AU. The Ulysses dust instrument showed that the mass of the interstellar dust particles ranged from about 10^-15 to 10^-10 grams (roughly 0.1 to 10 µm). We presume that Voyager 1 is detecting these same particles. The heliocentric radial variation can be fit within the error bars by a constant flux of about 1.2 x 10^-4 m^-2s^-1. However, the plot of the average count rates in 20 AU bins increases steadily from 10 to 100 AU, with a notable decrease beyond 100 AU, suggesting that there might be a slightly higher flux (by a factor of two) in the outer regions of the heliosphere than in the interstellar medium.