Detecting nanoparticles at radio frequencies: Jovian dust stream impacts on Cassini/RPWS

Abstract

We analyse wave observations by the Cassini/RPWS instrument performed during the Jovian fly-by, when the on-board dust analyser recorded dust streams which were interpreted as nanoparticles moving at about the solar wind speed. The observed wave pulses are produced by ionisation of dust grains impacting the spacecraft. Nanoparticles are detected because they move fast and the voltage produced by impact ionisation increases very fast with speed, so that they produce wave pulses as high as do much larger grains of smaller speeds. The observed wave level and spectral shape are compatible with those expected for the streams deduced from the dust analyser observations, and the impact rates observed on both instruments appear to vary similarly. The present result is the first wave detection simultaneous with a conventional detection by a dust analyser attributed to nanoparticles.