Frequency range of dust detection in space with radio and plasma wave receivers: Theory and application to interplanetary nanodust impacts on Cassini

Abstract

Abstract Wave instruments can detect dust in space via the charges released by impact ionization of fast dust grains. Each hypervelocity dust impact produces an electrostatic pulse whose short risetime is a major property determining the frequency range of detection. We propose a simplified analytical model to calculate this risetime and its variation with grains' mass and photoelectron or ambient plasma density, for pulses in spacecraft potential due to fast interplanetary nanodust impacts. We test these calculations by analyzing the high‐frequency receiver data of the radio and plasma wave instrument during the cruise phase of the Cassini mission between Earth and Jupiter. These data confirm the dependence of the risetime on grains' mass and speed and heliocentric distance predicted by our calculations. Furthermore, the data show that the nanodust properties follow closely the fluctuations of the solar wind velocity component perpendicular to the magnetic field, as predicted by dynamics. The calculations can be generalized to microdust detection on other spacecraft and might explain previous observations left uninterpreted. These calculations are also relevant for the design of wave receivers, by determining the optimal frequency range for dust detection on future missions.