What Does Really Happen in a Dust Impact?

Our current understanding of the solar systems micrometeoroid environment relies to a substantial extent on in-situ data acquired by impact ionization dust detectors such as Ulysses and Galileos DSS or Cassinis CDA. Such detectors derive the mass and speed of striking dust particles from the properties and evolution of the plasma created upon impact. In particular, empirical evidence suggests that the impact speed is a function of the duration of impact charge delivery onto the target - the so-called plasma rise time. Often, this dependence has been attributed to secondary impacts of target and projectile ejecta. During the recent years the capabilities of laboratory impact detectors have been significantly improved. In particular we have now ample evidence that secondary ejecta impacts are not responsible for the rise-time dependence, but is related to the ionization of target contaminants in the vicinity of the impact site. He we present new experimental data obtained with state-of the-art impact ionization mass spectrometers, which shed new light on what is really going on during a hypervelocity dust impact. We further discuss the implications for the interpretation of dust data obtained with previous generations of impact ionization detectors.