Observations of electromagnetically coupled dust in the Jovian magnetosphere

Abstract

We report on dust measurements obtained during the seventh orbit of the Galileo spacecraft about Jupiter. %which had a close flyby at Ganymede. The most prominent features observed are highly time variable dust streams recorded throughout the Jovian system. The impact rate varied by more than an order of magnitude with a 5 and 10 hour periodicity, which shows a correlation with Galileo's position relative to the Jovian magnetic field. This behavior can be qualitatively explained by strong coupling of nanometer-sized dust to the Jovian magnetic field. In addition to the 5 and 10 h periodicities, a longer period which is compatible with Io's orbital period is evident in the dust impact rate. This feature indicates that Io most likely is the source of the dust streams. During a close (3,095 km altitude) flyby at Ganymede on 5 April 1997 an enhanced rate of dust impacts has been observed, which suggests that Ganymede is a source of ejecta particles. Within a distance of about 25 $\rm R_J$ (Jupiter radius, $\rm R_J = 71,492$ km) from Jupiter impacts of micrometer-sized particles have been recorded which could be particles on bound orbits about Jupiter.