EJECTION OF DUST FROM JUPITER GOSSAMER RING

ONE of the most intriguing discoveries of the Ulysses mission so far h as been the detection of periodic, collimated streams of high-velocity , submicrometre-sized dust particles emanating from Jupiter1,2. To exp lain the Ulysses data, Horanyi et al. showed3 that electromagnetic for ces within Jupiter's magnetosphere can accelerate and eject small dust particles; they proposed a model in which Io is the source of the dus t, and the observed periodicity arises from a resonance between the or bital and rotational periods of Io and Jupiter respectively. Here we a rgue that the masses and velocities of the detected particles are bett er explained by an origin in Jupiter's gossamer ring. Following their ejection from the magnetosphere, the dust particles are accelerated by the interplanetary magnetic field (IMF). We find that it is the tempo ral evolution of the IMF which primarily determines the particle traje ctories, and hence which particles reach the spacecraft. Our model exp lains three main features observed in the Ulysses data: fewer streams are detected before closest approach than after, the observed periodic ity is closely related to the solar rotation period, and an extremely intense dust stream is detected immediately after closest approach.