THE STRUCTURE AND DYNAMICS OF JUPITER RING

JUPITER'S ring has posed a problem since it was first discovered 15 ye ars ago. Its inner edge flares into a torus, the shape of which has no t yet been accurately modelled, although it was recognized early (1-3) that electromagnetic effects might be important in determining the sp atial and size distribution of the dust particles comprising the ring. These early models suggested that sulphur and oxygen ions dominate th e plasma environment of the ring; as these ions diffuse inwards from I o, they produce negatively charged dust grains in the ring. Here we pr opose that Jupiter's ionosphere is the dominant source of plasma and t hat the low plasma density allows ultraviolet radiation from the Sun t o photoionize the grains, giving them a positive charge. The resulting gradient in the equilibrium charge distribution transports the grains rapidly-on surprisingly short timescales of hours to days-towards Jup iter. The brightness distribution resulting from this model matches cl osely the observed brightness distribution, suggesting that our model captures the most important processes that shape this ring.