JUPITER’S ring has posed a problem since it was first discovered 15 years ago. Its inner edge flares into a torus, the shape of which has not yet been accurately modelled, although it was recognized early (1-3) that electromagnetic effects might be important in determining the spatial and size distribution of the dust particles comprising the ring. These early models suggested that sulphur and oxygen ions dominate the plasma environment of the ring; as these ions diffuse inwards from Io, they produce negatively charged dust grains in the ring. Here we propose that Jupiter’s ionosphere is the dominant source of plasma and that the low plasma density allows ultraviolet radiation from the Sun to 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 Jupiter. The brightness distribution resulting from this model matches closely the observed brightness distribution, suggesting that our model captures the most important processes that shape this ring.