Spokes in Saturn´s B Ring: Could Lightning be the Cause?

Spokes are narrow markings across Saturn´s B ring, most likely caused by a cloud of micrometer-sized particles intermittently lofted from the larger boulders in the ring. They were observed by the Voyagers, the Hubble Space Telescope, and, more recently, the Cassini spacecraft in orbit around Saturn since 2004. Several explanations have been suggested over the years for the triggering and subsequent evolution of the spokes. In general, it is expected that spokes form due to sudden short-lived changes in the plasma environment of the rings. Most recently, lightning in Saturn´s atmosphere was suggested as a trigger for the spokes, based on Cassini observations of field-aligned high-energy (~100 keV) electron beams. In this paper, we examine the interaction of these beams with the ring and show that the expected amount of charge released in a lightning event could increase the surface charge density of the ring material itself to sufficiently high values to trigger spokes.