Saturn's rings. This is a simulated image based on data from the Cassini spacecraft. The rings are colour-coded by particle size: green regions contain particles smaller than five centimetres across, and purple regions do not contain particles this small. All regions of the ring contain particles up to several metres across. The broad white band in the B ring is too dense for particle sizes to be determined. To record these data, the Cassini spacecraft was positioned so that the rings lay between it and Earth. It then sent radio signals at three frequencies through them, and the signal change was used to calculate particle size. This was done on 3rd May 2005.