Saturn's rings. Optical (top) and radio data (bottom) images of Saturn's rings from the Cassini spacecraft. The optical view shows the colours of the rings, which vary from grey to cream to white. The radio data were obtained by sending radio signals through the rings to Earth. Measurement of the changes in the signals allowed particle size in the rings to be calculated. The outer rings (right) contain smaller particles than the inner rings. The radio measurements were made on 3rd May 2005.