Flight through Saturn磗 rings. The planet Saturn is encircled by an extensive system of rings, composed of small particles of water ice up to a few metres across at most. The main ring system has a diameter of some 270,000 kilometres 136,000 kilometres from the centre of the planet, although fainter, more diffuse rings extend much further out. Despite their great extent, the rings are extremely thin _ even the thickest ring is less than 30 metres deep, and many regions are thinner than that. One effect of this is that the rings are invisible when they are edge_on to Earth. The formation of the rings is not fully understood. It is thought that they are the remains of an icy moon that was either ripped apart by tidal forces, or destroyed in a collision with another body.