Saturn. Artist's impression of the planet Saturn, showing its ring system and two moons. Saturn is the second largest planet in the solar system and is usually visible to the naked eye as a bright star. The planet has by far the most visible ring system, which has intrigued astronomers since the invention of the telescope. The rings are disc-like aggregates of small rocky and icy particles. The planet itself is a 'gas giant', its visible 'surface' consisting of turbulent clouds. The Voyager spacecraft missions revealed complex structures in the rings such as 'spokes' and 'braids'. A further spacecraft, Cassini, is due to visit the Saturnian system in 2004.