Saturn's atmosphere, infrared Cassini image. Close up of the swirling clouds on Saturn's banded planetary surface. The banded appearance of the planet is caused by the variation in composition of clouds in its atmosphere. Saturn is a gas giant, where its primary constituent is not rock or liquid, but gas. This means that its surface is not well-defined, except for the atmospheric gases becoming more dense the closer they are to the planet's core. The Cassini-Huygens spacecraft was launched in 1997 to investigate Saturn, its rings and its moons. This image was obtained using Cassini's wide-angle camera on 19th August 2005, at a distance of approximately 492 thousand kilometres from Saturn.