Saturn, Cassini infrared image. This view is of a region of Saturn's northern hemisphere. A section of the rings (blue) is visible at upper left. 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 5th April 2007, at a distance of approximately 1.4 million kilometres from Saturn.