Density (g/cm³) - 0.69 g/cm³,

Saturn is the least dense of the planets; its specific gravity (0.7) is less than that of water. The internal structure of Saturn is belived to be similar to that of Jupiter and the other gaseous planets. A thin outer envelope of clouds covers a thick layer of hydrogen, which increases in density downward. A significant boundary is believed to exist at a depth of 30,000 km, where molecular liquid hydrogen converts to metallic liquid hydrogen. The core of Saturn may consist of ice and silicate rock at such a high temperature that it may be in a liquid state. Saturn does not have a well-defined solid surface.

Saturn is a large gas- and ice-rich planet well known for its ring system. Saturn consists principally of hydrogen and helium but appears to have an ice and rock core. The atmosphere has cloudy bands parallel to the equator and contains storms like Jupiter's but is not as colorful.

Saturn's ring system consists of many small ice particles in orbit around the planet. The rings are defined by small shepherd satellites and by resonances with larger satellites. The ice particles may be material that never accreted to form a moon or may be the result of collisions in the satellite system. Ring systems are not stable and must be regenerated by ongoing processes, probably the breakup of larger satellites.

Titan is larger than the planet Mercury and has an atmosphere rich in nitrogen. Its surface ( temperature is about 94 K) is obscured by haze but may be covered by hydrocarbons precipitated from the atmosphere. In fact, methane (natural gas) or ethane (another hydrocarbon) liquids may exist at the surface. At the surface, its pressure is more than 1.5 bar (50% higher than Earth's). It is composed primarily of molecular nitrogen (as is Earth's) with no more than 6% argon and a few percent methane. Interestingly, there are also trace amounts of at least a dozen other organic compounds (i.e. ethane, hydrogen cyanide, carbon dioxide) and water. The organics are formed as methane, which dominates in Titan's upper atmosphere, is destroyed by sunlight. The result is similar to the smog found over large cities, but much thicker. In many ways, this is similar to the conditions on Earth early in its history when life was first getting started.

Six icy satellites, ranging from 400 to 1500 km in diameter, lack atmospheres and reveal surfaces modified by impact, tectonic, and volcanic processes. Enceladus, Tethys, Dione, and perhaps Rhea had extended thermal histories, indicated by young plains. Tidal heating, particularly in the case of Enceladus may have extended the period of time over which their interiors remained warm. In addition, each of these bodies has large fractures or rifts, suggesting that each body cracked, perhaps while cooling.

Mimas and Iapetus are impact-dominated bodies. The surface of Mimas is dominated by an impact crater 130 km across, known as Herschel; it's almost 1/3 of the diameter of the entire moon. Herschel's walls are approximately 5 km high, parts of its floor measure 10 km deep, and its central peak rises 6 km above the crater floor. The impact that made this crater must have nearly disrupted Mimas. Fractures can be seen on the opposite side of Mimas that may be due to the same impact. It is possible that some of the satellites of Saturn were disrupted by collision with incoming projectiles and then reaccreted.