Saturn is the sixth closest planet to the Sun. It is the second largest planet in the solar system having a radius 9 times that of Earth (57,000 km) and a mass 95 times that of Earth.
Saturn orbits the Sun once very 29 years (at about 1400 million km) and is mainly comprised of gas (96% hydrogen and 3% helium) and is presumed to have a rocky core surrounded by a sea of liquid metallic hydrogen which forms a ball some 56,000km in diameter. The upper layers are thought to comprise of liquid water, ammonium hydrosulfide, hydrogen and helium.
Saturn's core is quite hot (11,700 degrees C) and it generates more heat than it receives from the Sun. The further from the planets centre, the less the temperature with the temperature reaching around -180 degrees in the upper atmosphere, and 0 degrees C at around 350km deep.
The cloud layers of Saturn are similar to those of Jupiter except that the banding is weaker and wider. Saturn also has a short lived but periodical storm called the great white spot which seems to occur every Saturnian year.
Saturn rotates at around 10 hours 39 minutes. The precise figure (like that of all gas giants) is not certain since there are several ways of measuring the rotation of a body which has no fixed visual references.
Saturn is of course best known for its ring system. These were first seen by Galileo Galilei in 1610 who, quite understandably, was confused by them and thought Saturn was being accompanied by two other planets which sat either side of it. In 1655 Christian Huygens using an improved telescope was able to see enough detail to suggest that there was a ring around Saturn.
The rings extend from 7000km to 120,000km above the surface of Saturn. Incredibly, they are estimated at being between 1 km to 10 meters thick comprising of mainly ice particles ranging in size from dust to boulders a few meters across. The gaps in the rings are caused by the gravitational effects of Saturn's moons, and also by larger "moonlets" which inhabit the rings causing particles to be nudged into banded orbits. Recent observations have discovered that there are some distortions in the rings causing particles to rise some 4km out of the normal ring plane due to the tilted orbit of certain moons. The rings are thought to be either the remnants of a moon destroyed in orbit or simply by material left over by the formation of the solar system.
Moons : Titan... and the others
Saturn has 62 moons with only seven being large enough to become spherical in shape. By far the largest of all of Saturn's moons is Titan which is larger than the planet Mercury, and the second largest moon in the solar system (Jupiter’s Ganymede being the largest). Titan is 5,150 km in diameter and has a dense atmosphere of nitrogen with traces of methane. It has large lakes of liquid methane/ethane on its surface and may have a subsurface ocean of liquid water which occasionally erupts to the surface.
Great video that explores Titan.
The next largest moon to Titan is Rhea which has a diameter of 1,530km (30% Titans diameter). It is an icy body (75% ice, 25% rock) with a heavily cratered surface. The other moons of Saturn tend to have similar characteristics being comprised mainly of ice and rock and all being heavily cratered. Two notable moons include Mimas which shows an impact crater with a radius 1/3rd that of the moon, Iapetus which has remarkable colouring with one side being black as soot and the other as white as snow. This colouring is thought to be the result particles being kicked up from impacts on the moon Phoebe which lay in Iapetus's orbit. As Iapetus passed through these particles they were deposited on Iapetus's leading hemisphere causing it to darken.
Saturn and Man
Saturn is named after the Roman gods Saturnus (equivalent to the Greek god Cronus) which was the god of agricultural and harvest.
Saturn was first visited by the Pioneer 11 spacecraft in 1979 which discovered among other things additional rings in the ring system, and the moon Epimetheus which it almost (within 4000km) collided with.
The Voyager probes were the next to study Saturn with Voyager 1 taking the first high resolution images of Saturn, its rings and moons in 1980. Voyager 2 took more images in 1981 but a failure in its camera pointing ability resulted in losing some expected imagery.
In 2004 the Cassini spacecraft became the first probe to enter into orbit around Saturn releasing the Huygens probe which entered Titans atmosphere early in January 2005. The Huygens probe successfully landed on the surface of Titan sending back images and data during its descent and from the surface. Cassini has made many fly-pasts of Saturn's moons and ring systems making many new discoveries including new rings and weather systems. The Cassini spacecraft is intended to continue to study the Saturnian system until 2017 when it will be deliberately crashed into Saturn.