Saturn (the Roman God of Agriculture) has a diameter of 120,000 km which makes it the second largest planet in the Solar System. Although this isn't quite as large as Jupiter, it still has a size to be reckoned with and across it's equator it could fit the Earth over nine times! Saturn is another 'Gas Giant' but, beneath the atmosphere it has an ocean of molecular liquid Hydrogen which enfolds a shell of metallic Hydrogen. A distinctive feature about Saturn is that it's shape is similar to that of a squashed football; it's flattened at the poles. This is because the planet spins so fast that the centrifugal force makes the equator bulge outwards.

Saturn's Rings

    The most famous feature about Saturn is the series of rings which encircle it. They were first spotted in 1610 by the great Italian astronomer Galileo Galilei, who was mistified as to why Saturn had two 'cup holders' on either side of it. It wasn't until a few decades later, in 1659, that Christiaan Huygens (a Dutch astronomer) discovered that they were seperate from the planet, and must therefore be encircling it. Just 16 years later Cassini discovered the Cassini division. Subsequently it has been found that there are actually many rings around Saturn and that they are made of rock and ice. The rings are quite insubstantial; at at some points they may be only 1km thick! However, the overall effect made by all of these small rocks around Saturn is quite astonishing, and unique on this scale in our Solar System.

    As you can see from the pictures, the rings themselves surround the planet totally and form a circle hundreds of thousands of kilometres in diameter. Indeed they stretch just about the same distance as the Moon is from the Earth. The rocks that form the rings are found to range in diameter from mere micrometres (1 micrometer = 0.000001 metre) to tens of metres.

Magnetic field

    As with the other Jovian planets, Saturn has a strong magnetic field - 1,000 times stronger than Earth's in fact. Its magnetosphere encompasses the entire ring system, as well as most of its known satellites. In fact, the Hubble Space Telescope has shown that Saturn has aurorae (or Northern & Southern Lights) similar to those visible on Earth, where charged particles from the Solar Wind become trapped by a planet's magnetic field and collide with molecules of the planet's atmosphere, above the poles.

Atmosphere & Core

    Saturn's atmosphere is a bit like Jupiter's except that it is colder and the cloud layers are thicker. The bands which are very visible on Jupiter are however fainter on Saturn, and have a tendancy to get wider in the equatorial regions. Like Jupiter, it also seems to have big oval-shaped storms raging in its atmosphere, though none on the scale of Jupiter's Great Red Spot.

    The core of Saturn is thought to be very similar to that of Jupiter, so small and rocky, and surrounded by a layer of liquid metallic Hydrogen, and a molecular Hydrogen layer. In addition to the Hydrogen and Helium which are the main ingredients in Saturn's atmosphere, there are also traces of water, methane and ammonia. In the core, there are traces of various ices.

    One notable feature of Saturn is that its core is thought to be at around 12,000°K, and it actually radiates more energy than it recieves from the Sun. This is most likely due to the same process of gravitational compression present in Jupiter, which provide the planet with heat. Around the equator winds sweep about at an impressive 1,800 km/h. It is not a particularly dense planet either, the mass is so spread out that on average it's less dense than water!

Moons

    Saturn has over 30 satellites, plus probably others as yet undiscovered. Saturn's first 22 moons are : Pan, Atlas, Prometheus, Pandora, Epimitheus, Janus, Mimas, Enceladus, Thethys, Telesto, Calypso, Dione, Helene, Rhea, Titan, Hyperion, Iapetus and Phoebe and 4 other out moons. The most important one is Titan and scientists hope to find out what the Earth was like long ago through studying it. It's also a rather large moon, being bigger than Mercury. Titan is the only moon in the Solar System to have an atmosphere. Scientists recently discovered day clouds on Titan and this adds to substantial evidence suggesting it has clouds, rain and seas like Earth.

    This is an exciting time for Saturn research, for at the time of writing the Cassini-Huygens mission is heading towards Saturn and its moon Titan. This mission, a joint European Space Agency, Italian Space Agency and NASA one, includes the most sophisticated and complete space probe ever sent to a distant planet, the final of the major spacecraft before NASA's 'cheaper, faster, better' philosophy kicked in. The mission consists of 2 parts - the Cassini orbiter will orbit Saturn for at least 4 years, whilst the European-built Huygens probe will be dropped into the atmosphere of Titan, and will perhaps even land on it.

    Galileo Galilei discovered Saturn's rings in 1610 and it was in 1659 that Chistiaans Huygens realised they weren't physically attatched to Saturn. Then in 1676 Italian-French astronomer Jean Dominique Cassini discovered the Cassini division in the rings. The first pictures of Saturn's polar regions were taken in 1979 by the Pioneer 11 and a year later, in 1980, Voyager (the probe, not the Star Trek starship) took 17,500 colour pictures of the planet, measured wind speeds in Saturn's equatorial region and measured Titan's size. Voyager 2 passed even closer than Voyager in 1981. On the 15th October 1997 the Cassini spacecraft was launched towards Saturn and it's expected to arrive in 2004. For loads of really exciting information and updates on the mission go to the NASA Cassini site.