Introduction

Saturn is the sixth planet of the solar system, and the second largest after Jupiter. Like the rest of the gas giants, Saturn has rings, but these are by far the most spectacular in the solar system and are easily visible through a telescope from Earth. Again like the rest of the gas giants, Saturn has many moons. The picture below shows the relative sizes of all these moons, courtesy of JPL :

The Cassini-Huygens probe has sent back images of Saturn's ring moons, most notably images of craters on Pandora and Rhea, and of dark patches on Janus which may be due to impacts.

Saturn's Rings

Saturn's rings are the most spectacular planetary rings in our solar system. Composed of ice and dust particles, the structure of them is quite complicated, consisting of many smaller rings and bands. The image of them, (courtesy of NASA) shows a false colour image in which it is easy to see all the individual rings. Saturn's rings are hazardous to pass through, due to possible damage to a spacecraft, even thought the Voyager 2 probe managed it successfully. NASA's Cassini orbiter, however, also passed through without damage and has recently discovered a tiny moon orbiting in the Keeler gap between two rings (image courtesy of NASA), and its passage is creating wave-like disturbances within the rings. Pan, another moon in the Encke gap, has a similar effect.

Titan

By far the largest of Saturn's moons, Titan was the destination of the Huygens lander, launched from the Cassini orbiter. Huygens landed on the surface of Titan on January 14th 2005, and during its lifetime sent back several fascinating images via Cassini. The surface of Titan is crossed by dark channels, which scientists believe could be made by flows of liquid methane. A circular structure that is believed to be a volcano has also been discovered, suggesting that the methane content of Titan's atmosphere could well be due to eruptions rather than the presence of a 'methane sea'. The rest of Titan's atmosphere is almost exclusively nitrogen, making it a fascinating study as this atmospheric composition has similarities to that of the Earth. There is also water ice on the surface of Titan, and evidence of organic compounds in the atmosphere.

Cassini has recently imaged a dark, lake-like feature on the Titan surface, which NASA scientists have hailed as the best evidence yet for the presence of liquid hydrocarbons (image courtesy of NASA).