Besides the ring system, Saturn also has 21 known moons. The most impressive of these satellites is Titan. It has a diameter of more than 5100 kilometers and is thus larger than the planet of Mercury.
The composition of its atmosphere is thought to be very similar to the original atmosphere of the Earth. Due to the extremely low temperatures of minus 200┬░ Celsius, scientists exclude the possibility of life on Titan.
The other of the larger Saturn moons are Mimas (390 km), Enceladus (510 km), Tethys (1060 km), Dione (1120 km), Rhea (1530 km) and Iapetus (1460 km). Enceladus is actually a very bright satellite made of ice. It reflects nearly all the sunlight that reaches it. Dione and Tethys are accompanied in their orbits by a group of smaller moons.
They respectively precede or follow the two larger moons at angles of approximately 60 degrees and are often referred to as Trojan satellites. Some of the smaller moons are known as "shepherd satellites".
Their orbits "keep the rings together". There are two such small moons located between the F and the G ring. Every four years, they switch orbit. The one closest to Saturn revolves around the planet at a higher speed. However, as the orbits of the two satellites are only a few kilometers apart from each other, the inner moon cannot "overtake" its outer companion.
Gravitation causes the two moons to switch orbit. The inner moon thus becomes the outer of the pair and its orbit speed is reduced. Far outside the ring system lies the orbit of Iapetus. Its distance to the planet is more than 3.5 million kilometers.
This moon consists mainly of water. The outermost moon of Saturn is Phoebe. As its diameter is only 220 kilometers, many scientists believed that it is actually a "captured" asteroid. There is a distance of approximately 13 million kilometers between this satellite and the planet of Saturn! Phoebe has a retrograde orbit. In other words, it revolves about the planet in the opposite direction to the other moons.
