Saturn is the one planet almost everyone will recognise. And what is it that makes it stand out? It is its ring system orbiting the planet. But before we talk about the rings, let’s first discuss the planet itself. Saturn is the second largest planet in the solar system and it is over 886 million miles from the Sun. Like Jupiter, it is a gas giant with an atmosphere made up mainly of hydrogen at 96% and helium with some trace gases making up the rest.
The structure of Saturn is in some ways similar to Jupiter. There is a rock and ice core which may be up to 20 times the mass of the Earth. Surrounding this is a layer of liquid metallic hydrogen and helium. The next layer is composed of liquid hydrogen and helium. Finally, we have the dense atmosphere which is the only part we can see using visible light telescopes.
Saturn has a relatively fast rotation speed of 10.67 hours which means that some mass is pushed out towards the equator creating a bulge. This results in the equator being about 10% wider than at the poles. Saturn takes nearly 30 Earth years to make one orbit around the Sun. The planet is tilted from its vertical axis by 26.7 degrees. This means that during one orbit of the Sun, Saturn is able to tilt both of its poles towards it. And this gives us an advantage when studying its ring system.
When the north-pole is tilted towards the Sun we get a view of Saturn’s rings from above. And when the south-pole faces the Sun, we see the rings from below. They are truly an amazing sight. But one of the most startling facts about them is that although they stretch out for hundreds of thousands of miles, they are only a few miles thick.
The rings themselves are mainly composed of ice with some carbon mixed in. They range in size from tiny particles to sizeable chunks. It is their ability to reflect sunlight so well that makes them so conspicuous. Careful observation reveals a large gap in the rings. This gap is known as the Cassini Division.
Saturn has a lot of moons but not as many as Jupiter. At the last count, 53 had been identified. But it is likely that many more will be discovered but they may become discounted because of their small size.
However, Saturn does possess some large moons. The biggest is Titan and at 3,500 miles across, it is larger than the planet Mercury. Titan has a claim to fame as it is the only natural satellite to have a thick atmosphere. It is mainly composed of nitrogen and appears as fog-like to an observer. The other gas present in any quantity is methane. Some scientists hoped that this combination may have caused a greenhouse effect to take place and thus raising the temperature on the surface. Unfortunately this is not the case and the temperature remains a very cold -180 degrees. In addition, the atmospheric pressure on Saturn is greater than that on the Earth. In 2004 the space-probe Huygens landed on Titan after a journey lasting for seven years.
Another interesting moon of Saturn is Phoebe. It is one of the outer moons at an average distance of just over 8 million miles. The surface shows plenty of impact craters from meteorites but that isn’t what is unusual about it. Phoebe orbits the planet backwards; in the opposite direction to the other moons.
Dione is another moon which earns our attention. It is the fourth largest of Saturn’s moons and its surface shows cliffs of ice as well as impact craters. But Dione is not alone. It is joined in its orbit by two smaller companions; one ahead of it and one behind. They are called Helene and Polydeucers respectively.
Some of the lesser moons perhaps should not even be considered as such. If we questioned the sizes of Mars’ two moons, Phobos and Deimos, then Saturn’s moon Pallene goes a step further or a size smaller. It is only 2.5 miles across.
Saturn remains one of the jewels of the solar system and if you get the chance to observe it through a good telescope, you should seize the opportunity.
John Pullen 