| MadSci Network: Astronomy |
Most introductory astronomy textbooks will have good diagrams of the interior of Saturn. Saturn is made up mostly of hydrogen and helium. We don't see them, because those gases are invisible to us. The clouds that we see are made up of ammonia ice, ammonium hydrosulfide ice, water ice, and possibly other molecules.
You would expect that, because it is mostly hydrogen and helium, Saturn would be nothing more than a big gas ball. This is mostly true. The radius of Saturn is about 60,000 kilometers, about 10 times larger than the Earth. You have to go 30,000 kilometers down before Saturn stops acting like a gas.
Saturn is so big that the gas inside has a very high pressure. By the time you go 30,000 kilometers below the clouds that we can see, the pressure is about three million times larger than the pressure of air on Earth! At that pressure hydrogen acts like a liquid metal (kind of like the element mercury that is used in thermometers).
Another 15,000 kilometers down (45,000 kilometers below the cloud tops), Saturn has a solid, rocky core. We don't know exactly what it is made of, but we know that it is there. It is probably about 10 times more massive than the Earth.
You can find a lot more information about Saturn at a Web site called The Nine Planets.