Tell me about Saturn

Question posed by Jennie.

Saturn is the second largest planet in our solar system and the sixth planet from the Sun. It is arguably the most easily recognisable planet that we know of, with its highly visible ring system and yellowish colour. Saturn has been known since prehistoric times, and was known by the ancients as the most distant of the five known planets. It was named after the ancient Roman god, Saturnus, god of agriculture and harvests. The ancient Greeks held the planet sacred to Kronos, who was the Greek equivalent of Saturnus.
Saturn's famous rings were discovered by Galileo in 1610, but he assumed that they were two moons. More powerful telescopes allowed Christian Hugens to identify them as rings.
Saturn has been visited by four probes:

• Pioneer 11, in September 1979 (flyby).
• Voyager 1 in November 1980 (flyby).
• Voyager 2 in August 1981 (flyby).
• Cassini-Huygens: entered into orbit around Saturn on July 1st, 2004; Huygens probe released on December 25th, 2004, and landed on the surface of Titan on January 14th, 2005. Since then, the probe has been instrumental in increasing our knowledge and understanding of Saturn, its rings and moons. The Cassini-Huygens primary mission officially ended in 2008, and is now in it's first mission extension.
  

Where is it?
Saturn orbits at an average distance of about 10AU* from the Sun, which is around 10 times further away than the Earth. It's 'year' (the time it takes to complete one orbit) is a bit more than 29 Earth years, but its day is only just over 10 1/2 hours. Like most planets, Saturn is not a perfect sphere (like a football); it is oblate (it bulges out at the equator, like a squashed football). Because of its fast spin, Saturn is the most oblate planet in our solar system.

How big is it?
Saturn is about 9 1/2 times wider than the Earth (making it over 60,000 km wide**). It takes up over 750 times the space that Earth does, but is only 95 times heavier. This is because Saturn has a very low density (density is how much stuff is squashed into the same area- imagine a golf ball and a table tennis ball: they're about the same size, but the table tennis ball is lighter because there's less stuff in there). In fact, Saturn's density is less than that of water. This means that if you could find a big enough bath to plonk it in, it'd float!


What's it made of?
Saturn is mostly hydrogen, with small amounts of helium and some trace elements. It has a small*** core which is probably mostly made of rock and ice.


What are the rings made of?
Mostly ice, with some rocky debris and dust. They're so easy to see because ice reflects sunlight really well. Having said that, if you look through a telescope at Saturn at the right time, you can hardly see the rings at all because they're edge-on to us, and they're so thin. To see Saturn's rings you'll need at least a 15 mm diameter telescope.


Does it have any moons?
Yes. So far we have discovered sixty-one moons in orbit around Saturn. Fifty-two of them have been named. Seven of them are large enough to have become spherical due to their own gravity, and would therefore be considered to be dwarf planets if they were orbiting the Sun on their own. The largest of these is Titan, which is also the second largest moon in the solar system. With a diameter of about 5150 km, it is larger than Pluto.




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* That's about 1500,000,000 km.
** The proper term for how 'wide' a planet is, is its 'diameter'.
*** Scientists aren't shure how big Saturn's core is, but the best guess at the moment is that it's about 10 - 15 times as massive as the Earth. So describing it as 'small' is a relative thing!