Saturn
Saturn is the second largest planet in the solar system, second to Jupiter. Its colour is somewhat yellow. Since it is one of the planets that are visible with the naked eye, its existence has been known since prehistoric times so we do not know who first discovered the planet. However, it is the faintest of the five visible planets, so it was probably discovered last. The first person to observe the planet using a telescope was Galileo in 1610. While he was the first person to see the rings, he was unable to explain what he saw.
It has an equatorial diameter of 120 536 km and a polar diameter of 108 728 km. The large difference (of 9.8 percent) between the equatorial diameter and the polar diameter is caused by the high speed at which the planet spins around its axis and the nature of the material that makes up the planet. Because the much of the material is in a fluid state, the spinning causes the material to move to the equator, resulting in the larger equatorial diameter. While the other gas planets are also oblate, (flattened at the poles), none of them exhibit this a much a Saturn. In addition, the mid-latitude areas of the planet are depressed inward by over 120 km. This is much greater than the depressed areas observed on any other planet.
Saturn has a mass of 5.69x1029kg; however, Saturn has a low density of only 0.69 g/cm3, and is the least dense of all known planets. In comparison, the density of water is 1g/cm3. Since the density of Saturn is lower than that of water, Saturn would float on water if a body of water large enough existed. Due to the low density, much less than that of earth, the planet has a volume 764 times larger than Earth, but is only 96 times more massive.
Above the clouds, the atmosphere is 97% hydrogen and 3.6% helium and 0.05% methane. However, the percent composition of helium is less than what was expected for the planet, a result of the "raining" of helium to the interior (explained further in section 1.5.). Other compounds and molecules present include deuterium (heavy hydrogen with one neutron), ammonia, ethane, ethylene, acetylene, and phosphine. Clouds exist down to the 1-3 bar level. (A bar is a measure of atmospheric pressure). A thick haze exists over the planet: the composition of this haze is believed to be ammonia crystals. They originate from a cloud deck at lower altitudes.
