SATURN

Saturn is the sixth farthest planet from the Sun and the second largest planet in the Solar System, after Jupiter. Without its rings, Saturn looks like a pale Jupiter, with striking similarities to its giant sister. Saturn borrowed its name from the Roman god of agriculture and harvest.

Saturn, along with the massive Jupiter, Uranus, and Neptune, is classified as a gas giant. Together, these four planets are sometimes called Jovian, meaning "Jupiter-like", planets. Saturn has average radii about nine times larger than the Earth's. However, it has only one-eighth the average density of Earth, due to its larger volume, Saturn's mass is just over ninety-five times greater than Earth's.

The observations of the disk of Saturn at the beginning of telescopic observations, in the 17th century, were rendered difficult by the presence of the rings, which perturbed even simple observations of the shape of the planet. The flattening of the planet was measured by William Herschel only in 1789 when the rings were observed on their edge, a configuration repeated only every 14 yr. After the Pioneer 11 observations in 1979, which gave important information about thermal structure and magnetospheric emissions, the Voyager observations in 1980–1981 provided the first accurate tracking of individual spots in the atmosphere, and the differential rotation of Saturn could be measured for the first time.

Because of Saturn's large mass and gravitational pull, the conditions produced on Saturn are extreme. The interior pressures and temperatures are far beyond what can be reproduced experimentally on Earth. The interior of Saturn is composed of a core of iron, nickel, silicon and oxygen compounds, surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium, and an outer gaseous layer. Electrical current within the metallic-hydrogen layer is assumed to give rise to Saturn's planetary magnetic field, which is slightly weaker than Earth's magnetic field and approximately one-twentieth the strength of the field around Jupiter. The outer atmosphere is generally plain in appearance, although long-lived features can appear. Wind speeds on Saturn can reach upto 1,800 km/h, significantly faster than those on Jupiter.

Due to combined effects of its lower density, rapid rotation, and fluid state, Saturn is an oblate spheroid; that is, it is flattened at the poles and bulges at the equator. There is little information known about Saturn's internal structure; it is thought that its interior is similar to that of Jupiter, having a small rocky core surrounded mostly by hydrogen and helium. Above this, there is a thicker and viscous liquid metallic hydrogen layer, followed by a layer of liquid hydrogen and helium, and in the outermost 1000 km a gaseous atmosphere. The outer atmosphere of Saturn consists of 96.3% molecular hydrogen and 3.25% helium.

Saturn has a system of nine rings, consisting mostly of ice particles with a smaller amount of rocky debris and dust. Sixty-two known moons orbit the planet, of which fifty-three are officially named. This does not include the hundreds of "moonlets" within the rings. Titan, Saturn's largest and the Solar family’s second largest moon (after Jupiter's Ganymede), is larger than the planet Mercury and is the only Moon in the  Solar System to possess a significant atmosphere.


Questions to ponder:

• Why are Saturn's rings flat?
• Why do some planets have a ring system and others don’t?