Formation

The formation of the outer planets began with the accretion of ice-covered dust in the outer, cold solar nebula. As ice-covered dust particles began to clump together, they began to collect more volatiles, creating increasingly massive bodies. This process of dust particles gradually adhering to one another eventually led to the formation of spherical bodies of asteroid size, called planetesimals. The collisions between these planetesimals led to the destruction of some; however, it also led to the creation of even larger planetesimals. Those that survived were able to trap the remains of those that did not, further increasing their masses.

Saturn formed at such a distance from the Sun that the temperatures were low enough to keep water ice frozen. As a result, Saturn had much more material at its disposal than any of the inner planets. In addition, the ice acted as a good “glue” to hold the other raw materials together. These two factors allowed Saturn to become very massive, increasing the strength of its gravitational attraction to a level appropriate for capturing hydrogen and helium. Since these gasses are not able to escape Saturn’s atmosphere, the planet was able to grow very massive indeed.

Composition

Saturn's composition is very much like Jupiter's, though there are some significant differences. Saturn has an even greater oblateness than Jupiter, of 9.8%, making it the most oblate of all the planets. While Saturn rotates at the same rate as Jupiter it has less mass and less gravity to pull it inward, resulting in a larger oblateness. However, if Saturn and Jupiter had the same internal composition, it oblateness would be even greater than 9.8%. Therefore, it is concluded that Saturn has a different mass distribution than Jupiter, with a concentrated rocky core consisting of 10% of the planets mass. It is also believed that the same liquid ‘ices’ surround the rocky core of Saturn as those of Jupiter.

For more information on the composition of Saturn, see Jupiter:Composition.

Atmosphere

The temperature of Saturn’s atmosphere increases from the outer levels in. The temperature at the cloud tops is 95 K and it rises while going deeper into the atmosphere. The rate of temperature change with altitude is half of that on Jupiter.

Saturn doesn’t have as many bands as Jupiter. The lower temperature means that there are chemical differences from Jupiter. This is evident by the fact that its bands do not show up as well as Jupiter’s. The patterns repeat in the Southern hemisphere and the cloud bands are symmetrical from the equator to the polar regions.

The southern hemisphere mirrors the northern hemisphere, with the exception of Saturn’s Great Red Spot. Saturn’s polar clouds are similar to those on Jupiter. The polar belts and zones give way to waves and turbulent eddies poleward of 60 degrees which are due to the Coriolis effect. Because of Saturn’s similarities with Jupiter, this may suggest that the two were formed from similar origins.

On Saturn and Jupiter cloud bands are generally wider in the equatorial latitudes because the Coriolis effect there is negligible. The width of the cloud bands poleward from the equator is inversely proportional to the magnitude of the Coriolis effect.

For more information about Saturn's atmosphere, see Jupiter:Atmosphere.

Magnetic Field

Saturn’s magnetosphere is similar to Jupiter’s but is only 10-20% as large and contains fewer charged particles. The lack of charged particles is due to the lack of a volcanic moon (like that of Io), which inject particles into the magnetosphere. The icy particles which Saturn’s icy rings are composed of also absorb a large number of charged particles. The charged particles which are present in Saturn’s magnetosphere are also concentrated in radiation belts.

Saturn also has a substantial magnetic field, nearly 600 times that of Earth’s. Despite this sizeable magnetic field, it is small relative to Jupiter’s. This suggests that because Jupiter and Saturn rotate at similar rates, there must be far less liquid metallic hydrogen present within Saturn’s interior. This is further supported by the fact that Saturn has a smaller mass and less gravity which means less internal pressure to compress hydrogen into liquid metallic hydrogen.

For more information on Saturn's magnetic field, see Jupiter:Magnetic Field.

Unique Features

Although other planets have ring systems, none has one as illustrious and eye-catching as Saturn.

Saturn is much less dense than the other planets. If there were a bathtub large enough to contain Saturn, it would float on water due to its low density.

The clouds at Saturn’s poles have very strange behavior. At its northern pole, the clouds form an almost perfect hexagon. In the south, there is a very large hurricane.

The Numbers

Discovered By	Known by the Ancients
Discovery Date	Unknown
Average Distance from the Sun	1,426,725,400 km (9.53707 AU)
Perihelion	1,349,467,000 km (9.021 AU)
Aphelion	1,503,983,000 km (10.054 AU)
Equitorial Radius	60,268 km
Equitorial Circumference	378,675 km
Volume	8.2713 * 1014 km³
Mass	5.6851 * 1026 kg
Density	0.70 g/cm³
Surface Area	4.3466 * 1010 km²
Equitorial Surface Gravity	10.4 m/s²
Escape Velocity	127,760 km/h
Sidereal Day	0.44401 Earth days
Sidereal Year	29.4 Earth years
Mean Orbital Velocity	34,821 km/h
Orbital Eccentricity	.0541506
Orbital Inclination to Ecliptic	2.484 degrees
Equitorial Inclination to Orbit	26.73 degrees
Orbital Circumference	8.725 * 109 km
Effective Temperature	-178 °C
Namesake	Roman god of agriculture

Source: http://sse.jpl.nasa.gov/planets