SATURN

=**Saturn**=


 * By.Rashawn Williams,Delon Ruffin**


 * Saturn ** is the sixth planet from the sun and the second largest planet in the solar system, after jupiter. Named after the roman god saturn, its astronomical symbol represents the god's sickle. Saturn is a gas planet with an average radius about nine times that of Earth. While only 1/8 the average density of Earth, with its larger volume Saturn is just over 95 times more massive than Earth. Saturn's interior is probably composed of a core of iron, nickel and rock (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 thought to give rise to Saturn's planetary magnetic field, which is slightly weaker than Earth's and around one-twentieth the strength of Jupiter's. The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800 km/h.

Physical characteristics

Saturn is classified as a gas giant planet because the exterior is predominantly composed of gas and it lacks a definite surface, although it may have a solid core. The rotation of the planet causes it to take the shape of an oblate spheroid; that is, it is flattened at the poles and bulges at the equator. Its equatorial and polar radii differ by almost 10%—60,268 km versus 54,364 km, respectively. Jupiter, Uranus and Neptune, the other gas giants in the Solar System, are also oblate, but to a lesser extent. Saturn is the only planet of the Solar System that is less dense than water; about 30% less. Although Saturn's core is considerably denser than water, the average specific density of the planet is 0.69 g/cm3 due to the gaseous atmosphere. Jupiter has 318 times the Earth's mass while Saturn is 95 times the mass of the Earth, yet Jupiter is only about 20% larger than Saturn. Together, Jupiter and Saturn hold 92% of the total planetary mass in the Solar System.

Planetary rings

Saturn is probably best known for its system of planetary rings, which makes it the most visually remarkable object in the solar system. The rings extend from 6,630 km to 120,700 km above Saturn's equator, average approximately 20 meters in thickness and are composed of 93% water ice with traces of tholin impurities and 7% amorphous carbon. The particles that make up the rings range in size from specks of dust up to 10 m. There are two main theories regarding the origin of the rings. One theory is that the rings are remnants of a destroyed moon of Saturn. The second theory is that the rings are left over from the original nebular material from which Saturn formed. Some ice in the central rings comes from the moon Enceladus' ice volcanoes.

Beyond the main rings at a distance of 12 million km from the planet is the sparse Phoebe ring, which is tilted at an angle of 27° to the other rings and, like Phoebe, orbits in retrograde fashion. Some of the moons of Saturn, including Pan and Prometheus, act as shepherd moons to confine the rings and prevent them from spreading out. Pan and Atlas cause weak, linear density waves in Saturn's rings that have yielded more reliable calculations of their masses.

In the past, astronomers believed the rings formed alongside the planet when it formed billions of years ago. Instead, the age of these planetary rings is probably some hundreds of millions of years. The outer atmosphere of Saturn contains 96.3% molecular hydrogen and 3.25% helium. The proportion of helium is significantly deficient compared to the abundance of this element in the Sun. The quantity of elements heavier than helium are not known precisely, but the proportions are assumed to match the primordial abundances from the formation of the Solar System. The total mass of these heavier elements is estimated to be 19–31 times the mass of the Earth, with a significant fraction located in Saturn's core region. Trace amounts of ammonia, acetylene, ethane, propane, phosphine and methane have been detected in Saturn's atmosphere. The upper clouds are composed of ammonia crystals, while the lower level clouds appear to consist of either or water Ultraviolet radiation from the Sun causes methane photolysis in the upper atmosphere, leading to a series of hydrocarbon chemical reactions with the resulting products being carried downward by eddies and diffusion. This photochemical cycle is modulated by Saturn's annual seasonal cycle. Saturn has at least 62 moons, 53 of which have formal names. Titan, the largest, comprises more than 90% of the mass in orbit around Saturn, including the rings.] Saturn's second largest moon, Rhea, may have a tenuous ring system of its own, along with a tenuous atmosphere.] Many of the other moons are very small: 34 are less than 10 km in diameter and another 14 less than 50 km. Traditionally, most of Saturn's moons have been named after Titans of Greek mythology. Titan is the only satellite in the Solar System with a major atmosphere. in which a complex organic chemistry occurs. It is the only satellite with hydrocarbon lakes. Saturn's moon Enceladu has often been regarded as a potential base for microbial life. Evidence of this life includes the satellite's salt-rich particles having an "ocean-like" composition that indicates most of Enceladus's expelled ice comes from the evaporation of liquid salt water.

Cloud layers [[image:http://bits.wikimedia.org/skins-1.19/common/images/magnify-clip.png width="15" height="11" link="http://en.wikipedia.org/wiki/File:Saturn_storm_circles_planet_PIA12826.jpg"]]
A global storm girdles the planet in 2011. The head of the storm (bright area) passes the tail circling around the left limb. Saturn's atmosphere exhibits a banded pattern similar to Jupiter's, but Saturn's bands are much fainter and are much wider near the equator. The nomenclature used to describe these bands is the same as on Jupiter. Saturn's finer cloud patterns were not observed until the flybys of the Voyager spacecraft during the 1980s. Since then, Earth-based telescopy has improved to the point where regular observations can be made The composition of the clouds varies with depth and increasing pressure. In the upper cloud layers, with the temperature in the range 100–160 K and pressures extending between 0.5–2 bar, the clouds consist of ammonia ice. Water ice clouds begin at a level where the pressure is about 2.5 bar and extend down to 9.5 bar, where temperatures range from 185–270 K. Intermixed in this layer is a band of ammonium hydrosulfide ice, lying in the pressure range 3–6 bar with temperatures of 290–235 K. Finally, the lower layers, where pressures are between 10–20 bar and temperatures are 270–330 K, contains a region of water droplets with ammonia in aqueous solution. Saturn's usually bland atmosphere occasionally exhibits long-lived ovals and other features common on Jupiter. In 1990, the Hubble Space Telescopy imaged an enormous white cloud near Saturn's equator that was not present during the Voyager encounters and in 1994, another, smaller storm was observed. The 1990 storm was an example of a Great White Spot a unique but short-lived phenomenon that occurs once every Saturnian year, roughly every 30 Earth years, around the time of the northern hemisphere's summer solstice. Previous Great White Spots were observed in 1876, 1903, 1933 and 1960, with the 1933 storm being the most famous. If the periodicity is maintained, another storm will occur in about 2020. The winds on Saturn are by far the fastest among the Solar System's planets. Voyager data indicate peak easterly winds of 500 m/s (1800 km/h). In images from the //Cassini// spacecraft during 2007, Saturn's northern hemisphere displayed a bright blue hue, similar to Uranus. The color was most likely caused b scatering Infrared imaging has shown that Saturn's south pole has a warm polar vortex, the only known example of such a phenomenon in the Solar System. Whereas temperatures on Saturn are normally −185 °C, temperatures on the vortex often reach as high as −122 °C, believed to be the warmest spot on Saturn.