Saturn is almost twice as far from the Sun as Jupiter at nearly 900 million miles. It is second in size in our solar system, surpassed only by Jupiter, but Saturn's mass is much smaller. Saturn's specific gravity is less than water's, meaning it would float on a body of water! Like Jupiter, Saturn rotates extremely fast, and completes a rotation in about 10 hours. It takes a little over 29 years to make one revolution around the Sun.

Saturn has over 30 known satellites (the most of any planet in our solar system), the most interesting in terms of atmospheric composition being Titan (mentioned below). More satellites may be found in the future as there appears to be an entire system of small, distant moons revolving around Saturn which may be fragments from a common parent body. NASA's Cassini spacecraft arrived at Saturn in 2004 and will spend at least four years studying Saturn, its rings, and old and newly discovered moons.

Atmosphere and Weather: One of the four gas giants, Saturn's atmosphere is much like that of Jupiter's. Hydrogen makes up nearly all of the atmosphere, with lesser amounts of helium and much lesser quantities of methane and ammonia. Saturn also has clouds made of ammonia ice crystals, but the clouds tops are considerably colder than Jupiter's approaching -400 degrees F. However starting around -300 degrees F., the ammonia would be frozen right out of the clouds. Like the other gas giants, Saturn's surface to atmosphere interface is rather nebulous, and likely has a small, rocky core surrounded by a liquid and very thick atmosphere.

Saturn is considerably colder than Jupiter being further from the Sun, with an average temperature of about -285 degrees F. Wind speeds on Saturn are extremely high, having been measured at slightly more than 1,000 mph, considerably higher than Jupiter.

One interesting aspect of Saturn is its largest satellite, Titan (in fact, Titan is the second largest satellite in the solar system behind Jupiter's Ganymede). Titan is the only satellite in the solar system known to have an atmosphere, consisting of nitrogen and methane.

Side notes: Saturn is the last planet in our solar system which is easily visible to the unaided eye. Saturn's rings are actually a complex series of hundred's of narrow "ringlets", which in turn are made of countless numbers of icy chunks. These chunks of ice range in size from a particle of dust to about 200 yards. But the average size is around three feet. The rings are no thicker than 10 miles in width.

Interior

Saturn's interior is similar to Jupiter's consisting of a rocky core, a liquid metallic hydrogen layer and a molecular hydrogen layer. Traces of various ices are also present.

Saturn's interior is hot (12000 K at the core) and Saturn radiates more energy into space than it receives from the Sun. Most of the extra energy is generated by the Kelvin-Helmholtz mechanism as in Jupiter. But this may not be sufficient to explain Saturn's luminosity; some additional mechanism may be at work, perhaps the "raining out" of helium deep in Saturn's interior.

Winds

The wind blows at high speeds on Saturn. Near the equator, it reaches velocities of 500 meters a second (1,100 miles an hour). The wind blows mostly in an easterly direction. The strongest winds are found near the equator and velocity falls off uniformly at higher latitudes. At latitudes greater than 35 degrees, winds alternate east and west as latitude increases.

Visibility from Earth

When it is in the nighttime sky, Saturn is easily visible to the unaided eye. Though it is not nearly as bright as Jupiter, it is easy to identify as a planet because it doesn't "twinkle" like the stars do. The rings and the larger satellites are visible with a small astronomical telescope. There are several Web sites that show the current position of Saturn (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program such as Starry Night.

Composition

Like Jupiter, Saturn is about 75% hydrogen and 25% helium with traces of water, methane, ammonia and "rock", similar to the composition of the primordial Solar Nebula from which the solar system was formed.

based

1. http://www.crh.noaa.gov/fsd/astro/saturn.htm - National Weather Service Forecast Office
2. http://saturn.jpl.nasa.gov/mission/images/saturn-tilt.jpg - JPL Image Laboratory