SATURN

NASA Saturn Image     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 60 confirmed satellites, many of which are buried inside Saturn's smaller ring systems which are being discovered by NASA's Cassini spacecraft.  It is very difficult for astronomers to count the number of moons revolving around Saturn, because it is difficult to distinguish between tiny moons and the numerous ice chunks composing Saturn's smaller ringlets.  The large moon Titan is the most interesting in terms of atmospheric composition (mentioned below).  It is likely more satellites will be found in the future when astronomers diagnose Saturn's small, thin rings, and separate the ice chunks from actual satellites. 

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 and is the most Earth-like object in the solar system.  Recently, the Cassini spacecraft and the European based Huygens probe has confirmed many theories involving Titan, including seeing clouds, evidence of rain, seasonal variations and even ice volcanoes.

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 several hundred yards.  But the average size is around three feet.  Some of the rings are no thicker than 10 miles in width.

QUICK FACTS
(Data is from NASA Goddard)

Average distance from Sun 887,000,000 miles
Perihelion 838,600,000 miles
Aphelion 940,000,000 miles
Sidereal Rotation 10.656 Earth hours
Length of Day 10.656 Earth hours
Sidereal Revolution 29.48 Earth years
Diameter at Equator 74,732 miles (2nd largest planet)
Tilt of axis 26.73 degrees
Moons 60 known
Atmosphere Hydrogen (96.3%), Helium (3.25%), trace amounts of methane and ammonia
Discoverer Unknown
Discovery Date Prehistoric

DEFINITIONS:

Average distance from Sun:  Average distance from the center of a planet to the center of the Sun. 
Perihelion:  The point in a planet's orbit closest to the Sun.
Aphelion:  The point in a planet's orbit furthest from the Sun. 
Sidereal Rotation:  The time for a body to complete one rotation on its axis relative to the fixed stars such as our Sun.  Earth's sidereal rotation is 23 hours, 57 minutes.
Length of Day:  The average time for the Sun to move from the Noon position in the sky at a point on the equator back to the same position.  Earth's length of day = 24 hours
Sidereal Revolution:  The time it takes to make one complete revolution around the Sun.
Axis tilt:  Imagining that a body's orbital plane is perfectly horizontal, the axis tilt is the amount of tilt of the body's equator relative to the body's orbital plane.  Earth is tilted an average of 23.45 degrees on its axis.


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