10. Saturn: lord of the rings


Fig. .. 

Majestic Saturn, the sixth planet from the Sun, was the most distant world known to the ancients, and it moved least rapidly around the zodiac. The Greeks identified the planet with Kronus, the father of Zeus, while the Romans named the planet Saturn after their god of sowing. Both the Greeks and the Romans associated Saturn with the ancient god of time, which later became Father Time.

You can see Saturnís oblong, golden disc with a small telescope, girdled by its beautiful rings, unattached to the globe. They set Saturn apart from all the other planets. Even though we now know that all four of the giant planets possess ring systems of some kind, Saturnís rings easily outclass the others.

Saturnís orbital radius is 9.5 times the radius of the Earthís orbit, and it takes 29.458 Earth years for Saturn to complete one revolution around the Sun. Perhaps because of its remote orbit and slow motion, the planetís name has been adopted for the word ďsaturnineĒ, to describe a cool and distant temperament.

The volume of Saturn is great enough to encompass 764 Earth-sized planets. But Saturnís mass is only 95 times greater than the Earthís mass, so the giant planet must be composed of material that is much lighter than rock and iron, the primary ingredients of the Earth.

From Saturnís mass and volume, we calculate its average mass density to be only 688 kilograms per cubic meter, the lowest of any planet and less than that of liquid water. If Saturn were placed in a large enough ocean of water, it could float. It has a low average density because it is mainly composed of the lightest elements, hydrogen and helium, in the gaseous and liquid states.

Physical properties of Saturna

Mass5.6865 x 1026 kilograms = 95.184 ME
Equatorial radius at one bar6.0268 x 107 meters = 9.46 RE
Polar radius at one bar 5.4364 x 107 meters
Mean mass density688 kilograms per cubic meter
Rotation period10 hours 39 minutes 22.3 seconds = 10.6562 hours
Orbital period29.458 Earth years
Mean distance from Sun1.4294 x 1012 meters = 9.539 AU
Age4.6 x 109 years
Atmosphere97 percent molecular hydrogen, 3 percent helium
Energy balance1.79 Ī 0.10
Effective temperature95.0 degrees kelvin
Temperature at one-bar level134 degrees kelvin
Central temperature13,000 degrees kelvin
Magnetic dipole moment600 DE
Equatorial magnetic field strength0.22 x 10-9 tesla or 0.72 BE
a The symbols ME, RE, DP, BE denote respectively the mass, radius, magnetic dipole moment and magnetic field strength of the Earth. One bar is equivalent to the atmospheric pressure at sea level on Earth. The energy balance is the ratio of total radiated energy to the total energy absorbed from sunlight, and the effective temperature is the temperature of a black body that would radiate the same amount of energy per unit area.

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Copyright 2010, Professor Kenneth R. Lang, Tufts University