9. Jupiter: a giant primitive planet
Jupiterís orbital radius is 5.2 times the radius of the Earthís orbit, so the planetís distance from Earth changes relatively little in the course of a year. As a consequence, its apparent size and brightness are fairly constant, unlike the behavior of Mars and Venus. When these nearby planets are on the same side of the Sun as the Earth, they appear much bigger and brighter than when they move to the opposite side of the Sun. Jupiter is a true monarch of the planets, the largest planet in the solar system with a radius of about 11 times that of the Earth. The giant is so large that it could contain more than 1,300 Earth-sized planets inside its volume. Yet, Jupiter is only 318 times as massive as our planet. So Jupiter must be composed of something lighter than the rock and iron that constitute the Earth.
If we divide the mass by the volume, we find a mean density of 1,330 kilograms per cubic meter, only about one quarter the mean mass density of the Earth. In fact, the mass density of Jupiter is only slightly greater than that of water, at 1,000 kilograms per cubic meter, and this implies that Jupiter, like the Sun, is composed primarily of hydrogen. No other element is light enough to account for the low density of the planet.
Physical properties of Jupitera
|Mass||1.8992 x 1027 kilograms = 317.894 ME|
|Equatorial radius at one bar||7.1492 x 107 meters = 11.19 RE|
|Polar radius at one bar||6.6854 x 107 meters|
|Mean mass density||1,330 kilograms per cubic meter|
|Rotation period||9.9249 hours = 9 hours 55 minutes 29.7 seconds|
|Orbital period||11.86 Earth years|
|Mean distance from Sun||7.7833 x 1011 meters = 5.203 AU|
|Age||4.6 x 109 years|
|Atmosphere||86.4 percent molecular hydrogen, 13.6 percent helium|
|Energy balance||1.67 Ī 0.08|
|Effective temperature||124.4 degrees kelvin|
|Temperature at one bar level||165 degrees kelvin|
|Central temperature||17,000 degrees kelvin|
|Magnetic dipole moment ||20,000 DE|
|Equatorial magnetic field strength||4.28 x 10-9 tesla or 14.03 BE|
a The symbols ME, RE, DE and BE denote respectively the mass, radius, magnetic dipole moment, and magnetic field strength of the Earth.
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Copyright 2010, Professor Kenneth R. Lang, Tufts University