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The Jovian Planets

Atmosphere (Pressure and Composition):

* Jupiter and Saturn are made of mostly Hydrogen and Helium, with just a few percent of the masses made of hydrogen compounds and even less in the form of rock and metal

* Jupiter is a failed star because it has the same composition, but lacked the nuclear fusion needed to make it shine. Jupiter is large, but less massive than any star. It lacks the gravity to compress it.

* Uranus and Neptune are much smaller than Jupiter and Saturn and also contain proportionally smaller amounts of Helium and Hydrogen. Uranus and Neptune are made mostly of hydrogen compounds such as water, methane, ammonia and small amounts of metal and rock

* Saturn is less dense than Uranus or Neptune. This is because they have proportionally less hydrogen and helium

* Jupiter is only slightly larger than Saturn, but is 3x as massive. The extra mass on Jupiter compresses its interior to a much higher density. If more gas was added to Jupiter, the planet would be compressed and become smaller. A lot of stars are smaller than Jupitor, but more massive.

* Jovian planets rotate much more rapidly than terrestrial planets. Defining their rotation rates can be difficult b/c they lack solid surfaces. We determine the rates by watching the cloud movements. The rotation rates differ with latitude. Equatorial regions complete each rotation in less time than polar regions. The reason why jovian planets are not perfect spheres. The size of the equatorial bulge depends on the balance between the strength of gravity and the rate of rotation

* Jupiter:

* As a spacecraft descends into Jupiter, greater temp and pressure

* No solid surface, but distinctive layers. The high pressures cause each phase of hydrogen to vary with depth

* Jovian planet interiors are all quite similar in composition and mass. The interiors differ mostly in the hydrogen/helium layers that surround their core.

* Saturn is...