This is a drawing of the evolution of the interior of a giant planet.
Click on image for full size
Image from: The New Solar System
How the Interior of Saturn Formed
The drawing shows how the interior of Saturn may have formed. As the planets
drew material from the
solar nebula, bits of heavy, solid material accumulated inside the forming planet, as illustrated in figure A.
Once the planet finished forming, these heavy, solid bits of material fell into the center of the planet, as illustrated in figure B. The heavy elements of the planet made up a much smaller portion of the planet than the gaseous elements. Saturn drew a large amount of gas to itself from the nebula because of where Saturn was in the primordial cloud.
Eventually, the heavy, solid material at the center solidified into a core, as illustrated in figure C.
Leftover heat from this process of Saturn's forming may still influence the motions in Saturn's atmosphere.
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