93. Why does the atmosphere of Saturn appear to have only half the helium content of Jupiter?

Question

astronomy

Answer 1

Light pressure during planetary formation preferentially drove lighter elements, like hydrogen, further from the sun, where they condensed into planets. So, Jupiter would naturally have more of the heavier helium in it.

An alternate (or additional) explanation might be that since jupiter is larger, it has retain more of its primorial heat of formation, so there is more thermal convection from the interior. The atmosphere certainly looks a lot more tubulent from probe photos. Lacking as much mixing, the elements would tend to stratify from lightest on top to heaviest on the bottom. That leaves mostly only hydrogen at the top of the atmosphere, where we can see it, for Saturn.