Eli5 Why was the sun made up of mainly just hydrogen when it was formed compared to inner planets that have so many more elements, especially higher ones?

Question

All,

I have a basic understanding that a lot of elements were brought to planets by comets, supernova explosions and so on.

Why didn’t the sun attract most of these comets and fragments from celestial explosions instead of the planets? And why was / is the sun mainly just hydrogen?

In: 105

Answer 1

Lighter gasses get pulled in easier. It takes more force to move rocky solids. So in what started out as a cloud of dust pretty thoroughly mixed, the lighter gasses began to clump. As that got bigger, gravity got stronger. From the inside-out, you have lighter gases followed by metals and silicates, because that is how each of those respond to gravity.

The metals and silicates clumped together in much the same way as the lighter gases. And planets formed. A stable orbit was then achieved.

Outside of that, you have gases and ices that are too far away to get pulled into the sun. They clumped together and formed the gas giants and ice giants. Out there, it was a little less hydrogen, as that was more easily pulled to the center, which is one of the reasons Jupiter missed its big break to be a star.