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

One reason terrestrial planets have less hydrogen and helium is these gasses float away into space. Planets’ and moons’ gravity isn’t strong enough to hold them.

[This chart shows which gasses various planets and moons can hold.](https://physics.stackexchange.com/questions/615311/what-is-this-atmospheric-escape-chart-actually-showing). Gasses below planets or moons can be held by gravity. Gasses above planets and moons float off into space.