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

The sun contains a LOT of matter other than hydrogen. Much more than all the inner planets combined. It’s just that the sun is, well, massive so the proportion of hydrogen to other elements is very high.

The inner planets do not have enough mass to hold on to their hydrogen, so what’s left is mostly heavy elements.

The outer planets (especially Jupiter) do have enough mass to hold on to hydrogen, so they are more similar to the composition of the Sun. Jupiter can be viewed as a failed star. Many star systems are binary, and Jupiter would have been the “other” star in our system if it were (considerably) larger.