Expert: Jayendra Upadhye - 10/21/2007

Question
Why is it the sun is mainly hydrogen and helium, while earth has lots of heavy
elements on it? Shouldn't all the heavy elements have fallen to the center of
the
solar system when it formed?

Answer
Hi,
You are right ofcourse!
But what you see on the sun is mainly because all the heavier elements have gone to it's center.

The core of the sun is indeed striated very much like the striations one sees on cliffs of plateaus.

This is all below the convective layer where the high pressure ensures that there is a boundary above which there is heat transfer by convection as well as radiation, below which the heat transfer is mainly radiative & conductive!

Its is dark down there, as the radiant energy occupies the higher energy "non-visual" part of the spectrum (gamma and x rays).

The energy transfer from further down within this area is mainly by successive absorption and re-radiation a scatter based transfer of energy which makes the photon take a million years just to emerge! [ref:Sagan in Cosmos].

The sun was formed from the same cloud as the earth and had all the elements higher than hydrogen in same proportion as elsewhere in the solar system.

During the protostar phase, it accumulated huge quantities of "everything" in its vicinity including hydrogen which was preponderant. When fusion started, the terrible heat (radiation pressure from various winds during formation and the later continuous solar wind (it is a hydrostatic flow), blew away the hydrogen atmospheres of the inner planets, leaving their "small" rocky cores.

That is why the outer planets are still large while the inner planets are percieved as "rocky.

Meanwhile the heavier elements inherited from the supernova generated cloud (like the m16 eagle stellar nursery) had subsided long ago into the hot solar interior.

Later in its life the sun will begin helium burning (red giant phase) and progress relatively fast to its death as a white dwarf star, all the time cooking up carbon / sulphur etc. But that is all far off in the future.

Then it will have only degenerate plasma as its constituent as no matter in elementary form can exist at surface temperatures common on white dwarf stars.

Jayen