Re: Article: "Sun is Mostly Iron, Not Hydrogen"

From: Robert J. Bradbury (
Date: Thu Jan 10 2002 - 12:12:20 MST

On Thu, 10 Jan 2002, Mike Lorrey wrote:

> So what happens during planetary formation when a dozen or so
> planetesimals get chucked into the sun by orbital resonances?

FIREWORKS... really BIG ones... and in this particular instance
size *does* matter.

> Doesn't the addition of preexisting heavy elements tend to
> spike the cocktail of stellar development?

Yes, but the mass differential means swallowed planets (be they
of the English or African variety) don't make much of a difference.
Interestingly(!), I believe there is a paper out where astronomers have
detected a recent swallowing event. I can't remember what the signature
element was, perhaps sodium -- I think those are bright lines.

> Furthermore, I haven't heard you or anyone speak to Jeff's earlier
> calculation that there was something like 535 Earth masses of iron in
> the Sun, based on the 0.15% iron content in the solar corona. Is this
> accurate?

Not according to my #'s. The Sun is 2.5E-5 Fe and 1.0E0 H. I believe
this is by atom count. Adjusting for the mass ratio, this gives a
solar mass fraction of ~0.02% Fe (about 7 times lower). Using the
Solar wind element abundances, I get ~0.07% Fe (about 2 times lower).
So we are more or less within an order of magnitude.

So you probably require a minimum of ~70 Earth masses of iron to
be deposited in the sun. That's probably more than the rest of
the iron in the solar system.

> If so, how does the presence of this amount of iron (and any
> other metals) spike the Sun's development?

Given the improbability of 70 Earth masses of iron being externally
injected into the sun, most of it was presumably there to start
with. That means a moderately metal rich gas cloud which was
presumably seeded by a SN is the source for the material in the Sun.

Worth noting is the fact that there are stars *more* metal rich
than the sun. They have either swallowed a lot of planets or
formed in a very metal enriched environment.


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