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

From: jeff davis (
Date: Thu Jan 10 2002 - 01:57:35 MST

--- Anders Sandberg <> wrote:

> You can fuse iron atoms, but the reaction is
> endothermic. So when this
> happens, the star core cools. There are other
> nuclear processes
> involving iron too, and all are endothermic and
> hence tend to cool the
> star, causing it to compress.

I'm no astrophysicist either,...but consider. Earth
has an iron core. The asteroid belt has asteroids
that are largely iron.

Iron is abundant in the solar system.

"Venus has a rocky crust, a thick basaltic rock mantle
and a nickel-iron core."

Referring to Mars: "The core is probably iron and
sulphides and may have a radius
of 800-1,500 miles"

"Jupiter is a gaseous planet; it does not have a
solid surface like the Earth does (but probably has a
solid, rocky core 10 to 15 times the mass of the
Earth)." What portion of that might be iron?

Regarding Saturn, "The hot, heavy, rocky core has a
radius possibly three times the radius of the Earth."
Again, how much of that might be iron?

"Core: Uranus has a molten rocky core about 10,500
miles (17,000 km) in diameter and about
12,500F (6927C). This core may have a mass five
times greater than the mass of the Earth."

By whatever method, supernova remnant or "condensed"
from the presolar nebula with--presumably--a
substantial iron component, the sun probably has a
substantial quantity of iron. Judging from the other
bodies in the solar system, would it be unreasonable
to suppose that iron and other "heavy" elements would
concentrate, ie sink, to the sun's core?

Iron constitutes 0.16% by "weight"
 of the sun's photosphere. If that fraction were
uniform throughout the sun--as opposed to a core
composed of a substantially larger fraction of dense,
highly-ionized, heavy elements (heavier than
helium!)--then the amount of iron in the sun would
equal 533 earth masses.

Regarding a cooling/collapse problem resulting from an
iron core, or a core with a substantial iron fraction:
it is currently accepted that iron lies at the energy
minimum for nuclear binding energy based on nucleon
number. Thus, as Anders states, moving away from the
energy minimum by transmuting iron into either heavier
or lighter elements would be an energy absorbing
process. However, as an alternative, might not this
process tend toward a steady reversibilty, with an
equilibrium condition established where there was no
ongoing loss of energy to nucleosynthesis? Wouldn't
it likely be the case that the energy would not be
systematically lost, but only stored temporarily in
elements with a distribution of nucleon numbers
centered around iron, and a correlated distribution of
binding energies?

Wouldn't the current empirical evidence of a stable
sun suggest just such a condition of stable
equilibrium, with equal numbers of nuclei transmuting
away from and then back to iron? I base this
supposition on the (thermodynamic?) principle that all
systems tend toward their energy minimums.


The question of the putative iron core of the sun was
a lot of fun to mull over.

I recently had to reformulate my mental picture of the
solar system. List discussion of comets, and Amara's
"spotlight on dust in the solar system", forced me to
enlarge the model--out to the furthest reaches of the
oort cloud-- and throw a substantial quantity of
"dirt"--gas, dust, and cometary debris--into the once
tidy familiarity of brilliant star and orderly planets
(and semi-disorderly asteriods).

Now, it seems I have to do the same with the sun, and
dump a couple of thousand earth masses of "debris"
into the mix. Makes perfect sense to me that the sun
should have a "core". Makes the sun an infinitely
more complex system. Gives it "character". Next time
I find myself, of an evening, North of Half Moon Bay,
walking with my dog--worthless piece of fur; prime
candidate for a vietnamese entree--along the bluffs
above the ocean, and I pause to watch the glowing
spaceship end its daily sojourn and slip gracefully
beyond the mist-shrouded ends of the earth, I'll stop
for a moment, perk up, dance a little dance to
celebrate the magnificence of life, and think to
myself, "It's got a core. A big honkin' system
complexifying core." And my dog will look up at me
and think,"What the hell's gotten into him THIS time?

I be happy.

Best, Jeff Davis

 "Everything's hard till you know how to do it."
                       Ray Charles


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