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

From: Anders Sandberg (
Date: Thu Jan 10 2002 - 05:48:25 MST

On Thu, Jan 10, 2002 at 12:57:35AM -0800, jeff davis wrote:
> 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.

A quick hint: which is retained most easily in a warm low gravity
environment like Earth and early asteroids, hydrogen or iron? Remember
that there has been several enriching processes going on for a long

> 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?

The binding energy curve has a quadratic minimum around iron, so energy
storage is unlikely. I haven't done the math (and I'm neither an
astrophysicist or skilled in statistical mechanics) but the chemical
equilibrium seems heavily iron-tilted. I think this is studied in most
textbooks in stellar astrophysics.

> 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.

But the sun isn't an equilibrium system, it is very much an open system
- fuel is consumed and heat radiated away.

> 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).

Yes, it is a wonderfully complex environment. I want to see it
> 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.

Me too.

I recently got myself a geology textbook, and it was a revelation. The
stories stones tell! How amazing a crack in a rock can be! The sheer
power of sand and waves!

I think everybody should read a bit of geophysics, astrophysics or
similar sciences to get a whiff of just how marvellous our world is.

Anders Sandberg                                      Towards Ascension!                  
GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y

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