Solar System Origin

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Dear All,


I understand that one of the most popular theories concerning the origin of the solar system begins with cloud of gas and dust (called a nebula), assumed to be the remnants of a supernova; in order to explain elements such as iron and above.


That this nebula begins to flatten into a spinning pancake shape with a bulge at the center, with the bulge forming the sun and with the various planets condensing out of the rest of the pancake. All of this I can understand and accept.


However, why is the sun composed mostly of hydrogen and not the denser elements such as iron and above, which should have headed to the center of the solar system, due to gravitational forces, the same way they did when earth condensed?


Is there any theory on why the sun does not contain the heavy elements and the planets the gaseous elements or or gas molecules?
 

Answers and Replies

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There simply is a lot more hydrogen than everything else - a LOT more.
Not only the Sun, but the gas giant planets are predominantly hydrogen.
The sun probably does contain minute traces of heavier elements.
 
mathman
Science Advisor
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Dear All,


I understand that one of the most popular theories concerning the origin of the solar system begins with cloud of gas and dust (called a nebula), assumed to be the remnants of a supernova; in order to explain elements such as iron and above.


That this nebula begins to flatten into a spinning pancake shape with a bulge at the center, with the bulge forming the sun and with the various planets condensing out of the rest of the pancake. All of this I can understand and accept.


However, why is the sun composed mostly of hydrogen and not the denser elements such as iron and above, which should have headed to the center of the solar system, due to gravitational forces, the same way they did when earth condensed?


Is there any theory on why the sun does not contain the heavy elements and the planets the gaseous elements or or gas molecules?
http://chemistry.about.com/od/geochemistry/a/sunelements.htm

From above:
Elements in the Sun

Element % of total atoms % of total mass
Hydrogen 91.2 71.0
Helium 8.7 27.1
Oxygen 0.078 0.97
Carbon 0.043 0.40
Nitrogen 0.0088 0.096
Silicon 0.0045 0.099
Magnesium 0.0038 0.076
Neon 0.0035 0.058
Iron 0.030 0.014
Sulfur 0.015 0.040
 
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thank you mathman, but it still does not explain why the earth, at least, has so much iron, etc., or why when we go beyond mars we run into the gas giants.

gravity forces in the original nebula should have brought all of the heavy elements to the centre of the solar system, while it was still in the particulate stage.
 
Vanadium 50
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gravity forces in the original nebula should have brought all of the heavy elements t
Not if they are in orbit. The same argument can be applied to the earth today, right?
 
3,377
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thank you mathman, but it still does not explain why the earth, at least, has so much iron, etc., or why when we go beyond mars we run into the gas giants.
The rocky inner planets probably did have thicker atmosphere including a lot of hydrogen in the earliest stages of formation.
Free hydrogen though, being very light is easily pushed away over time by solar wind leaving the remaining 10% of heavier material to agglomerate.
In the case of gas giants, their much greater gravity enabled them to hold on to more of the initial hydrogen
 
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Guys,

thank you all for your responses. however, I am still not certain that the question has been answered. I shall always feel that there is something amiss with the current theory.
 
3,377
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In a sense what you are saying is 'why are there planets?, why didn't everything simply just collapse into a central star?
Well in fact most of the nebula, over 99% of it, did just that.
The planets and other smaller bodies formed from relatively small localised eddies of matter within the broadly collapsing disk of material.
 
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rootone,

maybe that is the answer. assuming that the heavier elements were homogenous in the original nebula, and mercury, venus, earth and mars are only more dense because the lighter elements have been blown away by the sun.
 

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