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Name: Stephen
Status: other
Grade: other
Location: Outside U.S.
Country: Australia
Date: Spring 2012

The currently accepted theory of planet formation is that our Earth got its iron from super nova explosions. If this is so, then why don't all the planets in our solar system have the same amount of iron?

Hi Stephen,

Your question is a bit more complicated than it appears. Thermodynamic forces are at work, all with important contributions. Physical chemistry and space physics put aside… think of settling swirling muddy water: Heavier, dense substances fall toward gravity, our Sun, quickly. Lighter, fine materials take far longer to settle out.

Iron has a Formula Weight of 55.8 g/mole and is ferromagnetic. Iron is Earth’s most abundant metal, but is also distributed in the heavier, denser solid planets, moons, asteroids and meteorites of our Solar System. All of the elements of planets and asteroids are distributed based upon centripetal acceleration, precession effects, geomagnetic fields, thermal and gravitational forces.

Our Solar System consists mainly of lighter elements. Magnesium, 24.35 g/mole, is the second most abundant metal on Earth, followed by nickel, calcium and aluminum. Our range of natural abundance tops out with primordial elements weighing less than about 209 g/mole. Earth’s heavier primordial elements are believed to be largely prepared from nuclear interactions elsewhere and deposited here by bombardment of space material.

Our gas giant planets and Neptune have very few elements heavier than about 35 – 40 g/mole. The lighter and less dense planets tend to be farther from the Sun.

Hope this helps!

Peter E. Hughes, Ph.D.
Milford, NH


This observation emphasizes that the supernova event did not produce a uniform distribution of atoms or that the development of planets is not the same for every planet. We have many sources of evidence for this non-uniform distribution. For example, the outer planets are gas giants whereas the inner planets are rocky. Current evidence of exo-planet formation gives a picture to the contrary, that gas giants tend to form much closer to their stars. There is water on Earth but very little on Mars - suggesting that there is not an even distribution of light elements. The asteroid belt between Mars and Jupiter is theorized to have developed because of the gravitational effects of Jupiter - suggesting that uneven distributions can result from gravitational effects. ... you get the idea.

Greg (Roberto Gregorius)
Canisius College

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