Friday, March 21, 2008

Inner Planets May Have Different Origins

via National Geographic, a new analysis is challenging the long held theory that the inner rocky worlds in our solar system formed from the same general building block materials. The idea is that these planets are formed from the same mineral building blocks as the most common and oldest type of asteroids and meteorites, called chondrites. However, Earth's mineral composition doesn't quite match up, and a new French study (French?) of Mars and the Moon suggest that these worlds don't match up either.

"What our results suggest is that the sorting of the elements that make up these planets may have happened at a much earlier stage than had been believed," said Alex Halliday, a study co-author from Oxford University. "The composition of these worlds is inconsistent with them simply forming out of large 'lumps' of stony meteorites like those we see today in the asteroid belt."

Chondrites are commonly characterized by an abundance of the mineral neodymium 142, which is a byproduct of the decay of the metal samarium. However, Earth contains a higher percentage of neodynium than common chondrites, leading traditional earth science theorists to speculate that Earth's system of plate tectonics was "hiding" elements that would balance out the chemical ratio. However, the new study finds that both the Moon and Mars have the same excess of neodymium, even though they do not have active plate tectonics. These findings may suggest that the rocky planets may have formed earlier in the history of the solar system than the other chondrite type bodies.

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