[meteorite-list] Did The New Moon Lose Its Iron Heart?

[Ron Baalke]

http://space.newscientist.com/article/mg19325875.700-did-the-new-moon-lose-its-iron-heart.html

Did the new moon lose its iron heart?
New Scientist
23 January 2007

The moon may not be just a chip off the old planetary block. It could 
have formed at the same time as Earth from the same primordial stuff.

The current theory says that the material that now forms our moon was 
ejected when Earth was struck by another planet-sized body. But Peter 
Noerdlinger at Saint Mary's University in Halifax, Canada, says this 
theory has problems. "The collision has to be implausibly gentle. You 
practically need someone to hold a Mars-sized object just above Earth 
and drop it, to avoid messing up Earth's orbit."

The simpler idea that Earth and the moon were both created from the 
same gas cloud had been rejected because it could not explain why 
Earth formed an iron core and the moon did not. Now, Noerdlinger has 
an answer for that.

He suggests that the proto-moon did have an iron core, but that the 
satellite was ripped apart in a close encounter with Earth. His 
calculations show that iron from the core would be pulled towards 
Earth, while the remains of its rocky outer shell reassembled into 
our iron-free moon.

This fits with evidence that the Earth acquired a veneer of iron 
after it formed, Noerdlinger says. He presented the work at the 
American Astronomical Society meeting in Seattle, Washington, last 
week.

>From issue 2587 of New Scientist magazine, 23 January 2007, page 16