January 26, 2007 | David F. Coppedge

Moon Origins Not Set in Stone

The leading theory for the origin of the moon has been for some time now that a massive object hit the Earth, and the debris formed the moon.  New Scientist reported one astronomer who doesn’t buy it.  “The collision has to be implausibly gentle,” said Peter Noerdlinger to the American Astronomical Society.  “You practically need someone to hold a Mars-sized object just above Earth and drop it, to avoid messing up Earth’s orbit.
    His theory returns to the old idea that the Earth and the moon both formed from a primordial nebula.  He adds a twist that the moon was ripped apart by a close encounter with the Earth, then re-formed without its iron core.  The iron was redeposited as a layer on the early Earth.  “This fits with evidence that the Earth acquired a veneer of iron after it formed, Noerdlinger says.”

It’s premature to say whether Noerdlinger’s ideas will become accepted.  What’s notable at this time is that the accepted theory has problems, and that his theory seems even more ad hoc.
    Positing an unknown body to come in just at the right time and velocity to make two bodies from one seems a tremendously lucky accident.  The glancing-impact theory was a post-Apollo invention to overcome big objections to the three other hypotheses: the primordial nebula hypothesis, the spin-off hypothesis, and the impact hypothesis.  Now, at least one astronomer feels the consensus theory is also too improbable.  But is his any better?  He has to envision a close encounter with just the right conditions to break up the moon and make the Earth steal its iron.
    If nothing else, this article shows that people living today who weren’t there and don’t know everything have a hard time putting the pieces together.  There’s always a way out for them: believing in miraculous luck.  At least his miracle led to iron for the hemoglobin in his brain, and iron for the sword that defined human history.

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