History of The Big Splat hypothesis

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quantropy
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History of The Big Splat hypothesis

Postby quantropy » Thu Jan 06, 2011 3:28 pm UTC

Two or three years ago I read the book "The Big Splat or how our moon came to be" by Dana Mackenzie, which describes the Giant Impact Hypothesis for the formation of the moon from the impact of a Mars sized body. What really surprised me though, was that it became the consensus view for the formation of the moon in about 1984, and at that time and since I've been to lots of astronomical talks and read lots of science magazines, but reading the book was the first time this idea came to my attention. Now I sometimes nod off in talks, but I've seen other hypotheses move over the years from speculative ideas to the consensus viewpoint. Not this one though, which is odd, since it seems like the sort of thing everyone would be talking about. What do other people remember about how they heard about this hypothesis?

Moose Hole
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Re: History of The Big Splat hypothesis

Postby Moose Hole » Thu Jan 06, 2011 4:45 pm UTC

I'm pretty sure I saw this on NOVA about 10 years ago. There was also something in it about the dark spots being from the heavier, radioactive elements gravitating toward the Earth side of the moon and burning the surface, and that the back of the moon doesn't have the spots.

Carnildo
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Re: History of The Big Splat hypothesis

Postby Carnildo » Fri Jan 07, 2011 8:37 am UTC

Moose Hole wrote:I'm pretty sure I saw this on NOVA about 10 years ago. There was also something in it about the dark spots being from the heavier, radioactive elements gravitating toward the Earth side of the moon and burning the surface, and that the back of the moon doesn't have the spots.

These "dark spots" are called maria. It is true that the back of the Moon doesn't have them (or rather, the few it does have are much smaller than the nearside ones), but it is not true that the Earth's gravity pulled the radioactive elements towards the nearside. If you measure the Moon's gravitational acceleration in a rotating reference frame, you'll find that the near hemisphere feels a force pulling towards the Earth, and the farside feels an exactly identical force pulling away. In order for radioactive elements to concentrate on the nearside, there would have to have been an asymmetric distribution to begin with.

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Antimony-120
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Re: History of The Big Splat hypothesis

Postby Antimony-120 » Sat Jan 08, 2011 2:50 am UTC

Moose Hole wrote:I'm pretty sure I saw this on NOVA about 10 years ago. There was also something in it about the dark spots being from the heavier, radioactive elements gravitating toward the Earth side of the moon and burning the surface, and that the back of the moon doesn't have the spots.


Also, they don't "burn" the surface. What they might do is increase the heat on one side, and therefore lead to increase volcanism, which would cause the maria. But like Carnildo said, there's some issues with that hypothosis.
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