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Guru
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How Earth got its Moon

08/23/2006 12:05 PM

The European Space Agency's lunar-orbiting craft called SMART-1 has completed the first detailed chemical mapping of the lunar surface. The detected chemicals, such as calcium and magnesium, give a boost to the longstanding theory that the Moon formed from the debris flung into space after a collision between early Earth and a Mars-size planet - that's according to a Space.com article.

The term "Mars-size planet" puzzles me a bit - where did such a planet come from? May it be that the Asteroid belt originally had such a large planet that got disturbed, maybe even violently, creating the asteroids and a big piece that has hit Earth later?

It is unlikely that such a metal-rich planet could have originated in the Kuyper belt, for those bodies are mostly ice and dust. Then, who knows, is this not how Earth's massive oceans were formed?

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The Engineer
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#1

Moon Theory

08/23/2006 2:36 PM

I think part of the reason for the theory is due to the very low density of the Moon. Although the moon is much larger than Pluto, it has half the mass. The theory explains that a large object collided with Earth ejecting enough matter into orbit to form the moon. The matter ejected would have naturally been lighter elements and thus the moon isn't very dense.

It's a good theory, and its probably true, but I'm not willing to commit to the theory yet. It seems to create a ton of questions, some of which Jorrie is asking here.

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#2

Moon

08/23/2006 7:44 PM

It amazes me that this is hailed a a recent theory.In 1958, while still in grade school, my science teacher taught us that that was how the moon formed.(Except he said a "Large Asteroid" instead of a 'Mars-sized planet'") It seems to have been forgotten about for nearly 50 years, and is now appearing as a new and profound theory.Wish I still had my science text book from the fifth grade.......

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The Engineer
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#3
In reply to #2

Re:Moon

08/24/2006 12:13 AM

I didn't realize it was hailed as a recent theory.

I just have a hard time visualizing the event and the moon turning out all nice and round and in such a nice orbit. There does seem to be a lot of evidence to support it.

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Guru

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#5
In reply to #3

Re:Moon

08/24/2006 11:03 AM

I too, have a hard time visualizing the event. For the theory to hold up, it seems that BOTH the earth and its moon would have to have been blown to smithereens and re-coalesced. Otherwise, there would be a huge crater on earth the size of the moon.

So, if the earth blew up into two clouds (split in a ratio of 1:6 by the trajectory of this missing planet) then I'd expect the densities and constiuents of both earth and the moon to be more similar than they are.

I seems, to me, more reasonable to suspect that the two bodies formed independently and at roughly the same time. Proximity in the original cloud would dictate a high probablity that the bodies would share constituents, but that they could also be disimilar in some of the ways in which all the planets are disimilar.

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#6
In reply to #5

Re:Moon

08/24/2006 6:10 PM

The Theory, IIRC, (it was a long time ago), involved
a grazing collision, with surface matter ejected,
some of it recaptured, some lost, some forming
a ring, and eventually, the moon.
There is evidence of another high energy event, (the one that
tipped neptune on its side), which argues for another planetary
collision.
Such events were probably common in the early solar system
and possibly we find evidence only of the last ones.

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Guru
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#4
In reply to #2

Re:Moon

08/24/2006 3:16 AM

It's not a recent theory - it's one of many fairly old theories. It's just that this is new evidence in support of the collision scenario.

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