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Earth had two moons?

Miss_Kitt

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M
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Feb 20, 2008
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So I was watching a show on Science or National Geographic the other day, about the history of the solar system, and they said that scientists now believe that Earth most likely originally had TWO moons after the impact with Theia, and those two eventually combined into our current moon.

Does anyone have a good website or some articles to point me at? This is a new idea to me, and while I find it interesting, I'd like to know more about it. How well is this theory established? What evidence supports it? Who came up with it?

I'm hoping some of the astronomy buffs here can save me a lot of wasted time trying to find valid information instead of nutjobs saying there is a Second Evil Moon that will Bring About Armageddon, etc.

Thanks in advance, MK


PS Wish I could just buttonhole Phil, he could probably tell me before the elevator arrived.
 
OnlyTellsTruths said:
The first comment on that article echos my sentiments as to why this sounds like the less likely scenario.
Click to expand...

How long did it take for the spin-orbital resonance to occur? I can't find estimates of that. If it took long enough, I presume there wouldn't be that much of a difference between the two sides. Plus IIUC the article is saying that the far side differs in composition. For that to happen by infalling meteorites, there'd have to be a lot of them -- is there enough to explain that? And I guess underneath the far-sides mountains should be a layer of KREEP consistent with the near side -- would the recent radar mapping missions be able to detect that? And did they?

As to why it is the near side of the moon that is now showing the non-impacted side in the 2nd moon impactor hypothesis, I presume the impact caused a dipole moment along the impact axis, and that's where the spin-orbit resonance would settle.

It's an interesting hypothesis.
 
I love the comments on that page, with laymen positing their own theories as though what makes sense to them trumps actually checking if the math works out.
 
The_Fire said:
According to QI and the nice young man Stephen Fry, we actually currently have 9...
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... and he's wrong (lovely though he is). They got confused between satellites orbiting Earth and asteroids in resonant solar orbits -- such as Cruithne. The latter's orbits, when viewed in a rotating frame of reference synchronised with Earth, look as if they're bean-shaped. But they don't go round the Earth.

http://en.wikipedia.org/wiki/3753_Cruithne

another interesting factoid is the moon's orbit is always concave to the Sun.
 
Thanks again, fuelair, that was a good start!

When my neck feels a bit better I'll continue locating more information, since this intriguing theory could be tested in a number of ways.

I love that we now have, in a number of sciences, the ability to test things largely with a new examination of existing data. One more 'gift' of enormously more computing power and programming expertise available on the cheap.

-- MK
 
Miss_Kitt said:
Thanks again, fuelair, that was a good start!

When my neck feels a bit better I'll continue locating more information, since this intriguing theory could be tested in a number of ways.

I love that we now have, in a number of sciences, the ability to test things largely with a new examination of existing data. One more 'gift' of enormously more computing power and programming expertise available on the cheap.

-- MK
Click to expand...
Very true - and very neat - and hopefully that will continue right on!!:)
 
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