The Moon may have formed in a nuclear explosion

[jayfish]

http://www.physorg.com/news183884450.html

new theory suggests the Moon was formed after a natural nuclear explosion in the Earth's mantle rather than after the impact of a massive object with the Earth, as previously thought.The problem with the impact hypothesis is that simulations calculate the Moon should be composed of 80% impactor and 20% Earth, whereas in fact the isotope ratios of light and heavy elements found in Moon rocks so far examined are virtually identical to those on Earth.The fission hypothesis is an alternative explanation for the formation of the moon, and it predicts similar isotope ratios in the Moon and Earth. The hypothesis (credited to Charles Darwin’s son George in 1879) is that the Earth and Moon began as a mass of molten rock spinning rapidly enough that gravity was just barely greater than the centrifugal forces. Even a slight kick could dislodge part of the mass into orbit, where it would become the Moon. The hypothesis has been around for 130 years, but was rejected because no one could explain a source of the energy required to kick a moon-sized blob of molten rock into orbit.

I've never been a big fan of the impact hypothesis. This idea feels a bit more comfortable.

Jay

[El Supremo]

1. The biggest clue is that the moon orbits the Earth in the opposite...

direction that the Earth rotates. This explanation does not explain that. I'm still for a capture theory.

[jayfish]

3. I Think You Should Reconsider That ES. -NT-

Jay

[Ian David]

4. Well, it's all explained here in this video simulation

http://www.youtube.com/watch?v=8WZW4groJro

[AllenVanAllen]

19. That was great.

I always loved the opening of that show. The falling eagle is the best.
:hi:

[Kokonoe]

6. Hmm.. I don't see the moon orbiting in the opposite direction.

The Earth spins east and light from the waning moon is on the left, so that would be the same direction.

[caraher]

9. Not true... as seen from far, far above the north pole

Earth rotates CCW, orbits the Sun CCW, and the moon orbits Earth CCW. It's all basically the same direction.

[mike_c]

2. how does this fit the data that the Earth's rotational period...

...has been slowing since the event, presumably having been sped up by the impact? How would such an explosion and consequent loss of mass have affected the planet's rotation?

Jeeze, I hope I don't have to dig out an old physics text to try to figure this one out!

[jayfish]

5. Could It Be That Earth Had Been Gradually Slowing...

before the event? Perhaps as far back as the coalescence of the Suns accretion disk into the early solar system? The nuclear event and the drag induced by our new moon could have been major decelerators.

Jay

[mike_c]

7. well yes, but that begs the question "what accelerated it in the first place?"

The earth would have gained a great deal of angular momentum from such a collision and would have had a rotational period of about 5 hours or so after the collision, from which it has been slowing ever since. If we posit such rapid rotation without a collision, perhaps as a natural result of mass accretion during the planetary coalescence, what's the mechanism? IF the planet was spinning that quickly during the accretion phase, it's easy to see how shear forces could have created a molten crust and centrifugal force might have flung out enough mass to account for the Moon, but should such a sudden loss of mass have had a significant effect on the momentum of rotation? Would that have sped the Earth up even more? And would the lost mass have been flung outward intact, or piece-wise, a little at a time?

Gawd, I KNEW I should have paid more attention in physics, all those years ago!

[caraher]

10. It's not given that a collision would increase the angular momentum of Earth

It would all depend on the details of the impact whether rotation speeds up or slows down.

I'm really not sure what there is to explain here. Earth simply formed with nonzero angular momentum; there's no need to postulate some sudden acceleration at any special point in its history. Its rotational speed has been slowing, especially since the Moon formed, thanks to tidal interactions.

[jayfish]

17. Well, According To The Idea Put Forth In The Article;

it was a detonation coupled with the high rate of rotation (from mass accretion) that caused all that volume to leave Earth. Maybe if it was a powerful enough event(the moon is 1.2% the mass of the earth)and lasted for a long enough term it could itself have acted as a breaking mechanism. Sort of like a bottle rocket attached to the vane of a spinning pinwheel. All that relocated mass in the form of the moon might have done the rest.

Jay

[mindwalker_i]

8. Sorry, that can't be right.

If the moon orbited in the opposite direction that the Earth rotated, the moon would rise a little more often than once per day. The fact is that the moon rises about every 25 hours. so each day the moon is a little further in its orbit and the Earth's rotation has to catch up with it.

[Vinnie From Indy]

11. I am skeptical of the explosion theory

The odds are infinetly higher that it was an impact event. The evidence that the inner planets went through a long period of sustained bombardment by comets and space debris is overwhelming. Further, I would be interested to know how the explosion theory explains how enough explosive material could have been concentrated in one spot in the mantle to cause such an explosion.

[MicaelS]

15. The concentration is explained in the article

Their hypothesis is that the centrifugal forces would have concentrated heavy elements like thorium and uranium on the equatorial plane and at the Earth core-mantle boundary. If the concentrations of these radioactive elements were high enough, this could have led to a nuclear chain reaction that became supercritical, causing a nuclear explosion.

Not saying I agree with it, but it is definitely interesting.

[MicaelS]

12. So jayfish, why don't you like the impact hypothesis? n/t

[Vinnie From Indy]

13. WTF?

Are you having a debate with yourself?

[MicaelS]

14. No, I'm quoting jayfish in his original post.

And asking the question why he does not like the impactor theory. I forgot the quotation marks, sorry. Went back and made my post clearer.

[jayfish]

16. The Elemental Discrepancies Mentioned In the Article for Starters.

Another issue, for me anyway, is that we don't have direct evidence of a similar model. I would almost posit we have contradictory evidence in Mars. We are coming to accept the theory that Mars sustained its own massive impact. It was an impact so destructive that it blew away a third of the planets surface. Yet all mars has for satellites are the rubble piles known as Phobos and Deimos. I grant you that many of the particulars may be different but it's all theoretical anyway.

Jay

[MicaelS]

18. OK, thanks n/t