'Giant Impact Theory' of Moon's Origin Modified

[n2doc]

New research from geophysical scientist Junjun Zhang and colleagues at Origins Lab at the University of Chicago, suggests that the giant impact hypothes of the creation of the Moon might be wrong. The team found that in comparing titanium isotopes from both the moon and the Earth, that the match is too close to support the theory that the moon could have been made partly of material from another planet.
According to the giant impact hypothesis, there was once a Mars-sized body referred to as Theia orbiting in our solar system. Theia would have formed in about the same orbit as Earth, but about 60° ahead or behind. When the protoplanet had grown to be about the size of Mars, its size made it too heavy for its orbit to remain stable. As a result, its angular distance from Earth varied increasingly, until it finally it crashed into the Earth.
The collision would have occurred 4.533 billion years ago when Theia would have hit the Earth at an oblique angle, and destroyed itself in the process. Theia's mantle and a significant portion of the Earth's silicate mantle were thrust into space. The left over materials from Theia mixed with the materials from the Earth and eventually formed the Moon.

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http://www.dailygalaxy.com/my_weblog/2012/03/new-evidence-nixes-giant-impact-theory-of-moons-origin.html

[BlueIris]

1. Interesting. The 'giant impact' explanation for the Moon's existence

was the first thing I ever learned about the Moon. So I find it curious that it's changing.

[Orsino]

2. Not getting this.

Everything I'd ever read or seen televised about the collision theory implied that today's Earth didn't exist before the impact--that there was an Earth Mark I and Theia, and that today's Earth and its moon both coalesced from the remains of the impact (which obliterated the previous planets). If that were so, we would expect similar isotopic make-ups in the resulting bodies.

I guess they're now saying that today's Earth is made mostly of the same stuff as Mark I, and is in nearly the same orbit.

[n2doc]

3. It is a matter of degree

I think they thought enough of Theia survived in the collision to make the moon chemically distinct. Sort of a 'glancing blow'. This work says, no, both bodies were well mixed in the impact and are essentially the same chemically. Would have been something to see!

[Dead_Parrot]

4. What's been niggling me about this...

...is the assumption that Theia would have had the same isotopic composition as Mars and Vesta, rather than Earth mk I. I'm not seeing any particular reason why this would be the case.

Anyone got something I'm missing?

[sakabatou]

5. The giant impact theory is still right... just modified?

Is this what the article is stating?