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The Giant Impact Theory  (Source:
Two new studies attempt to prove the Giant Impact Theory in different ways

Two different studies say they've found evidence supporting the theory that the moon was created from a collision between Earth and a Mars-sized body.

The Giant Impact Theory, which was proposed back in 1975, suggests that the early Earth and a Mars-sized planet called Theia collided with one another. This completely obliterated Theia, and its composition created a ring around Earth and eventually came together to create the moon.

While scientists have been able to explain how this event occurred, one major thing didn't add up: the composition of the moon.

Scientists long believed that for this theory to be true, the moon would have to be composed mainly of Theia's elements. Moon rocks from that were brought to Earth were studied, and surprisingly, they had the same types and amounts of elements that the Earth had, including titanium, silicon and oxygen. This didn't make sense, and has left the theory wide open for the last 30+ years.

However, scientists from Washington University in St. Louis managed to measure a small excess of a heavier variant of zinc in moon rocks from that were brought to Earth in the 1970s. They believe the excess is due to heavier zinc atoms condensing out of the collision's cloud faster than the lighter zinc atoms, and the vapor that remained escaped before it condensed.

This bit of sorting by mass is called isotopic fractionation, and it's what scientists have been looking for all along. This shows that the moon rocks were depleted of easily evaporated elements called volatiles, and a large collision could explain this depletion while other theories can't.

"The magnitude of the fractionation we measured in lunar rocks is 10 times larger than what we see in terrestrial and Martian rocks," said Frédéric Moynier, PhD, from Washington University in St. Louis. "So it's an important difference."

But the Washington University team isn't the only one to bring new evidence to the table. Robin Canup, a planetary scientist from the Southwest Research Institute Colorado, used Harvard scientists' findings to create a theory of her own related to the collision.

According to the Harvard team, which used computer simulations to create its theory, ancient Earth had to have been spinning too fast for today's 24-hour rotation. They suggested that early Earth and a body half the size of Mars could have collided where both were obliterated and combined elements to create both the moon and Earth's heavy iron core/lighter rock layers.

At a later point, Earth's rotation could have slowed due to the moon and sun aligning in a way that changed Earth's orbit.

Canup used the idea that Earth's rotation was slowed and came up with the theory that two bodies similar in size collided at a slow speed, and their materials merged to create the Earth and moon.

Source: Science Daily

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I wonder
By bug77 on 10/20/2012 6:07:21 PM , Rating: 1
So, there were two planets sharing an orbit at the exact distance from the Sun necessary to sustain life. Could this mean the odds of life in other solar systems goes up if this collision theory is correct?

RE: I wonder
By Goty on 10/21/2012 1:21:21 AM , Rating: 2
They did not share an orbit, they had intersecting orbits. During planetary formation and heavy bombardment, there were many objects with (relatively) highly elliptical orbits. Frequent collisions resulted in the accretion of many of those objects onto the more massive bodies and circularization of the orbits of most of the bodies in the solar system.

Also, no.

RE: I wonder
By bug77 on 10/21/2012 2:09:16 PM , Rating: 2
Ok, let me explain a bit better. One of the arguments against life on other planets is that a planet needs to orbit in a rather narrow region around its sun so that life (as in human, not some exotic form) can develop. Now, of course two celestial bodies won't share exactly the same orbit, that would be a terrific coincidence. It could be downright impossible, I don't know the math. But the fact that another body, large enough to create the Moon was orbiting in the same neighborhood, I think that would mean the probability of planets forming within the comfort zone isn't so low after all.
Of course, astronomy is just a hobby of mine, so there's a lot of things I'm unaware of. That much I know.

RE: I wonder
By delphinus100 on 10/21/2012 12:56:21 PM , Rating: 2
Goty is right. Such collisions don't care if they occur in a biologically comfortable part of their systems, or not. It wouldn't seem to change the chances of life elsewhere, one way or another.

It would help if we could more easily detect Earth-mass (and smaller) exoplanets, to get a better sense of overall planetary formation dynamics, but give it time...

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