Mysterious Moon's Origins Confirmed? Scientists Are Close

The Moon: it's a heavenly body of changing faces and meaning. It's commonly associated with horror, romance, and above all, mystery. And even answers concerning how it came to be have remained unknown... until now.

Experts have long theorized that the Moon is NOT a true child of the Earth, but instead the remnants of a giant astronomical body that collided with our Blue Planet in a hit-and-run billions of years ago.

The collision occurred early on in the formation of our solar system, when dust and debris was still haphazardly flying around. It would not be unreasonable to assume then, that a rogue planetoid or massive Ceres-like asteroid could have bumped into a young Earth as it meandered along.

And this would not be unlike bumping into a stranger on a semi-busy street. The weird part would be his detached arm floating around you after the incident.

Experts named this hypothetical, rude customer Theia, and have estimated in the past that our Moon is made up of about 70 percent Theia material, with bits of Earth mixed in. This would then make the ratios of isotopes of oxygen, titanium, silicon and other elements from the Moon radically different from Earth's own ratios, as they came from predominately different sources.

Unfortunately, assessments of Moon and Earth geochemical compositions just don't back this theory. Early tests of Moon rocks and the Earth's mantle showed that they were stunningly similar, while newer tests showed that "the differences are small and difficult to detect, but they are there," according to Daneiel Herwartz, who led an analysis of samples provided by NASA from the Apollo 11, 12, and 16 missions.

And that's a problem for the Theia theory, explains Richard Walker, a professor of geology at the University of Maryland.

"The Mars-sized body that created the moon is expected to have been very different," he explained in a statement, noting that past models suggests that Theia likely came flying from a very different part of the Universe than the Earth's own material. "So the conundrum is that Earth and the Moon shouldn't be as similar as they are."

That's why Walker and his colleagues recently authored a new report investigating scenarios for the Moon's formation. (Scroll to read on...)

They looked, in particular, at the inevitable dust wave of material that would have followed Theia's initial impact. It was found that a lot of additional Tungsten - a robust free-element metal that could surive a planet-side impact - powedered the Earth's mantle around the estimated time of the collision. However, very little of it was isotope Tungsten-182. This, then, was assumed to be a signature for Theia material, and more of it would be found on the Moon.

And sure enough, this was right; but again, to a far lesser extent than was expected.

"The small, but significant, difference in the Tungsten isotopic composition between Earth and the Moon perfectly corresponds to the different amounts of material gathered by Earth and the Moon post-impact," Walker said. "This means that, right after the Moon formed, it had exactly the same isotopic composition as Earth's mantle."

This rules out the theory that Theia was simply similar to the Earth by coincidence. Having similar broad isotopic fingerprints is one thing - but such a perfect Tungsten-182 correlation would be near-impossible.

Walker and his colleagues now suggest that for this to have occurred, the impact was much less of a bump, and more of a hot and sloppy embrace - the surfaces of two astronomical bodies so tightly pressed against once another that their surface material thoroughly mixed.

This mixed material then broke away from Theia entirely - forming the Moon, while what remained cooled on the Earth's surface.

"We still need to work out the details," Walker added, "but it's clear that our early solar system was a very violent place."

The results were published in the journal Nature.

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