Science and Health

Lunar Rocks Show Signs Moon Formed After Planets Collided

Scientists have found a key difference between moon and earth rocks, which they say is evidence the moon was formed when two planets collided.

Lunar Rocks Show Signs Moon Formed After Planets Collided
Wikimedia Commons / Thomas Bresson

Ever since NASA's Apollo missions brought back the first lunar samples of rocks and soil, scientists have been learning a lot about our cosmic neighbor — including the theory that the moon was once a part of Earth.

Now, researchers in Germany studying those same samples have uncovered new evidence regarding a fundamental question about the moon: if it used to be part of Earth, how'd it get up there in the first place?

Currently, the prevailing theory about how the moon was formed is that a hypothetical Mars-sized planet dubbed Theia collided with Earth about 4.5 billion years ago. The moon then formed from the debris of the crash. (Via BBC)

Problem is, Theia should have left some evidence of the impact behind in the moon's chemical makeup. But the lunar samples scientists examined all looked pretty Earth-like, with no trace of Theia ... until now.

After analyzing samples using more precise techniques, researchers at Germany's University of Gottingen found lunar rocks have a slightly different level of one oxygen isotope than Earth rocks. The difference hadn't been detected yet because it's miniscule — only twelve parts per million. (Via Science)

Still, even the minor difference has many researchers overjoyed. One planetary scientist told Science"It is a relief that a [disparity in ratios] has been found, since the total absence of difference between Earth and moon would be hard to explain."

And without this disparity, scientists might have had to throw out the Theia impact theory altogether — which, as Time explains, is "a theory they were reluctant to see go simply because of its appealing simplicity."

But the findings might not have settled the issue just yet; one professor told the BBC he was surprised to see the difference was so small. "What you are looking for is a much bigger difference, because that is what the rest of the Solar System looks like based on meteorite measurements."

The findings were published in the journal Science on June 6, and will be presented at a geochemistry conference in California on June 11.