Moon Likely Formed By A Planet Hitting Earth

| 7 Jun 2014 00:03

New scientific evidence suggests that Earth underwent a massive moon-forming impact, most likely with a planet the size of Mars.

Despite having lived in our own little corner of the universe for hundreds of thousands of years, there are many things we're just figuring out about it. Take the moon, for example; even though there's only the one that we visited a few times, we're still not sure how it formed in the first place. The prevailing theory is that the Earth was struck by something massive, forcing pieces of debris into orbit that eventually coalesced into our moon. It's a theory that mostly works if whatever we hit was the size of a planet, and new evidence is suggesting that's exactly what seems to have occurred.

The basic idea is that when the solar system first formed, there were many more planetary bodies flying around that wouldn't settle into solar orbits. One of these planets, a Mars-sized object scientists dubbed "Theia", smacked into the Earth and broke off pieces from both objects. Eventually the debris merged into the moon we see in the sky, which scientists have tried to prove by checking lunar chemistry for irregularities.

Most studies haven't been detailed enough to pick up anything noticeable, but now Germany's Georg-August-Universität Göttingen has come across something unique. The lunar samples recovered during moon missions contain higher than expected amounts of oxygen-17, a heavy oxygen isotope, than the Earth normally contains.

"The differences are small and difficult to detect, but they are there," explained team lead Daniel Herwartz. "This means two things; firstly we can now be reasonably sure that the giant collision took place. Secondly, it gives us an idea of the geochemistry of Theia.

"Theia seems to have been similar to what we call E-type chondrites. If this is true, we can now predict the geochemical and isotopic composition of the Moon, because the present Moon is a mixture of Theia and the early Earth."

Based on this discovery, Herwartz suspects 30 to 50% of the moon was once part of Theia, but further study is needed. There are still other theories that might explain the oxygen-17 ratios, such as whether objects like comets altered Earth's oxygen chemistry. Getting cracked open by another planet certainly would be the more spectacular explanation, but we'll just have to see how future research proceeds.

Source: National Geographic

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