The Moon’s origins lie in Earth’s frontal collision with Theia, an international team of researchers has recently established.
The findings, featured in the Journal Science, on Friday, January 29, help shed light into our natural satellite’s earliest beginnings.
It had been a well-documented fact that the Moon formed approximately 4.5 billion years ago, when our planet crashed against Theia.
Some had speculated that this mysterious object which was orbiting through our Solar System was roughly the size of Mars, while others had suggested that its dimensions were actually much more impressive, comparable to Earth’s.
The real dilemma however wasn’t about Theia’s proportions; instead it concerned the actual collision that occurred between this space object classified as an Earth trojan and our budding planet.
More precisely, certain scientists had claimed that the impact had been a lateral one, at around 45 degrees or so, causing material from the two celestial bodies to be displaced and ejected into space. That debris was drawn closer and closer together until it eventually merged, giving birth to the Moon.
Another theory was that the crash between the Earth and Theia was in fact a frontal one, but some had been quick to discard this hypothesis claiming that such an occurrence would’ve been cataclysmic for the two Solar System objects, blowing them to smithereens and creating an asteroid belt between Mars and Venus.
Now however, recent research is suggesting that a head-on collision was actually behind the Moon’s origins after all, no matter how improbable this scenario had appeared at first.
The study was led by Edward Young, professor of cosmochemistry and geochemistry at the University of California Los Angeles (UCLA), and his fellow colleagues, Paul Warren and Issaku Kohl.
Also instrumental in this analysis were Alessandro Morbideli and Seth Jacobson, planetary scientists at the University of Nice Sophia Antipolis in France, as well as David Ruble, research professor at the University of Bayreuth in Germany.
Together, the team discovered that the Earth and the Moon share the same distribution of oxygen isotopes. Namely, on our planet’s rocks, the vast majority (99.9%) of oxygen atoms is represented by O-16 (with 8 neutrons and 8 protons), but there are also O-17 isotopes (with 9 neutrons), and O-18 isotopes (with 10 neutrons).
Although normally each Solar System body has a specific ratio between these oxygen isotopes, just like human beings can be distinguished based on their fingerprints, on lunar soil samples retrieved during the Apollo missions 12, 15 and 17, there is an identical correspondence between O-17 and O-16 to the one found on Earth (5 parts per million).
This suggests that our planet wasn’t struck from its side in a mere grazing after all, because then the Moon would’ve resulted mostly from debris scattered by Theia, thus sharing the chemical signature of that space object, and having little in common with oxygen isotope distribution identified in Earth’s rocky fragments.
Instead, the obvious similarly is indicative of the fact that the impact was a full frontal one, probably causing Theia to be completely obliterated.
Its debris was eventually equally distributed between the Earth and the moon, which would explain why our planet and its natural satellite have the same chemical signature when it comes to oxygen isotopes.
As study authors argue, if the impact hadn’t occurred, then Theia would’ve likely become a planet in its own right, as it was in its earliest stages of evolution and expansion.
Now that this mystery regarding the Moon’s origins appears to have finally been solved, researchers are toying with another theory, which states that when the two space objects crashed, the Earth was depleted of any water that may have been present on its surface.
However, tens of millions of years afterwards, asteroids that collided with our planet probably delivered water once again on its surface, allowing life to gradually flourish.
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