‘How did the moon form?’ It’s a question we’ve all asked and one scientists can’t 100% answer.

The ‘giant impact hypothesis’ is the most accepted theory.

About 4.5 billion years ago, a protoplanet (nicknamed Theia) about the size of Mars slammed into Earth. The theory makes sense on the physics side of things. But, one major issue always pops up with this theory. The material on the moon is incredibly similar chemically to material on Earth.

Here’s a video from the History channel showing the moment the moon began to take shape.

Each world has its own chemical signature. Venus, Mars and even asteroids have different chemical ratios of various materials.

If Theia formed in a different part of the solar system, then the majority of the moon shouldn’t look so similar to Earth’s mantle. Or, so scientists thought.

A new study says there’s a good chance Theia and Earth were nearly identical.

Researchers from the University of Bordeaux in France and the Israel Institute of Technology in Haifa say there is a decent chance that Theia and Earth were nearly identical chemically.

The researchers looked at 40 simulations of planetary accretion (gradual growth from the accumulation of smaller particles, or planetary bodies) of the solar system’s inner planets. Near the end of each simulation, there were 3-4 rock planets.

“We find that different planets formed in the same simulation have distinct compositions, but the compositions of giant impactors are statistically more similar to the planets they impact. A large fraction of planet-impactor pairs have almost identical compositions. Thus, the similarity in composition between the Earth and Moon could be a natural consequence of a late giant impact,” the researchers write in their study.

Earth Just Can’t Shake This Small Asteroid

theia and earth collision

Image credit: Joe Tucciarone

Previous studies put the odds of Theia and Earth being chemically similar at just 1%. This new study increases it to anywhere between 20% to 40%. It’s not 100%, but it’s a lot better than 1%.

“We conclude that our findings can potentially resolve the apparent contrast between the observed similarity of the Earth and the Moon composition and its difference from that of other Solar System bodies,” the researchers write.

More planetary studies will be needed to completely nail down the riddles of the moon. But, this one is looking a bit clearer.

Here’s a bonus video of the moon from the time it formed to today.

Image credit: Dana Berry

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