Earth vs. Theia! First and Last Round!

I have a thing for stuff that is outrageous, different and intriguing. Greek Gods, bizarre happenings in space, and archaic events? Yes, please! So, I just recently learned about how Moon was the result of an ancient collision between old Earth (or some people call it Gaia) and another theoretical planet named Theia 4.5 billion years ago. Also known as The Big Splash or The Theia Impact, the historical collision was believed to be the origin of Moon.

Simulation of how Theia (black), orbiting in Langrange point L4 before it collided head-on with Earth (blue) before the remnants condensed into Moon (gray) SOURCE

Theia, a hypothesized planetary-mass planet was said to be the size of Mars. In the early Solar System, Theia was an asteroid, also called Earth trojan, orbiting in Langrange points L4 and L5. Based on the investigation, astronomers think that the collision happened before our Solar System was formed, approximately 100 million years before. It was said that Theia had struck a nearly full formed Earth at a 45 degrees angle with a strapping side swipe, with an impactor velocity of 4m/s which is quite relatively slow. There is also a hypothesis which says that the impact initiated a vigorous mixing which made Theia’s iron core to mix into Earth’s core and Theia’s mantle assembled into Earth’s.

Due to the impact, shock wave spread out and materials from both planets were jumbled together and discharged out into the orbit. The materials, consisting of rocks and minerals orbit around the Earth for some time before they fused together, forming the Moon we know today.

The artist’s depiction of the collision. SOURCE

One of the evidences which support this event was the similarities in the oxygen isotopes of both Earth and Moon. Edward Young, a geochemistry professor at UCLA and also the one who lead the study, found that the oxygen isotopes that were found on Earth and Moon are indistinguishable. This furthermore support the argument that Theia had thoroughy mixed into Earth before their debris coalesced to form Moon. Further read can be done here.

More investigations are still being made, and many hypothesis are still being voiced out by astronomers. The verdict? I myself am still not sure. Whatever it is, I believe that everything has their own existence.






3 thoughts on “Earth vs. Theia! First and Last Round!

  1. Hey Naz, your blog is really cool and do you have any idea whether there are any other theories of the formation of the moon other than this large-impact collision of Theia and Earth.


  2. The Big Splash really sounds bizarre but at the same time very exciting as it tells us the origin of our beloved Moon. One of the other theories that I found was The Fission Theory. It tells us how Earth and Moon is actually one body, and that the Moon has separated from Earth through fission process early in the history of Solar System. The present Pacific Ocean is the most popular site for the part of the Earth from which the Moon came. This theory was thought possible since the Moon’s composition resembles that of the Earth’s mantle and a quickly spinning Earth that could have made Moon to be detached. Further investigation is still undergoing, so there is not much I can say about this theory.


  3. Hi, I found this blog post is very interesting and it helps me to understand the exception for the formation of a very large moon for a small planet like the earth. so, does this mean that, the our moon did not form the same way for the jovian planets’ moons? as for jovian moons, they are small planetesimals that got caught by strong gravity of the planet itself.


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