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  • Writer's pictureSiheli Siyathra

Theia, An Ancient Planet

If you could slice Earth in half, you would find the remains of another planet. That’s Theia. It has been hiding inside Earth for 4 billion years now. How did it get there? You’d have to go back in time to find out.

Imagine you went into space and travelled 4.5 billion years into the past. You would see a beautiful Nebula that would soon become our Solar System. Space dust and debris are slowly drifting to the centre of the Nebula. Soon, this jigsaw puzzle of debris becomes too heavy and dense. The temperature begins to rise and triggers a nuclear reaction. Another millisecond and there’s an explosion so powerful that the shock waves travel far into space. Our Solar System is created.

When the dust clears, you can see a bright light still shining in the middle. It’s our sun. 93 million miles away, you can see a hot, rocky mass. That’s the Earth. It’s still developing the core. Streams of lava that cover the Earth’s surface are gradually cooling down.

A few tens of millions of years after the sun’s birth, you notice a strange object hurtling toward Earth. This strange object is Theia. It’s a small planet that was born at about the same time as Earth. And now, it’s following a crazy spiral trajectory at enormous speed.

Okay, back to the present for a moment. Scientists believe that Theia was a ball Venus and Jupiter played with. Venus pulled Theia in one direction, while Jupiter pulled it in another. But the sun makes up 99.8% of the gravity in the Solar System. That’s why the star set its own rules, making Theia move in almost the same orbit as Earth.

Back to when Theia was hurtling toward Earth. A collision cannot be avoided, as Theia is travelling at 14,500 km/h. If it crashes into the Earth at a certain angle, both planets would be destroyed. But the collision happens at a perfect 45-degree angle. The impact literally vaporizes huge amounts of rock. The shock wave sends the remaining debris into Earth’s orbit. A huge crater is created at the impact site. It soon fills with boiling-hot lava. The debris and the remnants of Theia begin to orbit our planet. All the shards get pulled together by the remaining gravity of Theia. They later form the moon. The collision tilts our planet and accelerates its rotation.

Theia is still inside our planet. Of course, you won’t see a whole planet hiding inside ours; most of Theia has melted in Earth’s heat. If you get the chance to see the Earth’s mantle, you’d see two large and uneven blobs the size of entire continents. They are right below Africa and the Pacific Ocean. These are the remains of Theia. They didn’t mix with the Earth’s mantle because of different densities. Other remains of Theia might be on the moon. The Apollo spacecraft is being used to investigate soil samples from the moon. If the structure of the blobs in Earth’s mantel matched with the soil samples from the moon, it would be 100% proof that Theia did crash into Earth 4.5 million years ago.

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