The Earth may have huge undigested blobs of a planet that collided with it billions of years ago, and these chunks may be affecting our magnetic poles.

Well, that’s a statement, isn’t it? 

The blobs were actually discovered a while back, and have been known to be affected the Earth’s magnetic field. It’s also been thought for at least a few years that they might be leftover from the Moon’s formation. The Giant Impact Hypothesis, which was first proposed as a result of findings from the Apollo lunar missions, posits that a Mars-sized planet, nicknamed Theia, slammed into Earth at a grazing angle just a few tens of millions of years after Earth formed. The impact blasted a huge amount of material into orbit around Earth, which coalesced to form the Moon.

This hypothesis explain a lot about why the Moon is a little weird — it’s bigger than most other moons in relation to its parent planet, its composition is both similar to Earth (because it came form the same material) but also has some differences (the parts that came from Theia), and more. 

The parts of Theia that weren’t vaporized would have merged with Earth, and the two blobs just above the Earth’s core/mantle boundary have been thought to be some of those chunks. What the new research brings is some quantitative science to the question. Scientists used new simulations* to model what happens during such an impact, and found that big chunks can indeed form. They would be from Theia’s own mantle, and if they had a slightly higher iron content would have sunk to the bottom of Earth’s mantle to take up their current position. The total material from Theia would comprise about 2% of Earth’s mass. 

The scientists also found that the impact would have molten Earth’s upper mantle — despite a misconception, Earth’s mantle is actually a solid, even if it’s very hot — and caused the mantle to separate into two layers itself. This could explain a boundary seen about a thousand km below Earth’s surface, too.

Collisions on a planetary scale were almost certainly common in the early days of the solar system. A lot of planets would have formed, and as they got tugged by the gravity of the bigger gas giants, their orbits would have changed, putting them on trajectories that crossed those of the other planets. When that happens a collision is inevitable, and probably pretty rapidly, too. But we understand this now in part because of the idea that something hit the Earth to form the Moon. This would have had profound effects on the Earth, too, and it’s very interesting that we may now be finding those effects.

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* Using new computer model methods, which, to be honest, make me scientifically skeptical about their accuracy; you have to be pretty careful when using simulations in any situation let alone where the methods are novel. I’m not saying they’re wrong, just that, as usual with any science news item, a bit of skepticism is warranted.

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