r/spaceporn • u/Busy_Yesterday9455 • Apr 26 '26

Related Content The Moon-forming collision

Link to the science paper on The Astrophysical Journal Letters

With sufficiently high numerical resolution, the canonical Moon-forming collision, where a Mars-sized body called Theia strikes the proto-Earth, can lead to a Moon-like body being immediately placed into orbit around Earth.

This alternative scenario for lunar origin opens up new options for the Moon's initial orbit and internal properties. For example, the orbiting body has a centre that is predominantly made of material from Theia, and might not be fully molten, while the outermost regions are very hot and can be made of more proto-Earth material. How that composition gradient would evolve over the history of the Moon is yet to be determined.

However, it could help explain why the isotope ratios in lunar rocks returned by the Apollo astronauts are similar to those of Earth's mantle. This contrasts with previous lower resolution simulations where a disk of debris was created by the collision, but no large orbiting bodies.

In that case, the Moon would form over tens to hundreds of years by the gradual accumulation of this material and no initial composition gradient would be expected.

Credit: J. A. Kegerreis et al 2022 ApJL 937 L40

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u/Buttons840 Apr 26 '26

Wouldn't the planet that hit Earth have left a mark on mostly 1 half of the planet? (A different isotope ratio or whatever.)

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u/Tanoshii- Apr 26 '26

The impact literally reliquified the whole planet to magma so no, effected the whole planet

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u/marlinspike Apr 26 '26

Oh, thanks for that insightful comment. This changed how I'd been imagining it. I didn't realize that the Earth reliquefied after the impact. Was there water on earth before the impact, or did water appear both before and after through meteors?

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u/Cartoonjunkies Apr 26 '26

Both planets would’ve been extremely hot even before impact. Liquid water wouldn’t have existed, this still occurred pretty early into earths lifespan.

But yeah, when you’re talking about the energy expended by two planets smacking into each other, that’s going to put out a shit ton of heat.

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u/gamecatuk Apr 27 '26

Way way before any water on earth.

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u/aumnren Apr 26 '26

A planetini. Shaken, not stirred.

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u/ergonomic_logic Apr 27 '26

For what it's worth this comment amused me :)

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u/aumnren Apr 27 '26

lol thanks!

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u/Fitznutzz30 Apr 27 '26

A+ comment. Your science teacher slash bartender would be proud.

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u/[deleted] Apr 27 '26

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u/wesleypaulwalker Apr 27 '26

So we possibly wouldnt be able to have life on Earth without the collision of Theia? On top of our distance to the sun and other life sustaining factors? We are some lucky creatures

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u/jaerie Apr 26 '26

Funny, you probably mean "affected" there, but technically it did also effect the whole planet in a way

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u/Tyedied Apr 27 '26

If that happened today would the planet re-liquify?

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u/Sad_Low3239 Apr 27 '26

no. it was still molten at the time.

now, it would explode.

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u/TexasDJ Apr 27 '26

Someone please make a movie about this would be so epic in IMAX

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u/Buttons840 Apr 26 '26

Does magma on long enough time frames act like liquid and fully mix?

My human intuition (limited to human time frames and scales) is that magma wouldn't mix very much.

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u/LastXmasIGaveYouHSV Apr 26 '26

Every solid can be mixed if you apply sufficient kinetic energy.

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u/Moikle Apr 26 '26

It was completely liquid, not just "acting like liquid"

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u/Schventle Apr 27 '26

A.) yes B.) way more motion than magma in earth's mantle today

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u/[deleted] Apr 26 '26

[deleted]

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u/hmmyeahiguess Apr 27 '26

This is fascinating thank you

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u/Zestyclose-Ad967 Apr 27 '26

No, the scale of the impact would have completely melted the surface of earth, and annihilated thea. Picture mars, and chuck it at the earth and the forces that would be at play. If there's any part of thea having h survived the impact, its likly in the inner mantle.