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Let say that the Earth's Moon was knocked out of orbit and landed on the Earth with some damage but not world ending. Would Earth's atmosphere envelop to include the Moon? Would the moon sink into the Earth? What would happen?

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  • $\begingroup$ One theory of Earth's formation is that the Moon and Earth are the result of a collision of two early planets in the solar system. If the collision of those two planets created the Earth and Moon, it seems likely that Earth and Moon colliding would result in two new bodies being formed, although the devil is in the detail. Planetary sized bodies don't have gentle collisions. :-) $\endgroup$ – StephenG Oct 4 '18 at 0:07
  • $\begingroup$ At sizes like moon and earth, these objects have roughly the stability of piles of toothpaste in the bathroom sink. $\endgroup$ – Wayfaring Stranger Oct 5 '18 at 15:24
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This is a highly improbable scenario, since the Moon has a lot of momentum. However, let's say you teleport the Moon onto the surface of the Earth. Then Moon can't just sit on the Earth, and it will collapse under its own weight, probably killing everyone on Earth. The two would probably merge into a spherical shape (as most massive objects do).

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  • $\begingroup$ This is speculation. You should at least consider the total pressure imparted directly under the Moon and decide whether it's sufficient to, say, break the local mantle. $\endgroup$ – Carl Witthoft Oct 4 '18 at 18:49
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    $\begingroup$ @CarlWitthoft As another user said, at large scales solids aren't really solid, and are more like big balls of sand. $\endgroup$ – User24373 Oct 4 '18 at 18:52
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It can't happen. The moon is quite big and can't get knocked out of orbit easily.

If it were somehow knocked out of orbit and collided with the Earth, the energy released would melt the entire crust. Huge amounts of matter would be knocked into space. After everything had settled down, you would get a lifeless world, still spherical but now slightly larger.

The moon can't get knocked out of orbit. If it did, It can't "land". If it did "land" it would be crushed by its own weight, and all life would end in one way or another.

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  • $\begingroup$ Let say a comet or asteroid of size missed the Earth but hit the moon in the direction of orbit? $\endgroup$ – Muze Oct 3 '18 at 19:22
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    $\begingroup$ Okay, the moon is not knocked of of orbit in the scenario $\endgroup$ – James K Oct 3 '18 at 19:39
  • $\begingroup$ astronomy.stackexchange.com/questions/12220/… $\endgroup$ – James K Oct 3 '18 at 19:40
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At the scale of the Earth or the Moon there are no solid objects. The Earth does not behave like a solid, nor does the Moon.

You have to think of these objects as more like piles of sand, made round by their own gravity. So if one round pile of sand touches another round pile of sand, they just merge and make a bigger pile of sand, also round.

the Earth's Moon was knocked out of orbit and landed on the Earth with some damage but not world ending

That's essentially impossible. I can't think of any mechanism that would allow the Moon to gently touch the Earth. Regardless, both the Earth and the Moon would be severely bent out of shape before they even begin to touch - they would look more like eggs, or a teardrop shape, then they merge, and that's the end of everyone and everything on this planet.

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  • $\begingroup$ Probably true but perhaps some references to the largest (theoretical ) chunk of rock that would not collapse or deform into a 'fried-egg' shape over some region of the Earth. $\endgroup$ – Carl Witthoft Oct 4 '18 at 18:51
  • $\begingroup$ @CarlWitthoft -- Mountains on earth get as high as the crust can support. Asteroids are probably not as rigid as rocks in the crust. A 100 m asteroid somehow brought to a soft landing would collapse into a hill shape but probably wouldn't do much to the crust underneath. A one-km asteroid in a "soft" landing would still liquefy the crust underneath and sink deep into the ground; you'd still end up with something like an impact crater with a central peak. $\endgroup$ – antlersoft Oct 8 '18 at 18:00

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