If I dropped a heavy ball into some magma it would splash all over the place. So why would Theia create only one large drop of liquid (the moon) and if it impacted the Earths mantle (Bits of Theia might be in Earth's Mantle)?

What did it do to the Earth's core?

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    $\begingroup$ The impact created lots of splash, but that was a long time ago and all the bits either became part of the Earth, part of the Moon, or left the Earth-Moon system. $\endgroup$
    – Jon Custer
    Commented Nov 6, 2023 at 16:30
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    $\begingroup$ Do note that one recent theory is that two moons were created in the impact and those then merged together. This helps to explain the vast geological differences between the front and back sides of the moon. space.com/12529-earth-2-moons-collision-moon-formation.html $\endgroup$ Commented Nov 8, 2023 at 16:35

1 Answer 1


Most simulations generate multiple moonlets and streams that then fall into Earth, merge into the moon or escape (e.g. like this or this).

The initial orbit tends to be close to the Earth. This means that gravitational interactions will will be strong, making it hard for there to remain multiple moons since they will tend to destabilize each other's orbits. Simulations have shown that Earth at most can keep three moon-sized moons, and that requires careful arrangement so their Hill spheres do not overlap and they do not get into the wrong orbital resonances. The moon's Hill sphere has a radius of 60,000 kilometres, so its early very near-Earth orbit after the impact would have interfered with anything else orbiting nearby. Had it been lighter maybe extra (small) moons might have made it.

  • $\begingroup$ The simulations look convincing. But I still think that at a greater distance from Earth there could have been blobs of magma orbiting. I suspect that magnetic and electric fields have not been fully accounted for here. And over time they have repelled some magma into space and the rest onto the Earth and moon. $\endgroup$
    – user52803
    Commented Nov 7, 2023 at 18:43
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    $\begingroup$ @DaveTheWave - To send a blob of magma into a high orbit it needs to have a high velocity and then have it changed somehow to circularize it. Otherwise it will just have a very eccentric orbit and likely fall back in. This requires forces stronger than any plausible magnetic effects (and electric charge will be neutral on this scale). $\endgroup$ Commented Nov 8, 2023 at 1:48
  • $\begingroup$ @Jon Custer Where is the magma that left the Earth moon system.Is it in the asteroid belt? Did the sun and other planets attract it all. $\endgroup$
    – user52681
    Commented Nov 9, 2023 at 7:58

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