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Scientists believe the moon was formed by a collision into planet earth by another celestial body. Why didn't: 1. The other celestial body leave a very obvious

Scientists believe the moon was formed by a collision into planet earth by another celestial body. Why didn't: 1. The other celestial body leave a very obvious elemental makeup in the collision point on earth? We can detect other asteroids, but this one was 100% identical to Earth's crust? 2. Why didn't the debris left by the collision form a ring around earth like Saturn? Instead it all coalesced into one compact body and left zero debris in a ring around earth. I am not an astrophysicist but these seem like obvious questions with no clear answers online after my quick Google search.

towaway15463 4y ago
If the body was big enough it would have completely erased the earth’s crust, after cooling again our current crust would be a mixture of both bodies. Having an outsized moon might also degrade the orbit of any material that would have been left over after coalescing into the earth and moon.
causi 4y ago
1. The other celestial body leave a very obvious elemental makeup in the collision point on earth? We can detect other asteroids, but this one was 100% identical to Earth's crust? Earth's crust was rubble and magma. Sort of like how you couldn't find an impact point if you threw a water balloon into a can of paint. Why didn't the debris left by the collision form a ring around earth like Saturn? It did. Earth had very impressive rings for thousands of years after the impact.
- missedthecue 4y ago
  Ah ok first point makes perfect sense. How do we know we had rings around earth for so long? And where did they go?
  - vvilliamperez 4y ago
    Rings of space debris coalesce into small celestial bodies over time. That's one theory of how moons form.
  - Nux 4y ago
    Gravity had them I guess. Saturn's going to lose the rings as well, and "soon" (hundreds or thousands of years).
    - balfirevic 4y ago
      Did you mean hundreds or thounsands of millions of years?
      - moffkalast 4y ago
        About 100-300 million years, and they only formed sometime in the last 100 million. A blink of an eye from a cosmic standpoint. For comparison, the dinosaurs existed before than the rings did.
        petrocrat 4y ago
        did a large collision during the era of the dinosaurs also form Saturn's rings then? If so what residual evidence of that collision do we know about?
      - Nux 4y ago
        Yes, my bad
  - causi 4y ago
    The short answer is "math". The material either coalesced into the moon or eventually fell back to earth. It's actually a pretty short lifetime for the rings, compared to ring systems like Saturn. Earth has several disadvantages when it comes to maintaining a set of rings. It doesn't have gravity strong enough for tidal forces to tear orbiting bodies apart at far remove from the planet and it doesn't have "shepherd moons" to keep ring material in a stable orbit.
    - verisimi 4y ago
      Could maths be used to prove the exact opposite, to show why the earth still has rings? I know it doesn't, but I say you can use maths to prove whatever you like. So, 'maths' as an answer, is not satisfactory to me. AFAIK, all this discussion is in the realms of hypothesis.
      - toiletfuneral 4y ago
      - causi 4y ago
        AFAIK, all this discussion is in the realms of hypothesis. It is. It's just currently the best hypothesis, and it's refined to better match observation over time. For example, the impact with Theia was originally thought to be a glancing blow by a planet spinning similarly to earth, but more recent simulations indicate it was a head-on collision and that Theia had relatively little angular momentum. This hypothesis does make predictions about the moon's core that are falsifiable but it may be some time before we figure out a way to make the necessary measurements.
      - pungentcomment 4y ago
        Saying it' maths is simplifying it a bit. They use simulations. They can simulate how an object orbits and eventually fall down to earth. They can test those simulations everyday by predicting where a know object in orbit will be in the future. Multiply that by a billion and you can predict that earth's rings would have fall down eventually.
      - 4y ago
  - ru552 4y ago
    The earth is littered with moon rocks. Said rocks may have formed the rings that have dissipated.
    - Tagbert 4y ago
      Those rocks identifiable as moon rocks on the surface of the earth are from ejected debris from the later meteor collisions that formed the craters that we can see on the moon. The early collision debris would have fallen on the molten surface of the earth and been absorbed.
  - bmurphy1976 4y ago
    Saturn also has conveniently placed moons that help keep the rings locked in place.
ajross 4y ago
> but this one was 100% identical to Earth's crust? Given the size of this impact, the crust[1] didn't really survive. Most of the mantle material ended up vaporized and either falling back down or coalescing onto a single fragment, becoming the moon. It was a collision "of" the planet, not "on" the planet. [1] Which in any case wouldn't have survived this long anyway. The differentiation process that produces the crust we're standing on takes billions of years. There aren't any surface rocks that old, and wouldn't be even if the collision hadn't happened.
changoplatanero 4y ago
Some scientists believe that we can detect the place the moon hit the earth at. https://www.science.org/content/article/remains-impact-created-moon-may-lie-deep-within-earth https://www.science.org/content/article/remains-impact-creat...
- sokoloff 4y ago
  It would be the place the earth was hit by an extraterrestrial body, which resulted in the creation of the moon, not the earth being hit by the moon.
- cossatot 4y ago
  This isn't 'the place the moon hit', it's material from the colliding object (Theia) that has been added to the Earth's mantle. The mantle convects, and this material is a little more dense, and has pooled up at the bottom of the mantle, but because the mantle convects (the material circulates) there is no real reason to believe that these bodies are at the location of collision, especially considering that much of the mantle (and the parts of Theia that stayed behind) would have been reduced to flying bits of lava in orbit around the core, before coalescing.
g6762736 4y ago
One of the hypotheses to explain the Large low-shear-velocity provinces at the Earth Mantle-Core boundary is that they are remnants of the impactor that lead to the formation of the Moon: https://en.wikipedia.org/wiki/Large_low-shear-velocity_provinces#Possible_origin https://en.wikipedia.org/wiki/Large_low-shear-velocity_provi...
sfink 4y ago
My personal opinion, but informed by arguments from a number of "real" scientists: because that explanation is bogus. It never made much sense. A collision of a magnitude to break off a moon-sized chunk of mass would be enormous. And why wouldn't the chunk either escape or fall back down, rejoining the main mass? Do we have any evidence that such collisions ever result in significantly-sized orbiting bodies? Or maybe I'm just not understanding that "theory" well enough, because my current preferred hypothesis could be described in much the same way. Let's say there was a large collision, but it was when the Earth was hotter and more molten, and it added enough heat and instability (and perhaps angular momentum) that large globs were thrown off. Some escaped, some fell back down, and some were swept up by the largest glob, now the Moon. But either way, I think the answers to your objections are: (1) it was molten enough to meld together, OR it wasn't, in which case plate tectonics regularly replace the entirety of the crust (and underneath the magma layer is molten); and (2) the Moon cleared its orbit and the Earth is small enough to not support a large area to hold crud that makes up a ring? (All of this is guesswork.)
- hither_shores 4y ago
  At these scales, there are no rigid bodies, and so no single "chunk". If the giant-impact account is correct, the moon coalesced out of ejecta in orbit. > And why wouldn't the chunk either escape or fall back down, rejoining the main mass? Some material likely did escape, but that takes much more energy than getting into orbit. You need to leave the surface of the Earth at about 11km/s to escape, but only 6km/s to reach lunar orbit.
- GolfPopper 4y ago
  It wouldn't necessarily "break off" anything. If the angular momentum of the post-impact planetary mass reaches or exceeds orbital velocity, and its temperature is high enough, you get a novel type of celestial body - a synestia [1], a planet-sized hurricane of boiling rock. As the rock cools, magma rains inward re-fornming the Earth (Earth V2?) over decades, while everything far enough out (beyond the Roche limit [2]) would coalesce to form the Moon. 1. https://en.wikipedia.org/wiki/Synestia https://en.wikipedia.org/wiki/Synestia 2. https://en.wikipedia.org/wiki/Roche_limit https://en.wikipedia.org/wiki/Roche_limit
sixbrx 4y ago
Re #1, one really cool thing is that the remains of Theia (the other body that collided with Earth) may be visible in a big way in Earth's mantle still, if recent study is correct. See https://skyandtelescope.org/astronomy-news/bits-of-theia-might-be-in-earths-mantle/ https://skyandtelescope.org/astronomy-news/bits-of-theia-mig...

towaway15463 4y ago

If the body was big enough it would have completely erased the earth’s crust, after cooling again our current crust would be a mixture of both bodies. Having an outsized moon might also degrade the orbit of any material that would have been left over after coalescing into the earth and moon.

causi 4y ago

1. The other celestial body leave a very obvious elemental makeup in the collision point on earth? We can detect other asteroids, but this one was 100% identical to Earth's crust? Earth's crust was rubble and magma. Sort of like how you couldn't find an impact point if you threw a water balloon into a can of paint. Why didn't the debris left by the collision form a ring around earth like Saturn? It did. Earth had very impressive rings for thousands of years after the impact.

missedthecue 4y ago
Ah ok first point makes perfect sense. How do we know we had rings around earth for so long? And where did they go?
- vvilliamperez 4y ago
  Rings of space debris coalesce into small celestial bodies over time. That's one theory of how moons form.
- Nux 4y ago
  Gravity had them I guess. Saturn's going to lose the rings as well, and "soon" (hundreds or thousands of years).
  - balfirevic 4y ago
    Did you mean hundreds or thounsands of millions of years?
    - moffkalast 4y ago
      About 100-300 million years, and they only formed sometime in the last 100 million. A blink of an eye from a cosmic standpoint. For comparison, the dinosaurs existed before than the rings did.
      - petrocrat 4y ago
        did a large collision during the era of the dinosaurs also form Saturn's rings then? If so what residual evidence of that collision do we know about?
    - Nux 4y ago
      Yes, my bad
- causi 4y ago
  The short answer is "math". The material either coalesced into the moon or eventually fell back to earth. It's actually a pretty short lifetime for the rings, compared to ring systems like Saturn. Earth has several disadvantages when it comes to maintaining a set of rings. It doesn't have gravity strong enough for tidal forces to tear orbiting bodies apart at far remove from the planet and it doesn't have "shepherd moons" to keep ring material in a stable orbit.
  - verisimi 4y ago
    Could maths be used to prove the exact opposite, to show why the earth still has rings? I know it doesn't, but I say you can use maths to prove whatever you like. So, 'maths' as an answer, is not satisfactory to me. AFAIK, all this discussion is in the realms of hypothesis.
    - toiletfuneral 4y ago
    - causi 4y ago
      AFAIK, all this discussion is in the realms of hypothesis. It is. It's just currently the best hypothesis, and it's refined to better match observation over time. For example, the impact with Theia was originally thought to be a glancing blow by a planet spinning similarly to earth, but more recent simulations indicate it was a head-on collision and that Theia had relatively little angular momentum. This hypothesis does make predictions about the moon's core that are falsifiable but it may be some time before we figure out a way to make the necessary measurements.
    - pungentcomment 4y ago
      Saying it' maths is simplifying it a bit. They use simulations. They can simulate how an object orbits and eventually fall down to earth. They can test those simulations everyday by predicting where a know object in orbit will be in the future. Multiply that by a billion and you can predict that earth's rings would have fall down eventually.
    - 4y ago
- ru552 4y ago
  The earth is littered with moon rocks. Said rocks may have formed the rings that have dissipated.
  - Tagbert 4y ago
    Those rocks identifiable as moon rocks on the surface of the earth are from ejected debris from the later meteor collisions that formed the craters that we can see on the moon. The early collision debris would have fallen on the molten surface of the earth and been absorbed.
- bmurphy1976 4y ago
  Saturn also has conveniently placed moons that help keep the rings locked in place.

ajross 4y ago

> but this one was 100% identical to Earth's crust? Given the size of this impact, the crust[1] didn't really survive. Most of the mantle material ended up vaporized and either falling back down or coalescing onto a single fragment, becoming the moon. It was a collision "of" the planet, not "on" the planet. [1] Which in any case wouldn't have survived this long anyway. The differentiation process that produces the crust we're standing on takes billions of years. There aren't any surface rocks that old, and wouldn't be even if the collision hadn't happened.

changoplatanero 4y ago

Some scientists believe that we can detect the place the moon hit the earth at. https://www.science.org/content/article/remains-impact-created-moon-may-lie-deep-within-earth https://www.science.org/content/article/remains-impact-creat...

sokoloff 4y ago
It would be the place the earth was hit by an extraterrestrial body, which resulted in the creation of the moon, not the earth being hit by the moon.
cossatot 4y ago
This isn't 'the place the moon hit', it's material from the colliding object (Theia) that has been added to the Earth's mantle. The mantle convects, and this material is a little more dense, and has pooled up at the bottom of the mantle, but because the mantle convects (the material circulates) there is no real reason to believe that these bodies are at the location of collision, especially considering that much of the mantle (and the parts of Theia that stayed behind) would have been reduced to flying bits of lava in orbit around the core, before coalescing.

g6762736 4y ago

One of the hypotheses to explain the Large low-shear-velocity provinces at the Earth Mantle-Core boundary is that they are remnants of the impactor that lead to the formation of the Moon: https://en.wikipedia.org/wiki/Large_low-shear-velocity_provinces#Possible_origin https://en.wikipedia.org/wiki/Large_low-shear-velocity_provi...

sfink 4y ago

My personal opinion, but informed by arguments from a number of "real" scientists: because that explanation is bogus. It never made much sense. A collision of a magnitude to break off a moon-sized chunk of mass would be enormous. And why wouldn't the chunk either escape or fall back down, rejoining the main mass? Do we have any evidence that such collisions ever result in significantly-sized orbiting bodies? Or maybe I'm just not understanding that "theory" well enough, because my current preferred hypothesis could be described in much the same way. Let's say there was a large collision, but it was when the Earth was hotter and more molten, and it added enough heat and instability (and perhaps angular momentum) that large globs were thrown off. Some escaped, some fell back down, and some were swept up by the largest glob, now the Moon. But either way, I think the answers to your objections are: (1) it was molten enough to meld together, OR it wasn't, in which case plate tectonics regularly replace the entirety of the crust (and underneath the magma layer is molten); and (2) the Moon cleared its orbit and the Earth is small enough to not support a large area to hold crud that makes up a ring? (All of this is guesswork.)

hither_shores 4y ago
At these scales, there are no rigid bodies, and so no single "chunk". If the giant-impact account is correct, the moon coalesced out of ejecta in orbit. > And why wouldn't the chunk either escape or fall back down, rejoining the main mass? Some material likely did escape, but that takes much more energy than getting into orbit. You need to leave the surface of the Earth at about 11km/s to escape, but only 6km/s to reach lunar orbit.
GolfPopper 4y ago
It wouldn't necessarily "break off" anything. If the angular momentum of the post-impact planetary mass reaches or exceeds orbital velocity, and its temperature is high enough, you get a novel type of celestial body - a synestia [1], a planet-sized hurricane of boiling rock. As the rock cools, magma rains inward re-fornming the Earth (Earth V2?) over decades, while everything far enough out (beyond the Roche limit [2]) would coalesce to form the Moon. 1. https://en.wikipedia.org/wiki/Synestia https://en.wikipedia.org/wiki/Synestia 2. https://en.wikipedia.org/wiki/Roche_limit https://en.wikipedia.org/wiki/Roche_limit

sixbrx 4y ago

Re #1, one really cool thing is that the remains of Theia (the other body that collided with Earth) may be visible in a big way in Earth's mantle still, if recent study is correct. See https://skyandtelescope.org/astronomy-news/bits-of-theia-might-be-in-earths-mantle/ https://skyandtelescope.org/astronomy-news/bits-of-theia-mig...