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The asteroid which created the Vredefort impact crater in South Africa is estimated to have been between 10 and 16 km in diameter (the uncertainty is due to the age of the crater, which is more than 2 billion years).

Assuming the maximum estimate is correct, how deep could this asteroid have penetrated into the Earth's crust, and would the resulting crater have become filled or partly filled with magma like some of those on the moon?

The reason no mass extinction is associated with it is that at that time the most complex life on Earth was only single-celled. It should be remembered that the crust was thinner in those days, as was the case with the magma-filled craters on the moon.

Another important factor is the sped of the asteroid at the moment of impact, which we cannot know,therefore an average of mega-meteorite velocities will do. It is important to read this question carefully before answering,otherwise I have to keep repeating myself.

gerrit
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Michael Walsby
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  • Comments are not for extended discussion; this conversation has been moved to chat. – gerrit Jan 29 '20 at 08:49
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    This has appeared in the re-open queue because of the recent tidy-up edit. IMHO the "how deep" question is a clear duplicate as originally marked, so I'm voting to leave closed. However, the secondary question as to whether the crater would have been filled with magma might make a good question in its own right - perhaps generalised in some way to large early craters rather than this specific one. – Semidiurnal Simon Jan 29 '20 at 10:01

1 Answers1

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10–16 km

there is an interesting equation that demonstrates an rocky impactor hitting rock does not penetrate further than its diameter. Basically because a meteorite and the rock it hits have similar density several things cancel out so depth of penetration maxes out at the diameter of a spherical projectile.

Source

Source 2

enter image description here image from Wikipedia.

Here is more about impact craters in general. https://www.lpi.usra.edu/publications/books/CB-954/chapter3.pdf

Whether it hits on land or the ocean does not matter much either, although oceanic crust is thinner it is also denser, the mantle is even denser still so if it reaches the mantle it should penetrate even less than it would penetrating only crust. That said oceanic crust is only 5-10km in thickness so reaching the asthenosphere is completely possible.

Also keep in mind the depth of a crater is different than the depth of the penetration, a penetrator can generate a temporary crater deeper than it penetrated due to shockwave deformation, much like how a you can use your finger to push a depression into a balloon without penetrating it at all.

Would it fill with lava absolutely (at least partially) , just from the local rock melted from the impact alone.

gerrit
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John
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  • Comments are not for extended discussion; this conversation has been moved to chat. – gerrit Jan 29 '20 at 08:50
  • Velocity is an important factor, because velocity is power. Ask yourself which would dig the deepest crater, a 0.5 megaton hydrogen bomb or a Russian world record 50 megaton bomb? At the low velocity of some meteorites, the impact is equivalent to the meteorite's weight in TNT. At the higher velocities it could be the equivalent of 0.5 megatons, 50 megatons or 100 megatons. At the speed of light (yes, I know meteorites never travel that fast) it would be equivalent to the meteorites weight in antimatter! More power, deeper hole. – Michael Walsby Jan 29 '20 at 11:19
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    @MichaelWalsby it doesn't matter because the energy simply deformed or vaporizes the projectile, it doesn't penetrate any deeper. at the speed of light is is equivalent to significantly more energy than its weight in antimatter (at ~88% the speed of light a projectile can release the equivalent of its annihilation with an equal mass of antimatter) but it still doesn't cause it to penetrate any deeper it can actually penetrate less becasue it just becomes a spherical explosion. More energy is transferred yes but penetration is not any deeper, depth of hole =/= depth of penetration – John Jan 29 '20 at 20:47
  • The Soviet 50-megaton bomb was an airburst, high in the atmosphere,which is a pity because had it been on the ground we could have seen the crater.It would have been a big one,bigger than the US 10 megaton device made at Elugulab in1952, and much bigger than the US test at Alamogordo in 1945. I am not convinced that large explosions don't dig deeper craters than small explosions. Five times as powerful won't be 5 times as deep of course, but it will be deeper. I could have proved this with HE when I was in the Army, but in those days nobody disputed that larger explosions left deeper craters. – Michael Walsby Jan 29 '20 at 22:43
  • @John My last analogy wasn't a very good one, because the size of the crater depends on mass as well as velocity (power). A better analogy would be if you detonated a ton of gunpowder, then a ton of RDX or Cemtex. The latter two have more power (a quality called brisance in this case) and will therefore blast deeper craters. – Michael Walsby Jan 30 '20 at 10:15