We all know what sort of devastating impact an asteroid could have if it collided with the Earth.

But I'm curious to know what the effects would be if you removed the speed element from it, and were somehow able to casually 'place' a giant asteroid onto our planet?

I think I read somewhere that the Chicxulub asteroid was most likely around 9 miles long, and that the end of it would have extended beyond our atmosphere if it hit the Earth lengthways.

But would this have any effect if it was travelling at, say, 2mph? There would be nothing burning in the atmosphere or shockwaves etc.

Would it have any affect at all apart from squashing whatever was underneath?

If the answer is no... how about placing a moon-sized object onto the Earth?

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    $\begingroup$ Note: To remove the speed would require magic. The absolute minimum speed that an asteroid could have on hitting the atmosphere is almost 11km/s $\endgroup$
    – James K
    Commented Feb 15, 2021 at 12:37
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    $\begingroup$ I’m voting to close this question because this requires magic. $\endgroup$ Commented Feb 15, 2021 at 12:52
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    $\begingroup$ @Pel Please consider editing your question: I guess you are asking what the effect of placing a huge object on the Earth's surface would make, do you? If so, I would write it that way, e.g. "What happens if we could bring a body of $80 {\rm km}$ diameter and a mass of $10^{16} {\rm kg}$ on Earth's surface?" $\endgroup$
    – B--rian
    Commented Feb 15, 2021 at 13:50
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    $\begingroup$ You could ask on Worldbuilding Meta if they would be willing to take a question about this. You'd probably have to substantially reword the question to define the parameters for which you'd like to see an answer and give context about why you want to know. $\endgroup$
    – called2voyage
    Commented Feb 15, 2021 at 15:27
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    $\begingroup$ @Pel ha! better not advertise that you've "asked other ridiculous questions", or someone may go back and vote to close them as well! I always feel bad if my questions are closed. It's not a perfect system but since this site is completely open to the internet there needs to be some limits. For this one, you could consider asking a question in Earth Science SE about placing a very large body on Earth and how it would compress the Earth below it, or about the atmospheric forces on it. At 2 MPH it would displace a lot of air and make wind, but not make a shock wave. $\endgroup$
    – uhoh
    Commented Feb 15, 2021 at 23:44

1 Answer 1


An asteroid resting on Earth would be a mountain. Or, for smaller asteroids, a pile of gravel.

Mountains are limited in altitude by the strength of stone to resist compression: a too tall mountain would sink down as the base crumbled and spread out. The limit on Earth is about 10 km. Besides the strength issue mountains are also floating ("isostasy") on the fluid but denser interior of Earth, so even if it doesn't fall apart it may sink down partially.

So the impactor would not hold together that well. A big ball of rock 10 km in diameter would first definitely sink down several kilometres into the crust, and almost definitely break. That means that something like $10^{15}$ kg will descend several kilometres, giving an energy $mgh \approx 10^{19}$ J (and there are estimates 100 times larger for the mass). That is "just" like a big hurricane, but will mostly be released as localized seismic energy and heating. The end result would be a massive pile that likely destabilizes the crust in the vicinity a lot: far less than an actual high velocity impact, but still a major disaster.

If you do the same with the moon you will break up the crust, boil off the oceans and wipe out all life on the planet.

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    $\begingroup$ Lol wow - sounds interesting! Thanks for satisfying my curiosity $\endgroup$
    – user7845
    Commented Feb 15, 2021 at 17:09