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I recently read about the Psyche asteroid which is mostly metal. It got me wondering: what if a metal asteroid (not the size of Psyche - maybe about 1 mile long and 1 mile wide) impacted the Earth's surface?

Will the asteroid break apart into pieces? I am talking about a metal asteroid. What if the asteroid impacts a planet like Mars? Will the strength of gravity have an effect on whether the asteroid breaks apart or not?

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    $\begingroup$ I'm pretty sure "intact" is not something that you can call anything made out of matter that collides with a planet. $\endgroup$
    – Marcus Müller
    Sep 5, 2021 at 18:13
  • $\begingroup$ The energy of a fall from infinity is far beyond the destruction energy of anything out there. Chunks may survive, but even if it's big enough to go through the atmosphere intact it's going to be seriously shattered on impact. $\endgroup$
    – Loren Pechtel
    Sep 6, 2021 at 2:46
  • $\begingroup$ @MarcusMüller That might just be the best comment I've read all week. $\endgroup$
    – Hearth
    Sep 6, 2021 at 5:33
  • $\begingroup$ @Hearth thank you :) I like the parentheses in the first paragraph of James K's answer: haven't observed any, and this is a very good thing. $\endgroup$
    – Marcus Müller
    Sep 6, 2021 at 5:55
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    $\begingroup$ Quick calculation suggests that the kinetic-energy of an iron-object would, if converted into evenly-distributed thermal-energy, be sufficient to vaporize the iron-object if its velocity is at least ~4.09 km/s. (Note: Kinetic-energy increases with the square of velocity, so doubling the velocity would mean having 4 times the energy-to-vaporize.) $\endgroup$
    – Nat
    Sep 7, 2021 at 3:09

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Whether an asteroid survives the fall through the atmosphere depends on its size and structural integrity. Our understanding of large impacts is limited (we haven't observed any, and this is a very good thing) Howver there is a calculator that can use current knowledge to forecast what would happen.

For a one mile iron asteroid, hitting the atmosphere at 17km/s at an angle of 45 degrees, it would pass through the atmosphere and hit the ground relatively intact. If it hit sedimentary rock, it would carve out an initial crater that is is 7.5km deep and 21 km wide, though this would collapse and fill to give a final crater 800m deep and 35km wide.

At 100km from the impact, many buildings would be destroyed by violent shaking, and any trees would burst into flame from the heat of the fireball, which would be 300 times brighter than the sun. Five minutes after the impact, a blast of wind at 1000mph would hit and flatten everything else.

In case it's not obvious, although the asteroid would survive the passage through the atmosphere, it wouldn't survive the impact. Some of the asteroid would merge with the melted rock in the crater, other parts of it would form part of the ejecta that would fall around the crater.

Smaller asteroids are likely to break up (explosively) in the atmosphere, however the chunks then slow down and hit the ground at hundreds of mph, and not at hypervelocity. These chunks would then be meteorites, and iron meteorites are known.

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  • $\begingroup$ To put "a final crater 800m deep" into perspective, the lowest point on the Earth's surface is 400m below sea level. $\endgroup$
    – dotancohen
    Sep 7, 2021 at 10:25
  • $\begingroup$ @dotancohen Big facepalm here... The lowest point below sea level is 11,034m in the mariana trench.. The first google result his completely out of context $\endgroup$
    – Tofandel
    Sep 7, 2021 at 10:47
  • $\begingroup$ To put "a final crater 800m deep" into perspective, the lowest point of dry land on the Earth's surface is 400m below sea level. $\endgroup$
    – dotancohen
    Sep 7, 2021 at 11:01
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    $\begingroup$ @Tofandel "lowest point on the Earth's surface", not "lowest point below sea level". If we're being pedantic, the lowest point below sea level is around 6371km down, at the centre of the Earth. $\endgroup$
    – JBentley
    Sep 7, 2021 at 14:39
  • $\begingroup$ Makes a lot more sense then. Though if that where to happen then it's likely this crater would fill up with water, depending on where it lands $\endgroup$
    – Tofandel
    Sep 7, 2021 at 14:44
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No, it will not. The kinetic energy released upon impact is more than sufficient to vaporise even a metal asteroid. Barringer crater was caused by a metallic object, and there's nothing left of it. See the WikiPedia article for more information on this crater.

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    $\begingroup$ +1 for the mention of Barringer crater. Unfortunately, Barringer himself though the answer to this question was "parts will remain intact" and all the money invested in trying to mine for that metal was in vain. $\endgroup$
    – Michael
    Sep 6, 2021 at 23:25
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The Hoba meteorite is the largest known iron meteorite, ~60-70 tons. It survived impact because atmospheric braking removed most of its kinetic energy. The larger the object, the less effective atmospheric braking is. Since no larger example is known, we may conclude that this object is near the limit of mass for iron objects that may survive impact.

Psyche masses about 30 quadrillion tons.

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