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On this alternate Last Glacial Maximum Earth powerful psychics bring an asteroid into near earth orbit and deorbit it using entirely laser ablation. Bringing it carefully down onto the Laurentide Ice Sheet at no more than terminal velocity by ablating it from below during the descent.

The psychics can project intangible avatars from their body, from which they can fire optical or near-UV lasers. A small number of the most powerful psychics can generate lasers intense enough to rapidly melt through any material if needed.

The asteroid involved is 1986 DA or a similar sized (~3 km) metallic asteroid available at the necessary time.

What would the ramifications of such a massive likely glowing hot piece of metal hitting an ice sheet at terminal velocity be?
Would the the powerful nomadic psychics consider doing this to have been worth it (and potentially consider doing it in the future)? Or would the resulting natural disasters be too extreme?

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    $\begingroup$ What is "terminal velocity" in this context? $\endgroup$
    – Alexander
    Apr 27, 2022 at 0:07
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    $\begingroup$ ??? You will have a biggg chunk of metal coming at more than twice the speed of sound, which is fast but not so fast as to cause any problems outside the immediate area. It will make a big hole in the ice and a less big hole in the rocky ground. It will then stay there until a lucky entreneur will find it and start mining it. The real problem is that the kinetic energy of the asteroid still has to be dissipated into the atmosphere, plus all the waste heat produced by the braking mechanism. That is the bomb. $\endgroup$
    – AlexP
    Apr 27, 2022 at 0:39
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    $\begingroup$ The braking mechanism has to dissipate an enormous amount of energy (about the equivalent of one million megatons of TNT) in a very short time; that is the source of the disaster, and it is in no way natural. (The largest thermonuclear bomb ever detonated on the surface was about 50 megatons. One million megatons is about 20,000 Tsar Bombas.) I wouldn't want to be on the same continent. (The point being that the asteroid does not have to collide with the ground to be deadly; dissipating its energy in the atmosphere is just as deadly.) $\endgroup$
    – AlexP
    Apr 27, 2022 at 1:01
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    $\begingroup$ Twenty thousand fifty-megaton thermonuclear bombs. The nomads are history. The climate is altered in a chaotic and unpredictable way, worldwide. $\endgroup$
    – AlexP
    Apr 27, 2022 at 1:07
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    $\begingroup$ How exactly this asteroid is dropped? Is it brought to a stable low-Earth orbit (300-400 km altitude) and then deorbited, or it brought to a low-Earth orbit, geosynchronously suspended, and then dropped? $\endgroup$
    – Alexander
    Apr 27, 2022 at 1:33

1 Answer 1

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  • Assuming that the average density of the asteroid is 5000 kg/m³, its mass is about 70,000,000,000 kg.

  • A terminal velocity calculator says that a 70 million tonnes object with a cross-section of about 7 million m² has a terminal velocity of about 740 m/s.

    (Note that this is supersonic, and therefore very iffy. But let's roll with it.)

  • The impact itself will happen at ordinary bullet speeds, so that it won't be spectacularly destructive. Some ice will be melted, a big hole will be made in the ice sheet, but nothing remarkable will happen outside the immediate area.

  • But. The orbital kinetic energy of the asteroid still has to go somewhere. Assuming that the magical engines used by the magical wizards are somewhere on the ground, all that energy will have to be dissipated in the atmosphere.

    (Of course, you can say that the magical wizards magically teleport themselves in outer space and use magical magic to stop the asteroid dead on its track and let it fall. In this case, nothing spectacular will happen. Big chunk of metal hits, sizzles, and settles down. Thousands of years later, somebody becomes very rich from mining the metal. Stop reading here.)

  • But if the orbital kinetic energy of the asteroid is dissipated in the atmosphere, very bad things happen. A 70 million tonne object coming from outer space beyond Earth orbit has a kinetic energy of at least 4.3E21 J (That's 4.3 zettajoules.) One megaton of TNT equivalent is about 4.2E15 J (4 petajoules): the kinetic energy of the asteroid is about one million megatons TNT equivalent.

  • The bigggest thermonuclear bomb ever detonated (by the Russians, of course) was the Tsar Bomba, estimated at about 50 megatons TNT equivalent. This means that the kinetic energy of the asteroid is about 20,000 Tsar Bombas.

  • Overall, the magical engines used by the magical wizards, no matter how they work, must dissipate this energy. It doesn't matter how they do it: in the end, the effect is the same as detonating twenty thousand Tsar Bombas.

  • The effects would be incalculable. The worldwide climate is altered in some unpredictable way. A lllarge area is devastated.

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  • $\begingroup$ > "A 70 million tonne object coming from outer space beyond Earth orbit" I said it was deorbited from near earth orbit, so the energy dissapated should be a lot less than if you are talking about the full kinetic energy of something from outside Earth's orbit. Also I said how the energy was being dissapated, it's entirely laser ablation not just the final descent $\endgroup$ Apr 27, 2022 at 1:45
  • $\begingroup$ @VakusDrake You both seem in agreement the big rock is moving at terminal velocity. So it doesn't matter how far it moved or when it deorbited. $\endgroup$
    – Daron
    Apr 27, 2022 at 15:44
  • $\begingroup$ Krakatoa is estimated to be in the 200 megaton range and that was already heard thousands of miles away and noticed all around the world. This is thousands of times bigger. $\endgroup$
    – Daron
    Apr 27, 2022 at 15:47

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