Say that there is some mega-sized space tech that was developed to shoot a spear like object at a planet, and had enough power behind it to pierce the core. Perhaps something along the lines of a super huge magnetic accelerator that shot a metal pole.

If such a weapon was used on an earth-like planet and the spear pierced the core, but became lodged there, what would happen to Earth?

Would the magnetic field dissipate? What if the spear was able to pass all the way through earth?

I am thinking of an object no more than a mile wide as far as the spear is concerned.

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    $\begingroup$ Any chance for the spear to melt due to the high temperatures in the planet's core or is it made from some indestructible unobtanium? $\endgroup$
    – Philipp
    Commented May 5, 2018 at 20:54
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    $\begingroup$ Hey Lee! Welcome to Worldbuilding. To provide you with quality answers that can help you, we need to know more on your planet and sphere. Is the planet Earth? If not, what differences are there? Regarding the spear: What is it made of? How fast did it make contact(or with what amount of force)? Also, Habitable to who/what? Humans, dogs, bacteria and fish don't need exactly the same to live, and a specific creature could make a difference. The site's help center and tour pages can help a lot with asking great question if you have a moment to read them :) $\endgroup$
    – Rick M.
    Commented May 5, 2018 at 21:22
  • $\begingroup$ Hi Lee, Welcome! Glad you found an answer that works for you. we generally advise users to wait 24 hours to accept an answer. this is because 1) it gives users in different timezones a chance to answer and 2) some users do not bother adding new answers if there is an accepted answer. you may be missing out on a potential answer that you find even more helpful. If they really want to, they will add it but it does cut down the number of ppl willing to answer. Hope you have fun here :) $\endgroup$ Commented May 5, 2018 at 22:25
  • $\begingroup$ When it comes to planetary impact, shape has nothing to do with it. Your spear would need as much mass and velocity to reach the core of the Earth as any other asteroid or comet. Any of them would extinguish life as we know it before causing a tectonic breach. The most widely accepted hypothesis for the origin of the Moon has her being formed out of the debris of an impact that exposed the Earth's mantle, so... $\endgroup$ Commented May 6, 2018 at 5:12

2 Answers 2


No. The energies involved here are just too great.

First of all the "spear" would be gravitationally unstable, it would collapse upon itself and fold into a ball of metal, you couldn't make it strong enough.

Even if you solve that problem, then in the collision with the planet a lot of energy is released. This would be enough to vapourise the spear and the rock. If you get the rod moving fast and it is long enough you begin to dig a larger and larger crater, but before you get to the "impale" the planet, you have released enough energy to completely melt the planet, and in the process, completely melt the spear.

So no impaled but inhabitable planet, if you want to maintain realism.

If you magic away the impaling process, then there is not so much to change. The internal heat of the Earth melts the rod, the dynamo that powers the magnetic field would continue to operate. The rod would not be able to support its own weight (and if it broke up and fell to Earth, the damage would probably wipe out all complex life) so you will need more magic if you want to keep it sticking out the ground.

With sufficient application of magic almost anything is possible.


In order for the spear to pass into the planet without vaporizing it from the sheer force of the impact, it would have to be relatively slow moving and use some other process than impact to dig it's path into the planet. Then you're drilling into the planet rather than shooting something at it.

On a side note, throwing something heavy at high speeds at a planet (an artificial meteor impact essentially) will destroy it which is why the star wars death star is such a silly idea. Why go through all the effort to build that monster when you can just put a rocket on a rock and get the same effect?

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    $\begingroup$ "This space trebuchet is now the ultimate power in the universe!" $\endgroup$ Commented May 6, 2018 at 4:16

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