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What would happen if a powerful explosive went off in the core of a planet?

On Earth, you have several layers of the planet, the crust, the magma, the outer core, and the inner core. Right now, human technology can't really get past the crust. But say an alien civilization came that could get all the way to the inner core.

So this alien civilization comes and uses their technology to plant a powerful explosive, say at least as powerful as a Fusion bomb, in the inner core. What would happen?

And for a bonus, what would happen if an explosive with three times the power of a fusion bomb went off in the core?

superluminary
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DonyorM
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    A much more powerful 'device' was used in Greg Bear's the Forge of God (novel - 1987) whereby the attackers dropped complementary pieces of neutronium and anti-neutronium into the Earth's core, resulting in the graphic destruction of the planet when the pieces collided - however this is far more advanced than a fusion weapon. Well worth a read along with it's sequel. – Scott Downey Oct 22 '14 at 08:52
  • Energy of a fusion bomb just seems far far too low to be noticable at the surface....it's just a tiny amount of energy compared to the forces involved there. – Twelfth Oct 22 '14 at 23:39
  • "Fusion Bomb" Is so vague....I'm just going to assume you mean the strongest bomb we could possibly have...and for that purpose, see my answer below. – Zibbobz Oct 23 '14 at 19:19

3 Answers3

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On the surface the effect would be nothing in either case. We'd probably see a few tremors on seismographs but I'm not even convinced about that. It would depend on how well the shock-wave passes through the planet.

The explosion would be very thoroughly contained by the heat and pressure at the core and the shock-waves would have a huge distance to spread out before they reach the surface.

The core is a very long way down, and we have a lot of rock (most of it already a seething molten furnace) between the core and the surface.

An interesting follow on question though would be to ask how powerful a device would need to be to have an affect on the surface (you would need to define the desired affect). I'm not sure if we have any way to answer that though as we just don't know enough about conditions down there and how the shockwave from an explosion would propagate.

Tim B
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  • I think tremors from nuclear explosions can be detected around the world. Not sure about the effect of this at the core, but you might consider a really powerful nuke as roughly same as magnitude 7 or 8 earthquake - detectable worldwide, but with relatively local effects in terms of damage and noticeable consequences. – Neil Slater Oct 22 '14 at 08:57
  • @NeilSlater Yes, as I said we'd probably see a few tremors on seismographs. The reason I said probably though is that an explosion on the surface is already connected to the solid crust and can spread through that. An explosion in the core needs to transition through multiple layers of different mediums in different states which could well distort, absorb, or otherwise change the reading. – Tim B Oct 22 '14 at 09:00
  • What we know about the earth's internals is from seismic waves traveling through it. However, The solid/liquid core boundary has an impedance mismatch and will tend to reflect rather than transmit waves though, so might effectively contain the vibrations of quite powerful blasts (ringing like a bell). This causes a "shadow" on seismic transmissions from earthquakes, which was used to infer the core's existence. So yes, thinking about it, your "maybe" is better than my first comment. However I disagree slightly with your last para - we know quite a lot about density and could do the math. – Neil Slater Oct 22 '14 at 09:06
  • @NeilSlater True, but again we don't know how all the complex systems down there interact or how shockwaves from an incredibly powerful explosion propagate through a medium like the core. Having said that people could certainly make some solid fact-based theories about the results so as I said it would be an interesting question to have asked. – Tim B Oct 22 '14 at 09:10
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What is the core of the earth like?

The core of the earth is a moon sized ball of heavy metal, mostly iron, also gold and other metals. The pressure is so intense that the iron enters a new crystalline phase. It is so dense that even a very large human scale bomb would have little noticeable effect. An extremely large explosion might possibly be able to crack, shatter or damage the crystal structure in some way.

Function of the earth's core

The inner core rotates at a different speed to the rest of the planet. This generates a massive, but relatively weak magnetic field which shields the earth from solar rays by guiding them to the poles, giving us the aurora.

Without it, our atmosphere would be ionised by radiation from the sun and gradually stripped away killing everyone. The oceans would alternately freeze and boil as the earth rotated towards the sun. Everything would die.

It is possible to conceive of a bomb that might disrupt the earth's geomagnetic field in some way, perhaps switching it off temporarily, or reversing its polarity.

Geomagnetic Reversal

The polarity of the Earth's magnetic field naturally reverses every few eons. This generally takes place over a long period. Some people have associated these reversals with extinction events, and possibly with a temporary cessation of the geomagnetic field.

If a reversal could be triggered quickly, this might be a very damaging sudden event. Imagine all the magnetic rocks in the earth going "kachink" at the same instant. There would likely be earthquakes, volcanoes, cracking of the earth's surface, etc.

A slow reversal or temporary cessation would lead to damaging electromagnetic radiation reaching the earth's surface causing damage to organisms and eventual destruction of the atmosphere.

Reference

http://en.wikipedia.org/wiki/Geomagnetic_reversal

superluminary
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9

This is my new favorite question, because now I get to compare two of my favorite explosions side-by-side.

Let's assume we're limited to actual nuclear weapons that have been developed, and that we're using the one that will deliver absolutely the most powerful blow to the core of the Earth.

Tsar Bomba

The Tsar Bomba is the most powerful and funnest-to-say nuclear bomb ever constructed by humans. When detonated, it delivered 50 Megatons of force, with a blast radius of 4 KM, and 240 Petojouls of energy. But that was only half of the maximum yeild for the bomb, limited to allow the payload delivery plane to escape the blast and for a scout plane to take pictures. If we take those safeties off, we can double all those figures.

Krakatoa

...Which is still only one-half of what mother nature can do. In 1883, the volcanic island of Krakatoa erupted, blowing the entire island into pieces. This explosion had a force of 200 Megatons, four times that of the Tsar Bomba's explosion, and still twice the blast of a theoretical unhinged Tsar (but enough about Russian politics...). Both of these explosions occured essentially at the surface of the Earth, which helped the impact spread throughout the surface considerably.

Krakatoa Bomb

If we could deliver a Krakatoa bomb to the surface of the Earth's core, what would happen?

Well, this Physics question (which is a good question, but strangely posted on Skeptics and therefore closed) points out that this type of explosion would be equal to an 8.75 earthquake. Which sounds frightening, unless you factor in the fact that earthquakes are (believed to be) the result of the constant churning of the mantle beneath the surface of the earth, and that the forces further down will be even stronger than that.

So unless your Alien Fusion Bomb manages to be stronger than the Krakatoa explosion, we aren't likely to feel an earth-shattering effect from just one. At worst, we may suffer from a few seismic disturbances, but you'll need to step up your payload considerably to do any real damage.

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Zibbobz
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