How much TNT do you need to blow up the moon if you place it exactly in the middle? Just think of the explosion -- that there's no air in space doesn't matter!
What do you think is it possible and how much TNT do you need for this?
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12$\begingroup$ So...are we now going to be subjected to an endless series of "How much TNT to blow up __________?" $\endgroup$– JohnPJan 19, 2015 at 16:01
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6$\begingroup$ Given that the moon (unlike Everest) has its own gravitational bindings, I wouldn't call this a duplicate. The differences in the questions' respective answers makes that pretty clear. $\endgroup$– BobsonJan 19, 2015 at 17:27
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2$\begingroup$ I disagree with the closing; you clearly need different calculations to answer the two questions, as @Bobson said. The Moon's gravitational binding energy would need to be overcome in this case; in the other setup, other factors would have to be analyzed. Not all explosions are created equal. Voting to reopen. $\endgroup$– HDE 226868 ♦Jan 19, 2015 at 19:35
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4$\begingroup$ I, too, voted to reopen. That doesn't mean this is a well-written question, but it doesn't meet any current close criteria. As to @JohnP's concern, I'd say that all future questions about blowing up gravitational objects can be duplicates of this one, and all future questions about blowing up terrain features are duplicates of the other. If someone asks about blowing up a building, or an ocean, or a star, those would be new questions, the same way asking about turning Mt. Everest into sand wouldn't be a duplicate of the other one. $\endgroup$– BobsonJan 19, 2015 at 20:06
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1$\begingroup$ possible duplicate of The opposite to Worldbuilding: World Destruction $\endgroup$– Serban TanasaJan 20, 2015 at 1:54
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2 Answers
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To destroy the moon, you would need to provide at least $1.24\times10^{29}$J of energy to exceed the Moon's gravitational binding energy. (This provides a lower bound on the energy to "blow up" the moon.) A megaton of TNT releases 4.184 PJ of energy.
Put this together, and you would need at least: $2.96\times10^{13}$ megatons of TNT.
Said another way: you would need some 30 trillion million tons of TNT.
If you would like to perform this calculation yourself, see the Planetary Parameter Calculator. Based on a couple inputs, it will calculate the gravitational binding energy of a body.
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3$\begingroup$ For a sense of scale: 30 quadrillion tons of TNT = a 470 km sphere. That's large enough to be its own dwarf planet. Or you could use 6 trillion thermonuclear bombs (in the entirety of the Cold War, 60000 nukes of any size were produced, getting you at most 1/100000000th of the way there). For the most efficient option, you could use 10^12 kg of antimatter = a 10 km sphere. $\endgroup$– Foo BarJan 19, 2015 at 16:55
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6$\begingroup$ You calculations appear to assume that the Moon is "loose material held together by gravity alone". Your Moon destruction plot will fail or go over budget with this estimate. $\endgroup$– SamuelJan 19, 2015 at 17:23
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7$\begingroup$ As a side note, the 2.96*10^19 tons of TNT is around 35% of the mass of the Moon itself. You need a Moon-scale pile of TNT to blow up the Moon. $\endgroup$– cpastJan 19, 2015 at 19:33
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4$\begingroup$ @cpast And the moon has twice the density of TNT. Thus you'll have to use 70% of the volume of the moon--at that point you're more blowing up TNT than the moon. $\endgroup$ Jan 19, 2015 at 20:22
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2$\begingroup$ Honestly, this is a pretty ridiculous question in the first place. My answer is quite simply the amount of TNT you would need to blow up the moon. It speaks nothing to the amount of TNT you'd need to subsequently dispose of that TNT, or the energy cost that you'd expend getting the TNT to the moon, or in the moon. I'm assuming this is one of those random questions to satisfy a random curiosity, not something super serious. $\endgroup$– Nick2253Jan 19, 2015 at 23:17
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Nick2253 gave a good start to the answer but that's only part of it. When you look further you find it's impossible.
Note cpast's comment--it's 1/3 of the moon's mass in TNT. But that's just the energy to blow up the moon, not the energy to blow up the moon and the TNT you used to blow up the moon.
We need to increase the TNT by 1/3 to account for the TNT itself--but we need to add another 1/9 to blow that up and so on--this sequence sums to 1/2. Thus we need half the moon's mass in TNT to blow it up.
Oops--now we have increased the binding energy by 50%. We need still more TNT to overcome that. This sequence sums to 100%--now we are up to the entire moon's mass in TNT. We also need to add enough TNT to blow up the TNT we just added.
Edit: Given Nick's comments I tried to work it out by brute force. My feeling the sequence didn't converge was right. The closest it comes is when the mass of TNT exactly matches the mass of the moon, this provides 62% of the energy needed. (Note, however, that the curve is quite flat--within the margin of error of the data--for quite a range around 1.0.)
answered Jan 19, 2015 at 21:23
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1$\begingroup$ Actually you do not really need to blow up the TNT. When it explodes most of its mass will be converted to gas and if you successfully exploded the Moon first, the gas will escape on its own due to solar wind and Earth gravity. Would still need to cover the increase in binding energy though. $\endgroup$ Jan 19, 2015 at 22:02
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$\begingroup$ @VilleNiemi You can't simply assign the energy to the moon rocks and not the TNT gasses--if anything the gasses will have a disproportionate amount of the energy. $\endgroup$ Jan 19, 2015 at 22:31
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1$\begingroup$ The energy that is liberated from a TNT explosion is greater than the gravitational binding energy of the TNT. This is obvious, because the mass of TNT needed to blow up the moon is less than the mass of the moon. Therefore, it will converge, whether or not you believe it will. This answer is wrong. $\endgroup$– Nick2253Jan 19, 2015 at 22:36
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$\begingroup$ If the explosion is, as it really should, underground and contained by solid moon rock, the velocity of the gasses from the TNT can't exceed the velocity of the rock surrounding it. Since the rock has so much inertia the explosion should be converted to pressure and the bulk of the energy is transferred to rock as TNT has less mass and the velocity of gas expansion is proportional to radius. $\endgroup$ Jan 19, 2015 at 23:12
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$\begingroup$ @Nick2253 As you add TNT the moon gets heavier. I worked it out brute force, there's no solution. $\endgroup$ Jan 20, 2015 at 3:46