Take the 2-minute tour ×
Astronomy Stack Exchange is a question and answer site for astronomers and astrophysicists. It's 100% free, no registration required.

Often on television shows and in articles I see it mentioned that it'd always be bad to blow up an asteroid or comet because then the energy would just be spread out and cause even more damage.

According to some estimates I've seen around 100 tons (or more) of meteoroids hit the Earth each day. If all of this were combined together into a single asteroid, it could destroy an entire, large city.

Given that alone, it makes it seem to me that it be more logical to take the chance and blow up an asteroid and thereby trim its weight down, causing a lot more to be more easily burnt up on entry, so that when it did hit, it would cause less damage.

Is this logical at all? If my science/math/physics is incorrect, I want to understand why having more burn up by spreading out is worse compared to having it more concentrated and vastly more dangerous.

share|improve this question
If the 100 tons were ice and formed into a cube, it would be about 46.4 m on each side. A meteor this size would only affect a small area. When you get larger meteors, you would probably need more than one missile to fragment it into small enough chunks. –  LDC3 May 30 '14 at 5:36
@LDC3 but what if it were rocky and approaching at a steep angle (> 45deg)? –  Supuhstar Aug 21 '14 at 2:52

1 Answer 1

Well there are some things to consider. Initially if you could make sure that after you blow up an asteroid you will end up with numerous but small enough pieces so that they will either: one, burn up in the atmosphere or two, be headed away from Earth (and not hitting us five years later) then we are OK, and blowing up the asteroid with a missile would be a fair solution.

The problem here lies in the fact that we know little about the internal composition of asteroids in general, and presumably even less about a particular one, so it is very hard to predict exactly where the pieces of the asteroid generated by an impact are or aren't going to end up or, be headed towards or even its size.

Another scenario could be that if you effectively smashed the asteroid into small pieces that could then burn into the atmosphere, and if those pieces were coincidentally to end up being consumed by Earth's atmosphere, it would heat up provoking presumably an unpleasant day on Earth of course depending on the mass of the object.

But there is a much better solution than that Armageddon-Hollywood inspired one. It is call gravitational tethering. There is something we know, and we know very well about asteroids, and that would be their trajectory paths or orbits. Even when a new asteroid is discovered, its orbit can be computed pretty quick and with great accuracy (because we know the solar system's gravity very well). So if an asteroid is to impact Earth, it is likely that we will know with years, probably decades in advance. And so we can just send a space vehicle (called gravity tractor), with enough mass and time in advance, and place it just beside the asteroid, hence allowing us to tilt its orbit by just a tiny amount, due to the gravitational pull between the two objects. Now when you consider the effect of that tiny amount in the long run, it effectively deflects the path of the given asteroid from that of the Earth so that it won't hit us 20 or 30 years later.

And this is something we have control over, and something we can predict with great accuracy. It is the (safe) way to go.

If you are still not happy with my answer, you can listen to Neil de Grasse Tyson himself explaining it in this 5 min video.

Also check out this talk from the American Museum of Natural History on "Defending Earth from Asteroids" LINK

Further reference here.

share|improve this answer
"So imagine you blow up a 10 km asteroid and you end up with multiple 600 m pieces of rock rushing towards Earth, then you just made the problem worse." Doesn't that presume though that none of these would burn up in the atmosphere more so than one solid piece? You may have 600 m smaller objects, but if it's 10km wide anyway, I don't see how you could make it worse. –  simontemplar May 30 '14 at 4:35
Yes, in that sentence I am assuming that those pieces won't consume in the atmosphere and will produce multiple impacts on Earth surface. In any case, that was meant to work as an example of the complexity of that solution. And whether it is 10 or 30 km or 600 or 150 m pieces is irrelevant to the point I am trying to make. I just wanted to show you how blowing up an asteroid is potentially worse, which is what you asked; and provided you with what is most widely considered the right approach. –  harogaston May 30 '14 at 5:03
I strongly suggest you check out this YouTube video –  harogaston May 30 '14 at 5:12
I didn't ask the proper way to avoid an asteroid impact, I specifically asked whether or not spreading it out would actually lessen the impact because it would be in smaller pieces allowing more to burn up, if the answer is "no" on the basis that one isn't accounting for the fact the Earth has an atmosphere, then it's not what I'm asking about. –  simontemplar May 30 '14 at 6:38
I didn't say you asked for the proper way to avoid an asteroid impact, I said you asked "how blowing up an asteroid is potentially worse". And that I answered. I'm not disregarding Earth's atmosphere. I pointed out how our ignorance of the outcome of hitting an asteroid with a rocket could make it worse. Imagine you split it into two, then you will have to evacuate 2 places on Earth, and the energy on the asteroid is still there, it won't go away just because it is now two different rocks. –  harogaston May 30 '14 at 7:06

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.