Will a nuclear blast just above the surface of an asteroid push/nudge it, or just heat it and maybe produce outgassing? In other words, would nukes be actually useful to deflect asteroids?
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2$\begingroup$ Breaking an asteroid into many small pieces means a shower that might wipe out the satellites. It is usually better to leave the asteroid in one piece and just nudge it out of the collision course. $\endgroup$– naturallyInconsistentCommented May 7 at 10:18
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1$\begingroup$ @naturallyInconsistent - I don't think we've done it enough times for anything to be particularly "usual"... $\endgroup$– Jon CusterCommented May 7 at 12:43
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$\begingroup$ Why did NASA need to observationally confirm whether DART successfully redirected Dimorphos? $\endgroup$– mmesser314Commented May 7 at 14:39
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$\begingroup$ Easter egg alert - Watch Dart impact the Google Dart Mission page. $\endgroup$– mmesser314Commented May 7 at 14:41
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$\begingroup$ Note that many asteroids are rubble piles. How do rubble pile asteroids form? $\endgroup$– mmesser314Commented May 7 at 14:59
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2 Answers
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Would nukes be actually useful to deflect asteroids ?
Probably not. All the evidence that we have from flybys, orbiting missions and landings is that most asteroids are rubble piles with significant cracks and internal voids. A large explosion close to such a body is likely to break it into several smaller objects, which may still be large enough to cause significant damage if they hit the Earth. In which case you have replaced one asteroid with several asteroids - which are also now dusted with radioactive fallout.
The problem with explosions (either conventional or nuclear) is that their effects are hard to predict. There are several alternative strategies for deflecting an asteroid that are more controlled and more predictable in their effects - see the Wikipedia article on asteroid impact avoidance for a summary.
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A nuke just above the surface of an asteroid will blast loose lots of loose bits. The Dart mission showed the "explosive impact" - equivalent to 3 tons TNT blasted about a thousand tons of material from the asteroid and had a major effect on its orbit - about five times as much as the actual impact The best distance is probably as close as we can!!
https://en.wikipedia.org/wiki/Asteroid_impact_avoidance
Note any "Non Impact/Explosion" scenario has to cope with the horrible Rocket equation We need to hit the asteroid a long way out so that the small change in velocity is enough to add up to a miss This means that our "diverter" will need a decent delta V 10 km/sec (about the least that will be needed) to get there in time which means a 40:1 Fuel ratio But if we then have to match velocity we need another 40: ratio Giving a 1600:1 fuel ratio. We could send 100 Kg "bombs" - but not the tons of material needed for any type of rendezvous and push scenario.
The "The bomb blows it all to bits scenario" We should start off with the first bomb a decent distance away - the Dart impactor was the equivalent of 3 tons of TNT on the surface Start with say a 10 Kiloton nuke - but set it off 100 meters out - or 200 meters - more qualified people than I should argue about that!
We would use the data from the first impact to fine tune the distances for the later bombs in the string
Various studies have been done - reference the Wikipedia article - but they seem to have concentrated on stopping a relatively immediate impact - talking about 100 Megaton bombs
If we are diverting a number of years out smaller bomb(s) should be enough and would give us time to modify the operation on the fly
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$\begingroup$ Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center. $\endgroup$– Community BotCommented May 7 at 11:03