Hi.

I've seen plenty of discussions concerning what to do with an asteroid with collision course for Earth, when it comes.
And of course, many have suggested to blow it up with a nuke (how original ), and every time I see people saying that is a bad idea, because then we have to deal with the fragments instead.

But, isn't that a good thing, that the asteroid gets fragmented?
Sure, the damage to us will be more spread, but the total damage will be lower, because much more of the asteroid will burn up in the atmosphere, won't it?

Can't that be compared to something like this:
1. Take an ice cube and put it in a glass of water and see how long it takes before it melts.
2. Take an other ice cube of equal size, crush it to smaller pieces, put it in a glass of water with equal temperature as the one above, and see how long that takes to melt in comparison.

I bet that nr. 2 is melting a lot faster, and I think it will be the same with an asteroid. After all, "most" of the small rocks that fall from the sky burns completely up in the atmosphere, don't they? Because they are too small.

I share your view in general. A lot depends on how large the fragments are. If you could reduce it to objects of a few kilograms of mass, I'd expect little damage. Also, even larger fragments would have a large number of members that would not directly collide with the surface with catastrophic consequences such as tsunamis, fractured Earth crust, etc. I'm not sure whether anyone has worked out sets of optimal solutions regarding fragment sizes.

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The same amount of energy has to be dissipated whether in one big chunk or smaller ones. This helps only for small asteroids, in which the damage would have been "merely" local. If the atmosphere can't get rid of that much energy quickly enough to avoid incinerating a hemisphere, it doesn't much matter whether it arrives in one piece or many. Not so much that fragmenting an incoming asteroid is bad, but that it's not as much of a good thing for big rocks as one might initially think. Of course, if you can fragment it with so much authority that some of the pieces miss the planet, that is a net gain (hence the interest in how solid asteroids are - it's tough to split and blow up a loose pile of pebbles in this way).

I say keep h-bombing an incoming asteroid until it's gone. Our h-bombs vaporized bikini atoll, I think they could be made to put a dent in an asteroid thats only one or two miles across.

I have often heard the quibble that atomic bombs cannot behave the same way in space, and so we're still helpless and doomed. But, if there's no atmosphere to provide the necessay medium for the energy to express thermally, then just seal the bomb up in a lead lined container, and seal that in a tank of liquid hydrogen. Lead absorbs radiation and superheats. The hydrogen expands to provide the explosive force.

Maybe we could build an asteroid intercept vehicle or something to catch up with one in case it's on an earth-impacting trajectory. It certainly seems like a handy thing to have around. The only thing standing in the way is a cold-war era treaty against nukes in space that will have to go away eventually anyway if we want a manned mars mission or a lunar base.

And as for the naysayers:
1. Doing anything about a major earth impacting asteroid is better than doing nothing, and h-bombing it into dust and vapor is a better idea than most.
2. Some people get a kick out of human helplessness, the same people who scream about the energy crisis while demonstrating against nuclear power, and they need to be ignored.

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One problem is that all the weapons on earth are not big enough for the truly earth-threatening asteroids.

Also, there are far simpler, more effective, and more predictable ways of preventing a collision with Earth than simply lobbing a bomb at the intruder.

Compare the damage ten 200 kiloton nukes scattered over the East Coast would do compared to a single 2 megaton weapon...

Actually, how effective a bomb would be in dealing with a NEO depends in large part on how the NEO is constituted. IIRC, studies have shown that while solid rock would be effectively damaged or deflected, a "rubble-pile" asteroid would probably be unaffected by any weapon we could throw at it.

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If you take the ability to even break up an asteroid as a given for purposes of this conversation, lets look at the outcomes.

A major inbound asteroid has the potential to do a LOT of damage. Climate changes, dust, shockwaves, firestorms, that kind of thing. Its big, and as long as we're not looking at a multi-mile wide monster, its fairly localized, no worse, say, than a major volcanic eruption. If its a monster, you're really no better off with it hitting in one piece or ten pieces, honestly. Its going to hurt either way, but for a modest sized rock in the 1km range, you get major continental disruption, but it ain't the end of the world.

Now, breaking it up. You have now take a slug and turned it into buckshot. Even a modest, 1km crude diameter rock being broken apart, even if the largest piece is only .05% of the original mass, the odds are, its still big enough to cause a problem. That hole in Arizona was made by a rock only a few hundred feet across. Multiply that times the number of potential rocks created by bashing a 1km wide asteroid into pieces, knock off about 20% (this isn't based on any real calculation, just a nonsense factor for sake of conversation) for small stuff that will vaporize in the atmosphere, and maybe another 20% (same here) for stuff that will be disrupted enough that its trajectory will actually miss the planet from whatever process you used to bust the big one. That's still a LOT of rock thats coming in to make your day miserable that will cause Meteor Crater-ish level damage across the full footprint of the debris field.

Do you really accomplish much by turning a monstrous, but localized problem into a buttload of big problems spread across more area?

Localized impacts would really be better, because the odds are, we'll know far enough in advance approximately where the impact will occur to get most people out of the way, not counting delays, riots, recalcitrants and whatnot.

You break that thing up and spread the love, you have no way of effectively evacuating the impact area, because you run the risk of dumping evacuees into another impact area.

Its like the old saying, only a fool fights a war on two fronts. You have one known problem, address that problem, don't exchange it for an array of headaches you may not be able to predict.

I'm not talking about hitting it at the last possible minute. Turn it into buckshot while it's still 1AU away from earth, and most if not all of the shot will miss. Provide impulse to the asteroid, or blow it to bits while you still have a month or so, and you don't have the collision problem.

Furthermore, turning the asteroid into buckshot is still a good idea because it increases the amount of material that's blocked/burnt up in our atmosphere. a 1km wide single point collision could cause the gulf of mexico. Ten thousand 1m wide collisions won't cause anywhere near as much damage. It would set some forests on fire, maybe destroy fields and a few buildings, but most of it would burn up.

I don't agree at all with this popularized notion that we should roll over and die, meekly accepting our "fate", if an asteroid strike will happen. All of these excuses are lame if you hit the asteroid in time. That means you need to launch a vehicle capable of doing it, but we'd be better off for acting.

If our h-bombs could vaporize a 6 square kilometer island, then why can't they do damage to an asteroid? If the lack of atmosphere is a problem, put the bomb in a hydrogen tank. It seems like people just want to be helpless, or something. If one h-bomb doesn't do the job, nuke it again. Repeat as needed. You have plenty of time, assuming you launched enough explosives in enough time.

This is addressing the problem. Not acting is not adressing the problem. It's burying our heads in the sand and hoping for the best, like the dinosaurs and the rest of life before us.

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The safest thing to do is to intercept these things and change their orbits. That requires knowing about them well in advance. Attempting to blow them up is something we would no doubt try as a last ditch effort. Come to that, it may well be what will do anyway when it becomes a problem because we do not appear to be disposed to plan for such an even in advance.

1) We are not doing an especially great job of looking for them.
2) There does not appear to be any inclination to think about how to deal with them in any way other than using nuclear weapons.
3) As far as I know, we are not doing any serious design work on weapons with yields sufficient to do the job. Presumably, this can be rushed and well lob an untested weapon at it when the time comes.
4) One group of weapons designers have claimed that all we need to do us use a shaped nuclear charge. Uh-huh! That's why Rumsfeld is now talking about using kinetic energy weapons to deal with bunkers nowadays instead of using small nukes, right?

Don't get me wrong, we will make a gallant attempt when the time comes. We will try to blow one of these things up, but it most likely will NOT WORK.

one aspect of blowing them up that no one has mentioned is the possibility of somewhat large chunks of it ending up in earth orbit, taking out our satellites and rainig down on what's left of our civilization for a century or 2.
of course, i guess a large enough single impact could conceivably send up that kind of debris, as well.

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Sounds like part of this is just aversion to nukes magnified to irrational proportions. We suggest nukes because they cause lots of impulse, heat, and energy for their mass. You could do it with dynamite or chemical rocket boosters, if you insist, but it would require comparatively ridiculous amounts of mass to be launched.

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Wrong! I am against them in this application because I don't think that they will do the job. I am all for nuclear power, military and civilian.

But these ain't 20 KT firecrackers we are talking about here, okay? True, there is no theoretical limit to how big thermonuclear can be. That's been known for a long time. What is less well known is that the blooming things are not particularly robust. Worse, if there is way to "shape" a nuclear blast I have never heard of it.

They won't do the job. It is NOT safe to rely on them as a first solution to this problem. They are a last desperate measure, not an optimal solution.

If we disrupted an asteroid far enough away from Earth. The debris would spread out along it's orbit. So, instead of one big impact, or several medium sized impacts. Earth passes through the trail of debris, the same way we pass through the trails left by comets several times a year. There may be a danger of one or two Tunguska type events, but that would be localized and not a threat to the rest of the planet.

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Yes, we could do that. Then we might get a Tunguska type event in downtown Paris, London, Tokyo, Mexico City, or New York.

Blowing the darned things up reall is a last ditch, we-got-no-other-solution effort.

I think the problem is that most people don't believe that something like this could happen, or if it does happen, it will happen after they are long gone. The odds of such an event occuring well after anyone living today has already died from old ate IS pretty good. So they're right in a way. On the other hand, is it good morals? NO!

This is much more of a sure thing, taking enough time into consideration, than global warming is, but the weather has more impact on peoples lives on a daily basis than objects from space do. This one will most likely be ignored until the problem becomes acute.

You gotta understand the physics here, you break up a body without shifting its orbit, the debris is still gonna have a substantial amount of momentum wanting to carry it in the direction it was originally heading. Look at the recent Deep Impact mission. That slug didn't ram the comet, it got in the comet's way because that comet had a buttload more relative velocity than anything we've got, that represents a LOT of inertial momentum. Heck, the alteration of the comet's orbit after impact, while measurable, is negligable, not even enough to be called even a minor diversion. So even if we had managed to break up the comet with some theoretical warhead aboard Deep Impact, that minor bit of angular momentum away from the original direction of travel isn't going to be much, if anything. Look at Shoemaker-Levy 9, that thing, even after it did breakup, still headed on course to collision with Jupiter. If you look at the impact pattern on Jupiter after the impact as seen in the video of the impacts from Galileo, that grouping pattern was still pretty tight. You cannot guarantee that you'll divert the fragmented debris substantially, and even if you do manage it to some extent, the fact remains some parts will continue on course, and those smaller pieces won't have the inertial momentum to resist Earth's gravity that the monster would if it were on a near miss trajectory, so its entirely possible that the Earth's gravity would divert some of the smaller junk in more easily as it got closer.

Again, just spreading the problem over a large area, instead of dealing with a single large impact event or a single focused effort to divert the entire mass as a whole.

SL-9 was caught in Jupiters gravity, the debris had no where to go except Jupiter. An object on course for Earth, but in orbit around the sun, would spread the debris in a ring around the sun, the same as a comet. Once a year Earth would cross the trail. The risk of a smaller impact would be better than one large impact that may devastate most of a continent.

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Again, it goes back to how much it actually disperses. Heck, just coming up with the necessary energy to break it up is one hurdle we're nowhere near, to say nothing of giving it enough oomph to keep going.

To do this, we still have to know that it is coming and we have to know that it is coming long before it reaches you 1 AU limit.

We do not have the demolition charges needed for this job in the inventory. We do not have a launch system that could reliably deliver the charges. All of this stuff would have to be rushed up if tomorrow we saw one headed our way.

Furthermore, turning the asteroid into buckshot is still a good idea because it increases the amount of material that's blocked/burnt up in our atmosphere. a 1km wide single point collision could cause the gulf of mexico. Ten thousand 1m wide collisions won't cause anywhere near as much damage. It would set some forests on fire, maybe destroy fields and a few buildings, but most of it would burn up.

I don't agree at all with this popularized notion that we should roll over and die, meekly accepting our "fate", if an asteroid strike will happen. All of these excuses are lame if you hit the asteroid in time. That means you need to launch a vehicle capable of doing it, but we'd be better off for acting.

The results of that test are somewhat over-stated. Yes, we could indeed damage, even pulverize an asteroid given enough time to develop the necessary weaponry and a delivery system to get it there. What this will NOT necessarily do is deflect enough of the mass away from Earth so that we do not suffer major harm. There are many, many, many ifs involved with this scenario, most of which have bad endings.

This is addressing the problem. Not acting is not adressing the problem. It's burying our heads in the sand and hoping for the best, like the dinosaurs and the rest of life before us.[/quote]

Agreed! But nukes are not necessarily the best answer or even a good answer. Other approaches should be developed.