Why is nuking an asteroid a bad thing

[Wile_E]

Gee, I always thought nuking it was the only way to be sure.

[billfish678]

@Stranger_On_A_Train

[
One possibly deleterious side effect is that once this capability is developed, it does potentially offer the involved parties to use this as a threat, i.e. using the same technology to deliberately target another nation with a PHA. I personally don’t think this is very likely–it is substantially more difficult to target a precise intercept than it is to just push a PHA out of a collision zone, and would represent almost as much of a hazard to the aggressor nation as to that being targeted–but it would be virtually unstoppable and this has been used to argue against developing such a capability until we actually need it.

Stranger

Back in the day my high school library had an interesting book, probably written in the 50’s. It was fairly technical for a high school library book. Its main premise was/were? all the good reasons we should make a manned asteroid instead/before a moon landing. Then it went into how much more useful and easy it would be to exploit asteroids rather than the moon. And this was way back before we realized just how many of those suckers are out there.

They also observed that a large body orbiting the earth made a good defensive weapon. There would be no way you could deorbit it without folks knowing it. It would take a good bit of time to do it, so it would only make sense as a retalitory weapon. The victims would very likely know who the hell did it (way before it came in to boot). And, unlike two nations with lots of nukes, there is no incentive to strike first lest the other guy takes out your nukes first. So, its probably a more scenario stable MAD deterent as well.

[Chronos]

That’s if you’re the one in orbit, not the target.

EDIT: In reply to Wile E, not billfish.

[Damuri_Ajashi]

@dracoi

@jackdavinci

You seem to be saying two different things:

1. The pieces will still be too big to burn up in the atmosphere

2. Even if they all burn up, there will still be some sort of problem

I can understand #1 - actually being hit by the same total mass even if it’s not in one piece, will still cause major damage. But I’m asking about #2 - assuming a mass large enough to cause a major catastrophe, but broken up into pieces that are small enough to burn up in the atmosphere, what is the problem? I understand conceptually that, hypothetically, you are still introducing the same amount of destructive ‘energy’ if in a different form - but what is the actual physical thing which will occur? Will the atmosphere heat up to dangerous levels? Or will there be some kind of physical impact damage on the land from a wave of comet mist?

Tunguska is widely believed to have resulted from an asteroid or comet that came apart in the upper atmosphere without hitting the ground. It still did enough damage on the ground to take out a modern city, and produced enough light to be visible around much of the world.

The object that caused Tunguska is generally estimated as 20-50 meters in diameter. While that’s big in terms of average objects, it’s nothing compared to some of the monsters that are out there. Take Tunguska and multiply it by a million and it won’t matter whether anything hits the ground or not. At a certain scale, you’d have enough energy to turn the whole atmosphere into a fireball and smash everything on the ground with the shock waves.

So even if we pulverize a large asteroid into little pebbles. All those pebbles will create enough heat to turn our antmosphere into a blast furnace?

[Quartz]

I find it difficult to accept this concept of atmospheric heating, primarily because it seems to assume a perfect transfer of energy - complete disintegration - from the meteor to the atmosphere. That’s only going to happen with the very smallest meteors. Larger ones are going to transfer much of their energy to the surface when they impact, not the atmosphere. And the surface is a very good insulator, unless the meteor punches through the crust to the mantle. So I can’t help but conclude that breaking up an incoming medium-sized or larger meteor is better than leaving it intact.

Fight my ignorance.

[dracoi]

@Damuri_Ajashi

So even if we pulverize a large asteroid into little pebbles. All those pebbles will create enough heat to turn our antmosphere into a blast furnace?

For certain values of large, yes. I mean, the Tunguska object itself seems large - a 20 meter rock is big in my book. Turned into pebbles, it did enough damage to destroy a city had it hit one. But the Earth has been hit by mountains in the past.

[Chronos]

I find it difficult to accept this concept of atmospheric heating, primarily because it seems to assume a perfect transfer of energy - complete disintegration - from the meteor to the atmosphere. That’s only going to happen with the very smallest meteors. Larger ones are going to transfer much of their energy to the surface when they impact, not the atmosphere. And the surface is a very good insulator, unless the meteor punches through the crust to the mantle. So I can’t help but conclude that breaking up an incoming medium-sized or larger meteor is better than leaving it intact.

So it’s good if the energy transfer to the atmosphere is inefficient, and better if we make it as efficient as possible? I’m not sure which angle you’re coming at this from, here.

[PlainJain]

@Chronos

And PlainJane, I understood the question, and the reason for asking it. It’s a perfectly reasonable question; it’s just really hard to answer. About all we can say is that, with the current status quo, we stand an uncomfortably large chance to not have anywhere remotely near enough lead time.

Thanks for responding Chronos. I know that a single astereoid might not have killed the dinos and that we probably don’t have the technology to detect them early enough yet but my OP was assuming (like these scientist do when discussing this) we had the option to nuke early enough or not. Take the following…

@Grey

Assuming we figure it out of course.

Chronos, I was thinking the same thing but a quick BOE calculation makes me wonder – it also makes me think I forgot something like accounting for gravitational potential energy.

100 m wide sphere of rock (2500kg/m3) moving at 10km/s relative (asteroid plays catch up with us) to the earth would have a kinetic energy of 6.5x1016 J. If we flip that so the relative velocity is 44 km/s (now we’re playing chicken) it jump’s to 1.3x1018J.

With an atmospheric heat capacity of 1000 J/kg/K and a mass of 5x1018kg we would only see fractional changes in the atmosphere’s temperature on the order of 10-260 uK. Not an awful lot of heat assuming the thing is broken down to small enough pieces to burn up in the atmosphere.

Now a dino killer with a diameter of 10000 m is completely different - at 10 km/s it could heat the atmosphere by 13 degrees.

Yes, 13 degrees is quite significant but is it worse than the nuclear winter that would follow if we allowed it to strike the earth unimpeded?

[Grey]

Well that was for the lower impact velocity of 10km/s. The kinetic energy goes up as the square of velocities which makes higher numbers nastier. However, ripping a 10km wide asteroid into fist sized particles small enough to burn up is not something any one is suggesting. Stranger’s nuclear program is built to nudge the rock off course not take it apart.

But ultimately I’d have to say I don’t know.

[dracoi]

@PlainJain

Yes, 13 degrees is quite significant but is it worse than the nuclear winter that would follow if we allowed it to strike the earth unimpeded?

If you follow all of Grey’s math, though, that 13 degrees could be as much as 260 degrees depending on the velocity of the dino-killer. (13 degrees assumed 10km/s when 44 km/s is possible).

Grey also assume equal distribution of the heat throughout the entire atmosphere, which is virtually impossible in an impact. So double the numbers if the heat is distributed evenly over half the Earth. If the pebbles only hit, say, North America, then we could quadruple the numbers.

So now we’re talking about a dino-killer disintegrating in the atmosphere with as much as 510 degrees (and that’s C/K not F) of heating over 1/2 of the Earth’s surface. Ouch!

But I still think there’s a key problem with working it this way. Grey’s math shows that plenty of things can burn up with no overall atmospheric heating. The real problem is: if you break the asteroid up a little, but not into dust/pebbles, then you might be back to the old MIRV equation. We can agree that 13 C of atmospheric heating may be better than a ground impact. But if we get chunks instead of pebbles? I’m not sure I’d want to trade one Chicxulub for 8,000,000 Tunguskas.

[Quartz]

@Chronos

I find it difficult to accept this concept of atmospheric heating, primarily because it seems to assume a perfect transfer of energy - complete disintegration - from the meteor to the atmosphere. That’s only going to happen with the very smallest meteors. Larger ones are going to transfer much of their energy to the surface when they impact, not the atmosphere. And the surface is a very good insulator, unless the meteor punches through the crust to the mantle. So I can’t help but conclude that breaking up an incoming medium-sized or larger meteor is better than leaving it intact.

So it’s good if the energy transfer to the atmosphere is inefficient, and better if we make it as efficient as possible? I’m not sure which angle you’re coming at this from, here.

You’ve got things the wrong way around. Enabling a perfect transfer is Not Good; leaving the meteor to punch through the crust is equally not good. There’s got to be a happy medium, right?

[Chronos]

I think that no matter what you do, the total destruction is going to scale pretty much linearly with the total energy of the impact. No doubt there is some sort of “optimal impact” for any given amount of energy, but I don’t think that, for a given energy, the difference between a best-case scenario and a worst-case is going to be enough to bother with.

[Stranger_On_A_Train]

@Quartz

I find it difficult to accept this concept of atmospheric heating, primarily because it seems to assume a perfect transfer of energy - complete disintegration - from the meteor to the atmosphere. That’s only going to happen with the very smallest meteors. Larger ones are going to transfer much of their energy to the surface when they impact, not the atmosphere. And the surface is a very good insulator, unless the meteor punches through the crust to the mantle. So I can’t help but conclude that breaking up an incoming medium-sized or larger meteor is better than leaving it intact.

Fight my ignorance.

“Larger [meteorites] are going to transfer much of their energy to the surface when they impact” means enormous seismic impulses that would dwarf the destructiveness of terrestrially-caused earthquakes and tsunami. And although people are throwing around km or larger diameter meteorites, a 50m diameter bolide intersecting at half Earth’s orbital speed–say, about 15 km/s-- is large enough to literally obliterate a major metropolitan area by energy transfer alone, not even considering the effects of surface impact by whatever may remain of it.

Stranger

[Gray_Ghost]

Just wanted to chime in to point out this handy calculator for the terrestrial effects of bolide impact. (Used to be at the University of Arizona, guess they moved.) The calculator doesn’t get into the effects of whole-atmosphere heating, but is otherwise quite interesting. Playing around with it and a random number generator, my thought is that for the vast majority of detected NEOs, the tsunami is what’s going to be the big harm, not the fireball or seismic effects. The calculator also doesn’t get into large scale weather effects, like the aforementioned nuclear winter (yes, I know the TTAPS stuff was later discredited) or what was described in, e.g. Lucifer’s Hammer

Also wanted to ask Stranger a question…

@Stranger_On_A_Train

…For a reasonable sized PHO, this would be just an extension of existing space launch and space vehicle technology. The only real challenges are meeting a space booster production and launch schedule to support this (current production and launch rates of Atlas V and Delta IV boosters are 4-5 per year each for the single common core vehicles, so you’d either have to increase this substantially or enlist the aid of other nations that produce heavy-lift vehicles and integrate the payloads to this spectrum of vehicles) and develop the explosive focusing and ablative pusher system described above. Neither is trivial in terms of the effort and cost involved, but I don’t think it represents a dramatic advance in technology. The real advantage wouldn’t be so much international cooperation–which would likely fall apart after a successful effort anyway–as justifying the development of a robust and less costly space launch infrastructure rather than the haphazard and primarily military/surveillance customer base that currently exists.

One possibly deleterious side effect is that once this capability is developed, it does potentially offer the involved parties to use this as a threat, i.e. using the same technology to deliberately target another nation with a PHA. I personally don’t think this is very likely–it is substantially more difficult to target a precise intercept than it is to just push a PHA out of a collision zone, and would represent almost as much of a hazard to the aggressor nation as to that being targeted–but it would be virtually unstoppable and this has been used to argue against developing such a capability until we actually need it.

Stranger

In your opinion, would it be possible to cannibalize or gang together ICBMs to construct the deflection vehicle?

Interesting point on the technology for asteroid deflection being considered a weapon and therefore having its development disfavored. Seems to me though that if you can deflect asteroids, you already have ICBMs or the equivalent, and therefore don’t need yet another unstoppable city-killer, so the threat is perhaps overstated. Neat point, though.

[Stranger_On_A_Train]

@Gray_Ghost

In your opinion, would it be possible to cannibalize or gang together ICBMs to construct the deflection vehicle?

It depends on the size of your payload. Even the largest ICBMs like the LGM-25C ‘Titan II’ and the RT-23 Molodets (NATO reporting name SS-24 ‘Scalpel’) don’t really have enough throw weight to put a payload into more than a Low Earth Orbit orbit, while it is possible to add additional lift/kick stages to boost it up, it really takes a true exo-atmospheric upper stage like Centaur or Agena to achieve an Earth escape trajectory with a significant payload, and assuming that you’re going to want to reach the PHO as quickly as possible your payload is going to be mostly propellant. The exception is the R36M (NATO: SS-18 ‘Satan’) which is a monster booster for an ICBM and was used as the basis for the Dnepr and Tsklon , but even those rockets are near the bottom of the class of medium lift vehicles. And of course, almost all of these vehicles are demilled; no more Titan II vehicles exist (and the commercial/new production Titan line has been shut down for nearly a decade).

Decommissioned ICBM motors and rocket engines are used for some LEO space launch applications (and many current families of space launch vehicles were originally based on surplus ICBM assets) but it’s not a simple matter of glomming them together, especially for a task that is well and beyond their design capability. In terms of capability and schedule (which I’m assuming is predicated largely on launch vehicle availability) a purpose-designed trans-orbital injection launch system like the Delta IV or Atlas V-Centaur is probably a better choice for maximizing the number of payload assets to intercept.

Stranger

[Musicat]

Let’s look at it this way. A grain of sand-sized object can impact the Earth and burn up in the atmosphere without damage to the Earth.

There may be many grains of sand-sized objects doing this every day, if I can see the flashes in the sky at night. Loosk harmless to me. How many of these would there have to be to make a difference compared to the status quo?

Now suppose a solid meteor is broken up into grains of sand-sized objects, and in breaking up, they are spread apart, and once the initial impact is dissipated, they will continue to spread apart because any gravity and glue that once held them together isn’t there much anymore. So the particles will be heading in all different directions and continue to do so according to Newton’s laws.

Now if the original projected impact time to Earth is a long time off, by the time the first particle reaches it, the last particle will be way, far away, possibly on a path that will never intersect the Earth at all, or at least many moons hence.

So if a meteor is nuked into sufficiently small pieces with a sufficient force, although the original mass is still present, it will impact the Earth in tiny, harmless chunks over a very long time, or not at all. To me, this seems to be a big improvement over dinosaur extinction events.

Or to reverse the problem, if you took all the grains of sand that burn up in the atmosphere in a year and put them all together into a single, solid mass, striking the Earth all at once, what was once harmless would now be catastrophic.

[Stranger_On_A_Train]

@Musicat

So if a meteor is nuked into sufficiently small pieces with a sufficient force, although the original mass is still present, it will impact the Earth in tiny, harmless chunks over a very long time, or not at all. To me, this seems to be a big improvement over dinosaur extinction events.

Your assumption is that you can pulverize an unconfined, world-threatening PHO into dust or, at least sub-golf ball sized fragments. Trying running the calculation on how much energy it would take to evaporate the water in a 1 km diameter sphere of ice, and back out just how many 1 MT nuclear devices it would take to achieve that energy.

It’s going to take far less effort to push a threatening object to the side than to try to utterly destroy it.

Stranger

[Musicat]

@Stranger_On_A_Train

@Musicat

So if a meteor is nuked into sufficiently small pieces with a sufficient force, although the original mass is still present, it will impact the Earth in tiny, harmless chunks over a very long time, or not at all. To me, this seems to be a big improvement over dinosaur extinction events.

Your assumption is that you can pulverize an unconfined, world-threatening PHO into dust or, at least sub-golf ball sized fragments. Trying running the calculation on how much energy it would take to evaporate the water in a 1 km diameter sphere of ice, and back out just how many 1 MT nuclear devices it would take to achieve that energy.

So how many? I’m thinking of a rather small nuclear device and what it did to Hiroshima with a distant burst. Pretty much pulverized several city blocks. Now take a larger weapon and explode it closer to a smaller but still threatening-sized object, say 100 meters across. Seems likely to handle the situation.

Not that a slight nudge wouldn’t be a better option, and easier to track the result. And only a slight nudge would be needed if we had 10 years of warning.

[Chronos]

There may be many grains of sand-sized objects doing this every day, if I can see the flashes in the sky at night. Loosk harmless to me. How many of these would there have to be to make a difference compared to the status quo?

A lot, but then, when you convert a mountain-sized object to sand, you get a lot of sand. Well more than enough sand to not be harmless any more.

[Musicat]

@Chronos

There may be many grains of sand-sized objects doing this every day, if I can see the flashes in the sky at night. Loosk harmless to me. How many of these would there have to be to make a difference compared to the status quo?

A lot, but then, when you convert a mountain-sized object to sand, you get a lot of sand. Well more than enough sand to not be harmless any more.

But that mountain isn’t all coming arriving at once or at the same place. It’s spread out in both time and space – a lot of both, at least if the nuke device has adequately pulverized it.