"Destroying" the earth with nuclear weapons

[Kurgan]

As I'm not a scientist (and lazy), I ask you for your input here on just how plausible a scenario this is. Before you ignore this one, it's a little different than the usual scenarios (nuclear winter, killing ever human slowly, etc).


A friend (who is also not a scientist) insisted it would be possible, using all the world's nuclear weapons (that have ever existed) to destroy the earth, if we were somehow to devote all our energies to doing so intentionally. Presumably it had something to do with "burying" the bombs and so forth to try to "crack" the planet itself. The goal is not to create an explosion like the Death Star, but to destroy all life and render it uninhabitable, using only these man-made weapons.


I thought he was wrong, but again, I'm lazy, and not a scientist.
So how off base is he? How many bombs would you actually need?

PS: He also thought that this same arsenal would be sufficient to reduce a Dino-killer sized asteroid (detected early enough) into bits that would be "harmless" enough to us when they reached the surface of the planet.

[Chris OFarrell]

To put it one way. All the nuclear devices ever made, might, MIGHT together generate a total explosive force somewhere in the lower gigaton range.

To say this would be an expelled breath in the path of a hurricane in terms of actually doing anything to the planet, would be an understatement. Hell by burying all the nukes, you would just be using the Earths crust to absorb all the energy over a large area without any real problem on the surface, if its deep enough.

The 'killer Dino' asteriod as an extinction level event IIRC is calculated at about 100 million megatons. AKA 100 *Teratons* or there abouts. And while is fraked up the surface conditions for a while, it did jack to damage the planet as a whole.

[GrandMasterTerwynn]

Your friend is a fucking idiot. The maximum size of the combined nuclear arsenals of the world during the height of the Cold War was something in the neighborhood of twenty-three gigatons. An impressive bit of firepower, you say? Not really. A mature hurricane dissipates enough energy that it is the equivalent of a 3.1 gigaton bomb going off every day. The asteroid that ended the Age of Dinosaurs delivered 100,000 gigatons of energy.

None of these events have the destructive power necessary to destroy all life on Earth and render it uninhabitable. They don't even have the firepower to crack the planet open.

[Sikon]

A friend (who is also not a scientist) insisted it would be possible, using all the world's nuclear weapons (that have ever existed) to destroy the earth, if we were somehow to devote all our energies to doing so intentionally. Presumably it had something to do with "burying" the bombs and so forth to try to "crack" the planet itself. The goal is not to create an explosion like the Death Star, but to destroy all life and render it uninhabitable, using only these man-made weapons.

It wouldn't do anything like that. The yield of all of the world's nuclear weapons combined is about 10 gigatons, equivalent to the energy of 10 billion tons of TNT (~ 4000 J/g). For perspective, in energy terms, such is like vaporizing a bit less than 20 billion tons of water or a bit less than 4 cubic miles of water in oceans with 300 million cubic miles of water.

The world's nuclear arsenal obtains its destructive capability due to its effect on selected particular regions of the planet's surface, not doing much to the bulk of the mass in the planet (6 trillion billion tons). For example, it can't do almost anything to a lot of total ocean life spread over millions of square kilometers of area, especially that deep underwater, but it can destroy ships over a large area. It can't vaporize the oceans, but it can produce a rather large local wave on the surface, give people lethal burns from thermal radiation, etc.

Actually, this topic was discussed in a previous thread in more detail, in the case of a north pole detonation of all nukes, so here's just a shortened version of my old post:

If the formulas here are approximately valid even with extrapolation into the gigaton range, then thermal radiation would cause 3rd-degree burns out to about a 510-km radius (terrible, lethal for exposure over enough of the body). [...]

Other effects might be 4.6-psi overpressure out to on the order of 160-km radius (collapsing most structures) and initial prompt radiation of 500 rems out to around 18-km radius (a bit more than 50% mortality by itself if not for other lethal effects). [...]

Land detonation would make an apparent crater diameter of around 6 km with an apparent depth of around 1.4 km, excavating billions of cubic meters and many billions of tons. [...]

Assuming a similar ratio of fission to fusion yield, the amount of radioisotopes in fallout from the 10-gigatons of nukes detonating would be about 23 times greater than 440-megatons of past nuclear tests. [...]

Average natural radiation exposure is around 2.4 mSv per person annually for 6.5 billion people or around 16 million man-Sv a year, so the preceding might be on average equivalent to around a decade of natural radiation exposure. [...]

Of course, some people would receive vastly more, and some less, some dying if in areas where fallout was relatively concentrated. Localized fallout levels would initially be lethal, probably over thousands of square kilometers, although that area would be limited compared to the world's total surface area of 510 million square kilometers. [...]

In summary, considering all of the preceding, the devastation from the 10-gigaton North Pole detonation would tend not to reach Canada or Russia outside of their northern islands, aside from more limited indirect effects. The worst effect would be on any few people unfortunate enough to be within a few hundred kilometers or so of the North Pole at the time of detonation... [...]

The above discussion has a bunch of reference links, not shown here.

Much of the reason that the world's nuclear arsenals can cause so much destruction in a world war scenario is by them not all being detonated in one place. Rather, they would be detonated in thousands of different locations, corresponding more to the fraction of 1% of earth's total land area that has a huge fraction of the population (and military / industrial targets). Even then, they wouldn't kill everybody, killing perhaps some fraction of one billion people out of a population of 7 billion, depending upon assumptions and the details including indirect effects.

They have three orders of magnitude more explosive energy than all the conventional explosives used in WWII, yet their ~ 10000 megaton combined yield is thousands of times less than the dinosaur-killing asteroid of ~ 100 million megatons. And even that asteroid didn't come remotely close to wiping out all life on earth, although it caused global firestorms and wiped out notable large species on the surface.

When it comes to destruction, location is everything. Detonate a nuke in a city where the local population density is 10000+ people per square kilometer, and it will kill many people. Detonate it where the whole surrounding area has a handful to zero people per square kilometer, and it doesn't do as much. Overall, earth's land area averages about 40 people per million square meters, but the distribution is extremely uneven.

EDIT: The opening post states all the weapons that ever existed, rather than those existing at this time. That makes the figure up to several tens of gigatons instead of 10 gigatons, but it doesn't really matter for the order-of-magnitude general picture.

How many bombs would you actually need?

Wiping out almost all surface life on land beyond microbes would be possible at some imaginary, astronomical yield of nukes, even temporarily creating uniformly lethal radiation levels throughout the planet's 150 million square kilometer land area. However, literally accomplishing that would require orders of magnitude more nuclear yield than the world's arsenals, and it would be quite a project to manufacture that much. A more efficient technique to would be to gradually adjust the orbit of a really large asteroid to crash into earth, not that mankind would actually do that.

He also thought that this same arsenal would be sufficient to reduce a Dino-killer sized asteroid (detected early enough) into bits that would be "harmless" enough to us when they reached the surface of the planet.

Well, the way to deal with that would be to deflect the asteroid slightly from its course so it misses, keeping it intact. A form of nuke-pulse propulsion could be adopted, although a solar-powered or nuclear-reactor-powered mass driver would also work, using material from the asteroid itself for propellant, just gradually thrusting over a period of years until enough delta-v is provided. The main question is if the asteroid is detected sufficiently long in advance.

[Kurgan]

Thanks guys!

A small follow-up question: would there even resources enough on the earth (estimated) to build the huge number of bombs it would take to do what he thought was possible?

[Sea Skimmer]

The ocean contains millions of tons of uranium, so yeah, enough raw material probably doe exist to build enough nukes to wipe out all life.

Thing is, nuclear weapon material has a quite limited shelf life, so you can’t just haply spend 300 years stockpiling nuclear bombs, you’d have to be constantly remanufacturing the ones you’ve already built and constantly reprocess the nuclear weapons grade material you’ve already made. That would make the industrial effort in actually doing this far higher then it would first appear, and it first appears to already be a batshit insane endeavor all of humanity would have to commit to doing.

If you want to kill all humans on earth on paper, then take 1 ton of steel, turn it into needles and place one of the needles through the heart of every person on earth.

[fgalkin]

If you want to kill all humans on earth on paper, then take 1 ton of steel, turn it into needles and place one of the needles through the heart of every person on earth.

Won't work. Even assuming that those are lightweight needles that weigh 1 gram each, you'd still only kill a million people that way. You'll need 6600+ tons of steel to kill everyone.

EDIT: Moreover, if you go stabbing people one by one, you'll never manage it, since the Earth gains about 2 people every second

Have a very nice day.
-fgalkin

[Fingolfin_Noldor]

Bah... a biological weapon that is indiscriminate is probably the best. Just kill all life on the planet.

[Hawkwings]

I dunno... If you start killing at a constant rate, say 1 per second (for simplicity's sake) it would take 210 years to kill everyone. But if you kill children first, they wouldn't reproduce, which means 30 years later, there's less people for you to kill than there would have been.

Would that be possible?

[Peptuck]

Stardestroyer.net: Idly plotting the logistics of xenociding the human race.

[fgalkin]

I dunno... If you start killing at a constant rate, say 1 per second (for simplicity's sake) it would take 210 years to kill everyone. But if you kill children first, they wouldn't reproduce, which means 30 years later, there's less people for you to kill than there would have been.

Would that be possible?

True, and death from other causes will make a dent as well. On the other hand, if people begin having more babies as a response to your killing them, then they can still out-produce you in the long run.

Stardestroyer.net: Idly plotting the logistics of xenociding the human race.

Technically, it can't be "xenocide" since we're killing our own species. It's genocide, unless we're actually alien infiltrators destroying the human race for our Evil Alien Overlords.

Have a very nice day.
-fgalkin

[Peptuck]

Technically, it can't be "xenocide" since we're killing our own species. It's genocide, unless we're actually alien infiltrators destroying the human race for our Evil Alien Overlords.

Have a very nice day.
-fgalkin

I though genocide was more along the lines of eliminating a particular ethnicity, not the whole species.

[DavidEC]

The next step up from genocide is democide, and up from that, take the root of the word 'misanthropy' (hatred of people in general and possibly 'mankind') and we could have something like anthropocide.

Anyway, your friend probably doesn't realise that it is very easy simply to compare energy levels and realise that mankind ain't got nuffink on Mother Nature.

When people say 'nukes can destroy the world' they are correct only in the sense that 'nukes can destroy comfortable civilisation for the vast majority of those who have it now, and make life even worse for the rest of us'. A late 1980s nuclear exchange would not kill everyone - who the hell is gonna spend nukes on Amazonian tribesmen, most of Australia, Canada, Siberia, internal China, Mongolia, most of central Asia, hell, most of Africa! There are huge tracts of sparsely populated land which wouldn't be hit and still contain millions and millions of people. Of course, even the most pessimistic analyses I've read show that a nuclear exchange would leave at least half alive in the major players' countries.

[Napoleon the Clown]

Thanks guys!

A small follow-up question: would there even resources enough on the earth (estimated) to build the huge number of bombs it would take to do what he thought was possible?

To actually cause significant damage to the planet itself? That'd be a pretty tremendous explosion.

To even match the 100 teratons of the dino-killer it would take about 20,000 thermonuclear warheads (assuming an average yield of five megatons). Assuming we go the Tzar Bomba route and make as much of the power release a fusion reaction as possible, that means >160,000 kg of plutonium, using the Teller-Ubam design. U-238 (dunno how much) would be needed as well, though this is relatively easily obtained. A very large quantity of lithium-6 deutride would be needed, as it plays a big role in the yield of a bomb. Tritium, of course, needs to be present.


If you were to simply bury bombs instead of expecting them to be something you can transport there is the option of making the average yield higher, which will reduce the total amount of some components used. It would still require an obscene amount of very expensive materials though.


It is within the realm of current technology to produce, at very great expense, the materials needed. While it would theoretically be possible to match the dino-killer figure-wise, it would be wholly impractical.

Hell, look at Tambora's 1815 eruption. Mankind has yet to come close to even that, much less something that would blow a noticeable chunk out of the planet.

[Battlehymn Republic]

Send him over to this.

As for the burying the nukes deep underground idea, I also thought of that from an episode of (the Real Adventures of) Johnny Quest where Ezekiel Rage takes over a facility that sends geologists down 5 or 10 miles, and then had a nuke put in there. Then there was some nonsense about Johnny and Jessie using their Quest VR system to travel in time to stop him.

[Nephtys]

One famous idea that started a lot of this 'we can nuke ourselves to death' talk is the old notion that mankind has enough nuclear weapons to 'kill everyone on earth five times over'. We've all heard of that one. It's of course, based on not one or two, but many many silly notions.

First, it assumes all 6 billion people will gather in circles precisely in the same population density as 1945 Hiroshima. Then, the number of kilotons in all the combined world arsenals will be divided by 15 (the yield of the Hiroshima bomb) and multiplied by how many people died. The end result is about 30 billion, thus the 'we'll kill everyone 5 times over' spiel.

Of course, this is unrealistic. a 100 kiloton bomb does not have a destructive radius of 10 times a 10 kiloton bomb. It's about twice. Not to mention getting populations in that distribution is intensely unrealistic, or how exactly you divide a single megaton bomb exactly into so many 15 kiloton ones.

[Fingolfin_Noldor]

Question: someone suggested Asteroids, but what happens if nuclear warhead were accelerated to relativistic velocities then set off? Assuming the warhead survives the trip and doesn't blow up prematurely because the plutonium got too energetic?

[Ford Prefect]

Question: someone suggested Asteroids, but what happens if nuclear warhead were accelerated to relativistic velocities then set off? Assuming the warhead survives the trip and doesn't blow up prematurely because the plutonium got too energetic?

It would be pretty much pointless to detonate any nuclear warhead (or the earth's whole store of nuclear armaments) if you were accelerating it at any notable fraction of the speed of light. I mean, a cup of catfood hitting something at half the speed of light would take noticeable chunks out of Everest (or whatever).

[Nephtys]

Question: someone suggested Asteroids, but what happens if nuclear warhead were accelerated to relativistic velocities then set off? Assuming the warhead survives the trip and doesn't blow up prematurely because the plutonium got too energetic?

At above 3000km/s relative difference, your 150kt block of lead is going to have about as much energy as a 150kt nuclear bomb. (http://www.projectrho.com/rocket/rocket3x.html). At such a velocity, you don't need a warhead. Especially not on something as massive as an asteroid. It'll probably be nastier as well, given the various inefficiencies of a nuclear blast.

[Patrick Degan]

Stardestroyer.net: Idly plotting the logistics of destroying* the human race.

It's a hobby.

*corrected for accuracy

[Sikon]

A small follow-up question: would there even resources enough on the earth (estimated) to build the huge number of bombs it would take to do what he thought was possible?

Technically, yes, vastly more than needed.

An academic curiosity is that the tiny trace amounts of uranium in the average rock have as much energy content as a number of times the rock's mass in TNT explosive.

Earth's crust contains on average about 1.8 parts per million uranium concentration. This varies a lot, such as the above illustration shows the difference between concentrations in basalt versus granite rock. The total energy content of the uranium is slightly more than 17 kilotons per kilogram.

Per million kilograms or 1000 metric tons of average crustal rock, there are ~ 1.8 kilograms of uranium with an energy content equivalent to ~ 31000 tons of TNT high explosive ... like thirty times the rock's mass in chemical explosive.

Of course, this is not of direct, practical relevance. The only mechanism by which that energy can be released in principle is if the rock is mined; the uranium is separated out; and, either just uranium-235 is fissioned (0.7% of the total), or the uranium-238 (99%) is subjected to fast fission or converted to plutonium-239 to subsequently more easily be fissioned, e.g. in a breeder reactor.

The earth's crust alone masses ~ 100+ million trillion tons, containing around 200+ trillion tons of uranium. But, of course, nearly all of that is practically inaccessible to mankind. The concentration of uranium is too low for economical mining even of a small amount of the average crustal rock. Rather, uranium mining has historically involved finding ores where its local concentration is orders of magnitude greater than 2 ppm.

Short of uber-tech, the most mankind can do is obtain a lesser amount of uranium from conventional mining or separate out some portion of the billions of tons of uranium in the oceans. Uranium in seawater is actually of lesser concentration than in the average crustal rock in absolute terms, but it is far less expensive to extract, flowing water over adsorption fibers, actually affordable for commercial nuclear power, as discussed in other threads.

Actually, giant thermonuclear bombs wouldn't necessarily need much uranium relative to yield. They could have above a 100:1 fusion to fission yield ratio at least, so mainly lithium deuteride might be the nuclear fuel. There's a number of times more lithium on land than uranium, and deuterium is a higher concentration in the oceans than uranium (~ 1/6500th of 150 million trillion tons of hydrogen in seawater).

There's plenty enough to build giant thermonukes wiping out life on earth, aside from all of the practical impossibilities of this project, including mankind actually wanting to do it.

Incidentally, any readers unfamiliar with this topic may wonder why manmade radioisotopes can cause significant radiation exposure despite such vast amounts of natural radioisotopes existing in nature. Why do a few kilograms of fission products in fallout from a nuclear bomb matter when there are many trillions of tons of uranium, thorium, potassium-40, and other radioisotopes in nature? The reason is a combination of two factors: (1) The percentage of a radioisotope decaying per unit time and its energy release rate is inversely proportional to half-life. For example, a few grams of an isotope in nuclear bomb fallout with a half-life of days can very briefly put out as much radiation as millions of tons of uranium-238 that has a half-life of 4.5 billion years. (2) Manmade isotopes may be locally concentrated rather than dispersed throughout large amounts of rock underground. For example, as a result of the preceding two factors, a nuclear bomb's fallout can briefly cause lethal levels of radiation exposure over a localized area on the surface. But, overall, the nuclear waste from the world's reactors has vastly less radioactivity than natural radioisotopes in earth's crust, especially in the long-term, although it is more concentrated.

[kinnison]

I think that it might be possible to destroy all human life, maybe not all life, with nukes. Not because of the direct effects but because of such things as ozone layer depletion (putting billions of tons of nitric oxide into the stratosphere) and nuclear winter effects.

A sufficiently insane group of people could also probably massively increase the problems, by deliberately targeting nuclear reactors and nuclear waste storage sites; also by deliberately targeting things that will burn creating large amounts of smoke, such as oil storage depots and oil refineries.

In addition to this, by careful design a handful of large (gigaton-range) weapons could probably destroy modern civilisation by EMP effects; also, a gigaton-range weapon in low orbit would probably cause forest and grass fires over most of a continent, especially if it was summer. Imagine the recent Californian fires over an area 100 times as large - at least.

The whole point is to use the nukes as catalysts for larger effects.

[Ace Pace]

I think that it might be possible to destroy all human life, maybe not all life, with nukes. Not because of the direct effects but because of such things as ozone layer depletion (putting billions of tons of nitric oxide into the stratosphere) and nuclear winter effects.

Not this nuclear winter thing again.

"Bunk is a pretty fair description(of nuclear winter). The "nuclear winter" theory was predicated on a series of hypothetical models that had been constructed by a group of "concerned scientists" lead by Carl Sagan who constructed a computerized model of earth, cranked in a series of hypothetical statistics on the effects of nuclear weapons and then claimed that the results from that model constituted "facts".

There were a number of serious problems with this process. One of them was that, when the hypothetical effects of nuclear initiations were cranked into other models of earth, they didn't produce the results Sagan had reported. In fact, the results reported by Sagan's group were only achieved when his particular model of the earth was used. This was a remarkable thing so people looked at Sagan's model to see how it differed from the rest. The answer turned out to be quite simple. The model Sagan had shown to the world press to “prove” the danger of “nuclear winter,” depicted the earth as being a barren ball of rock with no mountains and no oceans. Oceans, as Sagan well knew, act as gigantic energy flywheels that moderate temperature, helping cool adjacent continents in summer and warm them in winter.

Sagan, in other words, knowingly committed deliberate scientific fraud. He cooked up a phony computer model to concoct the phony “nuclear winter” results he wanted for political reasons. It subsequently became apparent that he had avoided using the already-available NCAR computer climate model precisely because he knew it would not produce the “nuclear winter” he wanted to sell to gullible journalists and an ignorant public.

Once that point had been realized, Sagan's assumptions were examined in greater depth. It turned out that none of the people in his group of "concerned scientists" were nuclear weapons experts. What they'd done was taken some generalist public sources, cherry-picked the ones that suited them and used them without examining how the various nuclear weapons effects interacted. Again, there was a healthy dollop of deliberate scientific fraud here. Where effects didn't give the results required, they were exagerrated or morphed until they did. By the time the critique was over, "nuclear winter" as a concept was totally discredited; today its a touchstone. If somebody starts to spout forth on the dangers of "nuclear winter" they're nutcases. Sagan's credibility never recovered; he never got another hearing from the serious nuclear weapons and policy community.

However, one useful thing did come out of all this. In order to examine the probability of Sagan's fairy stories, people cranked real data on nuclear weapons into real atmospheric models. The results were actually quite interesting (there is a novel currently being posted in HPCA called "Anvil of Necessity" which draws on that work).

For those who like grim details, the following was the nuclear exchange used as a basis for these studies. The US was presumed to have been hit by 5,800 warheads witha total yield of 3,900 megatons. Nuclear devices initiated in Europe totalled 3,300 with a total yield of 1,200 megatons The USSR was deemed to have been hit by 6,100 devices having a total yield of 1,900 megatons. China got hit by 900 devices witha total yield of 1,300 megatons. By way of comparison in TBO, Germany got hit by 232 devices totalling 8.6 megatons.

Other areas receiving at least a dozen warheads include Canada, North and South Korea, Japan, Taiwan, Greenland, Puerto Rico, India, Israel, Australia, Guam, Cuba, Syria, and Egypt. Other countries got single devices, mostly on their capitals. Nobody didn't get hit by something. This massive exchange used about half the global strategic and theater nuclear arsenal; about 10% was launched but did not reach a target and 30% was destroyed on the ground. By the time we finished there were 10,000 nuclear weapons left in the arsenals out of the 67,000 that we started with. Initial casualties were 400 million dead; by the time things had worked out, this increased to 1.2 billion. Welcome to my world.

The smoke clouds from the fires etc peak three days after the exchange. Essentially, they would spread to form a doughnut shaped band around the world that would essentially cover North America, Europe and the USSR. This smoke (actually, its particulates rather than smoke) cloud consisted of 1,500 million tons of dust, 25 million tons of smoke from vegetation, and 80 million tons of smoke from cities and other manmade sources. It is very important to note that the last type of smoke has the greatest impact: smoke from petroleum and petroleum products is particularly effective at absorbing sunlight. Altogether, about 0.4 cubic km (0.1 cu. mi.) of dust and smoke is in the stratosphere. The general effect (and this is the peak remember) would be to reduce sunlight intensity and temperature by a degree comparable to an overcast day. That's a general comment, if the observer is downwind of a stricken target, the intense plume from the smoke generated by large continuing fires will reduced mid-day light levels to that of twilight. The average peak temperature will be reduced by around 13 degrees F. However, there is a peculiar effect here; average trough temperatures will be increased by roughly the same amount (for exactly the same reason that a cloudy night is warmer than a clear one; the smoke clouds also tend to hold warm air in. That was an effect that Sagan and his crew deliberately suppressed.

Within ten days, the smoke/particulate concentration would decline rapidly although smoke in the upper atmosphere still absorbs much sunlight. The primary effect ceased to become temperature and the gross temperature changes would already be a thing of the past. Instead, the patchyness of the initiation effects would cause unusual weather conditions including strong winds in some coastal areas (in effect we've dumped huge amounts of energy into the climatoscene and that starts to work its way out). A curious predictable phenomena is that dense fogs would develop over the oceans and along waterways. Another interesting effect is that the ozone layer would be reduced by nearly half yet nearly all of the Earth's surface would receive less solar ultraviolet radiation than before the war. The reason is curious; although smoke levels would be dropping rapidly, there would now be a thin veil of very fine high altitude particulates that effectively act as a block to UV radiation. The sunsets will be incredibly beautiful.

Twenty days after the nuclear exchange climatic effects would have peaked. By this time, areas alongside seas, oceans and other large bodies of water would have effectively returned to their pre-exchange temperature sets. High-altitude areas woudl actually be warmer than before the exchange, sometimes dramatically so. At an altitude of 40,000 feet, the air termperature would be no less than 70 degrees F higher than normal (!!!) Surface temperatures far inland will drop by around 20 degrees F but this is a transient phenomena. The critical thing is light level; although the veil of fine high-altitude dust doesn't have a critical temperature effect, it cuts light levels by around 25 percent, ensuring that crops fail.

Within three months, temperature effects are virtually over. Worldwide, peak temperatures will have been reduced by, at most, 2 degrees F while trough will be increased by the same amount. This will shorten crop growing seasons a bit but since the crops are failing anyway it won't make much difference. This temperature change will persist for two or three years. by which time the atmosphere will have been purged of dust and smoke.

The best way to describe the real climate change would be that a state of "nuclear autumn" would become widespread. In other words both the high and low ends of the temperature spectrum would be shaved so that things tend to the "median" situation."

[Nyrath]

Obligatory Atomic Rocket link:
http://www.projectrho.com/rocket/rocket3x.html#boom

# 4.2e21 joule: 1 teraton = 1000 gigatons = 1e6 megatons
# 4.2e24 j: 1 petaton = 1000 teratons
# 3.2e26 j: Energy required blow off Terra's atmosphere = 77 petatons
# 6.6e26 j: Energy required to heat all the oceans of Terra to boiling = 158 petatons
# 4.2e27 j: 1 exaton = 1000 petatons
# 4.5e27 j: Energy required to vaporize all the oceans of Terra = 1 exaton
# 7.0e27 j: Energy required to vaporize all the oceans of Terra and dehydrate the crust = 2 exatons
# 2.9e28 j: Energy required to melt the (dry) crust of Terra = 7 exatons
# 1.0e29 j: Energy required blow off Terra's oceans = 24 exatons
# 1.5e30 j: Energy required blow off Terra's crust = 359 exatons
# 4.2e30 j: 1 zettaton = 1000 exatons
# 2.9e31 j: Energy required to blow up Terra (reduce to gravel orbiting the sun) = 7 zettatons
# 5.9e31 j: Energy required to blow up Terra (reduce to gravel flying out of former orbit) = 14 zettatons
# 2.9e32 j: Energy required to blow up Terra (reduce to gravel and move pieces to infinity) = 69 zettatons

[Sarevok]

Question: someone suggested Asteroids, but what happens if nuclear warhead were accelerated to relativistic velocities then set off? Assuming the warhead survives the trip and doesn't blow up prematurely because the plutonium got too energetic?

At above 3000 km /s relative difference, your 150kt block of lead is going to have about as much energy as a 150kt nuclear bomb. (http://www.projectrho.com/rocket/rocket3x.html). At such a velocity, you don't need a warhead. Especially not on something as massive as an asteroid. It'll probably be nastier as well, given the various inefficiencies of a nuclear blast.

Are you sure it is not 3000 m/s ?