The scenario is the following: a civilization with technology level similar to humanity's current, on a planet similar to Earth, shall be hit by a massive celestial body in approximately one year.

The impact would be around three times more powerful than the one that caused the end of dinosaurs, but still not enough to completely destroy the planet.

The civilization know about it one year before impact, and know precisely when and where it would crash.

My question is: what would be the best way to save as most people as possible ?

Is there a way to destroy the asteroid ? or at least to damage it and reduce the impact strength ?

Else, what kind of preparations could be efficient, for the impact itself as well as adaptation to what the planet and its life forms would become after it ?

Is there a chance of long-term survival at all ?

I wonder as much for the explosion (or waves, depending if the asteroid crash on land or on ocean) as for consequences for potential survivors: animal and vegetable kingdom would be shaken, so if a large group survives, could a civilization rebuild just after?

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    $\begingroup$ Everybody should put a paper bag on his head and lay down on the floor. It won't help, but it is less stressful that way. $\endgroup$ – SJuan76 Jun 28 '15 at 16:24
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    $\begingroup$ Lucifer's Hammer. $\endgroup$ – Pete Becker Jun 28 '15 at 19:58
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    $\begingroup$ Work on spinal flexibility--that way, when it hits you're more likely to actually be able to bend over and kiss your nether regions goodbye. $\endgroup$ – Loren Pechtel Jun 28 '15 at 21:14
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    $\begingroup$ @HenryTaylor There is no difference. You are perturbing its course and it will take the same amount of energy to make it undershoot as to overshoot. To make it go wide would be different, less or more depending on the situation. Slowing it down is preferable just because it requires striking the near-side rather than the far-side. $\endgroup$ – Avon Jun 28 '15 at 21:14
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    $\begingroup$ @jokeSlayer94, better send Chuck Norris. No spacesuit or giant bomb required! $\endgroup$ – Martín-Blas Pérez Pinilla Feb 4 '16 at 7:53

11 Answers 11


Divert it

It takes only a tiny change in the course of the asteroid to make it miss if the change is made early enough. So with a year, start designing an interceptor from bits and pieces of space and weapons programs, build a couple of them (for redundancy), and launch them with some months to spare.

  • A big nuke, not in the asteroid but somewhere to the side. It might shatter the asteroid, but most parts would be nudged. Any change of course would make them miss.
  • A lander with a rocket engine to shove the asteroid.

Considering the partial success with Philae, you'd send more than one mission. If the first ones work good enough, send the rest an abort command.

The various space programs could work a lot faster if money and safety was no object. You couldn't design a new launch system from scratch, but you could get a lot of mass up to the ISS. Assemble and refuel the interceptors in space.

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    $\begingroup$ Rocket engines are problematic because you have to worry about rotation and keep the thrust aimed. Look at laser bees (a Planetary Society project!) Or gravitational tethering. For a one-year lead, the latter is probably too slow. $\endgroup$ – JDługosz Jun 28 '15 at 18:36
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    $\begingroup$ It takes more than "any" change to get a deflection. If you can actually deliver the change immediately .12 m/sec is enough to ensure a miss. If it takes 6 months to build and fly your bomb out there it's up to .24 m/sec deflection needed. 9 months to intercept means .48 m/sec. $\endgroup$ – Loren Pechtel Jun 28 '15 at 21:17
  • $\begingroup$ @LorenPechtel, that's why I called for an intercept as early as possible. Impart a tiny acceleration in roughly the right direction. Observe. Repeat. $\endgroup$ – o.m. Jun 29 '15 at 5:12
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    $\begingroup$ To impart the needed delta-v you need roughly 700 Tsar-Bomba's. - Assuming you can get them to the asteroid in 3 months, and all energy output from the nuke goes to changing the velocity of the asteroid. $\endgroup$ – Taemyr Jun 29 '15 at 10:46
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    $\begingroup$ A Gravity Tractor is what you want and you'd probably want more than a year (en.wikipedia.org/wiki/Gravity_tractor), everything else within our current technology is made problematic by the fact that most asteroids appear to be large piles of rock and gravel only weakly adhered together (if at all). $\endgroup$ – RBarryYoung Jun 29 '15 at 15:34

Well, you didn't specify the actual size of the meteorite, which could change things, so I'll assume it is similar to the one which caused the extinction of dinosaurs 65 million years ago.

I would guess that the impact area on Earth could be known with anticipation enough so that the populated areas probably could be evacuated in a more or less orderly way. The direct damage of the explosion would be limited in area and time.

Now, the main issue is the same that killed the dinosaurs: all of the soil and ashes thrown into the atmosphere and blocking the Sun's energy, making it impossible to grow crops as usual and making temperatures colder globally.

Fortunately, we have some technologies that the dinosaurs did not have[citation needed] to paliate that:

  • First, growing crops under artificial lightning. Nowadays, this is mostly used for growing weed; so there is plenty enough information on internet about how it would work. Things to take into account:

    • Source of power: solar power would be hardly hit, I do not know how hard eolic or hydroelectric energy generation would be affected1. Carbon/Oil would continue working, but a possible lack of rain or wind1 could make it more toxic than usual. Maybe it would time to go nuclear again.
    • Food to grow: even without power issues, you will only be able to grow crops in a limited area. You will want to restrict that to crops with a high yield of nutrients (rice, wheat, legumes for proteins, maybe even massive fields of algae). Definitely no grass --> no meat production.
    • Law & order: Maybe supply is not enough for everybody, so you should have to prepare your society for it. Namely, isolated, self-sufficient communities that grow their food and defend it from foreigners. If you are in one of these, good for you, if not, well... you had it coming. Some level of coordination between the communities would remain, though, for trade of specialized items (fertilizers, nuclear fuel, pharmaceutical drugs...)
  • Second, getting the dust down to Earth as fast as possible. I think little has been actually studied, but with the right incentive it could be developed quickly. V.g., lasers to stop the dust particles (so they fall), balloons dropping water from very high attitude (so it catches dusts while falling), maybe putting water to boil to saturate the atmosphere of H20 so it would rain the dust...

    The problem with all of those is that, while they could help to partially improve the situation, their effect would be medium-long term and you would need to put them into action in a gigantic scale (in a moment when you should be putting all of your resources on the food production issue).

For a way more massive impact, which makes surface outright uninhabitable, the only solution would be dig deep, create some of such food producing communities underground (with nuclear power). Of course, they would be more expensive to produce, so they would be fewer, smaller and without communication (all of which makes them way more vulnerable).

1: Since the actual motor behind winds and rains is, again, solar energy, such a disruption of solar rays could affect eolic or hydroelectric dams. Probably there would be still winds and rains, but it is hard to predict the changes (maybe the river that you have dammed dessecates or becomes frozen, maybe the zone where you eolic generator was installed is now completely calm).

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    $\begingroup$ The OP does mention that the "impact would be around three times more powerful than" Chicxulub. $\endgroup$ – Frostfyre Jun 28 '15 at 19:54
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    $\begingroup$ You are assuming the asteroid will hit land. ~70% chance it would hit ocean and that would trigger an enormous tsunami. The tsunami could be big enough to decimate entire continents even if the fireball isn't. Coping with an impact the size of Chicxulub is highly unlikely. $\endgroup$ – Avon Jun 28 '15 at 21:10
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    $\begingroup$ Such a large asteroid would be seen much earlier, and would be "charted" already. A surprise visit would be a long-term comet. Looking up some things, they do indeed get that large. "Mostly under 60km". I can just hope that a supernucleus first-time visitor would make a big show and be visible earlier. I wonder if anyone here can figure just when it would be visible? Hopefully something like LSST will be in both hemispheres, so we can expect to spot something at magnitude 24.5 within 3 days after appearing. $\endgroup$ – JDługosz Jun 29 '15 at 18:17

one year to divert an asteroid

If an object (more likely classified as a comet) comes in from the unknown, never before charted or seen earlier, it's probably coming from a direction far from the plane of the planets (say, from due North) and incoming at reverse escape velocity, a parabolic orbit (figured at the barycenter, not the sun: it will seem hyperbolic with normal sun-centered navigation).

A year is not long enough to travel far out, turn around and speed up again the other direction very much, to rendavous. Chemical rockets can't do it. So any kind of lander, like planting a rocket or more elaborate ideas that entail matching velocity with it, is not an option.

The dirty road approach still works. A rocket heads outward as fast as it can, leaving a trail of dust or pebbles or whatnot, which will still be travelling outward at high speed (just not as fast as the main craft).

The incoming commet will start running into them, and not matching speeds is the key to how it works! Each little impact will slow it down a tiny bit, without smashing it up like a single large impact would.

Given the assumed orbital characteristics, maybe someone can calculate the required ΔV needed to turn a hit into a miss. It's complicated because it's getting closer all the time and more change is needed the closer it comes.

another idea

Especially since it's comet-like, being new to the inner solar system, it is jetting at thrusting all by itself. This means that you will not be able to predict the impact accurately, BTW.

A beamed energy weapon can have some effect on this. A laser, or even a microwave radar beam of high power, can cause excessive heating and thus thrusting on the body. Even a big mirror could concentrate sunlight onto it.

That would certainly make for an exciting story, since the resulting thrust is random and chaotic. And you can demand "more power!" with realistic physics. Also, the people working on it are on Earth and can continue working on improvements, rather than having no more input after launch.

Huge lasers are doable now, as are various microwave emitters. Every nation can be throwing what they can at it, all in the same meele, with cumulative results.

  • $\begingroup$ I can't believe I had to scroll down this far before someone finally mentioned lasers. $\endgroup$ – evankh Jun 30 '15 at 8:16
  • $\begingroup$ I doubt anything we can do short of an existing asteroid or many nukes would have sufficient power to divert an asteroid within a year. $\endgroup$ – Cees Timmerman Jun 30 '15 at 12:00
  • $\begingroup$ Would the downvoter please explain? $\endgroup$ – JDługosz Jun 30 '15 at 21:18

Just some numbers for those who think about diverting the asteroid by pumping energy into it.



Other aritcles on wikipedia gives an estimate of 10km as the diameter of the asteroid. This reduces the energy needed to divert it by a factor of 216, meaning we would need the energy of between 3 and 4 Tsar Bombas to divert it.

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    $\begingroup$ The best option is to fragment it using successive nuclear blasts. $\endgroup$ – Cees Timmerman Jun 29 '15 at 13:24
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    $\begingroup$ @CeesTimmerman That will not change my answer. You still need to impart 0,27m/s delta-v to 2.262 kg of asteroid. Fragmenting it has the advantage of placing the nuke "inside" the asteroid, thus avoiding sending 50% or more of the blast into vacuum. But in my answer I assume that we somehow are able to use 100% of the energy from the nuke. $\endgroup$ – Taemyr Jun 29 '15 at 13:38
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    $\begingroup$ Earth's atmosphere would have an easier time to break it apart. If the asteroid was tumbling, perhaps it could split sooner. And we still have thousands of nuclear warheads. $\endgroup$ – Cees Timmerman Jun 29 '15 at 13:59
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    $\begingroup$ @CeesTimmerman you don't want Earth's atmosphere to break it apart. A hit is a hit, no matter how many pieces it's in. $\endgroup$ – JDługosz Jun 29 '15 at 17:56
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    $\begingroup$ @CeesTimmerman $((10km)^3/12)^{1/3}=4 368km$. You are off by a bit more than 1 order of magnitude. $\endgroup$ – Taemyr Jun 30 '15 at 12:02

Breaking News

SETI is having a series of talks on Asteroid Day.

The recient colloquium I'm watching now includes much of interest regarding this topic, including:

  • warm superconductors will be a transformative technology that will enable efficient megastructures in space, including
  • a 12-foot diameter payload (fits in existing rockets) inflates to a solar mirror that goes out to a lagrange point and brings back a 10-meter diameter asteroid (takes 2 weeks of focused sunlight burning to give 5km/s Δv) with 248 Mg material remaining at delivery.

Meanwhile, he was on an early think-tank planning board that considered asteroid (comet) strikes and how to deflect them.

He briefly notes that sending up a "nuke" is not a good idea, but taking one of these 10-foot asteroids and lobbing it into the path of a comet (see time code 24:23, New Mitigation Method: Terminal Defense by Placing 10 Meter NEO's on In-coming Path With Solar Concenteator) is a useful idea. This was studied in 1992 and presented at the "first congress for mitigation" (IOW, the real (possible) plans) as an offshoot of "star wars" technology. The imact with the incoming 70 km/s comet just throwing a rock in its path is big (he doesn't give the result but calculating from what he gave,

"The rule of thumb is 3½ km/s imact of anything with anything releases the same amount of energy as the equivilent mass of TNT.. kenetic energy scales as the square of velocity." 20× the speed means 400× the energy, and using the mass noted earlier that gives 100 megatons. That's like twice the largest thermonuclear device ever built, and many times what were developed as production weapons.

The comon advice is that simply "blowing it up" Bruce Willis style is not a good idea, but is a bad idea. The nuke portrayed in that scientifically awful movie would only have moved the two pieces apart by 7 feet! A bunch of loose rubble hitting the Earth could be worse than a single rock.

This idea means "terminating" the comet far enough away so the pieces dispurse significantly farther than the diameter of the Earth, so most of it misses; and being icy, this will melt and vaporize material rather than just breaking it up into smaller rocks. Mollecular sized debris will be blown by the solar wind and sunlight, which forms a comet's tail.

Again, working on deflection rather than messy destruction, such an industrial mining asteroid could be lobbed into place and then itself blown up: let the comet hit a string of smaller rocks in its path, vaporizing part and thrusting the rest.

enter image description here

Here is a video of the real thing.

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    $\begingroup$ I don't think the impactor idea as described is feasible for the scenario OP describes. You would need much more than one year to set it up. If you already had the asteroid in place ou might have a chance, but even then one year is a really short time. - Also at 100Mt we are still short by more than 2 orders of magnitude. $\endgroup$ – Taemyr Jun 29 '15 at 21:18
  • $\begingroup$ OK, we're doomed. I posted a Q on Astronomy SE to see how long we would really have, rather than an arbitrary 1 year. $\endgroup$ – JDługosz Jun 29 '15 at 22:02
  • $\begingroup$ "A bunch of loose rubble hitting the Earth could be worse than a single rock." - I've always wondered about this statement. Would it really? Loose rubble would have more surface area exposed to the atmosphere on entry and so more of it would be burned up. Also a lot of the rubble may miss the Earth f done early enough, so while there would be a greater spread of targets, the total mass hitting the surface would be lower. $\endgroup$ – colmde Jul 2 '15 at 12:36
  • $\begingroup$ Yes, more will burn up. missing is indeed an improvement, as I noted in my initial statement. As I said before, efficiently pumping the energy into the atmosphere will deliver more heating than using some of it to dig a big hole. $\endgroup$ – JDługosz Jul 2 '15 at 14:57

One problem you would have is to finance such project. There would be senators who would bring up bible and say such expenditure is a waste of taxpayer's money because God promised not to destroy Earth after the Flood. And other (also from other religion) who would welcome "End of Times" as good occasion to judge non-believers they don't like.

Such project would require central planetary government to focus resources of all humanity. What is the chance for that to get support? The best you can hope is that every faction will try to deflect impact point to hit any of the opponents instead.

There would be communities in mountains who would prefer to take chance on rugged survival than allowing central planetary government to save as many people as possible (or all).

Think about it: climate change is exactly such disaster: we know it is coming, science is clear, devastating consequences of the impact are clear, small changes now would deflect the impact from being devastating to just manageable. And "we" (our elected representatives) choose to do nothing instead, for various reasons. Why do you think that handling such asteroid impact would be any different? It would be worse, because you have less time to educate the public and elect politicians with some brains in their head.

Such people don't have to win the argument: just slow down response to be ineffective. So far they are winning the argument.

  • $\begingroup$ Ok, the U.S. would not fund it. But what of EU, China, Australia? Deflecting the impact point is pointless, as it's a global issue. The debris will re-enter all over the planet. How could it be changed to "just managable"? It's a hit or a miss, with nothing partial about it. $\endgroup$ – JDługosz Jun 29 '15 at 22:05
  • $\begingroup$ Getting hit by 1 asteroid with 100km diameter might be different thing than getting hit by debris of it after it split up - especially if big chunk of debris will miss. But "manageable" was about climate change, which we know is coming, is inevitable, and we do nothing. $\endgroup$ – Peter M. - stands for Monica Jun 29 '15 at 22:22
  • $\begingroup$ only if some of the debris misses. $\endgroup$ – JDługosz Jun 30 '15 at 0:38
  • $\begingroup$ What is the chance for that to get support? - About the same chance the USA was able to win WW2. $\endgroup$ – Cees Timmerman Jun 30 '15 at 11:39
  • $\begingroup$ You are right. Very, very close. :-) even if US-ians are misled to believe that victory over nazis was preordained. $\endgroup$ – Peter M. - stands for Monica Jun 30 '15 at 13:49

This question, like many older stories, postulates a sudden appearance of an enormous hazard. This is unrealistic and dated. I've watched semanars from SETI etc. and have learned what kind of surveying has already been done, how much better we can spot something like that now, and the amazing instruments kust around the corner.

Jules Verne was "prophetic" (or more appropriately, prophétique) because he kept up with scientific and technological progress.

Any near-future killer asteroid story would need to consider technology like the LSST which will automatically scan the visible half-sky every week, with particular notes on anything that changes.

I asked on Astronomy SE, and it's pointed out that a mere 3km comet (C/1996 B2 Hyakutake) would have been spotted 8 years out.

All things being equal, a 60km "supernucleus" would appear as a disk 400× the area. I don't know if the brightness figures in the analysis include any coma at that distance. But, the surface outgassing and general mess it leaves behind will also be 400× larger, while the irradiation falls off with distance... if it's twice as far out the irradiation is cut by 1/4, so the coma would only be 100× and further 1/4 the brightness from our viewpoint, or still 25× brighter than the object reported on, C/1996 B2 Hyakutake.

The comet moves fastest at perihelion, and much slower elsewhere. So doubling the distance will more than double the inbound time.

In short, any such object will be seen decades before they arrive.

The documents on C/1996 B2 Hyakutake state that "it's easy to push around". In contrast to the previous answers here, astronomers said that a 3km body was easy to push? The outgassing acts as a rocket with significant ΔV on the comet. The orbit of B2 Hyakutake was changed significantly, such that its previous visit was 17000 years ago and its next will be in 70000. The comet slowed down significantly, all by itself!

This suggests that directed energy would be very effective, adding to that effect. It will also be something of a wild ride, with nobody being sure just where it will wind up, with or without intervention. Slowing it to the point where we are sure of a miss, or heating the top or bottom to push it out of the plane, would start long before it's visible without a telescope.

I suggest the following elements for a more prophétique story set in the next 50 years.

When these instruments come on-line, a very large comet is seen 20 to 30 years out, with concerns of a possible impact.

The orbit is uncertain because it is self-powered and chaotic. Experts don't agree on models. After 2 or 3 years, watching all the (smaller) distant comets provides more certainty and experts agree that the risk is real.

Politicians deny any risk, and eventually a large part of the uneducated population does, too. After all, it's 25 years from now; not our problem.

Somehow or another, work does start. Maybe "other" nations step up and develop huge mirrors. The effort and the mirror technology itself turns out to be a huge boon to the economy and technological development, just as Apolo was for the U.S.

World power and economies shift. Work in other changes such as the effects of climate change 30 years from now, rise in computer power, superconductors, and limited nanotechnology.

Development of the superconductor-based large structures might be a major tech boon. Practical superconductors that work in ordinary and even hostile environments, and flux pinning as a construction technique can be applied to industry on Earth, too.

In short, the armageddon turns out to be a genesis instead: that which doesn't kill us makes us stronger. When the comet passes, large chunks are broken off to keep, and humans set up a manned base on what's left to ride it off to interstellar space, using the mirrors to boost it up to hyperbolic speed.


There is lots of discussion online about this (as Google will show you), and how Hollywood gets it dead wrong. You cannot "destroy" it. One approach is to sew a dust cloud in its path, slowing it down. When looking thhrough the Google or YouTube results, pay attention to proposals by physicists as opposed to screenplay writers.


Given the time frame and the energy needed there's only one option with any chance of success--Orion. It's going to be an absolute kludge of a system built on a 24/7, 9 women to make a baby in a month type basis. Assemble as many teams as you can, if you have 10 ideas you try them all at once and see what pans out. I rather suspect the logistics of moving the rocket from it's construction point to a launch point would prove impractical given the timeframe, they would probably launch right from the factory--even if that means you blow up part of a city in the process.

Figure how much of a nudge you can give the rock and stay below it's escape velocity, size the bombs you'll use for the deflection accordingly. If some bits get thrown off you don't care but if you break it up you now have several rocks to deflect rather than just one and Hollywood aside, breaking it up is worse than doing nothing at all.

  • $\begingroup$ But two halves have more friction than a whole, so there's more chance of disintegration and energy loss. $\endgroup$ – Cees Timmerman Jun 29 '15 at 14:17
  • $\begingroup$ @CeesTimmerman But when you're talking a rock this big it's not going to burn much in the atmosphere. On the flip side blast damage is subject to the square-cube law, by splitting the rock up you increase the total damage. Blowing up a Tunguska-sized object is good, blowing up a dinosaur killer is bad. $\endgroup$ – Loren Pechtel Jun 29 '15 at 14:54
  • $\begingroup$ The surface is not equal. We could divert half of the damage to a sparsely populated area. $\endgroup$ – Cees Timmerman Jun 30 '15 at 11:30
  • $\begingroup$ By "Orion", do you mean Project Orion to gently push the asteroid with a nuclear explosion-powered rocket? $\endgroup$ – Cees Timmerman Jun 30 '15 at 11:37
  • $\begingroup$ @CeesTimmerman Yes, I'm referring to a nuclear pulse engine--but both for pushing the rock (I wouldn't build anything elaborate as you don't care about ablation. Just use standoff detonations in the right spot above the rock) and for getting there in the first place. Remember, the rock is coming towards us and there's no time for sling turns and a tail chase--that means probably more delta-v than we can get with chemical rockets. The only things that can possibly provide the needed delta-v are ion and nuke--and ion is way too slow. $\endgroup$ – Loren Pechtel Jun 30 '15 at 16:03

The ever popuar "Next Big Future" blog has several interesting concepts. The most plausible is similar in some respects to a modern anti tank weapon; a small charge on the probe blows away any active or spaced armour while the main charge follows through the cleared space for the strike.

In space a small penetrator separates from the bus and impacts the comet or asteroid, creating a crater. A short time later, the nuclear explosive in the bus detonates inside the crater, so much of the energy is channeled and directed, rather than expended into space. Since there is no atmosphere, many of the coupling mechanisms we are familiar with won't work in space; even very large nuclear weapons would have to be at point blank range to affect the target. The X-ray and neutron radiation will vaporize the rock or ice and the crater will form an improvised rocket nozzle to direct the flow of plasma, hot gasses and ejecta to provide the deltaV needed to change orbits.

There are a few more complicated issues to deal with. As the bus approaches, the axis of rotation should be identified and the bus lined up to fire the impactor and thus the ejecta crater on the rotational axis. This way the actual impulse will through the axis of rotation and the resulting deltaV change and new orbital parameters can be known to observers on Earth. Firing the probe into a random place on the surface also means the nuclear charge will not be able to find the crater and deposit the energy in a useful manner.

Secondly, since this is a very near term thing, several different rockets will have to be sent with the same payloads, in order to ensure that at least one works. While Russian boosters are somewhat larger, American ones are more reliable. Heavy lift versions of the Atlas or Falcon 9 are about the only ones capable of doing the job. Considering the short time frame, the deflection might be very close to Earth and need lots of deltaV, you may actually need multiple strikes to deflect the body.

Finally, since this is near term, we must launch pretty much directly at the oncoming body, since we don't have years for elaborate orbital dances to match orbits (consider how long the current mission took to match orbits with a comet; we don't have 10 years). This means the most powerful boosters, with very large and powerful trans stages to break orbit carrying the smallest possible payloads. Even then it might be a very close run thing to deflect the incoming body before it is too close and the energy required to change its orbit becomes prohibitive (bigger bombs would help, but the "standard" size these days seems to be @ 300Kt, giving you an upper bound. Building "custom" physics packages is probably going to eat too much into your time, and supermassive devices like the Tsar Bomba would be far too large to boost on high energy impact orbits anyway).

So this might be possible with present day technology, but it would be at the very outside edge of possibility. Better have beer, peanuts and a paper bag ready for plan "b"...

  • $\begingroup$ To impart the needed delta-v you need roughly 700 Tsar-Bomba's. $\endgroup$ – Taemyr Jun 29 '15 at 10:46
  • $\begingroup$ A 250 ton rock impacting at parabolic speed would have double the yield of the Tsar Bomba, just from being in the way. $\endgroup$ – JDługosz Jun 29 '15 at 17:54
  • $\begingroup$ Of course, but the Tsar Bomba was so large it could barely fit aboard the carrying aircraft, and the mass would be far too much for any current single rocket to lift it straight into interplanetary space (which given the time frame is exactly what would be needed). Sending a series of 300Kt "physics packages" gives you redundancy and you can calibrate the deltaV by adjusting the number of strikes you make. $\endgroup$ – Thucydides Jun 30 '15 at 0:28
  • $\begingroup$ @Thucydides Tsar Bomba weighed only 27000 kg. A Saturn V has a payload to TLI of 48600 kg. $\endgroup$ – Cees Timmerman Jun 30 '15 at 11:24
  • $\begingroup$ We don't have a Saturn V. If the one year is a hard number, we only have Falcon 9's, Atlas and (possibly) Russian rockets. Also, since we are blasting straight into a transfer orbit and not LEO, we need the lightest possible vehicle to be able to reach the incoming body at all. $\endgroup$ – Thucydides Jun 30 '15 at 23:50

Trajectory Diversion of an Earth-Threatening Asteroid via Massive, Elastic Tether-Ballast System says this:

Several mitigation techniques have been proposed, including detonating nuclear or conventional explosives in, on, or near the NEO, guiding a retrograde NEO to impact the Earth-threatening NEO, using the Yarkovsky effect, or using a tug of some type, whether connected to the NEO21 or using gravity to pull the NEO. [...] For all cases, the time duration chosen was 10 years and the asteroid mass was 1e10 kilograms. The ballast mass was chosen to be 3e6 kilograms, about the same mass as a fueled Saturn V rocket.

Assuming the asteroid had 3 times the volume of the 10 km Chicxulub impactor, that's 3.0e15 kg.

Deflecting the entire asteroid in a year would be impossible with our current tech, so I'd shack up in a bunker on a mountain with mushroom/insect farms, solar panels, books, and other survival supplies. And (preferably nuclear) batteries for when light is scarce due to dust.

That's if humanity can't get its thousands of nuclear warheads to break the asteroid into pieces our atmosphere can handle:

The goal would be to fragment the asteroid into many pieces, which would then disperse along separate trajectories. Wie believes that up to 99 percent or more of the asteroid pieces could end up missing the Earth, greatly limiting the impact on the planet. Of those that do reach our world, many would burn up in the atmosphere and pose no threat.

A nuclear weapon is the only thing that would work against an asteroid on short notice, Wie added. Other systems designed to divert an asteroid such as tugboats, gravity tractors, solar sails and mass drivers would require 10 or 20 years of advance notice.

Even pieces that won't completely burn up could cause less of a wave than a single larger piece.

Depending on kinetic energy and impact location, many cities will be wiped out:

The huge impactor – between 37 and 58 kilometers (23 to 36 miles) wide – collided with the planet at 20 kilometers per second (12 miles per second). The jolt, bigger than a 10.8 magnitude earthquake, propelled seismic waves hundreds of kilometers through the Earth, breaking rocks and setting off other large earthquakes. Tsunamis thousands of meters deep – far bigger than recent tsunamis generated by earthquakes — swept across the oceans that covered most of the Earth at that time. Asteroid with 3 times the energy of Chicxulub crater asteroid The impact would have been catastrophic to the surface environment. The smaller, dino-killing asteroid crash is estimated to have released more than a billion times more energy than the bombs that destroyed Hiroshima and Nagasaki. The more ancient hit now coming to light would have released much more energy, experts said.

The sky would have become red hot, the atmosphere would have been filled with dust and the tops of oceans would have boiled, the researchers said. The impact sent vaporized rock into the atmosphere, which encircled the globe and condensed into liquid droplets before solidifying and falling to the surface, according to the researchers.

The impact may have been one of dozens of huge asteroids that scientists think hit the Earth during the tail end of the Late Heavy Bombardment period, a major period of impacts that occurred early in the Earth’s history – around 3 billion to 4 billion years ago.

That bunker should have some hefty insulation. Nuclear submarines and space flights with plenty of supplies and/or medically induced coma could allow also some to wait until it's safe to land.

Then again, the Chicxulub impactor had an estimated diameter of 10 km (6.2 mi) and delivered an estimated energy equivalent of 100 teratons of TNT (4.2e23 J). Even an impact releasing 1.06e24 J at the average ocean depth of 4.2672 km on the other side of the planet 20000 km away only causes some fallout and a tsunami amplitude between 16.0 and 32.0 m, so the easiest way for people to survive is to move away from the calculated impact site(s).

  • $\begingroup$ Hitting the atmosphere in pieces is worse. All the energy goes into heat, rather than using some to dig a big hole (think crumple zones in a car collision). Don't do that. Your link is titled deflection, too. $\endgroup$ – JDługosz Jun 29 '15 at 17:41
  • $\begingroup$ @JDługosz Hence the "our atmosphere can handle" part. If it's preferred to have fewer, bigger impacts, then don't break it up. Also, link titles don't cover everything in an article. I quote: The two-body spaceships are designed to strike an asteroid with a "one-two punch". The front body strikes first to make a crater, while the second part delivers a nuclear bomb to break up the asteroid into harmless pieces that would burn up in the Earth’s atmosphere. $\endgroup$ – Cees Timmerman Jun 30 '15 at 7:07
  • $\begingroup$ As I noted in another question, in accordance with Impact Depth en.wikipedia.org/wiki/Impact_depth, the atmosphere is good for maybe burning up a light rocky asteroid with a 5m diameter, anything larger than that has enough momentum to plow through the atmosphere and hit the ground. You would need to break the asteroid into at least 10 billion equal sized pieces, breaking it into merely a million or 10 million pieces would just make the problem much worse. Breaking up a 100m asteroid? Maybe practical. A 10km asteroid? No way. $\endgroup$ – Blake Walsh Jun 30 '15 at 9:41
  • $\begingroup$ @BlakeWalsh Dumping a bunch of pebbles into a pond (ocean) might be preferable to one large rock. $\endgroup$ – Cees Timmerman Jun 30 '15 at 9:53

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