Scientist says nuclear weapons may be best bet for saving Earth from asteroids

Jun 28, 2010 by Lisa Zyga weblog
Illustration of an asteroid impact. Credit: NASA.

(PhysOrg.com) -- If scientists detect an asteroid headed directly for Earth - one that was large enough to pose a serious threat to life on our planet - would it be wise to bring out nuclear weapons to prevent an impact? Over the past several years, scientists have expressed conflicting opinions on the use of nuclear weapons as a defense against asteroids. Part of the problem is that it’s very difficult to know what asteroids are made of, and how they will respond to different types of nuclear explosives. But at the semiannual meeting of the American Astronomical Society held last month, physicist David Dearborn of the Lawrence Livermore National Laboratory argued that nuclear weapons could be the best strategy for avoiding an asteroid impact - especially for large asteroids and little warning time.

According to Dearborn, the sheer power of a nuclear explosion may make it the most practical and cost-effective option for deflecting or fragmenting asteroids, compared with alternatives such as chemical fuel or laser beams. For one thing, a nuclear explosive would be cheaper to launch into space due to its large amount of energy per unit mass. In contrast, a non-nuclear blast might require several launches for an equivalent amount of power.

Also, the nuclear option could be implemented in a short amount of time; a detonation just 15 days before impact could fragment or divert the course of a 270-meter (the size of Apophis, which has a 1 in 250,000 chance of striking Earth in 2036) to avoid a collision. On the other hand, a laser such as one at the National Ignition Facility at Lawrence Livermore would take 6,000 years to sufficiently divert the course of the same size asteroid.

As far as the radiation released from a in space, Dearborn said that you wouldn’t even be able to measure the difference on Earth. The explosion would occur millions of miles out in space, where there is already an intense radiation environment.

Dearborn has developed models and run simulations to determine the effects of a nuclear detonation occurring both near and on the surface of an asteroid. His simulations show that the best strategy depends on both the size of the asteroid as well as how much time we have before impact. If a collision with a smaller asteroid is a few decades away, detonating a nuclear explosive near the asteroid could nudge it off course while still keeping it intact. But if a collision with a large asteroid is just weeks away, a direct detonation on the asteroid would be required, although some smaller fragments could still strike Earth.

While the size of the asteroid and its distance from Earth can be estimated quite well, the biggest unknown variable in any defense strategy is the asteroid composition. Asteroids are a diverse class of objects, and some materials fragment more easily than others. Dearborn advised that, if we had 30 years to avoid a collision, the best thing to do would be to launch a characterization mission to the asteroid. Even if Dearborn and other scientists would like to test a nuclear explosive in space, test ban treaties as well as political and public opposition make a test unlikely.

Fortunately, scientists aren’t expecting an any time soon. NASA has identified and categorized about 90% of near-Earth objects that are large enough (more than 10 km [6.2 miles] in size) to cause mass extinction on Earth, and none of these pose a significant risk of collision in the near future - even Apophis is considered to have very low risk. Smaller objects, on the other hand, are more difficult to track down. The smallest known asteroid, 1991 BA, measures 6 meters (20 feet) across.

"In a few more years, we'll be able to say that there's nothing out there to cause a global catastrophe,” said David Morrison, director of the NASA Lunar Science Institute and senior scientist for Astrobiology at NASA's Ames Research Center. “But, there'll be a million that will be big enough to wipe out an entire city. It'll take a long time, if ever, to find them and figure out their orbits. The bottom line is, we could be hit by one of those small ones at any time, with no warning at all. Right now, I can say almost nothing about the probability of one of those small objects hitting us, because we simply haven't found all of them."

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More information: via: Space.com and Scientific American

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antialias
3.4 / 5 (12) Jun 28, 2010
Oh wow...a scientist from Lawrence Livermore is arguing for nuclear warheads.

Let's see: Lawrence Livermore is funded by the DOE and develops/manufactures nuclear weapons.

Now the funding on nuclear weapons has dried up for LL (The RRW project - reliable replacement warheads - was not funded by congress anymore)
New designs aren't being developed.

Do I smell a smidegon of bias here?
axemaster
3.9 / 5 (11) Jun 28, 2010
Bias isn't very likely in my opinion, since the chance that the government or anyone is going to commission the development of special nuclear warheads is small. I'd say that this is just a physicist experienced with nuclear technology taking an interest in a difficult problem.

As a student working for a physics department, I can tell you that an instance in which people do research of that nature for the purpose of scaring up funding is... difficult to imagine happening.
akotlar
3.5 / 5 (6) Jun 28, 2010
Bias is very likely. Regardless of whether or not you think that this is a probable market for nuclear arms, the reality is that someone investing in the nuclear industry would like to see as much positive press for nuclear weapons as possible. Believe it or not, even esoteric uses such as this grant some leverage for the side wishing to push through policy on active warhead commission.

And no offense, but as as student who once majored in biomedical engineering, I know that work-study physics students are rarely exposed to the school bureaucracy and never consulted on the realities of industry pressure.
EarthlingX
3 / 5 (2) Jun 28, 2010
Perhaps it would be better idea to find those asteroids sooner than blasting them with nukes ?
Koljenkolja
5 / 5 (2) Jun 28, 2010
Why not use a rocket, put it on an asteroid and... push?
moebiex
5 / 5 (2) Jun 28, 2010
Humanity has lots of experience with trawling that might be adapted to at least some scenarios. It might even be possible to direct some of them to constructive uses for terraforming or artificial habitat(s)in useful orbits rather than just blowing them up.
Chef
4 / 5 (3) Jun 29, 2010
Why not use a rocket, put it on an asteroid and... push?


The biggest problem would be that the asteroids are not stable in rotation. They tumble in multiple axises. Also, if the asteroid is not solid, then you run the risk the rocket would not stay in place, and cause a worse orbital path.
ofnir1
1.7 / 5 (3) Jun 29, 2010
Why not just develop a giant rail gun, load it with a non nuclear missile, and shoot the missile at high speeds so it could impact the asteroid with a greater force, to divert the asteroids path.
HealingMindN
1.7 / 5 (6) Jun 29, 2010
Instead of worrying what's "out there" to cause a global catastrophe why not focus on putting together a low yield thermonuclear fusion device to seal that rift in the Gulf?
MarkyMark
3.7 / 5 (6) Jun 29, 2010
Nukes are one way that might stop an asteroid but why dont they use paper.

Afterall as anyone can tell you, paper beats rock!!!
plasticpower
3.4 / 5 (5) Jun 29, 2010
I think it's fairly obvious that the ONLY REAL solution we have to the asteroid thread is NUCLEAR. Anyone who thinks otherwise is not thinking clearly. Our technology TODAY allows us to detonate a nuclear warhead close enough to the asteroid to divert its path, why not consider using it if we have it? Nukes once posed a thread to wipe out the human civilization, now they are here (and in large quantities), ready to save us. This is the sort of realistic thinking that we need.
Bob_Kob
3.8 / 5 (4) Jun 29, 2010
Perhaps it would be better idea to find those asteroids sooner than blasting them with nukes ?


Then what?
Doug_Huffman
not rated yet Jun 29, 2010
Has anyone of y'all calculated the momentum transferred by a nuclear explosion? How about the impulse?

What ever happened to the left's old Precautionary Principle?
silviasaint2930
Jun 29, 2010
This comment has been removed by a moderator.
antialias
5 / 5 (4) Jun 29, 2010
Has anyone of y'all calculated the momentum transferred by a nuclear explosion? How about the impulse?


The momentum would be very little if the warhead was exploded next to an asteroid (since there would be no hockwave from heat expansion of air - only radiation pressure)

Exploding a warhead on contact poses other risks, since we generally don't know what such an asteroid is made of. A 270m asteroid might just split into many boulders which each pose a risk (anything larger than a house (i.e. 1000m^3) stands a fair chance of reaching earh's surface) An asteroid with 270m diameter can be broken up into roughly 60 such units. It is arguable what would be worse: one large chunk or 60 smaller and radiactive ones hitting the planet.

Tugging it out of the way by gravity:
http://en.wikiped..._tractor
is a much more controled way - but makes less of an action movie script.
Egnite
2 / 5 (1) Jun 29, 2010
[Pardon my ignorance but I missed the nuke in a vacuum experiment at school] Do we even know what happens when you detonate a nuke in space? How does the explosion react in an environment with no gravity or particles?
antialias
3.3 / 5 (3) Jun 29, 2010
Well, there were high altitude explosions like Starfish Prime
http://en.wikiped...sh_Prime

This site
http://www.johnst...ane.html
gives a more comprehensive listing of high altitude nuclear explosions performed. According to it a blast front is absent.

While radiation does carry an impulse it is very low (and in a nuclear explosion it is also omnidirectinal and very short). Might be enough if detonated early enough.
Javinator
1.7 / 5 (3) Jun 29, 2010
Breaking it up into 60 smaller units would most definitely be better.

There would be more total surface area due to the large asteroid being broken up. This would result in more of the impact mass being burnt up in the atmosphere and would reduce the total force of the impact.

Also, what hurt more? When someone hits you with a rock or a handful of pebbles? I'm pretty sure there would be less destruction with the force of the impact spread amongst smaller pieces than one large asteroid.
antialias
3.7 / 5 (3) Jun 29, 2010
As there is no guarantee that it will break up the asteroid

It would only do so if it was relatively fragile to begin with - and in that case the contact with the earth's atmosphere will break it up also.

If it's rather solid (e.g. a solid iron asteroid) then nukes won't even dent it.
Adriab
5 / 5 (1) Jun 29, 2010
How about splashing the asteroid with polished aluminum flakes, or something else that would increase its albedo.

The radiation pressure difference might not be very great, but considering the distances and velocities usually involved, it should at least modify the course of the asteroid enough.
Plus aluminum is cheaper than a nuke.
antialias
5 / 5 (4) Jun 29, 2010
Such a system has been proposed by the Russians (Yarkovsky effect using white paint or ash). Might work. Depends on whether (or how) the asteroid is rotating, though.

I do remember that someone did the calculations on that and the result was that the effect is very small (i.e. you'd have to splash the asteroid hundreds of years before a possible collision with earth)

The japanese have a solar sail currently being tested in space so we might get a solution that way.
Pkunk_
3.4 / 5 (5) Jun 29, 2010
I don't get the whole "anti-nuclear" thing when it comes to space.
For gods sake we're orbiting around the biggest polluter in light years. The sun pumps out enough cosmic rays, protons , X-rays etc. in one second to put even gigaton weapons to shame.

Also, there is no one around in space for fission rays to cause any damage. I say its a wonderful way to get rid of all the excess nuclear weapons we've piled up.

Adriab
3 / 5 (2) Jun 29, 2010
@antialias
Yeah, that sounds about right, I was probably reading about that and had forgotten the source.

@Pkunk
Well, a nuke too close to our atmosphere would cause a pretty serious cascade of electrons which could have a devastating effect down here on the surface. I'm not sure on the range for this effect.
Javinator
4 / 5 (1) Jun 30, 2010

@Pkunk
Well, a nuke too close to our atmosphere would cause a pretty serious cascade of electrons which could have a devastating effect down here on the surface. I'm not sure on the range for this effect.


A nuke in space would have little effect on the Earth. If the asteroid were close enough to us that a nuke hitting it would actually affect Earth... well we'd already be pretty much screwed.
Javinator
5 / 5 (2) Jun 30, 2010
If it's rather solid (e.g. a solid iron asteroid) then nukes won't even dent it.


But the as yet undeveloped gravity tractor (which as far as I understand is essentially a huge spaceship we'd send to the asteroid to hang out and slowly use gravity to pull it) is a good solution?

It's not that nukes are a guaranteed solution or anything, but we have them here now and blowing up a nuke far away from Earth won't hurt us.
CavemanDev
5 / 5 (2) Jun 30, 2010

The momentum would be very little if the warhead was exploded next to an asteroid (since there would be no hockwave from heat expansion of air - only radiation pressure)


So, first, the energy release of a nuclear bomb: most of the energy is NOT radiation pressure - it's the daughter products (the two halves of the split uranium atom) travelling at incredible velocity (ie. very, very high temperature particles). The shock wave is created when these particles hit the other particles around them (bomb materials, air, etc.) and transfer their energy. So, strictly speaking, you don't get the shockwave effect, but that energy still gets imparted to the asteroid anyway.
CavemanDev
5 / 5 (2) Jun 30, 2010

Tugging it out of the way by gravity:
http://en.wikiped..._tractor
is a much more controled way - but makes less of an action movie script.


Gravity Tractor: Please look into payload limitations on currently available spacecraft. I'll give you a tip: there's only one propulsion technology currently available to us that would allow for a sufficiently large mass to be lifted off the Earth's surface, and you wouldn't like it.

http://en.wikiped...pulsion)
Quantum_Conundrum
5 / 5 (2) Jun 30, 2010
Breaking something up into smaller fragments is definitely better, as explained.

For simplicity, consider a cube of 4 units per edge.

This gives a surface area of 96 square units

If it was broken up into 64 cubes of 1 unit per edge, then the total surface area would be 384 square units, which is more than 4 times increase.

But even if you only split a cube in half, you increase the surface area by 33% and distribute the damage over space and time.

Better to get hit by ten jabs and still be standing than to get hit by one knockout blow.
GDM
not rated yet Jul 01, 2010
QC, I agree somewhat. However, if we take a large asteroid and break it into 10 (or however many) radioactive pieces that then hit the Earth, I don't like the results. Seems to me I saw a Discovery channel article which investigated this problem and it all depends on the size and composition of the asteroid: A solid (stony) asteroid might just recombine due to gravity or not break into enough pieces to burn up completely. A small, gravel-pile (like Itokawa) would likely absorb the impact with little effect, and would probably break up early enough to not cause a problem.
Nartoon
4.5 / 5 (2) Jul 03, 2010
The story relates to last minute asteroids being found, if you have 15 days to do something it'll have to be a nuke or nothing. If you have years that's a completely different story.
zevkirsh
1 / 5 (2) Jul 03, 2010
stupid. if an asteroid were going to hit earth, technology advanced countries would allow it to hit earth and use the ensuing chaos as cover for annexing all non-technologically advanced countries. nukes? they'd use nukes to destroy anyone who tried to resist this plan. at least, that's what i would do.

also, odds are an asteroid would slam into the ocean.
only a truly massive asteroid would be able to do serious damage to the entire planet as opposed to a small quadrant. most of those massive stroids get sucked up by our planetary vaccums jupiter and saturn. so..if another tunguska event happens, its an opportunity to be exploited. the only country that would try to stop it is a country certain to be it's direct target impact.
Yes
not rated yet Jul 03, 2010
Maye there is resources on the asteroid. If they find that out, then entrepreneurs would pay much money to invent how to haul them in and have them safely strike a remote desert area or something.
I fear they are worthless rocks though. Most of them.
Better then proliferate nuclear tools.
Kedas
not rated yet Jul 04, 2010
I'm pretty sure that a nuclear weapon would do a good job in saving earth but wouldn't it be nice if they have a solution that includes saving the life forms on it.
droom
not rated yet Jul 04, 2010
The story relates to last minute asteroids being found, if you have 15 days to do something it'll have to be a nuke or nothing. If you have years that's a completely different story.


Exactly, solar sails and gravitational tugging would require decades of foresight.

But why just one nuke? Send in a big boy to smash the rock, meanwhile have a parameter of lower powered nukes to further shatter the larger debris. Yes, some may make it through, but if its the choice of mass extinction or a hundred million deaths, the choice is easy. We have an insane amount of warheads, if we only have a 15 day warning, they are really our only hope.
mosahlah
5 / 5 (1) Jul 05, 2010
Oh man. I don't think setting off nukes in space is politically correct. Not without an environmental impact statement and a few lawsuits from the Sierra club. Has anyone consulted the expert? I'm confident Al Gore could solve this issue with one printing and a sound bite.
Quarl
not rated yet Jul 06, 2010
I have difficulty believing that a nuclear-tipped rocket with sufficient range to do anything other than add radiation to the upper atmosphere would be ready within 15 days from a cold start. How long does it take to simply launch a satellite successfully? And the penalty for a satellite launch failure is considerably smaller than that of a nuclear weapon launch failure...
droom
not rated yet Jul 06, 2010
I have difficulty believing that a nuclear-tipped rocket with sufficient range to do anything other than add radiation to the upper atmosphere would be ready within 15 days from a cold start. How long does it take to simply launch a satellite successfully? And the penalty for a satellite launch failure is considerably smaller than that of a nuclear weapon launch failure...


ICBM's. They are always ready.
antialias
not rated yet Jul 06, 2010
But not for that range. They are designed for low orbit at best (and mostly not even that - that is what the 'B' stands for: Intercontinental BALLISTIC Missile)

and you definitely don't want nukes going off in low earth orbit. google "starfish prime" for what happened when they tried THAT stunt.
droom
not rated yet Jul 06, 2010
Yep, I know what you mean. I admit Im assuming when I think the military would be able to get an ICBM out of orbit. But if theres one thing our military is good at, its finding ways to blow stuff up. And since the Russians and now the Chinese have lots of space stuffs, we probably found ways to blow that all up too.