Don't blow that asteroid into little bits! Is this true or false?

[immortalfrieza]

Whenever I see a documentary about what would realistically happen if a asteroid was blown to bits to stop it from hitting Earth, I always hear the same argument.
It basically says that a bunch of asteroid bits hitting the Earth would cause more damage overall than one massive asteroid, often comparing a buckshot blast vs slug.

Personally, on simple logic this doesn't seem to hold up for me, due to a few things this argument fails to take into account, and I wonder if some people with the expertise could back up or explain them. Note that I'm talking about asteroids which are made of rock and thus can fractor into bits, not Meteors, which are made of metals and thus cannot fractor easily.

1. Many of the asteroid bits would be burned up in the Earth's atmosphere, would burn up easier than a much larger object, and those that remain would be smaller and thus less damaging.

2. Even before burning up, the asteroid bits would be smaller than a intact asteroid, as a result they would be less affected by gravity and more affected by wind resistance, thus the intact bits would be much slower and thus hit the Earth with much less force.

3. Even not taking into account 1&2, the asteroid bits that did it would impact with a bunch of comparatively small explosions which would likely have less fallout overall and that fallout would not be blown anywhere near as high into the air, and thus settle to the ground much faster.
The above would apply even if the asteroid were broken into only 2 pieces.

To use the shotgun comparison, would you rather be hit by a slug or buckshot? Both with equal amounts of mass, but with the buckshot many of the shots vaporize once they get close to you, the remainer moving comparatively slower, hitting with less force, and each piece only burrowing into you slightly. However, the slug would blow one massive hole through your chest.

 

[Lukeje]

2. Even before burning up, the asteroid bits would be smaller than a intact asteroid, as a result they would be less affected by gravity and more affected by wind resistance, thus the intact bits would be much slower and thus hit the Earth with much less force.

You realise that all things accelerate at the same rate towards the Earth, right? And that air resistance is proportional to surface area?

 

[Squilookle]

I don't think point 2 is really valid, because any speed that smaller particles lose in the atmosphere would have probably already been offset by the massive acceleration they experienced in the explosion that tore them away from the asteroid, but kept them on a collision path with earth. Far as I know- it's a much more popular theory to explode a device near the asteroid, so as to deflect it rather than just smashing it like a billiards break and hoping for the best.

And comparitively smaller is still extremely large- anything big enough to get through the atmosphere can still cause massive damage- especially if it impacts an ocean. There was some forest in Russia, if I remember correctly that in 1900 or sometime around then had a huge vast area of forest completely obliterated by a meteor that didn't even make it to the ground before disintegrating. Count your lucky stars it wasn't a populated area...

EDIT: yeah, this is it. Apparently the thing was only a few tens of meters across!!!

http://en.wikipedia.org/wiki/Tunguska_event

 

[bakan]

It depends on the dimensions and composition of the asteroid, generally smaller pieces will do less damage as their kinetic energy will be smaller than one big asteroid but the damage they inflict could be bigger as they spread out over a bigger area.

 

[immortalfrieza]

2. Even before burning up, the asteroid bits would be smaller than a intact asteroid, as a result they would be less affected by gravity and more affected by wind resistance, thus the intact bits would be much slower and thus hit the Earth with much less force.

You realise that all things accelerate at the same rate towards the Earth, right? And that air resistance is proportional to surface area?

Size and mass=the overall effect of gravity and air resistance. If you dropped a 8 pound bowling ball and a marble off the Empire state building at the exact same time, they would hit the ground at the same time, but the damage each would cause to the pavement below would be very different for each of them. Also, the smaller and lighter the object is, the greater the affect that air resistance has on the amount of force with which it hits the ground, and the wind resistance would affect where it hits the ground. However, except in cases when the object is able to use air and wind resistance to achieve some measure of lift, as with paper for instance, neither air nor wind resistance will affect when the object hits the ground

 

[Thaluikhain]

"It depends". There are all sorts of variables to consider, there's not going to be a flat answer.

Air resistance is a major factor, though, and it makes a big difference. Most meteors don't reach the ground, they have to start out big and solid to get anywhere close. If you could guarantee small enough fragments, none of the would do any damage.

Size and mass=the overall effect of gravity and air resistance. If you dropped a 8 pound bowling ball and a marble off the Empire state building at the exact same time, they would hit the ground at the same time, but the damage each would cause to the pavement below would be very different for each of them. Also, the smaller and lighter the object is, the greater the affect that air resistance has on the amount of force with which it hits the ground, and the wind resistance would affect where it hits the ground. However, except in cases when the object is able to use air and wind resistance to achieve some measure of lift, as with paper for instance, neither air nor wind resistance will affect when the object hits the ground

No, air resistance has a big effect on when it hits. You mention "lift"...although things falling don't tend to get any, as such, what you mean affects things to different extents. A bowling ball and a marble have the same shape, though.

Or, to put it another way, yes, air resistance affects the power something has when it hits the ground, by slowing it. And the slower it is, the longer it takes to hit the ground.

I don't think point 2 is really valid, because any speed that smaller particles lose in the atmosphere would have probably already been offset by the massive acceleration they experienced in the explosion that tore them away from the asteroid, but kept them on a collision path with earth. Far as I know- it's a much more popular theory to explode a device near the asteroid, so as to deflect it rather than just smashing it like a billiards break and hoping for the best.

Hey? If you're able to make some of it fly noticeably faster towards the Earth, wouldn't many of the other bits miss the planet completely. I don't think exploding a devide nearby would do much to deflect it...now, detonating it on the surface, blasting a bit free to propel the rest the otehr way, sounds feasible.

And comparitively smaller is still extremely large- anything big enough to get through the atmosphere can still cause massive damage- especially if it impacts an ocean. There was some forest in Russia, if I remember correctly that in 1900 or sometime around then had a huge vast area of forest completely obliterated by a meteor that didn't even make it to the ground before disintegrating. Count your lucky stars it wasn't a populated area...

Not exactly true. Plenty of meteors make it to the Earth (most of these, of course, landing in the ocean) all the time. Someone was hit by one in the 50s and received bruising, for example. You mean a really, really big one.

BTW, airburst are better than groundbursts are removing trees anyway, and the odds of any given meteor hitting a populated region are tiny. And hitting a populated region is always going to kill more people than hitting the ocean, unless it's big enough to fuck nations over when it hits.

 

[Heronblade]

It really depends on the composition of the asteroid. A rock with a very high level of metallic content will not lose much mass in the atmosphere whether it is solid or broken up. One made from a less... enduring material would probably lose nearly all of its mass if broken up, but those aren't the kind of asteroids we are generally worried about to begin with.

Concerning falling rates, the velocity of an impending projectile would not be significantly changed if blown up. A larger amount of smaller projectiles would in general have the same ratios of speed:mass:surface area.

Large enough asteroids can lose 50% of their total kinetic energy and still be world killers. For example, one asteroid that will be passing relatively close to us has the approximate kinetic energy of over 450 of the most powerful nuclear bombs ever tested. Oh sure, lets break that up into 400 individual bombs and spread them out...

Finally, a high powered buckshot blast from close range will do FAR more physical damage than one from a high powered rifle. I recall seeing a photo of some poor bastard who was shot with a 12 gauge barrel jammed into his stomach, angled up. The entire interior of his chest cavity was simply gone, no organs remained in bits larger than a cubic centimeter. It isn't until the pellets have lost a significant amount of momentum that the rifle and pistol do more damage.

 

[RobCoxxy]

For the greater good!

 

[Thaluikhain]

Large enough asteroids can lose 50% of their total kinetic energy and still be world killers. For example, one asteroid that will be passing relatively close to us has the approximate kinetic energy of over 450 of the most powerful nuclear bombs ever tested. Oh sure, lets break that up into 400 individual bombs and spread them out...

Well, bearing in mind that most of those will hit the ocean, and many that hit land will hit unoccupied (or mostly) areas anyway. I'm not saying it's not a major issue, but hardly world killing.

Finally, a high powered buckshot blast from close range will do FAR more physical damage than one from a high powered rifle. I recall seeing a photo of some poor bastard who was shot with a 12 gauge barrel jammed into his stomach, angled up. The entire interior of his chest cavity was simply gone, no organs remained in bits larger than a cubic centimeter. It isn't until the pellets have lost a significant amount of momentum that the rifle and pistol do more damage.

Shotguns don't suffer from over-penetration the way rifles do. Now, if a person was shot nicely lengthwise...

 

[Esotera]

As others have said, it's all very variable. Basically if the fragments are beyond a certain size when they hit the earth, they'll do a fair amount of damage, and it'll be more distributed. It depends a lot on how the explosion fragments the asteroid.

The best way of directing objects away from the earth is by slightly altering their course millions of miles away with rockets. This needs quite a lot of planning though, and would be really expensive.

 

[Robert Ewing]

It depends on both the size, and composites of the meteor.

If it's made up of relatively soft rock, and is huge. Blast the shit out of it.

If it's made up of relatively hard rock, and is huge. Do not blast it. It will split into just as powerful meteors. Plural. would cause a lot of problems. Maybe just knock it off course.

If it's made up of relatively soft rock, and is small, ignore it.

If it's made up of relatively hard rock, and is small. Blast it. The debris will be no bigger than regular asteroids that land on your roof normally. Nothing bigger than little pebbles.

 

[008Zulu_v1legacy]

Impact force = weight x velocity

A 1 kilo rock traveling at 1000kph will hit with 1 kiloton of force. Most US cruise missiles with nuclear armament have about a 5 kiloton yield.

A "shotgun" asteroid impact is ideal because there is less chance of all life on the planet being wiped out.

 

[twistedmic]

Whenever I see a documentary about what would realistically happen if a asteroid was blown to bits to stop it from hitting Earth, I always hear the same argument.
It basically says that a bunch of asteroid bits hitting the Earth would cause more damage overall than one massive asteroid, often comparing a buckshot blast vs slug.

I think a more apt comparison would be between a ballistic missile with a single large warhead and a ballistic missile with a MIRV (Multiple independently targetable reentry vehicle) warhead. Both missiles might carry the same amount of explosive/nuclear material, but the MIRV is going to cause more damage because the impact points are going to be spread out in a larger area. For example, a single warhead nuclear missile fired at Washington D.C. (this is for example purposes only, I am not advocating, condoning or wishing for a nuclear strike against America) will destroy D.C. and little else. A MIRV warhead nuclear missile however, can destroy major cities up and down the coasts of Virginia, Maryland and D.C.

1. Many of the asteroid bits would be burned up in the Earth's atmosphere, would burn up easier than a much larger object, and those that remain would be smaller and thus less damaging.

2. Even before burning up, the asteroid bits would be smaller than a intact asteroid, as a result they would be less affected by gravity and more affected by wind resistance, thus the intact bits would be much slower and thus hit the Earth with much less force.

Objects that are entering/re-entering the Earth's atmosphere are traveling at incredibly high speeds, regardless of size. Meteors/asteroids can enter the atmosphere going as fast as 30 miles per second. at that speed wind resistance isn't going to be an issue so even smaller asteroids are going to fall just as fast as a larger one.
And even if a smaller asteroid hit at a slower speed than a larger asteroid, say five miles per second instead of twenty, that's still incredibly fast, and would still cause massive damage due to energy transfer.

3. Even not taking into account 1&2, the asteroid bits that did it would impact with a bunch of comparatively small explosions which would likely have less fallout overall and that fallout would not be blown anywhere near as high into the air, and thus settle to the ground much faster.
The above would apply even if the asteroid were broken into only 2 pieces.

To continue with the nuclear weapons analogy, that would be like saying half a dozen ten megaton explosions, spread out over a wider area are less damaging than a sixty megaton explosion located in a single area. When asteroids hit the earth, they are coming in at high speeds and even comparatively small asteroids can cause massive damage. I don't know the specifics, but I think an asteroid (or asteroid chunk) only fifteen feet in diameter can strike with enough force to destroy a city.

 

[chocostarf]

It depends how big you are talking here. A small one would be better to leave seeing as though its small and wouldn't have much damage a large one would also be a bad thing to blow up because then multiple large fragments would hit the earth and if an asteroid is big enough or a fragment of an asteroid is big enough it can create a tsunami. More people would most likely survive a single large tsunami then multiple medium sized ones. Especially because the multiple medium sized or little ones would be spread all over the place.

Exploding an asteroid would make some fragments fly away from the earth but the majority of the asteroid would find its way to earth because of earth's pull and the original direction of the asteroid. A method that has been revised if an asteroid or meteor huge enough to wipe out humanity or a continent were to come into earth's orbit is to fly multiple space shuttles to it and then use it as a way to propels the object elsewhere. There are people in NASA and other places in the world whose job it is to keep track of large objects in space so if this could happen they could predict it years maybe even decades before the event would take place.

In fact there is a large object (forget whether asteroid or meteor) that has a chance of being pulled into earth's orbiting pattern and they have predicted where it would hit which I believe is the middle of the Atlantic and would create a huge tidal wave sinking continents. This might have already passed though it was meant to impact I think around 2030 but not really sure.

sorry for the TLDR lol

 

[Lukeje]

2. Even before burning up, the asteroid bits would be smaller than a intact asteroid, as a result they would be less affected by gravity and more affected by wind resistance, thus the intact bits would be much slower and thus hit the Earth with much less force.

You realise that all things accelerate at the same rate towards the Earth, right? And that air resistance is proportional to surface area?

Size and mass=the overall effect of gravity and air resistance. If you dropped a 8 pound bowling ball and a marble off the Empire state building at the exact same time, they would hit the ground at the same time, but the damage each would cause to the pavement below would be very different for each of them. Also, the smaller and lighter the object is, the greater the affect that air resistance has on the amount of force with which it hits the ground, and the wind resistance would affect where it hits the ground. However, except in cases when the object is able to use air and wind resistance to achieve some measure of lift, as with paper for instance, neither air nor wind resistance will affect when the object hits the ground

You claimed that it would be moving more slowly because it was smaller. This is in fact not the case.

 

[Sizzle Montyjing]

It depends on all sorts of things, like how big the asteroid is to start with, how many chunks you blow it up to, the size of those chunks and where they will land.

If the asteroid was say, double the size of the moon, yeah, do anything you can to lessen the impact, say you blew it up into 3 chunks that were going to hit the earth, no good.
But say that you blew them up in a way that made them avoid the earth, that's good.

Now, if you were to blow them up into lots of little chunks, then the damage would be more widespread, but less concentrated on one spot.
If you blew it up into millions of tiny chunks, then they would probably just burn up in the athmosphere anyway, and not cause any damage.

That being said... the tides of stuff have got to be getting mucked up...

 

[Apocalypse0Child]

Does air/wind resistance actually play an important part pre-earth's-atmosphere? There's no air/wind in space after all.

 

[Thaluikhain]

I think a more apt comparison would be between a ballistic missile with a single large warhead and a ballistic missile with a MIRV (Multiple independently targetable reentry vehicle) warhead. Both missiles might carry the same amount of explosive/nuclear material, but the MIRV is going to cause more damage because the impact points are going to be spread out in a larger area. For example, a single warhead nuclear missile fired at Washington D.C. (this is for example purposes only, I am not advocating, condoning or wishing for a nuclear strike against America) will destroy D.C. and little else. A MIRV warhead nuclear missile however, can destroy major cities up and down the coasts of Virginia, Maryland and D.C.

Bit off-topic, but that's not entirely accurate. Firstly, you don't destroy cities with single warheads, you attack specific targets (trying for overlap, if you can get it), though MIRVs are fairly inaccurate, and they can only target things in a limited area.

Also, one reason they developed MRVs (not MIRVs) was that doubling the nuclear material of a device does less than double its yield, and the effects radiate out in all three directions, while many targets tend to be two dimenionsal (cities spread horizontally for kilometres, but not too far vertically). Several smaller devices are more cost effective than one big one. With asteroids, though, several smaller ones will burn up more than one big one.

Objects that are entering/re-entering the Earth's atmosphere are traveling at incredibly high speeds, regardless of size. Meteors/asteroids can enter the atmosphere going as fast as 30 miles per second. at that speed wind resistance isn't going to be an issue so even smaller asteroids are going to fall just as fast as a larger one.
And even if a smaller asteroid hit at a slower speed than a larger asteroid, say five miles per second instead of twenty, that's still incredibly fast, and would still cause massive damage due to energy transfer.

Not true, or at least not for smaller ones. Meteorites can be slowed down (also, air cooled) quite alot. A few years ago, in New Zealand, I think, one about the size of a bowling ball went through someone's roof and ended up in their couch, cool enough not to set it on fire. The owner of the house sold it to a museum.

Though, this depends on your defintion of "small". The bigger it is, the less air resistance effects it (the volume (and therefore mass) to surface area ratio changes). If you mean one the size of, say, a car, it's going to have been slowed much less by air resistance than bowling ball sized.

To continue with the nuclear weapons analogy, that would be like saying half a dozen ten megaton explosions, spread out over a wider area are less damaging than a sixty megaton explosion located in a single area. When asteroids hit the earth, they are coming in at high speeds and even comparatively small asteroids can cause massive damage. I don't know the specifics, but I think an asteroid (or asteroid chunk) only fifteen feet in diameter can strike with enough force to destroy a city.

That would depend on how fast it came in, but, as a rule, cities are harder to destroy than people think. When using nuclear devices, for example, you use multiple devices to target specific areas of importance, you don't just let it off in the middle and hope for the best...though, that'd certainly cause a horrible mess.

Oh, and, Tunguska is estimated at around 50m across, and that was estimatd at 5-30 MT. The USSR Tsar Bomba was safely tested on land at 50 MT yield.

...

BTW, I looked alot of this up a while ago, when figuring out how much damage a spaceship crashing would do. I worked out that if you dropped a Nimitz Class aircraft carrier from geostationary orbit (starting with no velocity), and neglecting air resistance, burning/breaking up and munitions on board, it'd hit with the power of 70 MT only.

 

[Antari]

Either way science knows that its just as easy to place a high mass satillite beside the asteroid to drag it off course before it hits earth. The use of nuclear weapons or something similar to break up the asteroid is 1950's thinking. There's no need to break up asteroids with our current scientific knowledge.

Edit : In general the entry ANGLE is more important than its speed. If it comes down through the atmosphere at a 90 degree angle, not much of anything of reasonable size will burn up. At 30 degrees its a whole different story.