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Willowmound
03-03-2009, 02:21 PM
Not one for posting duplicate threads, may I nevertheless direct your attention here (http://www.absolutewrite.com/forums/showthread.php?t=133448)?

This is my question from that thread:

I'm trying to work out the range of the electromagnetic pulse created by an asteroid impact of a given size. So far I've been struggling. I know that a comet eight miles across, arriving at 135,000 mph, would send an EMP right around the world. But how far would the EMP of a comet or asteroid of, say, four miles across reach?

Any ideas?

I'd greatly appreciate any help.

MelancholyMan
03-05-2009, 09:22 PM
I don't understand why a cometary or asteroid impact would produce EMP. I'm not an expert on EMP but it must arise from accelerations of charged particles across a wide spectrum of energies. Where would this originate from a meteoritic strike?

Lhun
03-05-2009, 11:10 PM
I don't understand why a cometary or asteroid impact would produce EMP. I'm not an expert on EMP but it must arise from accelerations of charged particles across a wide spectrum of energies. Where would this originate from a meteoritic strike?
Meteorites exploding in the athmosphere ionize a lot of air, which will result in an EMP. Because of that though, i don't think you can actually say a meteorite of a given size will always produce an EMP of a certain strenght. A ferrous meteorite that stays more or less intact until it hits the ground would ionize a lot less air, and thus cause a lot less of an EMP than a rock meteorite that explodes in the upper athmosphere.
For an asteroid that size, the EMP doesn't matter anyway. Hell, anything not below the horizon will ignite from the thermal radiation alone.
Check this site out for some handy calculations: http://www.lpl.arizona.edu/impacteffects/
It doesn't calulate EMPs, but that's not as easy as kinetic effects anyway. I suppose you can make an educated guess if you assume the asteroid that explodes in midair produces around the same EMP as a nuke of the same yield, the underlying assumption here being that all the energy of the asteroid will be released in the explosion.

Pthom
03-06-2009, 01:56 AM
Some questions for Lhun:
Thermal radiation -- in other words is light in the infrared portion of the electromagnetic spectrum, no? So isn't a sudden burst of IR radiation a defacto EMP of sorts?

A meteorite that does explode in the atmosphere (as opposed to the nickel-iron ones that mostly survive intact until they impact the ground) or a comet, too, I suppose -- does the explosion destroy all the momentum of the mass of the object immediately prior to impact? Or, despite the violence of the explosion, does any of that mass continue on the original trajectory?

I've read that most objects that strike Earth enter the atmosphere at a more or less 45 angle to the ground. I assume this is because at a shallower angle, the object is more likely to skip off the atmosphere. But what about the occasional object that enters the atmosphere perpendicular to the ground? Is it more likely to survive atmospheric heating and hit the surface because the distance traveled is short, or is it more likely to explode higher in the atmosphere than otherwise?

Lhun
03-06-2009, 02:55 AM
Some questions for Lhun:
Thermal radiation -- in other words is light in the infrared portion of the electromagnetic spectrum, no? So isn't a sudden burst of IR radiation a defacto EMP of sorts?
Well, EMP usually doesn't refer to any pulse of electromagnetic radiation, but to a pulse that will cause inductive currents in conductors. That can be a burst of radiation in the microwave range, or a magnetic pulse. It will create a current in conductors, burning out any equipment that is attached and too fragile for the current.
A meteorite that does explode in the atmosphere (as opposed to the nickel-iron ones that mostly survive intact until they impact the ground) or a comet, too, I suppose -- does the explosion destroy all the momentum of the mass of the object immediately prior to impact? Or, despite the violence of the explosion, does any of that mass continue on the original trajectory?Well that depends totally on the explosion, which depends on the composition of the meteorite. Heck, even it's shape is important for that, a needle shaped meteorite will obviously encounter less air friction than a ball.
I've read that most objects that strike Earth enter the atmosphere at a more or less 45 angle to the ground. I assume this is because at a shallower angle, the object is more likely to skip off the atmosphere.Also because of the rotation and movement of earth.
But what about the occasional object that enters the atmosphere perpendicular to the ground? Is it more likely to survive atmospheric heating and hit the surface because the distance traveled is short, or is it more likely to explode higher in the atmosphere than otherwise?Perpendicular to the ground is quite hard because of the earth's rotation. Anyway, the effect on the meteorite is at first easy to predict: it will probably have a much higher speed than one impacting at 45 (else it wouldn't impact at 90) which means more air friction and more heat. Which means it would be somewhat more likely to explode i suppose. The friction would also rise faster, since it penetrates faster into higher air density.

Anyway, a meteorite basically explodes when it is made of low density matter. Best stuff like ice. When it heats up enough to vaporize the whole meteorite it can explode. If it is too small it will most likely just "slowly" burn up from the outside in. If it is big enough it might explode and fregment into pieces that still impact. It could contain clumps of iron big enough to reach the ground after the rest explodes. Etc. There is no general answer, it all depends on the specific meteorite.

scottVee
03-06-2009, 04:30 AM
I'm glad Luhn pounced on that "infrared should make an EMP" comment. Visible light is also EM radiation, but bright lights don't knock out computers. As he says, it must be EM radiation of the right type.

As such, I doubt anyone can calculate the amount of EM radiation from an impactor that is specifically hazardous to modern circuitry, or what its radius of effect might be. The effects of the trail of ionized gas may not radiate outwards at all.

I agree with the comment that a little EM burp would be the least of our concerns. Those same circuits will be melted by other forces moments later.

Willowmound
03-09-2009, 06:59 PM
For an asteroid that size, the EMP doesn't matter anyway. Hell, anything not below the horizon will ignite from the thermal radiation alone.

But it's the effect on places below the horizon I'm interested in. :)

Check this site out for some handy calculations: http://www.lpl.arizona.edu/impacteffects/
It doesn't calulate EMPs, but that's not as easy as kinetic effects anyway.

Yeah, I'm already using it. It's super-fantastic.

That the EMP can't be easily worked out, actually suits me brilliantly. That means I can have it the strength that's best for my story.

So, thanks a lot. I appreciate everyone's answers.

Lhun
03-17-2009, 10:33 PM
But it's the effect on places below the horizon I'm interested in. :)
What i wanted to hint was that hell, we just sterilized half the biosphere with thermal radiation alone, who cares about a few broken mp3 players?
Seriously, an asteroid of damn near crustbreaker size impacting is a catastrophe of such proportion that the EMP will be the least of our worries. Hell, there'll probably be a decently long ice age caused by the ejecta darkening the sky.

I think for the best EMP effect, you'd need comparatively small low-density asteroid, several at best, that impact in the athmosphere, causing little physical damage, but atypically large EMPs. (because of the explosions mid-air)

Bartholomew
03-17-2009, 10:38 PM
If a 4 mile wide object crashes into the earth, there will be problems far worse to worry about than EMP.

Dommo
03-18-2009, 08:27 AM
More like a ginormous fireball that will incinerate anything within hundreds of miles, and surviving the nuclear winter that will block the sun.

geardrops
03-18-2009, 08:41 AM
More like a ginormous fireball that will incinerate anything within hundreds of miles, and surviving the nuclear winter that will block the sun.

Technically not nuclear winter as it's not caused by a nuclear incident.

Willowmound
03-18-2009, 01:54 PM
What i wanted to hint was that hell, we just sterilized half the biosphere with thermal radiation alone, who cares about a few broken mp3 players?

Writing board. Writer here. Writing a story. Needing to know the progression of events in a fictional scenario. Not really giving a shit about what would have been more important to worry about, had it been real. Just needing some help on the EMP specifically.

Or needed. I've got a handle on it now, I think. :)

Lhun
03-18-2009, 09:48 PM
Writing board. Writer here. Writing a story. Needing to know the progression of events in a fictional scenario. Not really giving a shit about what would have been more important to worry about, had it been real. Just needing some help on the EMP specifically.Yeah, i got that, just mentioning that a 4 mile asteroid impacting is a really, really cataclysmic event, and even in a story should be kept in perspective. If a story features a tsunami, you don't make the main point of conflict the water damage in the protagonists basement, do you? ;)

Willowmound
03-18-2009, 10:39 PM
Who said it was the main point?

Bartholomew
03-18-2009, 11:24 PM
Who said it was the main point?

You're gonna have an EMP bomb that affects about half of the globe. The internet will basically die, because even though some computers will still work, a lot of the servers they connect to are gonna go KERFIZTbzzzz.

Other points to consider:

There'll be a giant dust cloud; this will affect all solar powered objects, and it'll clog up wind farms. Hydro might even go out, if the giant cloud of crap decides to settle in unfortunately placed rivers.

There will be no food for foraging for many, many miles around the area of impact.

At the right trajectory, this object could strike earth in such a fashion as to kick something back into night sky, giving us a second, but smaller, moon. (But the force required for this might actually end all life on the planet instantaneously. Not sure.)

Maybe your object should be smaller? I've read before that human civilization would end if a *one* mile wide object slammed into us. Four might be overkill.

The resulting cloud cover the planet would suffer might throw off the biological clocks of noctural creatures -- or even humans. It'll be much darker, most of the time, and animals we aren't familiar with might start appearing, simply because they're confused too.

After the fall, there would probably be a lot of sand storms or dust storms in area with high winds.

I think having people refer to the time after the impact as "After the Fall" is really cool; if you like that, feel free to use it.

Some species might evolve relatively quickly to adapt to their new environment -- perhaps even people? Eyes would get much brighter, as brightly colored irises help people see in cloudy conditions. Noses might get flatter and would have more hair, to help filter dust.

Will the earth heat up, or cool down because of such an impact? I suspect it would cool down, as most dust won't act as a green house gas - but massive amounts of dead and dying creatures would release equally massive amounts of methane, which IS a greenhouse gas. Maybe the temperature would spike, and then slowly settle to cooler conditions?

Compasses probably won't work correctly for a while; could the impact site actually become a third pole?

If humanity survives the cataclysm, the area of impact would be a point of great interest -- the object may have dug far enough to reveal geo-thermal vents, ideal for collecting as an energy source. Alternatively, it may become a vast (freshwater?) lake.

That's all I got. Hope some of it is useful.

Willowmound
03-18-2009, 11:52 PM
Thanks Bart. Most of this corresponds with what I already have. It's nice to have it confirmed.

I like your observation about the compass. I hadn't thought of that.

Lhun
03-19-2009, 03:14 AM
I'll expand a bit on the ideas here:
There will be no food for foraging for many, many miles around the area of impact.Well, that's a minor aftereffect of the major "Everything within line of sight of the impact, i.e. 2k miles or so, is dead. And burning."
At the right trajectory, this object could strike earth in such a fashion as to kick something back into night sky, giving us a second, but smaller, moon. (But the force required for this might actually end all life on the planet instantaneously. Not sure.)Kicking up serious amounts of material into orbit is very hard. You really need an asteroid of crustbreaker size for that. (i.e. an asteroid that punctures the earth's crust and throws material from the mantle into orbit) That's one of the few events that might have an actual chance at wiping out cockroaches. Let alone humans.
Maybe your object should be smaller? I've read before that human civilization would end if a *one* mile wide object slammed into us. Four might be overkill.
There's a kind of sliding scale here. Especially dependent on what exactly you mean by civilization. The total breakdown of society as we know would happen with (comparatively) minor damage. There's no way society can function when two thirds of humans are dead. Really wiping out humanity is a bit farther down the scale. We could concievably revert to cavemen level of civilization. Sure, most humans in industrialized society couldn't survive that way, but if it's only a million surivors worldwide that's enough for us a species to survive, even though more than 99.9% died.
Some species might evolve relatively quickly to adapt to their new environment -- perhaps even people? Eyes would get much brighter, as brightly colored irises help people see in cloudy conditions. Noses might get flatter and would have more hair, to help filter dust.Well the problem is that evolution needs to thing to work quickly, high mortality rate and high generation turnover. Rabbits have a perfect environment for quick evolution if three fourths of each generation dies without reproducing. Doesn't work for humans because each generation only consists of few children. So the speed of human evolution is severely limited by that. Which by the way goes for all creatures. The less offspring they have in a generation and the longer the generation time, the slower they evolve to adapt to change. Sorry to say, but the elephants are doomed with every major environmental change. So are whales, bears, tigers, lions and everything else big and slow. Rats and cockroaches on the other hand will happily adapt to about everything.
This also goes for plants by the way. Many trees are suprisingly fragile when it comes to even minor temperature change. It is quite possible that a major asteroid impact will wipe forests worldwide, killing even plants that are too big and specialized.
Compasses probably won't work correctly for a while; could the impact site actually become a third pole?That is very unlikely. The dynamo that generates earth's magnetic field is a process that happens deep down inside the earth and involves massive amounts of mantle and core material, no asteroid can seriously impact that. A magnetic (or simply metal) asteroid might screw up the magnetic field locally, but not on a global scale. Earth is too big for that.
If humanity survives the cataclysm, the area of impact would be a point of great interest -- the object may have dug far enough to reveal geo-thermal vents, ideal for collecting as an energy source. Alternatively, it may become a vast (freshwater?) lake.Impact craters that size are often connected to the nearest sea, but if it hits deep inland, yes you'd get a big lake. Well, provided it didn't hit the Sahara, the water has to come from somewhere.

benbradley
03-19-2009, 03:27 AM
If humanity survives the cataclysm, the area of impact would be a point of great interest -- the object may have dug far enough to reveal geo-thermal vents, ideal for collecting as an energy source. Alternatively, it may become a vast (freshwater?) lake.
You remind me of another possibility. If it hits the Supervolcano under Yellowstone, the impact could be just the start of Earth's troubles...