Earth almost distroyed last monday (??!?!?)

[Dr. Dalek]

I meant is it feasible in practice.. it takes time for something to reach far objects. For instance, I know it takes a few days for a rocket to reach the moon -- so will we have enough TIME to do that? ~moo

I sure hope so!

[Klaynos]

One of the big problems that has only recently begun to be solved is that we don't know the composition of the objects we might have to deal with so have no idea how much of the impact would be obsorbed by the object....

[mooeypoo]

"]I'd say; right now' date=' we'd be ****ed. We need another 50 years of infrastructure in space, experience, technology and telescopes. Then we might have a chance.

[/quote']

 

 

Oy vey.

[[Tycho?]]

One of the big problems that has only recently begun to be solved is that we don't know the composition of the objects we might have to deal with so have no idea how much of the impact would be obsorbed by the object....

 

Very true. Its now believed that many asteriods are little more than clumps of rock held together by gravity alone. Shooting something into an object like this would just disrupt it, but not deflect its course.

[swansont]

'']Very true. Its now believed that many asteriods are little more than clumps of rock held together by gravity alone. Shooting something into an object like this would just disrupt it, but not deflect its course.

 

But that's one strategy. Smaller objects would be more likely to burn up in the atmosphere.

[[Tycho?]]

But that's one strategy. Smaller objects would be more likely to burn up in the atmosphere.

 

Yeah, if its a small one and the goal is to just blow it apart. But if its a big one, like end of humanity kind of big, then it wont really matter if its in pieces or not. Your still going to be adding all that heat and dust to earths atmosphere, causing huge climate change.

[swansont]

'']Yeah, if its a small one and the goal is to just blow it apart. But if its a big one, like end of humanity kind of big, then it wont really matter if its in pieces or not. Your still going to be adding all that heat and dust to earths atmosphere, causing huge climate change.

 

That depends on how much of the effect is from the object itself and how much from terrestrial debris from the impact.

 

If the terrestrial debris is a significant effect, then the more surface area of the object you expose, the better off you are. You want to decrease the net impact energy. Terminal velocity varies as sqrt (Weight/Area), so the associated kinetic energy varies linearly. And W decreases faster than A as you get smaller (cube vs square dependence). And that's not even looking at the loss of material due to ram pressure heating; more exposed surface area should burn away more material prior to impact.

[[Tycho?]]

That depends on how much of the effect is from the object itself and how much from terrestrial debris from the impact.

 

If the terrestrial debris is a significant effect' date=' then the more surface area of the object you expose, the better off you are. You want to decrease the net impact energy. Terminal velocity varies as sqrt (Weight/Area), so the associated kinetic energy varies linearly. And W decreases faster than A as you get smaller (cube vs square dependence). And that's not even looking at the loss of material due to ram pressure heating; more exposed surface area should burn away more material prior to impact.[/quote']

 

Yes, so you wouldn't get the huge impact crater sort of deal. But I'm saying that if its a really really big one, ecosystem killer kind of thing, having it burn up will only buy you time.

 

The object that is believed to have killed off the dinosaurs was estimated to have an impact energy of 5.0×10^23 J. Earths atmosphere has a mass of about 5.1x10^18 kg. Specific heat capacity of air is 1.005.

 

Q=mcΔT

 

(5.0×10^23 J) = (5.1x10^21 g)(1.005 J/gK)ΔT

 

ΔT= 97.55 K

 

 

....what the hell? My argument is that even if such an object were to totally burn up in the atmosphere, the heat and dust added would still cause huge problems. But I must have made some mistake, because I dont believe that a singe object could raise the temperature of earths atmosphere by almost 100 degrees. Could someone check my work and see where this problem lies? There are several simplifications, for example 1.005 is the specific heat capacity of air at standard conditions, so this would obviouslly be different say 50km up. But since most of the atmosphere is close to the ground I figured I'd be able to get away with it. But there must be something wrong here.

 

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

http://en.wikipedia.org/wiki/Specific_heat_capacity#Table_of_specific_heat_capacities

http://en.wikipedia.org/wiki/Earth%27s_atmosphere#Density_and_mass

[[Tycho?]]

Ba bump? I am still curious about this, I'd like if someone could look over my above work and see if there are errors in math or reasoning. Because thats a pretty big number I got, one I still do not believe.

[Klaynos]

I saw an interesting BBC Horizon the other night about how some impacts create fireballs, which would mean if we could break up an incomming asteroid the smaller chunks might actually be more dangerouse as theirs a higher chance of one of them causing a fireball over a population centre....

 

http://news.bbc.co.uk/1/hi/sci/tech/5196362.stm

[Rasori]

I can't comment on your math, Tycho, but I've got a question relating to the whole issue of detection: Why is it that we rely on telescopes first, and then radar? Can't we launch satellites to scan space with radar for us? I would think we would have a lot more success if we were scanning for them with space-based radar system than with telescopes that are generally in the atmosphere (thus dealing with interference there) and require movement/light reflection for detection.

[insane_alien]

Tycho, remember that it didn't just burn up. it hit the ground and a lot of energy would be directly transfered into said ground and released a bit slower so the change in temperature is a lot slower and the energy emitted by the earth makes up for it.

 

I like the idea of detonating nukes close (but not on) to the surface to heat up one side of the asteroid so it partially vapourises causing a rocket like effect and nudging the asteroid off course.

 

then again, i also say we should start mining the asteroids so that theirs no big ones left to hit us.

[lavoisier]

']

The object that is believed to have killed off the dinosaurs was estimated to have an impact energy of 5.0×10^23 J. Earths atmosphere has a mass of about 5.1x10^18 kg. Specific heat capacity of air is 1.005.

 

Q=mcΔT

 

(5.0×10^23 J) = (5.1x10^21 g)(1.005 J/gK)ΔT

 

ΔT= 97.55 K

 

 

....what the hell? My argument is that even if such an object were to totally burn up in the atmosphere' date=' the heat and dust added would still cause huge problems. But I must have made some mistake, because I dont believe that a singe object could raise the temperature of earths atmosphere by almost 100 degrees. Could someone check my work and see where this problem lies? [/quote']

I guess the figure you got is incorrect because of some parameters you neglected.

The object would hit the Earth in a relatively short time and in a relatively small region compared to the whole planet's surface, therefore heat would be generated at a much higher rate (I guess) than the rate of the heat transfer from the collision area to the surroundings. So there would be a highly overheated area.

According to the BBC's Horizon programme someone's already mentioned in this thread, this would cause a big 'fireball', i.e. the overheated air would be violently expelled towards space due to the huge difference in density.

If so, most of the heat would be simply dissipated.

Concerning the remaining part of energy, is it possible to imagine that water (overall 1.4 × 109 km3 on Earth, cp about 4 J/(gK)) will slowly absorb some of it, making the deltaT somewhat more acceptable?

However, I still believe that a pretty big area around the impact point will be marginally less hospitable than before!

 

By the way, why did the dinosaurs die after that impact? Was it because of the increase in T or because of its decrease (as a consequence of the vapours and dusts shielding solar radiation)? They were cold-blooded animals, weren't they? I must have seen so many programmes about these catastrophic events, that I eventually got confused!

 

If I may add a final observation about the topics in this thread, I'm afraid that as usual mankind's worst enemy is man himself. We're likely to do ourselves an awful lot of irreversible damage centuries before any big meteor hits us or any big volcano explodes.

Don't get me wrong, it's great to see people trying to use logic, science and common sense for preventing natural catastrophes, and I read all the posts with great interest.

Unfortunately, the same good capabilities of human intellect are generally NOT used by governments and politicians for preventing or stopping things such as wars, social injustice, famines, which, unlike natural catastrophes, would be to a reasonable extent under our control.

So we can still devise cunning ways to fight against nature, but we can never forget that many of us live in pain, hunger and unhappiness because we're not fighting against our own evil.

Sorry if this sounds like a preach, it's aimed to myself in the first place.

[Dr. Dalek]

then again, i also say we should start mining the asteroids so that theirs no big ones left to hit us.

Then again if an asteriod were detected and predicted to hit earth within the month you would be unlikely to mine it away before it hit. You would still need a fast responce solution.

[[Tycho?]]

I can't comment on your math, Tycho, but I've got a question relating to the whole issue of detection: Why is it that we rely on telescopes first, and then radar? Can't we launch satellites to scan space with radar for us? I would think we would have a lot more success if we were scanning for them with space-based radar system than with telescopes that are generally in the atmosphere (thus dealing with interference there) and require movement/light reflection for detection.

 

I dont really know, but I can guess.

 

With telescopes we observe light or other radiation bouncing off asterioids. With radar, we would be sending out a radio signal and then listening for when it bounces back. I assume the problem would be that this would have to be a damn powerful radio signal, since the radar wave decreases with the inverse square of distance. A way to get around it would be to shoot a super focused beam of radio waves out in a singal place in order to get a larger effective range. But then it isn't useful in detecting a lots of objects.

[[Tycho?]]

I guess the figure you got is incorrect because of some parameters you neglected.

The object would hit the Earth in a relatively short time and in a relatively small region compared to the whole planet's surface' date=' therefore heat would be generated at a much higher rate (I guess) than the rate of the heat transfer from the collision area to the surroundings. So there would be a highly overheated area.

According to the BBC's Horizon programme someone's already mentioned in this thread, this would cause a big 'fireball', i.e. the overheated air would be violently expelled towards space due to the huge difference in density.

If so, most of the heat would be simply dissipated.

Concerning the remaining part of energy, is it possible to imagine that water (overall 1.4 × 109 km3 on Earth, cp about 4 J/(gK)) will slowly absorb some of it, making the deltaT somewhat more acceptable?

However, I still believe that a pretty big area around the impact point will be [i']marginally[/i] less hospitable than before!

 

By the way, why did the dinosaurs die after that impact? Was it because of the increase in T or because of its decrease (as a consequence of the vapours and dusts shielding solar radiation)? They were cold-blooded animals, weren't they? I must have seen so many programmes about these catastrophic events, that I eventually got confused!

 

If I may add a final observation about the topics in this thread, I'm afraid that as usual mankind's worst enemy is man himself. We're likely to do ourselves an awful lot of irreversible damage centuries before any big meteor hits us or any big volcano explodes.

Don't get me wrong, it's great to see people trying to use logic, science and common sense for preventing natural catastrophes, and I read all the posts with great interest.

Unfortunately, the same good capabilities of human intellect are generally NOT used by governments and politicians for preventing or stopping things such as wars, social injustice, famines, which, unlike natural catastrophes, would be to a reasonable extent under our control.

So we can still devise cunning ways to fight against nature, but we can never forget that many of us live in pain, hunger and unhappiness because we're not fighting against our own evil.

Sorry if this sounds like a preach, it's aimed to myself in the first place.

 

Yeah I realize its not transfering all this energy into the atmposphere alone, instead only a specific region. But I dont see this changing my general idea; that if a large object was totally burned up entering the atmosphere it wouldn't by much better than the object striking the surface.

 

The fireball created by this thing would be massive if it was totally burned up in the atmosphere. Like incinerating large portions of a continent kind of big. The shockwave produced would be unbelievable with such an enourmous volume of air being rapidly expanded; it would be like an atmospheric tsunami. Also, most of the mass of the asteriod would stay in the atmosphere as dust since it didn't hit the ground in the first place. This huge huge mass of dust and ash I would think would make big changes in earth's climate. PLUS the temperature rise over the entire earths surface would not be negligable I think, at least enough to kill crops and other plants/animals.

[lavoisier]

You're right, it would be a catastrophic event anyway. I was not trying to minimise it. We can all stay assured that if something like this happens, it won't be fun for anyone.

 

However, your starting point was the energy of the hypothetical meteor which is supposed to have killed the dinosaurs. So we're talking about an event that, if hasn't actually happened, at least has been simulated by someone (on the basis of a given set of parameters) in order to justify the extinction of these animals.

This means that its effects (according to the model used) are already known, nobody needs to reinvent them.

 

My worry is that sometimes we need to over-simplify models, and when we deal with VERY complex systems (let alone those subject to chaotic behaviour), at the end of the day our prediction may be largely unreliable.

[[Tycho?]]

You're right' date=' it would be a catastrophic event anyway. I was not trying to minimise it. We can all stay assured that if something like this happens, it won't be fun for anyone.

 

However, your starting point was the energy of the hypothetical meteor which is supposed to have killed the dinosaurs. So we're talking about an event that, if hasn't actually happened, at least has been simulated by someone (on the basis of a given set of parameters) in order to justify the extinction of these animals.

This means that its effects (according to the model used) are already known, nobody needs to reinvent them.

 

My worry is that sometimes we need to over-simplify models, and when we deal with VERY complex systems (let alone those subject to chaotic behaviour), at the end of the day our prediction may be largely unreliable.[/quote']

 

True, but I'm not attempting to model or reinvent anything. An object as large as the one I was using in my example obviously would not totally burn up in the atmosphere, most of the mass would impact the surface. But a lot of people have the impression that when an asteriod "burns up" there is no danger. My example was just a reminder that an object big or small has energy, and this energy has to go somewhere, so burning up doesn't necessarly get rid of the danger

[lavoisier]

True, but I'm not attempting to model or reinvent anything. An object as large as the one I was using in my example obviously would not totally burn up in the atmosphere, most of the mass would impact the surface. But a lot of people have the impression that when an asteriod "burns up" there is no danger. My example was just a reminder that an object big or small has energy, and this energy has to go somewhere, so burning up doesn't necessarly get rid of the danger

 

OK, I got your point.

 

In fact this raises an interesting question, i.e. in what cases would the energy of the meteor be transformed into different forms of energy which wouldn't directly affect our ecosystem (i.e. setting aside the effects of the suspended dusts and stuff)?

I'm trying to reason about that - I beg the physicists here to accept my apologies, I'm obviously not in the field.

The total mechanical energy of the meteor is the sum of its potential and kinetic energy. While it falls towards the Earth, the latter becomes the main term. I don't know if the kinetic energy of the meteor when it's very far from the Earth is a significant part of the total, but anyway...

If the kinetic energy was entirely transformed into heat, we'd have the consequences you calculated.

But what other forms of energy can we get? If, say, the meteor was 'unbreakable', it would hit the surface, and then what? Would it dissipate its energy by breaking the chemical bonds in the rocks it hits and/or as potential energy by changing the position of the rocks (i.e. forming a crater)?

And if the rocks on the surface were too hard to break, what would happen? Where would the energy go?

 

My impression is that it's quite difficult to predict exactly what would actually happen.

However, it's probably true that any impact which converts most of the energy of the meteor into heat or its equivalents (e.g. burning in the atmosphere or vaporizing a portion of the oceans), rather than into potential energy, is more dangerous for our ecosystem. Unless most of the heat and dusts are eventually expelled into space.

And it's also probably true that disintegrating the meteor before the impact wouldn't be particularly helpful, especially if all of its parts would hit us anyway.

[tomgwyther]

I'm not sure if you're aware, but...

At about 3:00am on british T.V. last night: it was reported that an NEO similar to that which wiped out the dinosaurs, has been calculated to be on a collision course with Earth.

Estimated time of impact is April 2029.

 

Again, like the report you heard mooey poo, it was broadcast very quietly, at a time when only geeks like us might be watching.

[[Tycho?]]

OK' date=' I got your point.

 

In fact this raises an interesting question, i.e. in what cases would the energy of the meteor be transformed into different forms of energy which wouldn't [i']directly[/i] affect our ecosystem (i.e. setting aside the effects of the suspended dusts and stuff)?

I'm trying to reason about that - I beg the physicists here to accept my apologies, I'm obviously not in the field.

The total mechanical energy of the meteor is the sum of its potential and kinetic energy. While it falls towards the Earth, the latter becomes the main term. I don't know if the kinetic energy of the meteor when it's very far from the Earth is a significant part of the total, but anyway...

If the kinetic energy was entirely transformed into heat, we'd have the consequences you calculated.

But what other forms of energy can we get? If, say, the meteor was 'unbreakable', it would hit the surface, and then what? Would it dissipate its energy by breaking the chemical bonds in the rocks it hits and/or as potential energy by changing the position of the rocks (i.e. forming a crater)?

And if the rocks on the surface were too hard to break, what would happen? Where would the energy go?

 

My impression is that it's quite difficult to predict exactly what would actually happen.

However, it's probably true that any impact which converts most of the energy of the meteor into heat or its equivalents (e.g. burning in the atmosphere or vaporizing a portion of the oceans), rather than into potential energy, is more dangerous for our ecosystem. Unless most of the heat and dusts are eventually expelled into space.

And it's also probably true that disintegrating the meteor before the impact wouldn't be particularly helpful, especially if all of its parts would hit us anyway.

 

In a normal impact a lot of the energy would go into the ground. This would form the crater as matter is ejected at very high velocities. Plus shock waves through the ground and air. Energy into breaking chemical bonds would be negligable I would think.