Recent cinema and TV documentary-drama concerning asteroid collision scenarios prompts this page dealing with "sensationalist science" , i.e. incomplete or hastily or wrongly formed hypotheses made to draw attention to one's branch of the scientific establishment.
It's puts me in mind of my few months spent on the street in NYC back in 1980. I encountered many streetwise individuals who asserted that I could never "make it" on the street. To which I observed (from first hand observation) that as there were multitudes of obviously mentally deranged persons "making it" I should have little trouble indeed. And in fact that was the case (though I nearly died of boredom).
I'm going to divide this into :
Collision ParametersLet's propose a 1 mile diameter comet (or asteroid) as a standard.
It will hit us about 6am in the mid-Atlantic.
It won't hit at 6pm ... (except at low relative velocity)
This is a good starting point for the collision itself because right off you're going to ask "Why not 6pm?"
Well, it has to do with rain hitting your windshield when you're moving. The faster you move the more rain you get on the front windshield and the less you get on the back. At a certain point, no rain at all will hit the back ... but there is no limit to the amount that can hit the front. You can scoop up all before you.
There was a "running" debate about which it is better: to walk normally, say, from your car door to your house ... or, ambulate with extreme alacrity. I don't know the best strategy.Anyway, the Earth's velocity in orbit is :
18.3 miles per second
It therefore moves through it's own diameter (8,000 miles) every 7.2 minutes.
Now consider that the earth can only reasonably be hit by a comet crossing it's path at approximate right angles (as is the case with meteor showers). An object might hit the earth head on from the opposite direction but that would require an object in retrograde orbit which isn't going to happen by natural means since the asteroid belt is already in a standard orbit.
Here the comet or asteroid, travelling about the same speed as the Earth hits the leading edge of the planet on it's way toward the sun. It would obviously be difficult to hit the trailing edge since that edge is falling away from the asteroid on account of the planet's shape and the fact that the Earth is displacing itself entirely every 7.2 minutes. A rear hit would require an asteroid velocity far in excess of 20 miles per second.
Note also that it is more probable to hit the night morning-side when the asteroid is inbound toward the sun and to hit the earth's sunny morning-side when outbound. And that the earth-asteroid closing speed is at maximum ~ 1.414 X 18.3 mps = 26.8 mps which is about 5 times faster than near earth orbital velocity (5 mps = ~18,000 mph).
You might also see that the trajectory of the asteroid (and part of it's consequent capacity to disrupt the crust) is dependent on the time of day at the point of impact. If it hits the leading edge (always 6 AM) the trajectory will be about 45 degrees. If it hits at the 3 AM spot the trajectory will likely be vertical. And as for the time you would be able to see the asteroid plummeting from the top of the atmosphere to the surface of the earth ... well ... 2/10 to 4/10 of a second is about right. All you would see is a blinding flash of light.
Asteroid Orbits of low eccentricity & double crossingsJust how does an asteroid get "perturbed"?
Mostly by collision with another asteroid or comet or gravitationally by Jupiter. What is needed is to slow down the asteroid causing it to drop into an elliptical orbit which crosses the Earth's path. The relative velocities of asteroids to one another are small so that repeated collisions may be necessary to get one to "fall" down.
In an asteroid collision some pieces need to break off with some measure of violence such that some are thrown rearward and the resulting velocity is too slow to maintain a circular orbit. It thus "drops" into an eccentric elliptical orbit. Every time it returns to the asteroid belt it will have a low velocity compared to the other unperturbed asteroids and if it hits one of these a more energetic collision will take place causing an elliptical orbit of even greater eccentricity till it crosses the Earth's path.These pieces will approach the earth at low velocities compared to a 90 degree crossing since they will be going in the same direction.
If the aphelion is the asteroid belt (it can't be much higher there being no force to cause this) and the perihelion is the earth's orbit, the asteroid will be going faster than the earth at that point in the earth's orbit since it must ascend back into the asteroid belt at the other end of its own orbit.How much faster?
Well, the earth's orbital velocity is about 18.5 miles per second and Jupiter's is about 8 miles per second so I think something on the order of 20 miles per second might do it. So if we get hit by one of these from behind ('cause it is going faster than us), it won't have much more relative velocity than ... say ... 2 miles per second?
Whatever ... it will be a far cry from a closing velocity of 20 miles per second. And the biggest asteroids can't get down here at all. There simply isn't anything to slow them enough to drop down to us. We just get stray pieces. Some of the pieces are pretty huge though. Not the size of Texas ... but maybe the size of your local city park.
Kinetic EnergyOne important point shoud be made at the outset. Calculations which deal with the amount of kinetic energy of the asteroid are really very straightforward. It's just velocity squared times mass ( KE = 1/2 mv2 ). However, a calculation indicating the amount of damaging energy (damaging to our way of life) is presently unavailable. A multitude of factors go into such a calculation none of which are easily programmed into a supercomputer simulation. So I now believe that they just use the kinetic energy as a "fair" guide to damage.
It isn't a fair guide however.
First, the amount of energy delivered to the crust is 100% only if the asteroid does not penetrate the crust and lodge itself in the mantle. If it does, ALL of the energy dissipated there is harmless to us. In the case of a "mighty dog" asteroid, nearly all the energy supposedly comin' ta' git us is ending up; in the mantle.
In fact, at the asteroid sizes 1 to 50 miles in diameter (possibly more yet) the damage to us is roughly proportional to the perimeter of the object so that an asteroid 10 miles in diameter will have about 1000 times the mass of a 1 mile 'stroid' and consequently have 1000 times the kinetic energy since they will all be going at about the same speed. But it will do us only about 10 times the harm because the energy is going into the mantle along with the crust, ocean, atmosphere it pushes into that unholy place. Thus,in general, if the Hole is twice as big we get twice the misery.
To wipe out all life on earth will take something not much less than a mantle disrupter ... maybe the size of Texas.
Note: The asteroid in the movie Armageddon was supposedly this size but I had to take it with a grain of salt because at that size you don't organize a mission ... you just have a smoke ... or pull down your pants, bend over and kiss it goodbye. Indeed, for this movie I ate so much salt that I nearly needed a nitroglycerin tablet. "Deep Impact" was better ... because it had human interactions in it.
The AtmosphereBy the time the asteroid enters the atmosphere it has about two seconds to conclude it's business. One thousand ... Two thousand ... the collision is over and the aftermath begins. At twenty miles per second it will easily go through twenty miles of atmosphere and twenty of crust before taking up residence in the mantle as an amorphous "hot sludge".
The atmosphere is ~ 14 lbs per square inch. If liquified a 14 pound column of Nitrogen/Oxygen would only be a few yards tall. So the situation is roughly equivalent to a humming bird hitting the windshield of a Greyhound Bus running late on Interstate 80.
Concerning the shock wave ... it will be truly awesome. But it's not gonna' go round the planet at 2000 mph and knock down every building on earth.
What's a shock wave anyway?
Briefly, the average speed of a molecule of air at room temperature is about 2000 miles per hour. That's why you can smell something upwind several yards away from the stink. The smell is random walking through the air faster than the wind is blowing it back. You could smell it all the way to Poughkeepsie upwind if it didn't thin out so much.
Well ... hmmm ... sound ... yes.
Each air molecule is like a little springy thing and they're twangin' around like bumper cars. When you talk, your vocal cords hit some of 'em and send them in this or that direction. These in turn hit others in the same direction and transfer the extra speed through the medium like a 5 ball pool shot. Meanwhile, your vocal cord has gone the other way and now comes back again to shove some more air molecules. So you create waves ... of sound.
Now if you make a big sound as in Back to the Future and blow something up, I suppose in some quarters that would constitute a shock wave. But not here. That's just another sound wave. Here, a shock wave is air forced to move at a velocity faster than sound (about 600 mph). The wave on the leading edge of a jet travelling faster than 600 mph is a shock wave. The wave you see in aerial pictures of B-52 bomb drops on Vietnam jungles is a genuine shock wave (I believe). Such a wave is not nearly as self-sustaining as a sound wave. They peter out fast and degenerate into the normal boom sound wave. A shock wave will knock down a tree and move on with less energy. A boom wave will push the tree back then forth, losing some energy but not as much. Both waves bend around objects as well.
An interesting note:
Back to the circus ...
Our asteroid is going much faster than the speed of sound and therefore creates a shock wave. More importantly, it's travelling so fast that the air beneath will not have a chance to 'get out of the way' and will be plasma'd and supercompressed and pushed into the crust along with a lot of ocean and then the whole kit 'n kaboodle goes on down home to the Big Mickey where it does nothing shocking at all.
This is why I say that the damage caused by an asteroid is roughly proportional to its perimeter. Everything under it ends up in the mantle because is has no chance to get squeezed out into a 90 degree vector parallel to the earth's surface (the damaging vector).
The Black CloudThe worst effect of the post collision scenario is the cloud of dust and smoke caused by the burning of everything on the earth. Ostensibly, as hot meteorites reenter the earth's atmosphere they will land and start forest fires (probably in your kitchen and back yard).
I am sure this will occur to some extent given the appearance of the Tycho crater debris field.
I have a bone to pick about the result of cutting off sunlight for extended periods. Namely, my view is that this type of cloud will cause the earth to heat up rather than cool down ... the exact opposite of what is proposed by the standard model of extraterrestrial catastrophe. Let us proceed to explain.
In order for the earth to cool off it is required that heat radiate from the planet in excess of what is received from the sun. The earth cannot convect heat away because there is no gas in space to convect to. Nor can it conduct heat away from itself as the earth has no physical connection to any other heat sink. This only leaves radiation.
It cannot lose heat by radiating it into the body of the earth because the earth is quite hot (enough to melt rock). So the heat at its surface must radiate into space. However, it cannot do so immediately because there is this new cloud in the way. Also, the cloud is black ... not white ... thereby decreasing the earth's albedo (black absorbs heat more than white). Hence, the atmosphere is retaining more of the sun's radiation than usual ... not less ... as would be the case with white clouds.
Therefore, when the warmth at the surface of the earth attempts to escape it must go through a wall of "hot black clouds". In fact, what the standard model proposes is nothing less than an inversion of known laws of thermodynamics. To wit, that heat flows from a hot body to a cold body. They are asking that California warm goes into stratopheric hot rather than vice versa. They are asking a warm beach to lose more heat by radiation through a hot black cloud than through clear, cool, starry skies.
If the clouds were white they would reflect light from the sun, keep the upper atmosphere cooler and allow the surface to gradually leak heat through it even though much surface radiation would be reflected back to the surface by those same clouds.
What is this? ... Both white clouds and black clouds make the earth cool down?! No difference?
So much for nuclear winter.
The OceanAhh ... the ocean ! ... riptides, sharks, jellyfish, David Hasselhoff ...
What happens to the ocean?
Speed ... maybe 2 - 3000 mph
Yes, wave height is controlled by forces outside of the asteroid's control ... namely the earth's gravitational field. Remember that things fall at 32feet per second per second. This means that after the first second any body will be falling at a velocity of 32 feet per second and will have fallen in that second just 16 feet. So a wall of water (with the dreaded pyramid shape) say, a mile high and going 2000 miles per hour just ain't gonna' happen because the top of the wave would have to fall back to sea level in a time much shorter than that determined by free fall. (This is callled "splash", i.e. water what don't come down too fast.)
In the movie "Deep Impact", a huge wave goes tearing through Pennsylvania some hundreds of miles from the ocean ... really ... hmmmmm.
In A, the pyramid cross-section shape, mile high wave form travels overland maintaining its shape in violation of the most basic rules of physics. Namely, a body in uniform motion is no different than a stationary body. And ... get this ... newsflash ! ... You can't stack water ... it falls down.
Scenario A is therefore laughably impossible given that this "stack" of water will fall down in a matter of ~ twenty seconds. Whereas it will take (at two thousand mph) about ~ 6 minutes to get to Pennsylvania.
In B, a huge basically flat "breaker" a mile high runs inland to the mountains. Since the water over the continental shelf is only about 600 feet deep (if that) where does the mile high water come from?! Since this is a wave form, it can't come from the deep ocean because in waves water stays basically in place while only the waveform moves.
Scenario B is therefore spurious. It can't go like that for lack of water.
In C, the continental shelf interferes with the wave, blocking the major part of it and sending spray into the upper atmosphere. The remainder is a huge tsunami running up the shelf and breaking up ~ twenty miles of coast ... maybe less. It will not make it to Pennsylvania. You need a bigger asteroid ... very, very much bigger. (As big as Texas ;o)
The SurfaceSurface ... surface ... who's got the surface?
The most important place ... our abode ... can we live through this ?
Some places are loose dirt, sand, landfill ... goodbye cruel world. Those of us on solid ground (and far enough away from the Event el Magnifico) will experience few immediate bad effects. One might conceivably retire to the basement or fifties bomb shelter for a few days. However, bad as direct hit on the earth might be, it pales to insignificance when compared to the ancillary effects of such a strike.
Namely, food production.
This is ultimately what will kill most people. Not fire & brimstone or freezing to death ... just simple starvation.
If the earth's food supply is even slightly undermined it may be cataclysmic. We grow what we eat ... little more. Agriculture invented "on time" ... not manufacturing. How many of you have stored up one year's supply of food? That's it ... all you good Mormons raise your hand (and maybe a few Jews as well). The rest ... nada. If we can't go to the store for two weeks, we're dead meat. And this will happen (guaranteed).
The CrustIt would help toward an understanding of collision effects in the crust to imagine a disc of finite radius being pulled from the mantle through the crust by a cable of unlimited potential force. If this disc were, say, 1 yard in diameter, how much would you expect to pull on it to lift the entire contiguous crust before the disc simply pulled through the rock? How much if 1 mile in diameter?
Of course it's not going to pull up much before the weight of the continent cracks up around the perimeter of the disc. Rock, cement and ceramics don't have much tensile strength though they are strong under compression (hence the use of rebar in construction).
Ultimately, this is why I say that the damage done to the earth's civilization by an asteroid which penetrates to the mantle is proportional to the perimeter of the hole it makes and not to its mass-energy which is dissipated in the mantle. This "formula" should be valid up to the point at which the mantle is severely perturbed (an unlikely prospect at this point in the history of the solar system).
An experience from my youth comes to mind. When in the 'cub scouts', my father arranged for our "troop" to shoot BB guns in the basement at assorted targets. These were the pump type rather than the CO2 powered.
To prevent the BB from riccocheting back at us off the basement brick walls, a bed sheet was hung behind the target. The sheet caught the BBs and they dropped straight down, their energy having been spent on pushing the sheet back. Because the BB did not have the energy to penetrate the sheet all of its energy went into pushing the sheet and the air behind it and a "wave" travelled through the sheet outward from the point of impact.
This, of course, would not work if we had been shooting 22's. Real bullets would simply have gone through the sheet, delivering little energy to the sheet. Its energy would have ended up being expended on the brick wall and in penetrating our flesh. Clearly, increasing the energy of a projectile only means delivering more to the target up to the point of penetration.
Secondly, and of much importance, if the velocity of a projectile exceeds the characteristic transmission velocity of energy through a medium, it may deliver less energy to that medium than a slower projectile since the exit cone made when coming out will have its angle reduced.
Is the characteristic rate of energy transmission for the earth's crust greater than 20 miles per second? I hardly think so. Thus, we are looking for a narrow hole with little energy transmission to the side even though the crust is about twenty times as thick as the proposed asteroid. I say it will be narrow anyway because the crust won't take a great deal of bending. It breaks away under the kind of stress delivered at the perimeter of the "hole".
The MantleThe remains of the asteroid (the amorphous blob) now enters the mantle. Where the bulk of its energy is dissipated harmlessly. It does not matter one jot how hot it is or how fast it is-was going. Nothing matters here at all. This is the end of the line.
A wave travels through the mantle just as is the case with any earthquake but such a wave carries no damaging energy. It is dissipated in the enoumous bulk of the mantle. I think here all would agree that the collision of any asteroid with the earth won't mean a thing to the planet as a bulk object. A fly alighting on a buffalo would be a matter of greater consternation.
The head of a pinThe picture represents a "slice" of the crust & mantle. The scale is accurate if you imagine a ball about as big as the house you are sitting in now, i.e. about 20 feet in diameter. If you were the earth, would you poop your pants?
Question: If the energy of the asteroid were directed at lifting the continents (up from the mantle), how high would they fly?
And remember ... the stuff of the mantle is not like water ... it is quite viscous. It will not carry a huge water type wave over its surface. The effect of the asteroid on it will not be like a stone into a pond but rather like a stone into wet mud. Splat ... blap ... fub ... glup.
ConclusionsThe asteroid impact will be not nearly as horrific as is supposed. The proof lies in the fact that many dumb animal species survive these events. How much better must our chances be? We possess the ability to do significantly more than just gawk, suffer, and die. We can move, act differently, make plans ... in general ... think about our situation, options, futures.
If an asteroid of "dino-deadly" size were to strike, perhaps less than a tenth of the earth's population would be deep sixed. Certainly not ALL of us. Cripe!
Which brings me to the :
Why Do People Do This?The bearer of bad news in ancient times was often killed by the king-emperor-potentate. Today, he gets attention. You go on talk shows & hawk your disease of the month or whatever. People are fascinated by death ... particularly their own in the company of others ... many others.
I believe this is because they recognize that something like this IS going to happen.
Psychologically (and only subconsciously) we see it coming but don't want consciously to acknowledge it. By sticking pins in the voodoo doll of asteroid impact we may gain magical control over the inevitable.
After all, anything is better than thinking and planning. Isn't it?