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Discussion Starter #1 (Edited)
You betcha.

Some scientists are predicting a possible collision with an asteroid and the Earth on the 13th of April 2029. The Asteroid, roughly 330m across, is expected to pass by so close that it will be between our Geosynchronous Orbit satellites and the Earth itself.

The major question is how much the Earth's gravitational pull will affect the trajectory of the asteroid. The chances of it hitting the Earth on 2029 are relatively low but still significant; the asteroid was only discovered two years ago. The chance of it hitting an orbiting satellite is somewhat greater, however.

Scientists seem confident, assuming it's trajectory does not change in the next 30 years, that it will miss the Earth proper. It most certainly will be easily visible with the naked eye as it passes.

However, it is unknown whether it's close proximity to the Earth's gravitational field will cause it's orbit to be affected enough to hit the Earth on it's next pass after the predicted near miss, in 2036 (also April 13; it crosses the Earth's orbit with the sun at the same point, therefore the same date).

NASA indicates that should an Asteroid (or Comet) with a diameter of 140m hit the Earth, it would release energy equivalent to all the world's nuclear weapons in existence today being set off in the same location at the same time.
 

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I get 149 megatons and I'm assuming a 90 degree impact whichis unlikely.

http://pirlwww.lpl.arizona.edu/~jmelosh/crater_c.cgi

Projectile Descriptors

Projectile Diameter 140 meters
Projectile Density 3000 kg/m3
Impact Conditions

Impact Velocity 17 km/sec
Impact Angle 90 degrees
Target Descriptors

Target Density 3000 kg/m3
Acceleration of Gravity 9.8 m/sec2
Target Type competent rock or saturated soil

Results

The three scaling laws yield the following transient crater diameters (note that diameters are measured at the pre-impact surface. Rim-to-rim diameters are about 1.25 times larger!)
Yield Scaling 2.49 x 103 meters
Pi Scaling (Preferred method!) 2.41 x 103 meters
Gault Scaling 1.34 x 103 meters
Crater Formation Time 8.71 seconds

Using the Pi-scaled transient crater, the final crater is a crater in the transition between Simple and Complex with a rim-to-rim diameter of 3.98 x 103 meters.

This impactor would strike the target with an energy of 6.23 x 1017 Joules (1.49 x 10 squared MegaTons).
I think you are off on your energy calculation for size against nuclear weapons.

http://www.uwgb.edu/DutchS/EnvirGeol/ImpactHazards.htm

When it gets in the KM sizes instead of meters THEN it gets horrendous and of course a 330m meteor would indeed make an enormous impact on civilization

100-meter objects

These have energies comparable to the largest nuclear weapons. Blast effects and flash burns will extend to distances of kilometers, and a surface impact will create a crater a couple of kilometers or so across. These impacts happen on thousand-year time scales.

Kilometer objects
These have energies comparable to thousands of large nuclear weapons.
Blast effects will extend to distances of tens or hundreds of kilometers. Flash burns will extend to the limits of visibility. These objects are big enough that an atmosphere has little shielding effect, and the object will hit the surface and create a crater 20-30 kilometers or so across. Ejecta will devastate the landscape far beyond the crater. These impacts happen on million-year time scales.

10-Kilometer objects
These have energies far greater than the total nuclear arsenal of the earth. Blast effects will extend to distances of hundreds or thousands of kilometers. Flash burns will extend to the limits of visibility. These objects will hit the surface and create a crater 200-300 kilometers or so across. Ejecta will devastate the landscape on continental scales and hot ejecta will fall globally. Dust raised by the impact will have global climatic effects. These impacts happen on 10-100-million-year time scales.
Now a comet is a different animal as the velocities are much greater tho the density is lower. the impact would be about 3 times that of a similar sized asteroid

Now if that happened to be a Leonid asteroid which comes retrograde against the earth's orbit and was made of solid iron then you have 7,000 megatons of energy released.

Total approx imate nuclear arsenal is around 27,000 megatons.
http://www.carnegieendowment.org/npp/numbers/default.cfm

If that 330m monster hit earth square it would be with the force of about 1,950 megatons not far off the same effect as iff all the immediately ready nuclear weapons were lit off. ( not total stockpiles )

Nuclear winter?? a certainty and some calculations show a nuclear winter arising from as low as 100 megaton explosion so from that standpoint even 100m meteor could kill billions with it's after affects depending on where it hit. :eek:

Nasty neighborhood we live in. ;)
 

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These beasts form a major item in the list of geohazards which, at the very least, could throw the whole of 'civilisation' into turmoil.
The 330m one is bad enough, but it's the sneaky ones, about the size of a car or a garden shed that could do damage out of all proportion to their size, depending on where they land. 'Sneaky' because we couldn't really see them coming. If one of them lands on or near a major city, the carnage would be horrendous enough, but the after effects on the specific national, and the wider international, economy would be significant. Public health, especially psychological health would be affected.

I remember seeing this comforting advice somewhere about 5 years ago:

"If you're feeling paranoid, you've got good reason to be. The Universe really is out to get you!"

Time for a beer.
 

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The Doug said:
Drink, drink, drain your glass, raise your glass high! :)
Yeah.

It's all been Intelligently Designed anyway. :lmao:
 

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I've seen the movie Armageddon. I sure hope Bruce Willis, Billy Bob Thornton and Ben Affleck are still alive then.

When an asteroid the size of Texas is headed for Earth the world's best deep core drilling team is sent to nuke the rock from the inside
 

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TroutMaskReplica said:
this may be the only legitimate use for nukes.
I completely agree. We should be able to break a 330m rock into pebbles with on (or two, if necessary) well-placed thermonuclear warheads. I'd love to see NASA use this as an excuse to launch a mission to rendezvous with this rock (robotically), collect samples, take pictures, then blow it to smitherines.

I'll bet that if you placed the charges right, and timed it properly, you could make a Nike 'swoosh' in the night sky... I'll bet Nike would fund the whole operation for that alone.

cheers
 

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I don't think that works - it does not change the kinetic energy hitting the atmosphere and there is some thoughts it may make it worse.
A nuclear explosion in space will have a far different effect than in atmosphere where there is gas to compress.

If done far enough out it might nudge it out of impact trajectory tho.
 

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Just saw Al Gore's An Inconvenient Truth last night. There might not be any of us left to suffer by then.
 

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Discussion Starter #13
MacDoc, they weren't my calculations, they were the calculations of a NASA scientist being interviewed by the BBC. Either he's right or you are but I won't wade into that.

But, just for fun, the impact at Kirensk site (Siberia, Russia, 1908) was due to an asteroid estimated to be a stone meteorite 50~60m in diameter traveling at least 12 but possibly more than 20 km/S, which exploded 15 km above the ground. There was no impact on the earth, thus no crater.

Calculations by meteorite researcher Christopher Chyba based on a 30m stone asteroid traveling at 15km/S and assuming 50% of the energy was wasted due to the overhead explosion give values of 2x 10\-15 Joules (where 10\-15 represents 10 to the fifteenth power) and the Hiroshima bomb = 3x 10\-13 Joules (18 KT) therefore the asteroid impacted the Earth with the equivalent of 60 Hiroshima bombs or 500 KT of TNT.

The closest humans to the area under the explosion were 30 km away, nomadic herders living in tents. The tents were blown over, the occupants rendered unconscious, and when they awoke they found themselves in the midst of a raging forrest fire.

One who was outside the tent was blown 10m into a tree; he later died of multiple fractures.

The composition of the meteorite was confirmed by Russian Scientists examining fragments embedded in trees in the area.

However, there are other values that could be punched in to the equation that would yield much larger energy figures; the size of 30m and 15 km/S are considered to be very conservative values for that particular asteroid.

Some more on the topic:
BBC News Online
Wired News
Scientific American: U.N. urged to take action on asteroid threat
 

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I suspect the NASA guy got his orders of magnitude tangled.....or he was referring to a nuclear winter scenario - no possible energy of a 140m meteor could be equal to the world's nuclear arsenal - nor even the "immediate launch" arsenal tho an iron one at retrograde impact speed comes close.

Now ANY meteor in a KM category - THAT's doomsday material - a 1.4km meteor certainly would be a near equivalent of the world's arsenal. The calculation shows between 149,000 megatons ( non retrograde impact ) of energy released to just around 3 million megatons ( 2.67 million ) :eek: for an iron meteor coming in retrograde at a 90 degree angle. ( had to read that number a couple of times )

Kiss us mostly all bye bye tho the KT event meteor was bigger yet -10-14 km and didn't quite do our ancestors all in.

If we assumed the KT was 14 KM at retrograde speeds......3 BILLION megatons of energy released.
If we make a reasonable assumption that it was not a rare retrograde monster why it drops to a mere 149,000,000 megatons......

only the equivalent of 5500 of our nuclear arsenals going off at once......pretty tough critters our ancestors to survive all that !!!!!
 

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MacDoc said:
I don't think that works - it does not change the kinetic energy hitting the atmosphere and there is some thoughts it may make it worse.
The idea, as I understand it, is to break the object into as many pieces as possible, which increases the surface area, both spreading the force of impact and increasing the amount of atmospheric burn-up.

A nuclear explosion in space will have a far different effect than in atmosphere where there is gas to compress.
That's why you can't just hit it with a missile, you've got to send a robot to rendezvous with the incoming object, which can drill into it and place the charges (the more the better) such that the object is blown apart. We still get hit by the same mass at the same speed, but we get hit with a bunch of gravel rather than a big rock.

If done far enough out it might nudge it out of impact trajectory tho.
Yeah, if we see it coming with enough warning, we could conceivably nudge it out of a collision course with a few well-placed explosions, but again, it seems like a better idea to either blow it up with some internal charges, or, if you've got long enough, attach a light sail to adjust it's orbit gradually.

Regardless, there are a few things that are clear about our situation: 1) We currently don't have any well-developed technologies for this purpose. 2) We're nearly blind in the southern hemisphere, so we could get hit with very little/no warning. 3) Such an impact would make issues like climate change, world wars, pandemics and economic fluctuations trivial by comparison. And 4) Earth most certainly will be hit by large asteroids and comets in the future.

Cheers
 

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Still does not change the energy release - just morphs it into less ground impact results in a single point.

The injection of the kinetic energy into the atmosphere remains and may be worse as a big rock tunneling down a few KM will release much of the energy into the bedrock instead of the atmosphere.

Think of the entire nuclear arsenal going off in an airburst instead of a ground burst - that's all "breaking it up" does.

The kinetic energy remains even if the chunks are smaller and it ends up in the air and ground of the planet - whether it's point source or spread out.

What it might do is avoid tsunamis but it also might wreak far more devastation on forests - that's a LOT of heat energy.

In a deep impact much heat energy remains in the "glowing hole"
Spread out the atmosphere is heated.

Which is worse??......:eek:

There must be airburst versus ground impact calculations somewhere. Surely the nuke boys have gamed this out. :(
 

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MacDoc said:
There must be airburst versus ground impact calculations somewhere. Surely the nuke boys have gamed this out. :(
Yes, I'm sure someone has this worked out. There's probably a critical size above which breaking it up into fragments that will burn up in the atmosphere becomes more damaging than letting it hit. However, I suspect at that size we're talking about a planet-killer anyway.

The scenario I think we should be focusing on (both because it's reasonably likely to occur and it's something we could actually do something about with existing technology) is the object that's big enough to cause devastating impacts, but not big enough to wreck the planet. The sort of thing that hit in Arizona a little while back.

If we saw such a thing coming, and we nuked it to break it into pieces, it wouldn't do much harm when the pieces hit us.

There are a lot of little rocks and balls of ice that are big enough to do some serious damage if they hit us, but we could probably break them up if we saw them coming. To me, the fact that there's a good chance we wouldn't see such an object coming is most worrisome.

Cheers
 

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Yep anything under perhaps a 100 megatons in released energy would likely be best busted up.- most would fall in the ocean and the resulting heat would be minor compared to what we are putting out.

Better some sort of "push" far enough out.

The big rockets have far and away enough energy to move a big asteroid. The first stage of the moon rockets shifted the earth about 6 inches.
It's applying it far enough away from earth.
6" far enough out ( anyone want to do the math :eek: ) is lots.

Also far enough out is simply parking something of a size in the path and letting physics do the work - trouble is - what size and how to lift it.

I suspect sheer mass is more important than explosive power.

Maybe we need to park a few smaller rocket equipped asteroids in the LaGrange points as "projectiles" to play billiards with a biggie.

It would take quite a feat to get a few "biggie busters" in place but that could be done over time whereas if we find something heading our way we may not have enough time to deal with it then but if we get a few rocks in place ahead of time equipped with nuclear propulsion.............

Hmmmmm enough ion rockets on a decent sized asteroid :D

Interesting concept here



http://www.space.com/businesstechnology/technology/nudging_not_nuking_000211.html

nuclear bomb is detonated several hundred yards away from the object. Surprisingly, it is the intense radiation generated by the explosion that does the job. In one scenario, the radiation grills one half of the asteroid and causes a very thin surface layer to vaporize and fly off into space.

"Yippee-Ki-Yay Hmmm, maybe not." Bruce Willis meant well in "Armageddon" but he could have doomed us all

Tens of tons of material blasting off the asteroid at high speed would be sufficient to jolt the asteroid in the opposite direction. The effect is like the recoil of a rifle -- a small bullet moving at high speed causes the heavier rifle to recoil at low speed.

One thing most scientists agree on is there is no need to maintain an arsenal of nuclear weapons in space ready to intercept rogue asteroids. They also point out that there are ways to deflect asteroids that don't require nuclear explosions and we should be looking at these methods more closely.

In theory, an asteroid that is found to be on a collision course with our planet can be deflected to avoid an impact.

The deflection involves changing the asteroid's course with a sideways push or, preferably, changing its orbital speed so that it arrives before or after, rather than when Earth crosses its path. In either case the deflection is far more effective if it can be carried out years or decades ahead of the predicted collision.

For example, after twenty years, a nudge of just 1 m.p.h. (1.6 kilometers per hour) would change an asteroid's location in space by about 170,000 miles (273,500 kilometers). That is more than halfway to the moon.

Recent discoveries suggest that deflection of some Earth-threatening asteroids may be easier than first thought. Most schemes for nudging asteroids into a safer orbit assumed a single catastrophic encounter with Earth. This meant changing the course of the object by at least 4,000 miles (6,300 kilometers) -- the radius of Earth.



Nuclear Deflection: A safer, more effective procedure

Alan Harris, from NASA's Jet Propulsion Laboratory, explains that scientists now realize an asteroid will usually make several close passes by the Earth before a collision occurs.

The recently discovered 1000-yard (1-kilometer) wide asteroid designated 1999 AN 10 provides an instructive example. It will make a close pass of Earth every few decades. During each pass the asteroid is deflected slightly by the Earth's gravity.

Astronomers in Italy have calculated that a critical deflection could occur in 2027. This would involve the asteroid passing through an imaginary hoop in space they call a "keyhole". If the asteroid were to pass through this keyhole, which is only about 60 miles (100 kilometers) across, then it would collide with the Earth on its return in 2039.

When the initial calculations were made, astronomers didn't know the orbit well enough to determine if it might pass through the keyhole. After important follow-up observations were made they have now pinned down the orbit enough to be sure that it will not pass through any keyhole in 2027 and there is no chance that it will collide with Earth in the next century or so.

If, however, they had determined instead that there was a chance it would pass through a keyhole in 2027, then a mission to place a transponder, like a radio homing device, on the asteroid would have been wise so that its orbit could be determined precisely.

Harris explains that such a high level of precision would likely be required to determine for sure if the asteroid were on a course through a keyhole and, if it came to be, to measure the success of any deflection efforts. In this case a deflection of just a few hundred miles prior to the 2027 keyhole event would be all that was needed to avoid the 2039 collision.

Deflection of dangerous asteroids that are not in a "keyhole" orbit is more difficult because a larger change in course is required. The task is still feasible provided that sufficient warning time is given.

If a serious global effort is made to discover most large near-Earth asteroids within the next decade, then we should have decades, or even centuries of warning before a devastating impact. With such lead times only a relatively small nudge is required to change an asteroid's course so that, decades later, it will miss Earth.
cool :clap:

To me, the fact that there's a good chance we wouldn't see such an object coming is most worrisome.
Yeah the unknown unknowns.....indeed.
Under 1 km objects are akin to big earthquakes - devastating but survivable.

If a big comet has it's sights set there is nada we can do about it so "don't worry..be Happy"....

We can however track the 1 KM+ asteroids.....and are...and should continue as those could be deflected if caught early enough.
 

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The problem with using nukes to break up asteroids is that you can't guarantee how big the resulting bits are going to be, how many there will be and where they'll be headed. Some asteroids are considered to be essentially rubble held together gravitationally, as opposed to monolithic lumps. You could be mutilpying the problem by smashing them up. Imagine standing underneath something, blowing it up, and then hoping that either nothing will hit you or that if it does it'll be too small to do any damage. A bit Russian roulette-ish. Then again, how on earth do you deflect a rubbley asteroid? A monolithic lump might be steered off-course by an explosive impact, but not the rubbley ones.
 
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