Planetary Defense Experiment

[Shadowy Man]

Note, however, that I was talking about city killers. Against such a rock blowing it up is a good idea. Against dinosaur killers it's absolutely the wrong thing to do.

Perhaps you were but I was responding to barbos’ hypothetical 10km asteroid.

 

[bilby]

Your lack of knowledge doesn't make it so. If you can blast the rock into small enough pieces that they'll burn in the upper atmosphere then that's a viable option.

That's what I said.

You’d still be depositing a lot of energy into the atmosphere. Whether it comes down in one chunk or in pieces it’s still raining devastation if it’s big enough and the pieces enter together.

In this case it comes down to the energy density. Remember, Chelyabinsk was half a megaton and yet killed nobody.

Sure, but we are discussing a gigatonne range impact.

It makes Chelyabinsk look like a wet firecracker.

 

[bilby]

And this begs the question of how we might break apart a 10km asteroid into chunks no larger than 20meters. How much energy would that take?

We have the firepower to do it. The problem is distributing it evenly. Big booms tend to blow rocks into large chunks, not little bits.

Yup. You need lots of little explosions to pulverise rock.

Nukes need not apply. Amatol or similar is ideal for the job - the tricky part is getting it in place, distributed throughout the target rock.

 

[steve_bank]

Multiple nukes tailored to the job buried inside the asteroid.

Conventional explosives might be better. They can be sequenced and made directional. Cut it into pieces one chunk at a time. Not all at once.

The downside would be a crew would have to go there and stay for a while.

Put a demolition company team of explosives experts and structural engineers on it and they will figure out how to do it. It's a job for engineers not scientists.

 

[barbos]

And this begs the question of how we might break apart a 10km asteroid into chunks no larger than 20meters. How much energy would that take?

Most asteroids are piles of small boulders already.

Sure, so how much energy would it take to separate that pile into 125 million pieces in a cloud large enough so only 1% hit the Earth? Have you calculated that?

I told you, assuming 100% efficiency - 2MT nuke.
So I recommend biggest nuke you can get.

I recommend you read papers like “A new hybrid framework for simulating hyper velocity asteroid impacts and gravitational reaccumulation” by El Mir et al. (Icarus 321, 2019) to get a sense of the energy requirements to disrupt asteroids.

But even a simple calculation of the binding energy (3/5*G*M^2/R) can give a sense of the scale of the problem.

I was not suggesting impact, I suggested placing an explosive charge in the center of the asteroid. And I already calculated binding energy.

 

[barbos]

You had said 200 km apart, so that would only be about 20 seconds apart in impacting time at best.

one more time, they will hit Earths atmosphere in different places spread over 200 km.
And the point of splitting asteroid is not really to have few smaller armagedons instead of one big. The point is to have parts small enough that they don't even reach upper atmosphere - render them harmless.

My point was that if you break it apart into smaller pieces but those smaller pieces all still hit then you’re still depositing a lot of energy into atmosphere and that’d still be bad. Need to break it up enough so that most of it missed.

No, atmosphere is perfectly capable of absorbing energy of 10km asteroid without much of consequences.

Check your math. You're looking at the ballpark of 1 MJ/kg.

I checked, still 10MJ per ton of atmosphere.

 

[barbos]

And this begs the question of how we might break apart a 10km asteroid into chunks no larger than 20meters. How much energy would that take?

We have the firepower to do it. The problem is distributing it evenly. Big booms tend to blow rocks into large chunks, not little bits.

Yup. You need lots of little explosions to pulverise rock.

Nukes need not apply. Amatol or similar is ideal for the job - the tricky part is getting it in place, distributed throughout the target rock.

So you have ability to put 2 million tons of explosives into space?
Call Elon, he wants to talk to you.

 

[lpetrich]

In Russia I believe a small object passed over a town and hit. Windows broke and buildings shook. Chelyabinsk? I thought it was the 90s. Meteors lighting up the night have been caught on video.

 Chelyabinsk meteor - there's lots of video of that event from different directions.

 

[bilby]

And this begs the question of how we might break apart a 10km asteroid into chunks no larger than 20meters. How much energy would that take?

We have the firepower to do it. The problem is distributing it evenly. Big booms tend to blow rocks into large chunks, not little bits.

Yup. You need lots of little explosions to pulverise rock.

Nukes need not apply. Amatol or similar is ideal for the job - the tricky part is getting it in place, distributed throughout the target rock.

So you have ability to put 2 million tons of explosives into space?
Call Elon, he wants to talk to you.

I don't. But a nuke doesn't substitute for all that amatol.

If you have a way to make a nuke with a yield in the kg, rather than the kt range, call the Pentagon, they definitely want to talk to you.

 

[barbos]

If you have a way to make a nuke with a yield in the kg, rather than the kt range, call the Pentagon, they definitely want to talk to you.

I am not sure that this is even a problem.
most asteroids are piles of loosely attached boulders, perfect for blowing them up.
And even if it is solid, I doubt large fragments will be produced in the explosion.

Rubble pile - Wikipedia

en.wikipedia.org

 

[Shadowy Man]

And this begs the question of how we might break apart a 10km asteroid into chunks no larger than 20meters. How much energy would that take?

Most asteroids are piles of small boulders already.

Sure, so how much energy would it take to separate that pile into 125 million pieces in a cloud large enough so only 1% hit the Earth? Have you calculated that?

I told you, assuming 100% efficiency - 2MT nuke.
So I recommend biggest nuke you can get.

I recommend you read papers like “A new hybrid framework for simulating hyper velocity asteroid impacts and gravitational reaccumulation” by El Mir et al. (Icarus 321, 2019) to get a sense of the energy requirements to disrupt asteroids.

But even a simple calculation of the binding energy (3/5*G*M^2/R) can give a sense of the scale of the problem.

I was not suggesting impact, I suggested placing an explosive charge in the center of the asteroid. And I already calculated binding energy.

I suggest you read past the title of the paper to understand the relevance of my citation.

As for binding energy I don’t get the number you got when I use that equation for a 10km asteroid.

 

[barbos]

I suggest you read past the title of the paper to understand the relevance of my citation.

I don't see how it's relevant to my estimation. I merely calculated gravitational energy, pretty straightforward exercise.

As for binding energy I don’t get the number you got when I use that equation for a 10km asteroid.

Your formula looks correct, at least as far as dimensional analysis concerned. So you must get the same order of magnitude value.
...
yes, you have exactly the same formula I got, so You should get the same result.

 

[Jimmy Higgins]

I recommend you read papers like “A new hybrid framework for simulating hyper velocity asteroid impacts and gravitational reaccumulation” by El Mir et al. (Icarus 321, 2019) to get a sense of the energy requirements to disrupt asteroids.

But even a simple calculation of the binding energy (3/5*G*M^2/R) can give a sense of the scale of the problem.

I was not suggesting impact, I suggested placing an explosive charge in the center of the asteroid. And I already calculated binding energy.

I'm suggesting using the power of prayer... which is tactically more feasible than putting a nuke near the center of an asteroid. Sure, prayer won't work and a nuke would, but what good is a plan if we can't actually do it?

 

[barbos]

Why not?
Pressure from the weight is equivalent to few meters on the earth.
You can literally dig yourself inside like into the sand.
You will need a power source - some kind of nuclear reactor.
In fact, chemical power source may be enough.

 

[Shadowy Man]

I suggest you read past the title of the paper to understand the relevance of my citation.

I don't see how it's relevant to my estimation. I merely calculated gravitational energy, pretty straightforward exercise.

As for binding energy I don’t get the number you got when I use that equation for a 10km asteroid.

Your formula looks correct, at least as far as dimensional analysis concerned. So you must get the same order of magnitude value.
...
yes, you have exactly the same formula I got, so You should get the same result.

You are correct. I made an error in my original calculation. I now do indeed get something on the order of a few megatons of TNT. I apologize for the mistake.

 

[barbos]

In any case, 10 km asteroids on short notice are astronomically rare.
The one which killed dinosaurs had tens of millions of years notice. Dinosaurs did not have NASA.

 

[Elixir]

In any case, 10 km asteroids on short notice are astronomically rare.
The one which killed dinosaurs had tens of millions of years notice. Dinosaurs did not have NASA.

What is our level of confidence that there are no "earth crossers" of that size that have yet to be cataloged?
If a new one were discovered today, how much notice would be required to do anything about it?

Seems to me that an object from the asteroid belt would be detected a lot earlier than say, a Kuyper Belt object whose orbit was somehow perturbed by collision or whatever, and took up an earth-crossing orbit in an orientation 60-90 degrees off the ecliptic. Such an object would probably blindside us.

 

[steve_bank]

I read a short story in the 70s about an asteroid strike.

A killer strike is predicted at a spot and time on the Earth. As the time approaches a big party grows at the spot. At the end of the story people look up, and sure enough there is an asteroid.

 

[Shadowy Man]

In any case, 10 km asteroids on short notice are astronomically rare.
The one which killed dinosaurs had tens of millions of years notice. Dinosaurs did not have NASA.

What is our level of confidence that there are no "earth crossers" of that size that have yet to be cataloged?
If a new one were discovered today, how much notice would be required to do anything about it?

Seems to me that an object from the asteroid belt would be detected a lot earlier than say, a Kuyper Belt object whose orbit was somehow perturbed by collision or whatever, and took up an earth-crossing orbit in an orientation 60-90 degrees off the ecliptic. Such an object would probably blindside us.

Why would it blindside us? I think it’d be easier to see those objects coming from outside our orbit than those that would be coming from the sunward direction.

 

[Elixir]

Why would it blindside us? I think it’d be easier to see those objects coming from outside our orbit than those that would be coming from the sunward direction.

My (likely flawed) understanding is that we simply don't look there so much as we look within and near the plane of the ecliptic.