Planetary Defense Experiment

[Jimmy Higgins]

So, you think the Tunguska event didn’t cause any damage? The energy involved was about 1000

tunguska was 60 meters and it had rather high speed (comet)
Chelabinsk was 20 meters and damage was minimal

Wait... we don't know what Tunguska was. Some studies say it was a hit, others that it was a broadside smack and it kept going, and others... aliens.

 

[Shadowy Man]

So, you think the Tunguska event didn’t cause any damage? The energy involved was about 1000

tunguska was 60 meters and it had rather high speed (comet)
Chelabinsk was 20 meters and damage was minimal

According to Wikipedia, that blast caused 1500 people to seek medical attention with over 100 hospitalized.

So, we are relying on the destruction of a 10km asteroid into chunks no larger than 20 meters? That’s about 125,000,000 chunks. With only 1% of those hitting the Earth that’s about 1.25 million Chelabinsk events over a few hours. Let’s say you spread that out over 6 hours, that’s still almost 60 chelabinsks per second.

I guess I don’t share your optimism that this would be harmless.

 

[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?

 

[barbos]

It’s not clear you are grasping the magnitude of the problem here.

Well, there will no extinction.

 

[barbos]

According to Wikipedia, that blast caused 1500 people to seek medical attention with over 100 hospitalized.

That's because they were not warned not to stay near closed windows.

 

[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.

 

[Shadowy Man]

It’s not clear you are grasping the magnitude of the problem here.

Well, there will no extinction.

A bit of moving the goalposts it would seem.

You earlier said: “atmosphere is perfectly capable of absorbing energy of 10km asteroid without much of consequences.”

Now we are talking about only 1% of that. And you’ve gone from “without much of consequences” to “no extinction”. I think there’s a lot of room between those two extremes.

 

[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?

 

[barbos]

It’s not clear you are grasping the magnitude of the problem here.

Well, there will no extinction.

A bit of moving the goalposts it would seem.

You earlier said: “atmosphere is perfectly capable of absorbing energy of 10km asteroid without much of consequences.”

Now we are talking about only 1% of that. And you’ve gone from “without much of consequences” to “no extinction”. I think there’s a lot of room between those two extremes.

anything less than extinction is inconsequential if we are talking about 10km asteroid.
And I was right about atmosphere, it's just too transparent to actually do that.

 

[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.

 

[Shadowy Man]

Anyway, I think I’ve made my point and quantified my understanding of the problem.

I guess it was my mistake to not read “without much consequences” as “at least we wouldn’t go extinct”. With that level of optimism almost nothing that happens on Earth is of much consequence.

 

[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.

 

[bilby]

We already know how to break large masses of rock into small pieces. Quarries do it all the time.

You need a certain amount of explosives, though in the order of tonnes, rather than megatonnes, of TNT equivalent; But the critical thing is to spread these explosives in small packets throughout a large number of boreholes, and to time the detonation carefully - if you don't, the results are lots of dust that's far smaller than your target size, plus several unbroken bits far larger than your target maximum size.

In short, a big bang - even a really big, nuclear sized, bang - likely gets you lots of rock vapour and fine dust, plus a handful of still dangerously large fragments.

The way to reduce a big rock to small rubble is with a large number of small explosions carefully placed and timed.

To say that this would be extremely challenging to set up in deep space on a rigid timetable would be a huge understatement.

Any quarryman can tell you that a small number of large explosions, or worse still a single massive explosion, is a shithouse way to try to break up a large mass of rock.

What you need is a large number of explosions, each of which can be really very small.

Of course, that rock is relatively static and not moving, and also, not 1 to 10 km in diameter size and all needs to be dismantled... quickly. Quarries and rock cuts usually involve small chunks at the edges.

Sure, but motion is relative, so not an issue once you match velocity with your asteroid to start work.

And quarries choose to work in small sections for various reasons, but there's no particular reason that they couldn't scale up to almost any size. You just need lots more holes and lots more small charges to detonate in them.

Which is why the best option to fight inertia is with more inertia. The idea of landing something on an asteroid, drilling, and getting a large bomb to blow it up is much more fantasy at this point than science fiction.

Absolutely.

I am just pointing out that a large bomb is incapable of doing the job effectively anyway - it has to be a lot of small bombs, or you are going to end up with some big pieces that are still dangerous.

Lots of small explosions are invariably better than a few large ones. Even when your nuclear weapons are targeting opposing nations, you get more bang for your buck with MIRVs.

Deflection is a far better option than destruction for several very good reasons.

 

[Loren Pechtel]

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.

 

[Loren Pechtel]

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.

If they are 200km apart they would burn in the atmosphere separately.

If they are coming in at escape velocity how long do you think the time difference is between impacts only 200km apart?

Unless you have a really huge mass of them it doesn't matter. Consider my standard example, Chelyabinsk. Let's say the object had really been ten times the mass but broke up before impact. 10 Chelyabinsk objects spread over the city, hitting simultaneously. Expected death toll: Still zero. The city gets pelted with 10 shockwaves instead of one, but each wave is no more damaging than the actual event was. There would be more blown windows but that's about it.

 

[Loren Pechtel]

I agree that if an asteroid impacts at 5km/hour it would not be an issue.

Escape velocity from 10km asteroid is 5 km/hour

But the relevant escape velocity for an impacting asteroid is Earth’s, not the asteroid’s.

If you blow up a dinosaur killer you must impart 5 km/hr to the fragments. Thus if you blow it up 2 months from impact a fair number of fragments miss.

 

[Loren Pechtel]

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.

If you're dealing with a dinosaur killer, yes, you must make just about all the mass miss. Spread it evenly over the planet and the thermal pulse will probably be worse than the actual event was.

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.

 

[Loren Pechtel]

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.

 

[steve_bank]

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.

I flew over St Helens on a commercial flight. If you did not know about the eruption that something exploded would be obvious. Trees knocked down all lined up pointed away from a center.

The law of inertia says that break up an asteroid and the results will be going in the same general direction. They will diverge over time. The resultant direction of any particle will be the vector sum of the initial momentum vector and the force from the explosion on each particle which will vary.

What happens if a satellite is exploded in orbit?

 

[Loren Pechtel]

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.