Did the Moon Form from a Nuclear Explosion?

Originally posted by Phage
reply to post by Arbitrageur

 

That is not a description of a nuclear explosion. It is a description of a transition from delayed to prompt criticality. There have been other cases similar events. They are not nuclear explosions.

Where are you getting your definition of "nuclear explosion" from?

If you mean that Chernobyl wasn't a nuclear weapon, of course I agree with that.

Nuclear weapons derive their explosive power from prompt criticality. Nuclear weapons are designed to use as much of the fissionable material as possible in the explosion, where as reactor accidents like at Chernobly only had a small fraction of the core involved in the explosion before it blew itself apart. From your source:

In the design of nuclear weapons, on the other hand, achieving prompt criticality is essential. Indeed, one of the design problems to overcome in constructing a bomb is to contract the fissile materials and achieve prompt criticality before the chain reaction has a chance to force the core to expand.

So a nuclear weapon is also based on prompt criticality. I'm not sure why you are trying to downplay prompt criticality in a nuclear reactor. Nuclear weapons also rely on prompt criticality except that the nuclear weapons are designed not to "fizzle" as they explode like Chernobyl did, meaning only a small part of the core went prompt critical. But Chernobyl's prompt criticality still resulted in an explosion, and even though it "fizzled" it still released a tremendous amount of energy before blowing the reactor core apart.

Originally posted by gortex
If this theory is correct would this not imply that most planets will have moons created through the same processes ?

Well, isn't THAT a good question. Are other planets' moons of the same composition as their surfaces? I don't know if there's been any real effort to find that out. Mars would be about the only one you could check, and it would be hell to put something on Phobos or Deimos.

Originally posted by Arbitrageur

Originally posted by Phage
reply to post by Arbitrageur

 

That is not a description of a nuclear explosion. It is a description of a transition from delayed to prompt criticality. There have been other cases similar events. They are not nuclear explosions.

Where are you getting your definition of "nuclear explosion" from?

If you mean that Chernobyl wasn't a nuclear weapon, of course I agree with that.

Nuclear weapons derive their explosive power from prompt criticality. Nuclear weapons are designed to use as much of the fissionable material as possible in the explosion, where as reactor accidents like at Chernobly only had a small fraction of the core involved in the explosion before it blew itself apart. From your source:

In the design of nuclear weapons, on the other hand, achieving prompt criticality is essential. Indeed, one of the design problems to overcome in constructing a bomb is to contract the fissile materials and achieve prompt criticality before the chain reaction has a chance to force the core to expand.

So a nuclear weapon is also based on prompt criticality. I'm not sure why you are trying to downplay prompt criticality in a nuclear reactor. Nuclear weapons also rely on prompt criticality except that the nuclear weapons are designed not to "fizzle" as they explode like Chernobyl did, meaning only a small part of the core went prompt critical. But Chernobyl's prompt criticality still resulted in an explosion, and even though it "fizzled" it still released a tremendous amount of energy before blew the reactor core apart.

That is a good question: Can radioactive ores as they appear in nature achieve criticality on their own?

A nuclear explosion that is big enough to eject enough material from the Earth to form the moon would have to be....mind bogglingly huge....

I do seem to recall an article somewhere that I read last year talking about radioactive materials being able to do this (a hypothesis for something else), but I can't remember where it was that I read it at.

Originally posted by wildespace
Does this look like a site of a nuclear explosion to you?

Nuclear explosions come in different sizes, and the location of the explosion makes a difference (underground versus atmospheric, or in this case, inside a reactor). I don't see how you can look at a picture and determine whether or not it's a nuclear explosion. You can put limits on the magnitude of the explosion from the picture, but you can't tell if it's a nuclear explosion from the picture.

It definitely looks like an explosion, and it's at the site of a nuclear plant, so yes, I think it's quite plausible it could be a nuclear explosion.

Originally posted by eriktheawful
That is a good question: Can radioactive ores as they appear in nature achieve criticality on their own?

If you read the paper cited in the OP, one of the scenarios suggested is that the explosion could have been triggered by an impact, so in that event I wouldn't say it happened on its own.

Originally posted by eriktheawful
A nuclear explosion that is big enough to eject enough material from the Earth to form the moon would have to be....mind bogglingly huge....

If the Earth wasn't spinning, yes. But keep in mind the origin of the "fission hypothesis" of the moon formation (which wasn't originally related at all to nuclear fission) was based on the idea that spinning motion alone might be enough to eject material, and it might be if the Earth was spinning fast enough, but they finally decided it wasn't spinning fast enough to do that on its own. But, it was spinning fast enough so all you really needed was an extra "kick" to do the job, so it's a combination of spinning motion plus the nuclear "kick" that's been hypothesized.

Originally posted by Mads1987
Thanks for the insight. I am surprised to learn about the natural nuclear reactors. Didn't know that kinda stuff happened on/in planets.

Well, you could at one time get a natural crust level georeactor to form, like Oklo. And it's believed that it's going on in the core all the time, so that's happening right this moment way down there.

There's a problem though, and that's this - you can't "creep up on it", that is, once the natural uranium and thorium reach a local density sufficient to reach criticality, then you start making heat. and lots of it. Just a tweak more concentration and you get orders of magnitude more heat, which makes your georeactor want to erupt, scatter, and fizzle out. Oklo puttered along on the edge of criticality for thousands of years before it used up its fuel. There's got to be some sort of sudden transition from just barely critical to wowser or your geobomb will just fizzle out.

The authors of the root article speculate that at the time of the Moon's ejection, the earth had a 3 hour day and was much more liquid, plus all the crustal fissiles hadn't been used up yet either by time or reaction. So they *might* have formed a pocket of fissile materials, and that *might* have concentrated due to higher spin into a stratified zone sufficiently enriched to begin a georeaction and that *might* not have had natural neutron poison in it (cadmium, boron etc) and that *might* not have then self-poisoned due to xenon, and that then *might* have been hit just right with a 100km wide asteroid which suddenly raised the density of said pocket of fissile materials sufficiently to cause a 250 million million megaton nuclear explosion.

Yipe! That's pretty big. And a lot of mights in that chain. That doesn't mean it didn't happen, and if they ever get a proper sort of sample from the Moon to see if the other end products are present below the crust (far enough below so you didn't get diffusion from the surface) then it'll be interesting.

Originally posted by Bedlam
Yipe! That's pretty big. And a lot of mights in that chain. That doesn't mean it didn't happen, and if they ever get a proper sort of sample from the Moon to see if the other end products are present below the crust (far enough below so you didn't get diffusion from the surface) then it'll be interesting.

Thanks for the post. Agreed that's a lot of "mights" and even the authors don't seem to convey an idea they think this is a "preferred" hypothesis, but rather just a possibility. They even invited others to come up with other alternate hypotheses to better fit observations, which shows an appropriate lack of commitment to the idea that the nuclear explosion is what happened.

I also don't see the harm in collecting samples to test the hypothesis, but I'm not sure exactly how deep they'd need to go to obtain untainted samples from the moon and how difficult that would be.I think the regolith depth can vary and I suppose they'd need to go below that to get samples.

Originally posted by eriktheawful
That is a good question: Can radioactive ores as they appear in nature achieve criticality on their own?

Technically, yes. If you properly arrange very carefully purified natural uranium with very very pure carbon moderator, excluding hydrogen (water) and any sort of neutron poison like cadmium or boron, you can, if you get it big enough, make a natural uranium reactor, and it'll go a bit past bare criticality.

That's how they built CP-1.

For a georeactor, you still have to have a lot of fissile material, only a lot more of it than CP-1, because it's mixed in with other crap, and you still have to have a very low rate of naturally occurring neutron poisons. But it can happen, and has. It's just that it's not very far above critical, or it'll spread itself over the landscape.

There's something else I just thought about, and that's the asteroidal impact required to trigger the thing. Your asteroid *also* has to hit the pocket in such a way that the pocket is massively compressed without splattering. If the earth at that time was so much more plastic, I'm not sure if the underlying mantle would have flowed under the impact to the point you couldn't GET that sort of compression, or if you could do it at all given Rayleigh-Taylor instabilities (the asteroid would have to have very high density to keep these from forming on impact and causing a jet - sort of like squeezing your hands together in the bathtub). Of course, maybe the size of the thing could prevent that under the center. It's tough to model criticality in shock waves in an uncontrolled system like that - DOE uses a dozen programs to solve this sort of thing by numeric methods and they all diverge wildly for creepy setups - you basically have to test a few and see which models are good for that arrangement, and I'm not sure how you'd be able to build a georeactor. I'm betting the authors didn't try to solve hydrocodes for bomb calculations and just skipped from 'georeactors existed' to 'if it went bang this big would it get the job done', which on the surface of things reading that paper, it seems like the modeling was mainly on what happens if you HAD that explosion, not could you possibly get that.

Since they're looking for alternatives, I hereby tender the planetary-derived* conjecture that it was an antipodal thwop. If they're going to invoke something as improbable as a 25 exaton super-mega-whompus nuke, I don't see why I can't counter with the antipodal thwop conjecture.

Consider - with an elastic spherical object, if I strike it, the shock wave will wrap around it and focus on the opposite side, or antipodal point. It's sort of like playing croquet and "sending" a ball by whopping an intermediate ball with the mallet.

If you had a near liquid earth, and you had a really *fast* very large incoming object that struck a direct (not glancing) blow, then the antipodal focus *might* have ejected a lunar-sized chunk of material into orbit without any contamination by the impactor. So you'll get a nice chunk of crust sans asteroid bits.

* planetary derivation: straight out of Uranus

supporting material

What is the smallest nuclear explosion that can occur? Something tells me it would still be extremely powerful, i.e. levelling a small city, or at least powerful enough to erase the building complex it's exploded in.

Prompt criticality, by itself, doesn't automatically lead to a nuclear explosion. It leads to a sudden spike in energy release, which can cause damage or destruction of the reactor through the physical means (meltdown, steam explosion, hydrogen explosion, etc.) To achieve a nuclear explosion, careful design is required to keep the chain reaction running for as long as possible. The so-called fizzle is not a nuclear explosion.

en.wikipedia.org...

You can achieve criticality without achieving a nuclear explosion: en.wikipedia.org...

Though dangerous and frequently lethal to humans within the immediate area, the critical mass formed is still incapable of producing a nuclear detonation of the type seen in fission bombs, as the reaction lacks the many engineering elements that are necessary to induce explosive supercriticality. The heat released by the nuclear reaction will typically cause the fissile material to expand, so that the nuclear reaction becomes subcritical again within a few seconds.

Originally posted by wildespace
The so-called fizzle is not a nuclear explosion.

en.wikipedia.org...

Where does it say that?

Let me put it another way. If the fissionable material is 100 times as large, and the fizzle means you only get 1/100th as much to explode as a nuclear weapon, it's exactly the same size nuclear explosion even though it "fizzled".

Originally posted by Bedlam
Consider - with an elastic spherical object, if I strike it, the shock wave will wrap around it and focus on the opposite side, or antipodal point. It's sort of like playing croquet and "sending" a ball by whopping an intermediate ball with the mallet.

If you had a near liquid earth, and you had a really *fast* very large incoming object that struck a direct (not glancing) blow, then the antipodal focus *might* have ejected a lunar-sized chunk of material into orbit without any contamination by the impactor. So you'll get a nice chunk of crust sans asteroid bits.

I like that hypothesis. The question is, how could we test it? Would you find a signature of some different isotopic ratios at the impact point and then would the Earth's shifting geology allow that to be found? I suspect the first answer is yes and the second answer is no so I'm not sure how to test it.

While I can't rule out the idea that Theia formed in the same orbit as Earth and that's why the composition was identical, I don't assume that's the case, and even if the nuclear explosion hypothesis is wrong, I do agree with the authors that alternative hypotheses should be considered.

Originally posted by wildespace
What is the smallest nuclear explosion that can occur? Something tells me it would still be extremely powerful, i.e. levelling a small city, or at least powerful enough to erase the building complex it's exploded in.

Five men stood directly under a 2 kiloton nuclear explosion high above them and they noticed little effects other than a bright flash. I don't know how much smaller they can get, but Chernobyl was estimated to be larger than 2 kilotons.

www.foxnews.com...

George Yo#ake, Don Luttrell, and four other officers stood directly underneath an exploding nuclear warhead 55 years ago -- and lived to tell their tale.

The blast was just a test, a bit of Cold War marketing designed to make the concept of nuclear war less scary for the public, but the 2-kiloton atomic explosion set off over the Nevada nuclear test site (and over the heads of those six men) was very real.

Originally posted by wildespace
What is the smallest nuclear explosion that can occur? Something tells me it would still be extremely powerful, i.e. levelling a small city, or at least powerful enough to erase the building complex it's exploded in.

Well, that depends. If you mean, what is the smallest nuclear explosion that has been done on purpose to be that small, you can go down to 50 tons or smaller by using a really inefficient topology, and we've tested them back when. Sub-ton nuclear munitions are an actual design sub-set at LANL - the so-called "nuclear hand grenade", not literally but close.

If you had you a really *efficient* neutron reflector, of course, you could make one any size you liked. Any size fissile mass in a 100% neutron reflector is supercritical. So you could make one in a 50bmg, I suppose.

Originally posted by Arbitrageur

I like that hypothesis. The question is, how could we test it? Would you find a signature of some different isotopic ratios at the impact point and then would the Earth's shifting geology allow that to be found? I suspect the first answer is yes and the second answer is no so I'm not sure how to test it.

Well, the first thing to do would be to simulate the thing given the state of the earth at that time, and run some simulations to see if you could thwop hard enough to eject a lunar sized mass of crust at the antipodal point without splitting the earth into bits, I'd suppose. Or the impactor coming right back out of the hole and contaminating the newly formed moon to the point you'd see it in assays.

Other than that, I guess your proof would be that there's your moon that is all crust and no denser bits or contaminants, and that could have done it, which is sort of circular.

Let's put it this way: I have never seen an authentic source calling the Chernobyl explosion nuclear. It was a steam explosion.

www.pbs.org...

The explosion was chemical, driven by gases and steam generated by the core runaway, not by nuclear reactions; no commercial nuclear reactor contains a high enough concentration of U-235 or plutonium to cause a nuclear explosion.

A nuclear excursion may have caused the secondary explosion, but it didn't lead to a nuclear explosion. A nuclear reactor isn't a nuclear bomb.

Originally posted by wildespace
A nuclear excursion may have caused the secondary explosion, but it didn't lead to a nuclear explosion.

Why a nuclear excursion that explodes can't be called a nuclear explosion escapes me.

A nuclear reactor isn't a nuclear bomb.

This seems to be the point you and Phage are trying to make is that Chernobyl was not a nuclear bomb or weapon. I already agreed with that.

However even a poorly designed nuclear weapon can "fizzle" when it explodes so I don't think the distinction about the "fizzle" type of explosion is such a big distinction since it can even happen with a weapon, it is a term that simply describes that most of the fissionable material was not involved in the explosion, rather only a small fraction was.

Originally posted by Arbitrageur
Why a nuclear excursion that explodes can't be called a nuclear explosion escapes me.

Because the force of the explosion doesn't come from the chain reaction, it comes from the secondary source like steam. If you put a water canister on a gas burner and heat it to the point of explosion, will it be a gas explosion or a steam explosion? Burning gas was the trigger, if you like, but the force of the explosion came from rapidly expanding steam.

Keep in mind that the nuclear fuel in Chernobyl was unenriched uranium rods, surrounded by graphite to moderate the reaction. There's no way that kind of assembly could have produced a nuclear explosion. It simply overheated, melted, and produced a steam explosion, possibly followed by a hydrogen explosion.

(another version of events is that the first explosion was due to the breaking and deformation of the fuel rod channels, while the secondary explosion was the steam one)

reply to post by wildespace

Please see my earlier post here:
www.abovetopsecret.com...
If that's true then the second explosion at Chernobyl was like a fizzled nuclear weapon.