Moon May Have Formed in Natural Nuclear Explosion

[Nyrath]

http://www.technologyreview.com/blog/arxiv/24721/

 

The moon formed after the explosion of a runaway nuclear georeactor in the Earth's mantle, according to a new theory of lunar formation.

 

But there's another theory called the fission hypothesis that could account for the similar isotopic content. This idea is that the Earth and Moon both formed from a rapidly spinning blob of molten rock. This blob was spinning so rapidly that the force of gravity only just overcame the centrifugal forces at work.

 

In this system, any slight kick would have ejected a small blob of molten rock into orbit. This blob eventually formed the Moon.

 

The fission hypothesis has been studied for 150 years but ultimately rejected because nobody has been able to work out where the energy could have come from to kick a lunar-sized blob into orbit.

 

Now Rob de Meijer at University of the Western Cape and Wim van Westrenen at VU University in Amsterdam say they know where that kick might have come from.

 

Their idea is that centrifugal forces would have concentrated heavier elements such as uranium and thorium near the Earth's surface on the equatorial plane. High concentrations of these radioactive elements can lead to nuclear chain reactions which can become supercritical if the concentrations are high enough.

 

The mind boggles...

[Kristopher]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

What happened to the "Theia impact" theory?

[Nyrath]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

What happened to the "Theia impact" theory?

 

From the article:

The standard theory of the origin of the Moon is called the giant impact hypothesis. It supposes that early in the Solar System's history, a massive object smashed into the Earth, cleaving it into two unequal parts. The smaller of these condensed into the Moon.

 

The best simulations of this process suggest that about 80 percent of Moon ought to have come from the impactor and 20 percent from the Earth.

 

That's hard to reconcile with the measured make up of Moon rock, which is almost identical to Earth rock in terms of isotopic content.

[Old Man]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Um, yeah, but how much of Earth would be made up of impactor under Theia?

 

I fail to see how fissionables could be made to go abruptly supercritical in a way that would cause an explosion. It could go critical, heat up, and even melt down, sure. But to make it go blooey you have to bring it all together very quickly.

[RexMundi]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Not really, you just need LOTS of it. Shoving a little bit of it together really fast, is just how we do it without having a Mountain sized piece of the material. Georeactors, the nuclear program difficult to protest against, heh.

 

~Rex

[Kristopher]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Not really' date=' you just need LOTS of it. Shoving a little bit of it together really fast, is just how we do it without having a Mountain sized piece of the material. Georeactors, the nuclear program difficult to protest against, heh.[/quote']

 

Georeactor != bomb.

[RexMundi]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Or the Earths Core, other Planetary Fission Reactors, or proto stars etc .......Someday they'll get around to testing for it. Just need to start building those Neutrino detectors. Think those are still a little on the big and clumsy Focus limitation side of the Detect: Neutrinos power.

 

~Rex

[Cancer]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Nuclear fission does not occur in any planetary core on anything other than a trivial scale. Radioactive decay is important (especially early on, with newly synthesized material), but very few naturally-occurring nuclides decay by spontaneous fission.

 

Old Man is right about the real reason this is a silly idea. To get a fission explosion, you need to assemble a critical mass very quickly from a noncritical distribution of fissile material. While that's not that hard to do for a mass on the scale of tens to hundreds of kilograms, to get a planetary-scale blast -- one capable of removing 1/80 of the pre-lunar Earth mass and moving it outside the Roche limit -- you'd need many orders of magnitude more fissile material, held apart into a subcritical assembly (i.e., WITHOUT having it blow up first), and THEN assembling it suddenly enough ... i.e., supersonically ... for it all to go supercritical more or less at the same time.

 

Too many tooth fairies in that idea, even for most cosmologists.

 

I am just about certain that a large enough fission blast would leave behind cosmochemical traces in both Earth and Moon large enough to tell something very strange had happened. The isotopic signature of fission products is pretty distinct. And that signature would show up by its absence in meteoritic material, that is, Solar System stuff that was not involved in/contaminated by the blast. And isotopic abundance anomalies are what the meteorite analysis are all about.

[Panpiper]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Centrifugal forces large enough to cause heavy elements to migrate 'upwards' to the equator instead of downwards to the center of gravity would 'require' that the centrifugal forces be 'greater' than the force of the gravity. If the gravity was greater, the elements would always migrate downwards, albeit perhaps at a slower pace given sufficient centrifugal forces. If the centrifugal forces were large enough to overcome the pull of gravity on those heavier elements, they would be large enough to pull the planet apart.

 

This theory on it's face, appears to me to be utter nonsense.

[Cancer]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

You could, in principle, get the fissile nuclides to float if their chemistry is such that they are predominantly in lower-density compounds compared to the rest of material in the molten proto-Earth. I don't think this is real likely, but I know very little about chemistry in general (I never took chem in college), or about uranium or thorium chemistry in particular. Both U and Th are listed as lithophiles (so there is some tendency toward silicate, i.e. less dense, compounds) but that is about the total extent of my geochemical understanding.

[Old Man]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

But if they are in lower-density compounds, then that makes supercriticality even less likely.

[Nagus Pantojan]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

And to be fission able material, it would be a higher atomic density. These elements would be more subject to gravity given their higher relative density.

[RexMundi]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Doesn't Density decrease when things are all like, Molten uber hot and spinning and what not or even in Gaseous form?

 

~Rex

[Cancer]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Usually but not always ... but what matters in the molten situation is still density differences. The relatively more dense stuff is still going to sink.

[RexMundi]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Right but in terms of centrifugal stuff, doesn't the Heavy material move outwards faster and easier eventually? Like swinging a Lead ball at the end of a rope, as opposed to a feather?

 

~Rex

[Kristopher]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Right but in terms of centrifugal stuff' date=' doesn't the Heavy material move outwards faster and easier eventually? Like swinging a Lead ball at the end of a rope, as opposed to a feather?[/quote']

 

If a molten ball is spinning fast enough to do that, the heavy stuff might very well go flying off! There's no string holding it in, just gravity, and if it's spinning fast enough for the heavier material to overcome gravity, why would it stop at the surface of the molten planet?

[Old Man]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

If a molten ball is spinning fast enough to do that' date=' the heavy stuff might very well go flying off! There's no string holding it in, just gravity, and if it's spinning fast enough for the heavier material to overcome gravity, why would it stop at the surface of the molten planet?[/quote']

 

Yes, if an external force causes it to spin that fast. Conservation of angular momentum alone, from gravitational accretion, won't put that much spin on the ball.

[RexMundi]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Because there's enough force to move it, and not enough for escape velocity, hence, moving it all into one spot relatively quickly, then Boom. Could work. Seems as viable as a the Big Rock hit us one day theory.

 

~Rex

[Cancer]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Cancer whispers, "You need a sophomore mechanics course and an upper-division fluids course to sink your teeth into this problem right."

 

But centripetal acceleration is velocity squared divided by radius. The mass (and density) do not enter. And while gravity scales with mass, so does inertia, so gravitational acceleration is independent of mass (and density) also.

[RexMundi]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Ah.....see now I know, and knowing half the battle. The other half, is unfettered brutal violence, but the first half is good to.

 

~Rex.....May or may not know, but then, if you don't ask, heh.

[Zeropoint]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Hmm. Okay, we can ignore surface tension and viscosity for something on this scale, so all we're dealing with is gravity and centripetal acceleration. If the net force on a denser particle is such that it is pulled upward, it will clearly NOT stop at the surface and will be flung outward. I wonder, though could it have come together in the first place like that? Could you get a lump of stuff continually tearing itself apart and reforming from the material falling back in?

[RexMundi]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

Dunno. Still the basic topic is that, It grouped up, and went Boom, and what was spewed out, became the moon. Looking at it though everyone seems to be saying the stuff spins out and goes off into space for *insert reasons here*, if such a thing is happening. What if though, that the stuff doesn't get anywhere NEAR the surface. Just close enough together with more of itself, down deep, to go Mega KAPOW!, and the planet sheds a 6th of itself, which them later, globs together as the moon?

 

~Rex

[Kristopher]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

The basic problem is that there's probably no way to get a fission detonation out of natural phenomena.

[RexMundi]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

At the only known location, three ore deposits at Oklo in Gabon, sixteen sites have been discovered at which self-sustaining nuclear fission reactions took place approximately 2 billion years ago, and ran for a few hundred thousand years, averaging 100 kW of power output during that time....etc etc etc ......and that's just a basic Google grab. So one can obviously get, a fission reaction out of a natural phenomena, so a detonation, should be possible as well. Stuff blows up all the time without our help.

 

 

~Rex

[Kristopher]

Re: Moon May Have Formed in Natural Nuclear Explosion

 

At the only known location' date=' three ore deposits at Oklo in Gabon, sixteen sites have been discovered at which self-sustaining nuclear fission reactions took place approximately 2 billion years ago, and ran for a few hundred thousand years, averaging 100 kW of power output during that time[/i']....etc etc etc ......and that's just a basic Google grab. So one can obviously get, a fission reaction out of a natural phenomena, so a detonation, should be possible as well. Stuff blows up all the time without our help.

 

Long, long step from "reaction" to "detonation" when it comes to fission.