The Moon may have formed in a nuclear explosion

Jan 28, 2010 by Lin Edwards report
The Moon. Image: NASA

(PhysOrg.com) -- A new theory suggests the Moon was formed after a natural nuclear explosion in the Earth's mantle rather than after the impact of a massive object with the Earth, as previously thought.

The problem with the impact hypothesis is that simulations calculate the should be composed of 80% impactor and 20% Earth, whereas in fact the isotope ratios of light and heavy elements found in Moon rocks so far examined are virtually identical to those on Earth.

The fission hypothesis is an alternative explanation for the formation of the moon, and it predicts similar isotope ratios in the Moon and Earth. The hypothesis (credited to Charles Darwin’s son George in 1879) is that the Earth and Moon began as a mass of molten rock spinning rapidly enough that gravity was just barely greater than the centrifugal forces. Even a slight kick could dislodge part of the mass into orbit, where it would become the Moon. The hypothesis has been around for 130 years, but was rejected because no one could explain a source of the energy required to kick a moon-sized blob of into orbit.

Dutch scientists Rob de Meijer (University of the Western Cape) and Wim van Westrenen (Amsterdam’s VU University) think they know the answer. Their hypothesis is that the centrifugal forces would have concentrated heavy elements like thorium and uranium on the equatorial plane and at the Earth core-mantle boundary. If the concentrations of these radioactive elements were high enough, this could have led to a nuclear chain reaction that became supercritical, causing a .

De Meijer and van Westrenen calculate the concentration of radioactive elements could have been high enough for a supercritical to take place. After it became supercritical the Earth basically became a natural nuclear georeactor that exploded and ejected into orbit the lunar-sized blob that became the Moon.

The researchers suggest the hypothesis explains the identical isotopic composition of light and heavy elements, and further propose it could be tested, since the explosion would leave evidence such as xenon-136 and helium-3, which would have been produced in abundance in the georeactor. Confirmation will be complicated by the fact that solar wind deposits these isotopes onto the moon in vast quantities, and that would have to be compensated for.

Georeactors are known to have existed on , such as that at Oklo in the Republic of Gabon in Western Africa, which was operating between 2.0 and 1.5 billion years ago.

Explore further: Astronauts to reveal sobering data on asteroid impacts

More information: arxiv.org/abs/1001.4243

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User comments : 47

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Doug_Huffman
1.7 / 5 (6) Jan 28, 2010
Non-nuclear fission is possible. Prompt critical disassembly is possible. Prompt supercritical assembly is very unlikely.

A thermal fission reactor, 'geo' or not, is supercritical on delayed neutrons to increase power. If it is even critical on prompt neutrons then it disassembles messily due to the slower energy transfer out of the power producing region.
gopher65
2 / 5 (3) Jan 28, 2010
This seems... incredibly unlikely. A more reasonable explanation is that the impactor was in a very, very similar orbit to that of Earth, and it eventually snuck up from behind us and hit the planet. Because it was in a nearly identical orbit, it would have a nearly identical composition.
Hernan
3.6 / 5 (5) Jan 28, 2010
Why not: The moon-earth proto-planet was ready for small jolt to break up and a much-smaller-asteroid-than-previously-thought hit the proto-planet...?
Skeptic_Heretic
2 / 5 (7) Jan 28, 2010
Because it was in a nearly identical orbit, it would have a nearly identical composition.

This thought process has been soundly disproven as the end all be all. To be clear, it is very possible that you're correct, but being in the same orbital plane doesn't guarantee similar composition, especially if the bodies are uneven in size. As an aside, I still subscribe to the impact hypothesis.

The explosion hypothesis is interesting, however there are other ways to impart great amounts of energy during the protoplanet life cycle.
gwrede
1.9 / 5 (8) Jan 28, 2010
Comparing the Earth to some stones found on the Moon, and then making theories based on the similarity, is reckless. The moon has been bombarded by meteorites for hundreds of millions of years, and any surface stone is likely to be meteorite shrapnel, and not from genuine Moon bedrock.
Royale
3.5 / 5 (2) Jan 28, 2010
very well put gwrede. i totally agree. I'm going to stick with the impactor theory for now. although this article is interesting I just don't see it being accurate, at least not without more evidence (deeper moon core samples for instance).
googleplex
1.6 / 5 (5) Jan 28, 2010
I have often wondered if the core has a nuclear reactor at its center. Isn't it supposed to be solid iron and cold by now unless some unknown heat generator was present.
If core is thermo nuclear then what evidence would we see. Would the many miles of iron and mantel act as a radiation shield. Uranium is a very dense metal and would naturally centrifuge to the center of the core. This we see in the iron outer core.
The only thing I can think of to detect is more neutrinos radiating from the core than from the sides. EM and other ionizing radiation would be aborbed by the outer core, mantel and crust.
Mayday
1.2 / 5 (6) Jan 28, 2010
Using a nuclear explosion to relieve the Earth of moon-sized mass of rock? Hmmm. That would be like using a champagne cork to relieve the Earth of the Rock of Gibraltar.

Good luck with that.
googleplex
3.5 / 5 (2) Jan 28, 2010
Using a nuclear explosion to relieve the Earth of moon-sized mass of rock? Hmmm. That would be like using a champagne cork to relieve the Earth of the Rock of Gibraltar.

Good luck with that.

I think the magnitude of nuclear explosion they are hypothesizing is much much larger than anything man made. Your talking about millions of tonnes of fissile material instead of kilos.
My own view is that the rate of rotation to counter gravity would have to be enormous in order to bring the dense Uranium and other nuclear fuel out from the center of the core.
rkolter
3.9 / 5 (8) Jan 28, 2010
My problem with this hypothesis is that when you accumulate enough material to go supercritical, it GOES supercritical. It doesn't wait for more material to show up. So, how do millions of kilograms of U235 for example, manage to accumulate to all go supercritical at once in a mind-bendingly huge natural fission bomb, without the few kilograms or so necessary for a supercritical reaction accumulating, and reacting, first? And, how do the millions of kilograms of material manage to stay together long enough to all fizz at once, as opposed to a higher density area fizzing first and blowing a great hole in the middle of your accumulating pile? Neat hypothesis, but very likely wrong.
antialias_physorg
3.5 / 5 (2) Jan 28, 2010
t doesn't wait for more material to show up. So, how do millions of kilograms of U235 for example, manage to accumulate to all go supercritical at once in a mind-bendingly huge natural fission bomb


Just hypothesizing here: If the rate of rotation is so large that the fissile material is far out and just marginally too thin to form a critical mass then a slowing of the rotation (by whatever means) would mean that the material starts to fall inward and thereby all of it reaches fission density at the same time (well, the part away from the sun would probably reach critical mass a tad earlier than the other side so the explosion would be slightly asymmetric.)
barakn
3.1 / 5 (8) Jan 28, 2010
This paper has not been published, and although I see it has been submitted and revised, there's no indication the revisions were due to a peer-review process. It still has spelling errors, and it just doesn't seem like it is ready for the limelight.
yyz
4 / 5 (4) Jan 28, 2010
@barakn, Yeah, I saw this on the arXiv servers a few days ago and had the same impression. I'm sorta surprised to see it here, though I see it has no related press release.
fixer
3 / 5 (2) Jan 28, 2010
I think Physorg moderators have snuck one in to see if we are paying attention.
Caliban
2.8 / 5 (5) Jan 28, 2010
And yet, there is still the puzzle of the "hot spots" that give rise to super-heated,(relatively)low density plumes of magma rising from somewhere deep within the mantle, possibly from the mantle/core boundary, or even the core itself. Possibly a relict of such an event, or similar?
dachpyarvile
1.5 / 5 (8) Jan 29, 2010
Yet another reason for a moon base. A few cores taken from underlying 'bedrock' far enough below the regolith to avoid contamination from solar wind particles might yield some very interesting information with respect to the elemental isotopes sought for confirmation.

However, that said, I still adhere to the 'Impactor Hypothesis' until more evidence is available to the contrary.
Parsec
3.4 / 5 (5) Jan 29, 2010
At the beginning of the earths life, the ratio of U235 to U238 was very close to 50%. It is only by the passage of time combined with the two isotopes having quite different decay rates that we see such low percentages today.

Uranium and thorium are actually quite common in the crust today. Its not inconceivable that a large number of smaller explosions put considerable molten rock into orbit, where it combined to form the moon. It really didn't have to be ejected all at once.
Skeptic_Heretic
2 / 5 (8) Jan 29, 2010
I think Physorg moderators have snuck one in to see if we are paying attention.

I'm fairly sure they sneak more than one in daily.
Arkwald
5 / 5 (1) Jan 29, 2010
At the beginning of the earths life, the ratio of U235 to U238 was very close to 50%. It is only by the passage of time combined with the two isotopes having quite different decay rates that we see such low percentages today.

Uranium and thorium are actually quite common in the crust today. Its not inconceivable that a large number of smaller explosions put considerable molten rock into orbit, where it combined to form the moon. It really didn't have to be ejected all at once.


Granted it could be an periodic ejection of material. However why wouldn't you see a similar behavior with Venus? It is ~82% of the mass of the Earth and presumably made from very similar material. If radioactives are collecting near the crust in proto-planets about the mass of the Earth then something similar should have occurred there as well.
baudrunner
1 / 5 (2) Jan 29, 2010
I like the early molten blob theory but it need not necessarily include a nuclear explosion. The moon might have formed during a very chaotic time when bodies were still orienting themselves in haphazard orbits, occasionally colliding and getting thrown around. I can see a mishapen almost molten liquid blob shaped like asteroid Toutatis, a smaller part of which eventually detaches as it hardens and literally bounces off an already hardened portion of the planet to assume an orbit some distance away. Earth and Moon are of the same chunk of debris. They are both spherical enough to have both once been soft so that their shapes could evolve.
MasterMind1776
3.5 / 5 (2) Jan 29, 2010
Forgive me if I sound nitpicky, but am I the only one who is disturbed by their references to a nonexistent force? "...barely greater than the centrifugal forces... Their hypothesis is that the centrifugal forces would have concentrated heavy elements like thorium and uranium..."
Skeptic_Heretic
1 / 5 (4) Jan 29, 2010
Seeing as there isn't really a cetrifugal force, I can agree with your discern.
Shootist
1 / 5 (3) Jan 29, 2010
This early in the formation of the planets weren't there still sizable percentages of exotic radio-isotopes lying about?

Assume for a minute that the pure radium crystals and chunks of aluminum-124 and such, on the proto-Earth, were not yet at critical mass but were brought to super-critically by the impact of the putative Theia and its own trove of fissionables?

Perhaps throw in quanities of D2 and T3?

Heat, pressure, density, BOOM!
brant
5 / 5 (2) Jan 29, 2010
"A new theory suggests the Moon was formed after a natural nuclear explosion in the Earth's mantle"

Thats not even a theory. Pure hypothesis. My theory(hypothesis) is the the moon was built by aliens as rest stop on the way to Andromeda. Just as valid.
Why elevate something like this to such a status in the eyes of the uninformed??
gregx
5 / 5 (2) Jan 30, 2010
No need to postulate alien rest stops, brant. Phsyorg has what you need!

From the article, "Physicists Investigate Possibility of an 'Unhiggs'"

"[UnHiggs unparticles] do not have a well defined mass; in fact, an unparticle can be thought of as a superposition of an infinite number of particles with different masses."

Infinite number, eh? So the UnHiggs must be REALLY BIG (infinity being the largish number that it is..)
Perhaps even the size of an iron-poor planetismal?

Also note this same article includes a diagram which clearly shows the moon rising over the ocean.

Conclusion: Luna is the UnHiggs.

Recommendation: California should name the LHC as a state historical resource.
PinkElephant
not rated yet Jan 30, 2010
I think the notion that Earth was a liquid blob fine-tuned to spin just fast enough to fission, is a much less likely scenario than the notion that two colliding planetoids (having formed within roughly the same volume of the protostellar cloud) had a very similar isotopic composition.

Also, even if the Moon is 80% impactor, the impact was supposed to strip mostly crustal material from the proto-Earth. This material being lighter than the core of either planetoid, would still be found at the surfaces of both. I don't even understand why the isotopic similarity is somehow an unsolved puzzle; I'd have thought it would actually be the expected outcome!
Skeptic_Heretic
1 / 5 (2) Jan 30, 2010
I don't even understand why the isotopic similarity is somehow an unsolved puzzle; I'd have thought it would actually be the expected outcome!
The problem is one of mass. If the moon is 80% impactor then due to what we know of it's composition it would have been too heavy to result in our current Earth-Moon dynamic.
Husky
not rated yet Jan 31, 2010
The moon shows oxygen isotope signature resembling earth material, however i read somewhere there is an iron defficiency. If there was indeed an impactor kicking up earth dirt, it possibly formed in the outer solarsystem, with less iron / heavy elemnts available far from the center of primordial cloud, btw how is the relative iron content / lack thereof measured between earth / moon ? Is that iron content of earth surface or in the mantle? and mooniron, calculated from surface sample rocks / apollo, or ?
YawningDog
5 / 5 (2) Jan 31, 2010
Nope. I'm not swallowing it. It's an extremely difficult engineering problem getting a critical mass together before the whole thing fizzles. A successful atomic explosion requires things to happen very, very quickly and they're talking about minerals migrating through the mantel.

This sound like an idea concocted in an Amsterdam coffee shop after sampling too much Blueberry or Northern Lights.
cay
1 / 5 (2) Jan 31, 2010
This hypothesis doesn't take into account how Pangaea formed. A collision would've created a moon and an oblong lump which eventually broke up to create the current continents. An internal explosion could've created an external moon, but not a landmass like Pangaea.
altino
1 / 5 (1) Jan 31, 2010
Hi ppl.
Sorry, i'm not very intelligent as some of you here or as the ppl behind this new theory.
I also have a theory to this theory:

Why don't we travel to the time of these events ( "moon formation" )and look with our own eyes who/how/why/...when...? :) hummm

And what about that?
Time travel.
Holly Wood.

Since time is an Illusion and we as humans like magic tricks... I would love to see it happen.
Like i would love to see life in other planets, or how dinosaurs lived in their time, or how plants developed as animals, or how some can live in their own space time universe without never need to manifest in our own.

Well... I'm always lacking on money to buy a new space time ship to travel around. :)

I wonder how they get the idea of explaining the event as "NATURAL". :)

MadMikeScott
not rated yet Jan 31, 2010
How about a Chernobyl dry reactor that keeps wet with comet water, that dries out and then, a boom? Or cometary objects that stir the crust and wet it to slow neutrons and allow for the thermal migration within the plastic crust and then a concentrating displacement and shock from an asteroidal body impact which gases off the moderating water and overlays multiple critical zones into super critical hot spots around the path of the impactor. ? ? ? A tangent graze and splash and the impacter remains
un-close-captured? until liberated terrestrial matter acriets around it ? ?

@shootist ?Al-124?
antialias
not rated yet Feb 01, 2010
I'm not swallowing it. It's an extremely difficult engineering problem getting a critical mass together before the whole thing fizzles.


Here's a thought: Let's say we're still at the stage where the earth hasn't solidified and is a 'nebulous ball of matter' gradually collapsing. If this is spinning then you'd get a pretty good separation of elements from high to low mass from the outside in in concentric shells (or the inside out if the spin is slow).

Now if just one part of the 'uranium shell' reaches critical mass then you produce a shockwave. Since all parts are close to critical mass this may be enough to push close by regions that bit more together and you have a chain reaction that could go on for some time.

This would create a moon almost with the same composition as the earth _only_ if the spin rate was _slow_ (not fast as inidcated in the artcle). For fast rotation only heavier elements than uranium would be pushed outwards.
dachpyarvile
1 / 5 (3) Feb 01, 2010
...

@shootist ?Al-124?


That one caught my eye, too. I know about isotopes 21-41 but 124 seemed really out of place. But, then on thinking about it I concluded that he probably did what I have done at times and fat-fingered the 2-key and hit the 1-key at the same time by mistake.

Speculation of course but that is the way I see it.
mrlewish
5 / 5 (1) Feb 01, 2010
Another simpler explanation is that the impact that formed the moon was from an object that had at one time been part of the earth that was blown away from an even earlier massive impact. that way the isotopes and all the junk would still be similar.
rkolter
not rated yet Feb 02, 2010

If this is spinning then you'd get a pretty good separation of elements from high to low mass from the outside in in concentric shells.

Now if just one part of the 'uranium shell' reaches critical mass then you produce a shockwave.


Neat idea, but no. Three big problems - first, the uranium density in that "shell" would have to be high enough to go supercritical - you're talking about a single cohesive layer,or band, planetwide, all simultaneously approaching a very specific value. It's just not credible.

The second issue is with shockwaves - the shockwaves from even a tremendously large explosion wouldn't shift the minerals planetwide, nor in a specific way to cause a propogating fission reaction.

Lastly, a hundred thousand individual big explosions across a landscape and over time does not equal one horrendous explosion all at once at a specific point (which is what you want, I think, to blow the moon into orbit?)
antialias
not rated yet Feb 02, 2010
With what is basically a gas as an initial state (with no real disturbances) a highly stratified state is almost a certainty. Whether there was enough uranium to get a band/shell of close to critical mass is indeed dubitable.

If you think of the example of a ring of uranium close to critical mass then an explosion at point A would cause a series of explosions all around the ring (part A's shockwave causing part B right next to it to become more dense/critical and blow, which in turn causes part C to become dense enough to blow etc., etc. )

What you'd get is some matter thrown outward which itself would then coalesce into an object - much like some parts of Saturn's rings formed moons.

Although the matter would _not_ be of the same makeup as the earth since it would only contain material that is either heavier or lighter than uranium (depending on initial rotation speed) - that's where it all falls down, of course.
Skeptic_Heretic
not rated yet Feb 02, 2010
(which is what you want, I think, to blow the moon into orbit?)
Unless you look at this as a secondary accretion mechanic. Several larger explosions tossing massive amounts of material off of a smaller, hotter, faster spinning Earth would send it into close earth orbit, as the moon was early in the solar system's history. It accretes like the Earth accretes as it revolves around the sun and viola, big moon. It's not an unreasonable hypothesis, just much less probable than the impactor theory.
otto1923
not rated yet Feb 02, 2010
"The underlying storyline of Space: 1999 centered on the plight of the inhabitants of Moonbase Alpha following a calamity on 13 September 1999. A huge nuclear waste dump on the far side of the Moon detonates in a massive thermonuclear explosion, initiated by the buildup of magnetic radiation which was released, causing a nuclear chain reaction. The force of the explosion causes the Moon to be sent hurtling out of Earth's orbit and into deep space at colossal speed" -Not again!!
rkolter
not rated yet Feb 02, 2010
Look, shockwaves just won't do it. Once one area "fizzes", it'll make a shockwave, sure. But that wave would have to be very special to actually compress, as opposed to disperse, the remaining material.

But say it DID compress it - you'd have multiple other areas "fizz" and produce their own shockwaves, creating not a single explosion, but a diffration pattern over the molten surface.

A slowly propogating diffration pattern. It may take hours to propogate across an area the size of north america. So you don't have, again, one giant explosion. You have tens of thousands of "little" (Mount Saint Helens?) sized explosions. In some places you'd get material into low earth orbit... but nothing Man or Nature has made since - including supervolcanos and fusion warheads - has lofted material into the Moon's orbit, nor a Moon's amount of material.

You'd need.. billions? trillions? of tons of U235 to loft as much material as made the moon. All fizzing at once. Good luck.
rkolter
not rated yet Feb 02, 2010
The Math, for the fun of it:

The Moon: 7.36x10^22 kilograms
Acceleration: 6 km/s (total guess - about 1/2 escape velocity)

Energy required: 1.32 x10^28 joules
Megaton of TNT has: 4.184x10^15 joules
Megatons of explosive force: 3,154,875,717,017

That assumes 100% perfect use of that energy into acceleration of future moon matter, and NO loss of matter falling back to the planet.

Amount of mass converted to energy in "Fat Boy" bomb - less than 1 gram in 6.2 kilograms - .00016

Amount of matter that has to turn into energy to equal required energy: 170 billion kilograms.

170 billion / .00016 = 1,062,500,000,000,000 kilograms of U235 that would have to fizz at once.

1.062 QUADRILLION TONS of Uranium.

That is what we're really talking about here. And that's a very, very, very rosy picture - more likely you'd need several times that to make up for inefficencies.

Mount Saint Helens was a meager 24 megatons.
Skeptic_Heretic
not rated yet Feb 02, 2010
The Moon: 7.36x10^22 kilograms
Acceleration: 6 km/s (total guess - about 1/2 escape velocity)

Energy required: 1.32 x10^28 joules
Megaton of TNT has: 4.184x10^15 joules
Megatons of explosive force: 3,154,875,717,017


Sorry but your math is pure speculation aside from the estimated mass of the Moon and what a megaton of TNT is in joules.
antialias
not rated yet Feb 03, 2010
A slowly propogating diffration pattern. It may take hours to propogate across an area the size of north america.

Depends on whether the earth was already a solid object or not. My guess is that this is before the majority of matter had coalesced. If we're till in the 'gaseous' stage (i.e. very hot and very mobile) then shockwaves could propagate very fast.
gopher65
5 / 5 (1) Mar 23, 2010
googleplex: Earth's core *is* partially heated by radioactive decay. It isn't exactly a reactor (self-sustaining reaction), but it's still heat produced via a nuclear process. It's basically a giant RTG.

MasterMind1776 & Skeptic_Heretic:
Actually, depending on the situation, it's sometimes helpful to think purely in terms of centrifugal force instead of centripetal acceleration.

But in any case, centrifugal force *is* a real thing. Centripetal acceleration can be broken down into two vector components: centrifugal force, and coriolis force. The reason why centrifugal force isn't a "real" force is because it doesn't exist independently of the coriolis force (and combined they're centripetal acceleration).

A lot of the time you just don't care about the coriolis effect though, so why bother using centripetal acceleration when you can just concentrate on the half of it that you're interested in (err, assuming that makes the math easier in your particular situation, anyway;))?
Skeptic_Heretic
1 / 5 (1) Mar 23, 2010
But in any case, centrifugal force *is* a real thing.

No, please, no.

CF is not a force, it is a combination of two forces. Momentum/velocity and whatever force is preventing escape be it gravity, tensile force of a string or bucket handle.

CF is not a force.
gopher65
5 / 5 (1) Mar 27, 2010
Whether or not centrifugal force is real (ie, and independent force) depends entirely on the frame of reference your calculations are occurring in:P. But one way or another it is still a useful way to think about and calculate things.

I hate it when people bash the use of centrifugal force for no reason except because the idiot gym teacher who was "teaching" (if you want to call it that) their grade 7 science course told them that it wasn't real.

(And yes yes, we all know that centripetal acceleration trumps centrifugal force as a more generalized, complete approach to the same thing, that more fully explains what's going on in any given situation. So what? Do you use relativistic equations every time you want to calculate the kinetic energy of ball being tossed across a room under standard conditions? Of course not. You use Newtonian physics even though it's horribly incomplete. Same idea.)
Skeptic_Heretic
1 / 5 (1) Mar 27, 2010
I hate it when people bash the use of centrifugal force for no reason except because the idiot gym teacher who was "teaching" (if you want to call it that) their grade 7 science course told them that it wasn't real.

That gym teacher was not an idiot. He's completely right, it's not real. There's no frame of reference in which the motion isn't divided into two parts.

Cetrifugal force is what we called it when we didn't know why the planets traveled around the sun. Now we know it's gravity and acceleration/velocity coupled. Please don't say it's real, it is not, in any sense, a real force.

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