Birth of the Moon: a Runaway Nuclear Reaction?

An anonymous reader writes "How the Moon arose has long stumped scientists. Now Dutch geophysicists argue that it was created not by a massive collision 4.5 billion years ago, but by a runaway nuclear reaction deep inside the young Earth."

Comments

Wouldn't there be an empty space?

[mnslinky]

Wouldn't there be evidence of this on the surface somewhere? I know the crust has shifted considerably, but that's a *lot* of material to suddenly vacate.

Re:Wouldn't there be an empty space?

[Fallen Kell]

If it happened during the time that the earth was mostly molten, then no, there would be on evidence...

Re:Wouldn't there be an empty space?

[Goaway]

Others mentioned the Earth being molten, but even as it is now, the Earth is plastic enough that if you removed a big enough chunk, the rest of the planet would flow and deform until it was spherical again.

Re:Wouldn't there be an empty space?

[CheshireCatCO]

Everyone who has replied so far makes fair points, but misses the biggest point: the Moon is over 4 billion years old. There are virtually no rocks on the Earth's surface that even approach its age. That means that the ENTIRE Earth's surface has been replaced and reshaped in the interim. Things haven't just "shifted considerably", we've got a totally different surface. Any scar from that period is long, long since erased. And hole as deep as the Moon has long since filled in since the Earth is still very much a fluid over these timescales.

Re:Wouldn't there be an empty space?

[hobbit]

Dude, the European definition of billion is a thousand million, just like in the USA.

You might be thinking of the UK, which used to call that a milliard, but even the UK has been with the program since the 1970s.

Re:Wouldn't there be an empty space?

[WhiplashII]

I'm not sure I agree - The moon has an ungodly amount of angular momentum. I'm having trouble coming up with a method whereby a section of object a leaves object a, and then has enough thrust perpendicular to the direction of object a to get up to it's 1km/s orbital velocity.

Re:Wouldn't there be an empty space?

[Futile Rhetoric]

Europe counts more languages than one, and "milliard" or something similar to it means a "thousand million" in all but one, which itself is influenced by the US bastardisation of the term and is closer to being the 51st state than a part of Europe, really.

Re:Wouldn't there be an empty space?

[CheshireCatCO]

You don't have to super-heat them at all, that's my point. The Earth is a fluid even today. Over timescales of billions of years, any wound would have been erased.

Re:Wouldn't there be an empty space?

[MooUK]

You've given up reading, but not commenting?

Re:Wouldn't there be an empty space?

[digitig]

Yes it is -- it's akin to trying to draw strong conclusions from the weak anthropic principle. How many "trials" have there been in the history of the whole universe? On an astronomical scale, rare events are relatively common, if you see what I mean. Since the presence and nature of our moon appears to be a great benefit to the development of advanced life forms, it's hardly surprising at all that we happen to be on one of the (possibly very many) planets with a moon like ours.

Re:Wouldn't there be an empty space?

[hkgroove]

Tidal Forces, also, it could act as a blocker for rogue material headed Earth's way. Jupiter is also extremely important in deflecting comets and debris also keeping the asteroids at bay. But at the same time, Jupiter is most likely responsible for the belt.

http://www.astronomytoday.com/astronomy/earthmoon.html

http://www.space.com/scienceastronomy/astrobio_jupiter_030122-1.html

Re:Wouldn't there be an empty space?

[Gyga]

The moon gave humans a goal in our space programs (which have spawned numerous advances). Do you think we would have been as willing to attempt to land on Mars right away without trying out the moon first?

Impactors all the way

[squoozer]

While it's certainly an interesting idea I can't see it being right (but I've only read the first page, the site seems to have collapsed). My problem with it is simple that the impactor idea seems to fit all the data so well I think it's unlikley to be wrong.

I wonder though if this could perhaps be tested. The huge explosion theory could well have left old rocks away from the explosion site untouched. The impactor would have melted the whole planet. If we find even one rock old than the impact date we have our answer.

Re:Impactors all the way

[Red Flayer]

What really throws this theory out for me however (And I admit, I can't view the page, it's been /.ed) was that most of Earth's fissle material is in the crust, not the core.

That may be a bit of a chicken-and-egg problem. Maybe the fissile material in the core was exhausted in the runaway reaction, or in later reactions within the core (perhaps critical T&P exist in the core)... this seems plausible to me if, as with the crust, materials in the core were isolated and concentrated via geologic processes.

It's also possible that the geological processes that occured over the past 4 Bn years have caused the fissile materials to accumulate in the crust instead of the core.

Loony, totally Loony

[Ancient_Hacker]

I can't get to TFA, but it seems mighty unlikely to have that much fissile material just so happen to gather together, and not be poisoned by cadmium, boron, lead, or other neutron absorbers, and have it stay together and not have a negative temperature coefficient slowing it down, and not form bubbles and geysers and other instabilities, and have it push asymmetrically in one direction, for many hours (cf: speed of sound). Wayaaay too many things to believe before breakfast.

Doesn't Make Sense to Me

[CheshireCatCO]

As noted, the site is Slashdotted so I can't read it straight up. That said, this doesn't make sense to me. A large explosion on the Earth's surface wouldn't launch material into Earth orbit unless it were launched at a very precise angle (probably nearly horizontal). The authors (based on previous comments) complain that the Giant Impact hypothesis requires a finely-tuned impact angle, but what about their model? I'd expect an explosion to blow material almost radially outward. To posit that you'd get the finely-tuned launch angle from their model seems much more of a stretch than that an impact should strike a glancing blow (especially when we don't know how many similarly-sized impactors hit with the wrong conditions and were simply absorbed).

Also, note that you need to loft a lot more material than just the Moon's mass to make the Moon. it's not an efficient process, a lot (most?) of the material rains back down on the Earth. It has to, it starts out in an orbit that intersects the Earth after all.

Re:Doesn't Make Sense to Me

[CheshireCatCO]

Not sure if the article addressed this, but another point is that you'd have to assemble the fissionable material very carefully since you need to get it super-critical, but not have any of it blow too early, before you have enough. It's the classic bomb-making problem, only without anyone to supervise it.