Birth of the Moon: a Runaway Nuclear Reaction? 355
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."
Re:Wouldn't there be an empty space? (Score:3, Interesting)
The pacific ocean is a big, empty space.
Nuclear Reactor (Score:5, Interesting)
Re:Impactors all the way (Score:5, Interesting)
Re:Impactors all the way (Score:5, Interesting)
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.
Further on they say that the impactor theory doesn't exactly fit the data. I'd blockquote, but I'm stuck on page three, I think we slashdotted it.
They give several reasons; one is that the object would have had to hit at a precise angle to become the moon and not completely vaporize the earth. Another is that the object would have had to have been formed very near the earth; they calculate from the moon rocks it would have had to be between Venus' and Mars' orbits.
Re:Teach the hypothetical controversy! (Score:5, Interesting)
Christian-minded skepticism would sound a lot less idiotic (no offense to those of you who can't stand that), and something like:
Why do we think this might have happened? Because it might be possible. Do we have any proof of it? None whatsoever. Does it seem likely or probable? Not enough data. Could the moon have been spontaneously created by an infinitely powerful being instead? Sure.
Re:Wouldn't there be an empty space? (Score:3, Interesting)
That's what George Darwin said, but no. There's not enough evacuated volume there. Think about it: the Pacific is huge, but not very deep on planetary scales. Volume-wise, you're off by orders of magnitude. (I don't believe Darwin knew the depth of the ocean, so he's off the hook.)
From TFA (Score:4, Interesting)
I know you're joking, but
Re:Wouldn't there be an empty space? (Score:2, Interesting)
I'd take anything in Cosmos magazine with a healthy dose of skepticism. Since the article is slashdotted these points may already be addressed but anyway...
There is growing evidence based on analysis of ancient crust and zircon crystals that cratons (continental cores) formed much earlier than thought and that the earth was only molten for a very short period, if at all.
I would say there should be evidence of a massive mineral anomaly in the earth's crust. No massive nuclear eruption big enough to put the mass of the moon into orbit could take place without leaving a very large geographic trace with anomalous minerals and elemental levels (iron, radiation decay products, olivine, etc). There is no evidence that such a thing has ever been the case. Even in areas where oceananic crust has been subducted there should be volcanic areas rich in these elements. The earth's big iron deposits are the banded iron desposits thought to have originated when oxygen was produced by the first photosynthetic life and the iron was oxidized out of the oceans. The african natural reactor example some have given is very small in terms of geography, certainly not enough to act as proof of a massive nuclear eruption.
Re:Wouldn't there be an empty space? (Score:2, Interesting)
In a molten scenario, center of mass a would have ejected center of mass b, and then the countless fragments would have spent a bunch of time coalescing.
It's been a long time since I have though about it, and I'm no expert, but I think that the Sun could have spent some time pulling on the moon, making the orbit both more in plane with the orbit of the Earth (the Earth is pulling too...), and faster, so not all of the momentum necessarily had to come from the explosion/ejection (tilting the plane of the orbit of the moon would, I think, lower the overall momentum of the Earth-moon system, but increase the momentum of the moon itself).
How Big the Earth, How Thin the Crust (Score:5, Interesting)
Example: imagine a model of the earth where 1 mm = 1 mile. (or you can use 1mm = 1 km, if you like)
The earth is 7926.28 miles (12756.1 km) in diameter.
At this scale, you can make out significant mountain ranges, etc. The Atmosphere would be 4 or 5 inches deep. The crust is an inch or 2 thick.
And the Earth itself is more than 8 yards across. That inch or two of crust is sitting on a chewy molten insides. (check volcano flows, etc.)
The Earth is really a molten droplet spinning in space with the thinnest external layer where life has happened to accumulate, like the layer of tarnish on a coin.
Re:Wouldn't there be an empty space? (Score:2, Interesting)
Hm, I don't think that a thrust is necessary, because you may think of the moon too much as a satellite. Think of the earth and moon as a double-planet.
The scenario: The pre-earth is rotating around its axis and has a centre of gravity. Now there is the explosion. Newton does its action-reaction thing and hence the new earth and moon move away from the center of gravity. Conservation of momentum requires that everything keeps spinning around the centre of gravity.
That 1 km/s orbital velocity is about the same as its orbital velocity around the centre of gravity. But the earth has an orbital velocity around that centre of gravity too and given its much higher mass, that speed is much lower. So, you may ignore that in practice, but in reality it is there.
Bert
Re:Teach the hypothetical controversy! (Score:3, Interesting)
That said, your point is exactly what drives me totally batshit about fundamentalists. If you examine almost any of "God's rules" in a historical context they are pretty simple. The majority of them are involved in health and wellness and the proper functioning of society. Don't steal, don't murder, don't be a dick were the jist of the big ones on the stone tablet story. Most of the rest like "don't eat these things, homo's are bad, etc" are nothing more than ancient medicine. Disease was punishment by God for offending him, so things that you did that were likely to get you diseased were clearly against God's will. Not properly preparing food (namely piggies) made you sick. Playing around the back door of other people and animals was a really good way to get E.Coli and a whole variety of other nasty bacteria and the like. God's "purpose" in these cases was to serve as the superstition that would keep us alive until we found ways to combat those things naturally. Cook your fucking meat, wear a rubber, wash your damned hands, get your shots, etc. Most of the sexual rules regarding monogamy and the like were there because spouse swapping/stealing and uncertain lineage would undermine the fabric of their society. So even back then the whole "Will of God" business was nothing more than science with a funny name. The laws came from direct observation of the evidence presented. And lo and behold, most of them were correct. We eventually found the causes for those diseases, we have learned how societies structure themselves and interact, and so on.
Re:Wouldn't there be an empty space? (Score:5, Interesting)
The sun's gravity accelerates things near the Earth by 0.006 m/sec^2. Two objects close enough to be meaningfully gravitationally linked while orbiting the sun in the Earth's orbit will have a maximum differential acceleration of maybe a thousandth of that. So to get to 1000m/s takes 5 years.
So this essentially posits that an explosion had enough force to blown the planet apart, and send the pieces into space, but not to escape velocity (11.2 km/s) but instead to a velocity just short of that (11.19 km/s or so), so that the moon goes flying away for 2.5 years but 2.5 years later comes back and settles into a nice, circular orbit.
That would be hard to accomplish on purpose - saying an accident did it is beyond belief.
Re:Wouldn't there be an empty space? (Score:3, Interesting)
Also important to note, the moon is pretty much tidally locked (the same side always faces the earth). It's inconceivable that Earth's gravitational field did not play an extremely key role in the current angular momentum of the moon. For more information, read the section Tidal Coupling in the Earth-Moon System [utk.edu] in the linked article.
Robert Heinlein, "Blowups Happen" (Score:5, Interesting)
It's really not the same at all, but the article did call this story immediately to mind.
"Blowups Happen" is a classic 1940s SF story about a future in which society is total dependent on nuclear power plants. The engineering theory behind them shows that they are intrinsically safe and cannot blow up like a bomb. Then someone discovers that there is a false assumption in the equations and that, in fact they can blow up like bombs.
Meanwhile, an expert in the theory of lunar formation has concluded the lunar craters cannot have been formed by meteor impact, because of the "rays." There had to have been enough energy to "crack an entire planet." The only possible explanation, he says, is that the Moon was once an inhabited planet with an atmosphere and that "Here at Tycho was located their main power plant, and here at Copernicus and Kepler, on islands of the middle of the great oceans, were secondary power stations."
In other words, not only can they blow up like bombs, but that is what reduced the Moon to its present airless, lifeless, cratered and cracked state.
As I say, that's a completely different theory from the one being discussed. Nevertheless, I would bet a nickel that at least one of the authors of that article had read "Blowups Happen."
Re:Wouldn't there be an empty space? (Score:5, Interesting)
A Spherical estimation is good enough for most purposes.
True, at least by the old engineer's rule of thumb that only three places are significant for practical purposes.
But there are some situations where it's not good enough. One is if you're dealing with the orbits of satellites. To the satellites, the Earth is decidedly lumpy, enough so to affect orbits on a time scale of weeks or months.
A fun case I ran across some years ago was a geography trivia question: Name the three "highest points on Earth", and for each, give the definition of "highest point" that it satisfies.
The only answer that most people know is Mount Everest, which is the point that's the highest above the local "geoid" (which is the extension of "sea level" to handle areas far from the closest open ocean).
Some people know another answer: Mauna Kea, which is the point that's the highest above the mean level of the surrounding land. Everest rises some 3,000 m above the surrounding land, the Tibetan Plateau, Mauna Kea rises from the bottom of the central Pacific Ocean, and it's a much taller pile of rock than Everest. Its peak is more than 10 km above its base.
Hardly anyone can even guess the third answer. It turns out to be Mount Chimborazo, which is on the equator in Ecuador, and is the point that's farthest from the Earth's center. It's a good-size volcano that rises some 2,500 m above the surrounding land, but its peak is estimated at 6,384.4 km above the Earth's center, several km higher than the peaks of Everest or Mauna Kea.
All of these "highest point" claims are mentioned in the wikipedia articles about them (which is where I checked the numbers). And you could probably find them reasonably quickly by googling for that phrase, though I haven't tried it. I also wonder if there are other definitions of "highest point" that have different answers.
(And Chimborazo is one of the answers to another trivia question that's fun in "global warming" discussions: What are the two places where there are glaciers on the equator? So far, nobody I've asked this one has got either answer right, though some people get close to the other answer. Both places' glaciers are retreating rapidly, and are predicted to disappear in a few decades.)