The Moon's Two Sides Look So Different Thanks To 4.5 Billion-Year-Old Physics (forbes.com) 96
StartsWithABang writes: 4.5 billion years ago, a giant object collided with our proto-Earth, kicking up debris that eventually coalesced into the Moon. While the near side contains dark maria and lunar lowlands, the far side is almost exclusive heavily cratered, high-mountainous regions. This was a mystery for a long time, but it appears that heating from the hot, young Earth caused a chemical and crustal difference between the two faces.
I could be missing something (Score:3)
but couldn't the far side have craters and the near side few because something big, like I don't know the earth, blocks one side and not the other?
Re:I could be missing something (Score:4, Informative)
As seen from the moon, the Earth is only about two degrees across, so the proportion of projectiles blocked by it would be miniscule. Even that small effect is reduced (possibly beyond zero) by 'gravitational focusing': projectiles which come towards the moon from the direction of the Earth which would otherwise have missed can be deflected by Earth's gravity such that they hit. (And this happens more often than projectiles that would have hit being deflected so they miss.)
Here [oxfordjournals.org] is a paper I found on gravitational focusing.
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"As seen from the moon, the Earth is only about two degrees across"
Now.
At the time of the late heavy bombardment, the moon was a _lot_ closer than it is now. Close enough that the earth was a fairly effective shield.
It also means that tidal forces and heating effects would have been a lot stronger too.
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No, they explain this in the article. This might account for maybe 1% difference due to the actual distance between the Moon and Earth, but that is about it.
Ironic, I was watching "The Universe" on Netflix earlier, the exact episode that covered most of this. Good stuff.
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Although the Moon was much closer to the Earth in the past, perhaps 20x closer. The article suggests that the Moon formed just outside of the Earth's Roche limit. However, the articles don't explain the difference in the number of craters on the two sides of the moons. I would guess that most of the visible craters were formed prior to the maria, although I'm not sure why the events that formed the maria occurred almost at the end of (or after) the heavy cratering periods.
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How's that asperger going?
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You are correct. But this sort of ignorant "X times to a lesser value" bullshit math is rampant. I use it to easily spot stupid people for me.
Sometimes I will ask them, please draw for me on a blackboard how you would work "20 times less than X" and laugh at them when they can't do it.
But the scary thing is how many people don't understand what's wrong. It is simply that you cannot multiply and reach a lower value. 10 times less can't work. Ever.
One tenth can. But fractions are apparently im
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You must be fun at parties.
What about 0.1 times x, when x is positive? Note : no fraction involved.
What about 2*x, when x is negative? Note : no decimal involved.
If you're gonna laugh at stupid people for math problems, you might want to check your math first.
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Sometimes I will ask them, please draw for me on a blackboard how you would work "20 times less than X" and laugh at them when they can't do it.
You must be fun at parties
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You must be fun at parties.
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And yet, somehow, we all knew exactly what he meant.
If you want to be really picky, how else would one define "closeness" except as 1/distance? Oh look, all the math works out perfectly - twice as close is half as distant. Problem solved.
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Last time I checked, English was a natural language, not a technical language. As long as the meaning is understood, the expression is valid. In English, it's perfectly valid to refer to reciprocal relationships from either direction. If something is twice as far, it is half as close. If something is half as far, it is twice as close.
Re: I could be missing something (Score:1)
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Re:I could be missing something (Score:4, Interesting)
Another interesting aside is that many have tried to explain gravity by postulating that the universe is full of tiny particles that fly about randomly in all directions and that gravity works because bodies block the particles from hitting one another.This is sometimes called the screening theory of gravity.
If you make some reasonable assumptions you will find that two nearby bodies would block particles from hitting one another, creating forces that follow the inverse square law...
These theories also predict that planets will de-orbit and crash into their stars, and that moons will similarly crash into their plants. But hey, no theory is perfect.
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The Illuminati wise tail about the formation of the moon. If this were the case, then the earth would have coalesced with iron deposits on one side after the collision and the orbit lock would have been to both celestial objects likely resulting in a solid iron core in the earth, and we probably wouldn't be here. I would have expected they would have better engineered a load of bull-crap to feed us based upon being German/English Blue Blood/Mongol origins of this organization. Why not? They did a hell of
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Similar to the theory of light bulbs as darkness absorbers?
In a sense yes. Attractive forces like gravity and magnetism have always been a challenge to explain in terms of direct contact.
The motivation for the screening theories is that some people, or perhaps most people, have a deep-seated intuition that all of physics ought to be reducible to direct contact interaction.
You could say that one of the prime motivations of the early scientist was to prove that there were no non-direct contact forces at work in the universe, except for the force of God himself.
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Ironic, I was watching "The Universe" on Netflix earlier, the exact episode that covered most of this. Good stuff.
No, it would be ironic if you had watched "The Universe" to find out about this topic and they explained the concept of irony to you instead!
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If only TFA specifically mentioned this and explained why not.
Oh wait, it does. You could indeed have missed something; in this case Reading TFA.
The moon could have been artificially created. (Score:5, Funny)
Another, more plausible explanation is that the moon was actually an ancient artificial space station, placed in a very specific orbit around the earth. Over time, debris has collected on it, giving it its current appearance. The fact that it always faces the earth, and orbits the earth once every month is very intriguing. This isn't something we'd expect to happen were the moon a natural creation. That suggests that it likely was created as an artificial space station which has since become, for lack of a better term, dusty over a long span of time.
Re:The moon could have been artificially created. (Score:5, Funny)
That's no space station. It's a moon!
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dang, where's my mod points when I need them?
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Not only that, but without the moon, Earth's day would not be even close to 24 hours. (Lunar tides over billions of years have modified the length of the day.) Think how inconvenient that would be! I think you're on to something.
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The earth's day has always been 24 hours, however the defined period of the 86400 seconds within it may have changed over the millenia.... :-)
Re:The moon could have been artificially created. (Score:5, Informative)
The fact that it always faces the earth,
Nothing remarkable about that. It's due to tidal locking [wikipedia.org] and is quite common. [wikipedia.org]
and orbits the earth once every month is very intriguing.
Yea, and Lou Gehrig died of Lou Gehrig's disease. [cue creepy music]
Re: The moon could have been artificially created. (Score:5, Funny)
Damned, you would think he had to see that coming.
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Yea, and Lou Gehrig died of Lou Gehrig's disease. [cue creepy music]
More creepily all the onomatopoeia words sound like the sound they describe! bang!
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Did you read the article? The moon was formed much closer to the than it is now, perhaps 20x closer. The authors did some calculations that suggest that the moon likely became tidally locked within a few hundred days of its formation due to its proximity to Earth at the time of its formation.
And as for it being curious that the moon orbits the earth once every month, that is plain silly. The month was originally defined in terms of the time it takes the moon to go through its phases. And if you're que
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The article mentions that the moon was tidally locked from the start but does not explain why. At first I was a bit suspicious because that is a huge assumption. The paper in http://iopscience.iop.org/2041... [iop.org] explains that in more details.
Also, another reason for having 12 months is that this number is, like 60 and 360, quite remarkable because it has a lot of divisors. Simply speaking 12 is the smallest number that can divided by 2, 3, 4 and 6 while 60 can also be divided by 5 and 10. That is why we still
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That would be neat, however if it were a station I would bet its inexplicable mass (probably much lighter) would be driving astrophysicists crazy. I assume that all of the equations are working out as this isn't the case.
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Re:Please StopWithABang (Score:5, Informative)
...and the Science would have been Better (Score:1)
Re: ...and the Science would have been Better (Score:1)
Good god the pedants are out tonight. 4.5 billion year old physics clearly means the physics in question began 4.5 billion years ago.
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But then StartsWithABank won't be able to feed his family. This isn't a Forbes problem, it's a Slashdot not standing up to submitters who submit every single one of their lame stories as front page news.
How could the Earth heat it? (Score:2)
I read the article and it mentioned the hot side faced Earth. Not that heat radiating tens of thousands of miles in a vacuum heated it thousands of degrees.
More than like the force of the bang pushing the material left it run towards the back facing Earth not to mention gravitational pulls swelled the molten core towards Earth. And a 100 degree heat difference from the side facing the sun as well might of had a very small role.
1 billion years ago the Earth had 100 to 1,000 foot tides as the Moon and the Ear
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And the "article" was misconstruing the actual research. The actual study didn't say RADIANT heat from the Earth somehow magically went through the vacuum of space. The latent heat of the impact could very well keep many silicate minerals in a gaseous form on early Earth though.
The study indicates that mathematically, higher levels of reflected solar radiation ("Earthshine") - which again, could be possible with post-impact silicate gas atmospheric compositions - contributed to the side that always faces t
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"The actual study didn't say RADIANT heat from the Earth somehow magically went through the vacuum of space."
That's kind of what radiant heat does.
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Only the Sun is allowed to send those magic rays!
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Oops, my bad. It was quite late and I meant to type "RADIATING" heat, as in heat being transferred through a medium, as should be obvious from the rest of the comment.
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I was being a smartass, but if you insist... your comment is incorrect throughout. The paper refers to "earthshine" which today is dominated by reflected sunlight. But the point of that paper is that right after the collision that created the moon, earthshine was dominated by radiated heat from the Earth, not reflected radiation from the sun, meaning that the earthshine was much more intense than today. The takeaway from the paper is literally the opposite of what your post said:
"The actual study [did] s
Re:How could the Earth heat it? (Score:5, Interesting)
1 billion years ago the Earth had 100 to 1,000 foot tides as the Moon and the Earth were much closer
My initial response is "I don't think so." My second response is to calculate, so here goes:
Current distance to moon = 384,400 km = 4 x 10^8m
Current rate of increase in distance to moon = 3.8 cm/year = 4 x 10^-2 m/year.
If this rate were constant over a billion (10^9) years, then a billion years ago the distance to the moon was 4 x 10^-2m/year*10^9year = 4 x 10^7 m closer, or 10% closer. Tidal effect strengths are inverse-cube in distance, so a billion years ago, lunar tides would have been about 30% larger than now.
This doesn't come close to "100 to 1000 foot tides."
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My facts were quoted from a college level biology book. It was believed the tides were much bigger.
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I've shown the claim is implausible, not impossible. I'd be interested to see what evidence there is to support it.
I don't see the need for the claim from an evolutionary point of view: there is no reason I am aware of to suppose that current tides are insufficient to drive organisms to evolve into terrestrial niches.
Re:How could the Earth heat it? (Score:4, Interesting)
Good, but the rate of increase in distance to the moon isn't constant (it was faster in the past), and it's thought [cornell.edu] that the moon formed at a distance of only about 20 to 30 thousand kilometers.
By your maths, 4B years ago would've put the moon at 60% its current distance, but at formation it is more likely to have been only 6% of current distance. Assuming similar mass to today, 60% closer implies more like 4.6x the current tidal force - but 6% distance might be 4,600x stronger forces (probably more, given that the distance to the Earth's surface was even closer). How this translates into actual tidal sizes is left as an exercise for someone who knows more than I do.
Of course back then there probably wasn't much water around, given terrestrial temperatures in the thousands of degrees, but there may have been some impressive magma tides instead.
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What happened 4 billion years ago is not the point - the claim was made in the context of the 'conquest' of the land by multicellular life, which was only about 0.5 billion years ago (not 1 billion, as I used in my analysis, and so tides were likely only about 15% higher then.) I agree that tidal conditions were very different four billion years ago, and that my linear extrapolation would not apply so far back.
10% (for a billion years, or 5% for 500 million) is a small enough change in distance that we woul
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Wait, I thought that everything ever published that tells us exactly how evolution happened is totally accurate? Is someone suggesting that there might be some minor mistakes in those textbooks? What's next? Are we going to hear some nonsense about the global warming models not quite predicting today with 100% accuracy?
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Much more accurate than your assorted straw men, anyway.
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The rate won't be constant. The moon is gaining momentum by stealing it from Earth by raising tides. The closer the moon is, the larger tides is raises, which means it steals more momentum. The actual relationship is likely complex, but it's probably at least quadratic.
Those _are_ some old physics. (Score:5, Insightful)
I wish we still had physics like that today... these new-fangled ones just don't coalesce like they used to.
Blame the conservationists (Score:2)
Repeal SLoTD! Now!! (Score:2)
Tidal Lock (Score:1)
This theory would require the moon to be tidal locked very early in its history. I didn't think that was true.
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sweet mysteries of life (Score:2)
Heating from hot young things tends to cause chemical and crustal differences in my underwear.
Sorry. It's Sunday night and my fantasy team is in the toilet and I've been drinking.
Don't link to Forbes articles (Score:1)
Forbes articles display just a blank page for anyone running browser protections, a clear sign that Forbes' web admins are totally clueless since they can't even get static content through to viewer eyeballs.
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Hang on, you run settings/extensions that purposefully disable and remove functionality from a website and then blame the web developers for not giving you a satisfying experience? Do you also remove the tires from your car and blame the manufacturer for the bumpy ride?
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I am not sure to see the relation between being static (or not) and running Javascript.
Anyway, I would not qualify their page as being static so I guess that we probably do not have the same definition for that word.
PS: I am not one of the two AC parents
Did the moon form after the earth? (Score:2)
How do they know the earth was first fully formed and only then collided with something large causing the moon to form? I can imagine it was a bit of a jumble at the time but this claim seems a bit arbitrary. Why the need for a collision with something large? Was it something larger than the moon?
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That does sound implausible indeed.But moons forming in an accretion disk and gobbling up whatever was not absorbed into the center, that does sound acceptable. The earth also wasn't created out of a collision with the sun. Maybe they think the moon is too large for having formed the way other moons are formed.
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IIRC the main piece of evidence is the similarity of isotope ratios in the moon and Earth, and the rarity of heavy elements in the moon. The moon appears to be enriched in silicates, which are the bits that would have been floating on top of a proto-Earth.
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With these samples and a lot of remote sensing it became fairly certain that the moon is made up of similar material as the earth's mantle or crust.
An (logic) extrapolation of this points to the moon being ripped out of the earth after the separation between core and mantle had already taken place.
Even the creationists have it from their own source: http://biblehub.com/genesis/2-... [biblehub.com]
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How do they know the earth was first fully formed and only then collided with something large causing the moon to form? I can imagine it was a bit of a jumble at the time but this claim seems a bit arbitrary. Why the need for a collision with something large? Was it something larger than the moon?
It comes basically from the various theories on the formation of the moon. It could have been created in place, spun off of the earth, captured while it passed by, the result of a collision with another object, etc. So there were lots of different theories, and then there was the actual evidence dealing with the chemical make up of the moon, the orbital mechanics, the conservation of angular momentum, etc. Some theories were better than others and explaining the various facts. Some were much worse than the
Wow!!! (Score:2)
This article uses way too many exclamation points (I counted 12). Putting exclamation points at the end of every other paragraph doesn't automatically make something interesting and exciting. It just looks like the writer has no confidence in capturing the reader's attention without them!
Question... (Score:2)
Gravitational locking already? (Score:2)
Seriously? The moon is gravitationally locked now, sure, but the Earth (and moon) still being liquid/hot when it slowed to a lock? I don't think so. For this to be plausible the moon would have had to coalesce, in an orbit, with nearly zero spin angular momentum, which seems absurdly unlikely. Otherwise, like a bird on a rotisserie, it would have been "roasted" pretty much equally on both sides. So maybe, but I doubt it.
Stop linking to Medium (Score:3)
Well I guess Slashdot did finally stop linking to Medium. Though it looks like StartsWithABang just moved his personal blog to Forbes and now reposts everything he writes from there.
Nothing new (Score:1)