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Searching for Theia, the mother of the Moon
Dear Yousuf Khan:
On Apr 14, 9:50*am, Yousuf Khan wrote: Odysseus wrote: In article , Yousuf Khan wrote: snip But still wouldn't we see some sort of tail or other formation on Earth at the point where the Moon might have plopped off? I think we see a difference in crustal thickness on the Moon between its Earth-facing side and its space-facing side. But we don't see a similar crustal difference on Earth. Unless, we talk about the crustal diffences between the oceanic plates and the continental plates, but they're distributed all over the place. I wonder if the formation of the Moon started this entire continental plate business? The Earth remains tectonically active; convective and density-driven flows in the interior have had plenty of time to smooth out irregularities or asymmetries. As for the surface, the continents must have been rearranged or recycled at least a dozen times since the crust cooled -- so although there might be some traces left, they'd be so well buried or widely scattered as to be more or less undetectable. I'm thinking the existence of the continents themselves are the smoking gun. Pour water on the Moon, and you'll have "continents" too. They won't follow tectonic plates around... *Think about it this way, we know that there is an imbalance in the crust of the Moon, but there should be some sort of corresponding imbalance in the crust of the Earth which we don't see. The Earth kept the heavy materials, including fissible ones. The Earth had an insulating atmosphere. The Earth has a larger volume-to- surface-area ratio, so it will retain heat longer. We *can't* still show the results of a "parting line"... David A. Smith |
#32
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Searching for Theia, the mother of the Moon
In sci.astro message
ooglegroups.com, Tue, 14 Apr 2009 07:43:23, dlzc posted: On Apr 13, 8:03*am, Dr J R Stockton wrote: After your unsuccessful attempt to do that to me in the matter of the gravity tractor, it seemed appropriate to demonstrate to you how it should be done. *One essential is to be factually correct. I expressed concern over methods that a "gravity tractor" could push away the object it is trying to "pull". You did nothing more in addressing these concerns, than tell me I needed to do the math to show it was a problem. This sends the message that *you* had not done the math, and simply don't "feel" it to be an issue. If you received that message, your receiver is faulty. You asserted, necessarily without proof, that the path of the asteroid might be significantly affected, in comparison with the gravitational effect, by heat from the tractor; it is for you to prove it. Manifestly you cannot. In any case, it does not matter; because Big G is in fact not at all big, the intended propulsive force is small. Clearly the line of thrust must average aft-wards, and the bulk of the thrust must miss the asteroid. Therefore one could, if necessary, mount the engine on, essentially, a long pole in the line of thrust so that the engine itself was aft of the asteroid, and any repulsive force from it would be of beneficial sign. Or one might interpose a thin shield. Consider, in SI, an asteroid radius 50, density 2500, clearance between exhaust and surface 5, tractor mass 5000, optimally orbiting. The effective accelerating force is about 56 mN (gravity2.htm). Postulate that the amount of the tractor's radiation impinging on and absorbed by the asteroid could be equivalent to that from unit area at temperature 1000. The Stefan-Boltzmann constant is 5.7e-8, so the power is 5.7e4 (!!!); the force is that over c, or 0.19 mN. Less than 1 %; it still needs to be resolved into the direction of motion; and in taking the entire radiation from a square metre at a thousand K I've been very generous indeed. We are of course not considering a typical chemical rocket, which has a large hot engine; an electric engine will itself not be hot; its exhaust may be, but it will also be narrow, optically thin, or both. I don't want you to supply the math. I am not interested in "oneupmanship". I am not interested in being right. I am just interested in someone providing answers to questions. I personally thank you for being just like the pompous, cubicle-minded jerks that sent me here nine years ago. With enough effort, perhaps you can be speeded on your way. Usenet is no place for those with an inferiority complex, however well-justified it may be. -- (c) John Stockton, nr London, UK. Turnpike v6.05 MIME. Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links; Astro stuff via astron-1.htm, gravity2.htm ; quotings.htm, pascal.htm, etc. No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News. |
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Searching for Theia, the mother of the Moon
dlzc wrote:
Dear Yousuf Khan: On Apr 12, 10:05 pm, Yousuf Khan wrote: But still wouldn't we see some sort of tail or other formation on Earth at the point where the Moon might have plopped off? No, it was essentially all liquified. What if it was semi-liquified? Parts that are liquid, and parts that are still solid. Read why I'm suggesting that below. I think we see a difference in crustal thickness on the Moon between its Earth-facing side and its space-facing side. The Earth provides a temperature above the CMBR, and some tidal heating (before the Moon becomes tidally locked), so it would make sense that the Earth-facing side had thinner crust. But we don't see a similar crustal difference on Earth. Look where the tectonic plates are most finely broken. Unless, we talk about the crustal diffences between the oceanic plates and the continental plates, but they're distributed all over the place. I wonder if the formation of the Moon started this entire continental plate business? No, I'd put that squarely on structures internal to the Earth, upwellings in the core flows and such. I'm sure parts of the continents were produced by pure volcanic activity, like you say. But I think the extreme level of continentalization on Earth must've been started by the lopping off of the Moon. You just have to look at the planet most nearest our size, Venus, to see that it's got nothing near the continents we got. It's got two major continents, Ishtar Terra & Aphrodite Terra. Ishtar is only the size of the continental US, while Aphrodite is only half the size of Africa. I think Venus' continents were probably produced through just standard volcanic processes alone. Venus Global Geography http://www.windows.ucar.edu/tour/lin...ontinents.html Venus - What the Earth would have been like http://www.spacedaily.com/news/life-01x2.html However, I think Earth's continents were started by the scar left over from the Moon scission. Where the Moon plopped off the Earth, it left a scar which became the basis of Earth's continents. The scar on Earth is probably bigger than the area from which the Moon arose. And over the years, the scars (the continents) redistributed themselves all over the Earth through tectonics. Our own Trojan asteroids. Yes, an asteroid belt. But do we see anything like that for any planet? Jupiter? Good question. I know Roche limit would apply had the Moon started significantly closer... If the Moon plopped off of a super-fast spinning Earth, the moment the Moon left it might have reduced the Earth's spin substantially, and been thrown a large enough distance away to avoid the Roche limit. What would happen to Earth's (and the Moon's surface) if a "dust cloud" at about 1000K blew by outside the heliosphere over a period of a few centuries? This would allow the Sun to be an Easy Bake Oven (R), and gloss over all sorts of formation details... Sure, but why would you need a special dust cloud to blow by it? At that time wouldn't there already be a lot of dust in the vicinity since the Solar system was forming at the time? Yousuf Khan |
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Searching for Theia, the mother of the Moon
dlzc wrote:
Dear Yousuf Khan: On Apr 14, 9:50 am, Yousuf Khan wrote: I'm thinking the existence of the continents themselves are the smoking gun. Pour water on the Moon, and you'll have "continents" too. They won't follow tectonic plates around... They'll follow impact crater rims though. Think about it this way, we know that there is an imbalance in the crust of the Moon, but there should be some sort of corresponding imbalance in the crust of the Earth which we don't see. The Earth kept the heavy materials, including fissible ones. The Earth had an insulating atmosphere. The Earth has a larger volume-to- surface-area ratio, so it will retain heat longer. We *can't* still show the results of a "parting line"... No, we can't show the original continent, no doubt, but I think the existence of such large continents at all might be the clue that was just lying there right under our noses, literally. Under our feet even. Venus never grew continents quite as large as us. Yousuf Khan |
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Searching for Theia, the mother of the Moon
Dear Dr J R Stockton:
"Dr J R Stockton" wrote in message nvalid... .... With enough effort, perhaps you can be speeded on your way. Usenet is no place for those with an inferiority complex, however well-justified it may be. Further insults, and continued pirating of an unrelated thread noted. David A. Smith |
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Searching for Theia, the mother of the Moon
Dear Yousuf Khan:
"Yousuf Khan" wrote in message ... dlzc wrote: Dear Yousuf Khan: On Apr 12, 10:05 pm, Yousuf Khan wrote: But still wouldn't we see some sort of tail or other formation on Earth at the point where the Moon might have plopped off? No, it was essentially all liquified. What if it was semi-liquified? Parts that are liquid, and parts that are still solid. Read why I'm suggesting that below. I think we see a difference in crustal thickness on the Moon between its Earth-facing side and its space-facing side. The Earth provides a temperature above the CMBR, and some tidal heating (before the Moon becomes tidally locked), so it would make sense that the Earth-facing side had thinner crust. But we don't see a similar crustal difference on Earth. Look where the tectonic plates are most finely broken. Unless, we talk about the crustal diffences between the oceanic plates and the continental plates, but they're distributed all over the place. I wonder if the formation of the Moon started this entire continental plate business? No, I'd put that squarely on structures internal to the Earth, upwellings in the core flows and such. I'm sure parts of the continents were produced by pure volcanic activity, like you say. I didn't say that, but those flows will have consumed the entire crust of the planet over billions of years. If you want to look for ther remains of "Mu", you'd need to look at subduction zones, like north of New Zealand. But I think the extreme level of continentalization on Earth must've been started by the lopping off of the Moon. Who says the opposite is not closer to the truth? You just have to look at the planet most nearest our size, Venus, to see that it's got nothing near the continents we got. It's got two major continents, Ishtar Terra & Aphrodite Terra. Ishtar is only the size of the continental US, while Aphrodite is only half the size of Africa. I think Venus' continents were probably produced through just standard volcanic processes alone. Hard to see a strong parallel. However, I think Earth's continents were started by the scar left over from the Moon scission. Where the Moon plopped off the Earth, it left a scar which became the basis of Earth's continents. .... or the floor of the Pacific ocean. The scar on Earth is probably bigger than the area from which the Moon arose. And over the years, the scars (the continents) redistributed themselves all over the Earth through tectonics. You keep saying this, but there is no evidence of rock this old, or concentrations of materials "idenitical" to that from which the Moon is made. Our own Trojan asteroids. Yes, an asteroid belt. But do we see anything like that for any planet? Jupiter? Jupiter is the major player, and I suspect assures that nothing inside its orbit is stable long term. Maybe it could have forced a slow migration of an Earth-trojan Theia into a collision... Good question. I know Roche limit would apply had the Moon started significantly closer... If the Moon plopped off of a super-fast spinning Earth, the moment the Moon left it might have reduced the Earth's spin substantially, and been thrown a large enough distance away to avoid the Roche limit. Roche applies to gravitationally bound objects. An object that is entirely liquid could get some additional "attraction" from self-affinity... What would happen to Earth's (and the Moon's surface) if a "dust cloud" at about 1000K blew by outside the heliosphere over a period of a few centuries? This would allow the Sun to be an Easy Bake Oven (R), and gloss over all sorts of formation details... Sure, but why would you need a special dust cloud to blow by it? Insulation between the Earth and the Sun lowers our temperature. And there was a post recently that the Earth is passing through such a dust cloud, if not as thick as it would need to be. At that time wouldn't there already be a lot of dust in the vicinity since the Solar system was forming at the time? Only dust outside our orbit places us "in the oven". David A. Smith |
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Searching for Theia, the mother of the Moon
"Yousuf Khan" wrote in message ... dlzc wrote: Dear Yousuf Khan: On Apr 14, 9:50 am, Yousuf Khan wrote: I'm thinking the existence of the continents themselves are the smoking gun. Pour water on the Moon, and you'll have "continents" too. They won't follow tectonic plates around... They'll follow impact crater rims though. Only in "local detail". The gross structure is different: http://rst.gsfc.nasa.gov/Sect19/Sect19_3.html Think about it this way, we know that there is an imbalance in the crust of the Moon, but there should be some sort of corresponding imbalance in the crust of the Earth which we don't see. The Earth kept the heavy materials, including fissible ones. The Earth had an insulating atmosphere. The Earth has a larger volume-to-surface-area ratio, so it will retain heat longer. We *can't* still show the results of a "parting line"... No, we can't show the original continent, no doubt, but I think the existence of such large continents at all might be the clue that was just lying there right under our noses, literally. Under our feet even. Venus never grew continents quite as large as us. If the Earth+Moon mass lobed, not single but double, then the supercontinent that spawned all of ours today was likely *opposite* where the Moon departed. David A. Smith |
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Searching for Theia, the mother of the Moon
In sci.astro message , Tue, 14 Apr 2009
17:30:10, John Park posted: Dr J R Stockton ) writes: In sci.astro message , Sun, 12 Apr 2009 16:52:19, Yousuf Khan posted: Dr J R Stockton wrote: Any gravitationally-bound two-body system has five Lagrange points; if the mass ratio is less than about 25:1, or if there are other sufficiently massive bodies near by, no points are dynamically stable, except in special cases - in which case they would not be the points for which Lagrange is known. What's special with the 25:1 mass ratio? The arithmetic is non-trivial. The actual figure is from 27(m1m2 + m2m3 + m3m1) = (m1 + m2 + m3)^2 as m3 - 0 m1^2 - 25 m1m2 + m2^2 = 0 so m1/m2 = 25 ± Root ((625-4) / 2) = 24.9599 . ^^^^^^^^^^^^^^^^^^^^^^^^ ( 25 ± Root (625-4) ) / 2, I think. Agreed : transcription error. What's special about this limit, m3 -- 0, that makes it the case universally referred to? Any reason m2 = m3 shouldn't occur, for instance? One only gets a two-body system when one of m1, m2, m3 is negligible. And that is the practical case. ISTM that Lagrange would surely have given some consideration to the more general case - and probably gave up on it quite rapidly; or else almost no-one could understand him on it. The further the mass of m3 gets from zero towards the masses of m1 and/or m2, the less "Lagrange" the points become; AFAIK, they may merge, fizzle out, or wander off to infinity. Read http://groups.google.com/group/rec.a...earch?group=re c.arts.sf.science&q=In+order+to+be+stable%2C+the+m asses+of+the+three+bod ies+must+obey+the+formula&qt_g=Search+this+group ! -- (c) John Stockton, nr London, UK. Turnpike v6.05 MIME. Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links; Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc. No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News. |
#39
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Searching for Theia, the mother of the Moon
In sci.astro message , Tue, 14 Apr 2009
18:44:01, Yousuf Khan posted: However, I think Earth's continents were started by the scar left over from the Moon scission. Where the Moon plopped off the Earth, it left a scar which became the basis of Earth's continents. The scar on Earth is probably bigger than the area from which the Moon arose. And over the years, the scars (the continents) redistributed themselves all over the Earth through tectonics. An impactor of the postulated speed size, and angle would have left the Earth's crust and much of the mantle, at least, substantially molten for many millennia, AIUI : and the Moon was not "excavated" as a lump, but accumulated from material splashed into orbit. Remember, any body which falls from infinity and is not slowed significantly by the atmosphere will hit the Earth's surface at 40,000 kph or more, substantially greater than the speed of sound in a solid. The impact is by no means as gentle as is flying a supersonic plane into a substantial cumulo-granite formation. If the Moon plopped off of a super-fast spinning Earth, the moment the Moon left it might have reduced the Earth's spin substantially, and been thrown a large enough distance away to avoid the Roche limit. A super-spinning Earth could not have accreted; an impact large enough to speed it up that much would spatter it. Spinning-up a gravitationally-bound ball would cause material in a multitude of relatively small pieces to pour up off the Equator; only a ball bound by uneven solid strength could come apart in lumps. -- (c) John Stockton, near London. Web URL:http://www.merlyn.demon.co.uk/ - FAQish topics, acronyms, & links. Correct = 4-line sig. separator as above, a line precisely "-- " (SoRFC1036) Do not Mail News to me. Before a reply, quote with "" or " " (SoRFC1036) |
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Searching for Theia, the mother of the Moon
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