Talk:Giant-impact hypothesis/Archive 1

Initial text
I was the one who originally made the edit link to this article several months ago but.... shouldn't the "I" in "impact" be lowercase per wikipedia naming conventions? What does everyone else think? --maveric149

If you want to treat "Giant Impact Theory" as a title, then capitalize it all. If you want to treat it just as a description, lowercase it all. Either seems reasonable to me, but in any case, an uppercase "I" and lowercase "t" is clearly incorrect. --LDC

Isotopic evidence
I am absolutely positive that there is a large volume of scientific research on the isotopic and radioisotopic composition of the moon, and that there must be some evidence in particular which is used to support this hypothesis. This includes Lu-Hf ratios from lunar basalts and anorthosites, etc. I don't have much access to the literature, but I think that the isotopic side of the evidence is a particularly poor oversight in this article.Rolinator (talk) 07:29, 29 September 2008 (UTC)

Secondary core
In my opinion "giant impact theory" has too many variables.The Moons origin can be explained by more subtle means.The Moon was born from a secondary core. The force of the young sun erupting on the embryonic Earth core would produce a bow shock wave and wake. In the wake of the Earth a secondary core would form. The position of the Lunar core at birth was dictated, it was naturally placed amoungst the lighter elements in the protoplanetary disc.When the Sun again became subdued, the Earth and Moon orbited the sun as separate planets .As the Earth grew at a faster rate than the Moon,it was forced to migrate away from the sun and gained on the Moon.,This caused a collision of forces on both planets the resulting clash of forces created the tilt of axis we see today,this clash of forces is also the trigger mechanism for the lunar orbit. &mdash; paulhesq

That is a modification the rejected theory of simultaneous formation, with a touch of planetary migration -- neither of which is supported by evidence. ....................................... If you accept as a power law that dense material takes up positon in eye of the main disc and lighter elements at the outer, then disloged heavy molten core material thrown out amongst the lighter material would be swept along by the disc and spiral back 'toward' the sun. Heavy molten material woud also have increased gravatational force on the lighter elements and so the planet would form more quickly. User:paulhesq

Of the three original theories of formation: (1) capture (2) spin-off and (3) simultaneous formation in the neighborhood, it has the same issues that cause both (1) 'and' (3) to be rejected. The Moon in this "secondary core" theory shouldn't be less dense than Mars, and should have comparable water and other volatile content. Furthermore, the intricate dynamics of planetary migration affect the larger masses of the OUTER solar system and involve transfers of angular momentum between scattered objects, Saturn, Uranus and Neptune. There is no equivalent mechanism available for Venus and Earth that would move Earth so far as to go to a position where an object as dense as the Moon would have coalesced on its own. And again, then the same impossibility of explaining current Earth-Moon system angular momentum that rejects (1) rejects "secondary core"--Sturmde 22:39, 22 October 2005 (UTC)

Single continent
I have very little knowledge of this subject, but would this be the reason there was one large continent? Is that what is meant by saying that the continents are made of a different type of rock than the ocean floors? the continents are the leftovers of the impact point? - Omegatron 18:53, Jan 9, 2005 (UTC)


 * There is no known relationship between there having been one single continent and this impact. Actually, from the composition of meteorites it appears that Earth should have a lot more of the less dense rocks which make up the continents.  The Moon has a lot more of such lighter rocks than it should have.  From your question about continents being leftovers of the impact point, perhaps you're thinking that the Earth was mostly nickel-iron and the impactor was made of lighter materials.  We don't know, but it seems quite unlikely for Earth to have not had many of the less dense materials.  Also, with such an impact, it seems unlikely that the impact site would have left much of a trace.  In addition, continents are not a single piece of rock, and there have been many slow additions to continents detected.  Start with craton for more info. (SEWilco 22:40, 30 May 2005 (UTC))


 * There was speculation at one point (1960s?) that the Pacific ocean basin could be a scar left over from the formation of the Moon. This was before plate tectonics was understood.


 * Also, Pangea coallesced from smaller continents, which were formed in the breakup of another mega-continent called Rodinia about 750 Ma (million years ago). Rodinia in turn had formed from the fragments of an even earlier supercontinent, and so on. However, the further back you go, the less continent there is, because while oceanic crust gets recycled, continental crust keeps growing. (Volcanic islands plastered onto the margins of continents add to their bulk.) It's speculated that very early in the Earth's history there were no continents at all; it was all oceanic crust.


 * If the Earth had kept all the lighter rocks that ended up in the Moon, we might have a lot more continent today. That could be a bad thing: without as much room for the plates to move around, continental drift could've stopped a long time ago, and the Earth might be much more like Venus. kwami 07:42, 2005 May 31 (UTC)

Discuss article, not theory

 * This page is for discussion of the Wikipedia article on the giant impact theory. It is not for discussion of the theory itself.  --Doradus 02:56, Jan 28, 2005 (UTC)
 * Is there some reason Omegatron shouldn't be allowed to call attention to questions they feel are raised by and could be addressed in the article itself? --John Kenneth Fisher 03:00, May 30, 2005 (UTC)
 * I hope I didn't give that impression. --Doradus 02:29, Jun 1, 2005 (UTC)
 * My apologies if I misread that then. :-) --John Kenneth Fisher 22:06, July 16, 2005 (UTC)

Probability. The trigger method for the birth of our moon is more likely to be action of the young Sun rather than some stray Mars sized planet impacting the Earth at a certain time, at a certain angle, at a certain speed. User:paulhesq

Read Delano's Discovery, search Wikipedia for a new look at the Earth-moon discussion. [John Delano Dec, 18, 2006]

References needed
This article is too good not to have any external links or references, We need the references that are referred to in the text, for a start. --Wetman 02:30, 28 Jan 2005 (UTC)

Animation direction
Doesn't the animation show the moon orbiring the earth in the wrong direction? I am assuming that we are looking "down" on the north pole as most literature show.

Common people, if you're going to put forth serious arguments, then you have to present the current facts correct. If Theia started at L4, then the animation is showing the Moon orbiting the Earth in the wrong direction!


 * Then we are looking up. ;)

Sure, we're looking at the south pole - but the Lagrange points are mislabeled. L4 is ahead, and L5 behind the main body. This has gone unfixed long enough - people have been commenting on this for a year! I'm going to relabel it. kwami 18:43, 30 September 2005 (UTC)


 * Actually, I asked Muriel (the artist) to relabel it. Also changed the text to say that L4 & L5 are mislabeled, rather than saying that the moon is going in the wrong direction. Most people could care less about which Lagrange point is which (who couldn't make that mistake?), but having the moon going in the wrong direction makes us sound like dimwits, even if they're the same thing. kwami 19:17, 30 September 2005 (UTC)


 * I think that the two figures are highly redundant, and suggest removing the animation. Also, the theory that the Moon formed at one of the Lagrange points is VERY new (published this year or last). While this hypothesis is somewhat attractive, the theory is in its infancy, and I find the overemphasis given to it in this article somewhat disturbing. Lunokhod 09:47, 15 November 2006 (UTC)

Date of impact 4.533Ga
The author of the article might want to incorporate this reference.

Conclusions: Luna is less than 65% Theia; impact occurred 4.533Ga.

Evolution of Planetary Cores and the Earth-Moon System from Nb/Ta Systematics Carsten Münker, Jörg A. Pfänder, Stefan Weyer, Anette Büchl, Thorsten Kleine, and Klaus Mezger Science 4 July 2003; 301: 84-87 [DOI: 10.1126/science.1084662]

Abstract It has been assumed that Nb and Ta are not fractionated during differentiation processes on terrestrial planets and that both elements are lithophile. High-precision measurements of Nb/Ta and Zr/Hf reveal that Nb is moderately siderophile at high pressures. Nb/Ta values in the bulk silicate Earth (14.0 ± 0.3) and the Moon (17.0 ± 0.8) are below the chondritic ratio of 19.9 ± 0.6, in contrast to Mars and asteroids. The lunar Nb/Ta constrains the mass fraction of impactor material in the Moon to less than 65%. Moreover, the Moon-forming impact can be linked in time with the final core-mantle equilibration on Earth 4.533 billion years ago. kwami


 * The anonymous contributor of the above did not explain that the ratio suggests that both the Earth and the Moon were subjected to unusually high pressures. Under this pressure, some Nb combined with mantle materials which it otherwise does not react with.  The Moon's ratio being higher than Earth also suggests that its material was subjected to somewhat less pressure. (SEWilco 06:57, 1 Jun 2005 (UTC))
 * Sorry for being anonymous. (I only wrote the first two lines, of course.) kwami 2005 July 7 19:08 (UTC)

Why subtle growth?
Why formulate a subtle process of growth to explain the Lunar birth?

The accretion of planets is simply a process of growth, all such processes are subject to abnormality. Sometimes the trigger event for change is a monumental, sometimes change is triggerd by more subtle means. It is more probable that the instability of a young Sun triggerd the birth of our Moon. Co-accretion theorys have been dismissed in the past becaus they have failed to answer the density question. If all science had was a tadpole, might it be mistaken for fish fry? It would take a great deal of imagination to envisage the adult frog and its various stages of growth. Why does the Moon have to be born orbiting the Earth? If the young Sun suddenly erupted on the Earths magma core, a bow shock wave and wake would form. In the wake,in the shadow of the Earth a secondary core would form..... Primary secondary shadow accretion. paul.


 * I suppose compared to solar energies, Giant Impact could be called subtle. Is there an article about shadow accretion? (SEWilco 05:13, 1 Jun 2005 (UTC))


 * Any material in the shadow would quickly drift out of shadow (by 'quickly' I mean in a matter of hours), because it's in a different orbit around the sun. Different material would be in the wake at different times. And even if it were to form a second core, it would still have to be captured into Earth orbit, and the angular momentum's all wrong for that. Lots and lots of speculation like this has gone into the moon, but the physics just doesn't work for most of it. kwami 2005 July 7 19:16 (UTC)

corrected image
Since I haven't heard back from the author, I went ahead and swapped the Lagrange points in the image, so they're labeled correctly for viewing the south pole. kwami 07:26, 28 November 2005 (UTC)

Getting the moon into a full orbit
I don't get it. Where is the moon (or the debris that eventually formed it) supposed to have gotten the second boost neccesary to achieve orbit? We have the impact event performing the "launch" (flinging the material off of earth's surface), and then we need an other boost around the apogee to raise the perigee above the surface and achieve orbit, or else the material will fall back to Earth (difference between sub-orbital and orbital spaceflights gives some info on this). I know that Tidal acceleration is widening the moon's orbit, but that would be much too weak to give a boost in one orbit. 12.37.33.3 03:49, 18 March 2006 (UTC)


 * There is no second boost, of course. I would guess that the momentum of the original body is involved, and that not all of the material in orbit is actual impact ejecta. It would be nice to have this clarified. kwami 04:27, 18 March 2006 (UTC)


 * No second boost UNLESS you subscribe to the theory that aliens launched the material into orbit and constructed it there. (Broad grin, Tongue very firmly in cheek). But in all seriousness, Could you elaborate on your previous statement? How would the momentum of the original body help (it would set up the first boost, but not the second as I see it), and what about this non-ejecta material? 12.37.33.3 05:46, 18 March 2006 (UTC)


 * Not much to elaborate on, since I didn't realize I didn't understand this until you brought up the question. In simulations I've seen, large amounts of the mantle of the colliding body 'skip' off the Earth and enter orbit. Not all of it is ejecta from the impact basin. Also, part of the linear momentum of the colliding body becomes the angular momentum of the system, and the barycenter shifts from the center of the Earth to somewhere outside that point, so that the shape of an orbit would have changed while the material was in orbit. Perhaps that had something to do with why the material didn't follow an ellipse leading back to the point on the Earth where it started - the focus of the ellipse moved. kwami 08:35, 18 March 2006 (UTC)


 * But any application of thrust to an object in orbit raises the opposite side of the orbit. However hard the impactor hit the Earth, it couldn't raise the side of the orbit it hit on. It might send all the material off at escape velocity, but that's about all. Maybe the best option is a really hard impact: Blows both objects concerned to smithereens, and then the Earth and Moon form from the debris cloud. Differences in composition could come from irregular distribution of debris within the cloud. Linguofreak 19:40, 18 March 2006 (UTC)


 * Simulations suggest the heat of the impact melted the Earth's mantle to a depth of a thousand km, and some of the mantle went into permanent orbit (much more of course reimpacted), which makes this geologic time zero, but not so much that the Earth was actually disrupted. kwami 03:33, 19 March 2006 (UTC)


 * But I'm suggesting that we use a harder impact than called for by the normal theory, such as would disrupt the earth. I could understand how this might end up with two bodies in the end, otherwise I can't see how you could have any mass that didn't either fall to earth or end up on an escape trajectory. Linguofreak 04:53, 19 March 2006 (UTC)
 * There's no point. They didn't the math wrong just because we don't understand it. kwami 07:44, 19 March 2006 (UTC)


 * From the articles I've seen in Science, during the impact, the blob that settled down to form the Earth was in a transient state that was FAR from spherical, and that the gravitational pull of a massive, swinging lobe transfered some of its angular momentum to the blob that later settled down to form the Moon. This process took less than an hour. There are detailed dynamical simulations, of course; I'm just giving a verbal sketch of the pretty graphics. Harold f 06:01, 23 July 2006 (UTC)


 * OK, so basically a process analagous to the tidal widening (I forget the exact technical term for it) of the Moon's orbit. Interesting. That works. Still a bit surprising that you'd end up with a circular orbit, but I don't know enough about the subject to object. Linguofreak 14:06, 8 August 2006 (UTC)

deleted paragraph
I removed the following paragraph:


 * Other than the existence of the Moon itself, the primary legacy of this event, say researchers, is the fact that the Earth does not have enough of the lighter-colored felsic and intermediate rock-types to completely cover its entire surface. Thus we have continents made from felsic rocks and ocean basins which are made of the darker-colored, heavier and more metal-rich mafic rock types. This difference in composition along with the presence of water allows for an extensively active system of plate tectonics on the Earth. Others have postulated that the axial-tilt and initial rotation of the Earth had their origin at this time.

Continental rock is produced by tectonic subduction: rock melt separates, with lighter rock rising as magma and heavier rock sinking into the mantle. It is thought that the surface of the Earth after the Big Whack would have been entirely basaltic, and the quantity of continental crust is still growing today. That is, there may be enough lighter rock to completely cover the Earth's surface, but it has yet to separate from the mantle. Tectonics is thought to be possible because of the amount of water in the upper mantle. It's possible that without the impact there would have been more continental rock, enough to clog up tectonics, but I'd like to see a good reference for that before putting it in the article. kwami 08:14, 19 March 2006 (UTC)

Okay, maybe this was the source of the idea:. There are some serious problems here, and I don't think we can take it seriously. The basic idea is this: "Today the ocean basins cover 70% of the planet; light rock from the moon can be used to make up the difference and fill in the ocean basins; therefore if the moon hadn't formed there would be no ocean basins and therefore no tectonics." This reads like an updated version of the idea that the moon is the size of the Pacific Ocean basin, therefore the Pacific may be the scar left over from the formation of the moon. What is ignores is that the 70% figure is only valid today; it's not a quantity that's been "missing" since the impact, crust "stored over our heads". Also, the vast majority of the material blasted out by the impact fell back to Earth. This material was of the same type of rock as the moon, yet the continents didn't form till later. It's asking a bit much of coincidence to suggest that if that extra 1% had fallen back to earth instead of forming the moon, the continents wouldn't have evolved much as they have. The bulk of the moon is like the Earth's mantle, not like its continents. kwami 09:11, 19 March 2006 (UTC)

Original hypothesis?
The idea that the moon was a piece of the earth that had broken loose was suggested back in 1879 by the British astronomer George Howard Darwin (second son of Charles Darwin). However, Darwin believed the matter which formed the moon was pulled away from the still molten earth by solar tides, and not an impact. Sources: Encyclopaedia Britannica and Asimov's New Guide to Science (p159).


 * Yes, that is one of the older suggestions. Does it belong in an article about the giant impact?  (SEWilco 05:30, 25 August 2006 (UTC))


 * Darwin attempted to calculate the moment of separation of the Moon from Earth, based on the observation that the Moon's distance from Earth is steadily increasing. He was not able to complete the calculation further than the point where the two bodies were about 1,000 mi apart, however. This was discussed in a recent episode (The Moon) of The Universe series on The History Channel. And yes, this is of historical significance to the theory/article and should be included. — Loadmaster 17:01, 20 July 2007 (UTC)

Data correct?
The article notes: Current estimates based on computer simulations of such an event suggest that some 2% of the original mass of the impactor ended up as an orbiting ring of debris, and about half coalesced into the Moon between 1 and 100 years after the impact. 1-100 years for the moon to form? Sounds too short to me. Can any astro-oriented type people look at this? —Preceding unsigned comment added by SparhawkWiki (talk • contribs) 02:51, 25 August 2006


 * With a quick look I found these:  (SEWilco 05:17, 25 August 2006 (UTC))

Bungled jargon
"Theia is thought to have formed Trojan to Earth". In addition to the dreaded "is thought to" passive of non-attribution, the rest is jargon. Almost any change would be clearer and more stylish. --Wetman 03:26, 28 August 2006 (UTC)

No response. Does my edit better reflect what is intended in this use of "Trojan"? --Wetman 01:11, 8 September 2006 (UTC)

volatile elements
From the article main section: ''Evidence for this impact comes from rocks collected during the Apollo Moon landings, which show an oxygen isotope composition nearly the same as the Earth's mantle. Chemical inspection of those rocks found them to be nearly devoid of volatile and lighter elements... ''

From "Difficulties": The Moon's volatile elements are not depleted as expected from the giant impact hypothesis.

This seems inconsistent... 24.85.239.188 11:52, 13 September 2006 (UTC)


 * The cited source for the line in the difficulties section gives an example of volatiles that don't seem to match the hypothesis. The lunar Rb/Cs ratio, according to the author of the cited source, ought to be less than the terrestrial ratio, where in fact it is greater. Supposedly, Rb is more volatile than CS, and so its relative concentration should have been reduced. One would assume, then, that most of the lighter and more volatile elements are depleted and it is just the Rb concentration that doesn't match this trend. Clearly the author of that 'difficulties' point does not believe in the giant impact theory, and so construed evidence that one element isn't as depleted as it ought to be to mean that no volatiles are depleted. I will change the difficulties point by adding the qualifier 'some' to clear up this ambiguity. Harperska 23:44, 25 September 2006 (UTC)


 * The cited source is not dated. Latest reference is 1997.  Is 1997 before the more complex simulations, which I think suggest that most of the Moon came from the impactor?  The source says the ratios are based on the assumption that the Moon's material came from Earth.  (SEWilco 06:05, 26 September 2006 (UTC))

Textual Error?
The current first paragraph reads "The original hypothesis was first proposed in a paper published in Icarus in 1975 by Dr. William K. Hartmann and Dr. Donald R. Davis." However, I have (or had) and old textbook from the 1960s which proposed this same theory. The title of the book was The Planets, but I cannot give more information just yet (I don't have it in front of me, and may not own it anymore). Firsfron of Ronchester 22:50, 25 September 2006 (UTC)


 * In the 1960s one theory was that as the Earth formed and its rotation increased, the material which became the Moon was spun off. The Pacific Ocean was considered as possibly having been created by that event.  Did "The Planets" refer to an impact event or to the three non-impact theories of the creation of the Moon?  (SEWilco 06:20, 26 September 2006 (UTC))

Siderophile elements
I propose deleting the following sentence


 * If the bulk of the proto-lunar material had come from the impactor, the Moon should be enriched in siderophilic elements, when it is actually deficient of those.[5]

This is not a mainstream view, and the cited article was published in what some might consider the "gray literature." Several publications have used the depletion in siderophile elements as an indication that some form of core forming event processed either the Impactor, Earth, or Moon (after re-accretion). In fact, the siderophile element depletions have been used to place constraints on the size of the lunar core. The most recent publication discussing this is Righter (2002, Does the Moon have a metallic core, Icarus, 158, 1-13).

Also, some of the other "difficulties" are in fact not difficulties at all. In my opinion, the scientific calliber of this article is very low, the text is heavily biased towards the recent and not fully accepted Lagrange point hypothesis, and this needs to be heavily edited by an expert. Lunokhod 13:58, 15 November 2006 (UTC)


 * How gray is the 2002 G.K. Gilbert Lecture at the annual meeting of the GSA ? Dan Watts 20:05, 15 November 2006 (UTC)


 * If you read the original paper that was cited, you will see that there is only one sentence that discussess the siderophile element abundances of the Moon. The claim that is made is not supported by citations, or detailed reasoning. The paper is all the more bothering in that they do not even cite the Righter (2002) paper, even though this paper was published in 2005! They do not even quote the work by Canup and Asphaug (2001, Nature) or Canup et al. (2001, Icarus). I maintain that this article, which was published in the Indian Journal of Earth System Science is not well researched. As for the article by Jack Schmitt, this was not peer reviewed. Good sources of peer reviewed articles can be found in the book "Origin of the Earth and Moon". If you are looking for articles that are highly critical of the giant impact and lunar magma ocean hypothesis, look at the chapters written by J. Jones. I'll add this to the refernce list. Lunokhod 20:38, 15 November 2006 (UTC)


 * Is this the same J. Jones referenced as author of an LPS paper? Dan Watts 14:59, 21 November 2006 (UTC)

English Please?
The the following excerpt is so poorly written that I have no idea what it is saying:

Iron oxide (FeO) content of 13% of the bulk Moon properties rule out the derivation of the proto-lunar material from any but a small fraction of Earth's mantle.[4]

Could anyone who knows what its supposed say make this readable? —The preceding unsigned comment was added by 68.231.220.133 (talk) 08:29, 14 December 2006 (UTC).
 * I wouldn't believe this. This entire article is poorly written and does not represent a consensus of the scientific community. Concerning this point, though, there was a recent article in Nature by Rubie et al. (2004) showing that the bulk silicate portion of the Earth and Moon could have had the same iron content. The idea is that during the crystalization of a terrestrial magma ocean, FeO is partitioned into the core. Their results nicely predict the present day FeO content for the mantle's of Earth, Moon, Mars, and Vesta. When I get some time in the next month of two I am going to clean up this article. Lunokhod 16:07, 14 December 2006 (UTC)

Date
First proposed in 1975? I remember reading about this "discredited" theory in primary school, which would be at least four years earlier. I believe it is decades older. Rich Farmbrough, 12:00 13 January 2007 (GMT).
 * This is the correct date for the first publication. Lunokhod 12:24, 13 January 2007 (UTC)

Early terran oceans a problem?
I stumbled across this 2001 New Scientist article, which suggests that the discovery of a water-affected zircon crystal dated to 4.404 billion years presents "real problems" for the impact theory of lunar formation.

I see no mention of this in the article: should I assume that those problems have been overcome, one way or another, since then? Hv 04:18, 23 March 2007 (UTC)

Selective removal of sial
SEWilco removed the following excerpt claiming that it is a speculation: "The Earth's crust is made of two layers called sima and sial. Sima is the lower and denser layer. It is 5 to 10 km thick and covers the entire surface of the Earth. Sial is 20-70 km thick and covers only 30% of the Earth's surface; this is the elevated part of the Earth's surface called continents. The remaining 70% of the Earth's surface is covered with oceans. None of the existing theories explain how the sial was selectively scooped up from 70% of the Earth's surface and deposited on the Theia/proto-Moon."

Is there any proof that any part of this excerpt is a speculation? I would rather call it a glaring omission. SEWilco's activities on Wikipedia have been restricted by illegal, unreasonable, and arbitrary restrictions and enforcement.

15:27 & 16:00, User:Towelhead
 * The same mantle movements that caused continental drift, pushed all the sial together in areas. Anthony Appleyard 16:07, 26 March 2007 (UTC)

Sial is sometimes called granitic layer of the crust, because it is made mostly of granite, which is made mostly of silica (SiO2 content = 72%), which is the main ingredient of glass.

The temperature of Earth increases about 36 degrees Fahrenheit (20 degrees Celsius) for every kilometer (about 0.62 miles) you go down. Near the center, its thought to be at least 7,000 degrees Fahrenheit (3,870 Celsius).

The meaning of these facts is that the top 10 kilometers of the sial is made of hard and rather cool rock. It is too hard and too brittle to deform under pressure. It is difficult to imagine what could generate the enormous force needed to break and pile up the granite into a pile up to 70 km high. Furthermore, the sial part of the crust does not look like a messy pile of rocks, but like a solid, rather uniform layer of bedrock. Towelhead 01:44, 3 April 2007 (UTC)

Article title
Does anybody else feel that the appropriate title for this article would rather be giant impact theory than giant impact hypothesis? The actual hypothesis here is [The Moon] is thought to have formed as a result of a collision between the young Earth and a Mars-sized body (...), all the rest is the surrounding theory. Nick Mks 12:16, 9 April 2007 (UTC)


 * I would suggest giant impact nonsense, since – as an example – the Lagrangian points L4 and L5 don't have any importance in the orbit of Earth, since the gravitation of Jupiter is much larger compared to Earth's gravity in those points. Clearly, the orbits of the protoplanets can't be treated as three body problem, and hence the Lagrangian points have no meaning at all. 84.59.63.152 08:15, 14 April 2007 (UTC)


 * The theory of Theia forming at a Lagrange point is only a very recent hypothesis (2005) and certainly isn't as widely accepted as the overall hypothesis of giant impact. As others have pointed out, the Lagrange point idea probably has too prominent a position in this article. Sakkura 11:45, 26 April 2007 (UTC)

You misunderstand the scientific meaning of theory, which is "a logically self-consistent model or framework for describing the behavior of a related set of natural or social phenomena". A theory has far-reaching applications and great explanatory power: it is just short of "truth". Thus we talk of atomic theory, number theory, etc. Urhixidur 13:21, 14 April 2007 (UTC)

Remains of previous earth
If such an impact occured would anything have survived? Even more importantly would any traces of what was here before (life or maybe civilization) survive?
 * The impact with Theia is proposed to have occurred just 34 million years after the Earth formed, which means it happened while the Earth was still an extremely inhospitable place for life. After the impact, Earth would actually have had an atmosphere of rock for as long as two thousand years, and that means nothing could possibly have survived even if it had existed on the planet previously. Bear in mind that the asteroid proposed to have wiped out the dinosaurs had a diameter of 10 kilometers - Theia would have had a diameter of several thousand kilometers! Sakkura 10:47, 27 April 2007 (UTC)
 * Theia would have had a diameter of several thousand kilometers!That's exactly why I was wondering if any TRACE could have survived. Thanks for the answer —The preceding unsigned comment was added by 86.121.75.80 (talk) 14:48, 28 April 2007 (UTC).


 * Since the hypothesized impact would have more or less completely restructured the surface of the Earth, involving massive amounts of heat, I doubt there would be any traces left at all of whatever was on the surface before the impact. — Loadmaster 17:09, 20 July 2007 (UTC)

Removing the How did the moon get into orbit? link
The website is creationist propaganda: it is linked to by the Edinburgh Creation Group, was made by the maker of that site; the author clearly has creationist intentions, which are expressed in the site itself. On top of this, the argument he lays out on the page is clearly fallacious: he claims that a point-mass simulation is enough to render all theories of moon formation invalid. I'm about to remove the link. Spottedowl (talk) 22:26, 21 February 2008 (UTC)

Distance of newly formed moon from Earth?
It would be useful to add it to article. This source:

http://www.sciencedaily.com/releases/1997/09/970929051120.htm

mentions 14000 miles (about 22500km) from Earth (I assume that they mean from surface). But this article is from 1997. Someone have more actual data or this is same today? —Preceding unsigned comment added by 87.206.80.6 (talk) 22:19, 30 July 2008 (UTC)
 * By the way, how fast Earth rotated after impact? I remember something like 16 hours, read somewhere like 6 hour... IMHO I find this article lacking of important informations. --87.206.80.6 (talk) 12:38, 10 August 2008 (UTC)

Reference
What does the remark "Note: The source notes evidence that suggests there might never have been a global magma ocean even though such a collision would be sufficiently energetic to melt the entire earth, but the source doesn't explicitly rule out the existence of a magma ocean, either." on reference 6 mean? I don't think that the problem referenced concerns whether there was magma, but rather, if the entire earth's surface was ever molten. Unless I can be enlightened as to some other meaning, then I believe that this note needs to be removed. Dan Watts (talk) 03:13, 14 August 2008 (UTC)

And this means?
A belt of warm dust in a zone between 0.25AU and 2AU......

Just read through the article and came across the above highlighted - what the hell does that mean? Could someone add in some laymans terms or wikilinks or something?--EnigmaMcmxc (talk) 22:33, 8 December 2008 (UTC)

Merger
I suggest merging and redirecting Theia (planet) into this article, as all that article can really say is "Theia is the name given by many proponents of the GIH for the hypothesized Trojan planet." Any objections? NJGW (talk) 02:32, 17 January 2009 (UTC)


 * Contrary to your assertions, the article does contain more content than what you say. It discusses various factors that led to the collision, as well as Theia's fate.  Tealwisp (talk) 03:29, 12 February 2009 (UTC)


 * My assertion is that the articles should be merged; that the information is more useful to readers if it's centralized on one page, and that the two articles are short enough to exist as one. NJGW (talk) 05:11, 12 February 2009 (UTC)


 * It's been one month and no substantial reasons have been put forward. There is no information which would be lost from a redirect, so I will do this in one week unless there is a substantial reason not to.  NJGW (talk) 21:06, 19 February 2009 (UTC)


 * Unfortunately, one cannot check every article of interest on a weekly basis. Why were you in such a hurry to remove Theia (planet)? --Sturmde (talk) 18:14, 19 March 2009 (UTC)


 * In any event, the combination looks well-done. --Sturmde (talk) 05:14, 23 March 2009 (UTC)

I merged it. Theia (hypothetical planet) already links here and there was nothing in that article that wasn't in this one.  Serendi pod ous  08:05, 1 April 2009 (UTC)

"back to" vs "away from"?
"Darwin's theory was that a molten moon was spun out of a parent planet, based on his belief that Newtonian mechanics showed the Moon had actually orbited much closer to the earth and was moving away from the earth. This was proved later by NASA and Soviet tests. Darwin's calculations could not be resolved, however, in a way that carried the moon back to the surface of the earth."

Shouldn't this be "in a way that carried the moon away from the surface of the earth"? Or "in a way that did not carry the moon back to the surface of the earth"?

I think it's obvious what this should be, but I know that "obvious" is not necessarily "correct", and I know my limits. DS (talk) 13:59, 1 April 2009 (UTC)


 * No, the statement as written is correct. It means that Darwin's calculations showed that the Moon was gradually moving away from the Earth, but he could not resolve them in such a way that he could extend the Moon's path backwards in time to where it started on the Earth's surface.  That is, "...carried the moon back to the surface of the earth" means "took an imaginary film clip of the Moon's gradual path away from the Earth and ran it backwards to the beginning, where the Moon starts at the Earth's surface."  Fumblebruschi (talk) 23:07, 9 April 2009 (UTC)

moon's orbit as evidence supporting big whack theory?
i recall seeing print articles that included the moon's orbit, close to the ecliptic plane, as evidence supporting the "big whack" theory (and as evidence against a "spin off" which should result in a moon orbiting in the equatorial plane). yet i cannot seem to find an article mentioning it; perhaps it's too obvious. should it be referenced, perhaps with a "citation needed" tag?ctj (talk) 15:28, 5 June 2009 (UTC)

Other terrestrial bodies?
What are terrestrial bodies? Which bodies are referred to as "the other [besides the moon] terrestrial bodies" which contain a certain amount of iron? Unfree (talk) 18:47, 14 June 2009 (UTC)


 * terrestrial planet —Tamfang (talk) 18:19, 13 July 2009 (UTC)

Excuse me, I wonder whether one's considered Mars as being the responsible party for the impact resulting in the creation of the Moon and the extinction of [assuming there once was] life on Mars, and potentially the reason for life on Earth... Thank you

September, 7th 2009 2:55 Central U.S. —Preceding unsigned comment added by Dabrijo (talk • contribs) 19:56, 7 September 2009 (UTC)

(dabrijo)

Impactor tidal forces
how can a body orbit the earth and hit it "with a suitably low velocity" without being torn apart by tidal forces?


 * Obviously that depends on what "suitably low" means. --Doradus 18:53, July 15, 2005 (UTC)

Identical, not just similar isotopes.
From : The research group from the ETH Zurich have presented results of their analysis of 31 samples of various types of lunar rocks, which were brought back from the Apollo missions 11, 12, 15, 16 and 17. Isotopes are atoms of the same element but with different mass because of differing numbers of neutrons.

The oxygen isotopes O16, O17 and O18 in the samples were measured using laser fluorination. This technique was developed over the past decade and is ten times more precise than previous methods.

The oxygen isotope composition of lunar rocks had been measured long before but, encouraged by the availability of the new method, the ETH researchers decided to carry out new measurements.

They were astounded by their results. Uwe Wiechert, senior assistant at the ETH Zurich and first-named author of the Science paper, explains: "We wanted to investigate how homogeneous the moon is and whether the samples contained parts of the proto-earth and the planet with which it collided. We already knew that the earth and the moon have a very similar isotopic composition. We never expected, however, that they would turn out to be identical."

The composition of the oxygen isotopes can be used to determine the origin of the rocks within the solar system because the oxygen isotope compositions are not uniformly distributed. If two rocks have identical oxygen isotopic composition then the probability is great that they were formed from the same "parent planet" or formed from the same average mixture of solar system debris.

The characteristic composition of meteorites from Mars, for example, is different from that of the earth and the moon, or from any other bodies in the solar system. If two big bodies, such as the earth and the moon, have an identical oxygen isotope composition, they formed from an identical mixture of components and were formed at very similar distances to the sun.

87.194.131.188 (talk) 06:06, 29 August 2009 (UTC)

Perhaps they (the Earth and the Moon) are "identical" but is it possible they contain traces of an impact with Mars, and that maybe Mars contains remnants of an impact with Earth, resulting in the creation of the Moon?

Thanks,

(dabrijo) —Preceding unsigned comment added by Dabrijo (talk • contribs) 19:59, 7 September 2009 (UTC)

Citation Quality
The first citation is for a simple point yet it refers to a 21 page portion of a paper. This may all be relevant, but it is highly unusual to use such a large reference. Given the statement "preferred theory" one would think that the source of this specific piece of information would be more concise. Would an advocator of the source consider elaborating on the location of the relevant piece of information?

TokenPassport (talk) 00:25, 1 December 2009 (UTC)

"Big Whack"?!
Do such alternative names really need to be included? They sound like something a hatchling would come up with.  -RadicalOne •Contact Me•Chase My Tail 06:04, 31 January 2010 (UTC)


 * Looking it up it looks like it was first added to the article in Nov 2004. -- Kheider (talk) 07:27, 31 January 2010 (UTC)
 * I fail to see the importance of its date of addition.  -RadicalOne •Contact Me•Chase My Tail 16:54, 31 January 2010 (UTC)
 * Can I remove it? If there is no reply here within 24 hours I will go ahead with the edit.  -RadicalOne •Contact Me•Chase My Tail 02:38, 5 February 2010 (UTC)

pokemon Theory
Hi everyone. A few days ago I was watching a documentary about the different theories concerning the Moon. To my surprise, one of the theories it talked about was that life has already existed on the Earth (named Orpheus by then) before the arrival of the Moon, stating Octopus and a few other deep-sea invertebrates among the pre-Moon life forms. I've little time to get more about it on the net right now, and I'm sorry about forgetting the details, but I'd be glad if you could get more out of it as it seems an interesting missing point in this article. Thol Garanin (talk) 10:32, 22 March 2010 (UTC)
 * At first glance that seems just a tad far-fetched. First you would need to evolve complex multi-cellular life forms within a few million years on a planet that was still cooling down from coallescence. Next, you would also need a way for those life forms to survive an enormously energetic impact that supposedly removed most of the volatiles from the surface, and a good chunk of the crust. Finally, those creatures would need some place to survive up until the ocean was recreated by comet impacts. I'd speculate that it is more likely that simple bacterial life forms may have evolved prior to impact, but nothing more. But this theory would need significant evidence to be demonstrated viable; otherwise it just seems like pure fantasy.&mdash;RJH (talk)
 * You're right. But it talked about a body half hitting and half getting trapped by an Earth with oceans; The theory's reasoning was the observation that these species had no biological dependence on the then irregular spinning of the Earth, nor did they depend on tides and moon's gravity. I'm sorry for ambiguity, but the very thing that has surprised you has surprised me too, and I'm trying my best to get the truth out of it. As I can remember, it was a NASA documentary, but I've fogotten the title. I'd be glad if you could look around the net a for some cues. Thol Garanin (talk) 08:55, 23 March 2010 (UTC)
 * Yes. It's an intriguing idea, almost like a variant of panspermia. But to have entirely separate biological lineages, I think you'd have to show that their DNA are unique. I don't believe that has been demonstrated yet, since the DNA of all life forms thus far examined appears to be traceable back to a single root. (Which would apply to the Octopus as well.) But I understand one group is looking for the existence of truly "alien" DNA in the biosphere.&mdash;RJH (talk) 16:05, 23 March 2010 (UTC)
 * One penultimate last thing. I found the name of the documentary; it is named "The Moon", from the Episode 1 of the series "The Universe" on the History Channel; It would be nice if you could perhaps give it a look. The theory I have talked about is near the ending minutes. I will be awaiting your watching and verfication. Thol Garanin (talk) 08:21, 25 April 2010 (UTC)
 * "The Universe" has had 4 complete seasons already so I might remember watching that episode ~4 years ago. But I do not think any proto-planet will develop complex life (say the Jelly fish or better) in less than 1 billion years.  I also think simple bacterial-like life is fairly common in the Universe and that the moons influence (requirement for intelligent life) is way over rated by the narrow-minded geocentric human viewpoint. -- Kheider (talk) 13:23, 27 April 2010 (UTC)
 * Also, sadly, I find that some of the History Channel content can be decidedly fringe, if not outright crank. I think it would be better to use a more reliable primary source for speculation of this nature.&mdash;RJH (talk) 16:05, 27 April 2010 (UTC)
 * Surely the important question here is what temperature the Earth was prior to the collision. As I understand it (and please let me know if I'm wrong) the Earth was still incredibly hot when this collision happened, as it had only formed a few hundred million years before. If the surface temperature had not cooled to less than 100 degrees before the collision, then without liquid water the evolution of life would be very close to a total impossibility. Kernow (talk) 03:33, 17 June 2010 (UTC)

Picture that needs a better caption
This picture, File:Big splash 3d.gif, could use a better caption. To me it looks like four circles, two red and two blue, with no further obvious meaning. The current caption simply says "Theia". I have no idea what it is trying to illustrate. Pfly (talk) 09:13, 12 April 2010 (UTC)
 * I agree, it makes no sense.&mdash;RJH (talk) 23:01, 25 April 2010 (UTC)
 * There was no objection, so I removed it.&mdash;RJH (talk) 16:01, 28 May 2010 (UTC)

Collisions and Commonsense
Where has the commonsense gone to in science? If natural satellites were formed by collisions, there is no reason why Mercury and Venus wouldn't have them. Now is it a coincidence that these two planets, the only two which rotate slowly due to gravitational braking by the sun, are also the only two which have no satellite? Given 8 planets, thats 1 chance in 28 or about 4%. Clearly satellites are formed by equatorial spin-off when an accreting planet starts to spin too rapidly. Thats why the moon bears close resemblance to the upper earth but not the mantle, and no resemblance at all to impacting bodies which would have generated great heat and introduced material which would have caused the moon's chemical signatures to deviate greatly from the Earth's...which they don't.

This 4%, by the way, is and always was the probability that the collision theory is correct (the Mercury-Venus observation)-- leaving a probability for the correctness of the equatorial spin-off theory of 100-4 =96%.

Great fads like the collision theory come and go. They have always done so, and indeed this is, in large measure, how science gets done. But phases are for passing through!! —Preceding unsigned comment added by 142.161.207.211 (talk) 18:33, 17 January 2011 (UTC)
 * Well, this is a little off topic for this page, which is supposed to be about improvements to the article. But I'll try to respond to your issues without turning this into a flame war. My way of looking at science is that it is a set of tools to correcting for human biases and sometimes faulty reasoning. Sure, common sense has a role: in suggesting which hypotheses to test. But if the tests contradict a hypothesis, then the hypothesis needs to be corrected or discarded. I think that is what the page is trying to address.


 * As for why Mercury or Venus don't have satellites, well I'd suggest that the particular collision needed to produce a Moon-like satellite may be of low probability. However, suppose for any one planet it is 50%, which is a fairly high probability, then the odds of Mercury, Venus and the Earth all having such a moon is only one in eight. That's pretty low. Now suppose you reduce it further to one chance in nine (which I saw in a journal somewhere) of an Earth-like planet having a Moon-like moon, then the odds of exactly one of Mercury, Venus or the Earth having a large moon is: (3 choose 1 => 3) × (1/9)1 × (8/9)2 = 26%. The odds of more than one moon: ((3 choose 2 => 3) × (1/9)2 × (8/9)) + (1/9)4 = (3 × .012 × .889) + 0.002 = 3%. So there is greater likelihood of being just one moon. There is good evidence that having a Moon is why we even exist, so odds are good that we would be on a planet with a Moon.


 * Yes, it may all just be about probability.&mdash;RJH (talk) 19:56, 17 January 2011 (UTC)

Oblique angle
Currently the text says the following:
 * Theia is thought to have struck the Earth at an oblique angle.

Well, virtually every angle is an oblique angle, so this doesn't really tell the reader much. The probability of a non-oblique collision should be virtually, if not exactly, zero. I'm guessing that the most likely type of collision (based on cross-sectional areas) is closer to a grazing impact than a down-the-middle impact, although I'm not certain about the effects of last minute gravitational perturbation.

Is there some information that could be used to clarify the above statement in the text? Maybe somebody has computed a collision probability function? Thank you.&mdash;RJH (talk) 16:00, 28 May 2010 (UTC)

Ga
What is Ga? This appears to be some sort of unit of time working backwards from the present. However, no definition is given, and there is no link to a Ga page. —Preceding unsigned comment added by 71.164.94.128 (talk) 19:04, 6 July 2010 (UTC)


 * Gigaannum now linked - there is an explanation after the first use, 'billion years ago', but an internal link is worth having as well. Mikenorton (talk) 19:19, 6 July 2010 (UTC)

ridicululous, my user page has a better hypothesis.--Murriemir (talk) 23:02, 9 August 2011 (UTC)

Theia = Orpheus
& what happened to Theia? Böri (talk) 07:54, 28 October 2010 (UTC)
 * Are you asking about this edit?&mdash;RJH (talk) 18:00, 28 October 2010 (UTC)


 * Thank you... No, I asked what happened to Theia(protoplanet)? Böri (talk) 06:30, 29 October 2010 (UTC)


 * It appears that Theia (planet) was merged into this article. (Old article) -- Kheider (talk) 14:45, 29 October 2010 (UTC)


 * :) Thanks! Sorry, I was asking: "What happened to Theia (protoplanet) after the collision?" Böri (talk) 17:22, 29 October 2010 (UTC)


 * Oops. Most of Theia (especially the heavier elements) combined with the Earth. Some of the Earths mantle and lighter elements from Theia reformed in space as the Earth's moon. -- Kheider (talk) 17:38, 29 October 2010 (UTC)


 * Thank you Böri (talk) 07:11, 30 October 2010 (UTC)

Alternate Hypotheses
It seems to me that one of the major alternate hypotheses, by Rob de Meijer, should at least be mentioned: that is a massive nuclear explosion ejecting the moon's mass. There are better articles than what follows (Google Rob de Meijer) -- and more standard ones (such as APS), but perhaps Cosmos magazine best explains the hypothesis. http://www.cosmosmagazine.com/features/print/2421/birth-moon. Maybe it should be mentioned, somewhere? 72.66.255.186 (talk) 03:59, 4 April 2011 (UTC)MJR
 * You'll have to provide a reliable source, and this isn't one. It's a "retired geophysicist" sitting in his farmhouse espousing what appears to be a fringe theory.  If more scientists jump on board, then maybe we can include it.   Orange Marlin  Talk• Contributions 05:34, 4 April 2011 (UTC)


 * Fringe indeed, since it requires either an unnatural aggregation of an incredible mass of nuclear fissile material, or some weird physics where local nuclear fusion explosions may occur outside the sun. Extraordinary claims require extraordinary proofs. Rursus dixit. ( m bork3 !) 07:58, 25 April 2011 (UTC)

Am I in error?
I've lurked around this article for a while and noted that it presents the theory as implying that some material from Theia coagulated to Moon. My impression is instead that the theory implies that Moon is almost entirely made from Earth crust, and that Theia was engulfed by Earth. Quite a few of the arguments against the GIH then become invalid. Rursus dixit. ( m bork3 !) 07:58, 25 April 2011 (UTC)


 * OK, that "fringe" link to cosmosmagazine in the previous post gave me a hint: it might be correct that the theory propones that Moon is made from Earth crust, but some important computer simulations instead indicate that Moon is made mostly from Theia mantle, which is hard to reconcile with the isotopic data on Earth and Moon. The article is missing information on these computer simulations, so the logic of the article is unclear, and somewhat distorts the original impact theory. I think this should be clarified. Rursus dixit. ( m bork3 !) 08:10, 25 April 2011 (UTC)


 * Yes, some information about the proportions each contributed would be useful, if it is available. However, if the original Earth and Theia were formed in the same part of the planetary disk, their compositions might not be that different.&mdash;RJH (talk) 18:59, 25 April 2011 (UTC)

Giant impact hypothesis
I have deleted this comment as I put it in here in error instead of under the rare earth hypothesis. —Preceding unsigned comment added by Dudley Miles (talk • contribs) 14:45, August 31, 2008

"Other remaining questions include: when did the Moon lose its share of volatile elements and why does Venus, which also experienced giant impacts during its formation, not host a similar Moon?"

isn't the answer that the sun's gravity well is too strong? — Preceding unsigned comment added by 66.108.202.193 (talk) 04:45, 17 January 2012 (UTC)

Please check my changes to the lead.
I changed a number of things in the lead to try to simplify it.

My goal was to have the three paragraphs accomplish:
 * 1) introduce what it is
 * 2) explain why it is the current favorite model
 * 3) introduce the difficulties.

I thought that the balance of the abstract was too shifted toward being against the hypothesis so I tweaked it a little. My knowledge of this comes mostly from teaching out of popular general education Astronomy textbooks like Universe and the Cosmic Perspective. If I erred too far or not enough in shifting the weight, then any corrections would be greatly appreciated.

The recent research on the possibility of two collisions forming the difference between the near and far side seemed too speculative and new and definitely too detailed for the lead so I moved it to a different section. I still don't have a good name for this section. (Alternate extensions?) I don't like the one I chose (after) but I don't have a better idea.

TStein (talk) 21:57, 19 October 2011 (UTC)
 * Your edits seem fine to me. I agree that the new hypothesis about a subsequent collision, while intriguing, is secondary to the main thrust of the article. It isn't necessary to explain the existence of the Moon, although in some sense it may provide supporting evidence for the collision process. Regards, RJH (talk) 22:10, 19 October 2011 (UTC)

Moon rotation
Computer simulations of the “giant impact hypothesis” appear to show that the collision must occur with a somewhat glancing blow. This will cause a small portion of the colliding body to form a long arm of material that will then shear off. This cloud of material turned around the earth before concentrating to form a sphere, the Moon. Question: After the formation, did the Moon, now a sphere, rotate faster or was it in synchrounus rotation from the beginning with Earth, always showing the same face. --hmaag (talk) 15:40, 26 November 2011 (UTC)
 * Well it's just a guess on my part, but I suspect the impact debris carried away a portion of angular momentum following the collision. After all, the colliding object probably had some amount of rotation. Hence, the newly coalesced Moon may have had some initial rotation, and tidal locking would have followed from the close proximity of the Moon to the Earth (at that time). I'm not sure how you would ever prove it though, although you could perhaps simulate it through the Monte Carlo method. Regards, RJH (talk) 16:34, 26 November 2011 (UTC)
 * RJHall, Thanks for your response. I'm sure the Moon had an initial rotation, stopped in a short (astronomical) time. I cannot proof it, but I think the outer components of the cloud had a higher energy potential than the inner components, so, after formation, the sens of the rotation would correspond to the sens of the movement around the earth. Hope you understand my English, my mother tongue is German. Yours, Hans, Switzerland --hmaag (talk) 12:03, 27 November 2011 (UTC)


 * From the simulations I've observed, all show both the Earth and moon rotating at a high velocity, the orbit of the moon "robbing" the Earth of rotational velocity, thereby increasing the orbital radius, which continues on today. The lunar rotation ceased quite soon after formation, again, due to exchanges of angular momentum, creating the current tidally locked condition of today in short order (can't remember offhand the time scale, but it was quite short).Wzrd1 (talk) 20:43, 18 February 2012 (UTC)

Lagrange point image
I suggested user:Thekaveman might want to discuss the following image before removing it. Here is his response, copied from my Talk page. -- Elphion (talk) 08:03, 30 November 2011 (UTC)


 * The figure that was removed was from a paper by Belbruno and Gott (2005) and assumed that the Moon-forming impactor came from the L4 or L5 Lagrangian point. However, no one has ever demonstrated that a planetary embryo could grow at these regions of space.  The N-body simulations of others (i.e. Chambers 2001 and others) have never discussed such a possibility.  Hence, the relevance of this paper to the question of lunar origin is dubious.  — Preceding unsigned comment added by Thekaveman (talk • contribs) 03:44, 30 November 2011 (UTC)


 * My point is simply that the image illustrates a concept discussed in the article. As long as that discussion is there, I think the image is relevant.  The article indicates that the hypothesis might not be correct, but not that it has been definitively refuted.  So many aspects of the Impactor Hypothesis are still speculative at this point; how is this different? -- Elphion (talk) 08:03, 30 November 2011 (UTC)

In science, new ideas are not accepted first, and then "definitely refuted". Instead, we have an openness to new ideas, but hold those ideas to the most stringent tests _before_ they become accepted knowledge. The giant impact hypothesis itself underwent a period of nearly a decade from its first serious proposal in modern times (1974) to its acceptance (1984). In the meantime, the case for this hypothesis was made stronger and stronger by more and more work being done on the problem until it was accepted. So I disagree with the characterization that "so many aspects of the impactor hypothesis are still speculative at this point" - which parts are speculative? The aspects of an hypothesis that are discussed in an encyclopedia article should have some level of scientific certainty associated with them. The idea illustrated in this figure has yet to gain any level of scientific certainty. So I think dedicating an entire figure (especially when there are no other figures in the article! - something else that must be fixed) would be misleading regarding the relative importance of the idea to the giant impact hypothesis. (Thekaveman (talk) 07:45, 4 December 2011 (UTC))


 * If we were to limit the article to what is more or less universally accepted, it would say (in its entirety) something like: "Some evidence suggests that the moon was formed by at least one large planetary object impacting the earth early in its history." Virtually none of the rest is "settled science" yet, and no theory currently accommodates all the evidence.  This is still very much a work in progress -- and so, perforce, is the article.  Unless you are prepared to suppress the Lagrange point hypothesis, the image is relevant.  That it's the only image is not a good argument for removing it, rather an argument for supplying more images. -- Elphion (talk) 15:43, 4 December 2011 (UTC)
 * Yes, I don't see an issue with including the image as it illustrates the concept being discussed in the text and the caption doesn't assert anything untrue. Regards, RJH (talk) 16:08, 4 December 2011 (UTC)

There is no evidence for a Lagrangian point origin of Theia. The idea that the isotopes between the Earth and Moon are identical and that Theia therefore formed "at 1 AU" is suspect, because the mass ratio between the Earth and impactor is far from one (it's about 9:1) and larger planets have broader source regions than smaller planets (see for example, Chambers, 2004 EPSL). Therefore, _the Earth itself_ sourced material from the whole of the inner Solar System and in this sense did not "form" at 1 AU. And the oxygen isotope difference between Earth and Mars tells us that there was large scale heterogeneity at large (~AU) scales. Therefore, the formation of Theia "at 1 AU" - even if it happened - could not have been responsible for the oxygen isotope match between the Earth and Moon. Other isotopes corroborate this idea. Tungsten isotopes, for example, are identical between the Earth and Moon, even though they are expected to be different between Earth and Theia (wherever the latter formed - see Nimmo et al. 2010). Therefore, the isotopes require some other explanation other than similar region of formation for Earth and Theia.

And I disagree that what is known with some certainty about the giant impact hypothesis can be summarized in one sentence. That is an overestimate of our ignorance, great as it may be. For example, the magma ocean is nearly universally accepted. The angular momentum of the Earth-Moon system constrains the mass of the impactor to be roughly Mars-sized. There is a lot of solid science that has been done by connecting theoretical ideas to observable properties of the Earth-Moon system (either dynamical or compositional properties). And it would be doing a disservice to take a speculative idea _not tied to any observation_ and present it as accepted knowledge. (Thekaveman (talk) 09:21, 7 December 2011 (UTC))
 * There's nothing wrong with presenting a scientific model of how this collision could have occurred. Your deletion of this entry under discussion, without reaching a consensus, is tantamount to disruptive editing. Please read WP:DISRUPT. On the other hand, if you can present properly cited evidence that specifically brings the Lagrangian point origin hypothesis into question (without violating WP:SYNTH), then please do so for the purpose of neutrality. Thank you. Regards, RJH (talk) 17:04, 7 December 2011 (UTC)

If the material is relevant enough to be in the article then I think an explanatory image is also relevant. This image's size does come close to WP:Undue, though. I think that reasonable people can come to very different conclusions. Further, I think it is possible for reasonable people to think, erroneously, that their decision is obvious enough that it doesn't need to be discussed here first.

A far worse problem, in my opinion, is the placement of the Lagrange hypothesis. I don't have a problem adding more speculative things IF it is published in a quality peer reviewed journal and it is taken seriously by the community. Perhaps, an indication of this is that more than one independent group of people have published peer reviewed papers about it. Such 'speculative' stuff needs to be isolated in its own section at the end, though. I am not near enough of an expert enough to know if the Lagrange hypothesis is relevant enough even to include in a 'recent hypotheses' section. None of my modern Astronomy texts mention the possibility, though, which suggests to me that the chance of it being accepted enough to include in the main text is not very good. TStein (talk) 17:39, 7 December 2011 (UTC)
 * The hypothesis was published in Astronomical Journal, which is a venerable and well-respected journal in the astronomy community. The article appears to be cited in multiple other equally respectable publications, which makes it notable in WP terms. The topic spans a single paragraph and seems to be in the appropriate location. The text appears to couch the hypothesis in the appropriate terms. The model doesn't really seem all that radical to me, once you accept the premise that the collision actually occurred. The stability of Trojan orbits is based on the ratio of the masses, so that seems valid. The fact that this isn't mentioned in textbooks doesn't seem all that meaningful, since the concept has only been around since 2005 and probably isn't worth mentioning at that level. Besides, WP guidelines prefer that we don't rely on tertiary sources such a textbooks. Hence, I am not quite seeing what the problem is here.


 * On the other hand, if the consensus proves to be that the image is too large for the subject matter, then I have no issue with getting rid of that. We can always use the other illustrations instead. Regards, RJH (talk) 19:18, 7 December 2011 (UTC)
 * Then it has enough support to be in the article, in my opinion. I disagree about where to put it, though. It is still my sense that the scientific community as a whole is not near as accepting of this particular model of how the giant impact occurred as they are of that fact that it did occur. Until the scientific community does judge them as equally reliable, which will take time, then the Lagrange Point model needs to be placed in a separate section after what is reliably known. I don't think it is right to mix strong consensus stuff with non-strong consensus stuff. It risks undue weight.
 * Personally, I think of textbooks as secondary sources not tertiary for this case. If there was strong enough consensus in the community, I have no doubt that the textbooks will mention it. (It is just too cool to leave out ;) ). TStein (talk) 21:02, 7 December 2011 (UTC)
 * Okie doke. Well, as I read it, WP:UNDUE has to do with the amount of text spent on a topic, rather than where it is placed. As long as it is clear that this is not yet a majority consensus, I think we're probably okay. I don't have anything in particular against moving it to a separate section, other than possibly the section length issue per WP:BODY. But I don't think we need to hide it at the bottom. It's not exactly fringe science. I think it would be okay in between the Theia and Impact sections, or maybe as a sub-section of Theia. Thank you. Regards, RJH (talk) 22:46, 7 December 2011 (UTC)

As a researcher who has spent the last 7 years working on the giant impact hypothesis, you must forgive my haste in editing this article and attempting to make it more reflective of the scientific consensus without prior discussion. WP:UNDUE states that: "undue weight can be given in several ways, including, but not limited to, depth of detail, quantity of text, prominence of placement, and juxtaposition of statements." I can tell you with confidence that the prominence given to this particular hypothesis is disproportionate to the level of support that this hypothesis enjoys in the scientific community. I would be OK with using a smaller image and moving the paragraph to a less prominent place in the article (199.115.243.152 (talk) 20:22, 8 December 2011 (UTC))


 * OK, but the article doesn't give much evidence of consensus; rather the opposite. (Several of the titles in the references end with question marks, e.g.)  The impression conveyed is that consensus has yet to form -- which at some level is certainly the case:  it's too easy to modify the hypothesis to fit the new evidence du jour, which indicates that the details are set only in jelly.  It may be that consensus disagrees with the Belbruno–Gott hypothesis, but in that case a reference to that effect would be helpful, and referenced discussion describing the consensus (which is what is really missing here) would also help.
 * I do agree that the paragraph discussing Belbruno–Gott is misplaced. I would suggest merging the Theia and Impact sections and moving the Belbruno–Gott paragraph down to precede the other paragraph discussing Lagrange lurkers.  As I've argued above, I think the image is appropriate -- it gets the idea across very succinctly.  I'm less enthusiastic about the animated image above -- though it grabs the attention, I suspect the time periods illustrated are not to scale, so it misleads people about what Belbruno and Gott are proposing. -- Elphion (talk) 21:11, 8 December 2011 (UTC)
 * Okay, it looks like that's enough of a consensus to relocate the Lagrange hypothesis in a separate section. If this concept has encountered resistance in the scientific community, I'm perhaps a little surprised that such hasn't appeared in print. But no matter.
 * A possible option for the current image would be to change it to a horizontal orientation, rather than vertical. That would keep it in the same section. Regards, RJH (talk) 21:43, 8 December 2011 (UTC)
 * I agree with Elphion- what is really missing is the consensus view for the origin of Theia. The image in the article now is simply too large for the level of support this hypothesis enjoys in the scientific community.  The animated image has the advantage that it is the right size for a speculative idea.  I suggest using the animated version and moving this hypothesis to the alternative hypothesis section (but only once the mainstream view is in the article). (69.181.18.60 (talk) 07:47, 9 December 2011 (UTC))
 * Perhaps so, but our problem is that Wikipedia should be based upon published sources (per WP:RELIABLE). If we are to present a mainstream/consensus view, it really needs to be based upon authoritative publications that present that viewpoint. Some type of published criticism of this paper by Belbruno–Gott would help. Regards, RJH (talk) 15:30, 9 December 2011 (UTC)

Well, that's not quite what I said. Belbruno–Gott does not belong under "Alternative Hypotheses", because it's a flavor of the Impact Hypothesis. It belongs in the discussion with the other impact versions; the alternatives refer to completely different mechanisms. The animated image is not a fair representation of Belbruno–Gott, the other is much better. And to date I've seen no refs that Belbruno-Gott is largely discounted. You have said that it does not have wide support, but no verifiable evidence has been forthcoming. Without that, this is just POV pushing. Pace RJHall above, it does matter if there no published resistance to the Lagrance hypothesis -- Elphion (talk) 08:31, 9 December 2011 (UTC)


 * I moved stuff around in a way that I hope reflects what you are saying. I am not wedded to this; please revert or change as necessary. My goal was to put all the stuff that applied to the general model (including the strengths and criticisms) before the details of the model and to put the more detailed features that are not as well known, together in an appropriately labeled section. Normally, I like discussing these things first; but, in this case I think it is better to just show you what I mean. TStein (talk) 21:43, 9 December 2011 (UTC)


 * That looks good -- much better organized than before. -- Elphion (talk) 23:11, 9 December 2011 (UTC)
 * Yep, the changes look good and the new organization makes sense. The article still needs work, of course. Thanks. Regards, RJH (talk) 02:21, 10 December 2011 (UTC)

Questions
This article poses some questions that I was hoping that someone can answer.


 * 1) Why is it surprising that Venus does not have a moon as well?  My understanding was that you needed a particular type of collision (a relatively glancing blow and a relatively slow collision.) Such collisions may happen fairly often, but they are not guaranteed to happen.
 * 2) I don't understand about the statement about no evidence of a magma Ocean after the impact. My understanding is that there is plenty of evidence of a deep magma Ocean during the accretion that created Earth (see recent physics today article.) Even then the main line of evidence that there was a magma Ocean is based on the 'coincidence' that a recent supernova explosion seeded the newborn solar nebula with radioactive refractory elements with suitable length half-lives. From that line of evidence, it wasn't clear to me that the model could be used one way or the other to say whether there was another magma Ocean after the collision that created the moon. (*Edit: see below.TStein (talk) 20:03, 20 December 2011 (UTC))
 * 3) The main illustration in the lead is the same illustration used in the physics today article where it is claimed that it was just a generic collision. This fits with my impression from before where, to me at least, the collision doesn't seem glancing enough.
 * 4) I think I finally understand why the Oxygen isotope ratio is used both to support the model AND as a problem for the model. Can someone explain it better in the article, though. Again, in the physics today article it says that it is not just the Oxygen Isotope ratios that are to similar, but that there are a number of others as well. Can someone elaborate?

Thanks for any help you can give. This topic reminds me of the story of Tantulus. The low hanging fruit is so close to my reach, yet it always seems to elude my grasp. TStein (talk) 05:13, 15 December 2011 (UTC)
 * I agree with you about the first point. That doesn't seem to be a significant concern for a random process like this. For the illustration, perhaps we should just change the text to say it is an example of a planetary collision, rather than being specific to this hypothesis? Regards, RJH (talk) 17:24, 15 December 2011 (UTC)

Part of the problem with this is my fault. I read the physics today article too fast (Phy. Today. Vol 64 no. 12 (Dec. 2011) p. 40-45). The evidence for a deep magma Ocean is based on the ratio of Ni and Co in the bulk silicate earth compared to the core. (The later is obtained, presumably, by comparing the bulk silicate to the chondritic ratios of these elements.) These ratios of silicate to core are consistent with them forming at 25 GPa which is not possible in the small bodies that accreted to form Earth. It is consistent with a depth of 700 km in a full-grown Earth. (the PT article references J.Li, C.B. Agee, Nature 381, 686 (1996), and B.J.Wood, M.J.Walter, J.Wade, Nature 441, 825 (2006) here, but I have not had time to chase them down.)
 * Just a quick drive by posting, but I believe #1 requires a glancing blow with orbital capture. I suspect that would not be common. -- Kheider (talk) 18:06, 19 December 2011 (UTC)
 * On that I'm not so sure, at least mathematically. Probability wise, the mostly likely impact would be off center by some amount, but I haven't seen a paper that works out the distribution based on the impact cross sections. Regards, RJH (talk) 19:31, 19 December 2011 (UTC)
 * From the reference about Q2: "Is There Any Evidence that the Earth Ever Had a Magma Ocean? No. Another anticipated result of the Giant Impact is a terrestrial magma ocean.... because there are mantle spinel lherzolites whose compositions closely approximate that of the bulk silicate Earth, this seems to imply that there was never a global magma ocean ...." Dan Watts (talk) 10:10, 20 December 2011 (UTC)
 * Regards, RJH (talk) 15:57, 20 December 2011 (UTC)
 * I think the differences are related to what depth the magma ocean exists/existed, with the previous source was discussing the surface and your reference discussing ~2900 km deeper. Dan Watts (talk) 17:31, 20 December 2011 (UTC)
 * I'm not clear what you mean by a "previous source". Your statement asserted that there was no evidence of the magma ocean. I presented a source which does show evidence. Ergo, your claim appears to be refuted. Regards, RJH (talk) 18:40, 20 December 2011 (UTC)
 * All I meant was that I understood this reference to be a description of the earth's surface while your reference is of a much deeper body of magma. It appears that statement may need to be clarified in the article to delineate between surface and subsurface magma. Dan Watts (talk) 19:35, 20 December 2011 (UTC)
 * All I meant was that I understood this reference to be a description of the earth's surface while your reference is of a much deeper body of magma. It appears that statement may need to be clarified in the article to delineate between surface and subsurface magma. Dan Watts (talk) 19:35, 20 December 2011 (UTC)

In any case it is still unclear to me what the relationship between this 'deep magma ocean' and global magma ocean expected after the giant impact. Estimates of when the core formed from this deep magma ocean seem to go from 30 to 100 Myr after the start of formation of solar system, which is close to the range of time for which the giant impact would have occurred. I would greatly appreciate any clarity you can give Dan. Thanks. TStein (talk) 20:04, 20 December 2011 (UTC)
 * My apologies if I misunderstood. Regards, RJH (talk) 21:27, 20 December 2011 (UTC)

#1) No moon around Venus
The anonymous poster finally supplied a reference for the question regarding Venus: There are some plausible explanations listed here: I've added a section to the article to attempt to address these. Regards, RJH (talk) 18:35, 22 December 2011 (UTC)

Here is an article and some evidence that should be used
Put it where you think it belongs. 7&amp;6=thirteen (☎) 19:23, 27 March 2012 (UTC)
 * We do have a section for Compositional difficulties. What isn't clear is whether these compositional issues challenge the theory as a whole, or just the specifics for how the collision happened. Based on the news story, it seems to be suggesting the latter. This may be the original source for the news stories. Regards, RJH (talk) 19:32, 27 March 2012 (UTC)
 * I agree. This is outside my ken, and I am not comfortable adding to this particular article. I defer to those with better expertise than I. 7&amp;6=thirteen (☎) 20:02, 27 March 2012 (UTC)
 * Yes, I don't have good familiarity with planetary geology so I'm also reluctant to try and develop that part. Regards, RJH (talk) 21:51, 27 March 2012 (UTC)

Shadow Accretion
Displacement of core material may be observed around Beta Pictoris.
 * What does this mean? Any links or refs? kwami 2005 July 7 19:18 (UTC)

Alternative hypotheses
I think that there should be some mention of the georeactor hypothesis. It has been out there for a while, and has gotten play not only in scientific journals, but in some lay science magazines as well. Considering that the lunar substance is almost entirely mantle, the georeactor theory is stating to look more probable. http://www.cosmosmagazine.com/features/print/2421/birth-moon?page=0%2C4

174.252.107.255 (talk) 00:42, 19 April 2012 (UTC)MikeRudmin
 * Yes it is getting some coverage and is probably worth a mention, per WP:WEIGHT. It could also be mentioned on Moon. Regards, RJH (talk) 01:31, 19 April 2012 (UTC)
 * The IP cites a 2008 popsci article as 'looking more probable'. This came up back when the authors initially put it on the arXiv. It hasn't been published in peer review. Iridia (talk) 02:37, 19 April 2012 (UTC)
 * Ah, found it. The discussion was here. Hope that provides enough information. Iridia (talk) 02:45, 19 April 2012 (UTC)

Problems
This theory has some issues. 1. If Theia hit the earth, where did it go? Some went into the moon, but obviously not all of it otherwise the moon would be huge. 2. Wouldn't the fragments the supposedly created the moon be separate? The fragments would not have enough gravity to stick together because their fragments. (more questions coming) Tntarrh (talk) 20:27, 17 September 2012 (UTC)


 * Most of Theia combined with the Earth, and some went into orbit around the Earth where an accretion disc took over. I suspect small fragments did wander beyond Earth's hill sphere. -- Kheider (talk) 21:36, 17 September 2012 (UTC)


 * It's thought that there may have been two sizable moons, whose later slow impact ('splat') led to the highlands on the Far Side which did not produce maria when later impacted by other large bodies.
 * The moon is massive enough that the fragments would have fused under their own gravity. See dwarf planet.
 * Theia's core would have dropped into the Earth's core. — kwami (talk) 20:40, 17 October 2012 (UTC)

Lagrangian stability
Our article on Lagrangian point is insufficient to understand why Theia destabilized. According to refs presented on the talk page (Talk:Lagrangian point), the situation would be stable as long as M[theia] + M[earth] < 0.04M[sol]. Since M[earth] is only 0.003M[sol], this obviously never happened. Is the reason that it wasn't a 3-body situation? Are these situations simply too chaotic to give any kind of generic account of limiting masses? — kwami (talk) 20:40, 17 October 2012 (UTC)

Each five times the size of Mars
our early Earth and moon were both created together in a giant collision of two planetary bodies that were each five times the size of Mars -- Kheider (talk) 22:33, 30 October 2012 (UTC)


 * You're misrepresenting it. "New research, funded by the NASA Lunar Science Institute (NLSI), theorizes that..." is more accurate William M. Connolley (talk) 22:36, 30 October 2012 (UTC)
 * It is all theory on the exact masses and impact angles/velocities... -- Kheider (talk) 22:45, 30 October 2012 (UTC)

Origin of Theia
Removed this sentence: Supporting this theory, extrasolar planets have been discovered in Lagrange points of each other, and are expected to collide, after co-orbiting for millions of years. Since as noted at the top of the cited reference this study has subsequently been updated with one of the planets found to have an orbital period twice that which was originally thought, and thus is not co-orbital with the other planet. Physdragon (talk) 16:51, 16 November 2012 (UTC)

I removed the Space.com simulation link
The URL cannot be found. Couldn't find the simulation on the site as well.Wzrd1 (talk) 23:24, 2 December 2012 (UTC)

The Apollo rocks
In Section 4 of this article, it says "the team found that the Apollo rocks carried an isotopic signature that was identical with rocks from Earth". What are "Apollo rocks"? Cemkay (talk) 22:09, 8 December 2012 (UTC)
 * I changed it to "rocks from the Apollo program" -- Kheider (talk) 23:00, 8 December 2012 (UTC)

Possible source
Nature are running an opinion piece on this area:

http://www.nature.com/news/planetary-science-lunar-conspiracies-1.14270#/b10

©Geni (talk) 22:45, 5 December 2013 (UTC)

Update
A recent article in Science ("Impact Theory Gets Whacked", 11 Oct. 2013) has a good review, and an update. ~ J. Johnson (JJ) (talk) 23:44, 6 December 2013 (UTC)


 * This is the article; unfortunately, it doesn't actually explain what the alternate theory is without a subscription. This space.com article (thanks Drumhead96) may be what is being referred to, but I'm not 100% sure yet.  Serendi pod ous  23:39, 9 December 2013 (UTC)

Theia (planet)
was recently recreated. It was previously merged into this article some years ago. -- 76.65.128.112 (talk) 06:11, 31 December 2013 (UTC)


 * I went ahead and merged. It's been a year since it was recreated, but it was still a stub with less info than this article has.  — kwami (talk) 08:06, 31 December 2013

Query re GRAIL ruling out minor Theia impact debris causing lunar locking
This article currently says:

“The resulting mass irregularities would subsequently produce a gravity gradient that resulted in tidal locking of the Moon so that today, only the near side remains visible from Earth. However, mapping by the GRAIL mission has apparently ruled out this scenario.[citation needed]”

http://www.es.ucsc.edu/~fnimmo/website/wieczorek_grail_science13.pdf

http://www.nasa.gov/mission_pages/grail/news/grail20130530.html#.U3H4cs4bQo8

Yes, I would like to see a citation. As far as I can tell the official report merely indicates that gravitational anomalies are indeed caused by early impacts when the Lunar mantle was soft and you can see from the crustal thickness map in the PDF that these seem to be caused by five concentrated events penetrating to the Lunar mantle or very near, with one hemisphere less effected. (Also, the PDF report says the lunar refractory element composition is similar to that of Earth.)

Star A Star (talk) 11:35, 13 May 2014 (UTC)

The crust of the Moon seems thicker on one side according to the GRAIL report above. This matches an earlier description of the issue at http://www.bbc.co.uk/news/science-environment-14391929

Star A Star (talk) 13:04, 13 May 2014 (UTC)

Useful source?
I'm not sure how useful this'd be from a scan of the article, but this may be of use: http://www.bbc.co.uk/news/science-environment-27688511 Irockz (talk) 01:39, 7 June 2014 (UTC)

Possible new evidence
I found a reference to possible new evidence for a giant impact:

http://www.bbc.com/news/science-environment-23180271

"Seismic data indicate that the western and eastern hemispheres of Earth's inner core differ, and this has led some to suggest that the core was once subjected to an impulse - presumably from the collision of a space rock or planetoid which shook the whole Earth."

I have been unable to find the "some" who are suggesting this. It is not mentioned in the scientific report the article is based on: http://www.nature.com/srep/2013/130628/srep02096/full/srep02096.html

I have emailed the author of the BBC article Professor Simon Redfern of the University of Cambridge http://www.esc.cam.ac.uk/people/academic-staff/simon-redfern

in order to try to ascertain if there is any proper source to quote from.

Star A Star (talk) 04:10, 17 March 2014 (UTC)

Alas Professor Redfern says "The suggestion to which I alluded was a verbal comment once made to me at a conference. It turns out, on further investigation, that I" too cannot find any written record of such a hypothesis. Indeed, the closest I can find is the work of Deguen and co-workers."

Star A Star (talk) 11:35, 13 May 2014 (UTC)

The new evidence can be found in the journal Science, and can be accessed at the following web page: http://www.sciencemag.org/content/344/6188/114 "Identification of the giant impactor Theia in lunar rocks" Science 6 June 2014: Vol. 344 no. 6188 pp. 1146-1150 DOI: 10.1126/science.1251117

Rafgkos (talk) 22:15, 8 June 2014 (UTC)

What happened to Theia?
...after it had collided with the Earth? Had it moved beyond our solar system unnoticed or is now one of the known planets? — Preceding unsigned comment added by 89.71.153.13 (talk) 11:27, 19 May 2014 (UTC)


 * Theia lost a lot of its independent orbital energy in the collision. Theia is now partly the Earth and partly the Moon. — Preceding unsigned comment added by 24.223.130.32 (talk) 01:16, 7 July 2015 (UTC)

Basic model problems
The Basic Model section says:

Astronomers think the collision between Earth and Theia happened at approximately 4.4 and 4.45[12] bya; about 30–50 million years after the Solar System began to form.

This is conflating two theories: old-moon and young-moon. The old-moon theory has the impact occurring at 4.53 ga, or about 38 million years after the date for the CAIs (Calcium–aluminium-rich inclusion) which is taken as a substitute for the age of the solar system and the beginning of the formation of the earth. The young moon theory was originally 4.45-4.47 but has since been revised to 4.47 ga. This was originally supported by re-analysis of Apollo 12 moon rocks, but has been independently corroborated by material from meteorites containing debris from the collision. Zyxwv99 (talk) 19:19, 14 April 2016 (UTC)

Theia, Thea as separate pages
The header at the top of the page says that Theia (planet) redirects here, but since 2013 it has had its own article. The spelling variation Theia (Planet) redirects there. On the other hand, Thea (planet) redirects here. I'm not proposing a resolution, just asking what people think the optimum solution would be. -- Elphion (talk) 23:33, 30 April 2016 (UTC)

possibility of giant impact
how was the main body and condition of Earth crust, when giant impact occurred? this is main and principal question. Which can bright the way of finding exact and real facts.--Akbarmohammadzade (talk) 13:29, 12 May 2016 (UTC)

Missing source
The very first source on this article is broken. This should probably be fixed? — Preceding unsigned comment added by 84.202.115.49 (talk) 11:51, 27 November 2016 (UTC)

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Representative image
The image for the "Simplistic representation of the giant-impact hypothesis" isn't really representative of our current understanding of the Moon's formation. I suggest this image be replaced by one more similar to this image:. Citronade (talk) 18:25, 3 August 2018 (UTC)

Out of date
"As of 2015...." — Preceding unsigned comment added by 2601:444:380:3A90:E5F8:E0F6:AE52:E4BF (talk) 11:26, 12 March 2019 (UTC)

Spinning/Tumbling Synestia Twin Moon Hypothesis
I propose that the 50mya giant impact event is also relevant...it uplifted the Himalayas, our youngest mountain chain.. I propose this North Polar Basin impact event ultimately increased tide raising forces so that vertical mixing of nutrients created a rich new plankton based food chain that crossed the entire globe... the transition of the dinosaur age to the mammalian age... I propose that a tumbling synestia would create two moons, each in orbit about the other.. analagous to Pluto and Charon.... I propose that our sister moon was captured by the Earth around 50mya and led to the low speed Arctic Impact Event shortly afterwards.. AL86.174.244.113 (talk) 07:36, 2 April 2018 (UTC)


 * Wikipedia is not a place for original research. --Kent G. Budge (talk) 01:29, 13 March 2019 (UTC)
 * Nor for original "proposals". The talk page is for improving the article, nothing else. -- Jibal (talk) 15:50, 16 March 2019 (UTC)

Hypothesis or theory?
Which is it?  —Biscuit-in-Chief :-)  (Talk – Contribs) 09:30, 23 December 2019 (UTC)


 * Hypothesis, I'd say. It does not yet have the solid buttress of evidence and widespread acceptance that would make it a theory. --Kent G. Budge (talk) 22:01, 23 December 2019 (UTC)
 * Just to be clear: I think the preponderance of evidence favors the hypothesis. I don't know that we've reached "clear and convincing" yet. --Kent G. Budge (talk) 16:37, 13 November 2020 (UTC)