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I'm not sure what you're getting at, but if Theia was destroyed in an impact with Earth the only place we might find evidence of it is in the Earth and the moon.
Originally posted by redoubt
Oh, no doubt... but their origins?
We have well over 30,000 pieces of evidence of what the rest of the solar system that might impact Earth is like, that don't require any faith.
Originally posted by redoubt
All in all, to say that the moon is identical to Earth while different from the most of rest of the solar system that we haven't even yet begun to explore in earnest, seems to be more a leap of faith than anything else.
If you have a source for that it would be helpful, but Meijer, Anisichkin, and van Westrenen suggest such models haven't been successful as I mentioned in this post. Maybe they're wrong, but that's their claim.
Originally posted by eriktheawful
I thought they had revised the impact theory in which when the impact happened, the majority of the material that made up the moon was material stripped off of the Earth, not the remains of the impactor.
This material quickly coalesced into the Moon (possibly within less than a month, but in no more than a century). Estimates based on computer simulations of such an event suggest that some twenty percent of the original mass of Theia would have ended up as an orbiting ring of debris, and about half of this matter coalesced into the Moon.
I don't see that in your source. But I went to your source and looked at the source cited, source #11:
Originally posted by eriktheawful
So only 20% of Theia ends up in orbit, and only half of that, 10% ends up forming part of the moon, meaning the other 90% is made up from the Earth.
That's from the source your source cites. I think you're misinterpreting what you're reading, and or the author of the article you cited might have but he didn't say what you seem to think he said, about 90% coming from Earth. Source 12 also says something similar on page 300 about most of the material coming from the impactor, so if you or the author are coming to a different conclusion, you're disagreeing with the sources being cited. I think the source of the misunderstanding is your apparent assumption that Theia and the moon are of similar mass, and this extreme case was considered, but simulations have shown it's more likely that Theia would have been significantly more massive than the moon:
In all cases, the vast majority of the orbiting material originates from the impactor, consistent with previous findings.
a giant impactor mass between 0.11 and 0.14 Earth masses
There's your ~90% of Theia right there, in the difference between 0.12 Earth masses and 0.012 Earth masses. The mass of the moon is about 10% of a 0.12 Earth mass impactor, meaning there's no need for much material to come from Earth.
The mass of the Moon is only 1.2% the mass of the Earth.
I don't see any way to interpret the wiki article as saying that 90% of the material for the moon came from Earth. However, I certainly admit the simulations that suggest most of the material came from the impactor might be flawed.
Originally posted by eriktheawful
reply to post by Arbitrageur
I was basing what the text I quoted in the wiki article had stated.
Yes, I see what you're saying and if this is true then it's enough to make us question the claim that there's only a 1% chance that Earth and Theia could have such similar isotopes. Good point.
Originally posted by eriktheawful
The operating model that we have for Theia means that it formed from the same material that formed the Earth (if in fact it formed in the same orbit).
When I first saw the title, I feared this would be about some ancient aliens theory of how a former civilization destroyed their world in a nuclear holocaust, and subsequently created the moon in the process.
The main reason Meijer and van Westrenem concocted their scenario was to explain why the composition of the moon and the Earth's mantle are identical when the moon should have been contaminated by material from the impactor. "The simple answer is that the impactor formed from material at the same distance from the sun as the Earth, and therefore had the same composition," says Gott. This could have happened if the body formed at either the stable Lagrange-4 or Lagrange-5 points, 60° behind and ahead of the Earth in its orbit around the sun. This idea was proposed by Gott and his Princeton colleague Edward Belbruno in 2004. "The impact scenario, with the impactor coming from a Lagrange point, fits pretty much all the observations," says Gott.
Thanks for posting that link. Some of the critics don't even understand the hypothesis, as this remark by Gott illustrates:
Originally posted by wildespace
Critics blast nuclear 'bomb' theory of moon's birth:
www.newscientist.com...
van Westrenen and de Meijer didn't try to hypothesize any such origin for other moons. The authors wrote a reply in the comments section which seems reasonable to me, as do some of the other comments noting they made a hypothesis and suggested a way to test it. If the hypothesis is tested and shown to be false they seem perfectly willing to accept that. I don't really see the harm in testing it, especially since China may be sending men to the moon anyway...collecting some samples might not be that hard for them while they are already there, and then we could determine the proper fate of the hypothesis with evidence rather than unrelated decrees about ice reactors on Pluto.
"But how do you explain Charon, the big icy moon of Pluto? That would require an 'ice-reactor', which is a nonsensical idea!"
But there was no nuclear explosion at Chernobyl. And I'm pretty sure the hypothetical natural reactor was not a really fast one.
As you know we have man-made nuclear reactors, and as seen in Chernobyl they have gone critical. We do know that there have been natural nuclear reactors:
How can you say that so confidently when the experts don't seem to know the cause of the second explosion? I don't think it's been ruled out as a possible cause.
Originally posted by Phage
reply to post by Arbitrageur
But there was no nuclear explosion at Chernobyl.
As you know we have man-made nuclear reactors, and as seen in Chernobyl they have gone critical. We do know that there have been natural nuclear reactors:
However, the sheer force of the second explosion, and the ratio of xenon radioisotopes released during the event, indicate that the second explosion could have been a nuclear power transient; the result of the melting core material, in the absence of its cladding, water coolant and moderator, undergoing runaway prompt criticality similar to the explosion of a fizzled nuclear weapon.[43] This nuclear excursion released 40 billion joules of energy, the equivalent of about ten tons of TNT. The analysis indicates that the nuclear excursion was limited to a small portion of the core.
Though dangerous and frequently lethal to humans within the immediate area, the critical mass formed is still incapable of producing a nuclear detonation of the type seen in fission bombs, as the reaction lacks the many engineering elements that are necessary to induce explosive supercriticality.