Findings Cast Doubt On Moon Origins 233
sciencehabit writes "A new analysis of isotopes found in lunar minerals challenges the prevailing view of how Earth's nearest neighbor formed. Geochemists looked at titanium isotopes in 24 separate samples of lunar rock and soil, and found that the moon's proportion was effectively the same as Earth's and different from elsewhere in the solar system. This contradicts the so-called Giant Impact Hypothesis, which posits that Earth collided with a hypothetical, Mars-sized planet called Theia early in its existence, and the resulting smash-up produced a disc of magma orbiting our planet that later coalesced to form the moon."
Not a contradiction (Score:5, Interesting)
It doesn't contradict it at all. The current version of the impactor theory pre-supposes that Theia was formed at Earth's L4 or L5 point. There, the fractional distillation effect in the solar nebula would give the same Ti isotope ratios as in Earth, since Theia would be orbiting at the same distance. Formation at L4 or L5 also gives a nicely low impact energy, agreeing with what is needed to form the moon.
Good conclusion bad logic (or writing) (Score:5, Interesting)
Conclusion sounds good, written logic is horrible.
found that the moon's proportion was effectively the same as Earth's
This contradicts the so-called Giant Impact Hypothesis, which posits that Earth collided with a hypothetical, Mars-sized planet called Theia early in its existence, and the resulting smash-up produced a disc of magma orbiting our planet that later coalesced to form the moon.
Does not explain why that doesn't work. The summary makes it sound very likely that something "smooshed off" the earth and became the moon, because both have the same ratios. Also does a poor job of explaining the more likely alternative explanation, by not discussing it at all. Fail.
I think part of the fail is assuming:
different from elsewhere in the solar system
That means we've sampled everything in the entire solar system both now and infinitely in the past? ha ha I think not.
Occam's Razor (Score:3, Interesting)
I am completely uninformed... but... (Score:2, Interesting)
I don't see how this contradicts anything. If a mars sized body impacted the earth, I doubt there was much that wasn't rendered into magma and mixed together.
Re:What are the implications? (Score:5, Interesting)
Re:Not a contradiction (Score:5, Interesting)
The Earth's mantle is fully convective, and around 6 times the mass of the impactor's mantle,
Wait, what? Where did you get 6 times? And where did the impactor get a mantle? That number is sheer conjecture, and the existence of a mantle makes so sense until you have an impactor large enough to have a differentiated body. That hasn't been proven.
Moon's core is different from earth's [wikipedia.org] by our best guesses. But the surface accretion in the eons after any impact is going to accumulate the same combination of protoplanetary disk material and ejecta material.
We've barely scratches the surface of earth, let alone the moon. These isotope measurements are akin to determining the structure of a large building by examining a paint chip scraped off of each.
And using hind sight, doesn't ANY outcome appear to be the result of "fine tuning"? Isn't any such argument just another form of intelligent creation dogma?
Re:What are the implications? (Score:5, Interesting)
I was thinking this. However, now you require two planetary bodies to occupy the same orbital zone for long enough for them to form without colliding, and yet to collide later on. This is tricky, but perhaps not impossible. They might initially form in some orbital resonance (probably one of the Trojan points) and then some other body comes by and destabilizes the orbits. (I don't know if Trojan points are stable in a still-accreting-planets disk.)
Another possibility is there were two collisions: Theia itself was formed from proto-Earth in a collision, and then later caused the moon-formation event.