Findings Cast Doubt On Moon Origins

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."

Comments

Huh?

[Lumpy]

"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"

and

" 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."

SO discovering that the Moon's and Earths isotopes match means it could NOT have formed from a splash of magma from the earth?

This whole thing contradicts it's self. How do they know that the other body was not a twin of the earth and formed from the same disc of dust and debris? do they have samples of this other planet?

Re:Huh?

[demonbug]

They're asserting that 40% of the Moon's mass must have come from the impactor, and thus would have a different isotope balance.

That's clear, but why would the impactor necessarily have a significantly different isotopic ratio than the Earth? Yes it theoretically had a significantly different mass, but the distance from the sun was similar. How much understanding do we have of the variation in these isotopes on other planetary bodies? We have samples from what, the Earth, the Moon, and probably asteroids (very small mass so not too surprising if their isotope ratio is very different)? Possibly Mars? That doesn't seem like a whole lot of data to base models of isotope variation on, so it seems like a weak argument to say that Theia should have had a substantially different isotopic ratio for oxygen and titanium than the Earth. It would be nice if this was discussed in the article, but it isn't (and the link to the original journal article is broken so I can't check for myself).

This is Real Science

[Spy Handler]

You know how you can tell astronomy is a real science? The people doing it are willing to look at new evidence... even if it casts doubt on their current beliefs.

• They do not insist that the "science is all settled".
• They do not belittle those who come up with hypothesis or evidence that contradicts their current views. (notice that they didn't call this new researcher a "Denier")
• They do not take polls amongst themselves and form a concensus, and then insist they're right on the strength of the fact that they have formed a concensus.

If you see people in a field of "science" doing any of the above, it's not science but something else entirely.

Re:Where is it ? (my keys)

[ShanghaiBill]

We have the technology to find and look very deep or far where isotopes are or where the fartest solar system is. But yet, I can't find my damn keys in my house sometimes.

If technology isn't solving your problem, you aren't using enough: Put an RFID tag on your key chain. While you are at it, you should tag the TV remote too.

Re:Where is it ? (my keys)

[holmedog]

I started to mod this insightful. Then, I thought "Wow, that's so cool I'm going to go actually buy that system and put chips in all my stuff". Then I did the research and realized it's $400 (source: http://www.dpl-surveillance-equipment.com/1000066086.html) .

I'll just keep putting the keys on my nightstand and the remote on the end table.

Re:Not a contradiction

[Quaoar]

The preferred giant impact model has a Mars-sized impactor with a core-to-mantle ratio equal to the Earth's, with approximately 30% of its mass being in an iron core (http://adsabs.harvard.edu/abs/2004Icar..168..433C). Mars is ~1/6th the Earth's mass. In this impact, the material liberated that eventually forms the moon is iron poor, as the iron core of the impactor sinks into the Earth. That has been the interpretation as to why the Moon's iron core is so small (no more than 3% its total mass), so in this sense the giant impact model produces a satisfactory outcome. Some fraction of the lunar surface is accumulated over the 4 billion years since the Moon formed, but this layer is thought to be very thin, and the meteorites + Apollo samples we use to measure the moon's isotopic ratios come from a range of depths that probe significantly deeper than this surface layer. The fine-tuning argument comes from the fact that for an arbitrary combination of impactor + Earth mass, impact angle, velocity, etc, you'd expect a scatter in the isotope ratios consistent with the typical scatter measured between other bodies in the solar system (say that between Mars and the Earth). Fine-tuning is often employed in intelligent design arguments as they rely on the anthropic principle, but as there's no reason to require the Earth and Moon to have identical isotopic compositions to explain the existence of life, there is no particular reason to favor any particular outcome over the myriad of other outcomes for this particular measurement.

Re:Occam's Razor

[Pope]

Learning is still fun. The trick is to ignore internet comments.

Re:Not a contradiction

[Coppit]

This is why I read Slashdot. I don't know what any of it means, but I do know I wouldn't read it elsewhere. :)