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## Comment Re:Not a contradiction (Score 5, Insightful)233

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.

## Comment Re:Not a contradiction (Score 5, Informative)233

The problem is that the ratio of Earth's mantle to Theia's mantle matters in the combination, even if mixing is efficient. The Earth's mantle is fully convective, and around 6 times the mass of the impactor's mantle, which means that you have to really fine-tune the conditions to achieve the exact right mixture. A good analogy would be trying to mix milk and water in a glass such that the fluid that splashes out of the glass has the same fraction of milk to water as the fluid remaining in the glass. With the original Oxygen isotope constraint, 95%+ of the lunar mantle needed to originate from the Earth, which is in direct conflict with the giant impact simulations that have been performed (which find 80% coming from the *impactor*), even for iron-rich impactors that preferentially remove Earth's mantle. This new constraint, if I am reading the paper correctly, is even stronger than the Oxygen isotope constraint, being at the part per million level rather than the part per ten thousand level.

## Comment Re:Not a contradiction (Score 4, Informative)233

This doesn't work. The fractional element abundances depend not only on the location in the protoplantery disk, but on the timescales of accretion, which depend on the mass of the object accreting. Thus, even if you formed Theia in L4/L5, the isotopic ratios should be different, as the two objects will have different masses.

## Comment Re:Mmm, paywall. (Score 4, Funny)64

If only someone invented some sort of laser that would allow me to see behind this paywall...

## Comment Chase blows (Score 1)398

Fuck Chase...I had Wamu before they were swallowed by Chase, and Wamu's website was FAR superior to the ancient web banking that Chase offers. I have to click through 5 screens just to transfer money across accounts with chase, and I doubt they're not using anything more sophisticated than plain https, so any BS reason they offer for not supporting certain modern browsers is just that...BS.

## Comment Re:nothing special... (Score 1)347

These results are specifically about the deviation of the spectrum produced by a human from a black body, and how that varies throughout the day. For a blackbody, the number of photons coming out as visible radiation is 1/10^3000 the total number (assuming a body temperature of ~280K, the number is so tiny because visible photons fall into the exponential Wein tail of the BB distribution), so you would naÃvely predict that no human has ever emitted a visible photon. Ever. So yes, it is something special.

## Comment Re:Or earth could turn into an elephant (Score 2, Informative)255

I realize the linked article doesn't have the 1% figure, here's a better article:

http://www.universetoday.com/2009/06/10/wild-little-mercury-to-cause-interplanetary-smashup-maybe/

## Comment Re:No big deal here (Score 1)255

Being able to quantify the odds is an achievement. Why belittle it? Where's your paper on the multi-billion year evolution of the solar system?

## Comment Re:Or earth could turn into an elephant (Score 1)255

1% in 5 billion years is actually fairly high...you're talking some major solar system engineering if Mercury's orbit suddenly starts to look funny.

## Comment Bad Title (Score 3, Informative)166

Quoth the conclusion of the referenced paper:

"These possibilities, combined with the observation that the
disrupted object be a carbon-rich star, rather than a normal
main sequence one appear to make the case for tidal disruption
somewhat contrived. Nonetheless, with only one object, and
thus an essentially unconstrained rate and space density for
such events, it remains a possibility."

So, while tidal disruption is a possibility, it is not the favored scenario.

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