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Monday, July 18, 2011

Nebular hypothesis unwinds? New data recovered from the Genesis spacecraft elucidate Earth's planetisimal past

Following the latest science news, Brian Thomas at ICR commented here on a recent publication in Science regarding the Nebular Hypothesis. McKeegan et al., 2011 presented oxygen isotopic data collected from solar wind by the spacecraft Genesis, which crashed into Earth in 2004 (the collectors were recovered from the wreckage, surprisingly intact). The new data suggest that the inner planets did not derive their oxygen (in the minerals, not atmosphere) from a source that was isotopically homogenous with the sun. Judging by the tone of the article at ICR—titled NASA Data Derail Nebular Hypothesis—I fully expected that our understanding of the solar system was on the verge of a paradigm shift.

But I was wrong.

The Nebular Hypothesis remains intact, only corroborated by the new data. As it turns out, Mr. Thomas understood little, if anything, from the article in Science. In a single reference to McKeegan et al. (2011), Mr. Thomas says, "The bottom line is that the sun is "highly enriched" in oxygen, and astronomers have no idea why." The original article had nothing to do with oxygen concentrations, however, but with isotopic abundances. In other words, the sun is enriched in the ratio of 16O (light oxygen) to 17O and 18O (heavy oxygen)—not in oxygen itself. Second, the whole point of the article was to explain that we do know why the enrichment occurs. We just didn't know how much, because until now, nobody had been able to directly measure oxygen isotopes in solar materials.

The sun is enriched in the lighter oxygen isotope because of mass-dependent fractionation—a process in which one isotope is favored simply because it is heavier or lighter. One earthly example is the evaporation of water: the light isotope (16O) is preferentially evaporated because it is lighter. Therefore, rainwater is 'isotopically depleted' with respect to seawater. In the sun, a process called inefficient Coulomb drag causes lighter isotopes to concentrate in the sun's edge (i.e. the source of solar wind) and heavier isotopes to concentrate nearer the core. As an aside, the isotopic discrepancy is less for heavier elements because the relative difference in mass decreases (e.g. heavy hydrogen is twice the mass of light hydrogen, whereas heavy oxygen is only 12.5% heavier than light oxygen, etc.).

In the inner solar system, where the rocky planets formed, "isotope-selective self-shielding during ultraviolet (UV) photolysis of CO" caused—and still causes—planetisimal source material to become enriched in heavier oxygen isotopes with respect to the solar mass (McKeegan et al., 2011). In fact, this model accurately predicted the new data collected by Genesis.

I would suggest, therefore, that Mr. Thomas jumped too hastily to his conclusion that "the nebular hypothesis is dead...and only supernatural beginnings can account for the peculiarities of the solar system, including the unique amounts of oxygen contained in the sun, planets, and moons." Moreover, this 'God of the Gaps' addendum to the non sequitur resulting from his misreading of McKeegan et al.'s is neither helpful nor convincing (I know, that's a mouthful). Presumably, by "supernatural beginnings", Mr. Thomas is referring to the sudden appearance of fully formed planets and a sun less than 10,000 years ago. But how can this arbitrary and unsupported proposition aid our investigation of the solar system? (By unsupported, I mean absent even from the text of Scripture.)

Not surprisingly, Mr. Thomas and other YEC proponents are confident they can explain any new piece of data. But their ability to explain new data retrospectively does not arise from the scientific, predictive power of YEC. Rather, it arises from the fact that YEC offers no definitive expectations. If the sun's isotopic composition turns out to be X, it is because God created it that way; if the isotopic composition is Y, it is because God created it that way. Mr. Thomas did not explain how the new isotopic data "lead to a purpose-minded designer," despite his likening them to "forensic clues". He merely stated, mistakenly, that the data contradict part of the Nebular Hypothesis.

So, we can all put our minds at ease. The new oxygen isotopic data presented by McKeegan et al. (2011) not only corroborate the Nebular Hypothesis, but allow scientists to estimate the average oxygen isotopic composition of the primordial solar system! And if that doesn't just double your pulse with an astronomical dose of adrenaline, then you probably have no idea what I'm talking about. In fact, you should probably check your pulse anyways...in case you are dying from boredom. Until next time!

1 comment:

  1. I'm glad you commented on this. I read that piece on the ICR and could tell he was jumping to the wrong conclusions, because, it seems, that's what desperate YECs do with evidence they don't understand.