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How the Moon Supports the Privileged Planet Hypothesis
Evolution News & Views
Three astronomers offer "state of the Moon" addresses in Nature, revealing a troubling state of affairs: the Moon's position and composition have so far baffled efforts to propose an unguided sequence of events that might have formed it. Since Apollo, multiple scenarios have been proposed, only to be rejected as either physically impossible or statistically improbable. In this, design advocates might see the Moon dropping through two stages of Dembski's Design Filter: chance and natural law.
Moon origin theories have been on a roller coaster ride since the 1960s. Planetary scientists were optimistic that the Apollo missions would help decide among three leading hypotheses: capture, fission, and accretion. After Apollo, all three were rejected, leaving theorists without a theory until the "giant impact" hypothesis came along in the 1980s. Till recently, the scenario of a Mars-sized object striking the Earth at a glancing blow was hailed as accepted truth. TV documentaries animated the event handsomely, in vivid color. However, new observations have cast doubt on the idea.
For one thing, the size and speed of the impactor had to be finely tuned. Too large or too fast would not leave sufficient material behind to re-form into the Earth and Moon. Worse, though, are findings that elements are too similar in the two bodies. Isotopic ratios of oxygen, titanium, silicon, chromium, tungsten and other elements -- both volatile and refractory -- are nearly identical to Earth in the lunar samples, contrary to what all the impact models predict (a Moon composed primarily of impactor material). Observations and theory both discount such a possibility from likely impactors beyond the Earth. Robin Canup writes in Nature:
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The main challenge is to simultaneously account for the pair's dynamics -- in particular, the total angular momentum contained in the Moon's orbit and Earth's 24-hour day -- while also reconciling their many compositional similarities and few key differences. The collision of a large impactor with Earth can supply the needed angular momentum, but it also creates a disk of material derived largely from the impactor. If the infalling body had a different composition from Earth, as seems probable given that most objects in the inner Solar System do, then why is the composition of the Moon so similar to the outer portions of our planet? (Emphasis added.)
Growing discontent with the standard model has left astronomers scrambling to come up with alternative impact models. Maybe two "half-Earths" collided, leaving the Moon behind. Maybe the impactor scoured a variety of depths from the Earth's mantle. Maybe a fast "hit-and-run" impactor took all its own material with it. Each of these proposals creates new problems. Getting rid of excess angular momentum would require a finely tuned resonance between the Earth, Moon and Sun involving precession to transfer the excess to the Moon. Keeping the refractory elements molten long enough to mix in the dust disk is unlikely. Each new "patch" to the impact theory creates new improbabilities.
This is where remarks by the astronomers reveal that they do not wish to entertain the hypothesis that our Moon somehow reflects the working out of a design…
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