Another Crash in Lunar Tunes
Our moon has two faces. One is the familiar man-in-the-moon side that always faces Earth. The other side is mountainous and heavily cratered, possessing a thicker crust with almost none of the large impact basins we see as dark maria on the Earth-facing side. The giant impact theory for the origin of the moon – that a Mars-size object hit the Earth and the debris coalesced into our planetary companion – has been controversial since it was first proposed. Will adding another impact help? It all depends on what one means by “scientific progress.”
In Nature this week,1 Jutzi and Asphaug presented a new model for the origin of the lunar highlands on the far side of the moon. They first proposed that the impact against Earth formed two moons, not one. The bigger piece formed the moon; the other piece, caught in a stable orbital position called a Trojan point, hung around for a few tens of millions of years. Being smaller, it crystallized faster. After awhile, something nudged it toward the bigger piece, and with a gentle collision less than the speed of sound in rock, it merged into the moon. Their computer models show it moving most of the magma to the near side of the moon and depositing material on the far side, forming the lunar highlands.
Maria Zuber considered this theory in the same issue of Nature.2 She said that since several alternatives can produce the lunar profile, “the current study demonstrates plausibility rather than proof.” The BBC News and Live Science summarized the theory with one frame from the computer simulation.
Being tied to the giant impact theory, the two-moon theory will suffer from the same defects (02/19/2007, 07/14/2008, 01/25/2009, 07/10/2010), but seems to offer some explanatory value at the price of complicating the picture with another body which, like the initial impactor, must be finely tuned to reside at the Trojan point for a period of time and then impact the larger body at the right speed. Future missions might be able to support the theory with better gravity maps and sample returns. For now, it is little more than a conjecture.
1. M. Jutzi and E. Asphaug, “Forming the lunar farside highlands by accretion of a companion moon,” Nature 476 (04 August 2011), pp 69–72, doi:10.1038/nature10289.
2. Mariz T. Zuber, “Planetary science: Making mountains out of a moon,” Nature 476 (04 August 2011), pp. 36-37, doi:10.1038/476036a.
Impacts seem to be evolutionists’ favorite tools. Whenever there is a feature in the solar system that defies explanation, send in a finely-tuned impactor to cause it. This is humorously illustrated in Spike Psarris’ educational video, “What You Aren’t Being Told About Astronomy, Vol 1: Our Created Solar System.” Of course, historic impacts can never be observed, so they provide theorists with handy magic bullets. They allow them to look busy and get grant money, play with computers, publish man-made pictures of imaginary scenarios, and stay employed, without having to ever prove anything.
One of the authors said of his theory compared to others, “Hopefully in future [sic], a sample return or a manned mission would certainly help to say more about which theory is more probable.” He said probable – not correct. Two percent is higher than one percent; does that make it closer to the truth? While they’re playing planetary billiards, why not throw in another moon at the other Trojan point? At what stage do the number of ad hoc variables render the theory a case of diminishing returns? When your field of possibilities excludes intelligent causes, you have to rest your case with whatever natural causes your assumptions permit, no matter how improbable. Whether that constitutes progress in scientific understanding is another issue.