spacetoday.net: New model explains formation of the Earth's Moon

Posted: Sat, Oct 20, 2012, 9:47 AM ET (1347 GMT)
Model of formation of the Earth's Moon (SwRI)

Scientists this week reported that they have developed new models of the formation of the Earth's Moon that reconciles one of the leading explanations with the compositions of the two worlds. The model, published in the latest issue of the journal Science, is based on the giant impact explanation for the creation of the Moon, where a Mars-sized protoplanet struck the early Earth, throwing off debris that formed the Moon. While that model had become widely accepted, it could not explain why the two worlds had similar ratios of oxygen isotopes. The new model uses much larger impactors, up to five times the mass of Mars. This creates oxygen radios similar for both world, although they produce an Earth rotating up to 2.5 times as fast as expected from the existing angular momentum of the Earth-Moon system. However, a companion paper explains how that angular momentum could have been reduced soon after the Moon's formation through a resonant interaction between the Moon and Sun.