A new piece in the Moon puzzle.The formation of the Moon has puzzled scientists for generations. The

A new piece in the Moon puzzle.The formation of the Moon has puzzled scientists for generations. The best theory we have at the moment is called the ‘Giant Impactor Hypothesis’. We’ve covered this before on Earth Story (http://goo.gl/k6HarI), but briefly, this theory says that Moon formed after a small rocky planet (around the size of Mars) collided with Earth. This collision threw up an enormous cloud of debris, much of which orbited the Earth and eventually coalesced into the Moon.This theory fits well with what we know about the Moon. The 'Giant Impact’ would have removed material from the outside of Earth, and left the molten iron core of our planet behind. As we’d expect in this scenario, the Moon has very similar geology to the outer surface of Earth, with very little iron. So far so good.However, the chemical make-up of the Moon, all the way down to the isotopic compositions of the elements, is very similar to the surface of the Earth. Too similar. So similar that the planet that collided with the Earth would have had to be nearly chemically identical to Earth to form the Moon we see today. Until this study, the odds of this happening were well below 1%, making the 'Giant Impact’ hypothesis extremely unlikely.The Israeli study, published in Nature this week, shows the results of state-of-the art computer models, based on our best understanding of solar system formation. They used the models to test the chances of two 'twin planets’, with nearly identical chemical composition, colliding. Their models showed that this was actually quite likely in the early solar system. The basic finding is that planets that form near each other are more likely to collide, and are also more likely to have similar chemical compositions. They are likely to be similar because they have formed as 'sister’ planets - at similar distances from the Sun, and form the same basic material.The study found that in planetary collisions like the 'Giant Impact’, there is a 20-40% chance that the planets are as similar as the Earth and the Moon are today. This translates to a 20-40% chance that the Giant Impactor Hypothesis is correct, promoting it from 'improbable’ to 'quite likely’ - a great improvement on the 1% chance we gave it before. This is a major missing piece in the puzzle of how the moon formed.OBImage credit: Hagai Perets, via http://goo.gl/S3KgKLNature News Article and PodCast: http://goo.gl/S3KgKLA more erudite summary: http://goo.gl/PhBJyfOriginal Article: http://goo.gl/2blKx9Other Moon-related Earth Story posts:- Formation theories: http://goo.gl/k6HarIMoon + asteroids = Earth’s iron core?: http://goo.gl/8wS6zfThe Moon and Life: http://goo.gl/CaupMB -- source link

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