The models result in an Earth with a 2.5-hour day

Oct 18, 2012 18:41 GMT  ·  By

The Moon should be the body we know the most about, it's the closest after all. And we do know a lot more about the Moon than many other objects in our Solar System. But the big question remains, how did it get there?

The recent popular hypothesis, of a giant impact resulting in the Earth as we know it and the Moon, is an interesting one and, while there is evidence and models for it, there are a few inconsistencies.

One of the big ones is that a huge impact that would have resulted in the destruction of both the proto-Earth and the object that hit it would have generated two bodies with different chemistry, at least with the collision models proposed so far.

Only a few days ago, some new research showed that the Moon and the Earth have some components in different quantities, as an impact model would predict.

Now, two new papers propose two different models for the impact that both result in the chemical composition of the current Earth and Moon.

One looks at the typical proposed collision, of an object significantly smaller than Earth hitting it and resulting in our current formation. The second looks at an impact between two similarly-sized bodies, one 80 percent heavier than the other.

Obviously, this type of models have been considered, but they've been discarded since they don't result in the movements we see today, specifically, an Earth rotation of 24 hours.

Because of the Moon's gravity, the Earth is slowing down, so for a day to last 24 hours now it should have lasted about 5 hours when the Moon formed.

But these two models both results in an Earth spinning much faster than that. The solution is a new explanation for the slowdown which takes into account the Sun's influence.

A faster spinning Earth and Moon would have resulted in the Moon being flung out of orbit around the Earth. However, the Sun's gravity brought it back towards the Earth.

This resonance model explains how a much faster spinning Earth could have still resulted in the conditions we see today.

Taking this new movement model into account, the two collision models show that both an impact between two similar bodies and an impact between a small one and a large one would result in the Moon and the Earth having largely the same chemical composition, with the heaviest elements remaining in the larger body, the Earth.

This also explains the Moon's small iron core compared to other bodies its size. Obviously, both collision models can't be right, but the fact that they both work is a boon for the giant collision hypothesis.