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Saturday, July 05, 2008

How did Earth Get the Moon?

This is Steven Petrick Posting.

I happened to catch a bit of a show about the Earth and the Moon. The show was discussing how the two came to be in their current dance. At the point where I began watching they were explaining why the idea that the moon was in fact "thrown off" by the Earth while it was still molten was mathematically impossible, and then entered into a discussion about "capture". They explained briefly the original concept and why it was not workable because the a slowing medium to reduce the velocity of the moon was not present.

It has been said that "God does not play dice with the universe", but it seems to me that given enough moving objects in a large enough body with enough time, any event no matter how improbable will eventually occur. That we, in turn, might massively benefit from such an improbability is not out of the question.

If one posits the moon as originally a separate body pursuing its own orbit around the solar system early in its formation, could not the following have occurred (extremely unlikely, but see the above comments about time and quantity)?

The Moon, pursuant to its own individual orbit within the Solar System, might have made a very close approach to the Sun, accelerating as it came in due to the gravitational pull of the Sun. Having completed that close approach, it moved away from the Sun, braking (due to the effects of that major gravitational influence). As it continued to slow, its orbital movement intersected with the orbit of the Earth. The gravitational influence of the Earth at that juncture was just enough to pull the moon into a stable orbit around itself.

It would obviously be an extremely delicate balancing act. The Moon would obviously be near the perigee of its outward bound orbit from the Sun, near the tipping point to begin its return journey towards the Sun, but still with enough momentum to enter into a stable orbit around Earth, i.e., be captured by the Earth's Gravity.

I do not possess the math skills to prove, or disprove, the above. It would obviously be a very rare event (a body the size of Earth capturing a body the Size of the Moon), but if you need a braking mechanism, one already exists in the form of gravity. What the orbit would be, I could not begin to fathom, but it seems to my untrained mind a perfectly rationale explanation for how the Earth captured the Moon.