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Earth's Moon is a Rarity
Smivs writes "Scientists have concluded that moons like the Earth's are actually quite rare. Only 5-10% of planetary systems are likely to contain moons formed by planetary collisions. 'By the time the Earth's moon formed, when the Sun was 30 million years old, the planet formation process in our Solar System should have been approaching its end. In the latest study, Dr Gorlova's team looked at the heat signature of stars using the infrared. This allows astronomers to predict how much of that heat comes from the star itself and how much is re-emitted by dusty material encircling it.'"
Isn't this rather old news? I thought that it was already pretty well known that Luna is rather rare, as shown in the Rare Earth hypothesis?
Earth and Pluto are similar in having a moon which is a decent fraction of their own mass. The two moons of Mars, and the moons of the four gas giant planets are minute in comparision to their primary bodies.
Earth and Pluto are sometimes called binary planets for this reason. And there is no easy way to show how they formed in this way, other than invoking chance impacts shortly after formation.
http://michaelsmith.id.au
While it's true that the moon is currently receding, it will eventually stop and begin approaching the Earth, then pass the Roche Limit, break up, and generally cause everyone to have a bad day. However, the universe might not last long enough for that to happen. As for the proto-earth/moon impactor, it was absorbed into the system, with the lighter materials of both it and proto-earth forming the moon, while the two cores sank to the bottom of what became Earth.
Since there are no -1: misinformation in the comment system, I instead reply to your post with wikipedia's article.
Antiope
Orbit of the Moon
Barycenter(Centre of mass)