Why do most scientists favor the collisional ejection theory for the Moon's formation?

Answer 1

Well, the collisional ejection theory explains virtually all of the characteristics of the moon and its orbit in a plausible fashion while the competing theories all have some major deficiencies, Like, facts or features that they do not adequately explain.

Answer 2

Before Apollo there were three competing hypotheses for the Moon's formation. It spun off from a young Earth, it formed near the earth and was captured into orbit, or it formed somewhere else and wandered in and was captured.

The 'spun off' hypothesis was not widely accepted, because no-one could produce a sensible scenario in which Earth could be spinning so fast that a bit spun off it. Studies by probes and the Apollo missions, which returned hundreds of kilos of rock and soil samples from various sites on the Moon, found evidence that did not square with any of the hypotheses. The elemental composition, including certain isotopes, was so similar to Earth that it could not have formed in another part of the solar system. The density of the Moon was much lower than Earth's, suggesting it had a very small iron core, if it had one at all. That seemed to rule out forming alongside the Earth, because if it formed independently it should have roughly the same proportions of rock and iron as Earth does. As it is, the density of the Moon is very close to the density of the rocky mantle of Earth.

The big surprise when analysing the lunar samples was their total lack of water. Not only was there no water in the rock, there was no sign of any hydration whatsoever. Additionally, samples suggested that the crust of the Moon was formed from a type of rock called anorthosite, which, according to geologists, could only be the case if the entire Moon was once a mass of molten rock. An object the size of our Moon that formed by simple accretion could never have been that hot, however.

The giant impact theory was formed as a result of all these observations. A young Earth, just barely differentiated into an iron core with a rocky mantle, was hit by a Mars-sized object. The core material of these two objects was dense enough that the cores manily fused, while huge amounts of rock from the mantle were melted and blasted off. The heat would have removed any water from the rock, and then some would have settled into orbit, where it could coalesce to form the Moon. Because there was little if any core material in the ejected stuff, the Moon would lack an iron core, and hence be less dense than the Earth.

Answer 3

I think they lean toward that theory because the rocks and dirt they brought back from the moon indicated that it was made of the same material of Earth.

And it may have occurred at a time when really radical collisions were taking place all over the place. It seems to me they said that most likely Earth was still pretty much boiling with molten rock and no life had started yet. Really big chunks of debris was cruising all around and whacked all the planets for a really long time before things settled down.
Certainly that is verified by the enormous craters on the moon itself, Mars, Jupiter, Saturn. Blasted by huge chunks of matter left over from the intial formation of the planets would certainly do the trick as far as creating all the various moons circling the planets.

Answer 4

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For the same reason that any scientific theory is favored over others: because that theory better explains the available data than competing theories.

Answer 5

1. Close similarity between terrestrial materials and those found on the moon;

2. Explains why Earth's axial rotation is tilted 23-degrees