[plain talk]

It seems the moon could have formed like the Earth formed. The Moon could have aggregated into what it is and gotten close enough for Earth’s gravity to capture it. I don’t understand why a grand collision had to necessarily take place to produce the Moon.

[CurlyDave]

...It seems the moon could have formed like the Earth formed. The Moon could have aggregated into what it is and gotten close enough for Earth’s gravity to capture it. I don’t understand why a grand collision had to necessarily take place to produce the Moon.

The problem is that two independent bodies can not "capture" each other. There is too much momentum and kinetic energy. Unless there is a collision, they will inevitably separate, essentially fly right past each other. If there is a third body, under exactly the right conditions, it may gain momentum and allow two bodies to be mutually captured, but this is very improbable.

OTOH, the earth-moon system is essentially a binary planet. Stand back and look at the whole forest instead of the individual trees. Binary stars are well known and actually very common. Why the earth-moon system could not form by a variation on the same mechanisms that form binary stars is the question we should be asking.

[SunkenCiv]

Some selections from the lunarorigin keyword, out of the FRchives:

• When the Days Were Shorter

  10/04/2004 10:31:59 AM PDT · by SunkenCiv · 54 replies · 2,195+ views

  Alaska Science Forum (Article #742) | November 11, 1985 | Larry Gedney

  Present-day nautilus shells almost invariably show thirty daily growth lines (give or take a couple) between the major partitions, or septa, in their shells. Paleontologists find fewer and fewer growth lines between septa in progressively older fossils. 420 million years ago, when the moon circled the earth once every nine days, the very first nautiloids show only nine growth lines between septa. The moon was closer to the earth and revolved about it faster, and the earth itself was rotating faster on its axis than it is now. The day had only twenty-one hours, and the moon loomed enormous in...

• Ancient impact may have bowled the Moon over

  10/30/2007 7:39:35 PM PDT · by SunkenCiv · 12 replies · 217+ views

  New Scientist | April 17, 2007 | David Powell

  An enormous impact basin located near the lunar south pole may have caused the Moon to roll over early in its history, new research suggests... Called the South Pole-Aitken (SPA) basin, it is 2500 kilometres wide and 12 kilometres deep and is thought to have been created about 4 billion years ago. Francis Nimmo of the University of California in Santa Cruz, US, believes the impact probably occurred near the Moon's equator. That is because the equator lies in the plane of most other objects in the solar system and therefore would more likely be in a hurtling space rock's...

• Far side of the moon 'could have been visible from earth'

  01/23/2009 12:23:42 AM PST · by LibWhacker · 23 replies · 685+ views

  Telegraph | 1/21/09 | Kate Devlin

  The far side of the moon could have been visible from earth billions of years ago, a new study suggests.The relative rotations of the moon and the earth mean that only the one side is ever visible. However, scientists believe that the impact of a large asteroid hitting the moon could have flipped it around, turning a different side that we now see towards earth. A study of craters on the far side of the moon suggests that it was hit by a large object around 3.9 billion years ago.

• The Moon may have formed in a nuclear explosion

  01/30/2010 12:03:32 AM PST · by LibWhacker · 30 replies · 787+ views

  PhysOrg | 1/28/10 | Lin Edwards

  (PhysOrg.com) -- A new theory suggests the Moon was formed after a natural nuclear explosion in the Earth's mantle rather than after the impact of a massive object with the Earth, as previously thought. The problem with the impact hypothesis is that simulations calculate the Moon should be composed of 80% impactor and 20% Earth, whereas in fact the isotope ratios of light and heavy elements found in Moon rocks so far examined are virtually identical to those on Earth. The fission hypothesis is an alternative explanation for the formation of the moon, and it predicts similar isotope ratios in...