I'm skeptical of the Lagrangian moons (although I haven't read his research paper, only the linked Fox news story).
You can't just toss stuff at a Lagrangian point and have it stick. Getting it to stay there is much like getting something to remain in orbit: You approach hyperbolically, then you have to brake into orbit.
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Lissauer and Chambers figure the two small moons would have orbited Earth for about 100 million years before the slight gravitational tugs from the solar system's other planets sent them spiraling off course, either to crash into the Moon or Earth or to drift off into space.
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And drifting off into space means orbiting the Sun in an Earth-crossing orbit for millions of years before striking the Earth or Moon.
But its not the solar system's other planets that would have perturbed Lagrangian moons out of orbit. It's the solar tide, which is magnitudes greater than perturbations from the other planets.
Quote:
Originally Posted by eburacum45
...I have been wondering if the impact of those moonlets might have caused the Imbrium or Crisium mare or some other major feature on the Moon's surface, like Tsiolkovskiy crater.
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I've wondered the same thing. But not from Lagrangian moons. Its very likely that Earth had multiple moons in the beginning, but for months, not millions of years. As the debris from the Mars-sized impactor coalaced, it likely formed several moons. The largest one (which became the current moon) dominated, and most of the smaller moons collided with it within the first few months. After it was almost its present size, it had enough gravity to eject some of the remaining moonlets into interplanetary space, where they would orbit the Sun in Earth-crossing orbits for millions of years, perhaps to return and punch large holes into Luna's the newly-formed crust.
It's also possible that there were some additional stable moons that lasted for millions of years. But as the Moon migrated outward, it would have destabalized their orbits.