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The Earth's Capture of The Moon
For a planet as small as the Earth to have so large a satellite, more than l% of its mass, is - some say - "improbable". The Moon is 1.23% of the Earth's mass. By comparison, Ganymede is only 0.008% of Jupiter's mass and Titan is only 0.024% of Saturn. Ganymede is a little over two Moon masses, and Titan is a little under two Moon masses.
Particularly difficult is the mathematical problem of exactly how the Earth in its present orbit, velocity 66,600 mph, could capture any stray body. It makes no difference if it is a sphere like a small moon of Saturn, a fragment-shaped asteroid, an icy comet, a particle of interplanetary dust or a meteor stream or any part thereof. Any of these, approaching the Earth, will of necessity have a velocity of 69,000 mph or more.
Theoretically such a body would speed up slightly while approaching the Earth, rather than slow down. The Earth's gravity has a zone of capture, where it can successfully hold on to an object, competing with the Sun's gravity. That zone of control has a radius of slightly less than 750,000 miles. Any object, whatever its size, would enter, and pass entirely through this "zone of control&q