Zero. That satellite we call "The Moon" has only been around for a couple of billion years (not as long as the Earth) and was either a wandering asteroid/comet or is a large fragment of the earth that came about as the result of a comet/asteroid hitting the earth. In approx 1986 astronomers discovered another "natural" satellite but that turned out to be a wandering asteroid that got picked up by the Earths gravitational field, and the one they found a few months ago is likely to be an old rocket booster
Either that or the aliens put them there, just like the implant in my nose.