Our moon is a very special satellite. Mercury and Venus have no moon. Mars has two moons which are shaped like irregular potatoes and appear to be captured asteroids.
The Moon is a spherical wonder. Its gravitational pull controls our tides. Moving away from the Earth at rate of about an inch per year, at times, its orbit is influenced by Jupiter and Venus. Rocks on the Moon do not contain the chemical signature for water and that points to a very strange origin.
Many students of astronomy believe that about 40 million years after the birth of the Sun, our Earth was hit by a sister planet, Theia, a Mars-sized planet with nearly the same orbit as the Earth. The debris of that collision created our Moon and it has been drifting away from the Earth ever since. The iron core from Theia fell back to Earth, enriching this planet.
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