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Re: [Phys-L] lunar craters

One important difference between Earth and Moon is the presence of Earth's atmosphere. Meteoroids smaller than a few centimeters in diameter vaporize in our atmosphere. But an observer standing on the Moon sees no meteors as flashes in the sky. Bombarding particles all the way down to the size of elementary particles reach the lunar surface at full orbital speed. Stated differently, outer space begins right at the surface of the Moon. Small meteoroids produce small craters, including the glass-lined zap pits on moon rocks, illustrated for example at . With surface area on the order of ten to the eighteenth square centimeters, the Moon can easily have on the order of ten to the nineteenth craters that look like craters. - - Ralph McGrew