|MadSci Network: Astronomy|
Well your question of the moon and craters are very much related. Our planet is covered by something that is called atmosphere; it's what keeps the oxygen, hydrogen, clouds and other gases in our planet. It also acts like a shield against debris from space. The moon also has an atmosphere but it is very thin so even tiniest meteor hits the surface of the moon at its full velocity at least 20 km/sec. When this impact happens rocks that get hit by the meteor smash up and get turned into dust; this impact will also create a crater depending on the size of the projectile. Imagine this happening for a few hundred million years the surface gets a lot of dust and craters, in some places the depth of the dust is around 2 meters in the oldest surfaces it can be around 20 meters. This powder blanket that covers the moon is called the lunar regolith, it is a term for mechanically produced debris layers on planetary surfaces. Many scientists also call it the "lunar soil" and some people use the term "sediment" for regolith. [Moderator's note: because the Moon has no atmosphere, it also has no weather. So the footprints left by the astronauts stay there because there's no wind, rain or snow to remove them.]
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