Monday, December 1st, 2008
Another question that has been on my mind for years. It didn't seem to matter where they were in the solar system and whether or not, the body in question had an atmosphere or not. Many years ago, a friend of mine conducted an experiment by firing air rifle pellets into a tray of wet sand. At low angles the pit marks were elliptical as you'd expect. So I repeat the question.
I researched it today and while it is true that almost all craters are circular, there are a few elliptical ones about. Best answer so far as I can see is that a meteorite explodes on contact and then the shock waves are sent out in a circular fashion in much the same way that the ripples are circular when you chuck a house brick into a pool of water. Now that makes sense.
Such few elliptical craters that exist are caused by a very shallow grazing incidence whereby the meteorite skips forward before breaking up. The air gun pellet does not break up which is why you get a decent ellipse.
Good, I'm happy now.
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