CRATER ORIGIN

The craters on the Moon are due to impacts rather than to say, volcanism despite the fact that the craters are, for the most part, circular in shape. A compelling argument against volcansim is that the craters are all below sea level, the average level of the lunar surface. They are not built-up above the sea-level as are volcanoes.

A puzzle had been, Why are craters circular in shape if they are produced by impacts?

Crater formation is more like a bomb exploding rather than something simply digging out a trench or a hole. A meteor carries a huge amount of energy. A smallish asteroid, diameter of 2 kilometers, traveling around 6.9 kilometers per second (the escape speed of the Earth), has kinetic energy E = 5x1020 Joules or, in units of Megatons the energy of one Million tons of TNT (=4.2x1015), the energy yield of this smallish asteroid is roughly 100,000 Megatons. A largish nuclear weapon carries energy ~ 50 to 100 Megatons. The conversion of this kinetic energy to heat after the asteroid buries itself leads to a huge explosion which digs the crater, thrwoing material into the atmosphere. Comments Note that rays can show the direction from which the objects approached. The centers of some craters show raised mounds in their centers.

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