October 30, 2020

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The Ultimate Meteor Shower

Originally published April 25, 2011 LPOD-Apr25-11.jpg
image from LRO NAC (NASA/GSFC/Arizona State University}

Add red color with wisps of green and this could be a magnificent auroral display. Leave it white and it is a blinding snowstorm carrying lumps of coal. Flatten it out and drape it across the surface and it is the ejecta from a fresh impact crater. It is a closeup, for the frame width is only 750 m and the out of the frame source crater is just 475 m across. The crater is a tiny bright spot just west of Firmicus, really too small to look like much from Earth, but spectacular with a telephoto lens from lunar orbit. The dark patches are each more recent impact craters that have excavated through the thin layer of bright ejecta to bring up darker material from below - the one at upper left is big enough to prove the point. "More recent" but how much? Perhaps only minutes if they are secondary craters from the main impact itself. If they are primary craters unrelated to the ejecta-creating event, counting them would be a way to gauge the age of the main crater. But you'd have to select your counting area carefully - too near the top and the crater would seem very young. Do you see why? There are very few small dark craters there because the ejecta is too thick for younger craters to excavate to the dark material below.

Chuck Wood

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