December 26, 2015
Keeping Up With The Smythiis
Originally published February 17, 2005
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Image Credit: Mario Santiago |
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Keeping Up With The Smythiis The equatorial eastern limb of the Moon is more interesting than much of the terrain immediately nearer the Earthside. The reason is twofold: (1) the area between Crisium and Fecunditatis and the limb is boring because it lacks any distinctive large fresh craters, and instead is a mishmash of older, look-alike craters flooded with and surrounded by mare material; and (2) the limb is home to two maria – Marginis and Smythii – that occupy two impact basins. Of the two, Smythii offers more vestiges of its basin structure – principally its well-defined, curved rim. When the sunset terminator is just east of Smythii you can observe the shadow cast by the rim and appreciate that the mare is substantially lower than the rim. In fact, Clementine altimeter readings show that the rim rises an amazing 6-8 km above the mare. The circular outline of the rim is clearly demonstrated in Mario’s rectified view (mouseover) of Smythii made using PlanetWarp. Also clear is the two different shades of mare lavas. Crater counts imply that the darker Smythii lavas may be among the youngest on the Moon, perhaps 1.5 b.y. old. Technical Details: Related Links: Yesterday's LPOD: A Newly Named Crater Tomorrow's LPOD: Memory of a Crater |
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