December 21, 2012
Not the End of the World
Three years ago LPOD featured an oblique image from Kaguya that surprisingly implied that the floor of Archimedes was higher than the surrounding maria. A little quantitative data soon refuted that interpretation. Now, with the remarkably high quality LRO altimetry data we can confirm that the floor of Archimedes is lower than the nearby maria. The LRO traverse shows a declining elevation of Mare Imbrium approaching Archimedes, leveling off at about 2500 m below the Moon's average elevation. At its western edge the floor is ~250 m below the nearby mare, and about half way across the floor's elevation slowly increases by 50 to 100 m, but is still lower than maria to the east in Palus Putredinis. When it seemed that lavas on the floor were higher than nearby maria a possible interpretation was that the floor lavas came from deeper sources which would likely have had higher pressure to push lava to higher levels. Now that we know that the floor of Archimedes is lower the interpretation would be the opposite. The lavas on the crater's floor were probably supplied from a different source than the nearby lavas, and that source was presumably higher than the mare source region. Although some egos may be dented when new facts disagree with earlier interpretations that is the way science works, and is not the end of the world.
Chuck Wood
Related Links
Rükl plate 22
21st Century Atlas chart 18.
Yesterday's LPOD: Background
Tomorrow's LPOD: Big Rims
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