May 19, 2012
Circumferential Ups And Downs
image from LRO QuickMap
In discussing the rim unevenness of Kies A yesterday I thought about comparing it a classic oblique impact crater. Using the LRO QuickMap I tried measuring the circumference of the rim crest of Proclus, but kept failing because I included too many vertices, places where I turned the line in a slightly different direction to better follow the rim. I never did find out the max number of vertices allowed but finally arrived at this rim topo map. Unfortunately, the LRO Path topo tool doesn't mark on the green traverse line the distances from the starting point, making it somewhat hard to correlate the red topo line with the exact location on the traverse. The starting and end point of my circumnavigation of Proclus is at the point marked 0, and the large dip in the rim occurs at 50 km along the traverse. It has long been known that the notch out of the rim of Proclus (at 50) is low, and these data show that it is about 1200 m lower than nearby parts of the rim. This was apparently the contact point for the obliquely impacting projectile, which seems to have continued moving eastward before finally forming the crater. The other variations of rim elevation may have resulted, as Mark Settle and Jim Head suggested 35 yer ago, from azimuthial variations in ejecta thickness. By the way, the Moon-Wiki LRO image of Proclus is much better than this image from the QuickMap.
Rükl plate 26
Yesterday's LPOD: Horns And Wings
Tomorrow's LPOD: Glancing At Ryder