November 19, 2014

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Inconstant Rings

image by William Pellissard, Paris, France

Mont Piton is a captivating bright peak, rising 2.4 km above the Imbrium plain. It lies along a low mare ridge that it interpreted as one of the inner rings of the Imbrium impact basin. On the nearside of the Moon, basin inner rings are mostly covered by thick piles of later lavas, but the Orientale Basin has little lava covering, and it's inner rings are well displayed. The thing I have always wondered about the inner basin rings of Imbrium is why there are only a few tall peaks that stick up far above the mare, whereas most of the rings are so low that they are completely covered by lavas, causing just low circular bumps in the surface. The inner rings of Orientale are not all the same height, being nearly missing in some places. But the Outer Rook Mountains are relatively high for about 75% of their circumference, so that if they were covered by a few kilometers of lavas they would either nearly all be covered, or large amounts would be exposed. The Inner Rook Mountains are lower and have only two arcs that might stick up above flooding lavas - see this LPOD. The higher and longer arc (between Lowell and Maunder) might, in fact, look like Imbrium's Montes Teneriffe if the lower peaks were buried in lavas. Pretty much all of the nearside basins have a lot of mare fill so that almost no Piton like peaks show anywhere. The Nectaris Basin, like Orientale, has little lava fill so its main two inner rings (Cyrillus to Fracastorius ring, and Catharina to Santbeck ring) are battered but visible. Both of these rings are not very continuous so if Nectaris had deeper mare fill there would be long arcs with no visible rings. By contrast, the similar nearly dry (little lava) Humboldtianum Basin has a massive and continuous inner ring (except for where truncated by Bel'kovich). A decent lava fill there would leave the inner ring well exposed. So, we can only say, I guess, that basin inner rings come in various states of continuity, with some remarkably tall peaks.

Chuck Wood

Technical Details
C14 à Paris, le 2014/09/16 à 03:31 TU. F/D 20, filtre rouge léger, ADC, Barlow Barcon. Caméra IDS UI 3240-NIR.

Related Links
21st Century Atlas chart 19.
William's lunar images

Yesterday's LPOD: Inconstant Star

Tomorrow's LPOD: Rillorama


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