July 23, 2011
LRO image WAC M119712464ME processed by Maurice Collins
There are thousands of craters on the Moon than nobody looks at. They seem to be absolutely generic depressions that are somewhat degraded and lack terraces and central peaks. The vast majority of highlands craters fall into this boring category. But then while looking at an LRO image of the nearside southern highlands one of these boring craters surprised me. A lot. Twenty-eight kilometer wide Tannerus is hardly identifiable because it looks a lot like many of the craters around it. Some of these 20 to 30 km wide flat-floored craters are probably secondary craters from the formation of the Orientale Basin. But no matter the origin of the hole in the highlands the fact that a rille occurs in it is very unusual. There is the Neadner fault/rille and the Janssen rille but very few other rilles are found in the highlands. Most small rilles like these are volcanic channels, and volcanism is said to be non-existent in the highlands. In looking closely at Tannerus I'd guess that the two rille segments were originally one continuous feature and that material slumped from the crater wall covered a piece of it. On the right side of the floor another fascinating feature is visible, This is a small ridge of floor material along the edge of the floor. Could it be floor material rolled up by material slumping off the walls? Is this ridge somehow related to the rille? FInally, A small off-center mound on the floor looks like the memory of a buried central peak.
PS - In researching this LPOD I discovered that I had noticed this rille in 2007!
Rükl plate 74
Yesterday's LPOD: Lion Moon
Tomorrow's LPOD: Smiling On the Moon