Thursday, November 29. 2012
Almost all lunar craters show evidence of mass wasting (slumping/avalanches) in their walls. Occasionally a crater is found where post-impact wall modification occurs non-uniformly along the crater rim, causing an asymmetric crater outline. This unnamed crater on the lunar farside highlands may show an example of this type of behavior. A slight enlargement of the crater diameter is visible along the southwestern rim (see WAC mosaic frame below), coincident with a voluminous deposit of slumped material on the crater floor. This material likely slumped shortly following the original crater excavation.
A variety of interesting floor patterns are visible in this deposit. As portions of debris reached the floor, lost energy, and ground to a halt, material still in motion piled up behind, producing a series of en echelon fault-like structures in the unconsolidated mound.
The final deposit is over 7 km wide. Resting loose on its upper surface are high-reflectance boulders in what appear to be linear arrays at rough right angles to the fault strikes. What might have caused this arrangement among the rocks? Are they ejecta from another impact, or related to the featured crater? It is quite possible that they simply represent the fragmentation of large blocks that rolled down the slope and broke up as they encountered the rugged terrain below. What additional clues could you look for to find a definitive answer?
A larger portion of this deposit can be seen in the full NAC image here. Areas affected by ejecta from this impact were recently explored in Scours and Ejecta Near Jules Verne Y. An example of a strongly asymmetric crater rim is covered in Ryder Spectacular!