April 19, 2010
Three of a Kind
image by Richard Hill, Tucson, Arizona
Kepler, Encke and Kunowsky are three of a kind. Each crater has a polygonal outline, delta-shaped rim profile, and shallow floor. Kunowsky (bottom right) has a lava-flooded floor with a bit of a central peak and terrace segment. Encke (bottom left with long rim shadows) is a floor-fractured crater, with part of a fracture showing brightly. Kepler (top left) is shadow-filled, but previous views reveal it to have slumped walls that encroach into the floor, embayed by patches of smooth material. The different interiors show that it is the polygonal shape and delta walls that are most unique about these craters. To the east that are two more similar craters, Gambart and Reinhold B. There must be some reason for the concentration of these unusual craters here. I wonder if it is that they impacted into very thin layers of mare lavas over thick Imbrium ejecta? I don't know of any modeling or experiments that would explain why impact into basin ejecta - presumably less consolidated than mare - would cause polygonal outlines. At Meteor Crater in Arizona, the strongly polygonal rim edges align with regional lines of weakness. The edges of these three lunar craters are roughly parallel, perhaps there is a regional stress field here.
26 March, 2010, 04:08 UT. C14 + 2X barlow f/22 + UV/IR blocking filter + DMK 21AU04. 200/2000 images. Registax 5 for the coadding of images and wavelet filtering and then iMerge for the making of the montage and PhotoWise plus Gimp for final touch up.
Rükl plate 30