September 27, 2014
A Rare Dark Collar
images from LRO QuickMap
While admiring an enhanced color image of the nearly full Moon I noticed a darkness around Zucchius, a youngish crater that marks the south end of the Schiller-Zucchius Basin. I checked it out on the LRO QuickMap no shadows image, which I have here radically enhanced to create one of the ugliest images to appear as an LPOD. But it is an interesting discovery (or rediscovery, or more complete understanding). Does this remind you of anything? It should make you think of the dark collar surrounding Tycho. That grey nimbus encircling the wall (according to Elger's The Moon) is due to a veneer of impact melt. Zucchius seems to be another example of this phenomena only seem on very young craters formed on the highlands. The right QuickMap image shows the Zucchius area under lower illumination, revealing no evidence for the ring - a high Sun is required. That the collar is impact melt is suggested by the occurrence of melt on the floor of the crater (bottom right image also from QuickMap) and also in small perched ponds on the rim. Notice that a substantial amount of darkness occurs on the southern wall of Bettinus B, a 25 km wide crater south of Zucchius. A closeup view reveals that that segment of the walls is veneered by a flow-like deposit of material - probably a brushing of impact melt from Zucchius. Three other major dark collar craters are Ohm, Vavilov and Jackson, all on the far side. Each of these is a bright ray crater with cracked impact melt on it's floor. A quick look revealed no other dark collar craters, but smaller ones may exist. In looking for these I realized that no modern listing of craters with impact melt seems to be available beyond the beginning one on the Moon Wiki.
21st Century Atlas chart 24.
Yesterday's LPOD: Mystery Region #2
Tomorrow's LPOD: Slopes, Dikes and a Sliver of Illumination