June 25, 2012
LRO images found and processed by Maurice Collins, New Zealand
In the comments about the colorful Mare Imbrium LPOD of June 23, Danny Caes of Belgium mentioned the small, elongated crater Piazzi Smyth V between the craters Kirch and Piazzi Smyth. In New Zealand, Maurice Collins found and processed various LRO images of the feature, and in Florida, Howard Eskildsen started measuring it using the map tool in the LRO Quick-Map. If only the United Nations could respond as quickly when there are emergencies! At the telescopic scale (LRO image 1) V looks like overlapping craters, perhaps secondaries from Aristillus off the image at bottom right. When Maurice found a higher Sun LRO image of the region (3) it became clear that V is a very special crater. It is about 3 times as long as is wide and has a ridge running down its floor. Maurice then found and mosaicked together two oblique images that beautifully reveal the boat-like shape of Piazzi Smyth V. According to Howard the feature is 8.6 km long, 3.7 km wide and 440 m deep; Howard and I both found that the central ridge is too low to be measured. This is another rare example of a crater formed by a very low angle impact, like Messier (length 13 km) and at a larger scale Schiller (180 km). Enlarging the LRO image 1 shows (2) faint ridges perpendicular to the long axis of V, as with simultaneous impacts. V is considerably more subdued than Messier and thus presumably older; no butterfly wing rays are visible on the high Sun Clementine image, consistent with significant erosion. Is this a secondary of Aristillus? It isn't radial to that crater and it seems considerably larger than other Aristillus secondaries so probably it is just a random impact, but at very low - a few degrees - angle. How many more near-grazing impacts are hidden away in the LRO images as we look at features only a few kilometers or less in size?
Note: The excitement of this discovery delays the promised continuation of the June 24 LPOD.
- Rükl plate 12
- In googling I see that someone at MoonZoo came across this in Dec 2011 although they included it a forum on volcanic vents.
- An extreme oblique view, showing V's raised walls (150 m), is visible on this Apollo 15 view - zoom all the way in!
- The inner ridge is visible in both Clementine and Lunar Orbiter IV images as seen in the LROC WMS Image Map (toggle layers)
Yesterday's LPOD: Is a Half Crater Better Than None?
Tomorrow's LPOD: The Evidence Piles Up