image by Christian Arsidi, Vernouillet, France
Will there always be new photos of familiar objects on which we see new things? I hope so! Posidonius is a favorite LPOD crater, most recently seen in a classic shot by Tamas Ladanyi. Here is another image that has higher resolution than any I’ve seen before, and reveals features more commonly seen on spacecraft views. The floor of Posidonius has been uplifted and tilted, creating the high concentric ridge on the left side in this south-up image. The uplifted block of older terrain is cut by three major and numerous minor linear rilles. In a broad arc along the right side of the crater, mare lava has welled up to cover the lower parts of the crater floor, and one of the Moon’s most remarkably sinuous sinuous rilles occurs. For terrestrial rivers, tight bends such as this occur when water flows over nearly flat land, and as a friend once said, the river doesn’t know what to do with itself. There is no high resolution topography of Posidonius’ floor, but I bet there is a slope of the smooth mare fill from left to right. But the rille itself goes from near the west rim to the north wall and then curves along the northeast wall - one direction must be downhill but I can’t tell which from this image. An Apollo 15 photo reveals that at its southern end (top) the rille bends to the west and literally hugs the western wall until it reaches the low spot in the rim. It looks like it emptied lava out on to Mare Serenitatis, but I have not yet seen evidence of that on the mare. Another thing to notice: the thin linear rille on the left edge is one seen before, but this low lighting suggests a second smaller rille parallels it.
Technical Details:
305mm Meade SCT.
Related Links:
Rükl plate 14
More of Christian’s images
Yesterday's LPOD: A Lost Peninsula
Tomorrow's LPOD: At the Edge of Certainty
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