September 20, 2009
Lunar Orbiter V-042 image from LPI Lunar Orbiter Photo Gallery
I wonder if anyone other than Danny Caes recognizes this area? Danny recently pointed out some Lunar Orbiter V images of the Secchi Rille, and in looking at them I came across this other LO-V view that illustrates a lot of small scale lunar landforms. For geologic context see Paolo Lazzarotti's great telescopic available at much higher resolution which shows that unlike the Hyginus Rille crater chain, these pits do not occur within a rille-like channel. Here the pits are the rille. These could be collapses into a lava tube, or perhaps blowholes above a tube. Looking diametrically across the image is the Messier Rille which has hints of within-rille pits but they could be a few random impacts. Also notice that the rille is not continuous - its middle section is offset about a rille width from the ends. When a linear geologic feature has such offsets it is said to have en echelon components. On Earth, faults at right angles to the linear feature cause the offset, but I am not sure here. In the middle of the image is less than half of a semi-circular mare ridge which looks to be an almost completely gone ghost crater. Below the ghost rim is a circular dark area with three elongated hills. These hills probably were the volcanic vents for pyroclastic eruptions that deposited the halo. A similar chain of vents with a more muted ash deposit is near the top center of the image. Finally, two more features to notice - the almost parallel bright streaks are the famous rays from Messier - see Paolo's image. There are a few other intriguing small features that I'll leave you to find.
Rükl plate 48
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