Crater Birt and Thebit A, Moon
Taken by Howard Eskildsen on January 25, 2021 @
Ocala, Florida, USA
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Camera Used: Unavailable Unavailable
Exposure Time: Unavailable
Aperture: Unavailable
ISO: Unavailable
Date Taken: 2021:01:27 10:46:18
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Details:
So many things leap out of this image, but for now I will concentrate on two small craters, Birt, and Thebit A. Birt lies near the center of this image with bright radial bands except where shadowed on the eastern side. It overlaps its smaller counterpart Birt A and the shared wall is convex towards the larger of the pair. This seems strange, since from Birt appears younger than Birt A and it would seem that the larger, younger crater would deform the contact wall in the opposite direction. Note also that there was massive slumping into Birt A and some slumping into Birt from the area of contact. Measurements from LROC QuickMap show the material slumped into Birt A is about 40 meters higher than the common wall, so perhaps this is a combination of slumping and of material shoved into Birt A by the later impact of Birt.
Is it unusual for the common wall between two craters of different ages to have a common wall with the convexity bulging towards the larger, younger crater? Apparently not. On the right of the image is a trio of overlapping craters that resembles a ladybug sipping a drop of dew. The middle crater is Thebit A and where it contacts the smallest crater of the trio, Thebit L, the convexity of the common wall bulges towards the larger of the two craters. Weathering of the craters visible on this image and on the LROC QuickMap suggest that Thebit A is the youngest and so impacted last, yet did not push the common wall into the smaller crater.
Why does this happen? I don't know, but I have some ideas that will have to await more data before I can speculate further.
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