James Fincannon of NASA took the two images of the Marius Hills lunar pit taken at different times by Lunar Reconnaissance Orbiter (which I posted here) and did an overlay so that the shadow produced by pit’s rim could be easily compared with the rim itself (see below). He then did some calculations based on the sun’s angle of light shining into the cave and came up with the following calculations:

I estimate it is 60 meters from rim to bottom. The floor is flat below the surface. The rocks on the flat surface below ground are in stark relief (hard shadows) compared to above ground due to the sun coming only at one angle while above ground the albedo/reflections makes for soft shadows at this high sun angle (65 deg elevation). I cannot tell if the black portion of the combo image is a slope or more flat floor. Need a different high sun angle or azimuth to fill that in. Still I like the general pattern of the rim matching the shadow on the floor, although the image I found originally has that edge of the cave rim in shadow for a large extent.

A 60 meter drop is about 200 feet deep. This result is reasonably close to the depth estimated by Japanese scientists, 88 meters or 288 feet, based on images of the same lunar pit taken by their Kaguya probe.

Knowing the approximate depth of the entrance pit raises the much more important question: How will future lunar explorers to get to the bottom of this pit? It is ironic » Read more