Today's Featured Image shows a bench crater in the lunar mare. Bench craters are so called because they have a small bench lining the interior of the crater wall. In fact, this bench is interpreted to be the contact between the bottom of the regolith (soil) and the basaltic bedrock below. The regolith is a layer of brecciated material that develops as a result of micrometeorite bombardment, it consists mostly of a fine powder containing numerous angular fragments. The regolith and the coherent basalt both have different strengths, with the regolith being easier to displace than the underlying basalt during an impact event. The result of a moderate impact (in this case one that produced a 160 m diameter crater) into this area then gave us a spectacular view of the local stratigraphy.
Regolith development takes time, and many meteor impacts. Since the impact flux (the number of meteors and comets hitting the Moon) has not been constant in the past, the mare have a thinner regolith than the highlands.
Can you find any more bench craters in the full LROC NAC?
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