May 10, 2021
Before And Way After
Originally published September 21, 2011
image from LRO Quick Map
I noticed this elusive feature in two recent LPODs - did you? Between Eudoxus (left) and Lacus Mortis (mostly out of view to the right) is the remnant of a likely old crater about 75 km wide. It has been filled in with ejecta from Imbrium, Eudoxus and perhaps the Lacus Mortis crater. It is nearly completely covered, with only pieces of its rim rising above the debris. If it were a fresh crater the fill must be 4 to 5 km deep. I called it an old crater, and it is probably older than 3.8 b.y., Imbrium's age, but it may have been quite fresh looking when inundated so that it's ageing was instantaneous. Consdiering that maria cover about 17% of the nearside, and thick basin ejecta may have buried another 5-10%, there have been many lunar craters that have long since been erased. A few like this are relicts of another time.
Rükl plates 13 & 14
Yesterday's LPOD: Sequencing
Tomorrow's LPOD: A Modelers Moon