Measurement and Analysis of Lunar Basin Depths from Clementine Altimetry

Moon’s early evolution (Safronov 1972, Kaula 1979). The geometries and subsurface structures of large impact basins Altimetric profiles from the Clementine LIDAR are used to calculate the depths of 29 large craters and basins on the Moon. preserve a record of the mechanics of impact, the nature Plotting the depths of the best preserved structures together of basin modification, and the thermal and physical properwith values for simple and complex craters measured in preties of the early Moon. Until recently, the geometries of Clementine studies reveals an inflection in the depth/diameter major basins could not be studied in detail in a collective (d/D) curve in addition to the one revealed by pre-Clementine sense because uniform, high quality topographic coverage data. This inflection occurs in the diameter range that corresdid not exist. Recently, the Clementine mission (Nozette ponds to the morphologic transition from complex crater to et al. 1994) provided near-global topography (Zuber et al. basin. The best empirical power law fit for basin depths is 1994, Smith et al. 1997) which is analyzed here to determine log10(d ) 5 0.41 3 [log10(D)]. This relationship is characterized the depths of major lunar basins. From the measurements, by a lower slope than that for complex craters, demonstrating we derive a basin depth/diameter (d/D) relationship which that this morphologic transition corresponds to a further deis used to address first order implications for the processes crease in the depth of an impact structure relative to its diameter with increasing size. Qualitative consideration of possible that control basin morphology and to place constraints on causes for the second inflection leads to the conclusion that the thicknesses of the maria in major basins. it is most likely a consequence of a short-term modification CRATER DEPTH: MORPHOLOGY AND mechanism that influences fundamental crater morphology, such as the increasing influence of gravity with diameter. ThickCONTROLLING MECHANISMS nesses of maria in the major basins are calculated by assuming that their unfilled depths would follow the d/D relation. Results Prior to the Clementine mission, the principal topoare compared with previous estimates and yield thicknesses graphic data set for studies of lunar impact structures was that are generally greater than those determined by studies of compiled by NASA and the U.S. Defense Mapping Agency flooded craters and less than those obtained from analysis of in the form of 1 : 250,000 lunar topographic orthophotogravity.  1998 Academic Press maps (LTOs). These contour maps were based on metric