Double-ringed and multiringed basins on the Moon and Mercury : morphologic correlations with size and other parameters

Clues to the formation of concentric-ringed basins were sought through examination of Lunar Orbitor and Mariner 10 images. Morphologic type, inner ring subtype, size, ring ratio, location, degree of modification, terrain and crustal thickness were determined and correlated with each other. Increase in size from central peak to double-ringed to multiringed basins is noted. Mercury exhibits a strong clustering of basins around 200 km in diameter while the Moon shows a more uniform size distribution. The larger basins are equatorial on both planetary bodies. On the Moon, the larger basins, with the greater ring ratios, are mainly on the nearside. Most inner rings are approximately one half the diameter of the next outer ring, though the ratio is generally smaller for central peak basins and larger for multiringed basins. No certain relationship was found for inner ring subtype, degree of modification or terrain. A rebound model of formation is preferred because it best conforms to the observations, involves a single main mechanism for all concentric-ringed basins, explains a transition from one type to another with increased energy, and confines the main energy within the basin.