Some Morphologic Systematics of Complex Impact Structures

Similarities among impact structures on different planets and satellites suggest that the cratering process transcends variations in both target and impactor. In particular, impact may control the spacing of concentric rings, if not their actual emplacement. In at least four respects the scaled horizontal dimensions of complex meteorite‐impact structures on Earth resemble those of multi‐ring basins and large craters on the Moon, Mars, Mercury, and some outer satellites: (1) Base diameter of the (topographic) central peak is a constant 20% to 25% of the rim diameter in small complex craters; (2) it averages only half as much in large structures that also have concentric rings; (3) the inner ring of a two‐ring crater lacking a central peak is half the diameter of the outer ring; (4) adjacent rings of complex craters that have more than two concentric rings are spaced at a constant interval of about (2.0 ± 0.2) 0.5 D, both inside and outside the main ring. Two minor differences in morphology suggest that uniquely terrestrial conditions may control some horizontal dimensions of meteorite craters: (1) the inner ring of a two‐ringed structure that also has a central peak is 0.5X the diameter of the outer, not 0.4X as it is for peak‐plus‐ring basins on the planets; and (2) two‐ring and multi‐ring meteorite craters occupy the same size range, whereas on planets most two‐ring basins are smaller than multi‐ring basins.