Comet craters versus asteroid craters

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Comet craters versus asteroid craters

Bailey, M.E.

Abstract The assumptions used to determine whether active comets or earth-crossing asteroids currently dominate the terrestrial cratering rate are reviewed and intercompared. The principal sources of uncertainty are the number and mass distributions of earth-crossing bodies, the adopted crater-diameter scaling law, and the question whether the present populations are in a steady state. Models in which long-period comets make a significant contribution to the cratering rate imply an excessive cometary mass (≳ 100 M ⊕) for the dynamically active Oort cloud. For this and other reasons it is concluded that the majority of observed terrestrial or lunar craters larger than about 10 km are probably produced by earth-crossing asteroids. This emphasizes the importance of studies aimed at determining whether earth-crossing asteroids are themselves predominantly cometary in origin or asteroidal.