Can Tidal Disruption of Asteroids Make Crater Chains

Crater chains, presumably formed by weak asteroids or comets stretched apart by planetary tides, have been tentatively identiied on both the Earth and Moon. By modeling tidal disruption by the Earth and Moon of \rubble-pile" bodies, we nd that the Earth disrupts enough objects over the last 3.8 billion years to account for one or two lunar crater chains, but that the reciprocal production rate of terrestrial crater chains is too low to make any in observable geological history. A crater chain is a regularly spaced row of three or more impact craters with similar sizes and apparently identical ages. A crater chain is formed when an asteroid or comet with low tensile strength is pulled apart by tides during a close approach to a planet and separates into a train of fragments which then impacts a moon of the planet rather than escaping to interplanetary space. The projectiles themselves can only be a few tens of km { or a few seconds { apart at impact. (In this study, we do not consider \secondary" crater chains formed by falling ejecta from a much larger impact, identiied by their radial orientation to the source crater, their associations with other secondary features, and their distinctive morphology.) Comet P/Shoemaker-Levy-9 (henceforth \SL9") provided a striking demonstration of tidal disruption during its penultimate encounter with Jupiter in 1992. Chains of craters probably formed by the impacts of fragment trains similar to that of SL9 have been found on Jupiter's Galilean satellites; Voyager images reveal 8 crater chains on Ganymede and 11 on Callisto (Melosh and Schenk 1993; Schenk et al. 1996). The chains are all nearly linear, range in length from 60{626 km, and consist of between 6 and 25 closely spaced, similarly sized craters. It has been suggested that two analogous crater chains may exist on Earth's Moon. One potential chain is the relatively fresh (i.e. post-Imbrian) Davy chain, which is 47 km long and contains 23 craters, each 1{3 km in diameter. Although its orientation is roughly radial to Orientale, its morphology and setting imply that it may not be a secondary crater chain A second is the Abulfeda chain, which is > 3:8 Gyr old, 200{260 km long and has 24 craters, each 5{13 km in diameter. Its orientation is not radial to any large impact structure on the Moon (Melosh and Whitaker 1994; Schenk et al. 1996). In addition, recent …