N-body Simulations of Lunar Accretion in an Impact-Generated Disk

R. M. Canup (University of Colorado), S. Ida (Tokyo Inst. of Tech.), A.G.W. Cameron (Harvard/CFA), H. F. Levison (Southwest Research Institute), G. R. Stewart (University of Colorado)

A recent work (Ida, Canup and Stewart 1997) describes results from the first N-body simulations of accretion in a protolunar disk generated by a giant impact with early Earth. Previous statistical modeling by Canup and Esposito (1996) suggested that a lunar-sized Moon was most easily formed from disks produced by impactors with about twice the angular momentum of the current Earth/Moon system. In Ida et al. (1997), we modeled accretion using the Canup and Esposito (1995) tidal accretion criteria and tracked the evolution of between 500-1500 initial particles. That work identified a relationship between the fraction of disk material that becomes incorporated in the moon or moons which accrete in the disk and the initial ratio of disk angular momentum to disk mass. Centrally-condensed disks are more likely to yield a single moon, but incorporate only 15-30% of the initial disk mass into the moon which forms. More radially extended disks yield systems of multiple moons which incorporate between 40-50% of the initial disk mass. Current work focuses on N-body simulations with improved resolution and direct comparison with output from the high-resolution smoothed-particle hydrodynamics modeling of the impact event presented in Cameron (1997).