Forming Binary Near-Earth Asteroids From Tidal Disruptions

Thus the reaccumulated bodies in the simulations would necessarily have a higher porosityand lower bulk density than the progenitor. The inability to collapse to an equallydense state as the progenitor was considered a possible reason for disparity in primary spinrate in previous simulations, and is tested here. New progenitors were taken from tidaldisruption runs, where the bodies were disturbed or distorted but not disrupted. Thesenew progenitors matched the original axis ratios closely, and had bulk densities ∼ 1.8 gcm −3 compared to ∼ 2.2 g cm −3 .The subset of parameters used for these tests was the same as that used in the previoussections. Overall the slight density change had a minimal effect on binary production andproperties (Figure A.3).A.4 Conclusions on Parameter TestsNone of the previous three tests provided definitive solutions to discrepancies observedbetween the results of Chapter 2 and the observed binary NEAs. Altering the bulk densityof the progenitor had an expected effect in dramatically changing the number of binariesproduced. Such an effect may become increasingly important as measurements of asteroidbulk densities become more common. The dramatic increase in binary production fora 1.0 g cm −3 progenitor suggests that the overall binary production of NEAs by tidaldisruption could depend on this property, but because binaries are disrupted by planetaryencounters in a similar manner it is unlikely to change the steady-state binary fraction.Varying the resolution of the simulations does change the resultant binary properties.However, the changes are not dramatic, and do not affect the outcome of this steady-statesimulation. These differences could become important in a more sophisticated modelin which the size distribution of the Main Belt and NEA populations is included andsimulations are performed at each step, using different resolution bodies to correspond to118