Forming Binary Near-Earth Asteroids From Tidal Disruptions

4.2.3 Influence of MBA shape/spin propertiesThe two different shape/spin distributions used produced similar results. Using the distributionsderived for SMBA shape and spin from lightcurve data, as in the Nominal case(see section 4.2.1), the steady-state binary fraction for tidal disruption formed binarieswas 1.2% (Table 4.2). This fraction increased slightly when the shape/spin distributionfor NEAs was used, increasing to 1.4%. The faster spinning NEAs generally are more effectiveat producing binaries via tidal disruption, but within this steady-state model wheredisruption by planetary encounters dominated, the overall affect is minimal.4.2.4 Influence of tidal evolutionTidal evolution during the simulation strongly change the eccentricity and semi-majoraxes of the binaries (Fig. 4.9). The lifetimes against disruption due to close encountersare greater for closer binaries, and for these binaries the eccentricity damping time-scalesare relatively short. The effects of eccentricity damping is quite noticeable with a strongpeak of nearly half the binaries at 0–0.1 eccentricity with small numbers spread out athigher values. This is vastly different than a simulation with no tidal effects where thebulk of the eccentricity values are greater than 0.1.Similarly the semi-major axis distribution is noticeably increased for the simulationwith tidal effects compared to the one without (Fig. 4.9). The peaks of the distribution arepushed from 3–5 R pri towards 5–8 R pri . This does move some bodies out beyond 10 R pri ,though time scales to move any beyond that are very long, and the lifetime of the binaryagainst disruption will decrease rapidly with increasing a.The overall binary fraction increases slightly from 1.2% to 1.7% (Table 4.2), thoughthe size ratio between the two components is essentially unchanged (Fig. 4.9). Though thetidal effects noticeably affect a and e they are not strong enough to increase a so rapidly101