Forming Binary Near-Earth Asteroids From Tidal Disruptions

of size ratios, including contact-binary formations.In the course of modeling asteroid family formation via reaccumulation of debris followinga catastrophic impact, Michel et al. (2001, 2004) found many companions of thelargest remnant. The works were focused on, and matched, many dynamical and physicalproperties of some asteroid families, but no comprehensive analysis of any binaries wascompleted.Durda et al. (2004) simulated large-scale (100 km diameter target body) catastrophiccollisions of asteroids to determine the efficiency of forming binaries via collision. Similarto Michel et al. (2001, 2004) these simulations used a smoothed particle hydrodynamics(SPH) code to model the collision and an N-body code to simulate the post-collisionevolution and re-accumulation of the fragments. The collisions were efficient at creatingbound systems out of the re-accumulated debris and many of the binaries producedare qualitatively similar to those observed in the Main Belt. Two main types of outcomesfrom these simulations were observed and classified as SMATS (SMAshed TargetSatellites) and EEBs (Escaping Ejecta Binaries). The SMATS consist of re-accumulatedfragments orbiting the largest remnant from the collision, whereas the EEBs are small andusually similar-sized fragments that have escaped from the largest remnant and becomebound to each other.Of the observed MBA binaries discovered via high-resolution imaging most are similarto SMATS, with primaries significantly larger than the secondaries. Some binarieswith small, nearly equal-sized components and large separations are suspected EEBs (see(4674) Pauling, (1509) Esclangona, (22899) 199 TO 14 , and (17246) GL 74 in Table 1.2).In the NEA population the collisional lifetimes are significantly longer than the veryshort dynamical lifetimes (∼10 Myr as determined through numerical simulations), makingcollisions an unlikely local source of binaries. The binaries observed in collisionsimulations typically have larger separations than is observed with NEA binaries. How-13