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The optical images of near-Earth asteroid 4179 Toutatis acquired by Chang'e-2spacecraft show that Toutatis has an elongated contact binary configuration,with the contact point located along the long axis. We speculate that suchconfiguration may have resulted from a low-speed impact between two components.In this work, we performed a series of numerical simulations and compared theresults with the optical images, to examine the mechanism and better understandthe formation of Toutatis. Herein we propose an scenario that an assumedseparated binary precursor could undergo a close encounter with Earth, leadingto an impact between the primary and secondary, and the elongation is caused byEarth's tide. The precursor is assumed to be a doubly synchronous binary with asemi-major axis of 4 $R_p$ (radius of primary) and the two components arerepresented as spherical cohesionless self-gravitating granular aggregates. Themutual orbits are simulated in a Monte Carlo routine to provide appropriateparameters for our \emph{N}-body simulations of impact and tidal distortion. Weemploy the \emph{pkdgrav} package with a soft-sphere discrete element method(SSDEM) to explore the entire scenarios. The results show that contact binaryconfigurations are natural outcomes under this scenario, whereas the shape ofthe primary is almost not affected by the impact of the secondary. However, oursimulations further provide an elongated contact binary configurationbest-matching to the shape of Toutatis at an approaching distance $r_p$ = 1.4$\sim$ 1.5 $R_e$ (Earth radius), indicative of a likely formation scenario forconfigurations of Toutatis-like elongated contact binaries.

The formation mechanism of 4179 Toutatis' elongated bi-lobed structure in a close Earth encounter scenario