In this work, we investigate the rotational dynamics of the ginger-shaped near-Earth asteroid 4179 Toutatis, which was closely observed by Change-2 at a distance of $770pm120~$ meters from the asteroids surface during the outbound flyby citep{Huang20
13} on 13 December 2012. A sequence of high-resolution images was acquired during the flyby mission. In combination with ground-based radar observations collected over the last two decades, we analyze these flyby images and determine the orientation of the asteroid at the flyby epoch. The 3-1-3 Euler angles of the conversion matrix from the J2000 ecliptic coordinate system to the body-fixed frame are evaluated to be $-20.1^circpm1^circ$, $27.6^circpm1^circ$ and $42.2^circpm1^circ$, respectively. The least-squares method is utilized to determine the rotational parameters and spin state of Toutatis. The characteristics of the spin-state parameters and angular momentum variations are extensively studied using numerical simulations, which confirm those reported by citet{Takahashi2013}. The large amplitude of Toutatis precession is assumed to be responsible for its tumbling attitude as observed from Earth. Toutatis angular momentum orientation is determined to be described by $lambda_{H}=180.2^{+0.2^circ}_{-0.3^circ}$ and $beta_{H}=-54.75^{+0.15^circ}_{-0.10^circ}$, implying that it has remained nearly unchanged for two decades. Furthermore, using Fourier analysis to explore the change in the orientation of Toutatis axes, we reveal that the two rotational periods are 5.38 and 7.40 days, respectively, consistent with the results of the former investigation. Hence, our investigation provides a clear understanding of the state of the rotational dynamics of Toutatis.
On 13 December 2012, Change-2 conducted a successful flyby of the near-Earth asteroid 4179 Toutatis at a closest distance of 770 $pm$ 120 meters from the asteroids surface. The highest-resolution image, with a resolution of better than 3 meters, reve
als new discoveries on the asteroid, e.g., a giant basin at the big end, a sharply perpendicular silhouette near the neck region, and direct evidence of boulders and regolith, which suggests that Toutatis may bear a rubble-pile structure. Toutatis maximum physical length and width are (4.75 $times$ 1.95 km) $pm$10$%$, respectively, and the direction of the +$z$ axis is estimated to be (250$pm$5$^circ$, 63$pm$5$^circ$) with respect to the J2000 ecliptic coordinate system. The bifurcated configuration is indicative of a contact binary origin for Toutatis, which is composed of two lobes (head and body). Change-2 observations have significantly improved our understanding of the characteristics, formation, and evolution of asteroids in general.
