The Ginger-shaped Asteroid 4179 Toutatis: New Observations from a Successful Flyby of Chang'e-2

摘要

On 13 December 2012, Chang'e-2 conducted a successful flyby of the near-Earthasteroid 4179 Toutatis at a closest distance of 770 $\pm$ 120 meters from theasteroid's surface. The highest-resolution image, with a resolution of betterthan 3 meters, reveals new discoveries on the asteroid, e.g., a giant basin atthe big end, a sharply perpendicular silhouette near the neck region, anddirect evidence of boulders and regolith, which suggests that Toutatis may beara 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$ axisis estimated to be (250$\pm$5$^\circ$, 63$\pm$5$^\circ$) with respect to theJ2000 ecliptic coordinate system. The bifurcated configuration is indicative ofa contact binary origin for Toutatis, which is composed of two lobes (head andbody). Chang'e-2 observations have significantly improved our understanding ofthe characteristics, formation, and evolution of asteroids in general.