S318p.12 — Asteroid 4179 Toutatis: boulders distribution as closely flew by Chang’e-2

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Aug 4th at 6:00 PM until 7:30 PM

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Author(s): Yun Jiang2, Jianghui Ji2, Jiangchuan Huang1, Simone Marchi3, Yuan Li4, Wing-Huen Ip4

Institution(s): 1. China Academy of Space Technology, 2. Key Laboratory of Planetary Sciences, Purple Mountain Observatory, Chinese Academy of Sciences, 3. Southwest Research Institute, 4. Space Science Institute, Macau University of Science and Technology

On 13 December 2012 at 8:29:58.7 UTC, Chang’e-2 flew by asteroid 4179 Toutatis successfully after it accomplished its primary objective and an extended mission. So far, this is the closest flyby with a distance of 770 ± 120 m (3σ) from Toutatis’surface and with highest-resolution images of better than 3 m/pixel. A total of 222 boulders are identified over the imaged area, with geometric mean sizes from 10 m to 61 m. The number density of boulders larger than 20 m on Toutatis is ~ 17/km2, which is smaller than that of Itokawa (~ 30/km2), but much larger than that of Eros (~ 2/km2). The estimated diameter of the source crater generating the largest boulder (~ 61 m) is ~ 2570 m, which is much larger than the largest impact crater (~ 530 m) observed on the surface of Toutatis. Further, the ratio of the total volume of the boulders to the total excavated volume of the craters on Toutatis is ∼10%, which is much larger than that on Eros (0.4%) and smaller than that on Itokawa (25%). These results imply that most boulders cannot solely be produced as products of cratering on the surface of Toutatis. Many boulders especially larger than 20 m ones are probably surviving fragments from the parent body of Toutatis, accreted after its breakup.