The origin of the surface material distribution on asteroid 25143 Itokawa

• Main Authors: Kai-Lung Sun, 孫凱隆
• Other Authors: Wing-Huen Ip
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/3y23pf

碩士 === 國立中央大學 === 天文研究所 === 94 === The surface material on asteroids plays important roles on the understanding of the formation and evolution of the solar system. The Japanese spacecraft Hayabusa launched in 2003 and arrived at asteroid 25143 Itokawa in 2005. The purpose of the mission is to observe the asteroid, collect samples from the surface, and return to Earth with these precious samples in 2010 if everything goes well. The observations by the imaging camera onboard the Hayabusa spacecraft found that asteroid Itokawa is an ellipsoidal-shaped asteroid with its three axes measured to be close of 540 × 270 × 210 meters. From pictures obtained by Hayabusa, people may easily found that the surface of the asteroid could be divided into two regions, the rough regions which are full of boulders and the smooth regions which have only centimeter and sub-centimeter sized particles. The smooth areas are located near the rotation axis. In this work, we try to explain why there is such a difference in surface material distribution. We assume that asteroid 25143 Itokawa is composed of a contact binary system, with the slit between the two components filled with collisional fragments and crater ejecta. Seismic resurfacing effect caused by impact events could mobilize the lighter particles. The small particles could therefore be moved to a potential minimum area (Cheng et al. 2002) and formed a ponded deposit area. In order to prove this assumption, tra jectories of crater ejecta have been simulated. We build a contact binary model using 1918 3-D grid points in our program with its total mass, size, and rotation period taken to be the same as asteroid Itokawa. The tra jectories of test particles are calcaulated by using the fourth order Runge-Kutta algorithm. In our simulation, all test particles are ejected randomly with elevation angle of 45 degrees. The ejection velocity is distributed between 0 and 15 cm/s. Tra jectories of 25,600 test particles are simulated. Results show that there is a concentration of re-impact sites near the rotation axis, especially for particles with initial velocity between 9 ∼ 12cm/s. Thus the surface material distribution of asteroid Itokawa could be explained by combining our results with the seismic resurfacing mechanism.