Model constructIon of Surface of asteroId 1996SF36 to be explored by MUSES-C

以下研究是为了预测隼鸟号（MUSES-C）任务的目标小行星Itokawa （25143 SF36）的表面。(1)在2001年地面观测机会的基础上，降低了小行星的性质。从小行星的光曲线中发现了以下结果：其自转周期为12.13h，比一般小行星的平均值要长，自转轴接近黄道垂直方向，自转方向为逆行，形状不规则。从光学到热红外波段的光谱观测发现，该小行星的光谱类型为s型，陨石类似物为普通球粒陨石。3微米波段的光谱数据表明，小行星表面几乎不存在水合矿物（不到1%）。利用不同相位角可见光波段的多波段光谱数据，研究了小行星表面材料的光散射特性（Hapke参数），发现该材料具有较强的正向散射特性。热红外数据提供了小行星的反射率和表面温度。这些数据表明，表面物质的热惯性比一般小行星大。反射率高于s型小行星的平均反射率。(2)以4km/s的射弹斜撞击石膏靶产生弹坑。研究了撞击产生的碎片的速度分布。结果弹射出少量速度小于1m/s的碎片。由于这些碎片的速度小于Itokawa的逃逸速度，这些碎片将落回并积聚在Itokawa上并形成风化层。

Following researches were conducted for anticipating the surface of an asteroid Itokawa (25143 SF36), the target of the Hayabusa (MUSES-C)mission.(1)The properties of the asteroid were reduced based on the results obtained in the opportunity for ground based observation in 2001. Following results were found from light curves of the asteroid; the rotational period is 12.13h that is longer than the average value of average asteroids, the spin axis is near the perpendicular to the ecliptic, the rotation is retrograde, and the shape is irregular. From spectroscopic observation in the optical to thermal infrared region the spectroscopic type of the asteroid was found to be S-type and the meteorite analog was found to be ordinary chondrite. The spectroscopic data at 3 micron band suggest that almost no hydrated minerals exist on the asteroid surface (less than 1%). Using the multiband spectroscopic data in the visible wavelength at various phase angles, the light scattering properties (Hapke parameters) of the asteroid surface material were investigated, and it was found that the material has the strong forward scattering property. Thermal infrared data provides the reflectivity and the surface temperature of the asteroid. These data suggest that the thermal inertia of the surface material is larger than the average asteroids. The reflectivity is higher than the average S-type asteroids.(2)Craters were produced on gypsum targets by the oblique impact of projectiles of 4km/sec. The velocity distribution of the fragments ejected by the impact were investigated. As the result a small number of fragments of velocity less than 1m/s Is ejected. Since these fragment velocities are less than the escape velocity of the Itokawa, these fragments will fall back to and accumulate on the Itokawa and form the regolith layer.