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

为预测隼鸟（MUSES-C）使命的目标小行星丝川（25143 SF 36）的表面，进行了以下研究。（1）根据2001年地面观测机会所获得的结果，该小行星的性质有所减弱。由小行星的光变曲线可以看出，其自转周期为12.13小时，大于一般小行星的平均值，自转轴接近于黄道的垂线，自转是逆行的，形状不规则。从光学到热红外区域的光谱观测发现，小行星的光谱类型是S型，而陨石类似物被发现是普通球粒陨石。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（小于1%）。利用可见光波段不同相位角下的多波段光谱数据，研究了小行星表面物质的光散射特性（Hapke参数），发现该物质具有较强的前向散射特性。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，表面物质的热惯性大于一般小行星。反射率高于一般的S型小行星。（2）4km/s的弹丸斜撞击石膏靶，在石膏靶上产生弹坑。研究了撞击产生的破片速度分布。结果，少量速度小于1 m/s的碎片被喷射出来。由于这些碎片的速度小于丝川的逃逸速度，因此这些碎片将落回并积聚在丝川上，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.