Light Scattering by Interplanetary Fractal Aggregates

（1）将分形凝聚模型应用于行星际空间中形状不规则的尘埃粒子。它们的散射特性进行了详细研究。在1992年，他们的吸收/压力系数的波长依赖性已被推导出来，并在1993年的相位角依赖性的散射函数已被获得。研究表明，离散偶极近似是一种有效的估计分形聚集体散射特性的方法。此外，我们还了解到，存在一个适用的限制，传统的方法称为麦克斯韦-加内特米氏理论。(2)A行星际尘埃的运动可以通过分析在黄道光中测量的多普勒频移来估计。在以前的研究中，留下了一个著名的问题，即为什么在地球轨道内，由多普勒频移推导出的颗粒速度大于开普勒速度。我们重新研究了观测到的多普勒频移的速度依赖性的理论公式，发现在该估计中缺乏重要的因素。我们的修正公式解决了这个长期存在的问题，从而预言了尘埃粒子的性质随太阳距离的变化。参照上述不规则形状粒子的散射模式，我们检验了近地小行星4179 Toutatis的观测偏振数据。发现Toutatis将被不均匀的粗糙表面和风化层覆盖。

(1)Fractal aggregate model has been applied to the irregularly shaped dust particles existing in the interplanetary space. Their scattering properties have been examined in detail. In 1992, a wavelength dependence of their absorption/pressure coefficients has been deduced and in 1993 a phase angle dependence of their scattering function has been obtained. It is found from these works that Discrete Dipole Approximation is useful method to estimate the scattering properties of fractal aggregates. Furthermore we have learned that there exists an applicable limit on the conventional method called as Maxwell-Garnett Mie theory.(2)A motion of interplanetary dust can be estimated from the analysis of doppler shifts measured in the zodiacal light. In the previous investigation one famous question has been left, namely why the velocity of grain deduced from Doppler shifts is larger than Kepler velocity inside the Earth's orbit. We have re-examined the theoretical formula of velocity-dependence of observed Doppler shifts and found a lack of important factor in that estimation. Our revised formula has solved the long standing problem and consequently it has predicted a variation of the nature of dust grains with a solar distance.Referring to the scattering pattern of irregularly shaped particles considered above, the observed polarimetric data of 4179 Toutatis, which is one of near-Earth asteroids, have been examined. It is found that the Toutatis would be covered by inhomogeneous rough surface with regolith.