系外行星研究组知识库

暗弱的近地小行星一方面存在碰撞地球的威胁,另一方面,也正因为它是离我们人类最近的自然天体,成为人们研究太阳系行星和小天体起源和演化以及未来人类所需矿物质补充采取的目标。但是,利用地面望远镜,很难直接"看到"近地小行星大小和形状,对其质量和内部结构的测量就更困难。目前,人们多是利用小行星光度的测量值及其时序变化开展小行星形状、自转参数及物质组成的反演研究。本文选取适用于无大气天体表面的散射律,假设从简到繁的小天体形状（三轴椭球-Cellinoid椭球-凸面体）,开展了包括近地小行星在内的小行星基本物理参数的反演研究。应用蒙特卡洛方法,实现了小行星凸面体反演参量（形状、自转轴指向、自转速率以及表面散射参数）的不确定性评估。利用Lommel-Seeliger椭球模型,分析了阿波罗型近地小行星（155140）2005UD的形状、自转轴及自转周期以及相位函数参数的测定;利用Cellinoid椭球体模型,实现了小行星（106）Dione的测光数据分析;利用凸面体模型,对小行星（103）Hera及（345）Hermentaria的测光数据进行了反演分析。针对观测数据少,且存在对地球碰撞危胁的近地小行星,可采用参数较少的Lommel-Seeliger椭球体光度模型,快速得到小行星的三维大小及自转参数的粗略估算。增加了3个形状参数Cellinoid椭球体模型可以提高对具有不对称峰值光变曲线的拟合。小行星凸面体模型对小行星光变曲线的拟合最好。新建立的凸面体模型加蒙特卡洛算法,实现了小行星凸面体模型中待测参数的最佳解及其不确定性的估算。

Near-Earth asteroids (NEAs), orbiting around the sun in the proximal space of the Earth, and they have become crucial for two reasons. Some of them, identified as protentially hazardous asteroids, pose the danger of collision with the Earth. They are adopted as the targets for investigating the origin of the planets and small bodies of the solar system, and for sampling and mining in future space missions. However, we couldnot "see" them in detail directly, even with the aid of the largest ground-based telescopes, owing to their small size. Hence, it is difficult to determine the size and shape of NEAs and more challenge to determine their mass and internal structure. Currently, some inversion techniques are applied to determine the basic physical proerties (spin parameters, size, shape, scattering parameters, and composition) of asteroids. Among these techniques, the photometry inversion method is widespread used, by which the spin parameters, shape, and scattering parameters of asteroids are subtracted from the photometric data of asteroids. Assuming cartain an experimental scattering law and certain a shape model a series of brightness models of asteroids, and the models were used to inverse the spin parameters, shape, and scattering parameters of asteroids using the least-squre and/or Markov chain Monte Carlo apporoaches. We used the Lommel-Seeliger ellipsoid model to estimate the physical parameters of the near-Earth asteroid (155140) 2005 UD based on its photometric data. Further, the photometric data of (106) Dione were analyzed using the Cellinoid shape model. Based on the convex shape model, we analyzed the photometric data of (103) Hera and (346) Hermentaria. Furthermore, a hierarchical analysis platform was built to determine the basic physical parameters of near-Earth asteroids efficiently, which contained a series of brightness models developed based on an assumed scattering laww and a selected shape model. For the targets with sufficient data (photometric data obtained for at least four apparitions), the best values of the parameters involeved in the convex inversion and their uncertainties can be estimated using a Monte Carlo simulation procedure.