Surface thermophysical properties on the potentially hazardous asteroid (99942) Apophis

We investigate the surface thermophysical properties（thermal emissivity, thermal inertia,roughness fraction and geometric albedo） of asteroid（99942） Apophis, using the currently available mid-infrared observations from CanariC am on Gran Telescopio CANARIAS and far-infrared data from PACS on Herschel, based on the Advanced Thermophysical Model. We show that the thermal emissivity of Apophis should be wavelength dependent from 8.70 μm to 160 μm, and the maximum emissivity may appear around 20 μm, similar to that of Vesta. Moreover, we further derive the thermal inertia,roughness fraction, geometric albedo and effective diameter of Apophis within a possible 1σ scale of Γ = 100（-52）^（＋100）＋Jm^（-2）s^-0.5K^-1, fr = 0.78~1.0, pv = 0.286（-0.026）^（＋0.030） and D（eff） = 378（-25）^（＋19）m, and 3σscale of Γ = 100（-100）^（＋240）Jm^（-2）s^-0.5 K^-1, fr = 0.2~1.0, pv = 0.286（-0.029）^（＋0.039） and D（eff） = 378（-29）^（＋27） m. The derived low thermal inertia but high roughness fraction may imply that Apophis could have regolith on its surface, where stronger space weathering but weaker regolith migration has happened in comparison with asteroid Itokawa. Our results show that small-size asteroids could also have fine regolith on the surface, and further infer that Apophis may have been delivered from the Main Belt by the Yarkovsky effect.

小行星热模型研究现状

从基本物理出发,详细地介绍在小行星热环境研究中常用的几个热模型,并结合观测论述其具体科学应用。一般来说,小行星热模型可以分为两大类:简化模型和热物理模型。简化模型主要用来估计小行星的反照率和直径;热物理模型则是用详细的形状模型,结合经典的热物理学规律来尽可能真实地模拟小行星表层的复杂热环境,可以较真实地模拟出小行星表层各局部区域的热环境状态,从而为研究小行星的热演化历史及与其相关的Yarkovsky和YORP效应等提供理论依据。

小行星表面热物理模型

回顾小行星热物理研究中两种热物理模型TPM(thermal physical model)和ATPM(advanced thermo physical model),讨论了其科学应用及适用范围,分析了其在未来小行星探测任务中可能的工程应用价值。基于TPM可推算小行星的表面热惯量性质,利用ATPM不仅可以研究小行星的表面热惯量与表面粗糙度等特性,还能深入研究小行星的YORP效应(Yarkovsky-O'Keefe-Radzievskii-Paddack effect)。研究表明,在目前的观测精度下,TPM和ATPM均可有效研究并揭示小行星基本热物理性质。