（25143）Itokawa巨砾的热辐射和YORP效应的一般意义
The thermal emission from boulders on (25143) Itokawa and general implications for the YORP effect
摘要：
从小行星表面发射的红外辐射会产生一个扭矩，该扭矩可以显著影响小行星的旋转状态。小地形特征对这种现象的影响，称为YORP效应，似乎是至关重要的。在这项工作中，我们表明，在适当大小的巨石的横向热扩散导致出现的局部YORP效果的幅度是由于全球形状的YORP效果相媲美。我们解决了一个三维热扩散方程中的巨石及其周围的有限元方法，使用FreeFem++代码。从计算的温度分布推断对总扭矩的贡献。我们的一般方法使我们能够计算一个现实的不规则巨石引起的扭矩。对于一个理想化的巨石，我们的结果是一致的，与现有的一维模型。我们还估计（和外推）（25143）Itokawa上的巨石的大小分布，从它的表面特写镜头的图像。我们意识到丝川的地形特征可能会产生相当于10^-7 rad day^-2量级的旋转加速度的扭矩，因此可以解释观察到的光变曲线中的相移。
英文摘要：
Infrared radiation emitted from an asteroid surface causes a torque that can significantly affect rotational state of the asteroid. The influence of small topographic features on this phenomenon, called the YORP effect, seems to be of utmost importance. In this work, we show that a lateral heat diffusion in boulders of suitable sizes leads to an emergence of a local YORP effect which magnitude is comparable to the YORP effect due to the global shape. We solve a three-dimensional heat diffusion equation in a boulder and its surroundings by the finite element method, using the FreeFem++ code. The contribution to the total torque is inferred from the computed temperature distribution. Our general approach allows us to compute the torque induced by a realistic irregular boulder. For an idealized boulder, our result is consistent with an existing one-dimensional model. We also estimated (and extrapolated) a size distribution of boulders on (25143) Itokawa from close-up images of its surface. We realized that topographic features on Itokawa can potentially induce a torque corresponding to a rotational acceleration of the order 10^-7 rad day^-2 and can therefore explain the observed phase shift in light curves.
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