The internal structure of asteroid (25143) Itokawa as revealed by detection of YORP spin-up
The internal structure of asteroid (25143) Itokawa as revealed by detection of YORP spin-up
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DOI：
10.1051/0004-6361/201322602
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发表时间：
2014-02
影响因子：
6.5
通讯作者：
S. Lowry;P. Weissman;S. Duddy;B. Rozitis;A. Fitzsimmons;S. Green;M. Hicks;C. Snodgrass;S. Wolters;S. Chesley;J. Pittichová;P. V. Oers
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作者：
S. Lowry;P. Weissman;S. Duddy;B. Rozitis;A. Fitzsimmons;S. Green;M. Hicks;C. Snodgrass;S. Wolters;S. Chesley;J. Pittichová;P. V. Oers
上下文。2005年，隼鸟号宇宙飞船访问了近地小行星（25143）Itokawa，得到了一个非常详细的形状和表面地形模型。这个模型已经对这颗小行星的预期辐射扭矩做出了几个预测，表明它的自旋速率应该在减速。目标。探测可能由于yorp引起的辐射扭矩而导致的旋转速率变化，进而可以用于研究小行星的内部结构。方法。通过2001年至2013年的一次观测调查，我们获得了这颗小行星近距离接近地球的五次不同时间的旋转光曲线数据。我们应用多面体形状建模技术来评估小行星的自旋状态及其长期演变。我们还对隼鸟号飞船确定的形状模型进行了详细的热物理分析。结果。我们成功地测量了Itokawa自旋速率的加速度，即ω/dt =（3.54±0.38）× 10-8 rad day-2，相当于其自转周期减少了约45 ms -1。从热物理分析中我们发现，为了使观测到的YORP强度与理论相符，Itokawa的质心必须沿着小行星的长轴移动~21 m。结论。这可以解释，如果Itokawa是由两个独立的物体组成，它们的体积密度非常不同，分别为1750±110 kg - m-3和2850±500 kg - m-3，并且是由两个独立的物体合并形成的，要么是一个较大的分化体的灾难性破坏的后果，要么是一个双星系统的崩溃。因此，我们证明了辐射扭矩的观测测量，当与详细的形状模型相结合时，可以提供对小行星内部结构的洞察。此外，这是第一次测量小行星体内的密度不均匀性，揭示了显著的内部结构变化。这通常需要一艘专门的航天器。
Context. Near-Earth asteroid (25143) Itokawa was visited by the Hayabusa spacecraft in 2005, resulting in a highly detailed shape and surface topography model. This model has led to several predictions for the expected radiative torques on this asteroid, suggesting that its spin rate should be decelerating. Aims. To detect changes in rotation rate that may be due to YORP-induced radiative torques, which in turn may be used to investigate the interior structure of the asteroid. Methods. Through an observational survey spanning 2001 to 2013 we obtained rotational lightcurve data at various times over the last five close Earth-approaches of the asteroid. We applied a polyhedron-shape-modelling technique to assess the spin-state of the asteroid and its long term evolution. We also applied a detailed thermophysical analysis to the shape model determined from the Hayabusa spacecraft. Results. We have successfully measured an acceleration in Itokawa’s spin rate of dω/dt = (3.54 ± 0.38) × 10-8 rad day-2, equivalent to a decrease of its rotation period of ~45 ms year-1. From the thermophysical analysis we find that the centre-of-mass for Itokawa must be shifted by ~21 m along the long-axis of the asteroid to reconcile the observed YORP strength with theory. Conclusions. This can be explained if Itokawa is composed of two separate bodies with very different bulk densities of 1750 ± 110 kg m-3 and 2850 ± 500 kg m-3, and was formed from the merger of two separate bodies, either in the aftermath of a catastrophic disruption of a larger differentiated body, or from the collapse of a binary system. We therefore demonstrate that an observational measurement of radiative torques, when combined with a detailed shape model, can provide insight into the interior structure of an asteroid. Futhermore, this is the first measurement of density inhomogeneity within an asteroidal body, that reveals significant internal structure variation. A specialised spacecraft is normally required for this.