预测 Apophis 在2029年最接近地球期间由形变驱动的自转演化
Prediction of Apophis's deformation-driven rotational evolution during its closest encounter to the Earth in 2029
AI总结：
本文用简化模型研究 Apophis 在2029年近地飞掠时内部形变对自转的影响，发现低杨氏模量可导致显著且持续的自转状态偏离。
AI中文摘要：
2029年，近地小行星（99942）Apophis 将在距地球6个地球半径以内接近地球。这一机会是最罕见的自然实验之一，我们可以借此通过望远镜观测和空间任务更好地表征一颗小天体。早期地质研究一致认为，在这次最接近期间，Apophis 上可能不会发生重大地质过程，包括表面改造和内部形变。不过，取决于局部地质条件，可能会发生轻微的表面重塑。一个关键发现是，自转演化由地球的潮汐效应引起。本研究为自转演化提供了另一个视角：它可能因内部性质的差异而变化。也就是说，即使形变不可测量，可能的形变过程也可能改变相对于刚体状态的自转状态变化。受 Hirabaya-shi（2023）和 Taylor 等人（2023）早期研究的启发，本研究致力于使用简化模型探讨这一问题。结果表明，由形变驱动的自转状态变化可能发生，具体取决于杨氏模量。如果这颗小行星的杨氏模量约为1 MPa或更高，那么在一年时间内，自转状态相对于刚体状态仅偏离几度。然而，如果其杨氏模量约为10 kPa或更低，即使在最接近相遇之后几天，自转状态偏离也可能达到几度。望远镜观测和空间任务都能为这一现象提供深刻认识。
英文摘要：
In 2029, the near-Earth asteroid (99942) Apophis approaches the Earth within six Earth radii. This opportunity is one of the rarest natural experiments that we can use to better characterize a small body through telescopic observations and space missions. Earlier geological investigations consistently suggested that major geological processes might not occur on Apophis during this closest encounter, including surface processing and interior deformation. However, minor resurfacing may occur, depending on local geological conditions. A critical finding is that the rotational evolution occurs due to the tidal effect from the Earth. The present study offers an additional perspective on the rotational evolution, which may vary due to variations in interior properties. Namely, possible deformation processes may change the spin state variation from the rigid body state, even if deformation is not measurable. The effort in this work is to explore this issue using a simplified model, motivated by earlier studies by Hirabayashi (2023) and Taylor et al. (2023). The results show that the deformation-driven spin state change may be possible, depending on Young's modulus. If this asteroid's Young's modulus is ~1 MPa or higher, the spin state only deviates a few degrees from the rigid body state over one year. However, if it is ~10 kPa or less, the spin state deviation may reach a few degrees, even a few days after the closest encounter. Both telescopic observations and space missions can provide strong insights into this phenomenon.
