Predicting the Earth encounters of (99942) Apophis
Predicting the Earth encounters of (99942) Apophis
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DOI：
10.1016/j.icarus.2007.09.012
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发表时间：
2008
期刊：
影响因子：
3.2
通讯作者：
J. Giorgini;L. Benner;S. Ostro;M. Nolan;M. Busch
中科院分区：
文献类型：
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作者：
J. Giorgini;L. Benner;S. Ostro;M. Nolan;M. Busch
阿雷西博延迟多普勒在2005年和2006年对阿波菲斯（99942）进行了测量，结果对2029年光学预测的接近地球的距离进行了5个标准偏差的轨道修正。雷达测量将进入相遇的统计不确定性区域的体积减少到雷达前解决方案的7.3%，但由于更接近地球的预测方法，整个相遇的轨迹不确定性增长率增加了800%。估计2036年撞击地球的可能性很小。由于2007-2010年的标准偏差天平面位置不确定性已经小于0.2角秒，最好的近期地面光学天文测量只能微弱地影响轨道估计。虽然在2013年（如果不是2011年）使用地面光学测量可能会排除2036年撞击的可能性，但用于估计和预测当前时代轨迹的标准动力学模型（SDM）内的近似值足以通过改变导致2029年相遇的动力学来模糊2036年预测撞击和未命中之间的差异。在不了解物体物理特性的情况下，基于SDM的正常撞击概率评估会出现问题；在实际动力允许的情况下，可以排除撞击。通过描述物理参数对轨迹的最小和最大影响，开发了校准的位置不确定性区间来补偿这一点。到2036年，与太阳辐射有关的加速度的不确定性可能导致相对于SDM的82至4720地球轨道半径的变化。如果存在可采取行动的危险，根据物理特性，2018年阿波菲斯太阳辐射总吸收率的2-10%的改变足以在2036年之前产生6个标准差的轨迹变化；到2036年，即使是0.5%的变化也会导致所有可能的自旋极和可能的质量的轨道移动一个地球半径。行星星历的不确定性是系统误差的第二大来源，导致高达23个地球半径的不确定性。SDM地球点质量假设引入了到2036年的额外2.9地球半径的预测误差。未模拟的小行星扰动产生的误差高达2.3个地球半径。我们发现，在2029年之前，未来的小天体碰撞不可能产生阿波菲斯的质量测定。然而，小行星（144898）2004 VD17本身在2102年对地球有统计上的影响，可能会在2034年在6.7个月球距离与阿波菲斯相遇，它们的不确定性区域在两个SDM概率分布中心附近接近1.6个月球距离。
Arecibo delay–Doppler measurements of (99942) Apophis in 2005 and 2006 resulted in a five standard-deviation trajectory correction to the optically predicted close approach distance to Earth in 2029. The radar measurements reduced the volume of the statistical uncertainty region entering the encounter to 7.3% of the pre-radar solution, but increased the trajectory uncertainty growth rate across the encounter by 800% due to the closer predicted approach to the Earth. A small estimated Earth impact probability remained for 2036. With standard-deviation plane-of-sky position uncertainties for 2007–2010 already less than 0.2 arcsec, the best near-term ground-based optical astrometry can only weakly affect the trajectory estimate. While the potential for impact in 2036 will likely be excluded in 2013 (if not 2011) using ground-based optical measurements, approximations within the Standard Dynamical Model (SDM) used to estimate and predict the trajectory from the current era are sufficient to obscure the difference between a predicted impact and a miss in 2036 by altering the dynamics leading into the 2029 encounter. Normal impact probability assessments based on the SDM become problematic without knowledge of the object's physical properties; impact could be excluded while the actual dynamics still permit it. Calibrated position uncertainty intervals are developed to compensate for this by characterizing the minimum and maximum effect of physical parameters on the trajectory. Uncertainty in accelerations related to solar radiation can cause between 82 and 4720 Earth-radii of trajectory change relative to the SDM by 2036. If an actionable hazard exists, alteration by 2–10% of Apophis' total absorption of solar radiation in 2018 could be sufficient to produce a six standard-deviation trajectory change by 2036 given physical characterization; even a 0.5% change could produce a trajectory shift of one Earth-radius by 2036 for all possible spin-poles and likely masses. Planetary ephemeris uncertainties are the next greatest source of systematic error, causing up to 23 Earth-radii of uncertainty. The SDM Earth point-mass assumption introduces an additional 2.9 Earth-radii of prediction error by 2036. Unmodeled asteroid perturbations produce as much as 2.3 Earth-radii of error. We find no future small-body encounters likely to yield an Apophis mass determination prior to 2029. However, asteroid (144898) 2004 VD17, itself having a statistical Earth impact in 2102, will probably encounter Apophis at 6.7 lunar distances in 2034, their uncertainty regions coming as close as 1.6 lunar distances near the center of both SDM probability distributions.