小行星阿波菲斯的自转状态及其2029年接近地球时的变化预测
The spin state of asteroid Apophis and a prediction of its change during the 2029 close encounter with Earth
AI总结：
通过2012-2013和2020-2021年的光度观测，研究阿波菲斯的自转状态，预测2029年接近地球时自转状态的变化，考虑地球引力扭矩影响。
AI中文摘要：
2029年4月13日，小行星阿波菲斯将接近地球，距离约为38,000公里。数值模型表明，飞越期间阿波菲斯的自转状态将严重依赖于其在飞越时的取向。我们旨在通过2012-2013年和2020-2021年的光度观测确定阿波菲斯的自转状态。这将使我们能够准确预测飞越前的自转状态，并通过考虑地球引力扭矩的影响，预测飞越后的可能自转状态。我们使用光曲线反演方法对旋转的小行星进行建模，以重建阿波菲斯的自转状态及其凸形模型。结果被用作描述阿波菲斯未来自转状态的数值模型的初始条件。两次飞越期间的数据不足以唯一确定阿波菲斯的自转和进动周期。正式的最佳拟合解为预进动周期27.374±0.001小时，自转周期262.2±0.1小时，但至少还有两种其他周期组合能同样好地拟合现有数据。所有目前可接受的模型在2029年初的阿波菲斯取向上大致相同。这是因为准确的光度数据是在两次相隔8年的飞越期间收集的，这与2021至2029年的间隔相同。尽管2029年4月的地球接近事件大大增加了阿波菲斯自转状态的后不确定性，但短轴自转模式将很可能被保留。2027和2028年的额外观测将消除阿波菲斯飞越前自转解的歧义，并使我们能够获得更准确的后自转状态预测。
英文摘要：
On April 13, 2029, the asteroid Apophis will pass near Earth at a geocentric distance of about 38,000 km. Numerical models have suggested that the post-encounter spin state will critically depend on the orientation of Apophis during the flyby. We aim to determine the spin state of Apophis from its photometric observations collected during two apparitions in 2012-2013 and 2020-2021. This will enable us to accurately predict the pre-encounter rotation state and, by accounting for Earth's gravitational torque, predict a range of possible post-encounter states. We used the light curve inversion method for tumbling asteroids to reconstruct the spin state of Apophis and its convex shape model. The result is adopted as the initial condition of a numerical model describing Apophis's future rotation state. The data from the two apparitions are insufficient to determine Apophis's rotation and precession periods uniquely. The formally best-fit solution is 27.374 +/- 0.001 h for the precession period and 262.2 +/- 0.1 h for the rotation period, but at least two other combinations of the periods provide a similarly good fit to the available data. All the currently acceptable models result in approximately the same pre-encounter orientation of Apophis in early 2029. This is because the accurate photometric data were collected during two apparitions separated by 8 years, which is the same interval as from 2021 to 2029. Although the close encounter with Earth in April 2029 hugely increases the post-encounter uncertainty of Apophis's spin state, the short-axis spin mode will be preserved with a high likelihood. Additional observations taken in 2027 and 2028 will break the ambiguity in Apophis's pre-encounter spin solution and allow us to get a more accurate post-encounter spin state prediction
