Asteroid 99942 Apophis will pass near Earth in 2029 April. Expected to miss our planet by a safe margin, that could change if Apophis's path were perturbed by a collision with another asteroid in the interim. Though the statistical chance of such a collision is minuscule, the high risk associated with Apophis motivates us to examine even this very unlikely scenario. In this work, we identify encounters between known asteroids and Apophis up to 2029 April. Here we show that Apophis will encounter the 1300 m diameter asteroid 4544 Xanthus in 2026 December. Their minimum orbit intersection distance is less than 10,000 km, with Apophis passing that closest point just 4 hr before Xanthus. Though a direct collision is ruled out, the encounter is close enough that material accompanying Xanthus (if any) could strike Apophis. We also identify other asteroid encounters that deserve monitoring.

中文翻译：

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小行星99942阿波菲斯的遭遇情况与已知小行星目录

小行星 99942 阿波菲斯将于 2029 年 4 月经过地球附近。预计阿波菲斯将以安全距离偏离地球，但如果阿波菲斯的路径在此期间因与另一颗小行星相撞而受到干扰，情况可能会发生变化。尽管这种碰撞的统计概率很小，但与阿波菲斯相关的高风险促使我们研究这种极不可能发生的情况。在这项工作中，我们确定了截至 2029 年 4 月已知小行星与阿波菲斯之间的相遇情况。在这里我们展示了阿波菲斯将于 2026 年 12 月遇到直径 1300 米的小行星 4544 Xanthus。它们的最小轨道交叉距离不到 10,000 公里，阿波菲斯仅比克桑托斯早 4 小时经过最​​近点。尽管排除了直接碰撞的可能性，但这次相遇足够接近，以至于伴随着克桑托斯的物质（如果有的话）可能会撞击阿波菲斯。我们还确定了其他值得监测的小行星遭遇事件。